Identification of a novel telomerase repressor that interacts with the human papillomavirus type-16 E6/E6-AP complex (original) (raw)
- Lindy Gewin1,2,
- Hadley Myers1,
- Tohru Kiyono1, and
- Denise A. Galloway1,3
- 1Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA; 2Molecular and Cellular Biology Program, University of Washington, Seattle, Washington 98125, USA
Abstract
The critical immortalizing activity of the human papillomavirus (HPV) type-16 E6 oncoprotein is to induce expression of hTERT, the catalytic and rate-limiting subunit of telomerase. Additionally, E6 binds to a cellular protein called E6-associated protein (E6-AP) to form an E3 ubiquitin ligase that targets p53 for proteasome-dependent degradation. Although telomerase induction and p53 degradation are separable and distinct functions of E6, binding of E6 to E6-AP strongly correlated with the induction of hTERT. Here, we demonstrate using shRNAs to reduce E6-AP expression that E6-AP is required for E6-mediated telomerase induction. A yeast two-hybrid screen to find new targets of the E6/E6-AP E3 ubiquitin ligase complex identified NFX1. Two isoforms of NFX1 were found: NFX1-123, which coactivated with c-Myc at the hTERT promoter, and NFX1-91, which repressed the hTERT promoter. NFX1-91 was highly ubiquitinated and destabilized in epithelial cells expressing E6. Furthermore, knockdown of NFX1-91 by shRNA resulted in derepression of the endogenous hTERT promoter and elevated levels of telomerase activity. We propose that the induction of telomerase by the HPV-16 E6/E6-AP complex involves targeting of NFX1-91, a newly identified repressor of telomerase, for ubiquitination and degradation.
Footnotes
Supplemental material is available at http://www.genesdev.org.
Article and publication are at http://www.genesdev.org/cgi/doi/10.1101/gad.1214704.
↵3 Corresponding author. E-MAIL dgallowa{at}fhcrc.org; FAX (206) 667-5815.
- Accepted July 21, 2004.
- Received April 23, 2004.
Cold Spring Harbor Laboratory Press