Human melanocytes and melanoma cells constitutively express the Bcl-2 proto-oncogene in situ and in cell culture.

The Bcl-2 proto-oncogene regulates cell survival by antagonizing events that lead to apoptotic cell death and has been reported to be expressed in situ in lymphoid tissues, glandular epithelium, neurons, and basal epidermal cells. When we performed immunostaining on cryostat sections of normal skin, anti-Bcl-2 reactivity was confined to scattered dendritic cells in the basal epidermal layer. Double-staining experiments showed that the Bcl-2+ cells were positive for vimentin but negative for cytokeratins, CD1a, and CD45 antigens, excluding keratinocytes and Langerhans cells as possible candidates for constitutive Bcl-2 expression. Bcl-2+ epidermal cells also reacted with the monoclonal anti-melanocyte antibody NKI/beteb, and were absent from lesional skin in vitiligo, confirming that they represented epidermal melanocytes. Western blot analysis of cultured melanocytes and melanoma cell lines revealed a 26-kd protein specifically reacting with the anti-Bcl-2 monoclonal antibody. Immunostaining of pigmented lesions revealed strong expression of Bcl-2 by five of five nevocellular nevi and seven of seven melanomas. Our observations demonstrate that, within normal human epidermis, melanocytes are the only cells that express Bcl-2 constitutively and that Bcl-2 is expressed in benign and malignant pigmented tumors of the skin in situ.