Hepatitis C Virus NS5A Targets Nucleosome Assembly Protein NAP1L1 To Control the Innate Cellular Response

Abstract

(HCV) is a single-stranded positive-sense RNA hepatotropic virus. Despite cellular defenses, HCV is able to replicate in hepatocytes and to establish a chronic infection that could lead to severe complications and hepatocellular carcinoma. An important player in subverting the host response to HCV infection is the viral nonstructural protein NS5A, which, in addition to its role in replication and assembly, targets several pathways involved in the cellular response to viral infection. Several unbiased screens identified nucleosome assembly protein 1-like 1 (NAP1L1) as an interaction partner of HCV NS5A. Here we confirmed this interaction and mapped it to the C terminus of NS5A of both genotype 1 and 2. NS5A sequesters NAP1L1 in the cytoplasm, blocking its nuclear translocation. However, only NS5A from genotype 2 HCV, and not that from genotype 1, targets NAP1L1 for proteosome-mediated degradation. NAP1L1 is a nuclear chaperone involved in chromatin remodeling, and we demonstrated the NAP1L1-dependent regulation of specific pathways involved in cellular responses to viral infection and cell survival. Among those, we showed that lack of NAP1L1 leads to a decrease of RELA protein levels and a strong defect of IRF3 TBK1/IKKε-mediated phosphorylation, leading to inefficient RIG-I and Toll-like receptor 3 (TLR3) responses. Hence, HCV is able to modulate the host cell environment by targeting NAP1L1 through NS5A. Viruses have evolved to replicate and to overcome antiviral countermeasures of the infected cell. Hepatitis C virus is capable of establishing a lifelong chronic infection in the liver, which could develop into cirrhosis and cancer. Chronic viruses are particularly able to interfere with the cellular antiviral pathways by several different mechanisms. In this study, we identified a novel cellular target of the viral nonstructural protein NS5A and demonstrated its role in antiviral signaling. This factor, called nucleosome assembly protein 1-like 1 (NAP1L1), is a nuclear chaperone involved in the remodeling of chromatin during transcription. When it is depleted, specific signaling pathways leading to antiviral effectors are affected. Therefore, we provide evidence for both a novel strategy of virus evasion from cellular immunity and a novel role for a cellular protein, which has not been described to date.

PRDM8 exhibits antitumor activities toward hepatocellular carcinoma by targeting NAP1L1

“…According to a recent study, depletion of NAP1L1 in hepatocytes leads to the down‐regulation of 358 genes, and Ingenuity Pathway Analysis of the downregulated genes indicates that PI3K/AKT signaling is one of the top canonical pathways. GAB1, an important upstream regulator of PI3K/AKT/mTOR, is among those downregulated genes . We therefore speculated that NAP1L1 might activate PI3K/AKT/mTOR signaling through GAB1.…”

Multiple Host Factors Interact with the Hypervariable Domain of Chikungunya Virus nsP3 and Determine Viral Replication in Cell-Specific Mode

“…Despite this methodological limitation, the list of NAP1L1 functions is continuously growing. Recent studies have demonstrated interaction of NAP1L1 with the intrinsically disordered, carboxy-terminal fragment of HCV NS5A protein (61). However, the data about the role of this interaction in HCV biology are somewhat contradictory (61,62).…”

Hepatitis C Virus: Evading the Intracellular Innate Immunity

“…It has also been demonstrated that HCV is able to induce PKR phosphorylation, activating its kinase function and inhibiting antiviral effector translation [84,86,87]. Recently, NS5A was also reported to interact with the nucleosome assembly protein 1-like 1 (NAP1L1), a nuclear-cytoplasmic chaperone reported to be involved in the regulation of several host pathways, such as transcription or cell cycle progression [91]. In HCV-genotype 2 infection, NS5A-NAP1L1 interaction results in the sequestration of NAP1L1, inducing its proteasomal degradation and impeding its nuclear translocation.…”

“…In HCV-genotype 2 infection, NS5A-NAP1L1 interaction results in the sequestration of NAP1L1, inducing its proteasomal degradation and impeding its nuclear translocation. NAP1L1 targeting downregulates the transcription of several genes essential for innate immunity, such as RIG-I-and TLR3-mediated responses [91]. Moreover, it has been shown that NS5A downregulates type I and type III IFNs activation induced by RIG-I-and MDA5-mediated responses.…”

“…cleaves MAVS, to impair production of IFNs and proinflammatory cytokines [31,37,[52][53][54][55]57] cleaves TRIF, to impair production of IFNs and proinflammatory cytokines [28,58] inactivates Riplet, inhibiting RIG-I and IRF3 activation [62,63] binds to LUBAC, impairing the polyubiquitynation of NEMO required for NF-κB activation [66] induces degradation of STAT1, impairing the expression of antiviral effectors [67] binds to TBK1, impairing IRF3 activation [59][60][61] Core blocks NF-κB, to suppress inflammatory response [98,99] targets JAK/STAT pathway by targeting STAT1 and STAT2, inhibiting the production of ISGs [52,67,[104][105][106][107][108][110][111][112] E2 interacts with PKR, repressing its antiviral effects [89] NS5A interacts with PKR, repressing its antiviral effects [88,90] induces NAP1L1 degradation, inhibiting gene transcription essential for RIG-I-and TLR3-mediated responses [91] impedes RIG-I-and MDA5 activation, impairing IFNs expression [33] NS4B downregulates TRIF protein, inhibiting TLR3 signaling [68] interacts with STING, inhibiting the production of IFNs [69,70] p7 interacts with IFI16-16, inhibiting its antiviral function [114] Growing evidence demonstrates that HCV modifies host microRNA (miRNA) expression to modulate a diverse range of host functions [115]. It was re...…”