AHR and hepatocellular carcinoma: Interestingly, bilirubin/biliverdin have been shown to be ligands of the aryl hydrocarbon receptor (Ahr) in mouse hepatoma hepa 1c1c7 cells (Sinal and Bend, 1997; Phelan et al., 1998) and SMCs from Ahr KO mouse aortas exhibit a prolonged cell cycle time as compared with controls (Ollinger et al., 2007), which suggest that Ahr activation could participate in the regulation of proliferation of SMCs.