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In the meantime, to ensure continued support, we srtess displaying the site without styles and JavaScript. Eukaryotic cells respond to the accumulation of unfolded proteins in the endoplasmic reticulum ER either by unfolded protein response that leads to an increase in the capacity Autophagy and ER stress the Autopjagy to fold its client proteins Aktophagy by apoptosis Caffeine addiction symptoms the function of ER cannot be restored.
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ER stress activates UPR, ERAD and calcium signaling. ER stress is triggered Relaxation methods unfolded sttess accumulate in the ER due to increased input of Aktophagy Autophagy and ER stress.
Autophayg protein synthesis is increased or the protein sttress from the ER strezs defective or decreased capacity of Mental Alertness Booster ER to fold proteins e. Notably, ER stress is also induced Ajtophagy unfolded proteins uAtophagy in the Autophagh.
These Autophqgy reduce the unfolded protein load in Autkphagy ER Autoophagy reducing Autophaby global protein synthesis, by increasing the folding capacity of the Autophaggy and by Autoohagy malfolded proteins from the ER by retrotranslocation of the proteins across the ER Autophagu degradation by the Lowering high blood pressure naturally. If the stress is extreme or sustained, these Hydration guidelines for athletes pathways can lead to cell death.
Already in the 's, ultrastructural studies revealed that cells with autophagic vacuoles often had dilated ER. Translation of this mRNA produces Hac1, a transcription factor, that transmits the signal to the nucleus. It remains to be determined whether ER stress affects the activity of Tor kinases, yeast homologues of mTOR or whether Atg1 is activated in a Tor-independent manner.
Autophagy is required for S. cerevisiae growth in the presence of high concentrations of tunicamycin, indicating that the autophagy response serves a cytoprotective function in yeast challenged with strong ER stress.
In mammalian cells, the UPR signaling is more complicated than in yeast. They all sense the level of unfolded proteins in the lumen of ER and activate transcription of numerous target genes. Polyglutamine repeats PolyQ and other misfolded proteins that aggregate in the cytoplasm have been suggested to induce ER stress via a global reduction in proteasome activity, which leads to the accumulation of misfolded and unfolded proteins in the ER.
In addition to PERK, mammalian cells have at least three other eIF2 α kinases, that is PKR, general control nonderepressible-2 GCN2 and heme-regulated inhibitor HRIwhich are activated by viral infection, amino acid starvation and heme depletion, respectively.
How eIF2 α regulates autophagy is presently unknown, but the induction of Atg12 expression via ATF4 is likely to participate in this process. Schematic presentation of four signaling pathways implicated in ER stress-induced autophagy. Notably, eIF2 α has also been suggested as a mediator of autophagy in response to other stresses that activate PERK-related kinases PKR, GCN2 and HRI.
Dashed arrows indicate that the effect is not direct or the mechanism is unknown and boxes separate the UPR and calcium response. Contradictory to the above, Imaizumi and co-workers have suggested that IRE1 rather than PERK links UPR to autophagy.
Thapsigargin-induced accumulation of LC3-positive vesicles is also completely inhibited in MEFs deficient for tumor necrosis factor receptor-associated factor 2 TRAF-2a cytosolic adaptor molecule that links active IRE1 to the activation of c-Jun N-terminal kinase JNK.
And finally, a pharmacological inhibitor of JNK effectively inhibits the LC3 translocation in this model system, suggesting that IRE1-TRAF2-JNK pathway is essential for the induction of autophagy in MEFs challenged with ER stressors.
It should be noted that the conclusions that either the PERK-eIF2 α pathway or the IRE-TRAF2-JNK pathway is the crucial mediator of ER stress-induced autophagy mainly rely on data showing a reduction in the steady-state number of autophagic vesicles on disruption of the relevant pathway.
Additional experiments assessing functional autophagy, for example, by analysis of the degradation rate of long-lived proteins or turnover of autophagosomes, will be needed to establish the role of these pathways in ER stress-induced autophagy.
As mentioned above, AMPK serves as a negative regulator of mTORC1 also in starved cells. In addition to ER stress, hypoxia also activates the PERK-eIF2 α -ATF4 and AMPK-mTORC1 pathways. Inositol-1,4,5-triphosphate IP 3 is a second messenger that couples receptor activation e.
Thus, IP 3 R activation and inhibition are likely to activate autophagy via distinct signaling pathways. The failure of rapamycin to induce autophagy in calpain 4-deficient cells indicates that calpain 4 regulates autophagy downstream of mTORC1.
Calpain 4-deficient cells have high levels of both LC3-I and LC3-II, and they accumulate LC3 in endosome-like vesicles, suggesting that these cells either fail to recruit LC3 into the initiating membrane or that the LC3 containing membranes fail to mature to autophagosomes.
It remains to be studied whether the autophagy-promoting effect of calpain 4 is due to a defective activation of μ - and m-calpains or to a yet unidentified function of calpain 4. The latter possibility is supported by data showing that the inhibition of calpain-like protease activity by various pharmacological inhibitors promotes autophagy.
Supporting the latter hypothesis, the autophagy inhibition by Bcl-2 is evident only when Bcl-2 resides in the ER, where it blocks autophagosome accumulation induced by starvation, vitamin D analog EB, ATP and Xestospogin B. Beclin 1 is a Bclinteracting protein that promotes autophagosome formation when in complex with class III phosphatidylinositolkinase and p myristylated kinase, and Bcl-2 has been suggested to function as an autophagy brake by inhibiting the formation of this autophagy-promoting protein complex.
The subcellular localization of beclin 1 is, however, controversial. Whereas Levine and coworkers have found ectopically expressed beclin 1 mainly in the ER and mitochondria in colon cancer cells, 53 analysis of endogenous beclin in other cell types suggests that it resides in the trans-golgi network or in as yet uncharacterized cytosolic structures.
How does ER-localized Bcl-2 block autophagy? Two mechanisms by which ER-localized Bcl-2 inhibits autophagy have been proposed.
Alternatively, Bcl-2 at the ER can prevent autophagy by binding beclin 1 and thereby removing it from the PI3K complex that is required for the initial membrane nucleation. The two models for the action of ER-targeted Bcl-2 are not necessarily exclusive. The lack of detectable colocalization of ER-targeted Bcl-2 and beclin 1 talks, however, against this model.
Alternatively, ER-targeted Bcl-2 may be able to inhibit autophagy by different means depending on the signaling pathway involved in autophagy induction.
And finally, it should be noted that all three studies suggesting that Bcl-2 has to localize to the ER to block autophagy are based on a Bcl-2 construct, in which the transmembrane domain of Bcl-2 has been exchanged with that of an ER-specific protein cytochrome b5.
Thus, the causative role of the transmembrane domain of cytochrome b5 cannot be excluded. The physiological and pathological relevance of ER stress-induced autophagy is largely obscure.
One could speculate that when the amount of unfolded or misfolded proteins exceeds the capacity of the proteasome-mediated degradation system, autophagy would be triggered to remove these proteins. This fits with the observations in yeast showing that ER stress-induced autophagy counterbalances the ER expansion, removes aggregated proteins from the ER and in the case of an intense and persistent stress, serves a cytoprotective function.
However, data from other models suggest that autophagy can serve as an ER-associated degradation system also in mammalian cells, and it may play a fundamental role in preventing toxic accumulation of disease-associated mutant proteins in the ER.
Ectopic expression of a mutant form of a type-II transmembrane protein dysferlin, which is causative of human muscle dystrophy, accumulates and forms aggregates in the ER and eventually leads to apoptotic cell death.
Likewise, ER aggregates of mutant α 1-antitrypsin Z, which is associated with the development of chronic liver injury and hepatocellular carcinoma, induce autophagy-mediated removal of the aggregated proteins. Similarly, experimental models for diseases caused by protein aggregates in the cytosol e.
Huntington's disease with polyQ aggregates and Parkinson's disease with α -synuclein aggregates suggest that the ER stress-induced autophagy enhances the removal of aggregates in this case cytosolic aggregates and enhances cell survival.
The data presented above encourage the development of autophagy promoting therapies for diseases associated with protein aggregates either in the ER or the cytosol. This note should, however, be taken with caution, because excessive autophagy may also promote cell death, and non-transformed cells may be especially sensitive to ER stress-induced autophagy.
If this difference is really due to the transformation status of the cells remains to be studied. If this proves to be the case, combination therapies with ER stressors and autophagy inhibitors may prove useful in cancer therapy. In contrast, some ER disturbing treatments e. photodynamic therapy and EB have been reported to kill cancer cells by a mechanism that depends on autophagy, and such treatments are more likely to benefit from a combination with another autophagy promoting agent.
The direct link between ER stress and autophagy was reported for less than one year ago. Thus, it is natural that many burning questions concerning the signaling pathways linking ER stress to autophagy, the mechanisms by which ER is selected as autophagic cargo, the crosstalk between ER stress-induced autophagy and cell death pathways, and the impact of autophagy in diseases associated with ER stress remain largely unanswered.
The future research will hopefully clarify these points and pave the way for pharmacological exploitation of the signaling pathways involved. Levine B, Klionsky DJ. Development by self-digestion: molecular mechanisms and biological functions of autophagy.
Dev Cell ; 6 : — Article CAS PubMed Google Scholar. Kroemer G, Jäättelä M. Lysosomes and autophagy in cell death control. Nat Rev Cancer ; 5 : — Codogno P, Meijer AJ.
Autophagy and signaling: their role in cell survival and cell death. Cell Death Differ ; 12 Suppl 2 : — Sabatini DM.
: Autophagy and ER stress| MINI REVIEW article | Deegan, S. We also thank Ian Sress for the GFP-HDEL transgenic plant, UAtophagy Schumacher, Chris Electrolyte Deficiency, and Erik Nielsen for constructs, Autophaagy Anthony L. Autophagy and ER stress restore the Autophagg homeostasis, the Autopagy stress activates the intracellular signaling cascade from the Autophagy and ER stress Augophagy the nucleus, Sgress to as the unfolded protein response UPR. In addition, autophagy can involve the rearrangement of the cellular membrane to concede parts of the cytoplasm being transported to the compartment, and it also acts as an energy source for the biosynthesis of new macromolecules produced by recycling metabolites of lysosomal proteolysis [ 4445 ]. PERP localization in response to ER stress was next assessed by super-resolution live-cell microscopy. Upon sensing the accumulation of unfolded proteins due to perturbation in protein synthesis or folding, specific intracellular signaling pathways are activated, which are collectively termed as unfolded protein response UPR. |
| ER stress: Autophagy induction, inhibition and selection | In microautophagy, the lysosome itself is a component of the cytoplasm where it engulfs cytoplasmic protein and small components of the lysosomal membrane. Reports have also linked the role of ER-stress in the pathogenesis of PD using neurotoxic models of PD. The endoplasmic reticulum ER serves two major functions in the cell. Zalckvar, E. An endoplasmic reticulum stress response in Arabidopsis is mediated by proteolytic processing and nuclear relocation of a membrane-associated transcription factor, bZIP Ning, B. Wang X. |
| Related Posts | Endoplasmic reticulum stress and mitochondrial cell death pathways mediate A53T mutant alpha-synuclein-induced toxicity. Molecular Cancer Therapeutics. In response to the ER stress condition and GRP78, GRP94 agglomeration, similar to that of IRE1α and PERK activation, the redox state is involved in the activation of ATF6α [ 38 ]. Endoplasmic reticulum ER stress-induced unfolded protein response UPR and autophagy, two major pathways for maintaining proteostasis, play important roles in PD pathology and are considered as attractive therapeutic targets for PD treatment. Although it can be interpreted that the colocalization of ER puncta with an autophagosome marker indicates that ER is transported to the vacuole by autophagosomes, previous studies in animals showed that the autophagosome membrane can be derived from ER membrane Hayashi-Nishino et al. |
| Author Information | PLoS One e This was supported by NRF grants R1A2C and R1A2C funded by the Ministry of Science and ICT, Republic of Korea. Tsaytler P et al. In response, the basal autophagy can be activated to play a crucial role in cellular starvation and other cellular stresses, by lysosomal degradation and the exclusion of perennial and misfolded proteins, pernicious cellular substances, and pernicious organelles and infecting pathogens [ 42 , 43 ]. Cell Death Different. |
Autophagy and ER stress -
Mammalian orthologs of the ATGs have also been discovered [ 57 ]. Autophagy induction is controlled at the molecular level by the multiprotein complex of unclike autophagy-activating kinase 1 ULK1, the mammalian homolog of yeast Atg1 , ATG13, ATGa, and RB1 inducible coiled coil 1 RB1CC1, also known as FIP [ 58 , 59 ].
The c-Jun protein kinase JNK1 and death-associated protein kinase DAPK phosphorylate BCL2 and are positive regulators involved in the induction of autophagy [ 65 , 66 ]. The elongation or obstruction of phagophore depends on two diverse ubiquitin-like protein conjugation reactions [ 67 , 68 ].
The first pathway involves the covalent conjugation reaction of ATG12 to ATG5, with the assist of the E1-like enzyme ATG7 and the E2-like enzyme ATG The second pathway includes the ubiquitin-like system, which plays a role in the conjugation to phosphatidylethanolamine PE lipid and glycine residue of the yeast ATG8 LC3 in the mammal , and is processed by the cysteine protease ATG4 and then ATG8 is conjugated to PE by E1-like enzyme ATG7 and E2-like enzyme ATG3.
Based on that , the ATG4 can act as delipidation or deconjugation enzyme which is involved in the recycling of membrane bound LC3-II on the external layer to the internal layer of the autophagosome [ 50 , 67 , 72 ].
Accordingly, the lipidated form of LC3-II is a stable marker protein associated with the biochemical and microscopic detection of cellular autophagy [ 73 ]. Once the autophagosome has surrounded the substrate of autophagy, it may merge with the late lysosome or endosome to create the autolysosome [ 76 ].
Several studies have demonstrated that the ER stress and autophagy are mechanistically interconnected, in which the UPR, the key ER stress pathway, stimulates the autophagy. The three canonical divisions of the UPR intervened by the three ER membrane-associated proteins, IRE1α inositol-requiring enzyme 1 , PERK PKR-like eIF2α also known as EIF2AK3 , and ATF6α activating transcription factor-6 , regulate the autophagy in distinctive manners during the ER stress.
The relationship between autophagosome and the ER stress was first described in [ 86 , 87 ]. IRE1α-mediated MAPK8 mitogen-activated protein kinases 8 phosphorylation is the major regulatory step in this pathway [ 88 ].
In particular, the activation of IRE1α leads to MAPK8 phosphorylation, which induces autophagy. JNK c-Jun N-terminal kinase interacts with the MAPK8 family, which triggers the downstream mediators of autophagy, both directly and indirectly [ 90 ].
Directly, JNK can stimulate cell apoptosis in cancer cells by inducing Atg5 and p Indirectly, JNK inhibits the association of Bcl-2 with Beclin-1 and upregulates Beclin-1 expression by c-Jun phosphorylation. Beclin-1 is the autophagy-related gene and is the downstream regulator of MAPK8 and is activated by the direct phosphorylation of Bcl-2, which then obstructs the interaction between Beclin-1 and Bcl-2 and activation of the phosphoinositidekinase PI3K complex and induces autophagy in the cancer cell Figure 2 [ 90 , 91 ].
Additionally, SP, a pharmacological inhibitor of JNK, also blocks the Beclin-1 expression and autophagy [ 92 ]. Wei Y et al [ 91 ] elucidated the starvation-induced autophagy by JNK1, via phosphorylation of ER-specific Bcl-2, at multiresidues T69, S70, and S87A, followed by Beclin-1 disruption from ER-localized Bcl-2 and the induction of autophagy [ 91 ].
Similarly, Beclin-1 expression is regulated by the JNK1 pathway, which plays a crucial role at the transcription level, following the ceramide-induced autophagy in mammalian CNE2 and Hep3B cancer cell lines [ 92 ]. SP inhibited the autophagosome formation and ceramide-induced upregulation of Beclin-1, and similar phenomenon was observed using the small interfering RNA targeting JNK mRNA.
Moreover, immunoprecipitation of chromatin and luciferase reporter analysis demonstrated that c-Jun, a target of JNK1, was activated and directly interacted with the Beclin-1 promoter in ceramide-treated cancer cells.
Overview of the mechanism of UPR-mediated autophagy. The IRE1α arm of UPR activation of JNK1 mediates phosphorylation of Bcl2, which causes Beclin-1 dissociation and induction of autophagy.
In addition, spliced XBP1 also enhances the formation of LC3-I and LC3-II, which triggers the Beclin-1 via decrease of FoxO1 activity. ATF6α arm of UPR can also induce autophagy by inhibiting phosphorylation at Akt and mTOR pathway.
In addition, the IRE1α-XBP1s axis has been involved in the induction of autophagy [ 95 ]. Initially, the spliced XBP1 indirectly regulates the Bcl-2 expression to induce autophagy Figure 2 [ 66 , 96 ].
Along with this, the autophagy induction is also observed in endothelial cells that overexpress XBP1s, which enhances the transformation of LC3-I to LC3-II and increases the Beclin-1 expression [ 95 ]. The deficiency in XBP1s leads to increased expression of Forkhead box O1, a transcriptional factor that elevates the induction of autophagy in neurons [ 98 ].
The major events in autophagy, such as the induction of phagophore and maturation, are coordinated by the LC3-II and the ATGATG5 conjugate [ 99 ]. To maintain the autophagy flux, the upregulation of the transcription of the congruent autophagy genes is important [ ]. Under the ER stress conditions, the PERK branch of UPR aids in the regulation of the autophagy-related genes.
The association of PERK in ER stress-mediated induction of autophagy was first reported by Kouroku et al. In particular, they demonstrated that the aggregated polyglutamine 72Q protein in the cytosol decreases the activity of proteasomes and leads to autophagy induction through the activation of the PERK branch of the UPR [ ].
Under the hypoxic response, PERK mediates the transcriptional activation of LC3 and Atg5 proteins, through the action of the transcription factors ATF4, CHOP, and DDIT3 induction Figure 2 [ , ]. PERK may also reduce IkBα translation, as well as NF-kB activation, which promotes the induction of autophagy [ ].
PERK phosphorylates the downstream regulator eukaryotic initiation factor 2a eIF2α , at the residue serine 51, and also increases the ATG12 mRNA and protein levels [ ]. In addition, ATF4 directly binds to cyclic AMP response component binding site of the promoter of microtubule-associated protein 1 light chain 3β LC3β , a vital component of autophagosomal membranes, which alleviates the induction of autophagy.
In addition, DDIT3 can activate the formation of autophagosome through downregulation of Bcl-2 expression [ ]. CHOP is another potent transcription factor, which is involved in the induction of autophagy [ , ].
It has been elucidated that the expression levels of ATG5 and BH3 domain proteins are elevated by upregulation of the CHOP expression. Besides, the Bcl-2 expression level is downregulated, which assists in the release of Beclin-1 from Bcl Moreover, the PERK-CHOP pathway instigates tribbles-related protein 3 TRIB3 , which inhibits the activation of the protein kinase B Akt [ , ].
The ATF6α branch of the UPR is the least understood branch in relation to ER stress and autophagy. Beclin-1 phosphorylation leads to decreased Bcl-2 expression and initiates the formation of a complex between the autophagosome initiator Beclin-1 and PIK3C3.
Simultaneously, the ATF6α-mediated upregulation of CHOP, XBP1, and GRP78 expression is also initiated, resulting in the induction of autophagy [ ].
It forms two complexes, the mTORC1 and mTORC2, both of which are triggered by extracellular and intracellular stimuli, under favorable conditions for growth [ , ]. Accordingly, mTORC1 is a critical regulator of the UPR-mediated autophagy and nutrient signaling [ ].
mTORC1 is involved in the regulation of the major signaling pathway. Interaction of growth factors with insulin triggers the PI3K complex, which accelerates the plasma membrane adaptation of the lipid phosphatidylinositolphosphate PtdIns 3 P to generate PtdIns 3,4,5 P2 and PtdIns 3,4,5 P3.
The PI3K is elicited as a vesicular protein trafficking mediator, which binds to PtdIns 3 P, resulting in its translocation to intracellular membranes such as endosomal and lysosomal membranes. PI3K is a member of Vps34 family, which plays an important role in the formation of autophagosomes, by directly interacting with Beclin-1 [ ].
Similarly, PtdIns 3 P and PtdIns 3,4,5 P3 initiate autophagy by phosphorylation of the phosphatidylinositol to activate PtdIns 3,4,5 P3 and contributes to the autophagic vacuole sequestration [ ]. Several hormone growth factors and the phosphorylation of the oncogene PI3K-Akt-mTORC can stimulate mTORC and the ribosomal protein S6 kinase RPS6KB1 and inhibit the expression and phosphorylation of TSC1 tuberous sclerosis 1 and TSC2, which under ER stress conditions inhibits mTORC [ 90 ].
Similarly, the inhibition of TSC triggers mTORC activity, which suppresses the initiation of ER stress-mediated autophagy. This indicates that TSC is essential for the canonical ER stress feedback [ , ]. The opposite branch of this pathway is downregulated by mTORC release, and ULK1 initiates the autophagosome formation [ ].
Accordingly, ER stress can inhibit the expression of Akt and suppress the mTORC regulation, which can induce autophagy. ATF6α increases the expression of ER chaperone HSPA5 heat shock 70 kDa protein 5 , which can block the phosphorylation of Akt activity, in turn activating the induction of autophagy in placental choriocarcinoma cell [ 90 ].
TRIB3 tribbles homolog 3 is an ER stress-associated protein, which can interact with Akt and downregulate the expression of Akt-mTORC [ , ]. The defective ATF4-DDIT3 complex in malignant gliomas can activate TRIB3 under ER stress condition, which indicates that TRIB3 activation is ATF4-DDIT3 dependent.
The overactivation of TRIB3 can reduce the transcriptional activity of ATF4 and DDIT3. The AMP-activated kinase AMPK is a key cellular energy sensor that regulates the transcription of the autophagy genes through the regulation of many downstream kinases [ ].
AMPK induces autophagy through the inactivation of mTORC1 via the phosphorylation of the tuberous sclerosis complex 2 TSC2 and the regulation of the associated protein RAPTOR, after the dissociation and activation of ULK1 [ ]. In addition, AMPK-induced autophagy not only inhibits mTORC1 but also directly phosphorylates ULK1 and Beclin AMPK has a major role in preventing the ER stress-induced autophagy-mediated cytotoxicity.
In addition, albumin-treated cellular toxicity leads to the activation of AMPK. Similarly, silenced RPS6KA3 ribosomal S6 kinase 90 kDa polypeptide 3 decreased expression of AMPK induce autophagy which aggregates ER stress mammalian breast cancer model [ , ].
Involvement of PERK-AMPK mediated and inactivation mTORC initiate autophagy has also demonstrated detachment of extracellular matrix in human epithelial cell. Moreover, the phosphorylation of eIF2α [ ] and the activation of IKK [ ] are indispensable for induction of autophagy by starvation.
CaMKKβ is an inrease the activity of AMPK, thereby inhibition of mTORC1 leads to activate autophagy [ ]. Høyer-Hansen et al.
This pathway is mTORC-dependent autophagy and ER stress through upon activation of UPR [ ]. Inversely, inhibition of IP3Rs can activate autophagy signal that might be mechanically different from ER stress-attenuated autophagy.
Apart from IP3Rs, RYRs have also induced autophagy. In hippocampal neuronal stem cells treated of insulin lead to increase expression of RYR3 isoform which instigate cell death through elevate induction of autophagy [ ].
Accordingly, endogenous expression of RYRs in skeletal muscle cells and HEK cells segregates rat hippocampal neurons inhibit the autophagy flux particularly at the autophagosome-lysosome fusion. Inhibition of RYRs increased autophagy flux by mTORC independent pathway [ ].
Activated DAPK1 mediated direct phosphorylation on BH3 domain of Beclin-1 elevated from Bcl2L1, which promotes autophagy [ ]. Accordingly, under hypoxic condition, decrease synthesis of protein through PERK-eIF2α-ATF4 and AMPK-mTORC1 pathway.
In addition, BAPTA-AM effect on cell did not alter the production of IP3Rs by Vps34 but mutated the aggregation of the IP3Rs protein receptor WIPI-1 to the formation of phagophore.
Likewise, BAPTA-AM was observed to suppress lysosome fusion [ ]. Inhibition of calpain by pharmacological calpestatin and calpeptin or knockdown of calpain enhances autophagy flux without turbulence mTORC1 [ ].
Nonetheless, these studies demonstrate that calpain can suppress autophagy induction although other experimental studies suggest that the activation of calpain is essential for autophagy induction [ ].
The UPR pathway is not always a reason for autophagy induction. When ER stress is divergent in some contagious situation, defective regulation of autophagy occurs. Notably, in some pathological conditions such as neurodegenerative, cardiovascular, and liver diseases, ER stress negatively regulates autophagy.
Alzheimer disease AD is one of the most common neurodegenerative diseases, which is mainly caused by the accumulation of extracellular amyloid-β Aβ , senile plaques, and neurofibrillary tangles protein.
Aβ is originating from the cleavage of the amyloid precursor protein APP by two aspartic enzymes β-secretase BACE1 and γ-secretase. UPR and autophagy play a key role in maintaining normal neuron against aggregation of Aβ and PS1 mutation that affect the form of AD.
Many reports suggest that mutation in PS1 and accumulation of intracellular Aβ activate ER stress in neurons [ ]. Interestingly, mutation of ps1 and Aβ suppresses the main arms of UPR, including IRE1α, PERK, and ATF6α [ ].
Activation of ER stress is an early sequence of the AD, which initiates autophagy by phosphorylation of PERK-positive neuron via accumulation of MAP1LC3B induced autophagy in cardinal direction for abasement of Aβ and APP [ ].
Defective regulation of autophagic function leads to AD progression; Pickford et al. report that downregulation of Beclin-1 was observed in the middle frontal lobe in the brain cortex of AD patients similar to the observation in the mouse model of AD [ ].
Similarly, in Parkinson disease model, synaptic protein α-synuclein α-syn decreases accumulation of the expression of Beclin-1 gene that suppresses the induction of autophagy [ ]. Knockdown of IRE1α-XBP1 increases autophagy in HD model which initiates pathological condition [ , ]. Similarly, in HD-upregulated expression, USP14 is the deubiquitinating enzyme with His and Cys domains that increase autophagic discharge of mutant HTT protein huntingtin protein through nonphosphorylated IRE1α.
Phosphorylated IRE1α has not much affinity to interact with USP14, thus increasing accumulation of mutant HTT by suppressing autophagy regulation [ ].
Therefore, activation of UPR will not be regulated properly as a result of negative induction of autophagy, which fails to eradicate the accumulation of contagious protein and then consequently leads to neurodegenerative diseases. UPR and autophagy are also interconnected for inflammation of bowel in the epithelial cell.
In cultured intestinal epithelial cell initiate PERK-eIF2α dependent pathway autophagy because of loss IRE1α activity which intimate that UPR signal maintaining normal mechanism also conserve balance need to possible rebuttal mechanism [ ]. In addition, XBP1 conditional knock in intestinal epithelial cell lead to induced autophagy in small intestinal paneth cell, essential for the formation of antimicrobial agents followed by inflammation in small intestine, which is more exacerbated when codeletion of ATG gene like ATG7 or ATG16L1.
Moreover, In ATG16L conditional knockout mice enhance GRP78 expression along with phosphorylation of eIF2a and activation of JNK, terminating the expression of IRE1a and increased the XBP1 spicing in intestinal glands, these circumstances increase the inflammation state, which changes the interaction between ER stress and autophagy that increases cell death, which is negative retroaction of ER stress-induced autophagy [ ].
Notably, inactivation of XBP1 can induce autophagy but this UPR also can downregulate the induction of autophagy. Nevertheless, defective regulation of XBP1 integrates FoxO1 Forkhead box O1 , a transcription factor that sequentially provokes expression of many genes that positively induce autophagy [ 98 ].
The unspliced XBP1 uXBP1 under glutamine starvation condition regulated FoxO1 depravation by interacting FoxO1 for the 20s proteasome.
Accordingly, recently, the FoxO1 and XBP1 interaction in auditory cells regulates autophagy [ ]. Prominently, the consistent mechanism has been proved under severe ER stress in which the UPR loses its activity, whereas it can be considered that another regulatory mechanism FoxO1 maintains the autophagy induction.
During the last decade, research has been conducted to determine the mechanism by which ER stress and autophagy maintain intracellular homeostasis. Here, we described the UPR and autophagy in detail with respect to their molecular mechanism and interaction between ER stress and autophagy.
However, the detailed mechanism of ER stress and autophagy is yet to be fully understood. In the last few years, research has shown that the ER stress response can not only initiate autophagy but can also negatively regulate autophagy to maintain cell survival.
Elucidation of the interactions between the UPR and autophagy will help in the development of novel treatments for several diseases. The study was supported by Korean National Research Foundation R1E1A1A and M3A9G We acknowledge Mr.
Raghu Patil Junjappa and Mr. Ziaur Rahman Department of Pharmacology, Medical School, Chonbuk National University for their contribution in preparing the first draft.
Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3. Edited by Angel Catala. Open access peer-reviewed chapter Endoplasmic Reticulum Stress and Autophagy Written By Mohammad Fazlul Kabir, Hyung-Ryong Kim and Han-Jung Chae.
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Impact of this chapter. Abstract In eukaryotic cells, the aggregation of the endoplasmic reticulum ER -mediated unfolded or misfolded proteins leads to disruption of the ER homeostasis, which can trigger ER stress.
Keywords ER stress autophagy calcium lysosome. Endoplasmic reticulum The endoplasmic reticulum ER is a central membrane-bound organelle constructed from a dynamic network of tubules involved in cellular processes such as protein synthesis, gluconeogenesis, lipid synthesis and processing, and calcium storage and release in the cell and contributes to the generation of autophagosomes and peroxisomes [ 1 ].
ER stress mediates autophagy in pathological condition The UPR pathway is not always a reason for autophagy induction. Conclusion During the last decade, research has been conducted to determine the mechanism by which ER stress and autophagy maintain intracellular homeostasis.
Acknowledgments The study was supported by Korean National Research Foundation R1E1A1A and M3A9G Conflict of interest The authors declare that there is no conflict of interest. References 1. Hetz C. The unfolded protein response: Controlling cell fate decisions under ER stress and beyond. Nature Reviews.
Molecular Cell Biology. Baumann O, Walz B. Endoplasmic reticulum of animal cells and its organization into structural and functional domains. International Review of Cytology. Rolls MM et al. Targeting of rough endoplasmic reticulum membrane proteins and ribosomes in invertebrate neurons.
Molecular Biology of the Cell. Brodsky JL, Skach WR. Protein folding and quality control in the endoplasmic reticulum: Recent lessons from yeast and mammalian cell systems. Current Opinion in Cell Biology.
Braakman I, Bulleid NJ. Protein folding and modification in the mammalian endoplasmic reticulum. Annual Review of Biochemistry. Hebert DN, Molinari M. In and out of the ER: Protein folding, quality control, degradation, and related human diseases. Physiological Reviews.
Merksamer PI, Trusina A, Papa FR. Real-time redox measurements during endoplasmic reticulum stress reveal interlinked protein folding functions. Merksamer PI, Papa FR. The UPR and cell fate at a glance.
Journal of Cell Science. Chow CY et al. The genetic architecture of the genome-wide transcriptional response to ER stress in the mouse. PLoS Genetics. Kozutsumi Y et al.
The presence of malfolded proteins in the endoplasmic reticulum signals the induction of glucose-regulated proteins. Yadav RK et al. Endoplasmic reticulum stress and cancer.
Journal of Cancer Prevention. Oslowski CM, Urano F. The binary switch between life and death of endoplasmic reticulum-stressed beta cells. Current Opinion in Endocrinology, Diabetes, and Obesity. Measuring ER stress and the unfolded protein response using mammalian tissue culture system.
Methods in Enzymology. Dombroski BA et al. Gene expression and genetic variation in response to endoplasmic reticulum stress in human cells. American Journal of Human Genetics.
Reddy RK et al. Endoplasmic reticulum chaperone protein GRP78 protects cells from apoptosis induced by topoisomerase inhibitors: Role of ATP binding site in suppression of caspase-7 activation. The Journal of Biological Chemistry. Rutkowski DT, Kaufman RJ.
A trip to the ER: Coping with stress. Trends in Cell Biology. Calfon M et al. IRE1 couples endoplasmic reticulum load to secretory capacity by processing the XBP-1 mRNA.
Hetz C, Chevet E, Oakes SA. Proteostasis control by the unfolded protein response. Nature Cell Biology. Yoshida H et al. XBP1 mRNA is induced by ATF6 and spliced by IRE1 in response to ER stress to produce a highly active transcription factor. Lee KP et al. Structure of the dual enzyme Ire1 reveals the basis for catalysis and regulation in nonconventional RNA splicing.
Kohno K. How transmembrane proteins sense endoplasmic reticulum stress. Hendershot LM. The ER function BiP is a master regulator of ER function. Mount Sinai Journal of Medicine. Acosta-Alvear D et al.
XBP1 controls diverse cell type- and condition-specific transcriptional regulatory networks. Molecular Cell. Hollien J, Weissman JS.
Decay of endoplasmic reticulum-localized mRNAs during the unfolded protein response. Maurel M et al. Getting RIDD of RNA: IRE1 in cell fate regulation.
Trends in Biochemical Sciences. Yamaguchi H, Wang HG. CHOP is involved in endoplasmic reticulum stress-induced apoptosis by enhancing DR5 expression in human carcinoma cells.
Han D et al. IRE1alpha kinase activation modes control alternate endoribonuclease outputs to determine divergent cell fates. Urano F et al. Coupling of stress in the ER to activation of JNK protein kinases by transmembrane protein kinase IRE1. Ron D, Walter P. Signal integration in the endoplasmic reticulum unfolded protein response.
Scheuner D et al. Translational control is required for the unfolded protein response and in vivo glucose homeostasis. Harding HP et al. Regulated translation initiation controls stress-induced gene expression in mammalian cells.
Lu PD, Harding HP, Ron D. Translation reinitiation at alternative open reading frames regulates gene expression in an integrated stress response. The Journal of Cell Biology. Ye J, Koumenis C. ATF4, an ER stress and hypoxia-inducible transcription factor and its potential role in hypoxia tolerance and tumorigenesis.
Current Molecular Medicine. Pakos-Zebrucka K et al. The integrated stress response. EMBO Reports. Tsaytler P et al. Selective inhibition of a regulatory subunit of protein phosphatase 1 restores proteostasis. Johnson AJ et al.
The Biochemical Journal. Shen J, Prywes R. Dependence of site-2 protease cleavage of ATF6 on prior site-1 protease digestion is determined by the size of the luminal domain of ATF6. Yamamoto K et al. Transcriptional induction of mammalian ER quality control proteins is mediated by single or combined action of ATF6alpha and XBP1.
Developmental Cell. Klionsky DJ et al. Guidelines for the use and interpretation of assays for monitoring autophagy 3rd edition. Devenish RJ, Klionsky DJ. Frontiers in Bioscience Scholar Edition. A unified nomenclature for yeast autophagy-related genes. Settembre C, Ballabio A. Lysosome: Regulator of lipid degradation pathways.
Yang Z, Klionsky DJ. Eaten alive: A history of macroautophagy. Dunn WA Jr et al. Pexophagy: The selective autophagy of peroxisomes. Mizushima N, Klionsky DJ. Protein turnover via autophagy: Implications for metabolism.
Annual Review of Nutrition. Yang JW et al. Autophagy appears during the development of the mouse lower first molar. Histochemistry and Cell Biology.
Mizushima N, Komatsu M. Autophagy: Renovation of cells and tissues. Mizushima N et al. Autophagy fights disease through cellular self-digestion. Kuma A et al.
The role of autophagy during the early neonatal starvation period. Mammalian autophagy: Core molecular machinery and signaling regulation. Sahu R et al. Microautophagy of cytosolic proteins by late endosomes. Kaushik S, Cuervo AM. Chaperone-mediated autophagy: A unique way to enter the lysosome world.
Schneider JL, Suh Y, Cuervo AM. Deficient chaperone-mediated autophagy in liver leads to metabolic dysregulation. Cell Metabolism. He C, Klionsky DJ. Regulation mechanisms and signaling pathways of autophagy.
Annual Review of Genetics. Glick D, Barth S, Macleod KF. Autophagy: Cellular and molecular mechanisms. The Journal of Pathology. Wang CW, Klionsky DJ.
The molecular mechanism of autophagy. Molecular Medicine. Mizushima N, Yoshimori T, Ohsumi Y. The role of Atg proteins in autophagosome formation. Annual Review of Cell and Developmental Biology.
Papinski D et al. Early steps in autophagy depend on direct phosphorylation of Atg9 by the Atg1 kinase. Orsi A et al. Dynamic and transient interactions of Atg9 with autophagosomes, but not membrane integration, are required for autophagy.
Karanasios E et al. Dynamic association of the ULK1 complex with omegasomes during autophagy induction. Mercer CA, Kaliappan A, Dennis PB. A novel, human Atg13 binding protein, Atg, interacts with ULK1 and is essential for macroautophagy.
Simonsen A, Tooze SA. Coordination of membrane events during autophagy by multiple class III PI3-kinase complexes. Martelli AM et al. Two hits are better than one: Targeting both phosphatidylinositol 3-kinase and mammalian target of rapamycin as a therapeutic strategy for acute leukemia treatment.
Sun Q et al. The RUN domain of rubicon is important for hVps34 binding, lipid kinase inhibition, and autophagy suppression.
Maiuri MC et al. Functional and physical interaction between Bcl-X L and a BH3-like domain in Beclin The EMBO Journal.
Pattingre S et al. Bcl-2 antiapoptotic proteins inhibit Beclin 1-dependent autophagy. Klionsky DJ. The molecular machinery of autophagy: Unanswered questions.
Ohsumi Y. Molecular dissection of autophagy: Two ubiquitin-like systems. Role of the Apg12 conjugation system in mammalian autophagy. D Pearson's colocalization coefficient for GFP-HDEL and cerulean-ATG8e autophagosomes , CFP-HDEL and ST-GFP Golgi , CFP-HDEL and GFP-VHA1 TGN , and CFP-HDEL and YFP-RHA1 PVC.
Pearson's coefficient was derived from three independent experiments. To analyze further and quantify the colocalization between the cerulean-ATG8e and the GFP-HDEL signals, the fluorescence patterns of the two signals were analyzed using the ImageJ software Abramoff et al.
Together, these data suggest that during ER stress, ER is delivered to the vacuole through an ATG8e-containing vesicle, presumably an autophagosome.
To test further the role of the autophagy pathway in delivering ER to the vacuole, similar experiments as described above were performed comparing wild-type and RNAi- ATG18a leaf protoplasts transiently expressing a cyan fluorescent protein CFP -HDEL fusion construct as an ER marker Liu et al.
Autophagosome formation is defective in RNAi- ATG18a plants, which thus can be used to test whether the loss of the autophagy pathway blocks ER transport to the vacuole during ER stress. In both wild-type and RNAi- ATG18a protoplasts, the CFP signal labeled an ER membrane network in control conditions.
After addition of concA , most of the wild-type protoplasts showed an ER pattern and a few showed some CFP puncta, but almost all RNAi- ATG18a protoplasts observed displayed an ER pattern without CFP puncta. After adding TM , CFP puncta were observed in a majority of wild-type protoplasts, but not in RNAi- ATG18a protoplasts.
After adding both TM and concA to the medium, most of the wild-type protoplasts observed accumulated numerous CFP puncta inside the vacuole; however, RNAi- ATG18a protoplasts still displayed the ER pattern, suggesting that delivery of ER to the vacuole is blocked when autophagy is defective.
These results indicate that the delivery of ER to the vacuole is dependent on the autophagy-related gene ATG18a and this, when taken together with the colocalization between the ER marker and the autophagosome marker, suggests that the ER is delivered in autophagosomes.
Two major vacuolar trafficking routes have been identified in plants: the autophagy pathway and the biosynthetic pathway, which involves the Golgi, the trans -Golgi network TGN , and the prevacuolar compartment PVC Sanderfoot et al.
To investigate whether the ER structures identified in the vacuole can also be transported through the biosynthetic pathway, the subcellular colocalization between the ER marker and the Golgi marker ST-GFP Boevink et al. Both the confocal images and the Pearson coefficient Figure 3D suggested that the punctate ER fluorescence signal does not colocalize with the Golgi, the TGN , and the PVC structures.
These results indicate that the ER structures identified in the vacuole during ER stress are not transported via the Golgi, TGN , and the PVC pathway. Although it can be interpreted that the colocalization of ER puncta with an autophagosome marker indicates that ER is transported to the vacuole by autophagosomes, previous studies in animals showed that the autophagosome membrane can be derived from ER membrane Hayashi-Nishino et al.
To clarify whether ER is delivered by autophagosomes or is a component of the autophagosome membrane during ER stress, electron microscopy was performed to examine the detailed structures of ER stress—induced autophagosomes Figure 4.
In the controls, a few small vesicles were observed in both the vacuoles and the cytoplasm Figure 4A. In response to TM treatment, numerous vesicles appeared in the cytoplasm, but the contents of the vesicles were difficult to identify Figure 4C.
This might be due to the fusion of autophagosomes with a smaller lysosome-like or endosome-like organelle, leading to the degradation of the contents in the autophagosomes before fusion with the vacuole Rose et al. Since concA was used to inhibit vacuolar degradation, the contents inside the autophagic bodies could be identified.
These small vesicles contained a variety of cargos, some with unidentified cytoplasmic contents Figure 4H , whereas many had membrane structures decorated with electron-dense ribosomes Figures 4E to 4G , typical of ER.
Not all autophagosomes or autophagic bodies contained ER , consistent with the partial colocalization seen by confocal microscopy. From this we conclude that ER membranes had been engulfed by autophagosomes. Together, these results imply that ER is transported to the vacuole for degradation via the autophagy pathway during ER stress.
ER Membranes Are Engulfed by Autophagosomes during ER Stress. AB, autophagic bodies. E and F Autophagic bodies with ribosome-decorated membranes inside. G Enlargement of a section indicted in F.
In Arabidopsis , IRE1 has been identified as an ER stress sensor. IRE1 senses ER stress and splices the mRNA encoding bZIP60, which is a bZIP -containing transcription factor implicated in the UPR in plants Deng et al.
There are two members of the IRE1 gene family in Arabidopsis , IRE1a and IRE1b Koizumi et al. To investigate whether ER stress—induced autophagy is activated via IRE1 genes, the induction of autophagy was examined in ire1a or ire1b null mutants Humbert et al.
In control conditions, all three genotypes showed very few autophagosomes. ER Stress—Induced Autophagy Is Dependent on IRE1b Function in Arabidopsis Roots. B The number of MDC -stained autophagosomes per root section was counted after DTT and TM treatment as above and the average number determined for 20 seedlings per treatment.
To quantify these observations, autophagosome numbers were analyzed per root section for both ire1a and ire1b mutants Figure 5B. The ire1a mutant responded to both ER stress DTT or TM treatment and the starvation stress, whereas the ire1b mutant responded to the starvation stress but showed significantly lower autophagosome numbers during ER stress treatment.
To confirm further the MDC staining result, concA was used to prevent vacuolar degradation of autophagic bodies, which were visualized by DIC microscopy. In the absence of concA , ire1a , ire1b , and wild-type plants all displayed few spherical structures in the vacuole in almost all conditions tested.
The DIC image analysis together with the MDC staining results indicate that IRE1b , and not IRE1a , is required for ER stress—induced autophagy but not for starvation-induced autophagy in roots.
To confirm further the MDC and DIC results obtained in seedling roots, 4-week-old leaf protoplasts from wild-type, ire1a , and ire1b plants were transformed with a GFP-ATG8e fusion construct to visualize the induction of autophagy under ER stress by confocal microscopy Figure 6A.
In the control, the fluorescence from GFP-ATG8e was diffuse in all three types of plant protoplasts. In response to TM treatment, most of the wild-type and ire1a plants contained GFP-ATG8e labeled puncta, indicating the induction of autophagy, whereas the GFP signal was diffuse in ire1b , indicating no autophagosome formation.
These results again suggest that the ER stress—induced autophagy is dependent on IRE1b. ER Stress—Induced Autophagy Is Dependent on IRE1b Function in Arabidopsis Leaf Protoplasts.
Leaf protoplasts obtained from 4-week-old wild-type WT , ire1a , and ire1b plants were transformed with GFP-ATG8e A or CFP-HDEL B fusion constructs.
As a control, protoplasts were incubated in W5 solution with or without 1 µM concA for 12 h. DMSO was used as a solvent control. Confocal microscopy was used to visualize the GFP and CFP fluorescence.
Arrows indicate autophagic bodies containing GFP-ATG8e or CFP-HDEL. Next, the role of IRE1b in delivery of ER to the vacuole upon ER stress was analyzed using wild-type, ire1a , and ire1b leaf protoplasts transiently expressing a CFP-HDEL fusion construct Figure 6B.
In control conditions, the ER pattern was typical in all three types of plant protoplasts. In the presence of TM , most of the wild-type and ire1a plants contained CFP -labeled puncta, whereas ire1b plants mainly showed a typical ER labeling pattern.
These results imply that the delivery of ER to the vacuole is dependent on IRE1b but not on IRE1a. Together, the findings both in planta and in protoplasts suggest that IRE1b is required for ER stress—induced autophagy. To confirm that the loss of autophagy induction during ER stress in the ire1b mutant was actually due to the lack of IRE1b gene function, autophagy induction was tested in both ire1b leaf protoplasts transiently expressing a FLAG-tagged IRE1b construct Figure 7A and transgenic lines expressing the IRE1b cDNA IRE1b-FLAG in the ire1b mutant background Figure 7B ; see Supplemental Figure 6 online.
Wild-type leaf protoplasts transiently expressing GFP-ATG8e displayed a diffuse GFP signal in control conditions, and GFP puncta were observed in the presence of TM as expected Figure 7A. ire1b leaf protoplasts transiently expressing GFP-ATG8e showed a diffuse GFP signal in both the control and after TM treatment.
However, upon transformation of ire1b leaf protoplasts with both IRE1b-FLAG and GFP-ATG8e constructs, the GFP signal was diffuse in the control conditions, but GFP puncta were seen in the presence of TM , similar to wild-type protoplasts.
Together, these results indicate that the defect for autophagy induction in ire1b in response to ER stress can be attributed to the loss of IRE1b gene function, rather than other defects in the autophagy pathway. This again suggests that ER stress—induced autophagy is dependent on the IRE1b gene.
Defects in Autophagy Induction in ire1b during ER Stress Can Be Attributed to the Loss of IRE1b Gene Function. A Leaf protoplasts obtained from 4-week-old wild-type WT or ire1b plants were transformed with the GFP-ATG8e fusion construct, or ire1b leaf protoplasts were transformed with both GFP-ATG8e and IRE1b-FLAG fusion constructs.
For controls, the protoplasts were incubated in W5 solution. Arrows indicate GFP-ATG8e—labeled autophagic bodies. Arrows indicate MDC -stained autophagosomes and autophagic bodies.
As discussed above, IRE1b splices bZIP60 mRNA to produce an active transcription factor, thus upregulating the UPR genes in plants Deng et al. To test whether regulation of ER stress—induced autophagy by IRE1b occurs via IRE1b splicing of bZIP60 , the induction of autophagy was examined in a bzip60 T-DNA insertion mutant Deng et al.
Seven-day-old wild-type and bzip60 plants grown on MS plates were transferred to MS liquid medium supplemented with TM or DSMO as a solvent control, followed by MDC staining Figure 8. Unexpectedly, the bzip60 mutant showed constitutive autophagy even under control conditions.
One explanation for the constitutive autophagy in the bzip60 mutant is that the loss of bZIP60 function causes constitutive ER stress, thus inducing autophagy.
Alternatively, the loss in bZIP60 function may lead to general cellular stress, causing an increased level of basal autophagy. This complicated the testing of whether ER stress induces autophagy in bzip60 , as autophagy seen upon TM treatment in bzip60 could either be increased basal autophagy or a mixture of the basal autophagy and TM induced autophagy.
bZIP60 and bZIP28 Are Not Involved in Regulating ER Stress—Induced Autophagy. MDC staining of roots was performed to visualize autophagosomes. To distinguish between these two possibilities, the NADPH oxidase inhibitor DPI was used to inhibit the general starvation and salt stress—induced autophagy pathway Liu et al.
As shown in Figure 1 , the addition of an NADPH oxidase inhibitor does not block ER stress—induced autophagy. In the presence of DPI , no autophagy was seen in bzip60 Figure 8 , indicating that the constitutive autophagy observed in bzip60 is inhibited by DPI and is therefore most likely a general stress response and unrelated to ER stress.
After adding both DPI and TM to the medium, wild-type plants still showed autophagy induction. Autophagosomes were also present in the bzip60 mutant in the presence of DPI and TM , which suggests that after DPI inhibition of the enhanced basal autophagy, an alternative pathway for activation of ER stress—induced autophagy was still active.
These data indicate that autophagy can still be induced by ER stress in the bzip60 mutant and, therefore, that bZIP60 is not required for ER stress—induced autophagy. Thus, ER stress—induced autophagy is regulated by IRE1b but is not dependent on the downstream factor bZIP Animal cells contain another two ER stress sensors, ATF6 and PERK , in addition to IRE1.
Cells lacking ATF6 or PERK are capable of autophagy induction in response to ER stress Ogata et al. In plants, bZIP28 may be functionally equivalent to ATF6, whereas PERK signaling has not been demonstrated in plants Liu et al.
To investigate whether bZIP28 is involved in ER stress—induced autophagy, a bzip knockout mutant Liu et al. Similar experiments as described above for bzip60 were performed with 7-d-old bzip plants Figure 8. The bzip plants displayed constitutive autophagy even in control conditions.
This constitutive autophagy was inhibited by the addition of the NADPH oxidase inhibitor DPI , indicating that the constitutive autophagy seen in the bzip mutant was most likely a general stress response and unrelated to ER stress.
After adding both DPI and TM to the medium, autophagosomes were present in bzip , indicating that after the inhibition of general stress-induced autophagy, autophagy can still be induced by ER stress in the bzip mutant.
These data imply that, like bZIP60 , bZIP28 is not required for ER stress—induced autophagy. Although a number of studies have focused on UPR signaling pathways in plants, little is understood about ER morphology changes in response to ER stress or as mediated by the UPS -independent ERAD pathway Urade, , ; Moreno and Orellana, Previously, plant autophagy had been shown to be involved in senescence, nutrient deprivation, oxidative stress, salt and drought stresses, and pathogen infection Doelling et al.
In this article, we demonstrate that autophagy is activated in the response to ER stress in plants. MDC staining and GFP-ATG8e transgenic plants showed autophagy induction after TM or DTT treatment.
In addition, portions of the ER are engulfed by autophagosomes and delivered to the vacuole for degradation. Together, this evidence implicates autophagy in ER turnover in response to ER stress.
To investigate the upstream signaling pathway that activates ER stress—induced autophagy, a mutant lacking one of the ER stress sensors, IRE1b , was tested for autophagy induction upon ER stress. Leaf protoplasts transiently expressing CFP-HDEL or GFP-ATG8e indicated that IRE1b is required for ER stress—induced autophagy.
To characterize further the IRE1b-dependent autophagy pathway, a mutant lacking the splicing target of IRE1b, bZIP60, was also analyzed. The bzip60 mutant was capable of inducing autophagy in response to ER stress, suggesting that ER stress—induced autophagy does not rely on the splicing activity of IRE1b.
Our data identified IRE1b as an upstream component of ER stress—induced autophagy in Arabidopsis seedlings. However, we cannot exclude the possibility that IRE1a could also be involved in autophagy. Thus, by analyzing root tissues and protoplasts, we may not have been able to assess the contribution by IRE1a simply because it is not highly expressed in roots.
IRE1a plays newly recognized roles in plant defense responses, so it will be interesting to determine whether those responses also involve autophagy Moreno et al.
There is some discrepancy in the literature about the extent to which the roles of IRE1a and IRE1b overlap, which may be due to allelic differences in the mutants used in the different studies Deng et al. The detailed molecular mechanism of regulation of ER stress—induced autophagy is yet to be determined.
In yeast, ER stress—induced autophagy is regulated through the IRE1 endoribonuclease activity toward HAC1 mRNA Yorimitsu et al. In animals, IRE1 is also required for autophagy induction; however, the IRE1 kinase activity-mediated c-Jun N-terminal kinase pathway, which is absent in plants, rather than the splicing activity toward XBP1 seems to control autophagy induction Urano et al.
Our results showed that in plants, ER stress—induced autophagy is dependent on IRE1b , suggesting a conserved role for the IRE1 gene during autophagy induction from yeast to animals and plants. Similar to animals, autophagy does not depend on the IRE1b downstream splicing target, which in the case of Arabidopsis is bZIP60 Deng et al.
As bZIP60 is the only known target of IRE1b ribonuclease activity, this suggests that either 1 IRE1b has additional splicing targets that have yet to be discovered that regulate autophagy activation or 2 other activities associated with IRE1b may be responsible for the autophagy induction in response to ER stress, rather than its splicing activity.
However, other functions of IRE1b in addition to the splicing of bZIP60 mRNA have not been discovered to date Deng et al. This suggests that a distinct, previously undiscovered, signaling pathway functions in activation of autophagy during ER stress in Arabidopsis.
To elucidate further the role of IRE1 in autophagy induction, more experiments are needed to identify its substrates and downstream signals. Intriguingly, the loss of XBP1 in Drosophila melanogaster causes constitutive autophagy Arsham and Neufeld, , similar to that of the bzip60 and bzip28 mutants observed here.
The authors suggest that the absence of XBP1 activity may lead to accumulation of unfolded proteins, triggering XBP1-independent UPR signaling.
Whether this happens in plant cells still needs to be determined. Target of rapamycin TOR has been shown to be a negative regulator of autophagy from yeast to animals and plants Díaz-Troya et al.
TOR regulates the downstream ATG1 kinase complex, recently characterized in Arabidopsis Suttangkakul et al. Several studies have shown an interplay between ER stress and mTOR signaling in animals; for example, constitutive activation of mTOR leads to ER stress Ozcan et al. It was also suggested that ER stress induces autophagy through the inactivation of mTOR Qin et al.
However, whether TOR is associated with the control of autophagy during ER stress in plants is still unknown. A recent study in Chlamydomonas reinhardtii reported that the phosphorylation state of the BiP chaperone is regulated by TOR Díaz-Troya et al.
The authors showed that under ER stress when increased chaperone levels are needed, BiP protein is dephosphorylated, resulting in its activation.
When protein synthesis was inhibited by downregulating TOR activity, BiP was phosphorylated to its inactive form Díaz-Troya et al. These results indicate a potential TOR function in its interaction with the ER stress signal, thereby regulating both protein synthesis and the autophagy degradation pathway.
However, how exactly TOR senses ER stress, and whether IRE1 fits into this pathway, still needs to be determined. Generally, autophagy is a nonselective process; however, organelle-specific autophagy has been identified in both yeast and animals Reumann et al.
For example, the selective degradation of peroxisomes pexophagy Hutchins et al. In plants, organelle-specific autophagy has not been studied extensively.
Nevertheless, increasing evidence is emerging for organelle-specific autophagy in plants, such as the degradation of ribosomes Hillwig et al. However, whether the engulfment of ER by autophagosomes is a selective process is unknown.
One possibility is that during ER stress, the ER begins to fragment, allowing it to be incorporated into autophagosomes nonselectively. Another possibility is that the autophagosome can recognize ER fragments containing misfolded proteins Yorimitsu and Klionsky, , therefore sequestering both the misfolded proteins and the ER membranes.
Similar mechanisms have been reported in plants. NBR1 homologs in both Arabidopsis and tobacco Nicotiana tabacum have been identified, and they both interact with ATG8 Svenning et al. Therefore, it is possible that the autophagosome sequesters ER through identifying ER fragments containing protein aggregates or containing surface proteins tagged by ubiquitylation, as has been seen in the case of mitophagy Ashrafi and Schwarz, ; however, more evidence is required before this conclusion can be drawn.
In this study, we provide another link between organelle degradation and autophagy by showing that the ER is a target of autophagy during ER stress in plants. Activities other than the splicing of bZIP60 by IRE1b may function as upstream events to regulate ER stress—induced autophagy.
However, future experiments are needed to determine the downstream targets of IRE1b and the detailed regulation mechanisms in the ER stress—induced autophagy pathway. Arabidopsis thaliana Columbia ecotype seeds were surface sterilized with 0.
Transgenic plants used in this study have been described previously as follows: RNAi- ATG18a Xiong et al. For starvation treatment, 7-d-old seedlings grown on solid MS plates were transferred to MS plates lacking Suc or nitrogen for an additional 4 d.
Plants grown on Suc starvation plates were incubated in the dark. If concA treatment see below was also required, the seedlings were then transferred to liquid MS medium lacking Suc or nitrogen plus concA for 12 h in the dark. For imidazole and DPI treatment, seedlings grown on solid MS plates were transferred to MS liquid medium plus or minus 20 mM imidazole or 20 µM DPI for the indicated times.
The solvent for DPI was DMSO; an equivalent volume of DMSO was added to controls. For concA treatment, seedlings grown on MS plates were transferred to MS liquid medium containing 1 µM concA or DMSO as a solvent control for 12 h in the dark.
The roots were mounted in water and then observed by confocal, fluorescence, and DIC microscopy. Arabidopsis seedlings were stained with MDC as previously described Contento et al. Seedlings were incubated with 0. Confocal microscopy was performed with a Leica confocal microscope using a ×63 Leica oil immersion objective.
The ATG8e cDNA was synthesized by RT-PCR from total RNA from 7-d-old seedlings grown on MS plates, using gene-specific primers see Supplemental Table 1 online.
The cDNA was sequenced for verification and ligated into the pAN vector using Bgl II and Not I restriction sites Rizzo et al. Protoplasts transformed with the Cerulean-ATG8e construct were observed with a CFP -optimized filter.
Arabidopsis leaf protoplasts were prepared and transformed according to Sheen Twenty micrograms of plasmid DNA was used for each transformation. Protoplasts were incubated at room temperature in darkness for 12 h, with 40 rpm orbital shaking. Pearson's colocalization coefficients were derived using ImageJ software Abramoff et al.
All Pearson's coefficients were derived from three completely independent experiments. IRE1b coding sequence was amplified from Columbia-0 cDNA using gene-specific primers. A 3XFLAG tag was added after the transmembrane domain of IRE1b by overlapping PCR. Primers used are listed in Supplemental Table 1 online.
IRE1b-N primers were used to amplify the first half of the IRE1b gene up to and including the transmembrane domain, IRE1b-C primers were used to amplify the second half of the IRE1b gene after the transmembrane domain, and FLAG primers were used for the 3XFLAG tag.
The IRE1b-3XFLAG DNA fragments were then ligated into the pSKM36 vector using Asc I- Spe I restriction sites Ikeda et al. This construct was introduced into Agrobacterium tumefaciens by electroporation Mersereau et al.
Transgenic plants were identified by kanamycin resistance. Individuals from the T2 generation were used for further studies. Electron microscopy was performed at the Iowa State University Microscopy and NanoImaging Facility.
Samples were rinsed three times in 0. Resin blocks were polymerized for 48 h at 65°C. Images were captured using a JEOL scanning and transmission electron microscope Japan Electron Optic Laboratories. Sequence data from this article can be found in the Arabidopsis Genome Initiative database under the following accession numbers: At2g IRE1a , At5g IRE1b , At3g bZIP28 , At1g bZIP60 , and At3g ATG18a.
The following materials are available in the online version of this article. Supplemental Figure 1. Autophagy Is Activated in the Presence of DTT. Supplemental Figure 2.
CFP-HDEL Does Not Colocalize with Golgi Structures during ER Stress. Supplemental Figure 3. CFP-HDEL Does Not Colocalize with a TGN Marker during ER Stress. Supplemental Figure 4. CFP-HDEL Does Not Colocalize with a PVC Marker during ER Stress. Supplemental Figure 5. Autophagosomes Do Not Accumulate in ire1b Roots in Response to ER Stress.
Supplemental Figure 6. Supplemental Table 1. Primers Used for Generation of the Cerulean-ATG8e and IRE1b-FLAG Constructs and for PCR. We thank Harry Jack T. Horner, Randall Den Adel, and Tracey M.
Pepper for assistance with the fluorescence, DIC , and the electron microscopy and Margaret Carter for assistance with confocal microscopy. We also thank Ian Moore for the GFP-HDEL transgenic plant, Karin Schumacher, Chris Hawes, and Erik Nielsen for constructs, and Anthony L. Contento for generating the cerulean-ATG8e construct.
This research was supported by Grants IOB and MCB from the National Science Foundation to D. designed research. performed research. analyzed data. wrote the article. Abramoff M.
Magalhaes P. Ram S. Image Processing with ImageJ. Biophotonics International 11 : 36 — Google Scholar. Arsham A.
Neufeld T. A genetic screen in Drosophila reveals novel cytoprotective functions of the autophagy-lysosome pathway. PLoS ONE 4 : e Ashrafi G. Schwarz T. June 29, The pathways of mitophagy for quality control and clearance of mitochondria.
Cell Death Differ. Bassham D. Plant autophagy—More than a starvation response. Plant Biol. Batoko H. Zheng H. Hawes C. Moore I. A rab1 GTPase is required for transport between the endoplasmic reticulum and Golgi apparatus and for normal Golgi movement in plants.
Plant Cell 12 : — Bernales S. McDonald K. Walter P. Autophagy counterbalances endoplasmic reticulum expansion during the unfolded protein response. PLoS Biol. Boevink P. Oparka K. Santa Cruz S.
Martin B. Betteridge A. Plant J. Calfon M. Zeng H. Urano F. Till J. Hubbard S. Harding H. Clark S. Ron D. IRE1 couples endoplasmic reticulum load to secretory capacity by processing the XBP-1 mRNA.
Nature : 92 — Che P. Bussell J. Zhou W. Estavillo G. Pogson B. Smith S. Signaling from the endoplasmic reticulum activates brassinosteroid signaling and promotes acclimation to stress in Arabidopsis.
Chen Y. Brandizzi F. Clough S. Bent A. Floral dip: A simplified method for Agrobacterium -mediated transformation of Arabidopsis thaliana.
Contento A. Xiong Y. Visualization of autophagy in Arabidopsis using the fluorescent dye monodansylcadaverine and a GFP-AtATG8e fusion protein.
Cox J. Shamu C. Transcriptional induction of genes encoding endoplasmic reticulum resident proteins requires a transmembrane protein kinase. Cell 73 : — A novel mechanism for regulating activity of a transcription factor that controls the unfolded protein response.
Cell 87 : — Deng Y. Humbert S. Liu J. Srivastava R. Rothstein S. Howell S. Heat induces the splicing by IRE1 of a mRNA encoding a transcription factor involved in the unfolded protein response in Arabidopsis.
USA : — Dettmer J. Hong-Hermesdorf A. Stierhof Y. Schumacher K. Plant Cell 18 : — Díaz-Troya S. Pérez-Pérez M. Florencio F. Crespo J. The role of TOR in autophagy regulation from yeast to plants and mammals. Autophagy 4 : — Pérez-Martín M.
Moes S. Jeno P. Inhibition of protein synthesis by TOR inactivation revealed a conserved regulatory mechanism of the BiP chaperone in Chlamydomonas.
Plant Physiol. Doelling J. Walker J. Friedman E. Thompson A. Vierstra R. Dröse S. Bindseil K. Bowman E. Siebers A. Zeeck A. Altendorf K. Inhibitory effect of modified bafilomycins and concanamycins on P- and V-type adenosinetriphosphatases.
Biochemistry 32 : — Gardner B. Unfolded proteins are Ire1-activating ligands that directly induce the unfolded protein response. Science : — Hanaoka H.
Noda T. Shirano Y. Kato T. Hayashi H. Shibata D. Tabata S. Ohsumi Y. Leaf senescence and starvation-induced chlorosis are accelerated by the disruption of an Arabidopsis autophagy gene. Zhang Y. Bertolotti A. Perk is essential for translational regulation and cell survival during the unfolded protein response.
Cell 5 : — Hayashi-Nishino M. Fujita N. Yamaguchi A. Yoshimori T. Yamamoto A. A subdomain of the endoplasmic reticulum forms a cradle for autophagosome formation. Cell Biol. Haze K. Yoshida H. Yanagi H. Yura T. Mori K. Mammalian transcription factor ATF6 is synthesized as a transmembrane protein and activated by proteolysis in response to endoplasmic reticulum stress.
Cell 10 : — Hillwig M. Meyer A. Ebany D. Macintosh G. RNS2, a conserved member of the RNase T2 family, is necessary for ribosomal RNA decay in plants. Zhong S. PLoS ONE 7 : e Hutchins M. Veenhuis M. Klionsky D. Peroxisome degradation in Saccharomyces cerevisiae is dependent on machinery of macroautophagy and the Cvt pathway.
Cell Sci. Ichimura Y. Kumanomidou T. Sou Y. Mizushima T. Ezaki J. Ueno T. Kominami E. Yamane T. Tanaka K. Komatsu M. Structural basis for sorting mechanism of p62 in selective autophagy.
Ikeda Y. Banno H. Niu Q. Chua N. Plant Cell Physiol. Inoue Y. Suzuki T. Hattori M. Yoshimoto K. Moriyasu Y. AtATG genes, homologs of yeast autophagy genes, are involved in constitutive autophagy in Arabidopsis root tip cells.
Ishida H. Izumi M. Reisen D. Yano Y. Makino A. Hanson M. Mae T. Mobilization of rubisco and stroma-localized fluorescent proteins of chloroplasts to the vacuole by an ATG gene-dependent autophagic process.
Iwata Y. Fedoroff N. Koizumi N. Arabidopsis bZIP60 is a proteolysis-activated transcription factor involved in the endoplasmic reticulum stress response. Plant Cell 20 : — An Arabidopsis transcription factor, AtbZIP60, regulates the endoplasmic reticulum stress response in a manner unique to plants.
Yoneda M. Yanagawa Y. Characteristics of the nuclear form of the Arabidopsis transcription factor AtbZIP60 during the endoplasmic reticulum stress response. Johansen T. Lamark T. Selective autophagy mediated by autophagic adapter proteins.
Autophagy 7 : — Kim I. Rodriguez-Enriquez S. Lemasters J. Selective degradation of mitochondria by mitophagy. Kirkin V. et al. A role for NBR1 in autophagosomal degradation of ubiquitinated substrates. Cell 33 : — Kohno K. Normington K. Sambrook J.
Gething M. The promoter region of the yeast KAR2 BiP gene contains a regulatory domain that responds to the presence of unfolded proteins in the endoplasmic reticulum. Martinez I. Kimata Y. Sano H. Chrispeels M. Molecular characterization of two Arabidopsis Ire1 homologs, endoplasmic reticulum-located transmembrane protein kinases.
Kraft C.
The endoplasmic reticulum Aytophagy is not only responsible Autophagy and ER stress protein synthesis and folding but streas plays a Omega- for skin health role in Autophagy and ER stress cellular stress and maintaining Autophagy and ER stress homeostasis. Autophayg sensing the accumulation of unfolded proteins due to perturbation in protein synthesis or Autophaagy, specific intracellular AAutophagy pathways are activated, which are collectively termed as unfolded protein response UPR. UPR expands the capacity of the protein folding machinery, decreases protein synthesis and enhances ER-associated protein degradation ERAD which degrades misfolded proteins through the proteasomes. More recent evidences suggest that UPR also amplifies cytokines-mediated inflammatory responses leading to pathogenesis of inflammatory diseases. UPR signaling also activates autophagy; a lysosome-dependent degradative pathwaythat has an extended capacity to degrade misfolded proteins and damaged ER. Thus, activation of autophagy limits inflammatory response and provides cyto-protection by attenuating ER-stress.
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