Production and utilization of extracellular matrix components by human melanocytes

Normal human melanocytes were separated from keratinocytes and maintained in culture using KGM medium supplemented with 12-O-tetradecanoylphorbol acetate and cholera toxin. The melanocytes were examined for the production of extracellular matrix molecules including fibronectin, laminin, and thrombospondin and for the utilization of these molecules in adhesion and motility assays. Melanocytes produced significant amounts of fibronectin as indicated by biosynthetic labeling/immunoprecipitation and by enzyme-linked immunosorbent assay (ELISA). Fibronectin was expressed on the surface of these cells. Laminin was also produced by melanocytes and expressed on the cell surface. The amount of laminin produced was significantly less than the amount of fibronectin. In contrast, melanocytes did not produce measurable thrombospondin as indicated by biosynthetic labeling/immunoprecipitation. Only traces of thrombospondin were detected by ELISA and no surface fluorescence was observed. When examined in adhesion and motility assays, melanocytes were found to utilize fibronectin for both processes. Laminin also stimulated adhesion but it was much less effective than fibronectin. Thrombospondin did not stimulate either attachment and spreading or motility. The pattern of extracellular matrix molecule production and utilization by melanocytes is significantly different from that shown previously for human epidermal keratinocytes (J. Varani et al., 1988, J. Clin. Invest. 81, 1537). These differences may underlie the differences with which the two cell types interact with basement membranes in vivo.