The molecular mechanism of endoplasmic reticulum stress-induced apoptosis in PC-12 neuronal cells: the protective effect of insulin-like growth factor I.
Endoplasmic reticulum (ER) stress has been implicated in several neurodegenerative diseases. Although CCAAT/enhancer-binding protein homologous protein (CHOP) has been shown to play a critical role in ER stress, the precise apoptosis cascade downstream of CHOP is unknown. In this report, we investigated the mechanism of ER stress-mediated apoptosis as well as the action of IGF-I in PC-12 neuronal cells. Our results demonstrated that tribbles-related protein 3 (TRB3), which is a target gene of CHOP, was responsible for tunicamycin (an ER stress inducer)-induced apoptosis. TRB3 could promote dephosphorylation of Akt in PC-12 cells. IGF-I inhibited ER stress-induced apoptosis by restoring the phosphorylation level of Akt. Both wortmannin (a phosphatidylinositide 3-kinase inhibitor) and SB 212090 (a p38 MAPK inhibitor) suppressed the protective effect of IGF-I on ER stress-induced apoptosis. Interestingly, IGF-I attenuated ER stress-mediated expression of TRB3 but not CHOP. This action of IGF-I was abolished by SB 212090 but not by wortmannin. Immunoprecipitation analysis revealed that IGF-I promoted the phosphorylation of CHOP by activating p38 MAPK, probably leading to a decrease in the transcriptional activity of CHOP. The dephosphorylation of Akt resulted in increased expression of a proapoptotic protein, p53 up-regulated modulator of apoptosis (PUMA), in a forkhead box O3a-dependent manner. Knockdown of PUMA by short hairpin RNA attenuated ER stress-mediated apoptosis. Thus, our current study indicates that both TRB3 and PUMA are critical molecules in ER stress-induced apoptosis. IGF-I effectively protects PC-12 neuronal cells against ER stress-induced apoptosis through the phosphatidylinositide 3-kinase/Akt and p38 MAPK pathways.
Zou
Cheng-Gang
CG
Laboratory for Conservation and Utilization of Bio-Resources, Yunnan University, Kunming, Yunnan 650091, China.
Cao
Xiu-Zhen
XZ
Zhao
Yue-Shui
YS
Gao
Shun-Yu
SY
Li
Shu-De
SD
Liu
Xian-Yong
XY
Zhang
Yan
Y
Zhang
Ke-Qin
KQ
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000187:drug effects / Q000235:genetics; D017931:DNA Primers; D004273:DNA, Neoplasm / Q000235:genetics / Q000302:isolation & purification; D015536:Down-Regulation; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D016716:PC12 Cells; D010673:Pheochromocytoma; D017346:Protein Serine-Threonine Kinases / Q000187:drug effects / Q000235:genetics / Q000037:antagonists & inhibitors; D012334:RNA, Neoplasm / Q000235:genetics; D051381:Rats; D012097:Repressor Proteins / Q000187:drug effects / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D018797:Cell Cycle Proteins; D017931:DNA Primers; D004273:DNA, Neoplasm; D012334:RNA, Neoplasm; D012097:Repressor Proteins; C474831:TRIB3 protein, human; D007334:Insulin-Like Growth Factor I; D017346:Protein Serine-Threonine Kinases; D048051:p38 Mitogen-Activated Protein Kinases