title: The human papillomavirus (HPV) E6* proteins from high-risk, mucosal HPVs can direct degradation of cellular proteins in the absence of full-length E6 protein.
abstract: The E6 oncoproteins from high-risk mucosotrophic human papillomaviruses (HPVs) target a range of cellular proteins for proteasome-mediated degradation. Apart from the tumor suppressor p53 and proapoptotic Bcl-2 family member Bak, many targets contain class 1 PDZ domains and are involved in cell junction stability and signaling. The targeting mechanism is considered to function by the E6 protein acting as an adaptor molecule linking a cellular ubiquitin ligase to the target protein. In each case, whether the target is the p53 tumor suppressor or a member of the group of PDZ domain-containing targets, this mechanism relies on a direct interaction between E6 and its cellular target. This study focuses on the impact of the HPV type 18 (HPV-18) E6*I protein on the stability of Akt, Dlg, MAGI-1, MAGI-2, and Scribble. We show that HPV-18 E6* expression can downregulate the expression levels of Akt, Dlg, and Scribble in the absence of full-length HPV-18 E6 protein. The reduction in Dlg levels by E6* is independent of transcription and does not require a direct interaction between the two proteins although the proteasome pathway is involved. Further, we provide evidence that activation of certain signal transduction pathways has a profound effect on the targeting of Dlg by E6* and suggest that high-risk HPV E6 oncoproteins can target certain substrates both directly and indirectly through the E6* proteins and may cooperate in their degradation.
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34012 Trieste, Italy. pim@icgeb.org
authors.forename: David
authors.initials: D
authors.lastname: Pim
authors.forename: Vjekoslav
authors.initials: V
authors.lastname: Tomaic
authors.forename: Lawrence
authors.initials: L
authors.lastname: Banks
mesh_terms: D001483:Base Sequence; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000378:metabolism*; D016158:Genes, p53; D006801:Humans; D008856:Microscopy, Fluorescence / Q000379:methods; D008954:Models, Biological; D008969:Molecular Sequence Data; D009092:Mucous Membrane / Q000821:virology; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D016366:Open Reading Frames; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012306:Risk; D012689:Sequence Homology, Nucleic Acid
chemical_list: D004268:DNA-Binding Proteins; C052603:E6 protein, Human papillomavirus type 18; D009856:Oncogene Proteins, Viral; D051057:Proto-Oncogene Proteins c-akt; D046988:Proteasome Endopeptidase Complex