Glucose-dependent insulinotropic polypeptide (GIP) stimulation of pancreatic beta-cell survival is dependent upon phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB) signaling, inactivation of the forkhead transcription factor Foxo1, and down-regulation of bax expression.
The hormone glucose-dependent insulinotropic polypeptide (GIP) potently stimulates insulin secretion and promotes beta-cell proliferation and cell survival. In the present study we identified Forkhead (Foxo1)-mediated suppression of the bax gene as a critical component of the effects of GIP on cell survival. Treatment of INS-1(832/13) beta-cells with GIP resulted in concentration-dependent activation of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB)/Foxo1 signaling module. In parallel studies, GIP decreased bax promoter activity. Serial deletion analysis of the bax promoter demonstrated that the region -682 to -320, containing FHRE-II (5AAAACAAACA), was responsible for GIP-mediated effects. Foxo1 bound to FHRE-II in gel mobility shift assays, and Foxo1-FHRE-II interactions conferred GIP responsiveness to the bax promoter. INS-1 cells incubated under proapoptotic and glucolipotoxic conditions demonstrated increased nuclear localization of Foxo1 and bax promoter activity and decreased cytoplasmic phospho-PKB/Foxo1. GIP partially restored expression PKB/Foxo1 and bax promoter activity. Similar protective effects were found with dispersed islet cells from C57BL/6 mice, but not with those from GIP receptor knock-out (GIPR(-/-)) mice. GIP treatment reduced glucolipotoxicity-induced cell death in C57 BL/6 and Bax(-/-) islets, but not GIPR(-/-) mouse islets. Chronic treatment of Vancouver diabetic fatty Zucker rats with GIP resulted in down-regulation of Bax and up-regulation of Bcl-2 in pancreatic beta-cells. The results show that PI3K/PKB/Foxo1 signaling mediates GIP suppression of bax gene expression and that this module is a key pathway by which GIP regulates beta-cell apoptosis in vivo.
Kim
Su-Jin
SJ
Department of Cellular and Physiological Sciences, University of British Columbia, 2146 Health Sciences Mall, Vancouver, British Columbia V6T 1Z3, Canada.
Winter
Kyle
K
Nian
Cuilan
C
Tsuneoka
Makoto
M
Koda
Yoshiro
Y
McIntosh
Christopher H S
CH
D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002460:Cell Line; D002470:Cell Survival; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D005749:Gastric Inhibitory Polypeptide / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D007515:Islets of Langerhans / Q000166:cytology*; D008156:Luciferases / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051381:Rats; D011924:Rats, Zucker; D015398:Signal Transduction; D013347:Subcellular Fractions; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D051028:bcl-2-Associated X Protein
D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D005749:Gastric Inhibitory Polypeptide; D008156:Luciferases; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D014157:Transcription Factors; D051028:bcl-2-Associated X Protein; C494826:BAX protein, human; C494827:Bax protein, mouse; C494828:Bax protein, rat; C467200:Foxo1 protein, mouse