Autocrine human growth hormone expression leads to resistance of MCF-7 cells to tamoxifen.

Tamoxifen is the most common antiestrogen used in the treatment of estrogen-positive breast cancer but its adverse effects and also resistance to this drug are serious challenges in the treatment of breast cancer. Characterization of mechanisms responsible for these adverse effects can lead to design of more efficient therapeutic strategies for the treatment of breast cancer. Here, we used a cellular model to evaluate the effects of autocrine expression of human growth hormone on responses of cells to tamoxifen. Our results imply for the first time that autocrine expression of growth hormone in human breast adenocarcinoma cell line, MCF-7, results in increase in cell proliferative capacity of cells even in the presence of tamoxifen. This effect may be due to up-regulation of G-coupled estrogen receptor, GPR30, which is activated by tamoxifen.