Transcriptional regulation of steroid receptor coactivator-1 (SRC-1) in glucocorticoid action

Glucocorticoids, their uses, sexual dimorphisms, and diseases: new concepts, mechanisms, and discoveries

The normal stress response in humans is governed by the hypothalamic-pituitary-adrenal (HPA) axis through heightened mechanisms during stress, raising blood levels of the glucocorticoid hormone cortisol. Glucocorticoids are quintessential compounds that balance the proper functioning of numerous systems in the mammalian body. They are also generated synthetically and are the preeminent therapy for inflammatory diseases. They act by binding to the nuclear receptor transcription factor glucocorticoid receptor (GR), which has two main isoforms (GRα and GRβ). Our classical understanding of glucocorticoid signaling is from the GRα isoform, which binds the hormone, whereas GRβ has no known ligands. With glucocorticoids being involved in many physiological and cellular processes, even small disruptions in their release via the HPA axis, or changes in GR isoform expression, can have dire ramifications on health. Long-term chronic glucocorticoid therapy can lead to a glucocorticoid-resistant state, and we deliberate how this impacts disease treatment. Chronic glucocorticoid treatment can lead to noticeable side effects such as weight gain, adiposity, diabetes, and others that we discuss in detail. There are sexually dimorphic responses to glucocorticoids, and women tend to have a more hyperresponsive HPA axis than men. This review summarizes our understanding of glucocorticoids and critically analyzes the GR isoforms and their beneficial and deleterious mechanisms and the sexual differences that cause a dichotomy in responses. We also discuss the future of glucocorticoid therapy and propose a new concept of dual GR isoform agonist and postulate why activating both isoforms may prevent glucocorticoid resistance.

Steroid receptor coactivator-1: The central intermediator linking multiple signals and functions in the brain and spinal cord

The effects of steroid hormones are believed to be mediated by their nuclear receptors (NRs). The p160 coactivator family, including steroid receptor coactivator-1 (SRC-1), 2 and 3, has been shown to physically interact with NRs to enhance their transactivational activities. Among which SRC-1 has been predominantly localized in the central nervous system including brain and spinal cord. It is not only localized in neurons but also detectable in neuroglial cells (mainly localized in the nuclei but also detectable in the extra-nuclear components). Although the expression of SRC-1 is regulated by many steroids, it is also regulated by some non-steroidal factors such as injury, sound and light. Functionally, SRC-1 has been implied in normal function such as development and ageing, learning and memory, central regulation on reproductive behaviors, motor and food intake. Pathologically, SRC-1 may play a role in the regulation of neuropsychiatric disorders (including stress, depression, anxiety, and autism spectrum disorder), metabolite homeostasis and obesity as well as tumorigenesis. Under most conditions, the related mechanisms are far from elucidation; although it may regulate spatial memory through Rictor/mTORC2-actin polymerization related synaptic plasticity. Several inhibitors and stimulator of SRC-1 have shown anti-cancer potentials, but whether these small molecules could be used to modulate ageing and central disorder related neuropathology remain unclear. Therefore, to elucidate when and how SRC-1 is turned on and off under different stimuli is very interesting and great challenge for neuroscientists.

Inhibition of steroid receptor coactivator-1 in the hippocampus impairs the consolidation and reconsolidation of contextual fear memory in mice

AIMS

Steroid receptor coactivator-1 (SRC-1) is a key coactivator for the efficient transcriptional activity of steroids in the regulation of hippocampal functions. However, the effect of SRC-1 on hippocampal memory processes remains unknown. Our aim was to investigate the roles of hippocampal SRC-1 in the consolidation and reconsolidation of contextual fear memory in mice.

MAIN METHODS

Contextual fear conditioning paradigm was constructed in adult male C57BL/6 mice to examine the fear learning and memory processes. Adeno-associated virus (AAV) vector-mediated RNA interference (RNAi) was infused into hippocampus to block hippocampal SRC-1 level. Immunofluorescent staining was used to detect the efficiency of transfection. High plus maze and open field test were used to determine anxiety and locomotor activity. Western blot analyses were used to detect the expression of SRC-1 and synaptic proteins in the hippocampus.

KEY FINDINGS

We first showed that the expression of SRC-1 was regulated by fear conditioning training in a time-dependent manner, and knockdown of SRC-1 impaired contextual fear memory consolidation without affecting innate anxiety or locomotor activity. In addition, hippocampal SRC-1 was also regulated by the retrieval of contextual fear memory, and downregulation of SRC-1 disrupted fear memory reconsolidation. Moreover, knockdown of SRC-1 reversed the increased GluR1 and PSD-95 levels induced by contextual fear memory retrieval.

SIGNIFICANCE

Our data indicate that hippocampal SRC-1 is required for the consolidation and reconsolidation of contextual fear memory, and SRC-1 may be a potential therapeutic target for mental disorders that are involved in hippocampal memory dysfunction.

Development of the HPA axis: where and when do sex differences manifest?

Sex differences in the response to stress contribute to sex differences in somatic, neurological, and psychiatric diseases. Despite a growing literature on the mechanisms that mediate sex differences in the stress response, the ontogeny of these differences has not been comprehensively reviewed. This review focuses on the development of the hypothalamic-pituitary-adrenal (HPA) axis, a key component of the body's response to stress, and examines the critical points of divergence during development between males and females. Insight gained from animal models and clinical studies are presented to fully illustrate the current state of knowledge regarding sex differences in response to stress over development. An appreciation for the developmental timelines of the components of the HPA axis will provide a foundation for future areas of study by highlighting both what is known and calling attention to areas in which sex differences in the development of the HPA axis have been understudied.

Regulation of mRNA expression encoding chaperone and co-chaperone proteins of the glucocorticoid receptor in peripheral blood: association with depressive symptoms during pregnancy

BACKGROUND

Major depressive disorder during pregnancy associates with potentially detrimental consequences for mother and child. The current study examined peripheral blood gene expression as a potential biomarker for prenatal depressive symptoms.

METHOD

Maternal RNA from whole blood, plasma and the Beck Depression Inventory were collected longitudinally from preconception through the third trimester of pregnancy in 106 women with a lifetime history of mood or anxiety disorders. The expression of 16 genes in whole blood involved in glucorticoid receptor (GR) signaling was assessed using real-time polymerase chain reaction. In parallel, plasma concentrations of progesterone, estradiol and cortisol were measured. Finally, we assessed ex vivo GR sensitivity in peripheral blood cells from a subset of 29 women.

RESULTS

mRNA expression of a number of GR-complex regulating genes was up-regulated over pregnancy. Women with depressive symptoms showed significantly smaller increases in mRNA expression of four of these genes - FKBP5, BAG1, NCOA1 and PPID. Ex vivo stimulation assays showed that GR sensitivity diminished with progression of pregnancy and increasing maternal depressive symptoms. Plasma concentrations of gonadal steroids and cortisol did not differ over pregnancy between women with and without clinically relevant depressive symptoms.

CONCLUSIONS

The presence of prenatal depressive symptoms appears to be associated with altered regulation of GR sensitivity. Peripheral expression of GR co-chaperone genes may serve as a biomarker for risk of developing depressive symptoms during pregnancy. The presence of such biomarkers, if confirmed, could be utilized in treatment planning for women with a psychiatric history.

Steroid receptor coactivator-3 differentially regulates the inflammatory response in peritoneal macrophages

Steroid receptor coactivator-3 (SRC-3) is a transcriptional coactivator that plays an important role in the regulation of cytokine mRNA translation. In the present study, SCR-3 gene knockout mice were used to study the effects of SCR-3 on the regulation of the inflammatory response in peritoneal macrophages induced by lipopolysaccharides (LPS). Peritoneal macrophages (PMs) of SRC-3^−/− mice showed a decrease in the release of TNF-α, IL-1β and IL-6, and an increase in the release of IL-10. Furthermore, results of RT-PCR also showed that levels of TNF-α, IL-1β and IL-6 mRNA expression were significantly lower, while the level of IL-10 mRNA expression was higher in the SRC-3^−/− mice, compared to those of wild-type mice, following treatment with LPS (p<0.01). In addition, western blotting revealed that: i) the extent of reduction of the glucocorticoid receptor in PMs from SRC-3^−/− mice was significantly lower than that in wild-type mice (p<0.01); ii) the extent of increase of AP-1 in PMS from SRC-3^−/− mice was significantly lower than that in wild-type mice (p<0.01); iii) the extent of increase of NF-κB p65 in PMs from SRC-3^−/− mice was significantly higher than that in wild-type mice (p<0.01). Collectively, our studies revealed that SRC-3 may play a key role in the maintenance of innate immunity. Furthermore, absence of the SRC-3 protein may result in the partial loss of inflammation and phagocytosis barrier function, including suppression of LPS-induced transcriptional activity, release of TNF-α, IL-1β and IL-6, and obstruction of the function of phagocytes and elimination of bacteria, as well as their production.

Effects of SCR-3 on the immunosuppression accompanied with the systemic inflammatory response syndrome

Steroid receptor coactivator-3 (SRC-3) is a multifunctional protein that plays an important role in mammary gland growth, development, and tumorigenesis. In this study, SCR-3 gene knockout mice were used to study the effects of SCR-3 on the immunosuppression accompanied with systemic inflammatory response syndrome (SIRS). Bacterial clearance assay was performed by blood culture and frozen sections, and the results showed that the absence of SCR-3 protein serious damaged the innate immune system and the body's ability to inactivate or phagocytosis of bacteria was significantly decreased, and the absence of SCR-3 protein also weakened phagocytes' ability to degrade bacteria and their metabolites. Furthermore, animal model of inflammatory reaction was established and the immune function was determined, and the results revealed that SRC-3 protein may play an important role in maintenance of T-cells' immune function, and severe T-cell immune function disorder would be resulted once SRC-3 protein is missing. In addition, the results of our study showed the steady-state of lymphocyte subsets was destroyed after SIRS, leading the suppression of cellular immune function, and the absence of SCR-3 protein may aggravate the suppression of T-lymphocyte function. Therefore, the present study demonstrated that the absence of SCR-3 protein would aggravate immunosuppression. In addition, SRC-3 protein is a significant regulator of infection and inflammation, and SRC-3 protein play an essential role in the development of immunosuppression accompanied with SIRS.

Recruitment of the p160 coactivators by the glucocorticoid receptor: dependence on the promoter context and cell type but not hypoxic conditions

In the nervous system, glucocorticoids exert beneficial or noxious effects, depending on their concentration and time-exposure. They act via the glucocorticoid receptor (GR) which recruits the p160 coactivators (SRC-1, SRC-2 and SRC-3). It was often shown that the three SRCs are interchangeable. The aim of the present study was to evaluate if the GR-SRCs interactions are dependent on several parameters like the target promoter structure, cell type or exogenous stressful parameters like hypoxia. We investigated the GR-SRCs interactions in two glial cells: astrocytes for the central nervous system and Schwann cells for the peripheral nervous system. We have shown by performing functional studies (overexpression and siRNA knock-down) that the recruitment of the three p160 by the GR is promoter-dependent and cell-specific. Moreover, we have shown that hypoxia (5% of oxygen) enhanced GR transactivation in both glial cells. Although hypoxia enhanced GR transactivation, it did not alter the interactions between the GR and the three p160s. Finally, we have shown that the potentiation of GR transactivation by hypoxia is due to an increase of the GR transcripts in Schwann cells but not in astrocytes. Altogether, these results reveal that the p160s are not interchangeable and that their recruitment by the GR is a multiparametric event.

Glucocorticoid regulation of genes in the amiloride-sensitive sodium transport pathway by semicircular canal duct epithelium of neonatal rat

The lumen of the inner ear has an unusually low concentration of endolymphatic Na+, which is important for transduction processes. We have recently shown that glucocorticoid receptors (GR) stimulate absorption of Na+by semicircular canal duct (SCCD) epithelia. In the present study, we sought to determine the presence of genes involved in the control of the amiloride-sensitive Na+transport pathway in rat SCCD epithelia and whether their level of expression was regulated by glucocorticoids using quantitative real-time RT-PCR. Transcripts were present for α-, β-, and γ-subunits of the epithelial sodium channel (ENaC); the α1-, α3-, β1-, and β3-isoforms of Na+-K+-ATPase; inwardly rectifying potassium channels [IC50of short circuit current ( Isc) for Ba2+: 210 μM] Kir2.1, Kir2.2, Kir2.3, Kir2.4, Kir3.1, Kir3.3, Kir4.1, Kir4.2, Kir5.1, and Kir7.1; sulfonyl urea receptor 1 (SUR1); GR; mineralocorticoid receptor (MR); 11β-hydroxysteroid dehydrogenase (11β-HSD) types 1 and 2; serum- and glucocorticoid-regulated kinase 1 (Sgk1); and neural precursor cell-expressed developmentally downregulated 4-2 (Nedd4-2). On the other hand, transcripts for the α4-subunit of Na+-K+-ATPase, Kir1.1, Kir3.2, Kir3.4, Kir6.1, Kir6.2, and SUR2 were found to be absent, and Iscwas not inhibited by glibenclamide. Dexamethasone (100 nM for 24 h) not only upregulated the transcript expression of α-ENaC (∼4-fold), β2-subunit (∼2-fold) and β3-subunit (∼8-fold) of Na+-K+-ATPase, Kir2.1 (∼5-fold), Kir2.2 (∼9-fold), Kir2.4 (∼3-fold), Kir3.1 (∼ 3- fold), Kir3.3 (∼2-fold), Kir4.2 (∼3-fold ), Kir7.1 (∼2-fold), Sgk1 (∼4-fold), and Nedd4-2 (∼2-fold) but also downregulated GR (∼3-fold) and 11β-HSD1 (∼2-fold). Expression of GR and 11β-HSD1 was higher than MR and 11β-HSD2 in the absence of dexamethasone. Dexamethasone altered transcript expression levels (α-ENaC and Sgk1) by activation of GR but not MR. Proteins were present for the α-, β-, and γ-subunits of ENaC and Sgk1, and expression of α- and γ-ENaC was upregulated by dexamethasone. These findings are consistent with the genomic stimulation by glucocorticoids of Na+absorption by SCCD and provide an understanding of the therapeutic action of glucocorticoids in the treatment of Meniere's disease.

Expression of Tip60, an androgen receptor coactivator, and its role in prostate cancer development

Prostate cancer (CaP) is initially androgen sensitive and responsive to hormone ablation therapy. However, cancer growth recurs despite androgen deprivation in the majority of cases of advanced disease. The molecular basis of this progression still remains unknown. The significance of androgen receptor (AR) coactivator proteins in this androgen-dependent malignancy is only beginning to emerge. In the present study, we examined the role of Tat interactive protein, 60 kDa (Tip60), an AR coactivator, in CaP progression. In hormone refractory CaP biopsies, we observed a nuclear accumulation of Tip60 expression in contrast to a more diffuse distribution pattern observed in benign prostate hyperplasia and primary CaP. Furthermore, in both the prostate xenograft model CWR22 and the LNCaP CaP cell line, we observed that androgen withdrawal promoted upregulation of Tip60 as well as nuclear accumulation. In contrast, androgen exposure resulted in decreased Tip60 expression that was more closely linked to a cytoplasmic presence. Chromatin immunoprecipitation analysis revealed Tip60's recruitment to the PSA gene promoter in both androgen-dependent and -independent cell lines. Thus, in vitro and in vivo data support a possible role for Tip60 in the molecular pathway leading to the development of androgen-independent CaP following long-term androgen deprivation therapy.

Cell-specific regulation of apoptosis by glucocorticoids: implication to their anti-inflammatory action

Glucocorticoids play a major role in attenuation of the inflammatory response. These steroid hormones are able to induce apoptosis in cells of the hematopoietic system such as monocytes, macrophages, and T lymphocytes that are involved in the inflammation reaction. In contrast, it was discovered recently that in glandular cells such as the mammary gland epithelia, hepatocytes, ovarian follicular cells, and in fibroblasts glucocorticoids protect against apoptotic signals evoked by cytokines, cAMP, tumor suppressors, and death genes. The anti-apoptotic effect of glucocorticoids is exerted by modulation of several survival genes such as Bcl-2, Bcl-x(L), and NFkB, in a cell-specific manner. Moreover, upregulation or downregulation of the same gene product can occur in a cell-dependent manner following stimulation by glucocorticoids. This phenomenon is probably due to composite regulatory cross-talk among multiple nuclear coactivators or corepressors, which mediate the transcription regulation of the genes, by their interaction with the glucocorticoid receptor. These observations suggest that the anti-inflammatory action of glucocorticoids is exerted by two complementary mechanisms: on one hand, they induce death of the cells that provoke the inflammation, and on the other hand they protect the resident cells of the inflamed tissue by arresting apoptotic signals. Moreover, the complementary action of glucocorticoids provides a new insight to the therapeutic potential of these hormones.

Effect of chirality at C-20 of methyl 11beta,17alpha,20-trihydroxy-3-oxo-1,4-pregnadien-21-oate derivatives on antiinflammatory activity

In an effort to determine the C-20 chirality effect on the antiinflammatory activity of 17beta-glycolate esters, methyl 11beta,17alpha,20-trihydroxy-3-oxo-1,4-pregnadien-21-oate and its 9alpha-fluoro analog, their acetonide and their carbonate derivatives were synthesized and evaluated. The agents were tested for their binding potency to the macrophage glucocorticoid receptor, and their effect on LPS-induced nitric oxide generation in RAW 264.7 cells. The acetonide derivatives showed the highest binding affinity while the triols and carbonates bound rather poorly to the receptors. With the exception of the triols, the alpha-isomer in each pair of the agents exhibited higher binding affinity to the receptor than its corresponding beta-isomer, clearly indicating that C-20 chirality has a significant effect on antiinflammatory activity. In addition, the alpha-isomers of the acetonides showed substantially higher binding affinity than the parent compound, prednisolone. In contrast to the high binding activity exhibited by some of the acetonides, all of the agents showed weak inhibitory effect on NO generation. Metabolic inactivation during assessment of NO inhibition may play a role in the divergence noted between receptor affinity and the measured biologic activity resulting from the binding.