In response to viral infection, the host induces over 300 IFNstimulated genes (ISGs), which are the central component of intracellular antiviral innate immunity. Inefficient induction of ISGs contributes to poor control and persistence of hepatitis C virus infection. Therefore, further understanding of the hepatocytic ISG regulation machinery will guide us to an improved management strategy against hepatitis C virus infection. In this study, comprehensive genome-wide, high-throughput cDNA screening for genes regulating ISG expression identified a tyrosine kinase nonreceptor 1 (TNK1) as a unique player in the ISG induction pathway. The immune-modulatory function of TNK1 has never been studied, and this study characterizes its significance in antiviral innate immunity. TNK1 is abundantly expressed in hepatocytes and maintains basal ISG expression. More importantly, TNK1 plays a critical role in type I IFN-mediated ISG induction. We discovered that the activated IFN receptor complex recruits TNK1 from the cytoplasm. TNK1 is then phosphorylated to enhance its kinase activity. The activated TNK1 potentiates JAK-STAT signaling through dual phosphorylation of STAT1 at tyrosine 701 and serine 727 amino acid positions. Our loss-of-function approach demonstrated that TNK1 governs a cluster of ISG expression that defines the TNK1 pathway effector genes. More importantly, TNK1 abundance is inversely correlated to viral replication efficiency and is also a determinant factor for the hepatocytic response to antiviral treatment. Taken together, our studies found a critical but unidentified integrated component of the IFN-JAK-STAT signaling cascade.hepatic immunity | nonreceptor tyrosine kinase | protein kinase C | PKC T he host response to viral infection results in the induction of IFN-stimulated genes (ISGs). ISGs are a collection of over 300 antiviral genes that play a central role in the intracellular antiviral defense program as well as in the mounting of adaptive immunity (1). Efficient ISG induction is linked to the successful clearance of viral pathogens, including hepatitis C virus (HCV). Therefore, synthesized IFN has been used as a central component of anti-HCV therapy in a clinical setting for many years (2-5). Despite its importance, our knowledge of IFN biology, including the function of individual ISGs and the host factors that regulate ISG induction pathways, is still on a steep learning curve. A recent overexpression-based, high-throughput study demonstrated that each ISG possesses a differential antiviral potency in a virusspecific manner (6). In addition, the basal and induced ISG expression exhibits a diverse profile among various cell types, thereby linking it to specific viral tropism (7). Thus, further investigation of cell type and pathogen-specific IFN biology is required to improve our management strategy of viral infectious diseases.Virus infection of mammalian cells triggers pattern recognition receptor (PRR) signaling upon engagement with pathogenassociated molecular patterns. The PRRs, such as RIG...

Persistent infection of HCV is one of the leading cause of end stage liver diseases such as decompensated cirrhosis and liver cancer. Of particular note, nearly half of HCV infected people in the United States are reported to be heavy drinkers. This particular group of patients are known to rapidly progress to the end stage liver diseases. Although, the accelerated disease progression among alcohol abusers infected with HCV is clinically well recognized, the molecular pathophysiology behind this manifestation has not been well elucidated. Hepatocytes metabolize ethanol (EtOH) primarily through two steps of oxidative catabolism in which alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) play central roles. The ADH-ALDH pathway also governs the metabolism of Retinol (Vitamin A) to its transcriptionally active metabolite, Retinoic Acid (RA). In this study, we defined that the ADH-ALDH pathway serves as a potent antiviral host factor in hepatocytes, which regulates the expression of Interferon Stimulated Genes (ISGs) via biogenesis of RA. ISGs constitute over 300 antiviral effectors, which cooperatively govern intracellular antiviral innate immunity. Our study revealed that intracellular RA levels greatly influence ISGs expression under basal conditions. Moreover, RA augments ISGs induction in response to viral infection or exposure to IFN in a gene-specific manner. Lastly, our results demonstrated that EtOH attenuates the antiviral function of the ADH-ALDH pathway which suggests the possibility that EtOH-Retinol metabolic competition is one of the molecular mechanisms for the synergism between HCV and alcohol abuse in liver disease progression. In conclusion, our study provides novel insights into the critical role of RA in the regulation of intracellular antiviral innate immunity in hepatocytes.