Calcium-calmodulin mediates bradykinin-induced MAPK phosphorylation and c-fos induction in vascular cells

The vasoactive peptide bradykinin (BK) has been implicated in the pathophysiology of a number of vascular wall abnormalities, but the cellular mechanisms by which BK generates second messengers that alter vascular function are as yet undefined. Exposure of vascular smooth muscle cells (VSMC) to BK (10(-7) M) produced a rapid and transient rise in intracellular calcium, which preceded an increase in tyrosine phosphorylation of mitogen-activated protein kinase (MAPK). MAPK activation by BK was observed as early as 1 min, peaked at 5 min, and returned to baseline by 20 min. Treatment of cells with the intracellular calcium chelator EGTA-acetoxymethyl ester inhibited BK-stimulated MAPK activation, suggesting that intracellular calcium mobilization contributes to the activation of MAPK. The calmodulin inhibitor W-7 also markedly inhibited BK-induced MAPK phosphorylation in the cytoplasm as well as in the nucleus. Moreover, the BK-induced increase in c-fos mRNA levels was significantly inhibited by the calmodulin inhibitor, indicating that calmodulin is required for BK signaling leading to c-fos induction. These results implicate the calcium-calmodulin pathway in the mechanisms for regulating MAPK activity and the resultant c-fos expression induced by BK in VSMC.