Uveal
malignant melanoma is the most frequent primary intraocular
tumor in adult humans. The cellular events leading to neoplasic transformation of normal uveal melanocytes are not well known when compared to other
cancers. In this study, we investigated the role of G1 and G1/S regulatory
proteins of the cell cycle in human
uveal melanoma (UM) primary cell cultures, since these
proteins are common targets in
tumor development. Further, freshly established and characterized
tumor cells are a better model for in vitro studies when compared to cell lines established long ago. Human primary cell cultures from eight different UM were established, as well as one primary culture from rhesus uveal normal melanocytes (UNM). Primary human UM cultures were characterized by a low establishment and growing rate. From four successful cultures, three showed a high expression of
cyclin D1,
cyclin E, p16NK4A, and p27KIP1 with no variations in
cyclin A,
cyclin-dependent kinase 2 (CDK2), and CDK4. Interestingly, in one of the cultured
tumors,
tumor suppressor protein retinoblastoma (Rb) did not bind E2F despite the fact that Rb was found in its hypophosphorylated form. No mutations in either RB1 or the Rb-binding pocket of E2F-1 were detected. Furthermore, we identified seven
proteins co-immunoprecipitating with Rb in this
tumor, including
Lamin A/C and six
proteins not previously reported to bind Rb: Hsc70, high mobility group
protein 1 (HMG-1), hnRPN,
glyceraldehyde 3 phosphate dehydrogenase (G3PDH),
EF-1, and
EF-2. Our results indicate that the overexpression of
cyclins D1/E and CDKIs p16 and p27, together with a deregulation of the Rb/E2F pathway, may be implicated in the development of human UM.