Bim nuclear translocation and inactivation by viral interferon regulatory factor

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 tgfb 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,colocalization 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. © 2010 choi,nicholas.