title: Suppression of p38 MAPK and JNK via Akt-mediated inhibition of apoptosis signal-regulating kinase 1 constitutes a core component of the beta-cell pro-survival effects of glucose-dependent insulinotropic polypeptide.
abstract: Glucose-dependent insulinotropic polypeptide (GIP) potentiates glucose-stimulated insulin secretion, insulin biosynthesis, and beta-cell proliferation and survival. In previous studies GIP was shown to promote beta-cell survival by modulating the activity of multiple signaling modules and regulating gene transcription of pro- and anti-apoptotic bcl-2 family proteins. We have now evaluated the mechanisms by which GIP regulates the dynamic interactions between cytoplasmic bcl-2 family members and the mitochondria in INS-1 cells during apoptosis induced by treatment with staurosporine (STS), an activator of the mitochondria-mediated apoptotic pathway. STS induced translocation of bad and bimEL, activation of mitochondrial bax, release of mitochondrial cytochrome c, cleavage of caspase-3, and apoptosis. Each response was significantly diminished by GIP. Using selective enzyme inhibitors, overexpression of dominant-negative Akt, and Akt siRNA, it was demonstrated that GIP promoted beta-cell survival via Akt-dependent suppression of p38 MAPK and JNK and that combined inhibition was sufficient to explain the entire pro-survival responses to GIP during STS treatment. This signaling pathway also explained the pro-survival effects of GIP on INS-1 cells exposed to two other promoters of stress: thapsigargin (endoplasmic reticulum stress) and etoposide (genotoxic stress). Importantly, we discovered that GIP suppressed p38 MAPK and JNK via Akt-mediated changes in the phosphorylation state of the apoptosis signal-regulating kinase 1 in INS-1 cells and human islets, resulting in inhibition of its activity. Inhibition of apoptosis by GIP is therefore mediated via a key pathway involving Akt-dependent inhibition of apoptosis signal-regulating kinase 1, which subsequently prevents the pro-apoptotic actions of p38 MAPK and JNK.
authors.affiliation: Department of Cellular and Physiological Sciences and the Diabetes Research Group, Life Sciences Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
authors.forename: Scott B
authors.initials: SB
authors.lastname: Widenmaier
authors.forename: Ziliang
authors.initials: Z
authors.lastname: Ao
authors.forename: Su-Jin
authors.initials: SJ
authors.lastname: Kim
authors.forename: Garth
authors.initials: G
authors.lastname: Warnock
authors.forename: Christopher H S
authors.initials: CH
authors.lastname: McIntosh
mesh_terms: D017209:Apoptosis; D002470:Cell Survival; D002478:Cells, Cultured; D005749:Gastric Inhibitory Polypeptide / Q000502:physiology*; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology*; D007515:Islets of Langerhans / Q000166:cytology; D048848:MAP Kinase Kinase Kinase 5 / Q000037:antagonists & inhibitors*; D048055:Mitogen-Activated Protein Kinase 8 / Q000037:antagonists & inhibitors*; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors*
chemical_list: D005749:Gastric Inhibitory Polypeptide; D051057:Proto-Oncogene Proteins c-akt; D048055:Mitogen-Activated Protein Kinase 8; D048051:p38 Mitogen-Activated Protein Kinases; D048848:MAP Kinase Kinase Kinase 5