CYP1B1 and fibrosarcoma: Conversely, NRF2 along with musculoaponeurotic fibrosarcoma (sMAF) proteins directly activate the AHR promoter and AHR target genes, such as CYP1A1 and CYP1B1, by recruiting the NRF2-sMAF complex to antioxidant response elements (AREs) in the gene promoters of AHR, CYP1A1, or CYP1B1 detoxification phase I enzymes 25.