Phenotypic analysis of cultured melanoma cells : Expression of cytokeratin-type intermediate filaments by the M5 human melanoma cell line

Expression of intermediate filament (IF) isotypes was studied in six human and two murine melanoma cell lines. With one exception, these lines expressed IFs only of the vimentin type; neurofilament peptides, desmin and GFAP were not detected. However, the M5 human melanoma line also expressed extensive cytokeratin tonofilament arrays, as visualized by immunofluorescence with a panel of eleven monoclonal antibodies and hetero-antisera to cytokeratins; only the keratin 19-specific antibody BA16 did not react. By 2 D gel electrophoresis, five major keratin peptides were detected (keratins 7, 8, 13, 17 and 18), and an additional 57 kD peptide was detected on immunoblots with several antikeratin antibodies. Also observed in M5 cells was focal collapse of tonofilament arrays in mitotic cells. All the melanoma lines tested were positive for S100; M5 and two other cell lines were also positive for the 220-240 kD neuroectoderm-associated cell-surface differentiation antigen defined by monoclonal antibody UJ 127:11. In all the melanoma cell lines, secretion of extracellular matrix proteins (fibronectin, laminin and collagen type IV) was sparse or absent, and all were negative for the epithelial cell markers HMG-1 and HMG-2. Co-expression of keratin and vimentin by a melanoma cell line is discussed in the light of recent controversy concerning expression of cytokeratins by other neoplasms of putative neuroectodermal origins.