Tyrosine phosphorylation and bradykinin-induced signaling in endothelial cells

If is generally accepted that in endothelial cells the occupation of bradykinin B(2) receptors, which are linked to the guanine nucleotide-dependent regulatory proteins, G(i) and G(q), results in the activation of phospholipase C-beta(1) (PLC-beta(1)), followed by a transient increase in the formation of inositol 1,4,5-trisphosphate (IP(3)) and diacylglycerol. The PLC-beta(1) isoform, in contrast to the gamma(1) isoform, is present only at a flow level in cultured endothelial cells, implying that PLC-gamma(1) activation may play an important role in endothelial signaling pathways. In cultured human endothelial cells, bradykinin induced a rapid increase in the tyrosine phosphorylation of several Triton-soluble proteins, Immunoprecipitation of tyrosine-phosphorylated proteins from bradykinin-stimulated cells followed by Western blotting using the respective antibodies facilitated the identification of a 77 kiloDalton (kDa) protein as paxillin, a 130 kDa protein as PLC-gamma(1), and a 42/44 kDa doublet as mitogen-activated protein (MAP) kinase. The bradykinin-induced tyrosine phosphorylation of PLC-gamma(1) was relatively transient and was associated with an increase in intracellular levels of IP(3). Bradykinin also induced the rapid and transient activation of phosphotyrosine phosphatases localized mainly in the Triton X-100-soluble cell fraction; this tyrosine phosphatase activity was apparently initiated after the release of Ca(2+) from intracellular stores. (C) 1997 by Excerpta Medica, Inc.