We previously reported that integrin alpha 3 beta 1 mediates epidermal intercellular adhesion as well as cell-substrate adhesion. P1B5, an anti-alpha 3 beta 1 specific monoclonal antibody, is a potent in vitro trigger of epidermal cell-cell adhesion and an inhibitor of cell-substrate adhesion. We now show that P1B5 specifically induces the intercellular localization of integrins alpha 2 beta 1 and alpha 3 beta 1, consistent with its role in inducing intercellular adhesion via these two integrins. P1F2, another anti-alpha 3 beta 1 antibody, does not induce either intercellular adhesion or intercellular accumulation of alpha 3 beta 1 and alpha 2 beta 1. Growth of epidermal cells in high calcium, known to induce epidermal differentiation, also induces intercellular accumulation of alpha 3 beta 1 and alpha 2 beta 1 and increased cell-cell adhesion. We therefore asked whether P1B5 treatment induces epidermal differentiation. P1B5 treatment induces changes consistent with epidermal differentiation, including increased involucrin expression, stratification, and production of squames. P1F2 treatment has none of these effects. In vivo, epidermal basal cells are in close contact with the epithelial basement membrane component epiligrin. Growth of keratinocytes on purified epiligrin but not other matrix components specifically reduces involucrin expression by P1B5-treated keratinocytes. These results suggest that integrin alpha 3 beta 1 has a unique role in epidermal differentiation, that the epitope recognized by P1B5 is involved in triggering this differentiation, and that keratinocyte adhesion to epiligrin inhibits alpha 3 beta 1-mediated differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)