Estrogen receptors are activated by the hormone estrogen and they control cell growth by altering gene expression as a transcription factor. So far two estrogen receptors have been found: ER alpha and ER beta. Estrogen receptors are also implicated in the development and progression of breast cancer. Here, we found that ER alpha, localized on the spindle and spindle poles at the metaphase during mitosis. Depletion of ER alpha generated unaligned chromosomes in metaphase cells and lagging chromosomes in anaphase cells in a transcription-independent manner. Furthermore, the levels of beta-tubulin and gamma-tubulin were reduced in ER alpha-depleted cells. Consistent with this, polymerization of microtubules in ER alpha-depleted cells and turnover rate of alpha/beta-tubulin were decreased than in control cells. We suggest that ER alpha regulates chromosome alignment and spindle dynamics by stabilizing microtubules during mitosis. (C) 2014 Elsevier Inc. All rights reserved.