MDM2 negatively regulates the human telomerase RNA gene promoter

Zhao, J., Bilsland, A. , Jackson, K. and Keith, W.N. (2005) MDM2 negatively regulates the human telomerase RNA gene promoter. BMC Cancer, 5, p. 6. (doi: 10.1186/1471-2407-5-6)

Abstract

<b>Background:</b> We have previously demonstrated that NF-Y and Sp1 interact with the human telomerase RNA (hTR) promoter and play a central role in its regulation. We have also shown that pRB activates the hTR promoter, but the mechanism of pRb directed activation is unknown. It has recently been reported that pRB induces Sp1 activity by relieving inhibition mediated by mdm2. The aim was to investigate possible roles for mdm2 in hTR promoter regulation. <b>Methods:</b> Chromatin immunoprecipitation was used to determine binding of mdm2 to the hTR promoter. Transfection and luciferase assays were used to investigate mdm2 repression of the promoter activity and interaction with known transcriptional modulators. <b>Results:</b> Here we show using chromatin immunoprecipitation that mdm2 specifically binds the hTR promoter in vivo. Transient co-transfection experiments using an hTR promoter luciferase reporter construct show that hTR promoter activity is inhibited by over-expression of mdm2 in 5637 bladder carcinoma cells (p53 and pRB negative, low mdm2). Titration of mdm2 was able to antagonise activation of hTR promoter activity mediated by pRB or Sp1 over-expression, although in the presence of pRB, mdm2 could not repress promoter activity below basal levels. Using an Sp1 binding site mutation construct we showed that mdm2 repression did not absolutely require Sp1 binding sites in the hTR promoter, suggesting the possibility of pRB/Sp1 independent mechanisms of repression. Finally, we show that NF-Y mediated transactivation of the hTR promoter was also suppressed by mdm2 in a dose-dependent manner. <b>Conclusions:</b> These studies suggest that mdm2 may inhibit the hTR promoter by multiple mechanisms. Mdm2 may directly repress activation by both pRB and Sp1, or activation by NF-Y. Furthermore, the ability of mdm2 to interact and interfere with components of the general transcription machinery might partly explain the general repressive effect seen here. Elucidation of new regulators affecting hTR basal promoter activity in cancer cells provides a basis for future studies aimed at improving our understanding of the differential hTR expression between normal and cancer cells.

• Item Type: Articles
• Additional Information: This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Keith, Professor Nicol and Bilsland, Dr Alan
• Authors: Zhao, J., Bilsland, A., Jackson, K., and Keith, W.N.
• Subjects: R Medicine > RC Internal medicine > RC0254 Neoplasms. Tumors. Oncology (including Cancer); Q Science > QH Natural history > QH426 Genetics
• College/School: College of Medical Veterinary and Life Sciences > School of Cancer Sciences
• Journal Name: BMC Cancer
• Publisher: BioMed Central Ltd.
• ISSN: 1471-2407
• Published Online: 18 January 2005
• Copyright Holders: © 2005 Zhao et al; licensee BioMed Central Ltd.
• First Published: First published in BMC Cancer 5 : 6
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher.