Ps. Leventhal et al., TYROSINE PHOSPHORYLATION OF PAXILLIN AND FOCAL ADHESION KINASE DURINGINSULIN-LIKE GROWTH FACTOR-I-STIMULATED LAMELLIPODIAL ADVANCE, The Journal of biological chemistry, 272(8), 1997, pp. 5214-5218
In the current studies, we examined whether focal adhesion kinase (FAK
) and paxillin play a role in insulin-like growth factor-I (IGF-I)-sti
mulated morphological changes in neuronal cells, In SH-SY5Y human neur
oblastoma cells, 10 nM IGF-I enhanced the extension of lamellipodia wi
thin 30 min, Scanning electron microscopy and staining with rhodamine-
phalloidin showed that these lamellipodia displayed ruffles, filopodia
, and a distinct meshwork of actin filaments, Immunofluorescent staini
ng identified focal concentrations of FAK, paxillin, and phosphotyrosi
ne within the lamellipodia, Immunoprecipitation experiments revealed t
hat FAK and paxillin are tyrosine phosphorylated during IGF-I-stimulat
ed lamellipodial extension, Maximal phosphorylation of FAK and paxilli
n was observed 15-30 min after the addition of 10 nM IGF-I, whereas ma
ximal IGF-I receptor phosphorylation occurred within 5 min, FAK, paxil
lin, and IGF-I receptor tyrosine phosphorylation had similar concentra
tion-response curves and were inhibited by the receptor blocking antib
ody alpha IR-3. These results indicate that FAK and paxillin are tyros
ine-phosphorylated during IGF-I-stimulated lamellipodial advance and s
uggest that the tyrosine phosphorylation of these two proteins helps m
ediate IGF-I stimulated cell and growth cone motility, These responses
contrast directly with recent reports showing insulin-stimulated deph
osphorylation of FAK and paxillin.