title: Novel roles of cytoplasmic ICP0: proteasome-independent functions of the RING finger are required to block interferon-stimulated gene production but not to promote viral replication.
abstract: The immediate-early protein ICP0 from herpes simplex virus 1 (HSV-1) plays pleiotropic roles in promoting viral lytic replication and reactivation from latency. Most of the known actions of ICP0 occur in the nucleus and are thought to involve the E3 ubiquitin ligase activity of its RING finger domain, which targets proteins for degradation via the proteasome. Although ICP0 translocates to the cytoplasm as the infection progresses, little is known about its activities in this location. Here, we show that cytoplasmic ICP0 has two distinct functions. In primary cell cultures and in an intravaginal mouse model, cytoplasmic ICP0 promotes viral replication in the absence of an intact RING finger domain. Additionally, ICP0 blocks the activation of interferon regulatory factor 3 (IRF3), a key transcription factor of the innate antiviral response, in a mechanism that requires the RING finger domain but not the proteasome. To our knowledge, this is the first observation of a proteasome-independent function of the RING finger domain of ICP0. Collectively, these results underscore the importance of cytoplasm-localized ICP0 and the diverse nature of its activities. Importance: Despite ICP0 being a well-studied viral protein, the significance of its cytoplasmic localization has been largely overlooked. This is, in part, because common experimental manipulations result in the restriction of ICP0 to the nucleus. By overcoming this constraint, we both further characterize the ability of cytoplasmic ICP0 to inhibit antiviral signaling and show that ICP0 at this site has unexpected activities in promoting viral replication. This demonstrates the importance of considering location when analyzing protein function and adds a new perspective to our understanding of this multifaceted protein.
authors.affiliation: Department of Biochemistry and Biomedical Sciences, McMaster Immunology Research Centre, Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Kathryne E
authors.initials: KE
authors.lastname: Taylor
authors.affiliation: Department of Pathology and Molecular Medicine, McMaster Immunology Research Centre, Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Marianne V
authors.initials: MV
authors.lastname: Chew
authors.affiliation: Department of Pathology and Molecular Medicine, McMaster Immunology Research Centre, Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Ali A
authors.initials: AA
authors.lastname: Ashkar
authors.affiliation: Department of Biochemistry and Biomedical Sciences, McMaster Immunology Research Centre, Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada Department of Pathology and Molecular Medicine, McMaster Immunology Research Centre, Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada mossk@mcmaster.ca.
authors.forename: Karen L
authors.initials: KL
authors.lastname: Mossman
mesh_terms: D000818:Animals; D002460:Cell Line; D003593:Cytoplasm / Q000821:virology*; D004195:Disease Models, Animal; D005260:Female; D006561:Herpes Simplex / Q000821:virology; D018259:Herpesvirus 1, Human / Q000276:immunology* / Q000502:physiology*; D006801:Humans; D017874:Immediate-Early Proteins / Q000378:metabolism*; D050838:Interferon Regulatory Factor-3 / Q000037:antagonists & inhibitors*; D051379:Mice; D008810:Mice, Inbred C57BL; D054829:RING Finger Domains; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D014779:Virus Replication
chemical_list: C494232:IRF3 protein, human; D017874:Immediate-Early Proteins; D050838:Interferon Regulatory Factor-3; D044767:Ubiquitin-Protein Ligases; C051804:Vmw110 protein, Human herpesvirus 1