title: High-risk human papillomavirus E6 oncoproteins interact with 14-3-3ζ in a PDZ binding motif-dependent manner.
abstract: Cervical cancer develops through the combined activities of the human papillomavirus (HPV) E6 and E7 oncoproteins. A defining characteristic of E6 oncoproteins derived from cancer-causing HPV types is the presence of a PDZ binding motif (PBM) at the extreme carboxy terminus of the protein which is absent from E6 proteins derived from the so-called low-risk HPV types. Within this PBM is also a protein kinase A (PKA) phospho-acceptor site, which is thought to negatively regulate the association of E6 with its PDZ domain-containing substrates. We can now show that phosphorylation of E6 by PKA and/or AKT confers the ability to interact with 14-3-3ζ. The interaction is direct and specific for the high-risk HPV E6 oncoproteins, although there are significant differences in the efficiencies with which HPV-16, HPV-18, and HPV-31 E6 oncoproteins can associate with 14-3-3ζ; this correlates directly with their respective susceptibilities to phosphorylation by PKA and/or AKT. We demonstrate here that the interaction between E6 and 14-3-3ζ also requires integrity of the E6 PBM, and downregulation of 14-3-3ζ results in a marked reduction in the levels of HPV-18 E6 expression in HeLa cells. Using phospho-specific anti-E6 antibodies, we also demonstrate significant levels of E6 phosphorylation in vivo. These studies redefine the potential relevance of the E6 PBM in the development of cervical cancer, suggesting that interaction with 14-3-3ζ, as well as the more well-established interactions with PDZ domain-containing substrates, is likely to be responsible for the biological activities attributed to this region of the high-risk HPV E6 oncoproteins.
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, Padriciano, Trieste, Italy.
authors.forename: Siaw Shi
authors.initials: SS
authors.lastname: Boon
authors.forename: Lawrence
authors.initials: L
authors.lastname: Banks
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006367:HeLa Cells; D054884:Host-Pathogen Interactions; D006801:Humans; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D054731:PDZ Domains; D027383:Papillomaviridae / Q000472:pathogenicity*; D010766:Phosphorylation; D011485:Protein Binding; D025941:Protein Interaction Mapping; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*
chemical_list: D048948:14-3-3 Proteins; D004268:DNA-Binding Proteins; C068651:E6 protein, Human papillomavirus type 16; C052603:E6 protein, Human papillomavirus type 18; C572886:E6 protein, Human papillomavirus type 31; D009856:Oncogene Proteins, Viral; D012097:Repressor Proteins; C572235:YWHAZ protein, human; D051057:Proto-Oncogene Proteins c-akt; D017868:Cyclic AMP-Dependent Protein Kinases