Serum And Glucocorticoid-inducible Kinase 1 Research Articles

1806 Molecular Mechanisms of Perinatal Lung Fluid Clearance in term Newborns

Background and AimThe perinatal switch from secretion to absorption in airway fluid transport includes increase in gene expression and activity of ion channels, e.g. apical amiloride-sensitive epithelial sodium channel (ENaC)...

Regulation of ion channels by the serum‐ and glucocorticoid‐inducible kinase SGK1

The ubiquitously expressed serum- and glucocorticoid-inducible kinase-1 (SGK1) is genomically regulated by cell stress (including cell shrinkage) and several hormones (including gluco- and mineralocorticoids). SGK1 is activated by insulin and growth factors through PI3K and 3-phosphoinositide-dependent kinase PDK1. SGK1 activates a wide variety of ion channels (e.g., ENaC, SCN5A, TRPV4-6, ROMK, Kv1.3, Kv1.5, Kv4.3, KCNE1/KCNQ1, KCNQ4, ASIC1, GluR6, ClCKa/barttin, ClC2, CFTR, and Orai/STIM), which participate in the regulation of transport, hormone release, neuroexcitability, inflammation, cell proliferation, and apoptosis. SGK1-sensitive ion channels participate in the regulation of renal Na(+) retention and K(+) elimination, blood pressure, gastric acid secretion, cardiac action potential, hemostasis, and neuroexcitability. A common (∼3-5% prevalence in Caucasians and ∼10% in Africans) SGK1 gene variant is associated with increased blood pressure and body weight as well as increased prevalence of type II diabetes and stroke. SGK1 further contributes to the pathophysiology of allergy, peptic ulcer, fibrosing disease, ischemia, tumor growth, and neurodegeneration. The effect of SGK1 on channel activity is modest, and the channels do not require SGK1 for basic function. SGK1-dependent ion channel regulation may thus become pathophysiologically relevant primarily after excessive (pathological) expression. Therefore, SGK1 may be considered an attractive therapeutic target despite its broad range of functions.

Neurotrophic Effects of Serum- and Glucocorticoid-Inducible Kinase on Adult Murine Mesencephalic Dopamine Neurons

Mesencephalic dopamine neurons are central to many aspects of human cognition, motivational, and motor behavior, and they are uniquely vulnerable to degenerative neurologic disorders such as Parkinson's disease. There is growing evidence that in the mature brain these neurons not only remain responsive to neurotrophic support, but are dependent on it for viability and function. Little is known of the cellular signaling pathways that mediate this support, although some evidence suggests that protein kinase Akt/PKB may play such a role. Another candidate for such a role is serum- and glucocorticoid-inducible kinase (SGK), a member of the AGC kinase family that is closely related to Akt. We have herein examined the responsiveness of adult mouse dopamine neurons in vivo to overexpression of wild-type and a constitutively active form of SGK by use of viral vector transfer in normal mice and both before and after 6-OHDA lesion. We find that SGK induces a broad spectrum of neurotrophic effects on these neurons, including induction of neuronal hypertrophy, protection from both neuron death and neurotoxin-induced retrograde axonal degeneration, and axon regeneration. Given the diverse and robust effects of SGK on these neurons, and its abundant expression in them, we suggest that SGK, like closely related Akt, may play a role in their responsiveness to neurotrophic factors and in adult maintenance. It therefore offers a novel target for therapeutic development.

Translational regulation of the serum- and glucocorticoid-inducible kinase-1 (SGK1) in platelets

Activation of platelets by thrombin opens pore forming channel protein Orai1 with subsequent store operated Ca2+ entry (SOCE) and Ca2+ dependent platelet granule release, integrin αIIbβ3 activation, adhesion, aggregation and thrombus formation. Orai1 and thus SOCE as well as platelet activation are up-regulated by the serum- and glucocorticoid-inducible kinase-1 (SGK1), which transcriptionally regulates Orai1 expression in megakaryocytes and thus determines Orai1 protein abundance in mature, circulating platelets. As platelets are devoid of nuclei, they are unable to modify protein abundance by regulation of transcription. However, they contain mRNA and thus could express novel protein by stimulation of protein translation. Translation is sensitive to actin polymerization and phosphoinositide-3-kinase (PI3K). Translational regulation of SGK1 expression has never been described before. The present study thus explored whether thrombin regulates SGK1 expression in platelets. As a result, according to RT-PCR mRNA encoding SGK1 is present in circulating platelets and significantly decreased by activation of platelets with thrombin (1U/ml). The protein abundance of SGK1 is significantly enhanced by thrombin treatment, an effect significantly decreased by inhibition of translation with puromycin (100nM) but not by inhibition of transcription with actinomycin (4μg/ml). The increase of SGK1 protein abundance is blunted by inhibition of PI3K with wortmannin (100nM) or LY294002 (25μM), and by disruption of the cytoskeleton with cytochalasin B (1μM). In conclusion, activation of platelets with thrombin stimulates the translation of SGK1.

Simulated Bladder Pressure Stimulates Human Bladder Smooth Muscle Cell Proliferation via the PI3K/SGK1 Signaling Pathway

A mechanical stimulus on detrusor tissue is critical to bladder outlet obstruction progression and functional bladder tissue engineering. A hypothesis is that mechanical stimulus triggers human bladder smooth muscle cell proliferation. To help better understand this relationship of bladder function to growth at the cellular level we used a novel method of applying cyclic hydrodynamic pressure that simulates the bladder cycle to cell cultures. We detected the proliferation response of human bladder smooth muscle cells (4310, ScienCell™) to different pressures as well as the signal transduction mechanism of this process. Human bladder smooth muscle cells cultured in scaffolds underwent 4 pressures (0, 100, 200 and 300 cm H(2)O) for 24 hours, as controlled by a BioDynamic® bioreactor. We then used flow cytometry to examine cell cycle distribution, and polymerase chain reaction and immunoblot to quantify SGK1 and AKT expression and activation in each group. SGK1 was silenced in human bladder smooth muscle cells using small interfering RNA to validate the role of SGK1 in mediating pressure induced cell proliferation. Compared with the 0 cm H(2)O control group, human bladder smooth muscle cells in the 200 and 300 cm H(2)O groups showed increased cell proliferation. SGK1 expression and activity were also increased while AKT, another downstream signal of PI3K, did not change significantly. SGK1 silencing abolished the increases in cell proliferation induced by pressure. To our knowledge we provide the first report of cyclic hydrodynamic pressure stimulating the proliferation of human bladder smooth muscle cells cultured in scaffolds. The signal transduction mechanism for this process is involved with the PI3K/SGK1 and not the PI3K/AKT signaling pathway.

Epithelial Na+ channel activity in human airway epithelial cells: the role of serum and glucocorticoid‐inducible kinase 1

Glucocorticoids appear to control Na⁺ absorption in pulmonary epithelial cells via a mechanism dependent upon serum and glucocorticoid-inducible kinase 1 (SGK1), a kinase that allows control over the surface abundance of epithelial Na⁺ channel subunits (α-, β- and γ-ENaC). However, not all data support this model and the present study re-evaluates this hypothesis in order to clarify the mechanism that allows glucocorticoids to control ENaC activity. Electrophysiological studies explored the effects of agents that suppress SGK1 activity upon glucocorticoid-induced ENaC activity in H441 human airway epithelial cells, whilst analyses of extracted proteins explored the associated changes to the activities of endogenous protein kinase substrates and the overall/surface expression of ENaC subunits. Although dexamethasone-induced (24 h) ENaC activity was dependent upon SGK1, prolonged exposure to this glucocorticoid did not cause sustained activation of this kinase and neither did it induce a coordinated increase in the surface abundance of α-, β- and γ-ENaC. Brief (3 h) exposure to dexamethasone, on the other hand, did not evoke Na⁺ current but did activate SGK1 and cause SGK1-dependent increases in the surface abundance of α-, β- and γ-ENaC. Although glucocorticoids activated SGK1 and increased the surface abundance of α-, β- and γ-ENaC, these responses were transient and could not account for the sustained activation of ENaC. The maintenance of ENaC activity did, however, depend upon SGK1 and this protein kinase must therefore play an important but permissive role in glucocorticoid-induced ENaC activation.

Insulin up-regulates epithelial sodium channel in LPS-induced acute lung injury model in rats by SGK1 activation

Activity of the epithelial sodium channels (ENaCs) in the lung tissue plays a critical role on sodium/fluid homeostasis and the lung fluid clearance. The serum- and glucocorticoid-inducible kinase-1 (SGK1), one of the critical regulation proteins of ENaC, is activated by insulin and growth factors possibly through 3-phosphoinositide-dependent kinase PDK1 or/and phosphatidylinositol 3-kinase (PI3K). However, it is uncertain whether insulin shows its stimulatory action on ENaC by activation of SGK1 in lipopolysaccharide (LPS)-induced acute lung injury (ALI) condition. In our study, Wistar rats were injected with LPS to induce ALI. Evans blue dye albumin (EBA) concentration was used to measure pulmonary oedema. For detecting the ratio of phospho-SGK1/SGK1 and α-ENaC protein, Western blot was performed. Real-time polymerase chain reaction (RT-PCR) was used to assess α-ENaC messenger RNA (mRNA). Immunohistochemistry was used to locate and quantitate α-ENaC expression. The EBA concentration was markedly increased by LPS alone but significantly reduced in rats that also received insulin injection. The ratio of phospho-SGK1/SGK1 was raised significantly in the insulin group and insulin+LPS group, compared with the control group and the LPS group, respectively. Furthermore, α-ENaC was up-regulated by insulin treatment. Simultaneously, injection with LPS significantly reduced α-ENaC expression. These findings demonstrated that insulin up-regulates ENaC in vivo possibly resulting from activation of SGK1.

Histone deacetylase 6 gates the synaptic action of acute stress in prefrontal cortex

The prefrontal cortex (PFC), a region responsible for high-order cognitive functions, such as decision-making, attention and working memory, is highly influenced by stress and corticosteroid stress hormones. Recently it has been shown that acute stress affects PFC functions by potentiating glutamatergic transmission via a mechanism dependent on glucocorticoid receptor (GR) and its downstream target, serum and glucocorticoid-inducible kinase (SGK). To identify the key regulators of stress responses, we examined the role of histone deacetylase 6 (HDAC6), a unique member of the HDAC family that could regulate the GR chaperone protein heat shock protein 90 (HSP90), in the synaptic action of acute stress in PFC. We found that HDAC6 inhibition or knockdown blocked the enhancement of glutamatergic transmission and glutamate receptor trafficking by acute stress in vivo or corticosterone treatment in vitro. In addition, HDAC6 inhibition blocked the up-regulation of SGK in animals exposed to acute stress. HSP90 inhibition or knockdown produced a similar blockade of the acute stress-induced enhancement of glutamatergic signalling. These findings have identified HDAC6 as a key molecule gating the effects of acute stress on synaptic functions in the PFC.

Role of Serum and Glucocorticoid induced kinase-1 (SGK1) in cardiac angiogenesis.

Role of Serum and Glucocorticoid induced kinase-1 (SGK1) in cardiac angiogenesis.

The mTOR (Mammalian Target of Rapamycin) Kinase Maintains Integrity of mTOR Complex 2

In higher eukaryotes, growth factors promote anabolic processes and stimulate cell growth, proliferation, and survival by activation of the phosphoinositide 3-kinase (PI3K)/Akt pathway. Deregulation of PI3K/Akt signaling is linked to human diseases, including cancer and metabolic disorders. The PI3K-dependent signaling kinase complex mTORC2 (mammalian target of rapamycin complex 2) has been defined as the regulatory Ser-473 kinase of Akt. The regulation of mTORC2 remains very poorly characterized. We have reconstituted mTORC2 by its assembly in vitro or by co-expression its four essential components (rictor, SIN1, mTOR, mLST8). We show that the functional mTOR kinase domain is required for the mTORC2 activity as the Ser-473 kinase of Akt. We also found that mTOR by phosphorylation of SIN1 prevents its lysosomal degradation. Thus, the kinase domain of mTOR is required for the functional activity of mTORC2, and it controls integrity of mTORC2 by maintaining the protein stability of SIN1.

Enhanced catecholamine release in mice expressing PKB/SGK-resistant GSK3

Glycogen synthase kinase 3 (GSK3) plays a decisive role in the regulation of multiple functions. GSK3 is phosphorylated and its activity inhibited by protein kinase B (PKB/Akt) and serum and glucocorticoid inducible kinase (SGK) isoforms, which are in turn activated by growth factors through phosphoinositide (PI) 3 kinase signaling. PI3/PKB/Akt/SGK-dependent inhibition of GSK3 is disrupted in gene-targeted knockin mice with mutated and thus PKB/SGK-resistant GSK3α,ß (gsk3 ( KI )) where the serine of the PKB/SGK phosphorylation site has been replaced by alanine. Recent experiments revealed that blood pressure is significantly higher in those mice than in wild type mice (gsk3 ( WT )). The present study was performed to elucidate the underlying cause. Blood pressure was determined with the tail cuff method, heart rate by ECG measurements, catecholamine concentrations by ELISA, and vanillylmandelic acid by high pressure liquid chromatography. As a result, blood pressure and heart rate were significantly higher in gsk3 ( KI ) than in gsk3 ( WT ) mice. The α-adrenergic blocker prazosin (1μg/g body weight, b.w.) and the ganglion blocker hexamethonium (40μg/g b.w.) decreased blood pressure to a larger extent in gsk3 ( KI ) than in gsk3 ( WT ) mice and virtually abrogated the difference between genotypes. Similarly, the β-adrenergic blocker atenolol (5μg/g b.w.) decreased the heart rate to a larger extent in gsk3 ( KI ) than in gsk3 ( WT ) mice and again dissipated the difference of heart rate between genotypes. Plasma epinephrine and norepinephrine concentrations, as well as urinary excretion of vanillylmandelic acid, were significantly higher in gsk3 ( KI ) than in gsk3 ( WT ) mice. The observations reveal a completely novel function of PKB/Akt/SGK-dependent GSK3 signaling, i.e., regulation of catecholamine release.

Serum- and glucocorticoid-induced kinase 3 in recycling endosomes mediates acute activation of Na+/H+exchanger NHE3 by glucocorticoids

Na(+)/H(+) exchanger 3 (NHE3) is the major Na(+) transporter in the intestine. Serum- and glucocorticoid-induced kinase (SGK) 1 interacts with NHE regulatory factor 2 (NHERF2) and mediates activation of NHE3 by dexamethasone (Dex) in cultured epithelial cells. In this study, we compared short-term regulation of NHE3 by Dex in SGK1-null and NHERF2-null mice. In comparison to wild-type mice, loss of SGK1 or NHERF2 significantly attenuated regulation of NHE3 by Dex but did not completely obliterate the effect. We show that transfection of SGK2 or SGK3 in PS120 cells resulted in robust activation of NHE3 by Dex. However, unlike SGK1 or SGK2, SGK3 rapidly activated NHE3 within 15 min of Dex treatment in both PS120 and Caco-2bbe cells. Immunofluorescence analysis showed that SGK3 colocalized with NHE3 in recycling endosomes, whereas SGK1 and SGK2 were diffusely distributed. Mutation of Arg-90 of SGK3 disrupted the endosomal localization of SGK3 and delayed NHE3 activation. Activation of SGK3 and NHE3 by Dex was dependent on phosphoinositide 3-kinase (PI3K) and phosphoinositide-dependent kinase 1 (PDK1), and Dex induced translocation of PDK1 to endosomes. Our study identifies SGK3 as a novel endosomal kinase that acutely regulates NHE3 in a PI3K-dependent mechanism.

Laminin-β1 Impairs Spatial Learning through Inhibition of ERK/MAPK and SGK1 Signaling

Laminin is a major structural element of the basal lamina consisting of an α-chain, a β-chain, and a γ-chain arranged in a cross-like structure, with their C-terminal inter-coiled. Laminin is abundantly expressed in the hippocampus of mature brain and is implicated in several psychiatric disorders, but its possible role involved in learning and memory function is not known. This issue was examined here. Our results revealed that water maze training significantly decreased laminin-β1 (LB1) expression in the rat hippocampal CA1 area. Transfection of LB1 WT plasmid to hippocampal CA1 neurons impaired water maze performance in rats. Meanwhile, it decreased the phosphorylation level of ERK/MAPK and protein kinase serum- and glucocorticoid-inducible kinase-1 (SGK1). By contrast, knockdown of endogenous LB1 expression using RNA interference (LB1 siRNA) enhanced water maze performance. Meanwhile, it increased the phosphorylation level of ERK/MAPK and SGK1. The enhancing effect of LB1 siRNA on spatial learning and on the phosphorylation of ERK/MAPK and SGK1 was blocked by co-treatment with the MEK inhibitor U0126 at a concentration that did not apparently affect spatial learning and ERK/MAPK phosphorylation alone. Further, the enhancing effect of LB1 siRNA on spatial learning and SGK1 phosphorylation was similarly blocked by co-transfection with SGK1 siRNA at a concentration that did not markedly affect spatial learning and SGK1 expression alone. These results together indicate that LB1 negatively regulates spatial learning in rats. In addition, LB1 impairs spatial learning through decreased activation of the ERK/MAPK-SGK1 signaling pathway in the rat hippocampus.

Harnessing the Tumor Suppressor Function of FOXO as an Alternative Therapeutic Approach in Cancer

The promotion of cellular survival, dedifferentiation, and uncontrolled proliferation via the suppression of apoptotic effectors is a fundamental characteristic of tumor cells. As substrates that are negatively regulated by oncogenic signaling cascades driven by AKT, SGK (serum- and glucocorticoid-inducible kinase), IkB kinase (IKK), ERK, and cyclin-dependent kinases (CDK), forkhead box-class O (FOXO) transcription factors have emerged as bona fide tumor suppressors. These transcription factors indeed regulate a variety of cellular responses and themselves are regulated by reversible phosphorylation, acetylation, ubiquitination and miRNAs. This review will discuss our current understanding of mechanisms for FOXO regulation and the potential implications for therapeutically restoring FOXO transcriptional activity.

Clozapine and lithium require Caenorhabditis elegans β‐arrestin and serum‐ and glucocorticoid‐inducible kinase to affect Daf‐16 (Foxo) localization

Numerous studies have implicated low levels of signaling in the Akt network with psychotic illnesses, and a growing body of literature has shown that all classes of antipsychotic drugs increase Akt signaling. The most clinically effective antipsychotic drug is clozapine. With Caenorhabditis elegans as a model system, this study demonstrates that clozapine is unique among antipsychotic drugs because it requires β-arrestin and serum and glucocorticoid-inducible kinase (SGK) in addition to Akt to suppress the nuclear localization of DAF-16 (Forkhead box O [FOXO]). Lithium, a mood stabilizer often used to treat psychosis, also requires β-arrestin and SGK to suppress the nuclear localization of DAF-16.

Foxo1 nuclear‐cytoplasmic movement in living skeletal muscle

The transcription factor Foxo1 is integral to the regulation of expression of proteins which promote muscle atrophy. Phosphorylation of Foxo1 causes its translocation to the cytoplasm and thus prevents Foxo1-DNA binding and consequent transcription of genes that cause muscle atrophy and cell death. Thus, phosphorylation of Foxo1 leads to cell survival and muscle hypertrophy. Maintenance of Foxo1 phosphorylation and its resulting cytoplasmic retention could be used to suppress muscle atrophy and thereby shift the atrophy/hypertrophy balance in favor of hypertrophy. Akt and serum- and glucocorticoid-inducible kinase (SGK) are important regulators of the phosphorylation status of Foxo1. These pathways have been well characterized and the effects on Foxo1 localization have been reported. However, the mechanisms which regulate nuclear influx and nuclear efflux have not been separately evaluated. Here, we determine the effects of Akt kinase activity specifically on nuclear influx of Foxo1. To accomplish th/is goal, we quantified nuclear and cytoplasmic levels of adenovirally expressed Foxo1-GFP in cultured flexor digitorum brevis. The nuclear influx during treatment with kinase inhibitor Akt IV alone and in combination with the nuclear efflux inhibitor lemptomycin B provides insight into the activity of Akt as a Foxo1 kinase. Surprisingly, Akt inhibition reveals Akt to have little effect on the rate of nuclear influx of Foxo1. To evaluate translocation of endogenous Foxo1 in a similar manner immunocytochemistry and western blotting techniques were used. These results indicate that Akt either phosphorylates Foxo1 primarily in the nucleus and not in the cytoplasm, or that there is a mechanism for cytoplasmic phosphorylation of Foxo1 other than via Akt. Supported by training grants T32 AR0075592 and T32 HL072751 and research grant R01 AR056477.

Glucocorticoid receptor is indispensable for mineralocorticoid receptor‐dependent induction of colonic epithelial Na+ channels

Introduction In the colon, electrogenic sodium absorption is controlled by the epithelial Na+ channel (ENaC). We characterized the interplay of glucocorticoids and mineralocorticoids in ENaC signaling which is only poorly understood due to the lack of epithelial cell lines co-expressing functional glucocorticoid (GR) and mineralocorticoid receptors (MR). Methods Interplay of the two receptors was studied in the highly differentiated, human colon cell line HT-29/B6-GR/MR equipped with the complete receptor repertoire of both GR and MR due to stable transfection. Results In contrast to HT-29/B6 cells solely expressing the MR, HT-29/B6-GR/MR cells displayed a physiological response to aldosterone regarding ENaC induction after a pre-incubation step with the GR agonist dexamethasone. Resulting from cooperative effects between the activated GR and the MR, MR protein levels were elevated and MR-dependent transcription of ENaC subunits β and γ was increased. As an additional mechanism involved, transcription of SGK-1 (serum- and glucocorticoid-induced kinase 1) and GILZ (glucocorticoid-induced leucin zipper) - both essential for the rise in apical ENaC levels - were also augmented by the activated MR. Conclusion After generating a new GR/MR colonic cell model we showed that GR expression and GR pre-stimulation were indispensable for the MR-dependent induction of ENaC.

Glucocorticoid receptor is indispensable for physiological responses to aldosterone in epithelial Na + channel induction via the mineralocorticoid receptor in a human colonic cell line

The epithelial Na+ channel (ENaC) plays a crucial role in electrogenic Na + absorption in the distal colon. ENaC induction via the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR) is differentially regulated by modulatory components. As most existing epithelial cell lines including colonic epithelial cell lines miss the co-expression of functional GR and MR, signaling on ENaC is only poorly characterized regarding the interplay of glucocorticoids and mineralocorticoids. In the present study, we show that GR expression and activity are indispensable for MR-dependent induction of ENaC-mediated Na + transport. Cooperativity of the two receptors has been studied in the highly differentiated, epithelial colonic cell line HT-29/B6-GR/MR which is equipped with the complete receptor repertoire of both GR and MR due to stable transfection. In contrast to HT-29/B6 cells solely expressing the MR, this cell line displays a physiological response to aldosterone regarding ENaC induction. To achieve this, a pre-incubation step with the GR agonist dexamethasone was required to allow for the subsequent stimulation of ENaC by aldosterone. As a result of cooperative effects between the activated GR and the MR, MR protein levels were elevated and MR-dependent transcription of ENaC subunits β and γ was increased. As an additional mechanism involved, transcription of SGK-1 (serum- and glucocorticoid-induced kinase 1) and GILZ (glucocorticoid-induced leucin zipper) – both essential for the insertion of ENaC into the apical enterocyte membrane – were also augmented by the activated MR.

Foxo1 Nuclear-Cytoplasmic Movement in Live Skeletal Muscle Fiber

The transcription factor Foxo1 is integral to the regulation of expression of proteins which promote muscle atrophy. Phosphorylation of Foxo1 causes its translocation to the cytoplasm and thus prevents Foxo1-DNA binding and consequent transcription of genes that cause muscle atrophy and cell death. Thus, phosphorylation of Foxo1 leads to cell survival and muscle hypertrophy. Maintenance of Foxo1 phosphorylation and its resulting cytoplasmic retention could be used to suppress muscle atrophy and thereby shift the atrophy/hypertrophy balance in favor of hypertrophy. This in turn may be utilized to develop therapeutic avenues in treatment of muscle wasting as seen in patients with denervation, age-related muscle wasting, and AIDS. Akt and serum- and glucocorticoid-inducible kinase (SGK) are important regulators of the phosphorylation status of Foxo1. These pathways have been well characterized and the effects on Foxo1 localization have been reported. However, the mechanisms which regulate nuclear influx and nuclear efflux have not been separately evaluated. Here, we determine the effects of Akt kinase activity specifically on nuclear influx of Foxo1. To accomplish this goal, we quantified nuclear and cytoplasmic levels of adenovirally expressed Foxo1-GFP in cultured flexor digitorum brevis. The nuclear influx during treatment with kinase inhibitor Akt IV alone and in combination with the nuclear efflux inhibitor lemptomycin B provides insight into the activity of Akt as a Foxo1 kinase. Surprisingly, Akt inhibition reveals Akt to have little effect on the rate of nuclear influx of Foxo1. To evaluate translocation of endogenous Foxo1 in a similar manner immunocytochemistry and western blotting techniques were used. These results indicate that Akt either phosphorylates Foxo1 primarily in the nucleus and not in the cytoplasm, or that there is a mechanism for cytoplasmic phosphorylation of Foxo1 other than via Akt. Supported by NIH-NIAMS Grants R01-AR056477 and T32-AR007592.

Pre-Existing High Glucocorticoid Receptor Number Predicting Development of Posttraumatic Stress Symptoms After Military Deployment

The development of posttraumatic stress disorder (PTSD) is influenced by preexisting vulnerability factors. The authors aimed at identifying a preexisting biomarker representing a vulnerability factor for the development of PTSD. To that end, they determined whether the dexamethasone binding capacity of leukocytes, as a measure of glucocorticoid receptor (GR) number, before exposure to trauma was a predictor of development of PTSD symptoms. In addition, the authors analyzed mRNA expression for GR subtypes and GR target genes. Participants were selected from a large prospective study on deployment-related disorders, in which peripheral blood mononuclear cells (PBMCs) were obtained prior to and 1 and 6 months after military deployment. Participants included armed forces personnel with high levels of PTSD symptoms 6 months after deployment (N=34) and comparison subjects without high levels of PTSD or depressive symptoms (N=34) matched for age, rank, previous deployments, educational level, and function during deployment. Before military deployment, the GR number in PBMCs was significantly higher in participants who developed high levels of PTSD symptoms after deployment relative to matched comparison subjects. Logistic regression analysis showed that the risk for inclusion in the PTSD group after deployment increased 7.5-fold with each GR increase of 1,000. No group differences were observed in mRNA expression of GR-α, GR-P, GR-β, glucocorticoid-induced leucine zipper (GILZ), serum and glucocorticoid-inducible kinase-1 (SGK-1), and FKBP5. The higher GR number in the PTSD group was maintained at 1 and 6 months after deployment. These results demonstrate that a preexisting high GR number in PBMCs is a vulnerability factor for subsequent development of PTSD symptoms.