Proenkephalin gene expression: interaction of glucocorticoid and cAMP regulatory elements.
We used gel shift assays to determine the affinities of a 15 base glucocorticoid response element (GRE) derived from the rat proenkephalin (Penk) gene for the glucocorticoid receptor. A DNA binding domain of the glucocorticoid receptor interacted with a rat GRE (RGRE) with an apparent affinity intermediate between that of a consensus positive GRE oligo (GRE+) and a mismatch GRE oligo (GRE-). When inserted in front of a chloramphenicol acyl transferase (CAT) construct that is driven by a Penk promoter containing a cAMP response element, dexamethasone (10 microM) produced a 5-fold increase with GRE+, a small increase with RGRE, and no change with GRE- or the Penk promoter alone. Forskolin (20 microM) stimulated CAT activity 4- to 9-fold with each construct. However, dexamethasone plus forskolin caused a synergistic induction of CAT expression with the GRE+ oligo, no effect with the RGRE and an antagonistic effect with the Penk promoter alone and the GRE- oligo. These results demonstrate that GRE+, and to a lesser degree RGRE, can mimic the response of the endogenous Penk gene to dexamethasone and forskolin. Furthermore, a dexamethasone activated glucocorticoid receptor may inhibit cAMP mediated transcription of the Penk gene when a GRE+ or RGRE is not present.
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Department of Pharmacology, Cornell University Medical College, New York, N.Y. 10021, USA.
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D000818:Animals; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D003907:Dexamethasone / Q000378:metabolism*; D004745:Enkephalins / Q000235:genetics*; D005786:Gene Expression Regulation / Q000187:drug effects; D010957:Plasmids; D011401:Promoter Regions, Genetic; D011498:Protein Precursors / Q000235:genetics*; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D014407:Tumor Cells, Cultured
D004745:Enkephalins; D011498:Protein Precursors; D011965:Receptors, Glucocorticoid; C029992:proenkephalin; D005576:Colforsin; D003907:Dexamethasone; D004247:DNA; D000242:Cyclic AMP; D015500:Chloramphenicol O-Acetyltransferase