Inhibition of cadherin function differentially affects markers of terminaldifferentiation in cultured human keratinocytes

Cadherin function is required for normal keratinocyte intercellular adhesio n and stratification, In the present study, we have investigated whether ca dherin-cadherin interactions may also modulate keratinocyte differentiation , as evidenced by alterations in the levels of several differentiation mark ers, Confluent keratinocyte cultures, propagated in low Ca2+ medium in whic h cadherins are not active, were pre-incubated with antibodies that block t he function of E-cadherin and/or P-cadherin; Ca2+ was then elevated to 1 mM to activate the cadherins and induce differentiation. In control cultures (incubated with no antibody or with antibodies to other cell surface molecu les), Ca2+ elevation induced an increase in type 1 transglutaminase, profil aggrin, and loricrin, as measured by western blotting and in agreement with previous results. However, the concurrent addition of antibodies against b oth E- and P-cadherin prevented this increase in transglutaminase 1 protein , Incubation with either antibody alone had no consistent effect. Profilagg rin and loricrin, which are later markers of keratinocyte differentiation, responded differently from transglutaminase 1 to addition of antibodies. In the presence of anti-E-cadherin antibody, both loricrin and profilaggrin l evels were dramatically enhanced compared to the high Ca2+ control cells, w hile addition of antibody to P-cadherin slightly attenuated the Ca2+-induce d increase. In the presence of both antibodies, loricrin and profilaggrin p rotein levels were intermediate between those observed in the presence of e ither antibody alone, The expression of involucrin, however, was unaffected by addition of antibodies, In addition, effects of the anti-cadherin antib odies were not secondary to alterations in proliferation or programmed cell death, as determined by several independent assays of these processes. Thu s, the consequences of cadherin inhibition depend upon both the particular cadherin and the differentiation marker under study. Taken together, these data suggest that E-cadherin and P-cadherin contribute to the orderly progr ession of terminal differentiation in the epidermis in multiple ways.