Biological activity and binding of estradiol to SK-Mel 23 human melanoma cells.
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 beta-estradiol and tamoxifen on the growth and tyrosinase activity of SK-Mel 23 human melanoma cells. Twenty-four-hour treatment with 0.4 nM beta-estradiol inhibited cell proliferation in 30% (0.70 +/- 0.03 x 10(5) cells) and increased tyrosinase activity in 50% (7130.5 +/- 376.5 cpm/10(5) cells), as compared to untreated cells (1.0 +/- 0.05 x 10(5) cells and 4769 +/- 25.5 cpm/10(5) cells, respectively). Both responses were completely (100%) blocked by 1 microM 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]-beta-estradiol, and that the tritiated analogue was displaced by the unlabeled hormone (1 nM to 100 microM, Kd = 0.14 microM, maximal displacement of 93%) or by 10 microM tamoxifen (displacement of 60%). Beta-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 beta-estradiol did not enhance phosphorylation; 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.
Sarti
M S M V
MS
Departamento de Fisiologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brasil.
Visconti
M A
MA
Castrucci
A M L
AM
D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D001667:Binding, Competitive; D015153:Blotting, Western; D004958:Estradiol / Q000494:pharmacology*; D006801:Humans; D008545:Melanoma / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D014442:Monophenol Monooxygenase / Q000187:drug effects* / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology*; D013997:Time Factors; D014407:Tumor Cells, Cultured / Q000187:drug effects
D018931:Antineoplastic Agents, Hormonal; D013629:Tamoxifen; D004958:Estradiol; D014442:Monophenol Monooxygenase