title: The Replicative Consequences of Papillomavirus E2 Protein Binding to the Origin Replication Factor ORC2.
abstract: The origin recognition complex (ORC) coordinates a series of events that lead to initiation of DNA strand duplication. As a nuclear double stranded DNA plasmid, the papillomavirus (PV) genome resembles a mini-chromosome in infected cells. To initiate its replication, the viral E2 protein binds to and recruits the E1 DNA helicase at the viral origin. PV genome replication program exhibits three stages: initial amplification from a single genome upon infection to a few copies per cell, a cell cycle linked maintenance phase, and a differentiation dependent late stage where the genome is amplified to thousands of copies. Involvement of ORC or other pre-replication complex (pre-RC) factors has not been described. We report that human PV (HPV) and bovine PV (BPV-1) E2 proteins bind to ORC2, however, ORC2 was not detected at the viral origin. Depletion of ORC2 enhanced PV replication in a transient replication model and in keratinocytes stably maintaining viral episomes, while there was no effect on copy number in a cell line with integrated HPV genomes. Consistent with this, occupancy of E1 and E2 at the viral origin increased following ORC2 silencing. These data imply that ORC2 is not necessary for activation of the PV origin by E1 and E2 but instead suppresses E2 replicative function. Furthermore, we observed that over-expression of HPV E2 decreased ORC2 occupation at two known mammalian origins of replication, suggesting that E2 restricts pre-ORC assembly that could otherwise compete for host replication complexes necessary for viral genome amplification. We infer that the ORC2 complex with E2 restricts viral replication in the maintenance phase of the viral replication program and that elevated levels of E2 that occur during the differentiation dependent amplification stage subvert ORC loading and hence DNA synthesis at cellular origins.
authors.affiliation: Department of Dermatology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America.
authors.forename: Marsha
authors.initials: M
authors.lastname: DeSmet
authors.affiliation: Department of Dermatology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America.
authors.forename: Sriramana
authors.initials: S
authors.lastname: Kanginakudru
authors.affiliation: Department of Dermatology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America.
authors.forename: Anne
authors.initials: A
authors.lastname: Rietz
authors.affiliation: Department of Pathology, Johns Hopkins University, Baltimore, Maryland, United States of America.
authors.forename: Wai-Hong
authors.initials: WH
authors.lastname: Wu
authors.affiliation: Department of Pathology, Johns Hopkins University, Baltimore, Maryland, United States of America.
authors.forename: Richard
authors.initials: R
authors.lastname: Roden
authors.affiliation: Department of Dermatology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America.|Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America.
authors.forename: Elliot J
authors.identifier: http://orcid.org/0000-0002-8104-0703
authors.initials: EJ
authors.lastname: Androphy
mesh_terms: D052688:Bovine papillomavirus 1 / Q000502:physiology; D002460:Cell Line; D047369:Chromatin Immunoprecipitation; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D051738:Origin Recognition Complex / Q000378:metabolism*; D027383:Papillomaviridae / Q000502:physiology*; D014779:Virus Replication / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D009856:Oncogene Proteins, Viral; D051738:Origin Recognition Complex; C076036:oncogene protein E2, Human papillomavirus type 1