Estrogen regulated expression of the p21Waf1/Cip1 gene in estrogen receptor positive human breast cancer cells

✍ Scribed by Soma Mandal; James R. Davie

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 183 KB
• Volume: 224
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.22078

✦ Synopsis

Abstract

The cyclin‐dependent kinase inhibitor protein p21^Waf1/Cip1^ is a potent tumor suppressor. Here, we demonstrate that estradiol regulates the p21^Waf1/Cip1^ gene. Estradiol induces p21^Waf1/Cip1^ mRNA expression within 30–60 min independent of new protein synthesis in the estrogen receptor α (ERα) positive human breast cancer cell line MCF‐7. Similar to other estradiol responsive promoters, the p21^Waf1/Cip1^ upstream promoter region has several estrogen response element (ERE) half‐sites nestled in AP‐1 binding sites, which are positioned upstream to Sp1 binding sites. Using the chromatin immunoprecipitation (ChIP) assay, we show that estradiol stimulation resulted in the recruitment of transcription factors ERα, Sp1, and Sp3 to the p21^Waf1/Cip1^ upstream promoter element. The Sp1 inhibitor mithramycin A abrogated Sp1, and to a lesser extent Sp3 binding, and markedly reduced the estradiol stimulated p21^Waf1/Cip1^ gene expression. However, ERα binding was not affected in the mithramycin A and estradiol treated cells. On closer examination of the half‐site ERE/AP‐1 sites upstream to the Sp1 sites in a separate ChIP experiment, we found a pronounced association of ERα upon estradiol treatment compared to almost negligible binding of Sp1 or Sp3. Together these studies provide evidence that ERα is recruited to the half‐site ERE/AP‐1 sites in the p21^Waf1/Cip1^ upstream promoter element. Although Sp1/Sp3 is not involved in the recruitment of ERα to the promoter, Sp1 is necessary for estrogen‐induced p21^Waf1/Cip1^ promoter activity. J. Cell. Physiol. 224:28–32, 2010 © 2010 Wiley‐Liss, Inc.