Corticosterone-induced rapid phosphorylation of p38 and JNK mitogen-activated protein kinases in PC12 cells

Protective effect of hygrolansamycin C against corticosterone-induced toxicity and oxidative stress-mediated via autophagy and the MAPK signaling pathway

BACKGROUND

Excessive stress, a major problem in modern societies, affects people of all ages worldwide. Corticosterone is one of the most abundant hormones secreted during stressful conditions and is associated with various dysfunctions in the body. In particular, we aimed to investigate the protective effects of hygrolansamycin C (HYGC) against corticosterone-induced cellular stress, a manifestation of excessive stress prevalent in contemporary societies.

METHODS

We isolated HYGC from Streptomyces sp. KCB17JA11 and subjected PC12 cells to corticosterone-induced stress. The effects of HYGC were assessed by measuring autophagy and the expression of mitogen-activated protein kinase (MAPK) phosphorylation-related genes. We used established cellular and molecular techniques to analyze protein levels and pathways.

RESULTS

HYGC effectively protected cells against corticosterone-induced injury. Specifically, it significantly reduced corticosterone-induced oxidative stress and inhibited the expression of autophagy-related proteins induced by corticosterone, which provided mechanistic insight into the protective effects of HYGC. At the signaling level, HYGC suppressed c-Jun N-terminal kinase and extracellular signal-regulated kinase phosphorylation and p38 activation.

CONCLUSIONS

HYGC is a promising candidate to counteract corticosterone-induced apoptosis and oxidative stress. Autophagy and MAPK pathway inhibition contribute to the protective effects of HYGC. Our findings highlight the potential of HYGC as a therapeutic agent for stress-related disorders and serve as a stepping stone for further exploration and development of stress management strategies.

Treating the Side Effects of Exogenous Glucocorticoids; Can We Separate the Good From the Bad?

It is estimated that 2% to 3% of the population are currently prescribed systemic or topical glucocorticoid treatment. The potent anti-inflammatory action of glucocorticoids to deliver therapeutic benefit is not in doubt. However, the side effects associated with their use, including central weight gain, hypertension, insulin resistance, type 2 diabetes (T2D), and osteoporosis, often collectively termed iatrogenic Cushing's syndrome, are associated with a significant health and economic burden. The precise cellular mechanisms underpinning the differential action of glucocorticoids to drive the desirable and undesirable effects are still not completely understood. Faced with the unmet clinical need to limit glucocorticoid-induced adverse effects alongside ensuring the preservation of anti-inflammatory actions, several strategies have been pursued. The coprescription of existing licensed drugs to treat incident adverse effects can be effective, but data examining the prevention of adverse effects are limited. Novel selective glucocorticoid receptor agonists and selective glucocorticoid receptor modulators have been designed that aim to specifically and selectively activate anti-inflammatory responses based upon their interaction with the glucocorticoid receptor. Several of these compounds are currently in clinical trials to evaluate their efficacy. More recently, strategies exploiting tissue-specific glucocorticoid metabolism through the isoforms of 11β-hydroxysteroid dehydrogenase has shown early potential, although data from clinical trials are limited. The aim of any treatment is to maximize benefit while minimizing risk, and within this review we define the adverse effect profile associated with glucocorticoid use and evaluate current and developing strategies that aim to limit side effects but preserve desirable therapeutic efficacy.

Role of Prednisolone in Platelet Activation by Inhibiting TxA2 Generation through the Regulation of cPLA2 Phosphorylation

Glucocorticoids have been commonly used in the treatment of inflammation and immune-mediated diseases in human beings and small animals such as cats and dogs. However, excessive use can lead to Cushing's syndrome along with several thrombotic and cardiovascular diseases. Although it is well-known that glucocorticoids exert a significant effect on coagulation, the effect of cortisol on platelet function is much less clear. Thus, we aimed to study the effects of prednisolone, one of the commonly used glucocorticoids, on the regulation of platelet function using murine platelets. We first evaluated the concentration-dependent effect of prednisolone on 2-MeSADP-induced platelet function and found that the 2-MeSADP-induced secondary wave of aggregation and dense granule secretion were completely inhibited from 500 nM prednisolone. Since 2-MeSADP-induced secretion and the resultant secondary wave of aggregation are mediated by TxA₂ generation, this result suggested a role of prednisolone in platelet TxA₂ generation. Consistently, prednisolone did not affect the 2-MeSADP-induced aggregation in aspirinated platelets, where the secondary wave of aggregation and secretion were blocked by eliminating the contribution of TxA₂ generation by aspirin. In addition, thrombin-induced platelet aggregation and secretion were inhibited in the presence of prednisolone by inhibiting the positive-feedback effect of TxA₂ generation on platelet function. Furthermore, prednisolone completely inhibited 2-MeSADP-induced TxA₂ generation, confirming the role of prednisolone in TxA₂ generation. Finally, Western blot analysis revealed that prednisolone significantly inhibited 2-MeSADP-induced cytosolic phospholipase A₂ (cPLA₂) and ERK phosphorylation in non-aspirinated platelets, while only cPLA₂ phosphorylation, but not ERK phosphorylation, was significantly inhibited by prednisolone in aspirinated platelets. In conclusion, prednisolone affects platelet function by the inhibition of TxA₂ generation through the regulation of cPLA₂ phosphorylation, thereby shedding light on its clinical characterization and treatment efficacy in dogs with hypercortisolism in the future.

Crosstalk between p38 MAPK and GR Signaling

The p38 MAPK is a signaling pathway important for cells to respond to environmental and intracellular stress. Upon activation, the p38 kinase phosphorylates downstream effectors, which control the inflammatory response and coordinate fundamental cellular processes such as proliferation, apoptosis, and differentiation. Dysregulation of this signaling pathway has been linked to inflammatory diseases and cancer. Secretion of glucocorticoids (GCs) is a classical endocrine response to stress. The glucocorticoid receptor (GR) is the primary effector of GCs and plays an important role in the regulation of cell metabolism and immune response by influencing gene expression in response to hormone-dependent activation. Its ligands, the GCs or steroids, in natural or synthetic variation, are used as standard therapy for anti-inflammatory treatment, severe asthma, autoimmune diseases, and several types of cancer. Several years ago, the GR was identified as one of the downstream targets of p38, and, at the same time, it was shown that glucocorticoids could influence p38 signaling. In this review, we discuss the role of the crosstalk between the p38 and GR in the regulation of gene expression in response to steroids and comprehend the importance and potential of this interplay in future clinical applications.

Glucocorticoid Receptor Signaling in Diabetes

Stress and depression increase the risk of Type 2 Diabetes (T2D) development. Evidence demonstrates that the Glucocorticoid (GC) negative feedback is impaired (GC resistance) in T2D patients resulting in Hypothalamic-Pituitary-Adrenal (HPA) axis hyperactivity and hypercortisolism. High GCs, in turn, activate multiple aspects of glucose homeostasis in peripheral tissues leading to hyperglycemia. Elucidation of the underlying molecular mechanisms revealed that Glucocorticoid Receptor (GR) mediates the GC-induced dysregulation of glucose production, uptake and insulin signaling in GC-sensitive peripheral tissues, such as liver, skeletal muscle, adipose tissue, and pancreas. In contrast to increased GR peripheral sensitivity, an impaired GR signaling in Peripheral Blood Mononuclear Cells (PBMCs) of T2D patients, associated with hyperglycemia, hyperlipidemia, and increased inflammation, has been shown. Given that GR changes in immune cells parallel those in brain, the above data implicate that a reduced brain GR function may be the biological link among stress, HPA hyperactivity, hypercortisolism and hyperglycemia. GR polymorphisms have also been associated with metabolic disturbances in T2D while dysregulation of micro-RNAs—known to target GR mRNA—has been described. Collectively, GR has a crucial role in T2D, acting in a cell-type and context-specific manner, leading to either GC sensitivity or GC resistance. Selective modulation of GR signaling in T2D therapy warrants further investigation.

Experimental Manipulation of Corticosterone Does Not Affect Venom Composition or Functional Activity in Free-Ranging Rattlesnakes

AbstractVenom is an integral feeding trait in many animal species. Although venom often varies ontogenetically, little is known about the proximate physiological mediators of venom variation within individuals. The glucocorticoid hormone corticosterone (CORT) can alter the transcription and activation of proteins, including homologues of snake venom components such as snake venom metalloproteinases (SVMPs) and phospholipase A₂ (PLA₂). CORT is endogenously produced by snakes, varies seasonally and also in response to stress, and is a candidate endogenous mediator of changes in venom composition and functional activity. Here, we tested the hypothesis that CORT induces changes in snake venom by sampling the venom of wild adult rattlesnakes before and after they were treated with either empty (control) or CORT-filled (treatment) Silastic implants. We measured longitudinal changes in whole-venom composition, whole-venom total protein content, and enzymatic activity of SVMP and PLA₂ components of venom. We also assessed the within-individual repeatability of venom components. Despite successfully elevating plasma CORT in the treatment group, we found no effect of CORT treatment or average plasma CORT level on any venom variables measured. Except for total protein content, venom components were highly repeatable within individuals ([Formula: see text]). Our results indicate that the effects of CORT, a hormone commonly associated with stress and metabolic functions, in adult rattlesnake venom are negligible. Our findings bode well for venom researchers and biomedical applications that rely on the consistency of venoms produced from potentially stressed individuals and provide an experimental framework for future studies of proximate mediators of venom variation across an individual's life span.

Behavioral tagging as a mechanism for aversive-memory formation under acute stress

The behavioral tagging (BT) hypothesis postulates that a weak learning experience, which only induces short-term memory, may benefit from another event that provides plasticity-related proteins (PRPs) to establish a long-lasting memory. According to BT, the weak experience sets a transient learning tag at specific activated sites, and its temporal and spatial convergence with the PRPs allows the long-term memory (LTM) formation. In this work, rats were subjected to a weak inhibitory avoidance (IAw) training and we observed that acute stress (elevated platform, EP) experienced 1 hr before IAw promoted IA-LTM formation. This effect was dependent on glucocorticoid-receptor activity as well as protein synthesis in the dorsal hippocampus. However, the same stress has negative effects on IA-LTM formation when training is strong, probably by competing for necessary PRPs. Furthermore, our experiments showed that EP immediately after training did not impair the setting of the learning tag and even facilitated IA-LTM formation. These findings reveal different impacts of a given acute stressful experience on the formation of an aversive memory that could be explained by BT processes.

Important lessons learned from studies on the pharmacology of glucocorticoids in human airway smooth muscle cells: Too much of a good thing may be a problem

Glucocorticoids (GCs) are the treatment of choice for chronic inflammatory diseases such as asthma. Despite proven effective anti-inflammatory and immunosuppressive effects, long-term and/or systemic use of GCs can potentially induce adverse effects. Strikingly, some recent experimental evidence suggests that GCs may even exacerbate some disease outcomes. In asthma, airway smooth muscle (ASM) cells are among the targets of GC therapy and have emerged as key contributors not only to bronchoconstriction, but also to airway inflammation and remodeling, as implied by experimental and clinical evidence. We here will review the beneficial effects of GCs on ASM cells, emphasizing the differential nature of GC effects on pro-inflammatory genes and on other features associated with asthma pathogenesis. We will also summarize evidence describing how GCs can potentially promote pro-inflammatory and remodeling features in asthma with a specific focus on ASM cells. Finally, some of the possible solutions to overcome these unanticipated effects of GCs will be discussed.

Involvement of mitochondrial apoptotic pathway and MAPKs/NF-κ B inflammatory pathway in the neuroprotective effect of atractylenolide III in corticosterone-induced PC12 cells

Atractylenolide III (ATL-III), a sesquiterpene compound isolated from Rhizoma Atractylodis Macrocephalae, has revealed a number of pharmacological properties including anti-inflammatory, anti-cancer activity, and neuroprotective effect. This study aimed to evaluate the cytoprotective efficiency and potential mechanisms of ATL-III on corticosterone injured rat phaeochromocytoma (PC12) cells. Our results demonstrate that ATL-III increases cell viability and reduces the release of lactate dehydrogenase (LDH). The results suggest that ATL-III protects PC12 cells from corticosterone-induced injury by inhibiting the intracellular Ca²⁺ overloading, inhibiting the mitochondrial apoptotic pathway and modulating the MAPK/NF-ΚB inflammatory pathways. These findings provide a novel insight into the molecular mechanism by which ATL-III protected the PC12 cells against corticosterone-induced injury for the first time. Our results provide the evidence that ATL-III may serve as a therapeutic agent in the treatment of depression.

Nongenomic glucocorticoid effects and their mechanisms of action in vertebrates

Glucocorticoids (GC) act on multiple organ systems to regulate a variety of physiological processes in vertebrates. Due to their immunosuppressive and anti-inflammatory actions, glucocorticoids are an attractive target for pharmaceutical development. Accordingly, they are one of the most widely prescribed classes of therapeutics. Through the classical mechanism of steroid action, glucocorticoids are thought to mainly affect gene transcription, both in a stimulatory and suppressive fashion, regulating de novo protein synthesis that subsequently leads to the physiological response. However, over the past three decades multiple lines of evidence demonstrate that glucocorticoids may work through rapid, nonclassical mechanisms that do not require alterations in gene transcription or translation. This review assimilates evidence across the vertebrate taxa on the diversity of nongenomic actions of glucocorticoids and the membrane-associated cellular mechanisms that may underlie rapid glucocorticoid responses to include potential binding sites characterized to date.

Non-genomic Effects of Glucocorticoids: An Updated View

Glucocorticoid (GC) anti-inflammatory effects generally require a prolonged onset of action and involve genomic processes. Because of the rapidity of some of the GC effects, however, the concept that non-genomic actions may contribute to GC mechanisms of action has arisen. While the mechanisms have not been completely elucidated, the non-genomic effects may play a role in the management of inflammatory diseases. For instance, we recently reported that GCs 'rapidly' enhanced the effects of bronchodilators, agents used in the treatment of allergic asthma. In this review article, we discuss (i) the non-genomic effects of GCs on pathways relevant to the pathogenesis of inflammatory diseases and (ii) the putative role of the membrane GC receptor. Since GC side effects are often considered to be generated through its genomic actions, understanding GC non-genomic effects will help design GCs with a better therapeutic index.

Membrane glucocorticoid receptors are localised in the extracellular matrix and signal through the MAPK pathway in mammalian skeletal muscle fibres

KEY POINTS

Many studies have previously suggested the existence of stress hormone receptors on the cell membrane of many cell types, including skeletal muscle fibres; however, the exact localisation of these receptors and how they signal to the rest of the cell is poorly understood. In this study, we investigated the localisation and the mechanism(s) underlying the physiological functions of these receptors in mouse skeletal muscle cells. We found that the receptors were present throughout muscle development and that, in adult muscle fibres, they were localised in the extracellular matrix, satellite cells (muscle stem cells) and close to mitochondria. We also found that they signalled to the rest of the cell by activating enzymes called mitogen-activated protein kinases. From these results we suggest that, at physiological concentrations, stress hormones may be important in skeletal muscle differentiation, repair and regeneration.

ABSTRACT

A number of studies have previously proposed the existence of glucocorticoid receptors on the plasma membrane of many cell types, including skeletal muscle fibres. However, their exact localisation and the cellular signalling pathway(s) they utilise to communicate with the rest of the cell are still poorly understood. In this study, we investigated the localisation and the mechanism(s) underlying the non-genomic physiological functions of these receptors in mouse skeletal muscle cells. The results show that the receptors were localised in the cytoplasm in myoblasts, in the nucleus in myotubes, in the extracellular matrix, in satellite cells and in the proximity of mitochondria in adult muscle fibres. Also, they bound laminin in a glucocorticoid-dependent manner. Treating small skeletal muscle fibre bundles with the synthetic glucocorticoid beclomethasone dipropionate increased the phosphorylation (= activation) of extracellular signal-regulated kinases 1 and 2, c-Jun N-terminal kinase and p38 mitogen-activated protein kinase. This occurred within 5 min and depended on the fibre type and the duration of the treatment. It was also abolished by the glucocorticoid receptor inhibitor, mifepristone, and a monoclonal antibody against the receptor. From these results we conclude that the non-genomic/non-canonical physiological functions of glucocorticoids, in adult skeletal muscle fibres, are mediated by a glucocorticoid receptor localised in the extracellular matrix, in satellite cells and close to mitochondria, and involve activation of the mitogen-activated protein kinase pathway.

Postexercise whole body heat stress additively enhances endurance training-induced mitochondrial adaptations in mouse skeletal muscle

A recent study demonstrated that heat stress induces mitochondrial biogenesis in C2C12 myotubes, thereby implying that heat stress may be an effective treatment to enhance endurance training-induced mitochondrial adaptations in skeletal muscle. However, whether heat stress actually induces mitochondrial adaptations in skeletal muscle in vivo is unclear. In the present study, we report the novel findings that 1) whole body heat stress produced by exposure of ICR mice to a hot environment (40°C, 30 min/day, 5 days/wk, 3 wk) induced mitochondrial adaptations such as increased mitochondrial enzyme activity (citrate synthase and 3-hydroxyacyl CoA dehydrogenase) and respiratory chain protein content (complexes I–V) in skeletal muscle in vivo and 2) postexercise whole body heat stress additively enhanced endurance training-induced mitochondrial adaptations (treadmill running, 25 m/min, 30 min/day, 5 days/wk, 3 wk). Moreover, to determine the candidate mechanisms underlying mitochondrial adaptations, we investigated the acute effects of postexercise whole body heat stress on the phosphorylation status of cellular signaling cascades that subsequently induce mitochondrial gene transcription. We found that whole body heat stress boosted the endurance exercise-induced phosphorylation of p38 MAPK, increased the phosphorylation status of p70S6K, a biomarker of mammalian target of rapamycin complex 1 activity, and unexpectedly dephosphorylated AMP-activated protein kinase and its downstream target acetyl-CoA carboxylase in skeletal muscle. Our present observations suggest that heat stress can act as an effective postexercise treatment. Heat stress treatment appeared to be clinically beneficial for people who have difficulty participating in sufficient exercise training, such as the elderly, injured athletes, and patients.

Stress signaling and the shaping of the mammary tissue in development and cancer

The postnatal mammary gland develops extensively through cycles of proliferation, branching, involution and remodeling. We review recent advances made in the field of stress signaling pathways and its roles in mammary gland organogenesis, how they contribute to normal organ specification and homeostasis and how its subversion by oncogenes leads to cancer. We analyze stress signaling in mammary gland biology taking into account the interrelationship with the extracellular matrix and adhesion signaling during morphogenesis. By integrating the information gathered from in vivo and three dimensional in vitro organogenesis studies, we review the novel contribution of p38(SAPK), c-Jun NH2-terminal kinase and PKR-like endoplasmic reticulum kinase (PERK) signaling pathways to the timely activation of cell death, correct establishment of polarity and growth arrest and autophagy, respectively. We also review the evidence supporting that the activation of the aforementioned stress kinases maintain breast acinar structures as part of a tumor suppressive program and that its deregulation is commonplace during breast cancer initiation.

Glucocorticoid regulation of brain-derived neurotrophic factor: relevance to hippocampal structural and functional plasticity

Glucocorticoids serve as key stress response hormones that facilitate stress coping. However, sustained glucocorticoid exposure is associated with adverse consequences on the brain, in particular within the hippocampus. Chronic glucocorticoid exposure evokes neuronal cell damage and dendritic atrophy, reduces hippocampal neurogenesis and impairs synaptic plasticity. Glucocorticoids also alter expression and signaling of the neurotrophin, brain-derived neurotrophic factor (BDNF). Since BDNF is known to promote neuroplasticity, enhance cell survival, increase hippocampal neurogenesis and cellular excitability, it has been hypothesized that specific adverse effects of glucocorticoids may be mediated by attenuating BDNF expression and signaling. The purpose of this review is to summarize the current state of literature examining the influence of glucocorticoids on BDNF, and to address whether specific effects of glucocorticoids arise through perturbation of BDNF signaling. We integrate evidence of glucocorticoid regulation of BDNF at multiple levels, spanning from the well-documented glucocorticoid-induced changes in BDNF mRNA to studies examining alterations in BDNF receptor-mediated signaling. Further, we delineate potential lines of future investigation to address hitherto unexplored aspects of the influence of glucocorticoids on BDNF. Finally, we discuss the current understanding of the contribution of BDNF to the modulation of structural and functional plasticity by glucocorticoids, in particular in the context of the hippocampus. Understanding the mechanistic crosstalk between glucocorticoids and BDNF holds promise for the identification of potential therapeutic targets for disorders associated with the dysfunction of stress hormone pathways.

Glucocorticoid regulation of human pulmonary surfactant protein-B (SP-B) mRNA stability is independent of activated glucocorticoid receptor

Adequate expression of surfactant protein-B (SP-B) is critical in the function of pulmonary surfactant to reduce alveolar surface tension. Expression of SP-B mRNA is restricted to specific lung-airway epithelial cells, and human SP-B mRNA stability is increased in the presence of the synthetic glucocorticoid dexamethasone (DEX). Although the mechanism of SP-B mRNA stabilization by DEX is unknown, studies suggest involvement of the glucocorticoid receptor (GR). We developed a dual-cistronic plasmid-based expression assay in which steady-state levels of SP-B mRNA, determined by Northern analysis, reproducibly reflect changes in SP-B mRNA stability. Using this assay, we found that steady-state levels of SP-B mRNA increased greater than twofold in transfected human-airway epithelial cells (A549) incubated with DEX (10(-7) M). DEX-mediated changes in SP-B mRNA levels required the presence of the SP-B mRNA 3'-untranslated region but did not require ongoing protein synthesis. The effect of DEX on SP-B mRNA levels was dose dependent, with maximal effect at 10(-7) M. DEX increased levels of SP-B mRNA in cells lacking GR, and the presence of the GR antagonist RU486 did not interfere with the effect of DEX. Surprisingly, other steroid hormones (progesterone, estradiol, and vitamin D; 10(-7) M) significantly increased SP-B mRNA levels, suggesting a common pathway of steroid hormone action on SP-B mRNA stability. These results indicate that the effect of DEX to increase SP-B mRNA stability is independent of activated GR and suggests that the mechanism is mediated by posttranscriptional or nongenomic effects of glucocorticoids.

Corticosteroids: way upstream

Studies into the mechanisms of corticosteroid action continue to be a rich bed of research, spanning the fields of neuroscience and endocrinology through to immunology and metabolism. However, the vast literature generated, in particular with respect to corticosteroid actions in the brain, tends to be contentious, with some aspects suffering from loose definitions, poorly-defined models, and appropriate dissection kits. Here, rather than presenting a comprehensive review of the subject, we aim to present a critique of key concepts that have emerged over the years so as to stimulate new thoughts in the field by identifying apparent shortcomings. This article will draw on experience and knowledge derived from studies of the neural actions of other steroid hormones, in particular estrogens, not only because there are many parallels but also because 'learning from differences' can be a fruitful approach. The core purpose of this review is to consider the mechanisms through which corticosteroids might act rapidly to alter neural signaling.

The effect of glucocorticoids on ERK-1/2 phosphorylation during maturation of lamb oocytes and their subsequent fertilization and cleavage ability in vitro

High levels of glucocorticoids may alter reproduction, but little is known about their direct actions on oocyte maturation, fertilization and subsequent development. Earlier work suggested negative effects of cortisol or dexamethasone on oocyte maturation but differences were noted between animal models. Both glucocorticoids reduce the p34(cdc2)-cyclin B1 complex but it is unknown if other signaling pathways important for meiosis progression are affected. In this study, using sheep oocytes as a model system, we assessed in vitro the effects of increasing concentration of glucocorticoids (0-250 microM) on oocyte maturation and underlying changes in the MAP kinase pathway, and the ability of oocytes to undergo fertilization and embryo development. Cortisol decreased oocyte maturation but only at the highest concentration, whereas dexamethasone had no effect. Fertilization and cleavage were not affected. On the other hand, both cortisol and dexamethasone inhibited ERK-1/2 activation in a concentration-dependent manner. It thus seems that oocytes can overcome deleterious effects of glucocorticoids during maturation despite the decrease in ERK-1/2 activity, but repercussions in vivo should be further explored.

Stress at the synapse: signal transduction mechanisms of adrenal steroids at neuronal membranes

As the key neuron-to-neuron interface, the synapse is involved in learning and memory, including traumatic memories during times of stress. However, the signal transduction mechanisms by which stress mediates its lasting effects on synapse transmission and on memory are not fully understood. A key component of the stress response is the increased secretion of adrenal steroids. Adrenal steroids (e.g., cortisol) bind to genomic mineralocorticoid and glucocorticoid receptors (gMRs and gGRs) in the cytosol. In addition, they may act through membrane receptors (mMRs and mGRs), and signal transduction through these receptors may allow for rapid modulation of synaptic transmission as well as modulation of membrane ion currents. mMRs increase synaptic and neuronal excitability; mechanisms include the facilitation of glutamate release through extracellular signal-regulated kinase signal transduction. In contrast, mGRs decrease synaptic and neuronal excitability by reducing calcium currents through N-methyl-D-aspartate receptors and voltage-gated calcium channels by way of protein kinase A- and G protein-dependent mechanisms. This body of functional data complements anatomical evidence localizing GRs to the postsynaptic membrane. Finally, accumulating data also suggest the possibility that mMRs and mGRs may show an inverted U-shaped dose response, whereby glutamatergic synaptic transmission is increased by low doses of corticosterone acting at mMRs and decreased by higher doses acting at mGRs. Thus, synaptic transmission is regulated by mMRs and mGRs, and part of the stress signaling response is a direct and bidirectional modulation of the synapse itself by adrenal steroids.

Signal transduction of MCP-1 expression induced by pancreatitis-associated ascitic fluid in pancreatic acinar cells

Pancreatitis-associated ascitic fluid (PAAF) is known to contribute to the progression of acute pancreatitis (AP). We have investigated the capability of PAAF to activate the expression of MCP-1 in pancreatic acinar cells and the involvement of MAPK, NF-kappaB and STAT3 as downstream signalling transduction pathways. The actions of dexamethasone (Dx) and N-acetylcysteine (NAC) on the PAAF's acinar effects have also been evaluated. Acinar cells were incubated for 1 hr with PAAF collected from rats with severe AP induced by sodium taurocholate in the absence or presence of Dx (10(-7) M) or NAC (30 mM). MCP-1 mRNA expression, phospho-p38-MAPK, IkappaB alpha, nuclear p65 levels and nuclear translocation of STAT3 were analysed. In response to PAAF, overexpression of MCP-1, phosphorylation of p38-MAPK, degradation of IkappaB alpha and increases in p65 nuclear levels and STAT3 activity were found in acinar cells. PAAF-mediated MCP-1 up-regulation was completely suppressed by Dx and NAC. MAPK activation was only inhibited by NAC, NF-kappaB activation was repressed by Dx and NAC, and STAT3 pathway was strongly blocked by Dx and significantly reduced by NAC. In conclusion, acinar cells were activated by PAAF to produce MCP-1, mainly via NF-kappaB and STAT3 pathways. Both downstream pathways were targeted by Dx and NAC to repress the PAAF-mediated acinar MCP-1 up-regulation.

Signal transduction of MCP-1 expression induced by pancreatitis-associated ascitic fluid in pancreatic acinar cells

Pancreatitis-associated ascitic fluid (PAAF) is known to contribute to the progression of acute pancreatitis (AP). We have investigated the capability of PAAF to activate the expression of MCP-1 in pancreatic acinar cells and the involvement of MAPK, NF-κB and STAT3 as downstream signalling transduction pathways. The actions of dexamethasone (Dx) and N-acetylcysteine (NAC) on the PAAF’s acinar effects have also been evaluated. Acinar cells were incubated for 1 hr with PAAF collected from rats with severe AP induced by sodium taurocholate in the absence or presence of Dx (10⁻⁷ M) or NAC (30 mM). MCP-1 mRNA expression, phospho-p38-MAPK, IκBα, nuclear p65 levels and nuclear translocation of STAT3 were analysed. In response to PAAF, overexpression of MCP-1, phosphorylation of p38-MAPK, degradation of IκBα and increases in p65 nuclear levels and STAT3 activity were found in acinar cells. PAAF-mediated MCP-1 up-regulation was completely suppressed by Dx and NAC. MAPK activation was only inhibited by NAC, NF-κB activation was repressed by Dx and NAC, and STAT3 pathway was strongly blocked by Dx and significantly reduced by NAC. In conclusion, acinar cells were activated by PAAF to produce MCP-1, mainly via NF-κB and STAT3 pathways. Both downstream pathways were targeted by Dx and NAC to repress the PAAF-mediated acinar MCP-1 up-regulation.

Minireview: rapid glucocorticoid signaling via membrane-associated receptors

Glucocorticoids are secreted into the systemic circulation from the adrenal cortex and initiate a broad range of actions throughout the organism that regulate the function of multiple organ systems, including the liver, muscle, the immune system, the pancreas, fat tissue, and the brain. Delayed glucocorticoid effects are mediated by classical steroid mechanisms involving transcriptional regulation. Relatively rapid effects of glucocorticoids also occur that are incompatible with genomic regulation and invoke a noncanonical mode of steroid action. Studies conducted in several labs and on different species suggest that the rapid effects of glucocorticoids are mediated by the activation of one or more membrane-associated receptors. Here, we provide a brief review focused on multiple lines of evidence suggesting that rapid glucocorticoid actions are triggered by, or at least dependent on, membrane-associated G protein-coupled receptors and activation of downstream signaling cascades. We also discuss the possibility that membrane-initiated actions of glucocorticoids may provide an additional mechanism for the regulation of gene transcription.

Cultured embryonic hippocampal neurons deficient in glucocorticoid (GC) receptor: a novel model for studying nongenomic effects of GC in the neural system

Glucocorticoid (GC) acts through both genomic and nongenomic mechanisms. It affects the structure and function of the central nervous system, especially the hippocampus. Here we report an in vitro culture system that can yield embryonic hippocampal neurons deficient in the expression of GC receptor as demonstrated by immunoblotting, immunocytochemistry, and RT-PCR. Owing to this unique feature, those neuron preparations can serve as an ideal model for studying the nongenomic actions of GC on neural cells. In this study, we found that the Erk1/2, c-Jun N-terminal kinase (JNK), and p38 MAPKs were activated in these neurons by BSA-conjugated corticosterone within 15 min of treatment. This activation was not blocked by RU38486, spironolactone, or cycloheximide. Therefore, it is concluded that the activation of MAPKs observed here was due to the nongenomic action of GC. Furthermore, a 24-h incubation with corticosterone at concentrations ranged from 10(-11)-10(-5) M did not have an effect on the viability of GC receptor-deficient neurons.

Rapid activation of JNK and p38 by glucocorticoids in primary cultured hippocampal cells

Rapid activation of JNK and p38 and their translocation to the cell nucleus by glucocorticoids, corticosterone (Cort), and bovine serum-conjugated corticosterone (Cort-BSA) were studied in primary cultured hippocampal cells by using immunoblotting and immunofluorescence confocal microscopy. The rapid activation occurred 5 min after stimulation and was maintained at plateau for as long as 2-4 hr; i.e., the response persisted for 2 hr after washing out the 15-min application of Cort-BSA. The activation occurred at a minimal concentration of 10(-9) M for Cort and 10(-8) M for Cort-BSA. GDPbetaS blocked the activation, but RU38486, a nuclear glucocorticoid receptor antagonist, could not block the activation, indicating the involvement of the membrane-delineated receptor in this reaction. The protein kinase C (PKC) inhibitor Go6976 blocked the response, whereas the protein kinase A inhibitor H89 could not, implying the involvement of PKC in the intracellular signal transduction pathway. The nongenomic nature of the responses and the transduction pathway and the significance of persistent action and biological significance are discussed.

Changes in androgen receptor nongenotropic signaling correlate with transition of LNCaP cells to androgen independence

A cure for prostate cancer (CaP) will be possible only after a complete understanding of the mechanisms causing this disease to progress from androgen dependence to androgen independence. To carry on a careful characterization of the phenotypes of CaP cell lines before and after acquisition of androgen independence, we used two human CaP LNCaP sublines: LNCaP(nan), which is androgen dependent (AD), and LNCaP-HP, which is androgen independent (AI). In AD LNCaP(nan) cells, dihydrotestosterone (DHT) stimulated in an androgen receptor (AR)-dependent way a phosphorylation signaling pathway involving steroid receptor coactivator (Src)-mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase (MEK)-1/2-ERK-1/2-cAMP-response element binding-protein (CREB). Activation of this pathway was associated with increased [(3)H]thymidine incorporation and resistance to apoptosis. Use of dominant-negative forms of MEK-1/2 and CREB demonstrated in LNCaP(nan) cells that DHT induced [(3)H]thymidiine incorporation through a thus far unidentified molecule activated downstream of MEK-1/2, and antiapoptosis through phosphorylation of the transcription factor CREB. In contrast, in AI LNCaP-HP cells, the Src-MEK-1/2-ERK-1/2-CREB pathway was constitutively active. Because it was not further stimulated by addition of DHT, no increase of [(3)H]thymidine incorporation or apoptosis resistance was demonstrated in LNCaP-HP cells. Additional experiments showed that Src and the scaffold protein MNAR coimmunoprecipitated with AR, indicating a role for Src as an apical molecule in the Src-MEK-1/2-ERK-1/2-CREB pathway. Interestingly, differences between the two cell lines were that in LNCaP-HP cells presence of an AI phenotype and lack of response to DHT were associated with constitutive activation of the protein kinase Src and interaction among Src, AR, and MNAR. In contrast, in LNCaP(nan) cells, presence of an AD phenotype and ability to respond to DHT were associated with DHT-dependent activation of Src kinase activity and interaction among Src, AR, and MNAR. Intriguingly, in LNCaP(nan) cells, we found that transcription through the prototypical CREB-responsive promoter c-fos could be induced in a DHT-dependent way, and this action was inhibited by the AR antagonist Casodex and MEK-1 inhibitor PD98059. In contrast, transcription through the PSA P/E promoter, a prototypical AR-dependent promoter directly activated by agonist, was obliterated only by Casodex. Additional experiments with genital skin fibroblasts derived from patients with a variety of AR abnormalities indicated that nongenotropic AR signaling does not depend on an intact DNA-binding domain or on the ability of AR to translocate to the nucleus. The results suggest the following: (1) Constitutive activation of the Src-MEK-1/2-ERK-1/2-CREB pathway is associated with the AI phenotype observed in LNCaP-HP cells. (2) Activation of the Src-MEK-1/2-ERK-1/2-CREB pathway is DHT dependent in AD LNCaP(nan) cells. (3) DHT activation of this pathway is associated with induction of [(3)H]thymidine incorporation by a molecule activated downstream of MEK-1/2 and of antiapoptosis through activation of the transcription factor CREB in AD LNCaP(nan) cells. (4) AR regulates transcription either directly upon ligand binding and nuclear translocation or indirectly through kinase pathways leading to activation of downstream transcription factors. (5) Nuclear translocation and ability of the DNA-binding domain of AR to interact with DNA are not prerequisites for nongenotropic AR activity.

Stress and immunological phagocytosis: possible nongenomic action of corticosterone

Some immunological responses triggered by stress can be mediated by corticosterone activity through cytosolic receptors regulating gene expression. There are, however some reports on the possibility of a nongenomic effect of this hormone to explain phenomena observed in a few minutes. We have found that macrophages from mice subjected to 10 min of cold stress (at -15 degrees C) showed a lower phagocytic capacity mediated by Fcgamma-receptors than cells from control animals. Treating mice with glucocorticoid antagonist RU 486 did not block the decrease in phagocytic capacity. This inhibitory effect on phagocytosis was also observed by experiments in vitro with corticosterone in the concentration found in serum after stress, and could not be prevented by RU 486, actinomicyn D or cycloheximide. These results indicate that corticosterone could affect phagocytosis by macrophages through a nongenomic mechanism, and may have physiological implications.

Dexamethasone induces rapid serine-phosphorylation and membrane translocation of annexin 1 in a human folliculostellate cell line via a novel nongenomic mechanism involving the glucocorticoid receptor, protein kinase C, phosphatidylinositol 3-kinase, and mitogen-activated protein kinase

Our recent studies on rat pituitary tissue suggest that the annexin 1 (ANXA1)-dependent inhibitory actions of glucocorticoids on ACTH secretion are effected via a paracrine mechanism that involves protein kinase C (PKC)-dependent translocation of a serine-phosphorylated species of ANXA1 (Ser-P-ANXA1) to the plasma membrane of the nonsecretory folliculostellate cells. In the present study, we have used a human folliculostellate cell line (PDFS) to explore the signaling mechanisms that cause the translocation of Ser-P-ANXA1 to the membrane together with Western blot analysis and flow cytometry to detect the phosphorylated protein. Exposure of PDFS cells to dexamethasone caused time-dependent increases in the expression of ANXA1 mRNA and protein, which were first detected within 2 h of steroid contact. This genomic response was preceded by the appearance within 30 min of substantially increased amounts of Ser-P-ANXA1 and by translocation of the phosphorylated protein to the cell surface. The prompt membrane translocation of Ser-P-ANXA1 provoked by dexamethasone was inhibited by the glucocorticoid receptor, antagonist, mifepristone, but not by actinomycin D or cycloheximide, which effectively inhibit mRNA and protein synthesis respectively in our preparation. It was also inhibited by a nonselective PKC inhibitor (PKC(9-31)), by a selective inhibitor of Ca(2+)-dependent PKCs (Go 6976) and by annexin 5 (which sequesters PKC in other systems). In addition, blockade of phosphatidylinositiol 3-kinase (wortmannin) or MAPK pathways with PD 98059 or UO 126 (selective for MAPK kinse 1 and 2) prevented the steroid-induced translocation of Ser-P-ANXA1 to the cell surface. These results suggest that glucocorticoids induce rapid serine phosphorylation and membrane translocation of ANXA1 via a novel nongenomic, glucocorticoid receptor-dependent mechanism that requires MAPK, phosphatidylinositiol 3-kinase, and Ca(2+)-dependent PKC pathways.

A rapid, nongenomic action of glucocorticoids in rat B103 neuroblastoma cells

We report here a new example in which glucocorticoids (GCs) acted in a rapid, nongenomic way. In rat B103 neuroblastoma cells, 5-hydroxytryptamine (5-HT) was found to evoke an immediate rise in intracellular free calcium concentration ([Ca(2+)](i)). Pre-incubation of B103 cells for 5 min with corticosterone (B) or bovine serum albumin-conjugated corticosterone (B-BSA) concentration-dependently (10(-4)-10(-8) M) inhibited the peak increments in [Ca(2+)](i). Cortisol and dexamethasone had a similar effect, while deoxycorticosterone and cholesterol were ineffective. This rapid inhibitory effect of corticosterone could be mimicked by protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) and abolished completely by PKC inhibitors Ro31-8220 or GF-109203X. Neither pertussis toxin (PTX) nor nuclear GC receptor (GR) antagonist RU38486 influenced the rapid action of B. Our results suggest that GCs can modulate the 5-HT-induced Ca(2+) response in B103 cells in a membrane-initiated, nongenomic, and PKC-dependent manner.

Rapid actions of steroid receptors in cellular signaling pathways

Steroid hormones regulate cellular processes by binding to intracellular receptors that, in turn, interact with discrete nucleotide sequences to alter gene expression. Because most steroid receptors in target cells are located in the cytoplasm, they need to get into the nucleus to alter gene expression. This process typically takes at least 30 to 60 minutes. In contrast, other regulatory actions of steroid hormones are manifested within seconds to a few minutes. These time periods are far too rapid to be due to changes at the genomic level and are therefore termed nongenomic or rapid actions, to distinguish them from the classical steroid hormone action of regulation of gene expression. The rapid effects of steroid hormones are manifold, ranging from activation of mitogen-activated protein kinases (MAPKs), adenylyl cyclase (AC), protein kinase C (PKC), and heterotrimeric guanosine triphosphate-binding proteins (G proteins). In some cases, these rapid actions of steroids are mediated through the classical steroid receptor that can also function as a ligand-activated transcription factor, whereas in other instances the evidence suggests that these rapid actions do not involve the classical steroid receptors. One candidate target for the nonclassical receptor-mediated effects are G protein-coupled receptors (GPCRs), which activate several signal transduction pathways. One characteristic of responses that are not mediated by the classical steroid receptors is insensitivity to steroid antagonists, which has contributed to the notion that a new class of steroid receptors may be responsible for part of the rapid action of steroids. Evidence suggests that the classical steroid receptors can be localized at the plasma membrane, where they may trigger a chain of reactions previously attributed only to growth factors. Identification of interaction domains on the classical steroid receptors involved in the rapid effects, and separation of this function from the genomic action of these receptors, should pave the way to a better understanding of the rapid action of steroid hormones.

Possible genomic consequence of nongenomic action of glucocorticoids in neural cells

The nongenomic, rapid effects of glucocorticoid activate multiple intracellular transduction pathways. This review proposes a possible genomic consequence of the nongenomic action of steroids. The genomic actions of hormonal steroids may be twofold: classic genomic and nongenomically induced genomic.