Glucocorticoid Regulation of Corticotropin-Releasing Factor₁Receptor Expression in Pituitary-Derived AtT-20 Cells

Abstract

SUMMARYCorticotropin-releasing factor (CRF) receptors represent one of the primary sites for negative feedback of the pituitary by adrenocortical glucocorticoid hormones; however, the molecular mechanisms involved have yet to be elucidated. The present study examines the mechanisms by which glucocorticoids regulate CRF-R1 expression in the pituitary cell line, AtT-20. Treatment of these cells with dexamethasone resulted in a concentration-and time-dependent inhibition of CRF-R1 mRNA that was significant by 1 hr and maximal after 4 hr. Levels of CRF-R1 mRNA then returned to control levels after 24 hr. Similar changes were observed when the cells were treated with corticosterone. Pro-opiomelanocortin mRNA was also decreased after dexamethasone pretreatment; however, the time course was much slower with a significant effect only detected after 6 hr. Further analysis of the mechanisms that mediate glucocorticoid regulation of CRF-R1 mRNA was conducted. These studies demonstrated that glucocorticoid incubation significantly decreases the rate of CRF-R1 gene transcription, as determined by nuclear run-on analysis. In addition, the results demonstrate that glucocorticoid incubation significantly decreases CRF-R1 mRNA stability by approximately 50%. The down-regulation of CRF-R1 mRNA was dependent on de novo protein synthesis, as it was blocked by pretreatment with cycloheximide. This represents a novel mechanism for glucocorticoid negative feedback regulation of CRF-R1 expression.Glucocorticoids are known to have a wide array of physiological actions, including cardiovascular, respiratory, immunological, reproductive, and neurobehavioral effects (1, 2). The release of glucocorticoids is regulated by the hypothalamic-pituitary-adrenal axis, and glucocorticoids, in turn, exert a strong, negative feedback effect on this neuroendocrine loop (3-5). Dysfunction of the hypothalamic-pituitary-adrenal axis is associated with and contributes to several psychiatric and endocrine disorders (6, 7), and a great deal of interest has focused on identification of the mechanisms, at the molecular level, that mediate feedback regulation of this neuroendocrine axis.A primary site of action for glucocorticoid negative feedback, in addition to the hypothalamus and hippocampus in brain, are the corticotrophic cells in anterior pituitary (5, 6). Stimulation of these cells by CRF results in the release of ACTH, which provides the principal stimulus for the synthesis and release of glucocorticoids from the adrenal cortex (8). Glucocorticoid negative feedback of corticotrophic cell function occurs at several levels, but the best characterized are the synthesis and release of ACTH (3, 4, 9 -11) and expression of CRF receptors (5, 12, 13). Synthesis of ACTH and its precursor, POMC, is negatively regulated by glucocorticoids (9, 14 -16). This occurs by decreasing the rate of POMC gene transcription (15,17,18). The level of CRF receptors is also decreased by glucocorticoids, but the mechanisms that mediate the down-regulation of these receptors have...

Corticotropin-releasing hormone receptor-1 in human endometrial cancer

“…A 24-h treatment with CRH failed to induce CRH-R1 mRNA down-regulation in ATT-20 cells (Pozzoli, unpublished data). This finding is in keeping with the observations by Iredale et al (14), and is also similar to that obtained in IMR32, a neuroblastoma cell line expressing CRH-R1 receptors (15). On the contrary, a paradoxical upregulation of CRH-R was found by Sakai and colleagues (16) in human adenoma cells in vitro.…”

Effect of Stress-Like Concentrations of Cortisol on Estradiol-Dependent Expression of Gonadotropin-Releasing Hormone Receptor in Orchidectomized Sheep1

“…Alternatively, persistent estrogenic stimulation may increase the formation of cellular factors that override C-dependent suppression. The transient nature of the glucocorticoid-dependent suppression of GnRH receptor expression is also similar to the short-lived effect of glucocorticoids on expression of the corticotropin-releasing hormone receptor in pituitary tissue [43,44].…”

Severe stress switches CRF action in the nucleus accumbens from appetitive to aversive

“…Stress-induced depressive disorders are associated with altered levels of several neurochemicals that interact with the CRF system, including serotonin 22 , dynorphin 23 and glucocorticoids 4,24 . Therefore, we targeted these systems to gain mechanistic insight into the stress-induced loss of CRF’s regulation of dopamine release.…”

“…This dysregulation is mediated by glucocorticoid, but not kappa, receptors and is not ameliorated by acute prophylactic administration of a selective serotonin-reuptake inhibitor. Glucocorticoid signaling has been shown to have genomic repressive effects of the CRF system, in particular the downregulation of CRF R1 24 . Indeed, genetic deletion of the CRF R1 gene selectively from dopamine neurons increases anxiety-like behavior 28 , further demonstrating that disruption of CRF-dopamine interactions alone is sufficient to produce a negative affective state similar to that following severe stress 29 .…”