Glucocorticoids induce transcription of ribosomal protein genes in rat liver

Transcription of rat liver ribosomal RNA is induced by glucocorticoids. In order to determine whether the expression of ribosomal protein genes is coordinately regulated, we measured the effect of dexamethasone on their transcription. Administration of this hormone to adrenalectomized rats led, within 1 h, to a 2.2-fold enhancement of transcription of liver ribosomal protein genes. To define the dexamethasone-responsive element, we isolated and tested mouse L32 gene sequences for the ability to confer glucocorticoid induction to the bacterial chloramphenicol acetyltransferase (CAT) gene in L cells. An 80 base pair region of the L32 gene, between nucleotide position -69 and +11, with respect to the start site of transcription, was sufficient for induction of the CAT gene by dexamethasone. Despite these stimulating effects, we have failed to detect elevation in the abundance of the ribosomal protein mRNAs both in rat liver and in mouse L cells. Possible interpretations for this seemingly ineffectual process are discussed.