CLONING OF ACTH-REGULATED GENES IN THE ADRENAL-CORTEX

To search for genes that are induced by ACTH in adrenocortical cells, we screened adrenal cortex cDNA libraries by a differential hybridizat ion method using cDNA probes representing mRNAs from cells with or wit hout ACTH stimulation. Forty clones were identified as ACTH induced (y ielding a frequency of about 1/2500 plaques screened), and two clones as ACTH repressed. The cDNAs isolated and sequenced include nuclear ge nes for microsomal steroidogenic enzymes and novel proteins of yet uni dentified functions, and mitochondrial genes encoding subunits of oxid ative phosphorylation enzymes. Northern blot analysis of RNA from cell s stimulated with ACTH confirmed the induction of these genes by ACTH, yet revealed important differences in the relative responses of the r espective mRNAs. The time courses showed the major increase in the ini tial 6 h; and a decline after 24-36 h. The enhancement of the levels o f the mRNAs could be ascribed to transcriptional activation. Since the mitochondrial genome is transcribed as a single polycistronic unit, t o account for the >20-fold differences in the levels of the mitochondr ial mRNAs it is necessary to invoke differential stabilities of these mRNAs. The synchronous increase in the expression of both the steroido genic enzymes and the mitochondrial oxidative phosphorylation system s ubunits, provides evidence for coregulation of steroidogenic and energ y producing capacities of adrenal cells to meet the metabolic needs of steroid hormone production. Suppression of beta-actin gene expression may be related to changes in actin polymerization during ACTH-depende nt cytoskeletal reorganization.