Pyruvate dehydrogenase kinase regulates hepatitis C virus replication

At least 185 million people around the world are infected by hepatitis C virus (HCV)1,2. Although complications of HCV infection, such as cirrhosis and hepatocellular carcinoma (HCC), develop decades after hepatocellular injury, these complications seriously affect mortality; therefore, optimal and timely management of chronic hepatitis C is necessary3. Current standard treatment of hepatitis C consists of the nucleoside analog ribavirin, which blocks guanine nucleotide synthesis, in combination with PEGylated interferon (IFN)-α, which activates the IFN-mediated antiviral response4. However, inefficient achievement of sustained virological response has prompted researchers to search for novel therapies. Recently approved antiviral agents include sofosbuvir, simeprevir, and daclatasvir, but the high costs of these drugs has limited their applications in clinical practice5,6. Recently accumulated evidence suggests that reprogramming tumor metabolism using glycolytic enzymes represents an effective anticancer strategy7,8,9. In this context, pyruvate dehydrogenase kinase (PDK) is a promising target for cancer metabolic therapy7,10,11,12,13. PDK phosphorylates pyruvate dehydrogenase (PDH) and inhibits its activity, thereby inhibiting the entry of pyruvate into the TCA cycle14. By decreasing the oxidation of glucose, elevated PDK activity in tumor cells provides precursors for macromolecular biosynthesis, such as amino acids and nucleotides10,15. During aerobic glycolysis (also called the Warburg effect), glycerate 3-phosphate generated from glucose is converted into serine by three consecutive enzymatic cascades; phosphoglycerate dehydrogenase (PHGDH), phosphoserine aminotransferase 1 (PSAT-1), and phosphoserine phosphatase (PSPH)16,17. Serine hydroxymethyltranferase converts serine into glycine, an amino acid that plays a key role in the biosynthesis of proteins, purines, and glutathiones, as well as in DNA and histone methylation16,17. Mounting evidence suggests that metabolic changes that favor aerobic glycolysis and serine/glycine biosynthesis also occur in virus-infected cells; in other words, rapidly replicating viruses modify the metabolism of infected cells in a way that resembles the alterations in rapidly proliferating cancer cells18. For example, human cytomegalovirus (HCMV), herpes simplex virus (HSV), human immunodeficiency virus (HIV), and Mayaro virus increase glycolytic flux and reprogram cellular central carbon metabolism to enhance viral replication19,20,21,22,23. HCV is no exception: the activity of the key glycolytic enzyme hexokinase (HK) is increased by its interaction with the HCV non-structural protein NS5A24. Furthermore, HCV infection induces changes that favor glycolytic activity25, and expression of PSPH and PSAT-1 is considerably increased in HCV-infected cells than in HCV-uninfected cells26. Given that modulation of PDK activity can determine the metabolic balance between oxidative phosphorylation and aerobic glycolysis within a cell15, and that serine is derived from the early glycolytic intermediate 3-phosphoglycerate, we reasoned that inhibiting PDK activity would disturb serine/glycine synthesis, thereby inhibiting HCV replication. However, it is unclear whether blocking glycolysis by modulating PDK will inhibit HCV replication, as it does for cancer cells. In this study, we show that the PDK inhibitor dichloroacetate (DCA) shifts glucose metabolism away from aerobic glycolysis and subsequently inhibits the serine biosynthetic pathway in HCV-infected hepatocytes, thereby blocking HCV replication.