Hepatitis C Virus Infection Induces Hepatic Expression of NF-κB-Inducing Kinase and Lipogenesis by Downregulating miR-122

Abstract

Hepatitis C virus (HCV) harnesses host dependencies to infect human hepatocytes. We previously identified a pivotal role of IκB kinase α (IKK-α) in regulating cellular lipogenesis and HCV assembly. In this study, we defined and characterized NF-κB-inducing kinase (NIK) as an IKK-α upstream serine/threonine kinase in IKK-α-mediated proviral effects and the mechanism whereby HCV exploits this innate pathway to its advantage. We manipulated NIK expression in Huh7.5.1 cells through loss- and gain-of-function approaches and examined the effects on IKK-α activation, cellular lipid metabolism, and viral assembly. We demonstrated that NIK interacts with IKK-α to form a kinase complex in association with the stress granules, in which IKK-α is phosphorylated upon HCV infection. Depletion of NIK significantly diminished cytosolic lipid droplet content and impaired HCV particle production. NIK overexpression enhanced HCV assembly, and this process was abrogated in cells deprived of IKK-α, suggesting that NIK acts upstream of IKK-α. NIK abundance was increased in HCV-infected hepatocytes, liver tissues from Alb-uPA/Scid mice engrafted with human hepatocytes, and chronic hepatitis C patients. NIK mRNA contains an miR-122 seed sequence binding site in the 3′ untranslated region (UTR). miR-122 mimic and hairpin inhibitor directly affected NIK levels. In our hepatic models, miR-122 levels were significantly reduced by HCV infection. We demonstrated that HNF4A, a known transcriptional regulator of pri-miR-122, was downregulated by HCV infection. NIK represents a bona fide target of miR-122 whose transcription is downregulated by HCV through reduced HNF4A expression. This effect, together with the sequestering of miR-122 by HCV replication, results in “derepression” of NIK expression to deregulate lipid metabolism. IMPORTANCE Chronic hepatitis C virus (HCV) infection is a major global public health problem. Infection often leads to severe liver injury that may progress to cirrhosis, hepatocellular carcinoma, and death. HCV coopts cellular machineries for propagation and triggers pathological processes in the liver. We previously identified a pivotal role of IKK-α in regulating cellular lipid metabolism and HCV assembly. In this study, we characterized NIK as acting upstream of IKK-α and characterized how HCV exploits this innate pathway to its advantage. Through extensive mechanistic studies, we demonstrated that NIK is a direct target of miR-122, which is regulated at the transcription level by HNF4A, a hepatocyte-specific transcription factor. We show in HCV infection that NIK expression is increased while both HNF4A and miR-122 levels are decreased. NIK represents an important host dependency that links HCV assembly, hepatic lipogenesis, and miRNA biology.

Non-Coding RNAs as Potential Novel Biomarkers for Early Diagnosis of Hepatic Insulin Resistance

“…Therefore, it is clear that miR-122 participates in the differentiation of hepatoblasts towards hepatocytes; however, its activity also extends towards other processes. As was previously described, miR-122 plays a pivotal role in regulating hepatic gene expression, affecting various aspects of cellular activity such as response to oxidative stress [81], viral infection [82], inflammation [83], and even tumorigenesis, as its dysregulation has notoriously been reported as an viable marker of HCC onset and development [84,85]. miR-122 has also been described to orchestrate lipid metabolism; as Cheung et al [28] demonstrated in their study, miR-122 inhibition in healthy mice resulted in a decreased expression of hepatic de novo lipogenesis genes such as FASN (fatty acid synthase) and ACC1 (acetyl-CoA carboxylase), which encode two rate-limiting enzymes.…”

The Crosstalk of miRNA and Oxidative Stress in the Liver: From Physiology to Pathology and Clinical Implications

“…Here, miR-122 directly binds to the viral genome and enhances viral RNA replication, thus resulting in reduced miR-122 expression within the cell [115,116]. The NFκB-inducing kinase (NIK) is usually a target of miR-122, but due to the decreased levels of miR-122, NIK is increased in HCV infection [117]. In addition, HNF4α, a transcriptional regulator of miR-122 expression and known for its OS-association [118], is downregulated in HCV infection, too [117].…”

“…The NFκB-inducing kinase (NIK) is usually a target of miR-122, but due to the decreased levels of miR-122, NIK is increased in HCV infection [117]. In addition, HNF4α, a transcriptional regulator of miR-122 expression and known for its OS-association [118], is downregulated in HCV infection, too [117]. Both effects result in disturbance of the NIK mediated lipid metabolism and HCV-induced lipogenesis and lipid droplet formation [117,119].…”

The Metabolic Profile of Tumor and Virally Infected Cells Shapes Their Microenvironment Counteracting T Cell Immunity

“…Viruses likewise manipulate their host cell's lipid metabolism, for example human cytomegalovirus (CMV) induces an increase in fatty acid production to synthesize lipids for incorporation into the viral envelope (63). Hepatocytes infected by Hepatitis C virus (HCV) are forced to increase lipogenesis and gluconeogenesis to support viral particle production via sophisticated mechanisms involving viral proteins and interference with host miRNAs (64, 65). Since hepatocytes are vital in regulating systemic glucose and lipid homeostasis these manipulations by HCV lead to a significantly increased risk for patients to develop metabolic disorders.…”