title: Beta human papillomavirus E6 expression inhibits stabilization of p53 and increases tolerance of genomic instability.
abstract: Infections with the beta genus of human papillomaviruses (β-HPVs) may contribute to the development of nonmelanoma skin cancers. However, β-HPV genomes are found at too low a copy number in tumors for the virus to be necessary for tumor maintenance. Instead, they are hypothesized to destabilize the host genome by allowing the persistence of mutations that can drive tumorigenesis independently of the viral genome. Supporting this premise is our previous finding that the expression of some β-HPV E6 proteins can attenuate p53 signaling in response to DNA damage. We show that β-HPV E6 proteins can prevent the stabilization of p53 in response to two types of genome-destabilizing events, aberrant mitosis and dysregulated centrosome duplication. The inability to stabilize p53 in response to these stimuli allows cells expressing HPV5, HPV8, or HPV38 E6 to remain proliferatively active, leading to further genome deterioration in a proportion of these cells. These phenotypes are lost by the introduction of a mutation into the p300 binding domain of HPV8 E6 or by the transfection of mutated p300 that is resistant to the degradation mediated by HPV5 or HPV8 E6. These findings expand the understanding of the role played by p300 in promoting the faithful resolution of mitotic figures as well as proper centrosome duplication. Finally, we describe a phenomenon by which binucleated cells are resolved via cytokinesis into two cells, each with one nucleus. These data support the hypothesis that β-HPV infections may promote tumorigenesis via genome destabilization.
  
  
  OBJECTIVE
  The work described in this report provides support for the hypothesis that β-HPV infections may contribute to nonmelanoma skin cancer by increasing the likelihood that tumorigenic mutations are introduced into the host cell's genome. We demonstrate that expression of the E6 proteins from some of these viruses increases the tolerance of two genome-destabilizing events, aberrant cell division and dysregulated centrosome duplication. Typically, these mutagenic occurrences elicit the stabilization of the tumor suppressor p53, which prevents further propagation of cells containing these errors. We show that the expression of β-HPV E6 restricts this stabilization of p53, leading not only to continued cellular proliferation but also to further accumulation of similar mutagenic events. Finally, in addition to supporting a role for β-HPV infections in certain skin cancers, we present studies with a mutated β-HPV E6 protein suggesting that the histone acetyltransferase p300 plays a role in promoting genome stability during replication.
authors.affiliation: Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Wallace
authors.forename: Kristin
authors.initials: K
authors.lastname: Robinson
authors.forename: Denise A
authors.initials: DA
authors.lastname: Galloway
mesh_terms: D000704:Analysis of Variance; D052686:Betapapillomavirus / Q000235:genetics*; D005434:Flow Cytometry; D042822:Genomic Instability / Q000235:genetics*; D006801:Humans; D008856:Microscopy, Fluorescence; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000378:metabolism*; D055550:Protein Stability; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D001616:beta-Galactosidase
chemical_list: C466081:E6 protein, Human papillomavirus type 8; C487708:E6 protein, human papillomavirus type 5; D009856:Oncogene Proteins, Viral; D016159:Tumor Suppressor Protein p53; D001616:beta-Galactosidase