Bradykinin enhances insulin receptor tyrosine kinase in 32D cells reconstituted with bradykinin and insulin signaling pathways

We have previously shown that bradykinin potentiated insulin-induced glucose uptake through GLUT4 translocation in canine adipocytes and skeletal muscles. The aim of this study was to determine the molecular mechanism of bradykinin enhancement of the insulin signal. For this purpose, 32D cells, which express a limited number of insulin receptors and lack endogenous bradykinin B2 receptor (BK2R) or insulin receptor substrate (IRS)-1 were transfected with BK2R cDNA and/or insulin receptor cDNA and/or IRS-1 cDNA, and analyzed. In 32D cells that expressed BK2R and insulin receptor (32D-BKR/IR), bradykinin alone had no effect on the phosphorylation of the insulin receptor, but it enhanced insulin-stimulated tyrosine phosphorylation of the insulin receptor. In 32D cells that expressed BK2R, insulin receptor and IRS-1 (32D-BKR/IR/IRS1), bradykinin also enhanced insulin-stimulated tyrosine phosphorylation of the insulin receptor and IRS-1. An increase in insulin-stimulated phosphorylation of IRS-1 by treatment with bradykinin in 32D-BKR/IR/IRS1 cell was associated with increased binding of 85 kD subunit of phosphatidylinositol 3 (PI 3)-kinase and increased IRS-1 associated PI 3-kinase activity. These effects of bradykinin were not observed in 32D cells which lack the expression of BK2R (32D-IR/IRS1) or insulin receptor (32D-BKR/IRS1). Furthermore, tyrosine phosphatase activity against insulin receptor beta-subunit in plasma membrane fraction of 32D-BKR/IR cells was significantly reduced by bradykinin, suggesting that the effect of bradykinin was in part mediated by inhibition of protein tyrosine phosphatase(s). Our results clearly demonstrated that bradykinin enhanced insulin-stimulated tyrosine kinase activity of the insulin receptor and downstream insulin signal cascade through the BK2R mediated signal pathway.