Mechanisms of MAPK activation by bradykinin in vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) proliferation is a prominent feature of the atherosclerotic process occurring after endothelial injury. A vascular wall kallikreinkinin system has been described. The contribution of this sy stem to vascular disease is undefined. In the present study we characterize d the signal transduction pathway leading to mitogen-activated protein kina se (MAPK) activation in response to bradykinin (BK) in VSMC. Addition of 10 (-10)-10(-7) M BK to VSMC resulted in a rapid and concentration-dependent i ncrease in tyrosine phosphorylation of several 144- to 40-kDa proteins. Thi s effect of BK was abolished by the B-2-kinin receptor antagonist HOE-140, but not by the B-1-kinin receptor antagonist des-Arg(9)-Leu(8)-BK. Immunopr ecipitation with anti-phosphotyrosine antibodies followed by immunoblot rev ealed that 10(-9) M BK induced tyrosine phosphorylation of focal adhesion k inase (p125(FAK)). BK (10(-8) M) promoted the association of p60(src) with the adapter protein growth factor receptor binding protein-2 and also induc ed a significant increase in MAPK activity. Pertussis and cholera toxins di d not inhibit BK-induced MAPK tyrosine phosphorylation. Protein kinase C do wnregulation by phorbol 12-myristate 13-acetate and/or inhibitors to protei n kinase C, p60(src) kinase, and MAPK kinase inhibited BK-induced MAPK tyro sine phosphorylation. These findings provide evidence that activation of th e B-2-kinin receptor in VSMC leads to generation of multiple second messeng ers that converge to activate MAPK. The activation of this crucial kinase b y BK provides a strong rationale to investigate the mitogenic actions of BK on VSMC proliferation in disease states of vascular injury.