Differential expression of the HLA-DR genes in various melanoma cell lines treated with interferon-gamma: methylation of the HLA-DR alpha gene in these lines is not correlated with its expression.

Melanoma cell lines treated with or without interferon-gamma were tested for the presence of DR alpha mRNA and protein. The six lines examined fell into three general categories: two that expressed high levels of DR alpha mRNA and protein before and after interferon-gamma treatment, one that expressed very low levels before treatment with interferon-gamma, but was induced to express high levels after interferon-gamma treatment, and three that expressed very low levels before treatment, and were only slightly inducible after treatment with interferon-gamma. The presence of DR-alpha protein on the melanoma cell surface was always positively correlated with the presence of DR alpha mRNA in the cells. Furthermore, in the cell line that was interferon-gamma-inducible, the time at which DR alpha mRNA and protein appeared and the doses of interferon-gamma needed to induce this appearance were directly correlated. Methylation patterns of the DR alpha gene in these cell lines were also studied in order to determine whether the degree of DR alpha gene methylation among the lines correlated with expression of the gene. Digestion of DNA with the restriction enzyme MspI, which recognizes the sequence 5'CCGG3' and 5'CmCGG3', led to the appearance of a 3.1 kb band from all lines tested. Hpa II digestion, which recognizes 5'CCGG3', but not 5'CmCGG3', led to the appearance of 3.1, 4.4, and 6.7 kb bands in all lines tested except for DUMEL 8, which showed only the 3.1 kb band. Interestingly, DUMEL 8 expressed very low levels of DR alpha mRNA and protein before and after interferon-gamma treatment. We conclude that interferon-gamma has a regulatory effect on DR alpha genes of various melanoma cell lines to varying degrees. This may reflect an effect of interferon-gamma on certain subpopulations of melanocytes in vivo. Our data also indicate that partial methylation of the DR alpha gene does not inhibit its expression. Furthermore, interferon-gamma does not appear to induce expression of the DR gene by altering methylation patterns within the region recognized by our probe.