MEMBRANE RUFFLING AND CHEMOTAXIS TRANSDUCED BY THE PDGF BETA-RECEPTORREQUIRE THE BINDING-SITE FOR PHOSPHATIDYLINOSITOL 3' KINASE

Activation of the platelet-derived growth factor (PDGF) beta-receptor results in motility responses in the forms of membrane ruffling and ch emotaxis. Porcine aortic endothelial cells expressing the PDGF beta-re ceptor or a chimeric fibroblast growth factor (FGF) receptor, in which the endogenous kinase insert was replaced with the corresponding regi on from the PDGF beta-receptor, migrated efficiently towards a concent ration gradient of PDGF-BB and bFGF, respectively, and exhibited both pronounced edge ruffling and circular membrane ruffling in response to ligand-stimulation. The wildtype FGF receptor-1 showed weak or no res ponse in these assays. Further analyses were conducted on mutant recep tors, in which tyrosine residues that can serve as autophosphorylation sites and thereby mediate interactions with specific signal transduct ion molecules, were changed to phenylalanine residues. Each one of the analysed mutants were mitogenically active, however, a mutant in whic h Tyr740 and Tyr751 were replaced failed to mediate ruffling and chemo taxis. These two residues are implicated in the binding of phosphatidy linositol 3' kinase. The notion that this enzyme is involved in PDGF b eta-receptor-induced cell motility is furthermore supported by the fin ding that another mutant, in which Met743 and Met754 were replaced, an d which failed to interact with phosphatidylinositol 3' kinase, was al so unable to mediate motility responses.