Human herpesvirus 8 (HHV-8) is a causal agent for Kaposi?s sarcoma, primary effusion lymphoma (PEL), and multicentric Castleman?s disease that are often associated with acquired immunodeficiency syndrome. HHV-8 lytic replication, in addition to latency, is important for maintaining viral load within the host as well as for related pathogenesis. Recent evidence shows that HHV-8-encoded viral interferon regulatory factor 1 (vIRF-1) plays an important role in promoting virus replication by suppressing apoptosis and innate immunity elicited by infection of host cells. We recently found, for the first time, that vIRF-1 localizes to mitochondria via a novel mechanism upon virus replication and mitochondria-localized vIRF-1 is essential for successful virus replication. However, the functional significance of mitochondria-localized vIRF-1 to HHV-8 biology and pathogenesis remains to be determined. Our preliminary results showed that mitochondrial content is reduced in lytic vIRF-1-positive PEL cells but restored by pharmacological inhibition of autophagy and mitophagy. Moreover, using recombinant HHV- 8 encoding vIRF-1 with impaired mitochondria targeting and a vIRF-1-derived peptide corresponding to the mitochondrial targeting region, we demonstrated that mitochondria targeting of vIRF-1 plays an important role in regulation of mitochondria content and apoptosis during HHV-8 replication. Our further studies revealed that vIRF- 1 interacts with autophagy-related proteins (GEC1 and EF-Tu) and is subject to posttranslational modifications (caspase-5-mediated cleavage and K63-linked polyubiquitination) upon HHV-8 replication and mitochondrial damage. Moreover, inhibition of mitophagy by Mdivi-1 enhances MAVS-mediated apoptosis induced by virus replication and inhibits HHV-8 productive replication. Based on these findings, we hypothesize that vIRF-1 can sense and respond to mitochondria damage induced by HHV-8 replication and promote removal of dysfunctional mitochondria by activating mitophagy, resulting in inhibition of mitochondria-mediated antiviral responses and promotion of HHV-8 replication. Therefore, an approach to interfere with vIRF-1-activated mitophagy could lead to the development of novel antiviral agents. To further define the mechanisms and functional significance of vIRF-1- activated mitophagy in HHV-8 replication, we propose to: 1) delineate the molecular mechanism(s) of vIRF-1- mediated mitophagy activated by HHV-8 replication, 2) determine the significance to mitophagy regulation of novel posttranslational modifications of mitochondria-localized vIRF-1, and 3) determine the functional significance of vIRF-1-activated mitophagy in MAVS regulation and HHV-8 biology. Successful completion of the studies in this application will delineate the molecular interactions and processes involved in vIRF-1-acitvated mitophagy and provide evidence for the antiviral and therapeutic potentials of mitophagy inhibition. Overall, this proposal will identify a novel paradigm of virus-host interaction via mitochondria and could potentially provide a basis for future development of antiviral agents targeting mitophagy-associated interactions of vIRF-1.
Human herpesvirus 8 (HHV-8), also called Kaposi?s sarcoma-associated herpesvirus (KSHV), is a tumor virus that causes Kaposi?s sarcoma, primary effusion lymphoma, and multicentric Castleman?s disease in individuals with acquired immunodeficiency after human immunodeficiency virus infection and organ transplantation. Based on our published and preliminary data, we hypothesize that HHV-8-encoded viral interferon regulatory factor 1 (vIRF-1) plays an important role in mitophagy activation to remove antiviral response-engaged mitochondria during HHV-8 replication and thereby contributes to the promotion of HHV-8 productive replication, which is, in addition to latency, important for maintaining viral load within the host as well as for HHV-8 pathogenesis. Successful completion of this application will reveal the molecular mechanism and functional significance of vIRF-1-activated mitophagy in HHV-8 biology as well as potentially provide a basis for future development of antiviral agents targeting vIRF-1-activated mitophagy.
