MIGRATION OF HIGHLY AGGRESSIVE MELANOMA-CELLS ON HYALURONIC-ACID IS ASSOCIATED WITH FUNCTIONAL-CHANGES, INCREASED TURNOVER AND SHEDDING OF CD44 RECEPTORS

Recent evidence indicates that CD44, a multifunctional adhesion recept or involved in cell-cell as well as in cell-matrix interactions, plays an important role in local progression and metastasis of malignant tu mors, We have studied a set of human melanoma cell lines differing in their metastatic potential in nude mice as well as in normal melanocyt es for changes in CD44 expression and function, All melanocytes and me lanoma cell lines tested highly expressed the CD44 standard form (CD44 s, 85 kDa) but variants at low levels only, With respect to one of the CD44-associated functions primarily involved in tumor progression we found that two highly metastatic tumor cell lines, MV3 and BLM, showed fivefold higher migration rates towards hyaluronate than melanomas wi th low metastatic potential and normal melanocytes, Moreover, the high ly metastatic cell lines expressed four- to sixfold higher levels of t he CD44 epitope involved in hyaluronic acid-binding (monoclonal antibo dy Hermes-1) than less aggressive melanomas and melanocytes, Hermes-1 efficiently blocked haptotaxis to hyaluronate, supporting the function al relevance of this epitope, In contrast, expression levels of other CD44s epitopes recognized by seven different anti-CD44 monoclonal anti bodies were unchanged, suggesting that the migratory behaviour of the cells depends on the formation of the hyaluronate-binding Hermes-l epi tope rather than on the overall CD44s surface expression, which was vi rtually identical in all melanoma and melanocyte cell lines tested, Di fferences in the accessibility of the hyaluronate-binding epitope defi ned by Hermes-l correlated with the phosphorylation state of CD44s, pr obably reflecting different activation states of the receptor, Further more, immunoprecipitation and pulse/chase studies revealed a three- to fivefold increase in CD44 synthesis in the highly aggressive melanoma cells as compared to the other cell lines and the melanocytes, indica ting a reduction of CD44 half-life and up-regulation of turnover, More over, highly aggressive melanoma cell lines were found to shed signifi cant amounts of CD44 from the cell surface and to secrete its ligand h yaluronic acid, which may refer to an 'autocrine' mechanism mediating melanoma cell motility.