Functional inactivation of p73, a homolog of p53 tumor suppressor protein, by human papillomavirus E6 proteins

Int J Cancer. 2001 Mar 15;91(6):822-7. doi: 10.1002/1097-0215(200002)9999:9999<::aid-ijc1130>;2-0.


Human papillomavirus (HPV) is strongly implicated as a causative agent in the etiology of cervical cancer. Of its gene products, E6 binds to and inactivates p53 tumor suppressor protein by ubiquitin/proteasome-dependent degradation. Recently, p73, a novel family of p53, has been identified and demonstrated, like p53, to activate p21(WAF1). Here we show that p73 is also inactivated by HPV-E6, but ubiquitin-mediated proteolysis is not responsive. Yeast two-hybrid and GST pull-down assays indicate a physical interaction between p73 and either HPV-16 or HPV-11 E6 proteins in vivo and in vitro, respectively. The transactivation domain (amino acid residues 1 to 49) is found to be absolutely required for the interaction. Transient co-expression of E6 significantly inhibits the p73-mdiated activation of p21(WAF1) promoter in a p53-defective C33A cell line. Using Gal4-p73 fusion protein, we demonstrate that E6 inhibition of p73 transactivation function is independent of sequence-specific DNA binding, which is confirmed by a direct electrophoretic mobility shift assay. Moreover, E6 inhibits p73 function by interfering with the activity of the amino-terminal activation domain. Co-transfection of E6 mutants reveals that the same portion of E6 appears to be responsible for the inactivation of p53 and p73 function. However, the inactivation mechanism of p73 is clearly different from that of p53, because p73, unlike p53, is inactivated by both high- and low-risk E6s and is not susceptible to E6-dependent proteolysis. These overall results, consequently, suggest that in addition to the inactivation of p53, the functional interference of p73 by HPV-E6 may, at least in part, contribute to E6-mediated transformation and hyperproliferation of cervical cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis
  • Blotting, Western
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins / metabolism
  • DNA / metabolism
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Electrophoresis, Agar Gel
  • Enzyme-Linked Immunosorbent Assay
  • Genes, Tumor Suppressor / physiology*
  • Glutathione Transferase / chemistry
  • Humans
  • Mutation
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Oncogene Proteins, Viral / genetics
  • Oncogene Proteins, Viral / metabolism*
  • Papillomaviridae / physiology*
  • Protein Binding
  • Recombinant Fusion Proteins / metabolism
  • Transfection
  • Tumor Cells, Cultured
  • Tumor Protein p73
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism*
  • Tumor Suppressor Proteins
  • Tumor Virus Infections / virology*
  • Two-Hybrid System Techniques


  • CDKN1A protein, human
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • DNA-Binding Proteins
  • E6 protein, Human papillomavirus type 6
  • Nuclear Proteins
  • Oncogene Proteins, Viral
  • Recombinant Fusion Proteins
  • TP73 protein, human
  • Tumor Protein p73
  • Tumor Suppressor Protein p53
  • Tumor Suppressor Proteins
  • DNA
  • Glutathione Transferase