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Brazilian Journal of Medical and Biological Research
On-line version ISSN 1414-431X
SARTI, M.S.M.V.; VISCONTI, M.A. and CASTRUCCI, A.M.L.. Biological activity and binding of estradiol to SK-Mel 23 human melanoma cells. Braz J Med Biol Res [online]. 2004, vol.37, n.6, pp. 901-905. ISSN 1414-431X. http://dx.doi.org/10.1590/S0100-879X2004000600016.
Patients expressing estradiol receptors in melanoma cells have been reported to have a better prognosis. We therefore decided to investigate the in vitro effects of ß-estradiol and tamoxifen on the growth and tyrosinase activity of SK-Mel 23 human melanoma cells. Twenty-four-hour treatment with 0.4 nM ß-estradiol inhibited cell proliferation in 30% (0.70 ± 0.03 x 105 cells) and increased tyrosinase activity in 50% (7130.5 ± 376.5 cpm/105 cells), as compared to untreated cells (1.0 ± 0.05 x 105 cells and 4769 ± 25.5 cpm/105 cells, respectively). Both responses were completely (100%) blocked by 1 µM tamoxifen. Higher concentrations (up to 1.6 nM) or longer treatments (up to 72 h) did not result in a larger effect of the hormone on proliferation or tyrosinase activity. Competition binding assays demonstrated the presence of binding sites to [2,4,6,7-3H]-ß-estradiol, and that the tritiated analogue was displaced by the unlabeled hormone (1 nM to 100 µM, Kd = 0.14 µM, maximal displacement of 93%) or by 10 µM tamoxifen (displacement of 60%). ß-estradiol also increased the phosphorylated state of two proteins of 16 and 46 kDa, after 4-h treatment, as determined by Western blot. The absorbance of each band was 1.9- and 4-fold the controls, respectively, as determined with Image-Pro Plus software. Shorter incubation periods with ß-estradiol did not enhance phosporylation; after 6-h treatment with the hormone, the two proteins returned to the control phosphorylation levels. The growth inhibition promoted by estradiol may explain the better prognosis of melanoma-bearing women as compared to men, and open new perspectives for drug therapy.
Keywords : SK-Mel 23 cell line; Human melanoma; ß-estradiol; Tamoxifen; Cell proliferation; Tyrosinase activity.