2 HUMAN-MELANOMA CELL-LINE VARIANTS WITH ENHANCED IN-VIVO TUMOR-GROWTH AND METASTATIC CAPACITY DO NOT EXPRESS THE BETA(3) INTEGRIN SUBUNIT

The alpha(v) beta(3) integrin complex is thought to play an important role in in vivo melanoma tumor growth and metastasis. However, not all human metastatic melanomas, present in lymph node biopsies, express a lpha(v) beta(3) In this study, we have investigated the possibility th at certain melanoma cell lines can grow aggressively in vivo in the ab sence of alpha(v) beta(3) expression. Established human melanoma cell lines (M(3)Da., M(4)Beu.) were isolated from an achromic skin metastas is or lymph nodes. Two stable variants (7GP, T1P26), derived from a po orly metastatic M(4)Beu. melanoma cell line, were isolated by sequenti al selection for spontaneous metastasis formation in an immunosuppress ed newborn rat model. Flow-cytometry analysis shows an absence of the beta(3) integrin subunit (less than 2% of parental levels) in the two variant melanoma cell lines (7GP, T1P26) compared to M(3)Da. and M(4)B eu. cell lines which express a relatively high number of beta(3) subun its. The expression levels of the integrin subunits beta(1) beta(5) be ta(6) and alpha(v) were found to be similar for all four melanoma cell lines. Northern blot analysis confirmed the absence of beta(3) in 7GP or T1P26 cell lines and its presence in M(3)Da. and M(4)Beu. Moreover , similar levels of alpha(v) transcript were present in the four melan oma cell lines. The functional effect of the absence of beta(3) was in vestigated by subcutaneously implanting the variants and the melanoma cell lines in nude mice. Variant 7GP and T1P26 cell lines yielded tumo rs which were larger and grew at a faster rate than tumors in M(3)Da. or M(4)Beu. cell lines. The beta(3) integrin subunit was not detectabl e on the surface of cells harvested from tumors after 20 or 35 days. S imilarly, subcutaneous innoculation of the two variants into immunosup pressed newborn rats gave rise to extensive spontaneous lung metastase s compared to the M(4)Beu. cell line. These results provide evidence t hat a population of melanoma cells can grow aggressively in vivo and m etastasize in the absence of beta(3) or alpha(v) beta(3) integrin comp lex. Our results may have clinical relevance and suggest that certain types of melanomas in patients may grow and spread in the absence of t he alpha(v) beta(3) integrin complex.