Hepatitis C Virus Infection Promotes Hepatic Gluconeogenesis through an NS5A-Mediated, FoxO1-Dependent Pathway

Abstract

Chronic hepatitis C virus (HCV) infection is often associated with type 2 diabetes.However, the precise mechanism underlying this association is still unclear. Here, using Huh-7.5 cells either harboring HCV-1b RNA replicons or infected with HCV-2a, we showed that HCV transcriptionally upregulated the genes for phosphoenolpyruvate carboxykinase (PEPCK) and glucose 6-phosphatase (G6Pase), the rate-limiting enzymes for hepatic gluconeogenesis. In this way, HCV enhanced the cellular production of glucose 6-phosphate (G6P) and glucose. PEPCK and G6Pase gene expressions are controlled by the transcription factor forkhead box O1 (FoxO1). We observed that although neither the mRNA levels nor the protein levels of FoxO1 expression were affected by HCV, the level of phosphorylation of FoxO1 at Ser319 was markedly diminished in HCV-infected cells compared to the control cells, resulting in an increased nuclear accumulation of FoxO1, which is essential for sustaining its transcriptional activity. It was unlikely that the decreased level of FoxO1 phosphorylation was mediated through Akt inactivation, as we observed an increased phosphorylation of Akt at Ser473 in HCVinfected cells compared to control cells. By using specific inhibitors of c-Jun N-terminal kinase (JNK) and reactive oxygen species (ROS), we demonstrated that HCV infection induced JNK activation via increased mitochondrial ROS production, resulting in decreased FoxO1 phosphorylation, FoxO1 nuclear accumulation, and, eventually, increased glucose production. We also found that HCV NS5A mediated increased ROS production and JNK activation, which is directly linked with the FoxO1-dependent increased gluconeogenesis. Taken together, these observations suggest that HCV promotes hepatic gluconeogenesis through an NS5A-mediated, FoxO1-dependent pathway.

Hepatitis C and Alcohol Exacerbate Liver Injury by Suppression of FOXO3

“…FOXOs are also required for lipid homeostasis. 37 HCV infection was shown to contribute to insulin resistance by increased FOXO1 activity, 20,38 and a similar observation has been made for nonalcoholic steatohepatitis. 39 It has more recently been shown that FOXO3 activity is increased by starvation/malnutrition in HCV infection, where it modulates innate immunity signaling.…”

“…18 The role of FOXO in injury processes is complex because FOXO transcriptional programs can be either cytoprotective or cytotoxic, and welldocumented examples of both phenomena are numerous. 19 There have been a limited number of reports of the effect of HCV infection on FOXO activity, and these have shown that activation of FOXO1 or FOXO3 by HCV may contribute to insulin resistance 20 and autophagy induction. 21 FOXO3 has also recently been shown to be part of a proapoptotic pathway in human peripheral blood cells.…”

HCV upregulates Bim through the ROS/JNK signalling pathway, leading to Bax-mediated apoptosis

“…We previously reported that HCV induces JNK activation through increased mitochondrial ROS production (Deng et al, 2011). We therefore tested whether HCV-induced JNK activation contributes to Bax activation.…”

“…Increasing evidence has suggested that c-Jun NH 2 -terminal kinase (JNK) plays a role in Bax-mediated apoptosis by regulating the function of Bim (Lei & Davis, 2003;Okuno et al, 2004;Putcha et al, 2003). Also, we previously demonstrated that HCV-induced ROS production causes JNK activation, resulting in increased gluconeogenesis (Deng et al, 2011). In the present study, we investigated the possible link between HCV-induced ROS/JNK signalling and Bim/Baxmediated apoptosis using the HCV cell culture system.…”

“…It is also known that Bim activity is modulated by JNK (Lei & Davis, 2003) and that transcription factors c-Jun and FoxO regulate Bim transcription by directly binding to the Bim promoter (Gilley et al, 2003;Heidari et al, 2012). Importantly, we previously found that HCV induces the sustained transcriptional activity of FoxO1 through JNK activation (Deng et al, 2011). Therefore, we sought to determine whether HCV-mediated ROS/ JNK signalling affects Bim expression.…”