Cytosolic receptor for aryl hydrocarbon hydroxylase induction by polycyclic aromatic compounds. Evidence for structural and regulatory variants among established cell cultured lines.

The effective doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for inducing half-maximally (ED,, values) aryl hydrocarbon (benzolalpyrene) hydroxylase activity (EC 1.14.14.2) in H-4-11-E, Hepa-l, VERO, and HTC established cell culture lines are about 0.23, 0.45, 110, and >200 nM, respectively, and the maximally induced hydroxylase activity is more than 100 times higher in TCDD-treated H-4-11-E and Hepa-l than in VERO or HTC lines. The former two lines are therefore regarded as “responsive,” and the latter two “nonresponsive,” to TCDD. The apparent Kd values for TCDD binding to a small, saturable, homogeneous population of cytosolic sites in all four of these cell lines are similar, however, ranging between 1.02 and 2.80 nM. The estimated mean numbers of cytosolic binding sites are also similar, ranging between 1400 and 2200 per cell in all four of these cell lines grown in control growth medium. The curve for high affinity TCDD binding is sigmoidal in shape, perhaps reflecting positive cooperativity. 3-Methylcholanthrene, benz[alanthracene, and /3-naphthoflavone three known inducers of aryl hydrocarbon hydroxylase activity are capable of displacing [3HlTCDD from the receptor similarly in all four cell lines, but the avidity of the receptor for TCDD is about 100 to more than 1000 times greater than that for these three other inducers. Phenobarbital, pregnenolone-16a-carbonitrile, dexamethasone, and two inactive congeners of TCDD are incapable of displacing 13HlTCDD from the receptor at concentrations lo4 times greater than that of L3HlTCDD. The receptors in the two responsive cell lines differ from those in the two nonresponsive cell lines with regard to relative thermolability in the absence of TCDD: the former are significantly more protected from denaturation at 45” for 10 min in the presence of TCDD but the latter are not. During induction of the hydroxylase in the responsive