R. Soldi et al., PLATELET-ACTIVATING-FACTOR (PAF) INDUCES THE EARLY TYROSINE PHOSPHORYLATION OF FOCAL ADHESION KINASE (P125(FAK)) IN HUMAN ENDOTHELIAL-CELLS, Oncogene, 13(3), 1996, pp. 515-525
Platelet-activating factor (PAF) is a potent activator of angiogenesis
and controls the motility and the shape of vascular endothelium. The
mechanism(s) whereby PAF exerts its action are in part known. Here we
report that the biological active (R)PAF enantiomer administrated to c
ultured endothelial cells induces the early phosphorylation in tyrosin
e residues of focal (p125(FAK)) and paxillin, two molecules early sign
aling and cytoskeleton assembly in cells that undergo integrin-mediate
d adhesion or are challenged by neuropeptides or lysophosphatidic acid
. The phenomenon is rapidly turned on, lasts for a few minutes and is
adhesion-independent indicating that the chain of events induced by (R
)PAF, including p125(FAK) activation, precedes adhesion. The inhibitor
y effect of WEB2086, a PAF receptor antagonist, and the lack of activi
ty exerted by the (S)PAF enantiomer, indicate that (R)PAF-mediated p12
5(FAK) activation, is PAF receptor-dependent. Calphostin C, an inhibit
or of protein kinase C blocks the effect of (R)PAF on p125(FAK); phosp
horylation suggesting that protein kinase C activation is up-stream th
e activation of this tyrosine kinase. When endothelial cells are expos
ed to a substratum that allows adhesion and spreading. (R)PAF-stimulat
ed cells, change their adhesive phenotype and start migrating. Inhibit
ors of tyrosine kinases, like 3-(1,4,-dihydroxytetralyl) methy-len-2-o
xindole and herbimycin A, reduce the cells migration, the transendothe
lial flux of albumin and the enhancement of p125(FAK) activity induced
by (R)PAF. The observation that increased tyrosine phosphorylation of
p125(FAK) and its ensuing association with focal adhesion occurs rapi
dly upon (R)PAF challenge indicates that this signaling molecule has a
primary and independent role also in the signaling cascade initiated
by (R)PAF.