SignificanceCancer cell proliferation is highly dependent on cap-dependent protein synthesis, which is generally assumed to be inhibited during mitosis. Using a viral oncoprotein that enforces mitosis, we show that CDK1 substitutes for mTOR interphase functions to phosphorylate eukaryotic initiation factor 4E-binding protein (4E-BP1) to a mitosis-specific δ isoform. Flow cytometric assays reveal that mitotic cells have high levels of inactivated 4E-BP1 and do not generally show specific loss of cap-dependent translation compared with interphase cells. This appears to be due to cyclin-dependent kinase 1 (CDK1) activity during mitosis. Mitotic cells typically represent less than 1% of all cells in bulk culture, and mitosis-arresting drugs, such as nocodazole, can directly inhibit mitotic protein translation, potentially explaining differences between our findings and previous studies showing reduced cap-dependent translation during mitosis.

Background & Aims-The cyclophilin (Cyp) inhihibitors -cyclosporine A (CsA), NIM811, Debio 025 and SCY 635 -block HCV replication both in vitro and in vivo, and represent a novel class of potent anti-HCV agents. We and others showed that HCV relies on cyclophilin A (CypA) to replicate. We demonstrated that the hydrophobic pocket of CypA, where Cyp inhibitors bind, and which controls the isomerase activity of CypA, is critical for HCV replication. Recent studies showed that under Cyp inhibitor selection, mutations arose in the HCV nonstructural 5A (NS5A) protein. This led us to postulate that CypA assists HCV by acting on NS5A.

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Background: NS5A is critical for HCV replication, but its role is poorly understood. Results: Cysteines Cys-39, Cys-57, Cys-59, and Cys-80 are vital for NS5A dimerization, RNA binding, and viral replication. Conclusion: NS5A dimerization, RNA binding, and HCV replication are correlated. Significance: This study addresses an important issue in HCV research with NS5A being a major drug target with inhibitors in advanced stages of clinical development.

SUMMARYHepatitis C virus (HCV) infects more than 3% of the world's population, leading to an increased risk of cirrhosis and hepatocellular carcinoma. The current standard of care, a combination of pegylated interferon alfa and ribavirin, is poorly tolerated and often ineffective against the most prevalent genotype of the virus, genotype 1. The very recent approval of boceprevir and telaprevir, two HCV protease inhibitors, promises to significantly improve treatment options and outcomes. In addition to the viral protease NS3 and the viral polymerase NS5B, direct-acting antivirals are now in development against NS5A. A multifunctional phosphoprotein, NS5A is essential to HCV genome replication, but has no known enzymatic function. Here we report how the design of small-molecule inhibitors against NS5A has evolved from promising monomers to highly potent dimeric compounds effective against many HCV genotypes. We also highlight recent clinical data and how the inhibitors may bind to NS5A, itself capable of forming dimers. HEPATITIS C VIRUS (HCV): AN INTERNATIONAL HEALTH CONCERNHepatitis C virus (HCV) infects approximately 170 million individuals, with an estimated 2.3-4.7 million new infections each year (1). The primary mode of transmission of HCV is via exposure to infected blood, including transfusions from infected donors, and through injection drug use. It is estimated that 15-30% of all HCV infections will spontaneously clear, but the remaining 70-85% of infections will develop into chronic hepatitis (2, 3). Chronic infections can subsequently lead to steatosis, cirrhosis and hepatocellular carcinoma (4). Among all recognized positive-strand RNA viruses, the ability to establish a chronic infection is exclusive to HCV (5), although how the virus mediates persistence remains unknown.Current treatment options for HCV are relatively poor. The standard of care is often a grueling 48-week combination of pegylated interferon alfa (IFN-α) and the nucleoside analogue ribavirin. Effective clearance of the virus is achieved in less than 50% of genotype

Background: How can HCV require only 10 proteins for decades-long evasion of the immune system? Results: Phosphorylation of the intrinsically disordered domain (IDD) of NS5A changes its dynamics, inducing unique structure and function. Conclusion: IDD phosphorylation expands the HCV proteome. Significance: Post-translational modification of a viral IDD represents a strategy to expand a viral proteome when coding capacity is limited.