Data suggesting that the hepatitis C virus (HCV) core protein influences normal cellular processes remain controversial. To determine the effects of core on cellular gene expression in hepatocytes, we developed a human hepatoma (Huh7)-derived cell line with tightly regulated core expression under the control of a tetracycline-regulated promoter. Cells expressing core did not have impaired proliferative abilities. Changes in gene expression profiles in response to core expression were determined using commercial oligonucleotide microarrays (Affymetrix GeneChip). Significant increases were observed in the abundance of mRNA-encoding members of the metallothionein (MT) family, as well as nicotinamide N-methyltransferase (NNMT) and glutathione peroxidase-like protein (GPLP). These changes did not result from removal of tetracycline from growth media, and were confirmed in reverse-transcription polymerase chain reaction (RT-PCR) assays. They suggest that core protein expression leads to intracellular oxidative stress, and that vital cellular functions are, in turn, protected by up-regulation of cellular antioxidant defense mechanisms. In conclusion, these findings can explain many potentially conflicting prior observations concerning the effects of core on cellular physiology, and are of relevance to the role of core protein in the pathogenesis of HCV-related fibrosis and hepatocellular carcinoma.