Surprisingly, however, the tryptophan photoproduct and non-carcinogenic endogenous AhR ligand FICZ (6 formylindolo[3,2-b]carbazole) induced LINE-1 retrotransposition in human hepatocellular carcinoma HuH-7 cells by a mechanism requiring ARNT and MAPK but not AhR (Okudaira et al., 2010). Here, AHR is linked to hepatocellular carcinoma.