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 cell adhesion and locomotion, and to further clarify this important property we investigated the possible mechanisms of beta(2)-integrin-induced activation of PtdIns 3-kinase. It has previously been demonstrated that clustering of beta(2)-integrins activates p21(ras) by a tyrosine kinase-dependent pathway, and here we show that active p21(ras) interacts with its downstream target, 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 with the p85 subunit of PtdIns 3-kinase. These findings suggest a mechanism whereby p58(c-fgr) and p59/61(hck) are directly involved in the activation of PtdIns 3-kinase. No coupling between p58(c-fgr) and p59/61(hck) could be detected; hence these kinases probably trigger independent but parallel signals to PtdIns 3-kinase. The effect of beta(2)-integrin clustering on PtdIns 3-kinase activity was monitored as the activation of protein kinase B (PKB). Stimulation of PKB by beta(2)-integrins was abolished by genistein and wortmannin but not by using methyl transferase inhibitors to abrogate the influence 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 mentioned interaction with p58(c-fgr) or p59/61(hck). These tyrosine kinases apparently activate similar pathways that operate in parallel and therefore have the potential to substitute for each other in mediating adhesion and regulating cell locomotion.
Axelsson
L
L
Division of Experimental Pathology, Lund University, Malmö, Sweden.
Hellberg
C
C
Melander
F
F
Smith
D
D
Zheng
L
L
Andersson
T
T
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D015703:Antigens, CD / Q000097:blood; D018821:CD18 Antigens / Q000097:blood*; D004789:Enzyme Activation; D006160:Guanosine Triphosphate / Q000097:blood; D006801:Humans; D066298:In Vitro Techniques; D009504:Neutrophils / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000097:blood*; D011505:Protein-Tyrosine Kinases / Q000097:blood; D011518:Proto-Oncogene Proteins / Q000097:blood; D051572:Proto-Oncogene Proteins c-hck; D016283:Proto-Oncogene Proteins p21(ras) / Q000097:blood; D015398:Signal Transduction
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D018821:CD18 Antigens; D011518:Proto-Oncogene Proteins; D006160:Guanosine Triphosphate; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; C496631:HCK protein, human; D051572:Proto-Oncogene Proteins c-hck; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)