Type 1 interferon (IFN) continues to be the foundation for the current standard of care combination therapy for chronic hepatitis C virus (HCV) infection, yet the component interferon-stimulated genes (ISGs) that mediate the antiviral actions of IFN are not fully defined. Interferon-induced transmembrane protein 1 (IFITM1) is an ISG product that suppresses early stage infection by a number of viruses through an as yet unknown mechanism of action. Moreover, the actions of IFITM1 on HCV infection are not fully elucidated. Here we identify IFITM1 as a hepatocyte tight junction protein and a potent anti-HCV effector molecule. IFITM1 expression is induced early during IFN treatment of hepatocytes and accumulates at hepatic tight junctions in HCV-infected human patient liver during IFN therapy. Additionally, we found that IFITM1 interacts with HCV co-receptors including CD81 and occludin to disrupt the process of viral entry. Thus, IFITM1 is an anti-HCV ISG whose actions impart control of HCV infection through interruption of viral coreceptor function. Conclusion This study defines IFITM1 as an ISG effector with action against HCV entry. Design of therapy regimens to enhance IFITM1 expression should improve the virologic response among HCV patients undergoing treatment with type I IFN.

Chromosomal instability is a hallmark of cancer, but mitotic regulators are rarely mutated in tumors. Mutations in the condensin complexes, which restructure chromosomes to facilitate segregation during mitosis, are significantly enriched in cancer genomes, but experimental evidence implicating condensin dysfunction in tumorigenesis is lacking. We report that mice inheriting missense mutations in a condensin II subunit (Caph2 nes ) develop T-cell lymphoma. Before tumors develop, we found that the same Caph2 mutation impairs ploidy maintenance to a different extent in different hematopoietic cell types, with ploidy most severely perturbed at the CD4 + CD8 + T-cell stage from which tumors initiate. Premalignant CD4 + CD8 + T cells show persistent catenations during chromosome segregation, triggering DNA damage in diploid daughter cells and elevated ploidy. Genome sequencing revealed that Caph2 singlemutant tumors are near diploid but carry deletions spanning tumor suppressor genes, whereas P53 inactivation allowed Caph2 mutant cells with whole-chromosome gains and structural rearrangements to form highly aggressive disease. Together, our data challenge the view that mitotic chromosome formation is an invariant process during development and provide evidence that defective mitotic chromosome structure can promote tumorigenesis.[Keywords: chromosome structure; condensin; genome instability; lymphoma; mitosis] Supplemental material is available for this article. Received May 23, 2016; revised version accepted September 15, 2016. Genome integrity is maintained by molecular machines that drive the duplication and segregation of the genome and by checkpoints that monitor for incorrect execution of these processes. As cells enter mitosis, chromosomes undergo profound structural changes, which are driven by topoisomerase II and condensins (Swedlow and Hirano 2003). This process removes catenations between sister chromatids, generates stiff rod-like structures that are competent for chromosome segregation, and is essential for genome propagation through the cell cycle in all eukaryotes.Condensins belong to the structural maintenance of chromosomes (SMC) complex family that also includes cohesin and SMC5/6. In eukaryotes, each SMC complex contains a heterodimer of SMC ATPase subunits, a single kleisin subunit, and additional accessory factors (Fig 1A;Losada and Hirano 2005;Nasmyth and Haering 2005). Within cohesin and condensin complexes, the C and N termini of kleisin interact with apposing SMC subunits to form a tripartite, asymmetric ring-like structure that can entrap DNA (Gruber et al. 2003;Onn et al. 2007;Nasmyth and Oliveira 2010;Cuylen et al. 2011; Piazza et al. Cold Spring Harbor Laboratory Press on May 10, 2018 -Published by genesdev.cshlp.org Downloaded from 2014). This mode of association has been proposed to allow SMC complexes to form topological linkages between chromosomes or different regions on the same DNA molecule.Metazoan genomes encode at least two distinct condensin complexes (Ono et al. 2003), whi...

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...