Melatonin down-regulates hTERT expression induced by either natural estrogens (17beta-estradiol) or metalloestrogens (cadmium) in MCF-7 human breast cancer cells.

The goal was to evaluate whether melatonin (Mel) down-regulates hTERT expression induced by 17beta-estradiol (E(2)) or cadmium (Cd) in breast cancer cells. We found that: (a) Mel inhibits E(2) or Cd-induced hTERT transcription in hTERT-Luc transfected MCF-7 cells, (b) Mel significantly reduces E(2)- and Cd-mediated hTERT transactivation triggered by ERalpha in transfected HeLa cells, (c) Mel inhibits hTERT expression induced by E(2) or Cd in MCF-7 cells. Melatonin inhibition of telomerase activity supports a possible role in treatment of estrogen-dependent tumors or carcinogenesis by environmental or occupational exposure to xenoestrogens.