Upon epidermal wounding, keratinocytes at the
wound edge become activated, deposit newly synthesized
laminin-5 into the extracellular matrix, and migrate into the
wound bed. The interaction between
integrin alpha3beta1 and
laminin-5 is essential for establishment of a stable, leading lamellipodium and persistent keratinocyte migration. We previously showed that
integrin alpha3beta1 activates the Rho family
GTPase Rac1 and regulates Rac1-dependent formation of polarized, leading lamellipodia in migrating keratinocytes. In the present study, we explored the role of
focal adhesion kinase (FAK) and src signaling in this process. We show that overexpression of the FAK inhibitor FAK-related non-
kinase or of the FAK(Y397F) auto-phosphorylation mutant, induced abnormal, non-polarized spreading of keratinocytes on
laminin-5.
Integrin alpha3beta1 was required for full FAK auto-phosphorylation at Y397, and subsequent
src kinase-dependent phosphorylation of FAK at residues Y861 and Y925, sites responsible for promoting signal transduction downstream of FAK, indicating that alpha3beta1 regulates the coordination of FAK/src signal transduction. Inhibiting either
src kinase activity or FAK signaling interfered with alpha3beta1-mediated Rac1 activation and polarized cell spreading. These findings reveal a novel pathway in migratory keratinocytes wherein alpha3beta1-laminin-5 interactions regulate
src kinase signaling through FAK, promoting Rac1 activation and polarized lamellipodium extension.