Expression and chromosomal localization of the cytochrome P1-450 gene in human mitogen-stimulated lymphocytes

Genetic differences in aryl hydrocarbon hydroxylase (AHH) (flavoprotein-linked monoxygenase EC 1.14.14.1) activity in cultured lymphocytes have been linked with individual risk for certain environmentally caused cancers. Cytochrome P1-450 is the form of cytochrome P-450 most closely associated with AHH activity. In this study the chromosomal localization and the expression of human cytochrome P1-450 gene were determined in phytohemagglutinin-stimulated lymphocytes. In situ hybridization analysis provides assignment of the structural gene for human cytochrome P1-450 to chromosome 15q22-q24. Treatment of lymphocytes with benzanthracene increased the amount of mRNA hybridized to the cloned cytochrome P1-450 gene. The level of cytochrome P1-450 mRNA in these lymphocytes correlates well with the induced AHH activity indicating that non-cytochrome P1-450 enzymes contribute little to the individual differences in the level of AHH activity in the lymphocytes. Southern analyses of genomic DNA from individuals with high and low induced AHH activity demonstrated no detectable differences in the pattern or intensity of restriction fragments after treatment with benzanthracene from either individual. This finding together with the excellent correlation between the induced cytochrome P1-450 and AHH activity, suggests that transcriptional control rather than gene amplification or gross form of gene rearrangement accounts for cytochrome P1-450 induction in man. Measurements of cytochrome P1-450 mRNA content in cultured lymphocytes provide an alternative approach to the assay of AHH activity in assessing AHH phenotype and predicting different susceptibilities to deleterious environmental agents.