USP15 Participates in Hepatitis C Virus Propagation through Regulation of Viral RNA Translation and Lipid Droplet Formation

Abstract

Hepatitis C virus (HCV) utilizes cellular factors for efficient propagation. Ubiquitin is covalently conjugated to the substrate to alter its stability or to modulate signal transduction. In this study, we examined the importance of ubiquitination for HCV propagation. We found that inhibition of deubiquitinating enzymes (DUBs) or overexpression of nonspecific DUBs impaired HCV replication, suggesting that ubiquitination regulates HCV replication. To identify specific DUBs involved in HCV propagation, we set up RNA interference (RNAi) screening against DUBs and successfully identified ubiquitin-specific protease 15 (USP15) as a novel host factor for HCV propagation. Our studies showed that USP15 is involved in translation of HCV RNA and production of infectious HCV particles. In addition, deficiency of USP15 in human hepatic cell lines (Huh7 and Hep3B/miR-122 cells) but not in a nonhepatic cell line (293T cells) impaired HCV propagation, suggesting that USP15 participates in HCV propagation through the regulation of hepatocyte-specific functions. Moreover, we showed that loss of USP15 had no effect on innate immune responses in vitro and in vivo. We also found that USP15-deficient Huh7 cells showed reductions in the amounts of lipid droplets (LDs), and the addition of palmitic acids restored the production of infectious HCV particles. Taken together, these data suggest that USP15 participates in HCV propagation by regulating the translation of HCV RNA and the formation of LDs. IMPORTANCE Although ubiquitination has been shown to play important roles in the HCV life cycle, the roles of deubiquitinating enzymes (DUBs), which cleave ubiquitin chains from their substrates, in HCV propagation have not been investigated. Here, we identified USP15 as a DUB regulating HCV propagation. USP15 showed no interaction with viral proteins and no participation in innate immune responses. Deficiency of USP15 in Huh7 cells resulted in suppression of the translation of HCV RNA and reduction in the amounts of lipid droplets, and the addition of fatty acids partially restored the production of infectious HCV particles. These data suggest that USP15 participates in HCV propagation in hepatic cells through the regulation of viral RNA translation and lipid metabolism.

Competing endogenous RNA network profiling reveals novel host dependency factors required for MERS-CoV propagation

“…In addition to MAP3K9, siRNA knockdown of circFNDC3B or circCNOT1 similarly resulted in significantly reduced expression of other target genes. Ubiquitin-specific protease 15 (USP15) promotes RIG-I-mediated antiviral signalling by interacting with ubiquitin E3 ligase tripartite motif protein 25 (TRIM25) and plays important roles in the replication of various DNA and RNA viruses, including human papillomaviruse (HPV), human immunodeficiency virus (HIV), and hepatitis C virus (HCV) [55][56][57][58]. Myocyte enhancer factor 2C (MEF2C) is a transcription factor that is associated with the super-enhancer activity and cancer progression of Epstein-Barr virus infection [59].…”

USP15 Deubiquitinates CARD9 to Downregulate C-Type Lectin Receptor–Mediated Signaling

“…Accordingly, USP15 is a ubiquitously expressed member of the ubiquitin-specific peptidase family and has a broad range of functions (32). USP15 is a host factor for hepatitis C virus propagation by regulating viral RNA translation and lipid metabolism (35). It acts as a counterpart to the endoplasmic reticulum-located E3 ligase RNF26; RNF26mediated ubiquitination of SQSTM1 retains vesicles in the perinuclear cloud, whereas deubiquitination of SQSTM1 by USP15 facilitates the release of vesicles for fast transport (36).…”

USP15 in Cancer and Other Diseases: From Diverse Functionsto Therapeutic Targets

“…Therefore, USP15 is not only recruited by UBE2S to suppress type I IFN production by deubiquitinating TBK1, but it also stabilizes TRIM25 to promote TRIM25 and RIG1-dependent type I IFN production, which is due to USP15 targeting different proteins and participating in different signaling pathways. Although USP15 does not interact with the hepatitis C virus (HCV) proteins and does not participate in innate immune responses, knockout of USP15 inhibits the translation of HCV RNA and the accumulation of lipid droplets in the hepatocellular carcinoma cell line Huh7, as well as the addition of palmitic acids, which partially recovers the production of infectious viral particles, suggesting that USP15 regulates HCV propagation by affecting viral RNA translation and lipid metabolism [ 118 ]. The above function of USP15 in the immune response suggests that USP15 may be a potential therapeutic target for cancer immunotherapy.…”