Regulation of mitogenesis by kinins in arterial smooth muscle cells

Recent evidence suggests that bradykinin (BK) plays a role in regulating neointimal formation after vascular injury. The present study examined the mechanism whereby BK regulates platelet-derived growth factor (PDGF) AB-induced mitogenesis in smooth muscle cells from rat mesenteric artery. BK, but not other activators of phosphoinositidase C (e.g., angiotensin II), inhibited PDGF-stimulated mitogenesis. The B-1 receptor agonist des-Arg(9)-BK (DABK) was more potent than the Bz agonist BK; smaller BK fragments had no activity. In studies in which the Bz receptor antagonist HOE-140 (D-Arg(0)[Hyp(3), beta-(2-thienyl)-Ala(5),D-Tic(7),Oic(8)]BC) and the B-1 receptor antagonist DHOE ([D-Arg(0),Hyp(3),beta-(2-thienyl)Ala(5),D-Tic(7),Oic(8),des-Arg(9)]BK] were used, both receptors independently mediated inhibition of PDGF-induced mitogenesis. There was no evidence for metabolism of BK to DABK. The rank potency for activating phosphoinositidase C and increasing intracellular Ca2+ (BK > DABK) was opposite that for inhibiting mitogenesis (DABK > BK). Inhibition of cyclooxygenase did not prevent the kinin-mediated inhibition. Kinetic analysis of the cell cycle effects of kinins on PDGF-stimulated mitogenesis revealed that continuous exposure to DABK or BK was inhibitory even when added shortly before the cells initiated DNA synthesis (S phase). However, short-term exposure (5-60 min) to DABK or BK was inhibitory only when added after exposure to PDGF. These data suggest that the B-1 and B-2 receptors potently inhibited PDGF-stimulated mitogenesis and proliferation by activating an alternative signal transduction cascade not involving phosphoinositidase C or prostaglandins. The inhibition occurred at a point late in progression of the cell cycle from G(1) to S and was dependent on the presence of kinins after exposure to PDGF.