Casein kinase II inhibitor enhances production of infectious genotype 1a hepatitis C virus (H77S)

Role of p38 mitogen-activated protein kinase signalling in virus replication and potential for developing broad spectrum antiviral drugs

Mitogen-activated protein kinases (MAPKs) play a key role in complex cellular processes such as proliferation, development, differentiation, transformation and apoptosis. Mammals express at least four distinctly regulated groups of MAPKs which include extracellular signal-related kinases (ERK)-1/2, p38 proteins, Jun amino-terminal kinases (JNK1/2/3) and ERK5. p38 MAPK is activated by a wide range of cellular stresses and modulates activity of several downstream kinases and transcription factors which are involved in regulating cytoskeleton remodeling, cell cycle modulation, inflammation, antiviral response and apoptosis. In viral infections, activation of cell signalling pathways is part of the cellular defense mechanism with the basic aim of inducing an antiviral state. However, viruses can exploit enhanced cell signalling activities to support various stages of their replication cycles. Kinase activity can be inhibited by small molecule chemical inhibitors, so one strategy to develop antiviral drugs is to target these cellular signalling pathways. In this review, we provide an overview on the current understanding of various cellular and viral events regulated by the p38 signalling pathway, with a special emphasis on targeting these events for antiviral drug development which might identify candidates with broad spectrum activity.

Potential for Protein Kinase Pharmacological Regulation in Flaviviridae Infections

Protein kinases (PKs) are enzymes that catalyze the transfer of the terminal phosphate group from ATP to a protein acceptor, mainly to serine, threonine, and tyrosine residues. PK catalyzed phosphorylation is critical to the regulation of cellular signaling pathways that affect crucial cell processes, such as growth, differentiation, and metabolism. PKs represent attractive targets for drugs against a wide spectrum of diseases, including viral infections. Two different approaches are being applied in the search for antivirals: compounds directed against viral targets (direct-acting antivirals, DAAs), or against cellular components essential for the viral life cycle (host-directed antivirals, HDAs). One of the main drawbacks of DAAs is the rapid emergence of drug-resistant viruses. In contrast, HDAs present a higher barrier to resistance development. This work reviews the use of chemicals that target cellular PKs as HDAs against virus of the Flaviviridae family (Flavivirus and Hepacivirus), thus being potentially valuable therapeutic targets in the control of these pathogens.

NMR and circular dichroism data for domain 2 of the HCV NS5A protein phosphorylated by the Casein Kinase II

The Hepatitis C Virus (HCV)1 nonstructural 5A protein (NS5A) is a phosphoprotein (Evans et al., 2004; Ross-Thriepland and Harris, 2014) [1], [2] composed of an N-terminal well-structured domain and two C-terminal intrinsically disordered domains (Moradpour et al., 2007; Bartenschlager et al., 2013; Badillo et al., 2017) [3], [4], [5]. So far, no precise molecular function has been identified for this viral protein (Ross-Thriepland and Harris, 2015) [6] which is required for viral replication (Tellinghuisen et al., 2008) [7]. In this article, we present datasets of NMR and circular dichroism analyses of the domain 2 of the HCV NS5A protein (NS5A-D2) phosphorylated in vitro by the Casein Kinase II (CKII) (Dal Pero et al., 2007; Clemens et al., 2015; Masak et al., 2014; Kim et al., 2014) [8], [9], [10], [11]. We describe the in vitro phosphorylation of the serine 288 (pS288) of NS5A-D2 by CKII and report the circular dichroism spectrum of the phosphorylated domain (NS5-D2_CKII). This data article also contains the ¹H, ¹⁵N and ¹³C NMR chemical shift assignments (HN, N, Cα, Cβ and C’) for the phosphorylated NS5A-D2 domain, and an assigned ¹H,¹⁵N-HSQC spectrum is shown. The NMR data have been acquired on an 800 MHz spectrometer. These NMR data have been used to calculate both the ¹H,¹⁵N combined chemical shift perturbations (CSP) induced by the phosphorylation of pS288 and the secondary structural propensity (SSP) scores that describe the structural tendencies in this intrinsically disordered domain. The circular dichroism spectrum and the SSP scores of NS5A-D2_CKII have been compared with those of unphosphorylated NS5A-D2 [12,13].

Cell culture-adaptive mutations of NS5A affect replication of hepatitis C virus differentially depending on the viral genotypes

Most of HCV RNAs require cell culture-adaptive mutations for efficient replication in cell culture and a number of such mutations have been described including a well-known S2204I substitution mutation in NS5A protein. In contrast, the replication of genotype 2a JFH1 RNA in cell culture does not require any cell culture-adaptive mutation. Rather, the presence of S2204I mutation impaired the JFH1 RNA replication. In this study, we examined the effect of reversions and substitutions of NS5A cell culture-adaptive mutations on virus replication in different genotypic backgrounds after either placing genotype 1a NS5A in the genotype 2a JFH1 or vice versa. The results from this investigation suggest that the S2204I mutation affects HCV RNA replication differentially depending on the viral genotypes but that the effect was not simply explained by the genotypic background. Perhaps, the effect of the S2204I mutation on HCV replication reflects both intra- and intergenic interactions of NS5A protein. J. Med. Virol. 89:146-152, 2017. © 2016 Wiley Periodicals, Inc.

Host-Targeting Agents to Prevent and Cure Hepatitis C Virus Infection

Chronic hepatitis C virus (HCV) infection is a major cause of liver cirrhosis and hepatocellular carcinoma (HCC) which are leading indications of liver transplantation (LT). To date, there is no vaccine to prevent HCV infection and LT is invariably followed by infection of the liver graft. Within the past years, direct-acting antivirals (DAAs) have had a major impact on the management of chronic hepatitis C, which has become a curable disease in the majority of DAA-treated patients. In contrast to DAAs that target viral proteins, host-targeting agents (HTAs) interfere with cellular factors involved in the viral life cycle. By acting through a complementary mechanism of action and by exhibiting a generally higher barrier to resistance, HTAs offer a prospective option to prevent and treat viral resistance. Indeed, given their complementary mechanism of action, HTAs and DAAs can act in a synergistic manner to reduce viral loads. This review summarizes the different classes of HTAs against HCV infection that are in preclinical or clinical development and highlights their potential to prevent HCV infection, e.g., following LT, and to tailor combination treatments to cure chronic HCV infection.

Profiling Kinase Activity during Hepatitis C Virus Replication Using a Wortmannin Probe

To complete its life cycle, the hepatitis C virus (HCV) induces changes to numerous aspects of its host cell. As kinases act as regulators of many pathways utilized by HCV, they are likely enzyme targets for virally induced inhibition or activation. Herein, we used activity-based protein profiling (ABPP), which allows for the identification of active enzymes in complex protein samples and the quantification of their activity, to identify kinases that displayed differential activity in HCV-expressing cells. We utilized an ABPP probe, wortmannin-yne, based on the kinase inhibitor wortmannin, which contains a pendant alkyne group for bioconjugation using bioorthogonal chemistry. We observed changes in the activity of kinases involved in the mitogen-activated protein kinase pathway, apoptosis pathways, and cell cycle control. These results establish changes to the active kinome, as reported by wortmannin-yne, in the proteome of human hepatoma cells actively replicating HCV. The observed changes include kinase activity that affect viral entry, replication, assembly, and secretion, implying that HCV is regulating the pathways that it uses for its life cycle through modulation of the active kinome.

Host cell kinases and the hepatitis C virus life cycle

Hepatitis C virus (HCV) infection relies on virus-host interactions with human hepatocytes, a context in which host cell kinases play critical roles in every step of the HCV life cycle. During viral entry, cellular kinases, including EGFR, EphA2 and PKA, regulate the localization of host HCV entry factors and induce receptor complex assembly. Following virion internalization, viral genomes replicate on endoplasmic reticulum-derived membranous webs. The formation of membranous webs depends on interactions between the HCV NS5a protein and PI4KIIIα. The phosphorylation status of NS5a, regulated by PI4KIIIα, CKI and other kinases, also acts as a molecular switch to virion assembly, which takes place on lipid droplets. The formation of lipid droplets is enhanced by HCV activation of IKKα. In view of the multiple crucial steps in the viral life cycle that are mediated by host cell kinases, these enzymes also represent complementary targets for antiviral therapy. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases.