Expression of an uncleavable N-terminal RasGAP fragment in insulin-secreting cells increases their resistance toward apoptotic stimuli without affecting their glucose-induced insulin secretion.
Apoptosis of pancreatic beta cells is implicated in the onset of type 1 and type 2 diabetes. Consequently, strategies aimed at increasing the resistance of beta cells toward apoptosis could be beneficial in the treatment of diabetes. RasGAP, a regulator of Ras and Rho GTPases, is an atypical caspase substrate, since it inhibits, rather than favors, apoptosis when it is partially cleaved by caspase-3 at position 455. The antiapoptotic signal generated by the partial processing of RasGAP is mediated by the N-terminal fragment (fragment N) in a Ras-phosphatidylinositol 3-kinase-Akt-dependent, but NF-kappaB-independent, manner. Further cleavage of fragment N at position 157 abrogates its antiapoptotic properties. Here we demonstrate that an uncleavable form of fragment N activates Akt, represses NF-kappaB activity, and protects the conditionally immortalized pancreatic insulinoma betaTC-tet cell line against various insults, including exposure to genotoxins, trophic support withdrawal, and incubation with inflammatory cytokines. Fragment N also induced Akt activity and protection against cytokine-induced apoptosis in primary pancreatic islet cells. Fragment N did not alter insulin cell content and insulin secretion in response to glucose. These data indicate that fragment N protects beta cells without affecting their function. The pathways regulated by fragment N are therefore promising targets for antidiabetogenic therapy.
Yang
Jiang-Yan
JY
Department of Cellular Biology and Department of Physiology, Faculty of Biology and Medicine, Lausanne University, Bugnon 9, Lausanne 1005, Switzerland.
Walicki
Joël
J
Abderrahmani
Amar
A
Cornu
Marion
M
Waeber
Gérard
G
Thorens
Bernard
B
Widmann
Christian
C
D000818:Animals; D017209:Apoptosis; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002945:Cisplatin / Q000494:pharmacology; D003432:Cross-Linking Reagents / Q000494:pharmacology; D016207:Cytokines / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D007249:Inflammation; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D007340:Insulinoma / Q000378:metabolism; D016086:Lentivirus / Q000235:genetics; D051379:Mice; D008856:Microscopy, Fluorescence; D016328:NF-kappa B / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D020703:ras GTPase-Activating Proteins / Q000737:chemistry*
D003432:Cross-Linking Reagents; D016207:Cytokines; D007328:Insulin; D016328:NF-kappa B; D020703:ras GTPase-Activating Proteins; D019869:Phosphatidylinositol 3-Kinases; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; D005947:Glucose; D002945:Cisplatin