Overexpression of insulin degrading enzyme: cellular localization and effects on insulin signaling

To investigate the role of insulin degrading enzyme (insulysin, EC 3.4.24.56) in insulin signaling, Chinese hamster ovary cells overexpressing the human insulin receptor were genetically engineered to also stably overexpress the rat insulin degrading enzyme. In comparison to the parental cells, these cells expressed 2.7-fold elevated levels of enzyme and insulin degradation was also increased 2-fold. These cells also exhibited a more rapid decrease in receptor tyrosine phosphorylation after removal of insulin. Moreover, low concentrations of insulin were less effective at stimulating proliferation of the cells overexpressing the enzyme. Finally, a fraction of the overexpressed enzyme as well a fraction of the endogenous enzyme could be detected on the plasma membrane surface of these cells. These results support the hypothesis that this enzyme may function in insulin signaling by degrading the insulin molecule.