Dual signaling by the αvβ3-integrin activates cytosolic PLA2 in bovine pulmonary artery endothelial cells

Vitronectin, which ligates the α v β 3 -integrin, increases both lung capillary permeability and lung endothelial Ca 2+ . In stable monolayers of bovine pulmonary artery endothelial cells (BPAECs) viewed with confocal microscopy, multimeric vitronectin aggregated the apically located α v β 3 -integrin. This caused arachidonate release that was inhibited by pretreating the monolayers with the anti-α v β 3 monoclonal antibody (MAb) LM609. No inhibition occurred in the presence of the isotypic MAb PIF6, which recognizes the integrin α v β 5 . Vitronectin also caused membrane translocation and phosphorylation of cytosolic phospholipase A 2 (cPLA 2 ) as well as tyrosine phosphorylation of the mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase (ERK) 2. The cPLA 2 inhibitor arachidonyl trifluoromethylketone, the tyrosine kinase inhibitor genistein, and the MAPK kinase inhibitor PD-98059 all blocked the induced arachidonate release. PD-98059 did not inhibit the increase of cytosolic Ca 2+ or cPLA 2 translocation, although it blocked tyrosine phosphorylation of ERK2. Moreover, although the intracellular Ca 2+ chelator MAPTAM also inhibited arachidonate release, it did not inhibit tyrosine phosphorylation of ERK2. These findings indicate that ligation of apical α v β 3 in BPAECs caused ERK2 activation and an increase of intracellular Ca 2+ , both conjointly required for cPLA 2 activation and arachidonate release. This is the first instance of a tyrosine phosphorylation-initiated “two-hit” signaling pathway that regulates an integrin-induced proinflammatory response.