Distribution of anionic surface sites on human melanocytes and human melanoma cells in culture

With cationized ferritin (CF) as an ultrastructural marker for anionic cell surface sites, cultured guinea pig melanocytes display a uniquely homogeneous labelling pattern and a striking absence of redistribution of marker material. In the present study, we applied the same technique to normal human melanocytes and melanoma cells. Unfixed primary human mixed epidermal cell cultures displayed CF labelling patterns identical to those in guinea pig epidermal cells: on keratinocytes, CF was found in distinct aggregations which, upon prolonged incubation, clustered and were shed. Melanocytes, in contrast, bound CF to the cell surface as a uniform diffuse monolayer. There were no signs of cluster formation or shedding. Melanoma cell cultures were derived from 10 primary (2 lentigo maligna, 1 lentigo maligna melanoma, 4 superficial spreading melanomas, 2 nodular portions of superficial spreading melanomas, 1 nodular melanoma) and from 7 metastatic melanomas (4 cutaneous, 3 lymph node metastases). The CF labelling patterns encountered were heterogeneous. Three out of 10 primary tumors and 5 out of 7 metastases showed alterations of the normal melanocyte labelling pattern: regions of typical CF distribution were irregularly interrupted by stretches of membrane free of marker. In some areas, CF occurred in small globular aggregates. There was considerable heterogeneity of CF labelling patterns in different clones of a given culture. Altered CF binding patterns in melanoma cells appear to be associated with high metastasizing protential of the cell clones and may thus represent an unfavourable prognostic sign.