Binding of benzo(a)pyrene and dibenz(a,h)anthracene to the Ah receptor in mouse and rat hepatic cytosols.

Binding of the polycyclic aromatic hydrocarbon (PAH) carcinogens [3H]benzo(a)pyrene (BP) and [3H]dibenz(a,h)anthracene [DB(a,h)A] to components in rodent hepatic cytosols was characterized by sucrose density gradient centrifugation and by gel permeation chromatography on Sephacryl S-300. In hepatic cytosols from Sprague-Dawley rats, [3H]BP and [3H]DB(a,h)A bound to a component which sedimented at 8 to 9S under low-ionic-strength conditions, and had a Stokes' radius of 4.7 nm. The 8 to 9S component also bound [3H]-2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and [3H]-3-methylcholanthrene (MC), two compounds previously established as Ah receptor ligands. In hepatic cytosols from C57BL/6J mice [a strain genetically "responsive" for induction of aryl hydrocarbon hydroxylase (AHH, cytochrome P1-450) by PAHs], [3H]DB(a,h)A bound to a component sedimenting at 8 to 9S which had a Stokes' radius of approximately 6 nm. The 8 to 9S component also bound [3H]TCDD and [3H]MC, but no direct binding of [3H]BP could be detected at 8 to 9S in hepatic cytosol from C57BL/6J mice, nor could specific [3H]BP binding to the 6 nm component be detected in C57BL/6J cytosol by Sephacryl S-300 chromatography. The 8 to 9S component was not detectable in hepatic cytosol from DBA/2J mice (genetically "nonresponsive" to AHH induction by PAHs) with [3H]BP or [3H]DB(a,h)A, nor with the previously established Ah receptor ligands [3H]TCDD or [3H]MC. In addition to binding to the 8 to 9S-6 nm component in C57BL/6J cytosols, [3H]BP, [3H]DB(a,h)A, and [3H]MC also bound extensively to a cytosolic component sedimenting at 4 to 5S with a Stokes' radius of approximately 3 nm. The 4 to 5S-3 nm component was present in hepatic cytosols from genetically nonresponsive DBA/2J mice, as well as in genetically responsive C57BL/6J mice. Binding of [3H]BP, [3H]DB(a,h)A, and [3H]MC to the 8 to 9S component in rodent hepatic cytosols was eliminated by incubation in the presence of a 100-fold molar excess of nonradioactive TCDD, whereas TCDD had no effect on binding of [3H]BP, [3H]DB(a,h)A, or [3H]MC to the 4 to 5S-3 nm component. The 8 to 9S component segregates with the Ahb allele in genetic crosses with mice, but the 4 to 5S component is not associated with the Ahb allele which governs AHH responsiveness. Specificity of chemicals that bind to the 8 to 9S component and segregation of the 8 to 9S component with the Ahb allele identify it as the Ah receptor which functions to regulate AHH induction in animals treated with PAHs.(ABSTRACT TRUNCATED AT 400 WORDS)