MODULATION OF INSULIN RECEPTOR FUNCTION

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Summary of work: The addition of a stearyl-conjugated synthetic peptide that corresponds to a discrete region within the insulin receptor carboxyl terminus results in the potentiation of insulin-mediated responses in intact cells. However, the hydrophobic interaction between stearyl conjugated peptides and the membrane lipid bilayer introduces a two-dimensional reaction environment, thus enabling efficiency and specificity that may be orders of magnitude lower (or higher) than would be possible with freely diffusing peptide. Therefore, we have attempted to express stably the same fragment of the insulin receptor carboxyl terminus using a minigene approach and to assess its effect toward insulin and IGF-1 responses in intact cells. Our study showed that stable expression of the minigene can increase insulin-induced insulin receptor autophosphorylation that was 2.4-fold higher when compared to that of cells transfected with empty vector. This was accompanied by a significant increase in activation of a number of signaling intermediates. Importantly, it was found that expression of the minigene was highly selective to insulin's action as it had no effect toward insulin-like growth factor I receptor kinase activity and function. The molecular determinant for activation of the insulin receptor catalytic function by the minigene remains unclear. However, we believe that the minigene [which encodes a sequence-specific 15 amino acid fragment of the receptor carboxyl terminus] binds with a non-catalytic region of the receptor beta-subunit and thus causes a conformational change that facilitates catalysis. Work is underway to assess this hypothesis.