Ultrastructural localization of alpha-3 integrin subunit in malignant melanoma and adjacent epidermis.

Eight cases of malignant melanoma were studied by immunohistopathology and immunoelectron microscopy. Alpha3 integrin localization was documented in malignant melanoma cells, basal and suprabasal keratinocytes, melanocytes, blood vessels and in basement membrane material. In melanoma cell membranes and, to a lesser extent, the interior of melanosomal vesicles were labeled. In addition, neighbouring cells such as basal and suprabasal keratinocytes and melanocytes showed strong alpha3-integrin expression. The labeling was much stronger in the plasma membrane than in the cytoplasm. Endothelial cells showed stronger labeling of the cytoplasm than of the plasma membrane. In some cases we found increased flocculent material surrounding melanoma cells or nests that seems to contain basement membrane protein components, specifically alpha3-integrin subunits. Compared to normal epidermis alpha3-labeling was stronger in tissues of malignant melanoma.