Transcriptional regulation of the tryptophan oxygenase gene in rat liver by glucocorticoids.

The enzyme tryptophan oxygenase (EC 1.13.11.11), which is synthesized in rat liver, is induced by glucocorticoids. We have used cloned tryptophan oxygenase genomic and cDNA sequences to study the mechanism of induction. Rat liver poly(A+) RNA was separated on a formaldehyde gel, blotted to nitrocellulose, and hybridized to a nick-translated tryptophan oxygenase cDNA clone to analyze the kinetics of tryptophan oxygenase mRNA accumulation. Transcription in isolated rat liver nuclei was investigated to determine the relative rate of transcription of the tryptophan oxygenase gene. Analysis of the accumulation of albumin mRNA, which is unaffected by glucocorticoids, served as an internal control. We show here that the synthetic glucocorticoid dexamethasone causes a 10-fold increase in the concentration of tryptophan oxygenase mRNA sequences in rat liver, and that this is a consequence of transcriptional activation of the tryptophan oxygenase gene.