Ligation of integrin alpha(3)beta(1) by laminin 5 at the wound edge activates Rho-dependent adhesion of leading keratinocytes on collagen

Wounding of the epidermis signals the transition of keratinocytes from quie scent anchorage on endogenous basement membrane laminin 5 to migration on e xposed dermal collagen. In this study, we attempt to characterize activatio n signals that transform quiescent keratinocytes into migratory leading cel ls at the wound edge. Previously, we reported that adhesion and spreading o n collagen via integrin alpha (2)beta (1) by cultured human foreskin kerati nocytes (HFKs) requires RhoGTP, a regulator of actin stress fibers. In cont rast, adhesion and spreading on laminin 5 requires integrins alpha (3)beta (1) and alpha (6)beta (4) and is dependent on phosphoinositide 3-hydroxykin ase (Nguyen, B. P., Gil, S. G., and Carter, W. G. (2000) J. Biol. Chem. 275 ,31896-31907). Here, we report that quiescent HFKs do not adhere to collage n but adhere and spread on laminin 5. By using collagen adhesion as one cri terion for conversion to a "leading wound cell," we found that activation o f collagen adhesion requires elevation of RhoGTP. Adhesion of quiescent HFK s to laminin 5 via integrin alpha (3)beta (1), and alpha (6)beta (4) is suf ficient to increase levels of RhoGTP required for adhesion and spreading on collagen. Consistently, adhesion of quiescent HFKs to laminin 5, but not c ollagen, also promotes expression of the precursor form of laminin 5, a cha racteristic of leading keratinocytes in the epidermal outgrowth. We suggest that wounding of quiescent epidermis initiates adhesion and spreading of k eratinocytes at the wound edge on endogenous basement membrane laminin 5 vi a alpha (3)beta (1), and alpha (6)beta (4) in a Rho-independent mechanism. Spreading on endogenous laminin 5 via alpha (3)beta (1), is necessary but n ot sufficient to elevate expression of precursor laminin 5 and RhoGTP, allo wing for subsequent collagen adhesion via alpha (2)beta (1), all characteri stics of leading keratinocytes in the epidermal outgrowth.