Increased cell proliferation is associated with genomic instability: elevated micronuclei frequencies in estradiol-treated human ovarian cancer cells

Estrogen-related cancers are often associated with the hormone's tumor promoting activity. Recently, estradiol has also been demonstrated to induce gene mutations in the physiological concentration range. Mitotic disturbances are found at higher concentrations. In the present study we demonstrate data suggesting an additional mechanism for the induction of genetic damage, i.e. chromosomal breakage. Estrogen receptor-positive (BG-1) and -negative (UCI) human ovarian cancer cell lines were investigated for micronucleus formation after treatment with estradiol. BG-1 cells but not UCI cells showed an increase in micronucleus formation which correlated with the estradiol-induced cell proliferation. The specific estradiol receptor antagonist hydroxytamoxifen suppressed the formation of micronuclei in BG-1 cells. Increased micronucleus frequencies were also seen after normalization of the data to the number of cell divisions. Kinetochore analysis revealed a difference between micronuclei induced by picomolar concentrations of estradiol (kinetochore-negative) and micromolar concentrations (predominantly kinetochore-positive) leading to mitotic disturbances. In accordance with this finding, analysis of the cell cycle revealed decreased cell numbers in G(2)/M phase after treatment with picomolar concentrations, usually not found after mitotic disturbances. We hypothesize that hormone-specific forcing of responsive cells through the cell cycle leads to an override of checkpoints operating under homeostatic control of the cell cycle, resulting in genomic instability.