CYP2E1 and hepatocellular carcinoma: Researchers have used genetically engineered hepatoma-based cell lines that express either alcohol dehydrogenase, cytochrome P450 2E1, or both of these enzymes (VA-13, E47, and VL-17A cells, respectively) to study the effects of ethanol metabolism on proteasome function (Dai et al. 1993; Clemens et al. 2002; Donohue et al. 2006).