Cycloheximide increases proenkephalin and tyrosine hydroxylase gene expression in rat adrenal medulla

The effect of cycloheximide (CHX; 5 mg/kg) on proenkephalin (proENK) and ty rosine hydroxylase (TH) mRNA expression in rat central and peripheral nervo us systems was studied. CHX increased proENK and TH mRNA levels in the adre nal gland, but not in hippocampus, striatum, midbrain, brainstem, pituitary , and hypothalamus. The pretreatment with actinomycin D (0.5 mg/kg) signifi cantly decreased CHX-induced proENK and TH mRNA expression, suggesting that the CHX-dependent increase of these mRNA levels may be caused by the incre ase of transcriptional activity rather than RNA stabilization. To investiga te the factors involved in CHX-induced proENK and TH mRNA expression, the e ffect of CHX on activator protein-1 (AP-1), cAMP response element (CRE) bin ding protein (CREB), and glucocorticoid response element (GRE) was tested. In AP-1, the basal expression of Fra-2 and c-Jun proteins and AP-1 DNA bind ing activity in the adrenal medulla was higher than other tissues tested, b ut CHX reduced these protein levels and AP-1 DNA binding activity. In CREB, CHX time dependently increased the level of phospho-CREB without altering total CRE level and CRE DNA binding activity. Furthermore, phospho-CREB act ively participated in CRE DNA binding activity. In GRE, although CHX increa sed plasma and adrenal corticosterone level, RU486 (10 mg/kg) reduced CHX-i nduced proENK, but not TH, mRNA level in a partial manner. These results su ggest that the basal expression of proENK and TH mRNA transcription in the adrenal gland seems to be tonically inhibited by de novo protein synthesis. In addition, CHX-dependent increase of proENK and TH mRNA expression in th e adrenal medulla is well correlated with phospho-CREB level, but not AP-1. Finally, glucocorticoid seems to be involved at least partially in CHX-dep endent proENK, but not TH, mRNA expression in the adrenal medulla.