Growth hormone regulates expression of rat liver cytochrome P-450 15 beta at a pretranslational level.

Polyclonal antibodies to rat liver microsomal cytochrome P-450 15 beta-hydroxylase were used to screen a female rat liver cDNA expression library. Recombinant plasmid C-6, isolated from a positive colony, contained a cDNA of 1000 base pairs which hybridized to a single, 1.7 kilobase class of mRNA on Northern blot analysis. Semi-quantitative slot blots showed that the level of this mRNA was 17-fold lower in male rat liver than in females. Continuous infusion of human growth hormone to male rats caused them to express female levels of C-6 mRNA, while the same daily dose of hormone given intermittently had no effect. A high degree of correlation of the levels of C-6 mRNA with 15 beta-hydroxylase protein levels and catalytic activities was found, demonstrating that the sexually differentiated, growth hormone-dependent expression of the 15 beta-hydroxylase is regulated at a step preceding translation.