Regulatory Mechanisms Underlying Corticotropin-Releasing Factor Gene Expression in the Hypothalamus

The hypothalamic-pituitary-adrenal (HPA) axis is activated under various stressors. Corticotropin-releasing factor (CRF) plays a central role in controlling stress response, and regulating the HPA axis. CRF, produced in the hypothalamic paraventricular nucleus (PVN), stimulates adrenocorticotropic hormone (ACTH) production via CRF receptor type I (CRF1 receptor) from the corticotrophs of the anterior pituitary (AP). Cyclic AMP (cAMP)-protein kinase A (PKA) pathway takes a main role in stimulating CRF gene transcription. Forskolin and pituitary adenylate cyclase-activating polypeptide (PACAP) stimulate adenylate cyclase, intracellular cAMP production, and then CRF and arginine vasopressin (AVP) gene expression in hypothalamic 4B cells. Interleukin (IL)-6, produced in the PVN, both directly and indirectly stimulates CRF and AVP gene expression. Estradiol may enhance the activation of CRF gene expression in response to stress. The HPA axis is regulated by a negative feedback mechanism, because glucocorticoids inhibit both CRF production in the hypothalamic PVN and ACTH production in the pituitary. Hypothalamic parvocellular neurons in the PVN are known to express glucocorticoid receptors, and glucocorticoids are able to regulate CRF gene transcription and expression levels directly in the PVN. Glucocorticoids-dependent repression of cAMP-stimulated CRT promoter activity is mainly localized to promoter sequences between -278 and -233 bp. Both negative glucocorticoid regulatory element (nGRE) and serum response element (SRE) are involved in the repression of the CRF gene in the hypothalamic cells.