Differential Effects of Endoplasmic Reticulum Stress-induced Autophagy on Cell Survival

Abstract

Autophagy is a cellular response to adverse environment and stress, but its significance in cell survival is not always clear. Here we show that autophagy could be induced in the mammalian cells by chemicals, such as A23187, tunicamycin, thapsigargin, and brefeldin A, that cause endoplasmic reticulum stress. Endoplasmic reticulum stress-induced autophagy is important for clearing polyubiquitinated protein aggregates and for reducing cellular vacuolization in HCT116 colon cancer cells and DU145 prostate cancer cells, thus mitigating endoplasmic reticulum stress and protecting against cell death. In contrast, autophagy induced by the same chemicals does not confer protection in a normal human colon cell line and in the non-transformed murine embryonic fibroblasts but rather contributes to cell death. Thus the impact of autophagy on cell survival during endoplasmic reticulum stress is likely contingent on the status of cells, which could be explored for tumor-specific therapy. Autophagy is a cellular response to adverse environment and stress, but its significance in cell survival is not always clear. Here we show that autophagy could be induced in the mammalian cells by chemicals, such as A23187, tunicamycin, thapsigargin, and brefeldin A, that cause endoplasmic reticulum stress. Endoplasmic reticulum stress-induced autophagy is important for clearing polyubiquitinated protein aggregates and for reducing cellular vacuolization in HCT116 colon cancer cells and DU145 prostate cancer cells, thus mitigating endoplasmic reticulum stress and protecting against cell death. In contrast, autophagy induced by the same chemicals does not confer protection in a normal human colon cell line and in the non-transformed murine embryonic fibroblasts but rather contributes to cell death. Thus the impact of autophagy on cell survival during endoplasmic reticulum stress is likely contingent on the status of cells, which could be explored for tumor-specific therapy. Endoplasmic reticulum (ER) 3The abbreviations used are: ER, endoplasmic reticulum; 3-MA, 3-methyadenine; BA, brefeldin A; MEF, murine embryonic fibroblast; TM, tunicamycin; TG, thapsigargin; UPR, unfolded protein response; siRNA, small interfering RNA; AFC, 7-amino-4-trifluoromethylcoumarin.3The abbreviations used are: ER, endoplasmic reticulum; 3-MA, 3-methyadenine; BA, brefeldin A; MEF, murine embryonic fibroblast; TM, tunicamycin; TG, thapsigargin; UPR, unfolded protein response; siRNA, small interfering RNA; AFC, 7-amino-4-trifluoromethylcoumarin. is critically involved in protein metabolism. Normal ER function is required for the correct folding of many proteins and their post-translational modifications, such as glycosylation and disulfide bond formation. ER stress is induced by the disturbance of the environment in the ER lumen, such as the calcium homeostasis or the redox status, or by the disturbance of ER function, such as glycosylation and transportation to Golgi complex (1.Kaufman R.J. Genes Dev. 1999; 13: 1211-1233Crossref PubMed Scopus (1930) Google Scholar). The typical chemicals that induce ER stress include A23187 and thapsigargin, both of which disturb the calcium homeostasis; tunicamycin, which suppresses glycosylation; and brefeldin A, which inhibits transportation to the Golgi complex (1.Kaufman R.J. Genes Dev. 1999; 13: 1211-1233Crossref PubMed Scopus (1930) Google Scholar, 2.Breckenridge D.G. Germain M. Mathai J.P. Nguyen M. Shore G.C. Oncogene. 2003; 22: 8608-8618Crossref PubMed Scopus (649) Google Scholar). Thus these chemicals cause protein folding dysfunction, and the accumulated misfolded/unfolded proteins induce ER stress. ER stress is frequently observed in pathological conditions where protein misfolding is caused by genetic mutations either in the molecule to be processed or in the machinery processing the folding (3.Perlmutter D.H. Lab. Investig. 1999; 79: 623-638PubMed Google Scholar, 4.Kopito R.R. Ron D. Nat. Cell Biol. 2000; 2: E207-E209Crossref PubMed Scopus (321) Google Scholar). The major protective and compensatory mechanism during ER stress is the unfolded protein response (UPR) (1.Kaufman R.J. Genes Dev. 1999; 13: 1211-1233Crossref PubMed Scopus (1930) Google Scholar, 5.Harding H.P. Calfon M. Urano F. Novoa I. Ron D. Annu. Rev. Cell Dev. Biol. 2002; 18: 575-599Crossref PubMed Scopus (808) Google Scholar), which leads to translational attenuation and selective up-regulation of a number of bZip transcription factors (1.Kaufman R.J. Genes Dev. 1999; 13: 1211-1233Crossref PubMed Scopus (1930) Google Scholar, 5.Harding H.P. Calfon M. Urano F. Novoa I. Ron D. Annu. Rev. Cell Dev. Biol. 2002; 18: 575-599Crossref PubMed Scopus (808) Google Scholar). UPR serves multiple functions, including the assistance of protein folding via the up-regulated ER protein chaperones and the enhanced degradation of misfolded proteins via the up-regulation of molecules involved in the ER-associated degradation pathway (1.Kaufman R.J. Genes Dev. 1999; 13: 1211-1233Crossref PubMed Scopus (1930) Google Scholar, 5.Harding H.P. Calfon M. Urano F. Novoa I. Ron D. Annu. Rev. Cell Dev. Biol. 2002; 18: 575-599Crossref PubMed Scopus (808) Google Scholar). However, if the stress is excessive, the compensatory mechanisms may not be able to fully sustain ER function, and ER decompensation could lead to cell death (2.Breckenridge D.G. Germain M. Mathai J.P. Nguyen M. Shore G.C. Oncogene. 2003; 22: 8608-8618Crossref PubMed Scopus (649) Google Scholar, 6.Rao R.V. Ellerby H.M. Bredesen D.E. Cell Death Differ. 2004; 11: 372-380Crossref PubMed Scopus (816) Google Scholar). It is not clear whether there are other mechanisms that can regulate ER stress. Macroautophagy (referred as autophagy hereafter) is mainly responsible for the degradation of long-lived proteins and subcellular organelles (7.Mizushima N. Ohsumi Y. Yoshimori T. Cell Struct. Funct. 2002; 27: 421-429Crossref PubMed Scopus (755) Google Scholar, 8.Levine B. Klionsky D.J. Dev Cell. 2004; 6: 463-477Abstract Full Text Full Text PDF PubMed Scopus (3189) Google Scholar, 9.Meijer A.J. Codogno P. Int. J. Biochem. Cell Biol. 2004; 36: 2445-2462Crossref PubMed Scopus (547) Google Scholar). Autophagy is frequently activated in response to adverse environment or stress (10.Kamada Y. Sekito T. Ohsumi Y. Curr. Top. Microbiol. Immunol. 2004; 279: 73-84Crossref PubMed Google Scholar, 11.Kuma A. Hatano M. Matsui M. Yamamoto A. Nakaya H. Yoshimori T. Ohsumi Y. Tokuhisa T. Mizushima N. Nature. 2004; 432: 1032-1036Crossref PubMed Scopus (2386) Google Scholar, 12.Lum J.J. Bauer D.E. Kong M. Harris M.H. Li C. 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Cell Biol. 2005; 6: 505-510Crossref PubMed Scopus (842) Google Scholar). Although some studies indicate that autophagy is responsible for the non-apoptotic cell death (13.Shimizu S. Kanaseki T. Mizushima N. Mizuta T. Arakawa-Kobayashi S. Thompson C.B. Tsujimoto Y. Nat. Cell Biol. 2004; 6: 1221-1228Crossref PubMed Scopus (1190) Google Scholar, 15.Bursch W. Cell Death Differ. 2001; 8: 569-581Crossref PubMed Scopus (558) Google Scholar, 17.Baehrecke E.H. Nat. Rev. Mol. Cell Biol. 2005; 6: 505-510Crossref PubMed Scopus (842) Google Scholar, 18.Yu L. Alva A. Su H. Dutt P. Freundt E. Welsh S. Baehrecke E.H. Lenardo M.J. Science. 2004; 304: 1500-1502Crossref PubMed Scopus (1098) Google Scholar, 19.Pyo J.O. Jang M.H. Kwon Y.K. Lee H.J. Jun J.I. Woo H.N. Cho D.H. Choi B. Lee H. Kim J.H. Mizushima N. Oshumi Y. Jung Y.K. J. Biol. Chem. 2005; 280: 20722-20729Abstract Full Text Full Text PDF PubMed Scopus (468) Google Scholar), others indicate that autophagy is protective against cell death (12.Lum J.J. Bauer D.E. Kong M. Harris M.H. Li C. Lindsten T. Thompson C.B. Cell. 2005; 120: 237-248Abstract Full Text Full Text PDF PubMed Scopus (1263) Google Scholar, 20.Boya P. Gonzalez-Polo R.A. Casares N. Perfettini J.L. Dessen P. Larochette N. Metivier D. Meley D. Souquere S. Yoshimori T. Pierron G. Codogno P. Kroemer G. Mol. Cell. Biol. 2005; 25: 1025-1040Crossref PubMed Scopus (1431) Google Scholar, 21.Kamimoto T. Shoji S. Hidvegi T. Mizushima N. Umebayashi K. Perlmutter D.H. Yoshimori T. J. Biol. Chem. 2006; 281: 4467-4476Abstract Full Text Full Text PDF PubMed Scopus (219) Google Scholar, 22.Hara T. Nakamura K. Matsui M. Yamamoto A. Nakahara Y. Suzuki-Migishima R. Yokoyama M. Mishima K. Saito I. Okano H. Mizushima N. Nature. 2006; 441: 885-889Crossref PubMed Scopus (3108) Google Scholar, 23.Komatsu M. Waguri S. Chiba T. Murata S. Iwata J. Tanida I. Ueno T. Koike M. Uchiyama Y. Kominami E. Tanaka K. Nature. 2006; 441: 880-884Crossref PubMed Scopus (2829) Google Scholar, 24.Kouroku Y. Fujita E. Tanida I. Ueno T. Isoai A. Kumagai H. Ogawa S. Kaufman R.J. Kominami E. Momoi T. Cell Death Differ. June 23, 2006; DOI 10.1038/sj.cdd.4401984PubMed Google Scholar). The condition under which autophagy may be pro-survival or prodeath is not clear. In the current study, we found that autophagy could be activated by the classical ER stress inducers in mammalian cells. However, autophagy alleviates ER stress and reduces cell death in cancer cells but not in non-transformed cells. This unique feature may be explored for certain types of cancer therapy in which ER stress constitutes a major cause of cell death. Reagents−The following antibodies were used: anti-Atg6/Beclin 1 (BD Biosciences), anti-Atg8/LC3B (25.Kabeya Y. Mizushima N. Ueno T. Yamamoto A. Kirisako T. Noda T. Kominami E. Ohsumi Y. Yoshimori T. EMBO J. 2000; 19: 5720-5728Crossref PubMed Scopus (5433) Google Scholar), anti-Atg5 (26.Mizushima N. Yamamoto A. Hatano M. Kobayashi Y. Kabeya Y. Suzuki K. Tokuhisa T. Ohsumi Y. Yoshimori T. J. Cell Biol. 2001; 152: 657-668Crossref PubMed Scopus (1158) Google Scholar), anti-ubiquitin (Santa Cruz Biotechnology), anti-β-actin (Sigma), and anti-glyceraldehyde-3-phosphate dehydrogenase (Chemicon). All chemicals were from Sigma or Invitrogen. Plasmids, siRNA, and Transfection−One to two μg of GFP-LC3B (rat) (25.Kabeya Y. Mizushima N. Ueno T. Yamamoto A. Kirisako T. Noda T. Kominami E. Ohsumi Y. Yoshimori T. EMBO J. 2000; 19: 5720-5728Crossref PubMed Scopus (5433) Google Scholar) was transfected into 2 × 105 cells using Effectene according to the supplier’s protocol (Qiagen). Alternatively, murine embryonic fibroblasts (MEFs) and CCD-18Co cells were infected with Ad-GFP-LC3B (human) for 24–48 h before being analyzed. siRNAs (0.24 μm) were transfected into 1 × 106 cells using Oligofectamine (Invitrogen) for 48 h before analysis. siRNAs against the following human genes were used: Atg6/Beclin 1 (5′-GGUCUAAGACGUCCAACAA-3′) and Atg8/LC3B (5′-GAAGGCGCUUACAGCUCAA-3′). Cell Culture and Microscopy−HCT116 Bax-positive and Bax-negative cell lines (27.Zhang L. Yu J. Park B.H. Kinzler K.W. Vogelstein B. Science. 2000; 290: 989-992Crossref PubMed Scopus (794) Google Scholar) were maintained in McCoy’s 5A with the routine supplements. DU145 cell lines were maintained in Dulbecco’s modified Eagle’s medium with routine supplements. Wild type and Atg5-deficient MEFs were immortalized through SV40 large T overexpression and cultured in Dulbecco’s modified Eagle’s medium with standard supplements (11.Kuma A. Hatano M. Matsui M. Yamamoto A. Nakaya H. Yoshimori T. Ohsumi Y. Tokuhisa T. Mizushima N. Nature. 2004; 432: 1032-1036Crossref PubMed Scopus (2386) Google Scholar). The non-immortalized human colon cell line CCD-18Co was purchased from ATCC (CRL-1459™) and cultured in Dulbecco’s modified Eagle’s medium with standard supplements. All cell lines were maintained in a 37 °C incubator with 5% CO2. Cells (2 × 105/well) were seeded into 12-well plates. After 24 h, cells were treated as indicated in the figure legends. For electron microscopy, cells were fixed with 2% paraformaldehyde and 2% glutaraldehyde in 0.1 m phosphate buffer (pH 7.4) followed by 1% OsO4. After dehydration, thin sections were stained with uranyl acetate and lead citrate for observation under a JEM 1016CX electron microscope. To examine distribution of GFP-LC3B, cells were observed under a fluorescence microscope and digital images were acquired for analysis (SPOT, Diagnostic Instruments, Inc.). To examine and quantify cellular vacuolization, digital phase-contrast images were of Cell death was using and by digital cells with or were were using μg of proteins and and for and The fluorescence were by a as H.M. D. 2004; PubMed Scopus Google Scholar). is as H.M. D. 2004; PubMed Scopus Google Scholar). Cells were in and in of protein was by and to The were stained with the indicated and antibodies and with of Macroautophagy by ER in feature of autophagy is the of the Atg8/LC3B from the to the (25.Kabeya Y. Mizushima N. Ueno T. Yamamoto A. Kirisako T. Noda T. Kominami E. Ohsumi Y. Yoshimori T. EMBO J. 2000; 19: 5720-5728Crossref PubMed Scopus (5433) Google Scholar, Y. Mizushima N. Cell Dev. Biol. 2004; PubMed Scopus Google Scholar). The mammalian Atg8/LC3B is by to the and to via a by a and a protein This is by and Atg6/Beclin 1 (25.Kabeya Y. Mizushima N. Ueno T. Yamamoto A. Kirisako T. Noda T. Kominami E. Ohsumi Y. Yoshimori T. EMBO J. 2000; 19: 5720-5728Crossref PubMed Scopus (5433) Google Scholar, Y. Mizushima N. Cell Dev. Biol. 2004; PubMed Scopus Google Scholar). The of Atg8/LC3B is in the the to the (25.Kabeya Y. Mizushima N. Ueno T. Yamamoto A. Kirisako T. Noda T. Kominami E. Ohsumi Y. Yoshimori T. EMBO J. 2000; 19: 5720-5728Crossref PubMed Scopus (5433) Google Scholar). The ER stress A23187 could a of the in a in a colon cancer cell HCT116 of the of the which is to in cell line ER stress including and brefeldin could induce such and not This could be by the (12.Lum J.J. Bauer D.E. Kong M. Harris M.H. Li C. Lindsten T. Thompson C.B. Cell. 2005; 120: 237-248Abstract Full Text Full Text PDF PubMed Scopus (1263) Google Scholar, 13.Shimizu S. Kanaseki T. Mizushima N. Mizuta T. Arakawa-Kobayashi S. Thompson C.B. Tsujimoto Y. Nat. Cell Biol. 2004; 6: 1221-1228Crossref PubMed Scopus (1190) Google Scholar, S. A. 79: PubMed Scopus Google Scholar) or by the against Atg6/Beclin 1 or Atg8/LC3B not the of the caused by the ER stress cells GFP-LC3B a of the GFP-LC3B from the to the following the of the ER stress inducers and the of GFP-LC3B could be by or a against Atg6/Beclin 1 and indicated that a of was in HCT116 as as in a prostate cancer cell following the of A23187, TM, TG, or and with could be of autophagy A, HCT116 or DU145 cells were treated with A23187 a and and and or and for Cells were fixed and to electron The of is and are the number of was in and DU145 cells. were as from ER homeostasis or function the of misfolded which in induce ER stress (1.Kaufman R.J. Genes Dev. 1999; 13: 1211-1233Crossref PubMed Scopus (1930) Google Scholar, 2.Breckenridge D.G. Germain M. Mathai J.P. Nguyen M. Shore G.C. Oncogene. 2003; 22: 8608-8618Crossref PubMed Scopus (649) Google Scholar, D.H. Lab. Investig. 1999; 79: 623-638PubMed Google Scholar, 4.Kopito R.R. Ron D. Nat. Cell Biol. 2000; 2: E207-E209Crossref PubMed Scopus (321) Google Scholar, 5.Harding H.P. Calfon M. Urano F. Novoa I. Ron D. Annu. Rev. Cell Dev. Biol. 2002; 18: 575-599Crossref PubMed Scopus (808) Google Scholar). the protein into the ER could the stress and thus autophagy of cells with the or the translational the of and the of GFP-LC3B to these indicate that a of chemicals could via the of ER stress. Autophagy Cells from ER and Cell the significance of autophagy in the of ER stress. In HCT116 and DU145 cells, ER stress inducers could cause cellular vacuolization to ER under stress on electron not of autophagy with either or a against Atg6/Beclin 1 and or Atg8/LC3B not the of cells with vacuolization, enhanced of ER stress. The accumulated misfolded proteins in the ER are through ER-associated degradation pathway via the following B. C. E. T. Nat. Cell Biol. 2005; PubMed Scopus Google Scholar). Thus of polyubiquitinated proteins could indicate the of misfolded proteins and the of ER stress. both A23187 and could the of polyubiquitinated proteins in HCT116 cells and DU145 cells and protein aggregates could be in treated cells and which that the of these proteins the of for degradation R.R. J. Cell Biol. PubMed Scopus Google Scholar). autophagy by or a against Atg6/Beclin 1 and to in polyubiquitinated protein that autophagy can function to ER stress on its on cellular vacuolization and polyubiquitinated protein the of ER stress could with the of cell we whether autophagy induced in these cancer cells could on ER stress-induced cell death. in HCT116 cells is on the of (27.Zhang L. Yu J. Park B.H. Kinzler K.W. Vogelstein B. Science. 2000; 290: 989-992Crossref PubMed Scopus (794) Google Scholar). The cells from the Bax-positive cells to into through the mechanism D. G. D.G. J. Biol. Chem. 2005; 280: Full Text Full Text PDF PubMed Scopus Google Scholar). In the where ER stress and autophagy could be Bax-positive HCT116 cells were to or the HCT116 cells of autophagy with either not or a against Atg6/Beclin 1 or Atg8/LC3B and to in the Bax-positive HCT116 cells. The of both and the ER were enhanced and under a of HCT116 cells with enhanced of death autophagy was in cell death could be observed in the DU145 cells not that autophagy can against cell death in cancer cells, likely by the of ER stress and the of death Autophagy Cell Death in Cells with ER the significance of autophagy in ER stress-induced cell death in types of cells, we the of the of immortalized MEFs that are Atg5-deficient (11.Kuma A. Hatano M. Matsui M. Yamamoto A. Nakaya H. Yoshimori T. Ohsumi Y. Tokuhisa T. Mizushima N. Nature. 2004; 432: 1032-1036Crossref PubMed Scopus (2386) Google Scholar). All ER stress inducers could induce GFP-LC3B and the in the MEFs in and of these cells indicated that there was of However, of ER stress inducers not induce cellular vacuolization in the MEFs whether is or in to was observed in HCT116 and DU145 cells, of autophagy in MEFs to Thus Atg5-deficient MEFs were to and induced by A23187, TG, TM, or the type MEFs of into the Atg5-deficient MEFs their to the of ER stress of ER stress-induced autophagy reduces cell death in A, type and MEFs were treated for 24 h with A23187 a and and and and and for 24 The of cells was by the of cellular vacuolization in treated cells and the cell death in cells. and the of cells and cells were by or were using as the MEFs were transfected with murine or the for 24 h and treated with A23187 or for 24 h before being for as The on and in these cells. was as the complex with All were shown as To the that of autophagy may be to the status of the we a non-immortalized normal human colon cell line which be with HCT116 colon cancer cells. of cell line with A23187 or induced autophagy that could be by However, not lead to cell death but rather in cell death with the in these not induce cellular vacuolization in cell line these in the non-transformed cells are in to in HCT116 and DU145 cells, that the role of ER stress-induced autophagy in cell survival is contingent on the status of the cells and can be in cancer cells and in non-transformed cells under a of of Macroautophagy by ER the major processing post-translational and correct protein ER the mechanisms to proteins that to be modified B. C. E. T. Nat. Cell Biol. 2005; PubMed Scopus Google Scholar). proteins are and by This ER-associated degradation pathway is important for ER The of the such as that to the of TM, TG, or BA, can lead to ER stress. The UPR is a classical mechanism that cells to ER stress, which to cellular protein protein and ER-associated degradation (1.Kaufman R.J. Genes Dev. 1999; 13: 1211-1233Crossref PubMed Scopus (1930) Google Scholar, 5.Harding H.P. Calfon M. Urano F. Novoa I. Ron D. Annu. Rev. Cell Dev. Biol. 2002; 18: 575-599Crossref PubMed Scopus (808) Google Scholar). Here we show that autophagy is activated in response to ER stress in the mammalian cells and could be mechanism ER stress and the ER stress could induce autophagy in the T. Klionsky D.J. J. Biol. Chem. 2006; 281: Full Text Full Text PDF PubMed Scopus Google Scholar), that response is ER stress leads to the of autophagy is not up-regulation of certain such as Y. Fujita E. Tanida I. Ueno T. Isoai A. Kumagai H. Ogawa S. Kaufman R.J. Kominami E. Momoi T. Cell Death Differ. June 23, 2006; DOI 10.1038/sj.cdd.4401984PubMed Google Scholar) and Atg8/LC3B not been observed and could be Although the of cellular protein is during ER stress, a of such as the transcription factors and are activated of which is important of the UPR (1.Kaufman R.J. Genes Dev. 1999; 13: 1211-1233Crossref PubMed Scopus (1930) Google Scholar, 5.Harding H.P. Calfon M. Urano F. Novoa I. Ron D. Annu. Rev. Cell Dev. Biol. 2002; 18: 575-599Crossref PubMed Scopus (808) Google Scholar). transcription factors could be involved in the autophagy has been found to be important for autophagy induced by the Y. Fujita E. Tanida I. Ueno T. Isoai A. Kumagai H. Ogawa S. Kaufman R.J. Kominami E. Momoi T. Cell Death Differ. June 23, 2006; DOI 10.1038/sj.cdd.4401984PubMed Google Scholar), and W. D. Kaufman R.J. B. S. A. 2002; PubMed Scopus Google Scholar). UPR response such as by and could be Although other mechanisms may be required for a of indicate that from ER stress are for the of which in the The of Autophagy in ER and ER Cell the cancer cells, autophagy to ER stress, and the cell death. autophagy ER stress is not clear indicate that autophagy is important for the of proteins and reduces ER stress induced by these This is by the in with of or in the which leads to the of polyubiquitinated proteins in the T. Nakamura K. Matsui M. Yamamoto A. Nakahara Y. Suzuki-Migishima R. Yokoyama M. Mishima K. Saito I. Okano H. Mizushima N. Nature. 2006; 441: 885-889Crossref PubMed Scopus (3108) Google Scholar, 23.Komatsu M. Waguri S. Chiba T. Murata S. Iwata J. Tanida I. Ueno T. Koike M. Uchiyama Y. Kominami E. Tanaka K. Nature. 2006; 441: 880-884Crossref PubMed Scopus (2829) Google Scholar). In has been found that misfolded such as the protein and the could induce autophagy in to ER stress, of their cellular Y. Fujita E. Tanida I. Ueno T. Isoai A. Kumagai H. Ogawa S. Kaufman R.J. Kominami E. Momoi T. Cell Death Differ. June 23, 2006; DOI 10.1038/sj.cdd.4401984PubMed Google Scholar, J.H. Perlmutter D.H. J. 2000; 279: PubMed Google Scholar, R.V. Bredesen D.E. Curr. Opin. Cell Biol. 2004; 16: PubMed Scopus Google Scholar, T. Urano F. Ron D. Genes Dev. 2002; 16: PubMed Scopus Google Scholar). Although of autophagy the of the molecules and reduces the of autophagy in the T. Shoji S. Hidvegi T. Mizushima N. Umebayashi K. Perlmutter D.H. Yoshimori T. J. Biol. Chem. 2006; 281: 4467-4476Abstract Full Text Full Text PDF PubMed Scopus (219) Google Scholar, 24.Kouroku Y. Fujita E. Tanida I. Ueno T. Isoai A. Kumagai H. Ogawa S. Kaufman R.J. Kominami E. Momoi T. Cell Death Differ. June 23, 2006; DOI 10.1038/sj.cdd.4401984PubMed Google Scholar, B. C. S. F. R. Nat. 2004; 36: PubMed Scopus Google Scholar, M. T. T. A. Mizushima N. Yoshimori T. M. B. J. J. Biol. Chem. 2006; 281: Full Text Full Text PDF PubMed Scopus Google Scholar). Thus autophagy can be protective against ER stress in a number of including cancer cells. ER homeostasis by the chemicals could autophagy in the colon cells, of autophagy does not cell death but reduces cell death. In of autophagy induced by the same chemicals in the immortalized but non-transformed MEFs by of reduces cell death. that autophagy can to ER stress-induced cell death in which may be on cellular status under a However, the mechanisms such a are to be In the of the current we that the role of autophagy in cell survival in the cancer cells and non-transformed cells may be to the ER stress is MEFs and CCD-18Co be in response to the for is that of ER stress inducers not cause cellular vacuolization, and autophagy not to vacuolization in these cells and Although autophagy could be involved in clearing misfolded its degradation to be for the cells, in which autophagy may lead to of normal cellular and to cell be to to However, current has indicated the of the mechanism and a of such that the of autophagy in cancer cells and non-transformed cells may be explored for tumor-specific therapy. are to Yoshimori of and Mizushima of for the and Atg5-deficient MEFs and anti-Atg5 are to Vogelstein for the HCT116 Bax-positive and Bax-negative cell and for assistance in electron