Glucose-dependent insulinotropic polypeptide promotes beta-(INS-1) cell survival via cyclic adenosine monophosphate-mediated caspase-3 inhibition and regulation of p38 mitogen-activated protein kinase.
The incretin glucose-dependent insulinotropic polypeptide (GIP) is a major regulator of postprandial insulin secretion in mammals. Recent studies in our laboratory, and others have suggested that GIP is a potent stimulus for protein kinase activation, including the MAPK (ERK1/2) module. Based on these studies, we hypothesized that GIP could regulate cell fate and sought to examine the underlying mechanisms involved in GIP stimulation of cell survival. GIP potentiated glucose-induced beta-(INS-1)-cell growth to levels comparable with GH and GLP-1 while promoting cell survival in the face of serum and glucose-deprivation or treatment with wortmannin or streptozotocin. In the absence of GIP, 50% of cells died after 48 h of serum and glucose withdrawal, whereas 91 +/- 10% of cells remained viable in the presence of GIP [n = 3, P < 0.05; EC50 of 1.24 +/- 0.48 nm GIP (n = 4)]. Effects of GIP on cell survival and inhibition of caspase-3 were mimicked by forskolin, but pharmacological experiments excluded roles for MAPK kinase (Mek)1/2, phosphatidylinositol 3-kinase, protein kinase A, Epac, and Rap 1. Survival effects of GIP were ablated by the inhibitor SB202190, indicating a role for p38 MAPK. Furthermore, caspase-3 activity was also regulated by p38 MAPK, with a lesser role for Mek1/2, based on RNA interference studies. We propose that GIP is able to reverse caspase-3 activation via inhibition of long-term p38 MAPK phosphorylation in response to glucose deprivation (+/-wortmannin). Intriguingly, these findings contrasted with short-term phosphorylation of MKK3/6-->p38 MAPK-->ATF-2 by GIP. Thus, these data suggest that GIP is able to regulate INS-1 cell survival by dynamic control of p38 MAPK phosphorylation via cAMP signaling and lend further support to the notion that GIP regulation of MAPK signaling is critical for its regulation of cell fate.
Ehses
Jan A
JA
Department of Physiology, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
Casilla
Vanbric R
VR
Doty
Tim
T
Pospisilik
J Andrew
JA
Winter
Kyle D
KD
Demuth
Hans-Ulrich
HU
Pederson
Raymond A
RA
McIntosh
Christopher H S
CH
D000818:Animals; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D000242:Cyclic AMP / Q000502:physiology*; D005749:Gastric Inhibitory Polypeptide / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000502:physiology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism* / Q000502:physiology; D010766:Phosphorylation; D011964:Receptors, Gastrointestinal Hormone / Q000378:metabolism / Q000502:physiology; D048051:p38 Mitogen-Activated Protein Kinases
D061945:Caspase Inhibitors; D011964:Receptors, Gastrointestinal Hormone; D005749:Gastric Inhibitory Polypeptide; C041086:gastric inhibitory polypeptide receptor; D000242:Cyclic AMP; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D053148:Caspase 3; D020169:Caspases