Abstract
A bidirectional negative relationship between Hepatitis C virus (HCV) replication and gene expression of the catecholamine biosynthetic enzyme L-Dopa decarboxylase (DDC) was previously shown in the liver and attributed at least to an association of DDC with phosphatidylinositol 3-kinase (PI3K). Here, we report that the biosynthesis and uptake of catecholamines restrict HCV replication in hepatocytes, while HCV has developed ways to reduce catecholamine production. By employing gene silencing, chemical inhibition or induction of the catecholamine biosynthetic and metabolic enzymes and transporters, and by applying the substrates or the products of the respective enzymes, we unravel the role of the different steps of the pathway in viral infection. We also provide evidence that the effect of catecholamines on HCV is strongly related with oxidative stress that is generated by their autoxidation in the cytosol, while antioxidants or treatments that lower cytosolic catecholamine levels positively affect the virus. To counteract the effect of catecholamines, HCV, apart from the already reported effects on DDC, causes the down-regulation of tyrosine hydroxylase that encodes the rate-limiting enzyme of catecholamine biosynthesis and suppresses dopamine beta-hydroxylase mRNA and protein amounts, while increasing the catecholamine degradation enzyme monoamine oxidase. Moreover, the NS4B viral protein is implicated in the effect of HCV on the ratio of the ~50 kDa DDC monomer and a ~120 kDa DDC complex, while the NS5A protein has a negative effect on total DDC protein levels.