FUNCTIONAL ASSOCIATION OF PLATELET ENDOTHELIAL-CELL ADHESION MOLECULE-1 AND PHOSPHOINOSITIDE 3-KINASE IN HUMAN NEUTROPHILS

In this paper we show that the engagement of the platelet-endothelial cell adhesion molecule-1 (PECAM-1/ CD31) up-regulates the adhesion of human neutrophils to the EA.hy926 endothelial cell line through a phos phoinositide S-kinase (PI3K)-dependent pathway. Indeed, LY294002 and w ortmannin prevented the effect of PECAM-1/CD31 cross-linking on cell a dhesion, at concentrations known to inhibit PI3K without affecting oth er kinases. Both compounds blocked neutrophil binding to murine fibrob lasts transfected with human ICAM-1, to purified ICAM-1 protein, or to fibronectin, suggesting that PECAM-1/CD31-mediated up-regulation of b eta 2 and beta 1 integrin-mediated adhesion is PI3K-sensitive. We also provide evidence for the association of PECAM-1/CD31 to PI3K, because PI3K was detectable in neutrophil lysates after PECAM-1/CD31 cross-li nking and immunoprecipitation. PECAM-1/CD31-dependent recruitment of P I3K was suggested by the finding that the serine/threonine kinase p70 S6 kinase (S6K), a signaling protein downstream of PI3K, is activated in neutrophils upon PECAM-1/CD31 cross-linking, based on the appearanc e of serine phosphorylation in S6K immunoprecipitates. In turn, S6K is not directly involved in the up-regulation of integrin function becau se rapamycin, which can inhibit S6K independent of PI3K, did not block PECAM-1/CD31-induced adhesion of neutrophils to beta 1 and beta 2 int egrin substrates. In conclusion, PECAM-1/CD31 appears to be one of the molecules functionally coupled to PI3K, suggesting that this enzyme m ay represent a common pathway of integrin and adhesiveness regulation in leukocytes.