Role of the 17-beta-hydroxysteroid dehydrogenase type 12 (HSD17B12) in hepatitis C and related flaviviruses replication.

Infections with viruses are major recurrent socio-economical and health problems worldwide. These include infections by viruses of the Flaviviridae family, which present a substantial global health burden and are among the priority areas of medical virology according to the Global Virus Network 2016 report. While the current treatment regimens for hepatitis C virus (HCV) infection have cure rates of more than 98%, other important members of Flaviviridae like dengue virus (DENV) and zika virus (ZIKV) have no specific licensed treatments. By taking advantage of the most-studied HCV, which our lab has developed a vast expertise in the last 20 years, we used proteomics data of an HCV interactome study, combining viral protein immunoprecipitation (IP) coupled to tandem mass spectrometry identification (IP-MS/MS) and functional genomics RNAi screening. The study uncovered the 17-beta-hydroxysteroid dehydrogenase type 12 (HSD17B12, also named DHB12), as a specific host interactor of core that promotes HCV replication. HSD17B12 catalytic activity is involved in the synthesis of very-long-chain fatty acids (VLCFA) upon the second step of the elongation cycle. In this study, taking HCV as a virus model, we elucidated the dependency of HCV, dengue virus (DENV) and zika virus (ZIKV) replication on expression and metabolic capacity of the host factor HSD17B12. We investigated the effects of the inhibition of gene expression by RNAi and of its pharmacological enzymatic inhibition on flavivirus replication in a broad-spectrum antiviral approach. We showed that silencing expression of HSD17B12 decreases viral replication, viral proteins and iv infectious particle production of the JFH1 strain of HCV in Huh7.5 cells. The cellular localization analysis of HSD17B12 showed a co-staining with double-stranded RNA (dsRNA) at viral replication sites and with core protein (and lipid droplets) at virus assembly sites. Furthermore, HSD17B12 gene silencing drastically reduced the number and size of lipid droplets. In association, the reduced expression of HSD17B12 by RNAi decreases oleic acid levels and lipids such as triglycerides (TG) and phosphatidylethanolamine (PE) in whole-cell extract. The data suggested the requirement of the metabolic capacity of HSD17B12 for HCV replication. Similarly, we provide evidence that HSD17B12 silencing significantly reduces DENV and ZIKV infectious particles. The studies support a role of HSD17B12 for effective viral RNA replication and particle assembly processes. Moreover, the specific HSD17B12 inhibitor, INH-12, reduces HCV replication at concentrations for which no appreciable cytotoxicity is observed. The treatment of DENV- and ZIKV-infected Huh- 7.5 cells with 20 μM of INH-12 dramatically reduces production of infectious particles by up to 3-log10 in infection assays, and completely block viral protein expression. In conclusion, these studies extends our understanding of the role of HSD17B12 in VLCFA synthesis required for the replication of HCV, allowing to explore the inhibition of HSD17B12 and elongation of VLCFA as a novel therapeutic approach for the treatment of a broad-spectrum of viruses of the Flaviviridae family.

Keyphrases: Molecular Medicine, Drug Discovery, Antiviral host target, Broadspectrum antiviral,, Flaviviridae, HSD17B12, DHB12, KAR, very-long-chain fatty acids, very long- chain 3-oxoacyl-CoA reductase, HSD17B12 inhibitor, Zika virus, Dengue virus, Hepatitis C virus, 17-beta-hydroxysteroid dehydrogenase type 12, Enzyme inhibitor, Agents antiviraux à large spectre, DENV, ZIKV