Enhanced expression of melanocortin-1 receptor (MC1-R) in normal human keratinocytes during differentiation: Evidence for increased expression of POMC peptides near suprabasal layer of epidermis

Immunohistochemical staining of human skin specimen showed the stronger loc alization of proopiomelanocortin peptides near the suprabasal layer of the epidermis, where keratinocytes are mostly differentiated. To test the possi bilities of whether the production of proopiomelanocortin peptides or their receptor-binding activity or both is increased during differentiation of k eratinocytes, we treated the cells in culture with Ca2+ to induce their dif ferentiation. The production of proopiomelanocortin peptides and its gene e xpression were not induced significantly, but the binding ability of melano cortin receptor, as well as its gene expression were stimulated by Ca2+. Ul traviolet B irradiation, an inducer of differentiation, stimulated both pro opiomelanocortin production and melanocortin receptor expression. These dat a show that normal human keratinocytes express melanocortin receptor simila r to melanocytes, and that it is induced during differentiation.