Identification of a glucocorticoid response element in the 3'-flanking region of the human Dexras1 gene

Acute stress response on Atlantic salmon: a time-course study of the effects on plasma metabolites, mucus cortisol levels, and head kidney transcriptome profile

Farmed Atlantic salmon (Salmo salar) welfare and performance can be strongly influenced by stress episodes caused by handling during farming practices. To better understand the changes occurring after an acute stress response, we exposed a group of Atlantic salmon parr to an acute stressor, which involved netting and transferring fish to several new holding tanks. We describe a time-course response to stress by sampling parr in groups before (T0) and 10, 20, 30, 45, 60, 120, 240, 300, and 330 min post-stress. A subgroup of fish was also subjected to the same stressor for a second time to assess their capacity to respond to the same challenge again within a short timeframe (ReStressed). Fish plasma was assessed for adrenocorticotropic hormone (ACTH), cortisol, and ions levels. Mucus cortisol levels were analyzed and compared with the plasma cortisol levels. At 5 selected time points (T0, 60, 90, 120, 240, and ReStressed), we compared the head kidney transcriptome profile of 10 fish per time point. The considerably delayed increase of ACTH in the plasma (60 min post-stress), and the earlier rise of cortisol levels (10 min post-stress), suggests that cortisol release could be triggered by more rapidly responding factors, such as the sympathetic system. This hypothesis may be supported by a high upregulation of several genes involved in synaptic triggering, observed both during the first and the second stress episodes. Furthermore, while the transcriptome profile showed few changes at 60 min post-stress, expression of genes in several immune-related pathways increased markedly with each successive time point, demonstrating the role of the immune system in fish coping capacity. Although many of the genes discussed in this paper are still poorly characterized, this study provides new insights regarding the mechanisms occurring during the stress response of salmon parr and may form the basis for a useful guideline on timing of sampling protocols.

Histone methyltransferase KMT2D contributes to the protection of myocardial ischemic injury

Histone H3 lysine 4 (H3K4) methyltransferase 2D (KMT2D) plays an important role in cell development in early life. However, the function of KMT2D in adult cells such as cardiomyocytes or neurons has not been reported. In this study, cardiomyocyte-specific KMT2D knockout (KMT2D-cKO) and control (KMT2D-Ctl) mice were exposed to sham or myocardial ischemia (MI) surgery. Depletion of KMT2D aggravated the ischemic area, led to the increased mortality (26.5% in KMT2D-cKO vs 12.5% in KMT2D-Ctl) of the mice, and weakened the left ventricular systolic function. RNA-seq analysis in cardiac tissues identified genes whose expression was changed by MI and KMT2D deletion. Combined with the genome-wide association study (GWAS) analysis, cardiac disease-associated genes Rasd1, Thsd7a, Ednra, and Tns1 were identified. The expression of the Rasd1 was significantly decreased by MI or the loss of KMT2D in vivo. Meanwhile, ChIP assays demonstrated that either MI or loss of KMT2D attenuated monomethylated H3K4 (H3K4me1) enrichment on the enhancer of Rasd1. By generating a KMT2D knockout (H9C2-KO) H9C2 monoclone, we verified that the expression of Rasd1 was controlled by KMT2D, and the expression of Rasd1 was decreased by serum starvation but not low-(O₂) treatment in H9C2 cells. KMT2D has a protective effect on ischemic myocardium by regulating cardiac disease-associated genes including Rasd1. KMT2D is required for the H3K4me1 deposition on the enhancer of Rasd1. Our data for the first time suggest that KMT2D-mediated Rasd1 expression may play an important protective effect on adult cells during nutritional deficiency caused by ischemic injury.

Expression of Rasd1 in mouse endocrine pituitary cells and its response to dexamethasone

Dexamethasone-induced Ras-related protein 1 (Rasd1) is a member of the Ras superfamily of monomeric G proteins that have a regulatory function in signal transduction. Rasd1, also known as Dexras1 or AGS1, is rapidly induced by dexamethasone (Dex). While prior data indicates that Rasd1 is highly expressed in the pituitary and that the gene may function in regulation of corticotroph activity, its exact cellular localization in this tissue has not been delineated. Nor has it been determined which endocrine pituitary cell type(s) are responsive to Dex-induced expression of Rasd1. We hypothesized that Rasd1 is primarily localized in corticotrophs and furthermore, that its expression in these cells would be upregulated in response to exogenous Dex administration. Rasd1 expression in each pituitary cell type both under basal conditions and 1-hour post Dex treatment were examined in adult male mice. While a proportion of all endocrine pituitary cell types expressed Rasd1, a majority of corticotrophs and thyrotrophs expressed Rasd1 under basal condition. In vehicle treated animals, approximately 50-60% of corticotrophs and thyrotrophs cells expressed Rasd1 while the gene was detected in only 15-30% of lactotrophs, somatotrophs, and gonadotrophs. In Dex treated animals, Rasd1 expression was significantly increased in corticotrophs, somatotrophs, lactotrophs, and gonadotrophs but not thyrotrophs. In Dex treated animals, Rasd1 was detected in 80-95% of gonadotrophs and corticotrophs. In contrast, Dex treatment increased Rasd1 expression to a lesser extent (55-60%) in somatotrophs and lactotrophs. Corticotrophs of the pars intermedia, which lack glucocorticoid receptors, failed to display increased Rasd1 expression in Dex treated animals. Rasd1 is highly expressed in corticotrophs under basal conditions and is further increased after Dex treatment, further supporting its role in glucocorticoid negative feedback. In addition, the presence and Dex-induced expression of Rasd1 in endocrine pituitary cell types, other than corticotrophs, may implicate Rasd1 in novel pituitary functions.

Rasd1, a small G protein with a big role in the hypothalamic response to neuronal activation

Background

Rasd1 is a member of the Ras family of monomeric G proteins that was first identified as a dexamethasone inducible gene in the pituitary corticotroph cell line AtT20. Using microarrays we previously identified increased Rasd1 mRNA expression in the rat supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus in response to increased plasma osmolality provoked by fluid deprivation and salt loading. RASD1 has been shown to inhibit adenylyl cyclase activity in vitro resulting in the inhibition of the cAMP-PKA-CREB signaling pathway. Therefore, we tested the hypothesis that RASD1 may inhibit cAMP stimulated gene expression in the brain.

Results

We show that Rasd1 is expressed in vasopressin neurons of the PVN and SON, within which mRNA levels are induced by hyperosmotic cues. Dexamethasone treatment of AtT20 cells decreased forskolin stimulation of c-Fos, Nr4a1 and phosphorylated CREB expression, effects that were mimicked by overexpression of Rasd1, and inhibited by knockdown of Rasd1. These effects were dependent upon isoprenylation, as both farnesyltransferase inhibitor FTI-277 and CAAX box deletion prevented Rasd1 inhibition of cAMP-induced gene expression. Injection of lentiviral vector into rat SON expressing Rasd1 diminished, whereas CAAX mutant increased, cAMP inducible genes in response to osmotic stress.

Conclusions

We have identified two mechanisms of Rasd1 induction in the hypothalamus, one by elevated glucocorticoids in response to stress, and one in response to increased plasma osmolality resulting from osmotic stress. We propose that the abundance of RASD1 in vasopressin expressing neurons, based on its inhibitory actions on CREB phosphorylation, is an important mechanism for controlling the transcriptional responses to stressors in both the PVN and SON. These effects likely occur through modulation of cAMP-PKA-CREB signaling pathway in the brain.

Accessory proteins for heterotrimeric G-proteins in the kidney

Heterotrimeric G-proteins play a fundamentally important role in regulating signal transduction pathways in the kidney. Accessory proteins are being identified as direct binding partners for heterotrimeric G-protein α or βγ subunits to promote more diverse mechanisms by which G-protein signaling is controlled. In some instances, accessory proteins can modulate the signaling magnitude, localization, and duration following the activation of cell membrane-associated receptors. Alternatively, accessory proteins complexed with their G-protein α or βγ subunits can promote non-canonical models of signaling activity within the cell. In this review, we will highlight the expression profile, localization and functional importance of these newly identified accessory proteins to control the function of select G-protein subunits under normal and various disease conditions observed in the kidney.

The Roles of Rasd1 small G proteins and leptin in the activation of TRPC4 transient receptor potential channels

TRPC4 is important regulators of electrical excitability in gastrointestinal myocytes, pancreatic β-cells and neurons. Much is known regarding the assembly and function of these channels including TRPC1 as a homotetramer or a heteromultimer and the roles that their interacting proteins play in controlling these events. Further, they are one of the best-studied targets of G protein-coupled receptors and growth factors in general and Gαi/o and Gαq protein coupled receptor or epidermal growth factor and leptin in particular. However, our understanding of the roles of small G proteins and leptin on TRPC4 channels is still rudimentary. We discuss potential roles for Rasd1 small G protein and leptin in channel activation in addition to their known role in cellular signaling.

Activators of G protein signaling in the kidney

Heterotrimeric G proteins play a crucial role in regulating signal processing to maintain normal cellular homeostasis, and subtle perturbations in its activity can potentially lead to the pathogenesis of renal disorders or diseases. Cell-surface receptors and accessory proteins, which normally modify and organize the coupling of individual G protein subunits, contribute to the regulation of heterotrimeric G protein activity and their convergence and/or divergence of downstream signaling initiated by effector systems. Activators of G protein signaling (AGS) are a family of accessory proteins that intervene at multiple distinct points during the activation-inactivation cycle of G proteins, even in the absence of receptor stimulation. Perturbations in the expression of individual AGS proteins have been reported to modulate signal transduction pathways in a wide array of diseases and disorders within the brain, heart, immune system, and more recently, the kidney. This review will provide an overview of the expression profile, localization, and putative biologic role of the AGS family in the context of normal and diseased states of the kidney.

Localization and expression profile of Group I and II Activators of G-protein Signaling in the kidney

Activators of G-protein Signaling (AGS) are a family of accessory proteins that were discovered as modulators of heterotrimeric G-protein subunits. The primary aim of the present study was to localize Group I and II AGS proteins and determine the renal expression profile using immunohistochemistry and quantitative RT-PCR, respectively, during normal and injured states of the kidney. Group I AGS1 was found to be predominantly localized to the proximal tubule, Group II AGS3 and AGS5 were exclusively localized to the distal tubular segments, and Group II AGS6 was ubiquitously expressed in every nephron segment of the rodent kidney. In rat kidneys following ischemia-reperfusion injury (IRI), Group I AGS1 mRNA was dramatically increased after 24 h by fivefold (P < 0.05), whereas Group II AGS3 and AGS4 mRNA was significantly decreased at the same time point (P < 0.05). No significant change in the transcript levels were detected at other time points for any of the AGS genes between control and IRI groups. In polycystic diseased kidneys, mRNA levels for AGS3, AGS4 and AGS6 was significantly increased (P < 0.05) by 75-80 % in PCK rat kidneys. The identification of Group I and II AGS mRNA and protein in the kidney may provide insight into the potential mechanism of action during normal and varying states of renal disease or injury.

Small G Proteins Dexras1 and RHES and Their Role in Pathophysiological Processes

Dexras1 and RHES, monomeric G proteins, are members of small GTPase family that are involved in modulation of pathophysiological processes. Dexras1 and RHES levels are modulated by hormones and Dexras1 expression undergoes circadian fluctuations. Both these GTPases are capable of modulating calcium ion channels which in turn can potentially modulate neurosecretion/hormonal release. These two GTPases have been reported to prevent the aberrant cell growth and induce apoptosis in cell lines. Present review focuses on role of these two monomeric GTPases and summarizes their role in pathophysiological processes.

The regulation of Rasd1 expression by glucocorticoids and prolactin controls peripartum maternal insulin secretion

The transition from gestation to lactation is characterized by a robust adaptation of maternal pancreatic β-cells. Consistent with the loss of β-cell mass, glucose-induced insulin secretion is down-regulated in the islets of early lactating dams. Extensive experimental evidence has demonstrated that the surge of prolactin is responsible for the morphofunctional remodeling of the maternal endocrine pancreas during pregnancy, but the precise molecular mechanisms by which this phenotype is rapidly reversed after delivery are not completely understood. This study investigated whether glucocorticoid-regulated expression of Rasd1/Dexras, a small inhibitory G protein, is involved in this physiological plasticity. Immunofluorescent staining demonstrated that Rasd1 is localized within pancreatic β-cells. Rasd1 expression in insulin-secreting cells was increased by dexamethasone and decreased by prolactin. In vivo data confirmed that Rasd1 expression is decreased in islets from pregnant rats and increased in islets from lactating mothers. Knockdown of Rasd1 abolished the inhibitory effects of dexamethasone on insulin secretion and the protein kinase A, protein kinase C, and ERK1/2 pathways. Chromatin immunoprecipitation experiments revealed that glucocorticoid receptor (GR) and signal transducer and activator of transcription 5b (STAT5b) cooperatively mediate glucocorticoid-induced Rasd1 expression in islets. Prolactin inhibited the stimulatory effect of GR/STAT5b complex on Rasd1 transcription. Overall, our data indicate that the stimulation of Rasd1 expression by glucocorticoid at the end of pregnancy reverses the increased insulin secretion that occurs during pregnancy. Prolactin negatively regulates this pathway by inhibiting GR/STAT5b transcriptional activity on the Rasd1 gene.

Amphetamine up-regulates activator of G-protein signaling 1 mRNA and protein levels in rat frontal cortex: the role of dopamine and glucocorticoid receptors

Acute and chronic exposure to psychostimulants results in altered function of G-protein-coupled receptors in the forebrain. It is believed that neuroadaptations in G-protein signaling contribute to behavioral sensitivity to psychostimulants that persists over a prolonged drug-free period. Proteins termed activators of G-protein signaling (AGS) have been characterized as potent modulators of both receptor-dependent and receptor-independent G-protein signaling. Nevertheless, the regulation of AGS gene and protein expression by psychostimulants remains poorly understood. In the present study, we investigated amphetamine (AMPH)-induced changes in expression patterns of several forebrain-enriched AGS proteins. A single exposure to AMPH (2.5 mg/kg i.p.) selectively induced gene expression of AGS1, but not Rhes or AGS3 proteins, in the rat prefrontal cortex (PFC) as measured 3 h later. Induction of AGS1 mRNA in the PFC by acute AMPH was transient and dose-dependent. Even repeated treatment with AMPH for 5 days did not produce lasting changes in AGS1 mRNA and protein levels in the PFC as measured 3 weeks post treatment. However, at this time point, a low dose AMPH challenge (1 mg/kg i.p.) induced a robust behavioral response and upregulated AGS1 expression in the PFC selectively in animals with an AMPH history. The effects of AMPH on AGS1 expression in the PFC were blocked by a D2, but not D1, dopamine receptor antagonist and partially by a glucocorticoid receptor antagonist. Collectively, the present study suggests that (1) AGS1 represents a regulator of G-protein signaling that is rapidly inducible by AMPH in the frontal cortex, (2) AGS1 regulation in the PFC parallels behavioral activation by acute AMPH in drug-naive animals and hypersensitivity to AMPH challenge in sensitized animals, and (3) D2 dopamine and glucocorticoid receptors regulate AMPH effects on AGS1 in the PFC. Changes in AGS1 levels in the PFC may result in abnormal receptor-to-G-protein coupling that alters cortical sensitivity to psychostimulants.

Dex-ras1 and serum- and glucocorticoid-inducible protein kinase 1: regulation of expression by dexamethasone in HEK293 cells

The molecular and cellular basis of the psychotropic actions of adrenal corticosteroids is poorly understood. Previously, we reported that modulation of large conductance Ca2+-activated potassium channel (BK-channel) function by glucocorticoids can be recapitulated in human embryonic kidney293 (HEK293) cells (J Physiol 537:57, 2001). In the present paper, we examined the effect of dexamethasone on the expression of candidate mediator proteins of glucocorticoid action, dex-ras1 and serum and glucocorticoid inducible protein kinase 1 (SGK), in HEK293 cells. Dex-ras1 mRNA was readily detectable under basal conditions however, no changes of dex-ras1 mRNA expression occurred upon exposure to 100 nM of dexamethasone for 2 h. In contrast, a 2.5-fold increase of SGK mRNA was found under similar conditions. Total levels of cellular SGK protein were unaltered upon exposure to dexamethasone, but a marked increase of SGK in a Triton-X100 insoluble fraction was observed. BK-channel alpha-subunits could not be co-immunoprecipitated with SGK. In summary, SGK, but not dex-ras1, mRNA is rapidly induced by glucocorticoid stimulation in HEK293 cells. However, there appears to be no direct protein-protein interaction between SGK and BK-channel alpha-subunits.

Mechanistic pathways and biological roles for receptor-independent activators of G-protein signaling

Signal processing via heterotrimeric G-proteins in response to cell surface receptors is a central and much investigated aspect of how cells integrate cellular stimuli to produce coordinated biological responses. The system is a target of numerous therapeutic agents and plays an important role in adaptive processes of organs; aberrant processing of signals through these transducing systems is a component of various disease states. In addition to G-protein coupled receptor (GPCR)-mediated activation of G-protein signaling, nature has evolved creative ways to manipulate and utilize the Galphabetagamma heterotrimer or Galpha and Gbetagamma subunits independent of the cell surface receptor stimuli. In such situations, the G-protein subunits (Galpha and Gbetagamma) may actually be complexed with alternative binding partners independent of the typical heterotrimeric Galphabetagamma. Such regulatory accessory proteins include the family of regulator of G-protein signaling (RGS) proteins that accelerate the GTPase activity of Galpha and various entities that influence nucleotide binding properties and/or subunit interaction. The latter group of proteins includes receptor-independent activators of G-protein signaling (AGS) proteins that play surprising roles in signal processing. This review provides an overview of our current knowledge regarding AGS proteins. AGS proteins are indicative of a growing number of accessory proteins that influence signal propagation, facilitate cross talk between various types of signaling pathways, and provide a platform for diverse functions of both the heterotrimeric Galphabetagamma and the individual Galpha and Gbetagamma subunits.

Non-receptor activators of heterotrimeric G-protein signaling (AGS proteins)

G-protein coupled receptor (GPCR) signaling represents one of the most conserved and ubiquitous means in mammalian cells for transferring information across the plasma membrane to the intracellular environment. Heterotrimeric G-protein subunits play key roles in transducing these signals, and intracellular regulators influencing the activation state and interaction of these subunits regulate the extent and duration of GPCR signaling. One class of intracellular regulator, the non-receptor activators of G-protein signaling (or AGS proteins), are the major focus of this review. AGS proteins provide a basis for understanding the function of heterotrimeric G-proteins in both GPCR-driven and GPCR independent cellular signaling pathways.

Activation of heterotrimeric G-proteins independent of a G-protein coupled receptor and the implications for signal processing

Heterotrimeric G-proteins are key transducers for signal transfer from outside the cell, mediating signals emanating from cell-surface G-protein coupled receptors (GPCR). Many, if not all, subtypes of heterotrimeric G-proteins are also regulated by accessory proteins that influence guanine nucleotide binding, guanosine triphosphate (GTP) hydrolysis, or subunit interactions. One subgroup of such accessory proteins (activators of G-protein signaling; AGS proteins) refer to a functionally defined group of proteins that activate selected G-protein signaring systems in the absence of classical G-protein coupled receptors. AGS and related proteins provide unexpected insights into the regulation of the G-protein activation-deactivation cycle. Different AGS proteins function as guanine nucleotide exchange factors or guanine nucleotide dissociation inhibitors and may also influence subunit interactions by interaction with GBgamma. These proteins play important roles in the generation or positioning of signaling complexes and of the regulation of GPCR signaling, and as alternative binding partners for G-protein subunits. Perhaps of even broader impact is the discovery that AGS proteins provide a foundation for the concept that heterotrimeric G-protein subunits are processing signals within the cell involving intrinsic cues that do not involve the classical signal input from a cell surface GPCR.

The properties of CpG islands in the putative promoter regions of human immunoglobulin (Ig) genes

CpG island is a GC-rich motif occurred in gene promoter region, which can play important roles in gene silencing and imprinting. Here, we present a set of discriminant functions that can recognize the structural and compositional features of CpG islands in the putative promoter regions (PPRs) of human and mouse immunoglobulin (Ig) genes. We showed that the PPRs of both human and mouse Ig genes irrespective of gene chromosomal localization are apparently CpG island poor, with a low percentage of the CpG islands overlapped with the transcription start site (TSS). The human Ig genes that have CpG islands in the PPRs show a very narrow range of CpG densities. 47% of the Ig genes fall in the range of 3.5-4 CpGs/100 bp. In contrast, the non-Ig genes examined have a wide range of the density of CpG island, with 10.5% having the density of 8.1-15 CpGs/100 bp. Meantime, five patterns of the CpG distributions within the CpG islands have been classified: Pat A, B, C, D, and E. 21.6% and 10.8% of the Ig genes fall into the Pat B and Pat D groups, respectively, which were significantly higher than the non-Ig genes examined (8.2% and 3.8%). Moreover, the length of CpG islands is shorter in human Ig genes than in non-Ig genes but is much longer than in mouse orthologues. These findings provide a clear picture of non-neutral and nonrandom occurrence of the CpG islands in the PPRs of human and mouse Ig genes, which facilitate rational recommendations regarding their nomenclature.

Intronic hormone response elements mediate regulation of FKBP5 by progestins and glucocorticoids

Expression of FKBP51, a large molecular weight immunophilin, is strongly enhanced by glucocorticoids, progestins, and androgens. However, the activity of a 3.4-kb fragment of the FKBP51 gene (FKBP5) promoter was only weakly increased by progestin and we show here that it is unresponsive to glucocorticoids and androgens. The entire FKBP5 was scanned for consensus hormone response elements (HREs) using MatInspector. We found that 2 regions of intron E, which are conserved in rat and mouse FKBP5, contain HRE-like sequences with high match scores. Deoxyribonucleic acid fragments (approximately 1 kb in length) containing these regions were amplified and tested in reporter gene assays for steroid responsiveness. One region of intron E of FKBP5 (pIE2) conferred both glucocorticoid and progestin responsiveness to 2 heterologous reporter genes, whereas the other, less-conserved region of intron E (pIE1) was responsive only to progestins. The inclusion of pIE1 upstream of pIE2 (pIE1IE2) enhanced progestin but not glucocorticoid responsiveness. None of the constructs containing intronic sequences was responsive to androgens. Mutation of the putative HREs within pIE1 and pIE2 eliminated hormone responsiveness. Electrophoretic mobility shift assays demonstrated that progesterone receptors (PR) bound to the HRE in pIE1, whereas both PR and glucocorticoid receptors interacted with the HRE in pIE2. These data suggest that distal intronic elements significantly contribute to transcriptional regulation of FKBP5 by glucocorticoids and progestins.

The Ras-related protein AGS1/RASD1 suppresses cell growth

AGS1/RASD1 is a Ras-related protein identified as a dexamethasone-inducible cDNA and as a signal regulator in various functional and protein-interaction screens. As an initial approach to define the role of AGS1/RASD1 as a Ras-family member, we determined its influence on cell growth/survival. In clonogenic assays with NIH-3T3 murine fibroblast cells, the MCF-7 human breast cancer cell line and the human lung adenocarcinoma cell line A549, AGS1/RASD1 markedly diminished the number of G418-resistant colonies, whereas the Ras subgroup member K-Ras was without effect. A549 cell infection with adenovirus engineered to express AGS1/RASD1 (Ad.AGS1) inhibited log phase growth in vitro and increased the percentage of cells undergoing apoptosis. The anti-growth action was also observed in vivo as the expression of AGS1/RASD1 inhibited the subcutaneous tumor growth of A549 cells in athymic nude mice. These data indicate that AGS1/RASD1, a member of the Ras superfamily of small G-proteins that often promotes cell growth and tumor expansion, plays an active role in preventing aberrant cell growth.