Distal cis-acting promoter sequences mediate glucocorticoid stimulation of cardiac atrial natriuretic factor gene transcription

Abstract

Although receptors for most steroid hormones are present in the heart, few cardiac-specific target genes have been identified and studied at the molecular level. Transcription of the atrial natriuretic factor (ANF) gene, which encodes the major secretory product of the heart, is induced by glucocorticoids. In both atrial and ventricular cardiac cells in primary cultures, ANF mRNA levels are increased 3-4-fold after dexamethasone treatment in a time- and dose-dependent manner. This response to glucocorticoids is completely abolished by the antagonist RU486. Interestingly, ventricular myocytes appear to be more sensitive to glucocorticoids than atrial myocytes. DNA-mediated gene transfer studies indicate that glucocorticoids affect ANF gene transcription via a glucocorticoid response element located in the distal 5'-flanking sequences of the rat ANF gene between -697 and -1,029 base pairs. In vitro DNase I footprinting experiments reveal the presence of two binding sites for purified glucocorticoid receptor within this region. Mobility shift assays and competition experiments show that binding of the glucocorticoid receptor to both ANF sites results in a DNA-protein complex similar in affinity and specificity to that of the well characterized mammary tumor virus glucocorticoid response element. Since glucocorticoid activation of the ANF promoter appears specific to cardiac cells, the interaction between the glucocorticoid receptor binding sites and cardiac-specific regulatory elements of this promoter could provide a model to study a mechanism of hormone-dependent signal transduction in the heart.