title: Bim nuclear translocation and inactivation by viral interferon regulatory factor.
abstract: Viral replication efficiency is in large part governed by the ability of viruses to counteract pro-apoptotic signals induced by infection of the host cell. Human herpesvirus 8 (HHV-8) uses several strategies to block the host's innate antiviral defenses via interference with interferon and apoptotic signaling. Contributors include the four viral interferon regulatory factors (vIRFs 1-4), which function in dominant negative fashion to block cellular IRF activities in addition to targeting IRF signaling-induced proteins such as p53 and inhibiting other inducers of apoptosis such as TGFbeta receptor-activated Smad transcription factors. Here we identify direct targeting by vIRF-1 of BH3-only pro-apoptotic Bcl-2 family member Bim, a key negative regulator of HHV-8 replication, to effect its inactivation via nuclear translocation. vIRF-1-mediated relocalization of Bim was identified in transfected cells, by both immunofluorescence assay and western analysis of fractionated cell extracts. Also, co-localization of vIRF-1 and Bim was detected in nuclei of lytically infected endothelial cells. In vitro co-precipitation assays using purified vIRF-1 and Bim revealed direct interaction between the proteins, and Bim-binding residues of vIRF-1 were mapped by deletion and point mutagenesis. Generation and experimental utilization of Bim-refractory vIRF-1 variants revealed the importance of vIRF-1:Bim interaction, specifically, in pro-replication and anti-apoptotic activity of vIRF-1. Furthermore, blocking of the interaction with cell-permeable peptide corresponding to the Bim-binding region of vIRF-1 confirmed the relevance of vIRF-1:Bim association to vIRF-1 pro-replication activity. To our knowledge, this is the first report of an IRF protein that interacts with a Bcl-2 family member and of nuclear sequestration of Bim or any other member of the family as a means of inactivation. The data presented reveal a novel mechanism utilized by a virus to control replication-induced apoptosis and suggest that inhibitory targeting of vIRF-1:Bim interaction may provide an effective antiviral strategy.
authors.affiliation: Sidney Kimmel Comprehensive Cancer Center, Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Young Bong
authors.initials: YB
authors.lastname: Choi
authors.forename: John
authors.initials: J
authors.lastname: Nicholas
mesh_terms: D017209:Apoptosis / Q000502:physiology; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D015153:Blotting, Western; D002460:Cell Line; D005455:Fluorescent Antibody Technique; D006566:Herpesviridae Infections / Q000378:metabolism*; D019288:Herpesvirus 8, Human / Q000378:metabolism* / Q000472:pathogenicity*; D006801:Humans; D047468:Immunoprecipitation; D050835:Interferon Regulatory Factors / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D050835:Interferon Regulatory Factors; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D014764:Viral Proteins; C413486:viral interferon regulatory factors