Regulation of integrin‐mediated adhesion to laminin and collagen in human melanocytes and in non‐metastatic and highly metastatic human melanoma cells

We compared integrin‐mediated adhesion to extracellular matrix (ECM) components of cultured human melanocytes and 6 human melanoma cell lines with different metastatic capacities in nude mice. Cultured melanocytes and most melanoma cell lines adhered strongly to fibronectin (FN), whereas only highly metastatic cell lines adhered to laminin (LM), collagen type I (COI) and type IV (COIV). Adhesion to LM and CO could be blocked by anti‐α6 and anti‐α2 monoclonal antibodies (MAbs) respectively. This observation is consistent with the finding that expression of LM receptor α6β1 and LM/CO receptor α2β1 was low on melanocytes and non‐ or poorly metastatic cell lines, whereas these integrins were strongly expressed on highly metastatic cell lines. In addition, immunoprecipitation from [35S]‐methionine‐labeled cells demonstrated increased synthesis of α6, α2 and β1 in highly metastatic cell lines and immunohis‐tochemistry showed expression of α6β1 and α2β1 only in xenograft lesions from highly metastatic cell lines. Furthermore, the observation that adhesion of melanocytes and non‐ or poorly metastatic cell lines could be stimulated with anti β1 MAbs demonstrates that these receptors, on these cells, are expressed in an inactive state. Our results suggest that α2β1 and α6β1 play a role in human melanoma metastasis in nude mice and demonstrate that interactions of these integrins with their ligands can be regulated at the level of surface expression and activation state of the receptor.