EFFECTS OF INTERFERONS ON CULTURED HUMAN MELANOCYTES INVITRO - INTERFERON-BETA BUT NOT INTERFERON-ALPHA OR INTERFERON-GAMMA INHIBIT PROLIFERATION AND ALL INTERFERONS SIGNIFICANTLY MODULATE THE CELL PHENOTYPE

The effects of human recombinant interferon-alpha-2a (rIFN-alpha), natural interferon-beta (nIFN-beta) and recombinant interferon-gamma (rIFN-gamma) on the proliferation, morphology and antigen expression of cultured human melanocytes were studied in vitro. The investigations were performed in 12-O-tetradecanoylphorbol-13-acetate (TPA)- and serum-containing melanocyte growth medium (MGM), in TPA-and serum-free complete melanocyte medium (CMM) and its mitogen reduced variant (RMM). In MGM, none of these interferons inhibited the growth of normal melanocytes at concentrations 1 - 10,000 international units (IU)/ml over a period of 5 d. Only nIFN-beta, dose dependently, inhibited melanocyte proliferation in CMM and RMM in a 6- and 12-d assay (growth inhibition at 10,000 IU/ml; 77-80% of the controls, p < 0.001). In contrast, rIFN-alpha and rIFN-gamma exerted no (RMM), or minor effects (CMM) on melanocyte proliferation (only in 12-d assays at 10,000 IU/ml: 24% and 21% of the controls respectively, p < 0.01). In parallel experiments performed on melanoma cells, all three interferons were potent inhibitors of proliferation in a 5-d serum-free assay (growth inhibition at 10,000 IU/ml; rIFN-alpha 59%, nIFN-beta 78%, rIFN-gamma 56%, all p < 0.001). In addition nIFN-beta and also rIFN-gamma caused striking morphologic changes of normal melanocytes in vitro. Especially under greater-than-or-equal-to 10 IU/ml rIFN-gamma cytoplasmic spreading and flattening of the cultured melanocytes and their nuclei were seen, thus resembling melanoma cells in vitro. Untreated human melanocytes grown in MGM showed high expression of the melanoma-associated antigens HMB-45 (95-100%) and K.1.2(40-100%), whereas the progression marker A.1.43 was present only on < 5% of the cells. Cultured melanocytes were 95-100% positive for histocompatibility antigen class I (HLA-I), 30-75% were positive for ICAM-1, whereas they were negative for HLA-DR. After treatment with rIFN-alpha, increased expression of HLA-I antigens was found; nIFN-beta and rIFN-gamma decreased the labeling with HMB-45 (75-100%) and with K.1.2 (25-80%), whereby the expression of A.1.43 was found slightly increased (5-15%). The HLA class I antigens were upregulated by both nIFN-beta and rIFN-gamma, nIFN-beta being the most potent agent. Also, both nIFN-beta and rIFN-gamma increased the expression of ICAM-1 (nIFN-beta, 75-90%; rIFN-gamma, 90-95%) and induced de novo expression of HLA-DR antigen (nIFN-beta, 15-20%; rIFN-gamma, 65-95%). The decreased antiproliferative activity of rIFN-alpha and rIFN-gamma on skin-derived normal human melanocytes is in sharp contrast to the marked growth inhibition seen on melanoma cells in vitro. This implies that malignant transformation in the melanocytic system evokes increased sensitivity to the antiproliferative action of rIFN-alpha and rIFN-gamma in vitro. On the other hand, nIFN-beta and rIFN-gamma induced changes of melanocytic morphology and antigenic profile causing close similarities to cultured melanoma cell lines.