Bradykinin stimulates the tyrosine phosphorylation and bradykinin B2 receptor association of phospholipase Cγ1 in vascular endothelial cells

Bradykinin (BK) B2 receptor signaling involves activation of phospholipase C (PLC). PLC activation by other receptors consists of either allosteric activation of PLCβ isoforms by G-proteins or tyrosine phosphorylation of PLCγ isoforms. Because the B2 receptor is a G-protein-coupled receptor, it has been assumed that the receptor signals through PLCβ. In the present study, however, we have found that BK stimulation of IP₃ production and the Ca²⁺ signal in endothelial cells is dependent on tyrosine phosphorylation. Furthermore, stimulation of B2 receptors in these cells is accompanied by a transient tyrosine phosphorylation of PLCγ1. Phosphorylation is correlated with increased IP₃ production and association of PLCγ1 with the C-terminal intracellular domain of the B2 receptor. The B2 receptor can thus physically associate with intracellular proteins other than G-proteins. Activation of PLCγ isoforms, rather than PLCβ isoforms, may, therefore, be primarily responsible for BK-stimulated IP₃ generation in endothelial cells.