Transcriptional regulation of the liver beta-galactoside alpha 2,6-sialyltransferase by glucocorticoids

Abstract

Hepatic expression of the beta-galactoside alpha 2,6-sialyltransferase is at least in part specified by circulatory glucocorticoids. In this report we use the glucocorticoid agonist, RU362, and the antagonist, RU486, to demonstrate the participation of the glucocorticoid receptor pathway in beta-galactoside alpha 2,6-sialyltransferase regulation. The existing pool of sialyltransferase mRNA is turned over with an approximate half-life of 13 h, and presence of dexamethasone does not alter this rate of degradation. By means of nuclear run-off assays and measurement of nuclear unprocessed transcripts we demonstrate that dexamethasone induction of beta-galactoside alpha 2,6-sialyltransferase mRNA in rat Reuber H35 cells is mediated by a transcriptional enhancement mechanism. The same initiation site is utilized for sialyltransferase transcription in both basal- and hormone-stimulated synthesis. Sialyltransferase sequences residing upstream of this transcriptional initiation point are used to control chloramphenicol acetyltransferase expression in fusion constructs following transient transfection into H35 cells to demonstrate the presence of a functional promoter. Although no element with similarity to the known GRE consensus sequence resides within this promoter region, chloramphenicol acetyltransferase expression under the control of the sialyltransferase promoter is subject to a low (1.6-fold) but reproducible induction in response to dexamethasone. Implications of this observation to glucocorticoid regulation are discussed.