Identification of a novel telomerase repressor that interacts with the human papillomavirus type-16 E6/E6-AP complex

Genes Dev. 2004 Sep 15;18(18):2269-82. doi: 10.1101/gad.1214704.

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Binding Sites
  • Cells, Cultured
  • DNA-Binding Proteins
  • Enzyme Activation
  • Genes, myc
  • Humans
  • Macromolecular Substances
  • Molecular Sequence Data
  • Mutation
  • Oncogene Proteins, Viral / genetics
  • Oncogene Proteins, Viral / metabolism*
  • Promoter Regions, Genetic
  • Protein Isoforms
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Telomerase / genetics
  • Telomerase / metabolism
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism
  • Ubiquitin-Protein Ligases / genetics
  • Ubiquitin-Protein Ligases / metabolism

Substances

  • DNA-Binding Proteins
  • E6 protein, Human papillomavirus type 16
  • Macromolecular Substances
  • NFX1 protein, human
  • Oncogene Proteins, Viral
  • Protein Isoforms
  • Repressor Proteins
  • Tumor Suppressor Protein p53
  • UBE3A protein, human
  • Ubiquitin-Protein Ligases
  • Telomerase