Overexpression of CAR inhibits cell cycle progression in HepG2 and Hep3B cells. Cell cycle progression was analyzed in HepG2-hCAR and Hep3B-hCAR cells 3 days after treatment with vehicle control or Dox (1 μg/ml). The percentage of cells in different cell cycle phases was compared between vehicle control and Dox-treated HepG2-hCAR (A), Hep3B-hCAR (B), as well as normal HepG2 and Hep3B (C) cells. D, Western blotting was carried out to measure the protein levels of p21 in HepG2-hCAR, Hep3B-hCAR, HepG2, and Hep3B cells treated with vehicle control or Dox as detailed in the “Experimental procedures” section. Relative blot densitometry was quantified using ImageJ from three separately prepared cell experiments and normalized to the density of the loading control. Data were expressed as mean ± SD (n = 3). ∗∗p < 0.01. CAR, constitutive androstane receptor; Dox, doxycycline; hCAR, human CAR.