title: Withaferin a suppresses estrogen receptor-α expression in human breast cancer cells.
abstract: We have shown previously that withaferin A (WA), a promising anticancer constituent of Ayurvedic medicine plant Withania somnifera, inhibits growth of MCF-7 and MDA-MB-231 human breast cancer cells in culture and MDA-MB-231 xenografts in vivo by causing apoptosis. However, the mechanism of WA-induced apoptosis is not fully understood. The present study was designed to systematically determine the role of tumor suppressor p53 and estrogen receptor-α (ER-α) in proapoptotic response to WA using MCF-7, T47D, and ER-α overexpressing MDA-MB-231 cells as a model. WA treatment resulted in induction as well as increased S15 phosphorylation of p53 in MCF-7 cells, but RNA interference of this tumor suppressor conferred modest protection at best against WA-induced apoptosis. WA-mediated growth inhibition and apoptosis induction in MCF-7 cells were significantly attenuated in the presence of 17β-estradiol (E2). Exposure of MCF-7 cells to WA resulted in a marked decrease in protein levels of ER-α (but not ER-β) and ER-α regulated gene product pS2, and this effect was markedly attenuated in the presence of E2. WA-mediated down-regulation of ER-α protein expression correlated with a decrease in its nuclear level, suppression of its mRNA level, and inhibition of E2-dependent activation of ERE2e1b-luciferase reporter gene. Ectopic expression of ER-α in the MDA-MB-231 cell line conferred partial but statistically significant protection against WA-mediated apoptosis, but not G2/M phase cell cycle arrest. Collectively, these results indicate that WA functions as an anti-estrogen, and the proapoptotic effect of this promising natural product is partially attenuated by p53 knockdown and E2-ER-α.
authors: Department of Pharmacology & Chemical Biology, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pennsylvania, USA.
authors: Eun-Ryeong
authors: ER
authors: Hahm
authors: Joomin
authors: J
authors: Lee
authors: Yi
authors: Y
authors: Huang
authors: Shivendra V
authors: SV
authors: Singh
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects*; D047628:Estrogen Receptor alpha / Q000235:genetics* / Q000378:metabolism; D005260:Female; D006801:Humans; D012333:RNA, Messenger / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation; D032341:Withania / Q000737:chemistry*; D054358:Withanolides / Q000494:pharmacology*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; C506487:ESR1 protein, human; D047628:Estrogen Receptor alpha; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D054358:Withanolides; C009684:withaferin A