AHR and cancer: Although the mechanisms of TLS polymerase overexpression in cancer cells remain to be elucidated, overexpression of Pol κ is regulated through activation of the aryl hydrocarbon receptor (AhR) by the endogenous tryptophan-derived ligand kyneurin, as well as by DNA damaging agents such as benzo[a]pyrene (B[a]P) (131, 132, 172, 173).