ANTIAPOPTOTIC FUNCTION OF THE INSULIN RECEPTOR

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Summary of work: Apoptosis, or programmed cell death, is a natural phenomenon that plays a major role in normal turnover of cells and pathological processes, including autoimmune diabetes and diabetic neuropathy. Numerous evidences indicate that activation of the insulin receptor confers cell survival, in part, by activating transcription factors that are known to be involved in the control of the apoptotic process. In a recent published study, we reported that farnesylation of Ras-related small GTP-binding proteins may be involved in the antiapoptotic protection conferred by the insulin receptor. There are only three members of the Ras family that are known to be farnesylated and targeted at the plasma membrane. Transfection of cells with wild- type and dominant-negative mutant of these small GTP-binding proteins is underway. Meanwhile, we established that expression of a transdominant inhibitory mSOS1 mutant blocked insulin-mediated activation of p21Ras but not the antiapoptotic effects of insulin, as assessed by levels of peroxynitrite, activity of caspase-3, DNA fragmentation, cytochrome c release from mitochondria, and fluorescence-activated cell sorting. The pretreatment with pertussis toxin (PTX) markedly attenuated protection offered by insulin. We concluded that insulin inhibits apoptosis via a Ras-independent, but PTX-sensitive, pathway. There are several signaling molecules that are implicated in the control of cell death. Interestingly, the interaction between the insulin receptor and PTX-sensitive inhibitory G-proteins represents a regulated integrative point for cross-talk between tyrosine kinase receptor- and cyclic AMP-dependent signaling cascades. Consequently, we plan to use antisense strategies to investigate the role of selective inhibitory G-proteins (e.g., i1, i2 or i3) in the antiapoptotic function of insulin. Lastly, the devastating complications of diabetes are the results of prolonged periods of hyperglycemia. Byproducts of cellular respiration as well as high glucose concentrations found in diabetic conditions can result in cell death. We plan also to characterize the mechanisms by which glucose and its metabolites function as apoptotic inducers. - Insulin receptors; Signal transduction; Apoptosis; CHO cells; Farnesylation