Regarding the mechanisms underlying the down-regulation of the CYP2C19 gene in the tumor tissue of HCC, the expression of the CYP2C19 gene was regulated by several nuclear receptors and transcription factors, including the constitutive androstane receptor (CAR), pregnane X receptor, glucocorticoid receptor, and hepatocyte nuclear factor-3g. The gene discussed is NR1I2; the disease is hepatocellular carcinoma.