Mechanisms of MAPK activation by bradykinin in vascular smooth muscle cells

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Abstract
Vascular smooth muscle cell (VSMC) proliferation is a prominent feature of the atherosclerotic process occurring after endothelial injury. A vascular wall kallikrein-kinin system has been described. The contribution of this system to vascular disease is undefined. In the present study we characterized the signal transduction pathway leading to mitogen-activated protein kinase (MAPK) activation in response to bradykinin (BK) in VSMC. Addition of 10−10–10−7M BK to VSMC resulted in a rapid and concentration-dependent increase in tyrosine phosphorylation of several 144- to 40-kDa proteins. This effect of BK was abolished by the B2-kinin receptor antagonist HOE-140, but not by the B1-kinin receptor antagonist des-Arg9-Leu8-BK. Immunoprecipitation with anti-phosphotyrosine antibodies followed by immunoblot revealed that 10−9 M BK induced tyrosine phosphorylation of focal adhesion kinase (p125FAK). BK (10−8 M) promoted the association of p60src with the adapter protein growth factor receptor binding protein-2 and also induced a significant increase in MAPK activity. Pertussis and cholera toxins did not inhibit BK-induced MAPK tyrosine phosphorylation. Protein kinase C downregulation by phorbol 12-myristate 13-acetate and/or inhibitors to protein kinase C, p60src kinase, and MAPK kinase inhibited BK-induced MAPK tyrosine phosphorylation. These findings provide evidence that activation of the B2-kinin receptor in VSMC leads to generation of multiple second messengers that converge to activate MAPK. The activation of this crucial kinase by BK provides a strong rationale to investigate the mitogenic actions of BK on VSMC proliferation in disease states of vascular injury.

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