A Tyrosine Kinase-Signaling Pathway Involving ERK-2 Activation Links Bradykinin B2 Receptors with AP-1 and is Crucial for Bradykinin-Induced DNA Synthesis in Mesangial Cells. • 1646

Abstract

We have recently shown that bradykinin (BK), acting via B2 receptors, stimulates DNA synthesis and proliferation of rat mesangial cells and that these responses were preceded by induction of c-fos and AP-1 binding activity (Kidney Int. 50: 1850, 1996). The present study was designed to examine the role of protein tyrosine phosphorylation in coupling the B2 receptors with AP-1 and DNA replication. BK (100 nM) induced tyrosine phosphorylation of distinct substrates of 170, 120-130, 70, 55-60, and 44-42 kDa as detected by antiphosphotyrosine immunoblotting. Immunoblotting with a polyclonal ERK antibody of BK-stimulated cells revealed predominant phosphorylation of the 42-kDa MAP kinase (ERK-2). Inhibition of tyrosine kinase activity with genistein (15-100 μM) abolished the stimulatory effect of BK on tyrosine phosphorylation and ERK-2 activation. Furthermore, genistein attenuated BK-mediated c-fos and c-jun induction and AP-1-DNA binding activity and suppressed BK-stimulated DNA synthesis in a dose-dependent manner. Herbimycin A (50-200 nM), a chemically and mechanistically distinct tyrosine kinase inhibitor, also abolished BK-stimulated DNA synthesis. Thus, tyrosine phosphorylation is an essential requirement in the mitogenic signaling of BK in glomerular mesangial cells. The data implicate the MAP kinase, ERK-2, and the transcription factor, AP-1, as the downstream signals linking BK-B2 receptor stimulation with DNA replication.