Molecular Pharmacology, Vol 6, 293-303, Copyright © 1970 by the American Society for Pharmacology and Experimental Therapeutics

Fate of Inducer during Induction of Aryl Hydrocarbon Hydroxylase Activity in Mammalian Cell Culture

I. Intracellular Entry, Binding, Distribution, and Metabolism

¹ Section on Developmental Enzymology, Laboratory of Biomedical Sciences, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20014

The fate of the inducer benz[a]anthracene has been examined during the induction of aryl hydrocarbon hydroxylase, a microsomal enzyme system inducible by polycyclic hydrocarbons in hamster fetal cells grown in culture. Diffusion of the inducer into the cell is a passive phenomenon; a net accumulation of intracellular polycyclic hydrocarbon is reached after about 30 min of exposure of the cells to benz[a]anthracene. Less than 1% of the total intracellular polycyclic hydrocarbon content is bound covalently to cellular macromolecules. This binding process is enzymatic and can be inhibited by 2-diethylaminoethyl-2,2-diphenylvalerate HC1 (SKF 525-A).

More than one-half of the covalently bound polycyclic hydrocarbon is located in the nuclear and microsomal fractions. About one-half of the physically bound polycyclic hydrocarbon is associated with the nuclear fraction, but this chemical has a strong affinity for all subcellular organelles and for cytoplasmic macromolecules. In cells derived from various hamster fetal tissues, there are differences in the maximal saturating levels of intracellular polycyclic hydrocarbon and in the rates of hydroxylase induction. Polar metabolites of benz[a]anthracene appear in the medium during the process of hydroxylase induction, and this accumulation is prevented by cycloheximide.

Note:
ACKNOWLEDGMENTS The authors appreciate their valuable discussions with Dr. H. V. Gelboin in the development of the cell culture experimental system, and his encouragement to investigate this aspect of the enzyme induction problem. We also gratefully acknowledge the critical reviews of this manuscript by Drs. G. Guroff, D. N. Teller, and J. C. Robinson.

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