title: STAT-5 Regulates Transcription of the Topoisomerase IIβ-Binding Protein 1 (TopBP1) Gene To Activate the ATR Pathway and Promote Human Papillomavirus Replication.
abstract: The life cycle of high-risk human papillomaviruses (HPVs) is dependent upon epithelial differentiation. Following infection of basal cells, HPV genomes are stably maintained at low copy numbers, and productive replication or amplification is restricted to highly differentiated suprabasal cells. In high-risk HPV infections, the ATM pathway is constitutively activated in the absence of external DNA-damaging agents and is required for productive viral replication. The ataxia telangiectasia (ATM) pathway repairs double-strand breaks in DNA, while the ataxia telangiectasia and Rad3-related (ATR) pathway targets single-strand breaks. Our studies show that the ATR pathway, like the ATM pathway, is activated in HPV-positive cells and that inhibitors of ATR or CHK1 phosphorylation block both amplification and late viral gene expression in differentiated cells while moderately reducing stable copy numbers in undifferentiated cells. TopBP1 is a critical upstream activator of the ATR pathway and is expressed at elevated levels in HPV-positive cells. This increased expression of TopBP1 is necessary for ATR/CHK1 activation in HPV-positive cells, and knockdown blocks amplification. Furthermore, TopBP1 activation is shown to be regulated at the level of transcription initiation by the innate immune regulator STAT-5, which is activated by HPV proteins. STAT-5 has also been shown to be a regulator of the ATM response, demonstrating that these two pathways are coordinately regulated in HPV-positive cells. These findings identify a novel link between the innate immune response and activation of the ATR DNA damage response in regulating the life cycle of high-risk HPVs.
  
  
  OBJECTIVE
  High-risk human papillomaviruses (HPVs) are the causative agents of cervical and other anogenital cancers, as well as many oral cancers. HPVs infect epithelial cells and restrict productive viral replication or amplification and virion production to differentiated cells. Our studies demonstrate that HPVs activate the ATR single-strand DNA repair pathway and this activation is necessary for HPV genome amplification. The innate immune regulator STAT-5 is shown to regulate transcription of the ATR binding factor TopBP1, and this is critical for the induction of the ATR pathway. Our study identifies important links between innate immune signaling, the ATR DNA damage pathway, and productive HPV replication that may lead to the characterization of new targets for the development of therapeutics to treat HPV-induced infections.
authors.affiliation: Department of Microbiology-Immunology, Northwestern University, Feinberg School of Medicine, Chicago, Illinois, USA.
authors.forename: Shiyuan
authors.initials: S
authors.lastname: Hong
authors.affiliation: Department of Microbiology-Immunology, Northwestern University, Feinberg School of Medicine, Chicago, Illinois, USA.
authors.forename: Shouqiang
authors.initials: S
authors.lastname: Cheng
authors.affiliation: Department of Microbiology-Immunology, Northwestern University, Feinberg School of Medicine, Chicago, Illinois, USA.
authors.forename: Andre
authors.initials: A
authors.lastname: Iovane
authors.affiliation: Department of Microbiology-Immunology, Northwestern University, Feinberg School of Medicine, Chicago, Illinois, USA l-laimins@northwestern.edu.
authors.forename: Laimonis A
authors.initials: LA
authors.lastname: Laimins
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation; D053263:Gene Regulatory Networks; D054884:Host-Pathogen Interactions; D006801:Humans; D015603:Keratinocytes / Q000821:virology; D009687:Nuclear Proteins / Q000378:metabolism*; D027383:Papillomaviridae / Q000502:physiology*; D050799:STAT5 Transcription Factor / Q000378:metabolism*; D014158:Transcription, Genetic; D014764:Viral Proteins / Q000378:metabolism*; D014779:Virus Replication
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D050799:STAT5 Transcription Factor; C110513:TOPBP1 protein, human; D014764:Viral Proteins; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins