Bradykinin B1 receptor blocks PDGF-induced mitogenesis by prolonging ERK activation and increasing p27Kip1

The mechanism by which the bradykininB₁ receptor (B1R) inhibits platelet-derived growth factor(PDGF)-stimulated proliferation was investigated in cultured ratmesenteric arterial smooth muscle cells. The B1R agonistdes-Arg⁹-bradykinin (DABK) was found to inhibitPDGF-mediated activation of the cyclin E-cyclin-dependent kinase 2 (Cdk2) complex and to prevent hyperphosphorylation of retinoblastomaprotein. DABK did not inhibit upregulation of cyclin E expression butincreased expression of the Cdk2 inhibitor p27Kip1 and the associationof p27Kip1 with the cyclin E-Cdk2 complex. In addition, DABK inhibited the PDGF-stimulated expression of cyclin D that would otherwise siphonp27Kip1 away from inhibition of cyclin E-Cdk2. The signaling mechanismby which DABK regulated p27Kip1 was explored. DABK was found tostimulate the activity of mitogen-activated protein kinase kinase (MEK)and extracellular signal-regulated kinase (ERK) and to prolongactivation of MEK and ERK by PDGF. Inhibition of ERK activation withthe MEK inhibitors PD-98059 and U-0126 as well as the Src family kinaseinhibitor PP2 completely blocked the effect of DABK to increase p27Kip1and partially reversed the DABK-mediated inhibition of PDGF-stimulatedproliferation. These studies demonstrate that the B1R inhibitsPDGF-stimulated mitogenesis in part by prolonged activation of ERKleading to increased expression of p27Kip1.