Reversal of Glucocorticoids-Dependent Proopiomelanocortin Gene Inhibition by Leukemia Inhibitory Factor

Abstract

We previously have described molecular mechanisms converging at the Nur response element-signal transducer and activator of transcription (STAT) composite site responsible for synergistic activation of the proopiomelanocortin (POMC) gene promoter by leukemia inhibitory factor (LIF) and CRH. In this study, we asked how glucocorticoids (GC), the physiological negative regulators of POMC gene expression, modulate this synergism. In the corticotroph cell line AtT-20, the response of the wild-type promoter to LIF+CRH was barely inhibited by GC, whereas a distal promoter subregion (-414/-293) encompassing the Nur response element-STAT site and devoid of the negative GC-responsive element located in the proximal domain, displayed a cooperative response to LIF+dexamethasone (DEX) and LIF+CRH+DEX treatments. LIF+CRH-stimulated ACTH secretion was also inefficiently inhibited by DEX in the same cell line. This study was focused thereafter on LIF+DEX cooperativity, which may be responsible, on the wild-type promoter, for lack of negative regulation by DEX of the LIF+CRH synergy. The STAT1-3 low-affinity site, in the context of the (-414/-293) subregion of the POMC promoter, was found necessary and sufficient for transcriptional synergism between activated GC receptor (GR) and STAT1-3. Moreover the activities of reporters specific for STAT1-3 or GR were reciprocally enhanced by DEX or LIF. Single and sequential chromatin immunoprecipitations revealed 1) a STAT-dependent corecruitment of coactivators after LIF and LIF+DEX stimulation and 2) a more lasting recruitment of both STAT3 and GR in the same enhanceosome on the endogenous POMC promoter after LIF+DEX joint stimulation than after the single one. Such events may be responsible for a lack of repressive property of GR unmasked on the whole POMC promoter during LIF+CRH stimulation and may contribute to the tonicity of the hypothalamic-pituitary-adrenal axis during inflammatory-infectious diseases.

Regulatory Network Analyses Reveal Genome-Wide Potentiation of LIF Signaling by Glucocorticoids and Define an Innate Cell Defense Response

“…This conserved motif is entirely consistent with the previously defined STAT3 binding site [27],[39]. It is noteworthy that this analysis did not reveal enrichment of any other motif: it might have been expected that some transcription factor binding motifs might have been enriched in association with STAT3 targets since STAT3 has already been shown to act in association with a variety of factors including GR [40]. Failure to detect particular enrichment of one binding motif with STAT3 binding sites may reflect the fact that STAT3 binding sites is associated with a large array of conserved binding motifs for many structural classes of DNA binding proteins and/or that these other factors act by protein∶protein interactions with STAT3.…”

Stress and glucocorticoid receptor transcriptional programming in time and space: Implications for the brain–gut axis

“…Thus, although GR occupancy of a GRE may be short‐lived, it acts cooperatively through assisted loading to enable GRE binding for the estrogen receptor at the same site . The mechanisms by which the GR enables other transcription factors to bind, resulting in either a positive or negative transcriptional outcome at composite response elements, has been extensively studied using the MMTV promoter as a model . In the central nervous system, corticotropin‐releasing hormone (CRH) expressed by neurons of the paraventricular nucleus of the hypothalamus is critical for the release of adrenocorticotropic hormone from the anterior pituitary, and the subsequent release of cortisol from the adrenal glands.…”

Comparison Between Zofenopril and Ramipril in Combination With Acetylsalicylic Acid in Patients With Left Ventricular Systolic Dysfunction After Acute Myocardial Infarction: Results of a Randomized, Double‐Blind, Parallel‐Group, Multicenter, European Study (SMILE‐4)

“…However, unfortunately, we were not able to show clearly how Dex may have affected the STAT3‐dependent regulation of ALP levels in response to BMP‐2. Direct interactions between STAT3 and GR have already been reported in other experimental cell systems (Zhang et al, 1997; Lerner et al, 2003; Latchoumanin et al, 2007). In addition, binding of Dex‐bound GR acts as a co‐activator for STAT3 (Zhang et al, 1997).…”

“…The antibodies used for the ChIP assay were purchased from Cell Signaling Technology. Subsequent ChIP steps were performed as previously reported (Latchoumanin et al, 2007). Finally, DNA from each sample was resuspended in 30 µl water, and then RT‐PCR was performed with 3 µl of this template DNA.…”