Transgenic mice expressing Shb adaptor protein under the control of rat insulin promoter exhibit altered viability of pancreatic islet cells

Background: The Src-homology 2 domain-containing adaptor protein Shb was re cently cloned as a serum-inducible gene in the insulin-producing beta-TCl c ell line. Subsequent studies have revealed an involvement of Shb for apopto sis in NIH3T3 fibroblasts and differentiation in the neuronal PCl2 cells. T o assess a role of Shb for beta-cell function, transgenic mice utilizing th e rat insulin promoter to drive expression of Shb were generated. Materials and Methods: A gene construct allowing the Shb cDNA to be express ed from the rat insulin 2 promoter was microinjected into fertilized mouse oocytes and implanted into pseudopregnant mice. Mice containing a low copy number of this transgene were bred and used for further experimentation. Sh b expression was determined by Western blot analysis. The insulin-positive area of whole pancreas, insulin secretion of isolated islets and islet cell apoptosis, glucose tolerance tests, and in vivo sensitivity to multiple in jections of the beta-cell toxin streptozotocin were determined in control C BA and Shb-transgenic mice. Results: Western blot analysis revealed elevated islet content of the Shb p rotein. Shb-transgenic mice dis played enhanced glucose-disappearance rates in response to an intravenous glucose injection. The relative pancreatic b eta-cell area neonatally and at 6 months of age were increased in the Shb-t ransgenic mice. Islets isolated from Shb-transgenic mice showed enhanced in sulin secretion in response to glucose and increased insulin and DNA conten t. Apoptosis was increased in islets isolated from Shb-transgenic mice comp ared with control islets both under basal conditions and after incubation w ith IL-1 beta + IFN-gamma. Rat insulinoma RINm5F cells overexpressing Shb d isplayed decreased viability during culture in 0.1% serum and after exposur e to a cytotoxic dose of nicotinamide. Shb-transgenic mice injected with mu ltiple doses of streptozotocin showed increased blood glucose values compar ed with the corresponding controls, suggesting increased in vivo susceptibi lity to this toxin. Conclusion: The results suggest that Shb has dual effects on beta-cell grow th: whereas Shb increases beta-cell formation during late embryonal stages, Shb also enhances beta-cell death under certain stressful conditions and m ay thus contribute to beta-cell destruction in type 1 diabetes.