title: The transcription map of HPV11 in U2OS cells adequately reflects the initial and stable replication phases of the viral genome.
abstract: BACKGROUND
  Although prophylactic vaccines have been developed against HPV6, HPV11, HPV16 and HPV18 there is the clear unmet medical need in order to justify the development of drugs targeting human papillomavirus replication. The native host cells of HPVs are human primary keratinocytes which can be cultivated in raft cultures. However, this method is difficult to use in high-throughput screening assays and the need for a cost-effective cellular system for screening potential anti-HPV drug candidates during all stages of HPV genome replication remains.
  
  
  METHODS
  U2OS cells were transfected with HPV11 wt or E8- minicircle genomes and their gene expression was studied via 3' RACE, 5' RACE or via real time PCR methods. The DNA replication of these genomes was detected by Southern blot methods.
  
  
  RESULTS
  The analysis of HPV11 transcripts in U2OS cells showed that the patterns of promoter use, splice sites and polyadenylation cleavage sites are identical to those previously characterized in human HPV-related lesions, human squamous carcinoma cell lines (e.g., SSC-4) and laryngeal papillomas. Transcriptional initiation from the three previously described HPV11 promoters in the E6 and E7 ORFs (P90, P264, and P674-714) were functional, and these promoters were used together with two promoter regions in the E1 ORF (P1092 and P1372). Mutating the E8 ORF ATG start codon to ACG eliminated the translation of fusion proteins from the E8 ORF coupled to E1 and E2 proteins C-terminal sequences, leading to the de-repression of gene expression (particularly from the P1092 promoter) and to the activation of genome replication. These data suggested that the expression of the functional E8^E2 protein is used to control viral gene expression and copy number of the HPV11 genome. The analysis of HPV11 E1 expression plasmids showed that the E6/E7 region, together with the E1 coding region, is crucial for the production of functionally active E1 protein.
  
  
  CONCLUSIONS
  The data presented in this paper suggest that in human osteosarcoma cell line U2OS the gene expression pattern of the HPV11 truly reflect the expression profile of the replicating HPV genome and therefore this cellular system is suitable for drug development program targeting HPV replication.
authors.affiliation: Institute of Technology, University of Tartu, Tartu, Estonia. helen.isok-paas@ut.ee.
authors.forename: Helen
authors.initials: H
authors.lastname: Isok-Paas
authors.affiliation: Icosagen Cell Factory OÜ, Tartu, Estonia. andres.mannik@icosagen.ee.
authors.forename: Andres
authors.initials: A
authors.lastname: Männik
authors.affiliation: Institute of Technology, University of Tartu, Tartu, Estonia. ene.ustav@ut.ee.|Estonian Biocentre, Tartu, Estonia. ene.ustav@ut.ee.
authors.forename: Ene
authors.initials: E
authors.lastname: Ustav
authors.affiliation: Institute of Technology, University of Tartu, Tartu, Estonia. mart.ustav@icosagen.ee.|Icosagen Cell Factory OÜ, Tartu, Estonia. mart.ustav@icosagen.ee.|Estonian Academy of Sciences, Tallinn, Estonia. mart.ustav@icosagen.ee.
authors.forename: Mart
authors.initials: M
authors.lastname: Ustav
mesh_terms: D045744:Cell Line, Tumor; D004261:DNA Replication; D015967:Gene Expression Regulation, Viral; D016679:Genome, Viral; D052140:Human papillomavirus 11 / Q000235:genetics* / Q000502:physiology; D006801:Humans; D030361:Papillomavirus Infections / Q000821:virology*; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D014779:Virus Replication
chemical_list: D014764:Viral Proteins