Isolation and Characterization of a Glucocorticoid Response Element in the First Intron of the Gene*

At least two genes encode isoenzymes of rat 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. Alternative splicing of one of these genes generates a skeletal muscle-specific transcript from an upstream promoter and a liver-specific transcript from a downstream promoter. A potent glucocorticoid response element was identified in the first intron of the gene, i.e. between liver exon I and exon 11. The element is approximately 3.5 kilobase pairs (kb) downstream of the liver isoenzyme transcription start site and 13 kb upstream of exon I1 of the gene and confers dexamethasone-sensitive expression of chloramphenicol acetyltransferase (CAT) activity from a heterologous thymidine kinase promoter and from both homologous 5’flanking regions of the gene. This glucocorticoid response element also exhibits androgenbut not estrogen-sensitive expression of CAT activity in HeLa cells cotransfected with the appropriate receptor expression vector. DNase footprint and sequence analysis revealed that the element is comprised minimally of two adjacent 15-mer glucocorticoid receptor dimer binding sites situated in opposite orientations. Glucocorticoid regulation of 6-phosphofructo-2-kinase/fructose-2,6bisphosphatase gene expression in liver and skeletal muscle is mediated by a single complex glucocorticoid response element located in the first intron f the skeletal muscle/liver gene.