Estradiol differently affects melanin synthesis of malignant and normal melanocytes: a relationship with clock and clock-controlled genes.

Melanin production within melanocytes is regulated, among others, by estradiol, whose effects on melanogenesis are still not completely elucidated. Here we show that although 10(-7) M 17β-estradiol (E2) increased tyrosinase mRNA levels in B16-F10 malignant melanocytes, there was a transient decrease and abolishment of the temporal variation of melanin content. Both parameters were much higher in the malignant than in normal Melan-a cells. Considering that silencing clock machinery in human melanocytes increases melanogenesis, we investigated clock gene expression in those cell lines. Except for Melan-a Bmal1 and B16-F10 Per2 expression of control cells, Per1, Per2, and Bmal1 expression increased independently of cell type or E2 treatment after 24 h. However, melanoma cells showed a marked increase in Per1 and Bma11 expression in response to E2 at the same time points, what may rule out E2 as a synchronizer agent since the expression of those genes were not in antiphase. Next, we investigated the expression of Xpa, a clock-controlled gene, which in Melan-a cells, peaked at 18 h, and E2 treatment shifted this peak to 24 h, whereas B16-F10 Xpa expression peaked at 24 h in both control and E2 group, and it was higher compared to Melan-a cells in both groups. Therefore, malignant and normal melanocytes display profound differences on core elements of the local clock, and how they respond to E2, what is most probably determinant of the differences seen on melanin synthesis and Tyrosinase and Xpa expression. Understanding these processes at the molecular level could bring new strategies to treat melanoma.