Human herpesvirus 8 (HHV-8) specifies four viral interferon regulatory factor homologues (vIRFs) that function to inhibit cellular IRFs in additionto other components of cellular defense pathways that promote cell cycle arrest and apoptosis in response to virus infection. Cellular proteins targeted for inhibition by vIRF-1 include p53, ATM, GRIM19, Smad transcription factors, and p300/CBP transcriptional co-activators required for IRF-?mediated responses. This laboratory has identified an entirely novel class of interaction,between vIRF-1 and stress-responsive, pro-apoptotic BH3-only proteins (BOPs) Bim and Bid, demonstrated to be inhibited by vIRF-1 binding, and other newly recognized BOP targets. Furthermore, we have identified partial localization of vIRF-1 to mitochondria, suggesting that vIRF-1 can inactivate BOPs directly at their site of action. vIRF-1- induced nuclear translocation of Bim represents a secondary, unique mode of inactivation. vIRF-1:BOP interaction is via the Bid-BH3B-related BOP-binding domain (BBD) of vIRF-1 (residues 170-187) and the BH3 domains of targeted BOPs. Both Bim and Bid are induced by HHV-8 lytic replication and Bim, at least, is a powerful inhibitor of virus production, suggesting that Bim and probably other BOPs need to be controlled effectively by HHV-8 for virus replication to occur. Indeed, vIRF-1 BBD-mediated interactions contribute specifically and significantly to promotion of HHV-8 productive replication and vIRF-1-mediated apoptotic inhibition. However, the precise contributions of each vIRF-1:BOP interaction and the significance of other vIRF-1:protein interactions in virus biology are at present unknown. Furthermore, our newly-identified mitochondrial localization of vIRF-1 has yet to be assessed functionally. This application proposes: identification of the molecular/specificity determinants of BOP/BH3 targeting and inhibition by vIRF-1 (Aim 1); molecular dissection and dissociation of other protein-binding and functional domains of vIRF-1 (Aim 2); establishing the contributions of each vIRF-1:protein interaction and mitochondrial-localized activity of vIRF-1 in the context of HHV-8 infection (Aim 3). The project comprises a comprehensive, yet focused analysis of an HHV-8 protein with a demonstrated positive role in virus replication and which provides a uniquely valuable tool to study the relative importance of multiple (vIRF-1-targeted) cellular defense pathways in virus biology. Information generated from this study could provide the basis for development of novel anti-viral therapies.
Human herpesvirus 8 (HHV-8), linked etiologically with endothelial and B cell malignancies, encodes an interferon regulatory factor homologue, vIRF-1, that contributes to viral resistance to innate host cell defenses against viral infection. This function is mediated by inhibitory interactions of vIRF-1 with key cellular effector proteins, including members of a family of pro-death proteins (BOPs) that can function as powerful negative regulators of virus replication and that we have identified as novel interaction partners of vIRF-1. The goal of the proposed research is to characterize the mechanisms of BOP and other pro- death/anti-viral protein targeting by vIRF-1 to enable elucidation of the significance o each in virus biology, thereby advancing fundamental understanding of virus evasion from host cell defenses and enabling future development of anti-viral strategies that interfere with these mechanisms.
|Cousins, Emily; Nicholas, John (2014) Molecular biology of human herpesvirus 8: novel functions and virus-host interactions implicated in viral pathogenesis and replication. Recent Results Cancer Res 193:227-68|