Clustering of beta(2)-integrins on human neutrophils activates dual signaling pathways to PtdIns 3-kinase

The beta(2)-integrins on leukocytes can serve as a signaling unit during ce ll adhesion and locomotion, and to further clarify this important property we investigated the possible mechanisms of beta(2)-integrin-induced activat ion of PtdIns 3-kinase, It has previously been demonstrated that clustering of beta(2)-integrins activates p21(ras) by a tyrosine kinase-dependent pat hway, and here me show that active p21(ras) interacts with its downstream t arget, PtdIns 3-kinase, Engagement of beta(2)-integrins also activates the tyrosine kinases p58(c-fgr) and p59/61(hck) and causes them to associate wi th the p85 subunit of PtdIns 3-kinase, These findings suggest a mechanism w hereby p58(c-fgr) and p59/61(hck) are directly involved in the activation o f PtdIns 3-kinase, No coupling between p58(c-fgr) and p59/61(hck) could be detected; hence these kinases probably trigger independent but parallel sig nals to PtdIns 3-kinase, The effect of beta(2)-integrin clustering on PtdIn s 3-kinase activity was monitored as the activation of protein kinase B (PK B), Stimulation of PKB by beta(2)-integrins was abolished by genistein and wortmannin but not by using methyl transferase inhibitors to abrogate the i nfluence of p21(ras)-related proteins. Thus, even if PtdIns 3-kinase is not activated by p21(ras), it can maintain full enzyme activity due to the men tioned interaction with p58(c-fgr) or p59/61(hck). These tyrosine kinases a pparently activate similar pathways that operate in parallel and therefore have the potential to substitute for each other in mediating adhesion and r egulating cell locomotion. (C) 2000 Academic Press.