Estrogen induces cell death in non- reproductive cancer cells through disrupting mitotic spindle assembly

Cancer epidemiology shows consistent sex dimorphism across many non reproductive cancers: males typically have earlier onset, higher incidence, and worse outcomes. While these differences have been partly attributed to differential exposure to risk factors, they persist after adjustment, implicating intrinsic biological contributors. Changes in cancer behavior around the menopausal transition further implicate estrogenic environments in modulating core processes such as cell division and tumor survival. Here, we examine effects of high concentrations of estrogen on proliferation in multiple non reproductive cancer types, including bladder cancer. We find that estrogen induces tumor cell death through a mechanism independent of classical estrogen receptors (ERalpha, ERbeta, and GPER). To identify mediators of this cytotoxicity, we conducted an unbiased whole genome CRISPR knockout screen. Notably, the ten most significant genes-KIFC1, TPX2, LIN37, KIF4A, KIF18B, KIF2C, WDR62, CLASP1, CLIP1, and VPS37C-are all required for spindle assembly and function. These results implicate spindle assembly as a key determinant of cellular sensitivity to estrogen. Kinetic studies showed that estrogen inhibits both microtubule polymerization and depolymerization. Biochemical analysis identifies estrogen binds alphabeta-tubulin dimers and acts as a negative catalyst of microtubule dynamics, impairing spindle assembly, disrupting mitosis, and triggering cell cycle-associated death pathways. Consistent with this model, overexpression of the microtubule polymerase Ch-TOG attenuates estrogen's effects. Together, these data suggest that elevated estrogen levels can compromise spindle assembly and promote tumor cell death, providing a potential mechanism by which reproductive age females may be relatively protected from many non reproductive cancers and offering insight into the sex disparities observed in epidemiological studies.