title: Inhibition of S-phase progression by adeno-associated virus Rep78 protein is mediated by hypophosphorylated pRb.
abstract: Adeno-associated virus (AAV) has an antiproliferative action on cells. We investigated the effect of the AAV replication proteins (Rep) on the cell division cycle using retroviral vectors. Rep78 and Rep68 inhibited the growth of primary, immortalized and transformed cells, while Rep52 and Rep40 did not. Rep68 induced cell cycle arrest in phases G(1) and G(2), with elevated CDK inhibitor p21 and reduced cyclin E-, A- and B1-associated kinase activity. Rep78-expressing cells were also impaired in S-phase progression and accumu lated almost exclusively with hypophosphorylated retinoblastoma protein (pRb). The differences between Rep78 and Rep68 were mapped to the C-terminal zinc finger domain of Rep78. Rep78-induced S-phase arrest could be bypassed by adenoviral E1A or papillomaviral E7 proteins but not by E1A or E7 mutants unable to bind pRb. Rb(-/-) primary mouse embryonic fibroblasts displayed a strongly reduced S-phase arrest when challenged with Rep78, compared with matched Rb(+/+) controls. These results suggest that physiological levels of active pRb can interfere with S-phase progression. We propose that the AAV Rep78 protein arrests cells within S-phase by a novel mechanism involving the ectopic accumulation of active pRb.
authors.affiliation: Swiss Institute for Experimental Cancer Research (ISREC), 1066 Epalinges, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Saudan
authors.forename: J
authors.initials: J
authors.lastname: Vlach
authors.forename: P
authors.initials: P
authors.lastname: Beard
mesh_terms: D016475:3T3 Cells; D017500:Adenovirus E1A Proteins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002453:Cell Cycle; D002455:Cell Division; D002478:Cells, Cultured; D019925:Cyclin A / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism; D056744:Cyclin B1; D019927:Cyclin E / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D000229:Dependovirus / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism / Q000821:virology; D006801:Humans; D008168:Lung / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009856:Oncogene Proteins, Viral / Q000378:metabolism; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism*; D016196:S Phase; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014764:Viral Proteins / Q000378:metabolism*; D016335:Zinc Fingers
chemical_list: D017500:Adenovirus E1A Proteins; C534699:CCNB1 protein, human; C493956:CDKN1A protein, human; C534700:Ccnb1 protein, mouse; C493957:Cdkn1a protein, mouse; D019925:Cyclin A; D019926:Cyclin B; D056744:Cyclin B1; D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D009856:Oncogene Proteins, Viral; D011994:Recombinant Proteins; D016160:Retinoblastoma Protein; D014764:Viral Proteins; C068734:rep proteins, Adeno-associated virus 2