Identification of regions in the rat serine dehydratase gene responsible for regulation by cyclic AMP alone and in the presence of glucocorticoids.

Transcription of the rat serine dehydratase (SDH) gene is induced by glucagon, mediated by the action of cAMP. To identify the nucleotide sequences in the SDH gene responsible for this regulation, we constructed chimeric genes containing different portions of the 5' flanking region of the rat SDH gene fused to the structural sequence encoding the bacterial reporter enzyme, chloramphenicol acetyltransferase (CAT). The transcriptional activities of the fusion genes introduced into the rat hepatoma cell line 7AD-7 were assayed by measuring CAT activity in the cell lysates. Chlorophenylthio-cyclic AMP (CPT-cAMP), a potent protein kinase A activating agent, stimulated the expression of SDH-CAT fusion genes, and these inductions could be enhanced further by the addition of dexamethasone, although the glucocorticoid alone had no effect on CAT activity. Deletion analysis demonstrated that an 80 bp region located approximately 3.5 kb upstream from the transcription initiation site of the rat SDH gene was responsible for stimulation of transcription by CPT-cAMP, whereas the 120 bp region immediately upstream of the cAMP responsive element (CRE)-containing sequences is essential for the enhancement of CPT-cAMP induction by the glucocorticoid.