Deposition of laminin 5 by keratinocytes regulates integrin adhesion and signaling

Deposition of laminin 5 over exposed dermal collagen in epidermal wounds is an early event in repair of the basement membrane. We report that depositi on of laminin 5 onto collagen switches adhesion and signaling from collagen -dependent to laminin 5-dependent, Ligation of laminin 5 by integrin alpha( 6)beta(4) activates phosphoinositide S-OH-kinase (PI3K) signaling. This act ivation allows for adhesion and spreading via integrin alpha(3)beta(1) on l aminin 5 independent of RhoGTPase, a regulator of actin stress fibers. In c ontrast, adhesion and spreading on collagen via alpha(2)beta(1) is Rho-depe ndent and is inhibited by toxin B, a Rho inhibitor. Deposition of laminin 5 and ligation of alpha(6)beta(4) increases PI3K-dependent production of pho sphoinositide di- and triphosphates, PI3K activity, and phosphorylation of downstream target protein c-Jun NH3-terminal kinase, Conversely, blocking l aminin 5-deposition with brefeldin A, an inhibitor of vesicle transport, or with anti-laminin 5 monoclonal antibodies abolishes the PI3K-dependent spr eading mediated by alpha(3)beta(1) and phosphorylation of c-Jun NH2-termina l kinase. Studies with keratinocytes lacking alpha(6)beta(4) or laminin 5 c onfirm that deposition of laminin 5 and ligation by alpha(6)beta(4) are req uired for PI3K-dependent spreading via alpha(3)beta(1). We suggest that dep osition of laminin 5 onto the collagen substratum, as in wound repair, enab les human foreskin keratinocytes to interact via alpha(6)beta(4) and to swi tch from a RhoGTPase-dependent adhesion on collagen to a PI3K-dependent adh esion and spreading mediated by integrin alpha(3)beta(1) on laminin 5.