ROLE OF INTEGRINS IN MELANOCYTE ATTACHMENT AND DENDRICITY

Integrins are a family of proteins known to mediate attachment of cell s to extracellular matrix materials. The substratum specificity and ca tion dependence of specific integrin heterodimers have been extensivel y characterized, and to a lesser degree specialized roles in cell atta chment versus dendricity have been defined in some cell types. In the past decade, melanocyte attachment rate and morphology have been found to have strong substratum dependence, suggesting a major role for int egrins in these processes. In order to investigate this aspect of pigm ent cell biology, human newborn melanocytes were subjected to flow cyt ometry analysis and plated on a variety of substrata under conditions known to promote or block the binding of specific integrin pairs. Mela nocyte attachment to laminin and type IV collagen was promoted by Mg2 and Mn2+ but not by Ca2+, in the range of concentrations examined. Ho wever, dendrite outgrowth from melanocytes already attached on laminin or type IV collagen was promoted by Ca2+ to a far greater degree than by Mg2+, and Mn2+ had no effect on dendrite outgrowth. Flow cytometry analysis revealed that melanocytes expressed beta(1), alpha(2), alpha (3), alpha(5), alpha(6) and alpha(v) integrin subunits as well as the alpha(v) beta(3) heterodimer. The influence of substratum on the profi le of integrin expression was minimal, but alpha(6) and beta(1) integr ins were observed by confocal microscopy to be expressed over the enti re cell surface, while alpha(2), alpha(5) and alpha(v) beta(3) integri ns localized along dendritic processes or at their tips. In accordance with the implications of these distribution patterns, anti-beta(1) an d anti-alpha(6) integrin monoclonal antibodies blocked melanocyte atta chment to laminin, while anti-alpha(2), anti-alpha(5) and anti-alpha(v ) beta(3) inhibited dendrite outgrowth but did not block substratum at tachment on either laminin or type IV collagen. On the basis of these data and the known characteristics of integrin molecules, we conclude that melanocyte attachment to laminin is mediated primarily by alpha(6 ) beta(1) integrin in a Ca2+-independent, Mg2+- and/or Mn2+-dependent manner, while dendrite outgrowth on laminin and type IV collagen requi res extracellular Ca2+ and is mediated by alpha(v) beta(3) as well as alpha(2) and alpha(5) integrins.