IDENTIFICATION OF DIFFERENTIALLY EXPRESSED MESSENGER-RNAS IN HUMAN MELANOCYTES AND MELANOMA-CELLS

The phenotype of malignant lesions is a reflection of genetic events a ltering the RNA and protein expression patterns of normal cells. We ha ve investigated RNA expression patterns distinguishing normal melanocy tes (FM 902), a primary melanoma cell line (WM 793), and its variant c ell line (1205-LU), selected for metastatic phenotype in athymic mice. Using mRNA differential display, we identified 42 different cDNA PCR products with cell line-specific expression patterns. Direct sequence analysis matched approximately 50% of the cDNA PCR products with gene sequences accessible in DNA databases. Among the known genes, two func tionally distinct groups were recognized: (a) genes encoding ribosomal and mitochondrial proteins that were predominantly up-regulated in th e malignant cells; and (b) genes encoding modulators of the immune res ponse. Among the immunomodulators, the T-cell antigen MART-1 and the p rotease inhibitor alpha 2-macroglobulin were detected in the melanocyt e cell line but not in the tumor cells. By contrast, mRNAs for the com plement inhibitor CD59 and the cytokine IL-1 beta were found to be ove rexpressed in the malignant melanoma cells. RNA slot blot hybridizatio n on a larger panel of melanocyte and melanoma cell lines confirmed di fferential expression of 15 of 42 genes including MART-1, alpha 2-macr oglobulin, and CD59. This molecular screening approach identified also three partially characterized and three novel sequences with differen tial expression patterns in normal and malignant melanocytes.