BIOLOGIC DETERMINANTS OF UVEAL MELANOMA METASTATIC PHONOTYPE - ROLE OF INTERMEDIATE FILAMENTS AS PREDICTIVE MARKERS

The long-range goal of our research is to develop intervention strateg ies based on newly discovered biologic mechanisms responsible for the invasive dissemination of metastatic uveal melanoma. To accomplish thi s goal, we have focused on the biologic relevance of novel marker prot eins contributing to the uveal melanoma metastatic phenotype. The expr ession of vimentin intermediate filaments (Ifs), a mesenchymal marker, is typical of melanomas, whereas carcinomas typically express keratin Ifs, which are markers for epithelia. Thus, cells that coexpress both Ifs are regarded as ''interconverted'' in that they display both mese nchymal and epithelial phenotypes. Although the biologic functions of Ifs have remained enigmatic, there is substantial support to suggest t hat the significance of vimentin/keratin coexpression is linked with p oor patient outcome in cutaneous melanoma. Our data demonstrate that h uman uveal melanoma cell lines (isolated from primary choroidal or cil iary body melanomas and from foci of metastatic uveal melanoma to the liver), which contain predominant populations of cells that coexpress vimentin/keratins 8 and 18 (keratins 8,18) Ifs, were B-fold more invas ive through collagenous extracellular matrices in vitro, compared with uveal melanoma cells expressing vimentin only, and were 8- to 13-fold more invasive than normal uveal melanocytes. Colocalization of viment in/keratins 8,18 in cell cultures was corroborated by immunohistochemi stry in histologic sections of tumors from which the cell lines were d erived. Minor populations of these cells also coexpressed keratins 13 and 17. Experimental down-regulation of the predominant keratins 8,18 in the interconverted cells, using 16-mer antisense oligonucleotides, resulted in a significant decrease in the migratory ability of the cel ls-similar to levels achieved by cells positive only for vimentin. The se findings provide justification for additional studies of the associ ation between coexpression of IFs vimentin/keratins 8,18 and uveal mel anoma metastasis.