DIFFERENTIAL EXPRESSION OF G1 CYCLINS AND CYCLIN-DEPENDENT KINASE INHIBITORS IN NORMAL AND TRANSFORMED MELANOCYTES

PURPOSE. To investigate the levels of the different regulatory protein s involved in the G1 progression and G1/S transition in normal and tra nsformed human choroidal melanocytes (CM). METHODs. Three choroidal me lanoma cell Lines and three CM cultures were used. The purity of the C M cultures was assessed by different approaches, including morphologic study specific immunostaining, cell proliferation behavior, and trans forming growth factor-beta(1) responsiveness. The cell cycle protein l evels were evaluated by specific immunoblotting of total extracts obta ined from the different cell lines. RESULTS. Alterations were observed in the expression of cylins D1 and E in the transformed cells, wherea s the amounts of the cyclin-dependent kinases (CDKs) CDK2 and CDK4 wer e almost identical in both cell types. Although the expression of cycl in H was slightly increased in transformed cells, neither the CDK7 lev el nor the CDK7 and cyclin H localizations were altered when compared with those in normal CM. The results suggest the absence of the CDK in hibitor (CKI) p21 in two of the three melanoma cell lines and, as a ma in feature, a striking underexpression of p27 in the three transformed cell Lines. Finally, although the p16 level was almost the same in no rmal and transformed cells, a loss of p16-CDK4 interaction was observe d in two of the three melanoma cell lines. CONCLUSIONS. Deregulated ex pression of G1 cyclins and CKIs and alteration in the interaction of C KIs with CDKs may be implicated in the neoplastic transformation of hu man ocular melanocytes to malignant melanoma cells.