| Corticotropin-releasing Hormone (CRH) is a peptide produced in the hypothalamus and secreted into the hypophyseal-portal circulation, ultimately binding to anterior pituitary cells in response to stress. There, it stimulates the production of adrenocorticotropic hormone (ACTH) which, in turn, stimulates the production of steroid hormones, including glucocorticoids, in the adrenal cortex. Glucocorticoids have been shown to mediate a range of physiological responses to stress. The Repressor-Element-1 (RE-1) is a 21-base-pair (bp) element thought to mediate transcriptional repression of neuronal genes by the Repressor Element Silencing Transcription Factor (REST) in non-neural cell-types and tissues. The presence of a highly conserved RE-1 element in the CRH intron suggested that the RE-1/REST system might be important in the regulation of CRH transcriptional activity. We report here that the RE-1 found in the intron of the CRH gene does repress CRH transcriptional activity, both in vitro and in the endogenous genomic setting. ES cells containing a knocked-in version of the CRH gene lacking specifically the RE-1 element show up-regulation of expression from the endogenous CRH gene, in the context of the whole genome. Based on in vitro evidence, this repression occurs by the binding of REST to the CRH RE-1, likely recruiting a variety of chromatin remodeling complexes, including the Sin3A/HDAC complex and the SWI/SNF ATP-dependent chromatin remodeling complex. This study provides direct evidence for the first time of repression of gene expression by the RE-1 in its natural genomic context. |
