MODULATION OF INTERCELLULAR-ADHESION MOLECULE-1 EXPRESSION ON HUMAN MELANOCYTES AND MELANOMA-CELLS - EVIDENCE FOR A REGULATORY ROLE OF IL-6, IL-7, TNF-BETA, AND UVB LIGHT

Intercellular adhesion molecule-1 (ICAM-1) is involved in cell-cell interactions of leukocytes and parenchymal cells and thus plays an important role in immunologic and inflammatory reactions. The expression of ICAM-1 that is found on many different cells such as melanocytes and melanoma cells is induced by various cytokines, including interferon-gamma (IFN-gamma), interleukin (IL)-1 and tumor necrosis factor alpha (TNF-alpha). Because expression of ICAM-1 in melanoma was found to correlate with increased risk of metastasis, the regulation of ICAM-1 expression on human melanocytes and melanoma cells was investigated. Foreskin-derived melanocytes and melanoma cell lines (A375, G361) were incubated with different cytokines and ICAM-1 expression was evaluated by fluorescence-activated cell sorter. IFN-gamma, IL-1, IL-7, TNF-alpha, and TNF-beta significantly upregulated ICAM-1 expression in a dose-dependent manner. Most interestingly, the cytokine IL-6, which does not influence adhesion-molecule expression on other cells, significantly upregulated melanocyte and melanoma cell ICAM-1 expression. This effect was dose dependent and could be blocked by an IL-6 antibody. Irradiation with ultraviolet (UVB) light did not influence constitutive ICAM-1 expression on melanoma cells and melanocytes, but suppressed cytokine-induced ICAM-1 expression when cells were harvested 16 h after irradiation. These findings were further confirmed by Northern blot analysis, showing a marked accumulation of ICAM-1 mRNA after cytokine treatment, which was reduced by irradiation with UVB light. However, when UVB-exposed melanoma cells were cultured for at least 48 h induction of ICAM-1 expression was observed. These data indicate that, similar to other cells, ICAM-1 expression on melanoma cells and melanocytes is regulated by cytokines and that UVB light affects ICAM-1 expression on melanocytic cells in a biphasic manner.