A NOVEL SMALL MOLECULE INHIBITOR THAT BLOCKS HEPATITIS B VIRUS REPLICATION BY INHIBITING HBX PROTEIN RNAI SUPPRESSOR ACTIVITY.

摘要

Persistent or chronic infection with the hepatitis B virus represents one of the most common viral diseases in humans. We show here that the siRNA mediated silencing of Drosha, Dicer and Ago2 transcripts in Huh7 cells resulted in elevated levels of HBV specific RNAs, and conversely, we observed a decrease in mRNA and protein levels of same RNAi components in HepG2 cells infected with HBV. Similar reductions were also detectable in chronic hepatitis B (CHB) patients. Analysis of CHB liver biopsy samples, with high serum HBV DNA load o (logio IU/ml), revealed a reduced mRNA and protein levels of Drosha, Dicer and Ago2. The low expression levels of key RNAi pathway components in CHB patient samples as well as hepatic cells established a link between HBV replication and RNAi components. The HBV proteins were also examined for RNA silencing suppressor properties. Using the GFP- based reversion of silencing assays, its been identified here that HBx protein is an RSS protein. Through a series of deletions as well as substitution mutants, we found that the full-length HBx protein is required for the optimum RSS activity. The in vitro dicing assays revealed that the HBx protein inhibited the human Dicer mediated processing of dsRNAs into siRNAs. Together, our results suggest that the HBx protein might function as RSS to manipulate host RNAi defense especially by abrogating the Dicer function. The hepatitis B virus deploys the Hepatitis B Virus X Protein as a suppressor of host defenses consisting of RNAi-based suppression of viral genes.Because of its critical role in countering host defenses, HBx represents an attractive target for antiviral drugs. Here, we developed and optimized a loss-of-function screening procedure, which identified a potential pharmacophore that abrogated HBxs RNAi suppression activity. In a survey of 14,400 compounds in the Maybridge Screening Collection, we prioritized candidate compounds via high-throughput screening based on reversal of green fluorescent protein (GFP)-reported, RNAi-mediated silencing in a HepG2/GFP-shRNA RNAi sensor line. The screening yielded a pharmacologically active compound, N-(2,4-difluorophenyl)-N-[3- (lH-imidazol-l-yl) propyl] thiourea (TR415), which blocked HBx-mediated RNAi suppression indicated by the GFP reporter assay. We also found that IR415 reversed the inhibitory effect of HBx protein on activity of the Dicer endo ribonuclease. We further confirmed the results of the primary screen in IR415-treated, HBV-infected HepG2 cells, which exhibited a marked depletion of HBV core protein synthesis and down regulation of pre-genomic HBV RNA. Using a molecular interaction analysis system, we confirmed that IR415 selectively targets HBx in a concentration-dependent manner. The screening assay presented here allows rapid and improved detection of small-molecule inhibitors of HBx and related viral proteins. The assay may therefore potentiate the development of next-generation RNAi pathway-based therapeutics and promises to accelerate our search for novel and effective drugs in antiviral research.