title: HPV 16E7 and 48E7 proteins use different mechanisms to target p130 to overcome cell cycle block.
abstract: BACKGROUND
  Retinoblastoma like protein 2 (RBL2) or p130 is a member of the pocket protein family, which is infrequently mutated in human tumours. Its expression is posttranscriptionally regulated and largely G0 restricted. We have previously shown that E6/E7 oncoproteins encoded by human papillomavirus (HPV) type 16, which is a high-risk type for cervical cancer development, must target p130 to promote the host cell to exit from quiescence (G0) state and enter S phase of the cell cycle. P130 is associated with the DREAM (DP, RB-like, E2F and MuvB) complex in G0/G1, which prevents S phase progression by repressing transcription of E2F-regulated genes. E7 proteins could potentially disrupt the p130-DREAM complex through two known mechanisms: direct interaction with p130 or induction of cyclin dependent kinase 2 (CDK2) phosphorylation by interacting with its inhibitor, p21(CIP1).
  
  
  METHODS
  In this study we have used p130 mutants deficient in binding the E7 LXCXE domain (p130mE7), unphosphorylatable by CDK2 (p130PM22) or a combination of both (p130PM22/mE7) to investigate these mechanisms used by E7 proteins to disrupt the p130-DREAM complex and promote cell cycle progression.
  
  
  RESULTS
  We found that HPV16 E7 binding to p130 through its LXCXE domain was absolutely required to disrupt p130-DREAM to promote S phase of the cell cycle, as HPV16 E7 was unable to suppress p130mE7 but could suppress p130PM22. In contrast, the E7 protein encoded by a cutaneous HPV type that lacks a functional LXCXE domain, HPV 48 E7, was also able to disrupt p130-DREAM to promote cell cycling, but through the alternative mechanism. Thus, HPV48 E7 could suppress a cell cycle block imposed by p130mE7, but was unable to suppress p130PM22.
  
  
  CONCLUSIONS
  Overall, these results indicate that suppression of p130 is required for HPV-induced cell cycling, and that different HPV E7 proteins can use alternative mechanisms to achieve this.
authors.affiliation: Section of Virology, Department of Medicine, Imperial College London, London, UK. nurshamimi@um.edu.my.|Department of Molecular Medicine, Faculty of Medicine, University of Malaya, 50603, Kuala Lumpur, Malaysia. nurshamimi@um.edu.my.
authors.forename: Nurshamimi
authors.initials: N
authors.lastname: Nor Rashid
authors.affiliation: Section of Virology, Department of Medicine, Imperial College London, London, UK. yongzlno1@gmail.com.
authors.forename: Zi Ling
authors.initials: ZL
authors.lastname: Yong
authors.affiliation: Department of Molecular Medicine, Faculty of Medicine, University of Malaya, 50603, Kuala Lumpur, Malaysia. rohana@um.edu.my.
authors.forename: Rohana
authors.initials: R
authors.lastname: Yusof
authors.affiliation: Section of Virology, Department of Medicine, Imperial College London, London, UK. r.watson@bham.ac.uk.|Institute of Biomedical Research, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK. r.watson@bham.ac.uk.
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Watson
mesh_terms: D052685:Alphapapillomavirus / Q000145:classification* / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D059447:Cell Cycle Checkpoints; D006801:Humans; D009154:Mutation; D050725:Papillomavirus E7 Proteins / Q000378:metabolism*; D030361:Papillomavirus Infections / Q000378:metabolism / Q000821:virology; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D050717:Retinoblastoma-Like Protein p130 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D050725:Papillomavirus E7 Proteins; C493837:RBL2 protein, human; D050717:Retinoblastoma-Like Protein p130; C059731:oncogene protein E7, Human papillomavirus type 16