IL-6 activates serum and glucocorticoid kinase via p38alpha mitogen-activated protein kinase pathway

Matrix stiffness influences response to chemo and targeted therapy in brain metastatic breast cancer cells

Breast cancer is the most common malignancy accounting for 12.5% of all newly diagnosed cancer cases across the globe. Breast cancer cells are known to metastasize to distant organs (i.e., brain), wherein they can exhibit a dormant phenotype for extended time periods. These dormant cancer cells exhibit reduced proliferation and therapeutic resistance. However, the mechanisms by which dormant cancer cells exhibit resistance to therapy, in the context of brain metastatic breast cancer (BMBC), is not well understood. Herein, we utilized hyaluronic acid (HA) hydrogels with varying stiffnesses to study drug responsiveness in dormant vs. proliferative BMBC cells. It was found that cells cultured on soft HA hydrogels (∼0.4 kPa) that showed a non-proliferative (dormant) phenotype exhibited resistance to Paclitaxel or Lapatinib. In contrast, cells cultured on stiff HA hydrogels (∼4.5 kPa) that showed a proliferative phenotype exhibited responsiveness to Paclitaxel or Lapatinib. Moreover, dormancy-associated resistance was found to be due to upregulation of the serum/glucocorticoid regulated kinase 1 (SGK1) gene which was mediated, in part, by the p38 signaling pathway. Accordingly, SGK1 inhibition resulted in a dormant-to-proliferative switch and response to therapy. Overall, our study demonstrates that matrix stiffness influences dormancy-associated therapy response mediated, in part, via the p38/SGK1 axis.

Distinct phases of cellular signaling revealed by time-resolved protein synthesis

The post-translational regulation of protein function is involved in most cellular processes. As such, synthetic biology tools that operate at this level provide opportunities for manipulating cellular states. Here we deploy proximity-triggered protein trans-splicing technology to enable the time-resolved synthesis of target proteins from premade parts. The modularity of the strategy allows for the addition or removal of various control elements as a function of the splicing reaction, in the process permitting the cellular location and/or activity state of starting materials and products to be differentiated. The approach is applied to a diverse set of proteins, including the kinase oncofusions breakpoint cluster region-Abelson (BCR-ABL) and DNAJ-PKAc where dynamic cellular phosphorylation events are dissected, revealing distinct phases of signaling and identifying molecular players connecting the oncofusion to cancer transformation as new therapeutic targets of cancer cells. We envision that the tools and control strategies developed herein will allow the activity of both naturally occurring and designer proteins to be harnessed for basic and applied research.

Distinct phases of cellular signaling revealed by time-resolved protein synthesis

The post-translational regulation of protein function is involved in most cellular processes. As such, synthetic biology tools that operate at this level provide opportunities for manipulating cellular states. Here, we deploy a proximity-triggered protein trans-splicing technology to enable the time-resolved synthesis of target proteins from pre-made parts. The modularity of the strategy allows for the addition or removal of various control elements as a function of the splicing reaction, in the process permitting the cellular location and/or activity state of starting materials and products to be differentiated. The approach is applied to a diverse set of proteins, including the kinase oncofusions BCR/ABL and DNAJB1/PRKACA where dynamic cellular phosphorylation events are dissected, revealing distinct phases of signaling and identifying molecular players connecting the oncofusion to cancer transformation as novel therapeutic targets of cancer cells. We envision that the tools and control strategies developed herein will allow the activity of both naturally occurring and designer proteins to be harnessed for basic and applied research.

Upregulated TNF-α and lactate following ERK-SGK1 activation in the spinal dorsal horn underlies chronic postsurgical pain

Skin/muscle incision and retraction (SMIR) during surgeries can lead to chronic postsurgical pain (CPSP). The underlying mechanisms are still unclear. In the present study, we showed that SMIR of the thigh induced phosphorylation of extracellular signal-regulated kinase (ERK), followed by serum- and glucocorticoid-inducible kinase-1 (SGK1) activation in the spinal dorsal horn. Intrathecal injection of PD98059, an ERK inhibitor, or GSK650394, a SGK1 inhibitor, significantly attenuated mechanical pain hypersensitivity in SMIR rats. The level of tumor necrosis factor α and lactate in spinal cord was significantly decreased by PD98059 or GSK650394 injection. Furthermore, PD98059 decreased the activation of SGK1 in the spinal dorsal horn. These results indicate that ERK-SGK1 activation followed by proinflammatory mediator release in the spinal dorsal horn underlies CPSP.

Curcumin and Carnosic Acid Cooperate to Inhibit Proliferation and Alter Mitochondrial Function of Metastatic Prostate Cancer Cells

Anticancer activities of plant polyphenols have been demonstrated in various models of neoplasia. However, evidence obtained in numerous in vitro studies indicates that proliferation arrest and/or killing of cancer cells require quite high micromolar concentrations of polyphenols that are difficult to reach in vivo and can also be (geno)toxic to at least some types of normal cells. The ability of certain polyphenols to synergize with one another at low concentrations can be used as a promising strategy to effectively treat human malignancies. We have recently reported that curcumin and carnosic acid applied at non-cytotoxic concentrations synergistically cooperate to induce massive apoptosis in acute myeloid leukemia cells, but not in normal hematopoietic and non-hematopoietic cells, via sustained cytosolic calcium overload. Here, we show that the two polyphenols can also synergistically suppress the growth of DU145 and PC-3 metastatic prostate cancer cell cultures. However, instead of cell killing, the combined treatment induced a marked inhibition of cell proliferation associated with G₀/G₁ cell cycle arrest. This was preceded by transient elevation of cytosolic calcium levels and prolonged dissipation of the mitochondrial membrane potential, without generating oxidative stress, and was associated with defective oxidative phosphorylation encompassing mitochondrial dysfunction. The above effects were concomitant with a significant downregulation of mRNA and protein expression of the oncogenic kinase SGK1, the mitochondria-hosted mTOR component. In addition, a moderate decrease in SGK1 phosphorylation at Ser422 was observed in polyphenol-treated cells. The mTOR inhibitor rapamycin produced a similar reduction in SGK1 mRNA and protein levels as well as phosphorylation. Collectively, our findings suggest that the combination of curcumin and carnosic acid at potentially bioavailable concentrations may effectively target different types of cancer cells by distinct modes of action. This and similar combinations merit further exploration as an anticancer modality.

Interaction Between Serum/Glucocorticoid-Regulated Kinase 1 and Interleukin-6 in Chronic Rhinosinusitis

PURPOSE

Serum/glucocorticoid-regulated kinase 1 (SGK1) has recently emerged as a critical regulator of inflammatory diseases. In this study, we examined SGK1 expression and its possible pathogenic roles in chronic rhinosinusitis (CRS).

METHODS

Immunohistochemistry, western blotting, Bio-Plex assay, enzyme-linked immunosorbent assays, and quantitative real-time polymerase chain reaction were performed to assess protein and gene expression levels. The mRNA expression levels of SGK1 and interleukin-6 (IL-6) were extracted from a CRS database to perform correlation analysis. Stable cell lines with SGK1 overexpression (16HBE) and knockdown (A549) were constructed to investigate the interaction between SGK1 and IL-6 in vitro.

RESULTS

SGK1 exhibited strong cytoplasmic and nuclear staining in the epithelial layers and the lamina propria of nasal polyps (NPs) and in the mucosal tissues of CRS without nasal polyps (CRSsNP). The mRNA and protein expression levels of SGK1 and IL-6 were significantly increased in NPs and CRSsNP tissues, compared to control tissues. SGK1 phosphorylation was significantly greater in NPs than in CRSsNP tissues (P < 0.01). The mRNA levels of SGK1 and IL-6 were significantly correlated (P < 0.001, r = 0.649). Exposure to IL-6 significantly increased SGK1 expression in cultured dispersed NP cells, 16HBE cells, and A549 cells. IL-6 expression was significantly down-regulated in SGK1-overexpressing 16HBE cells (P < 0.01) and significantly up-regulated in SGK1-knockdown A549 cells (P < 0.05). Administration of GSK650394, a SGK1 inhibitor, significantly increased IL-6 self-induced mRNA expression in cultured dispersed NP cells and 16HBE cells.

CONCLUSIONS

The interaction between SGK1 and IL-6 may play an anti-inflammatory role in IL-6-induced inflammation in the pathogenesis of CRS.

Emerging Role of Serum Glucocorticoid-Regulated Kinase 1 in Pathological Pain

Currently, the management of acute and chronic pain in clinical practice remains unsatisfactory due to the existence of limited effective treatments, and novel therapeutic strategies for pathological pain are urgently needed. In the past few decades, the role of serum and glucocorticoid-inducible kinase 1 (SGK1) in the development of pain and diurnal rhythms has been implicated in numerous studies. The expression levels of SGK1 mRNA and protein were found to be elevated in the spinal cord and brain in various pathological pain models. Blocking SGK1 significantly attenuated pain-like responses and the development of pathological pain. These studies provide strong evidence that SGK1 plays a role in the development of various types of pathological pain and that targeting SGK1 may be a novel therapeutic strategy for pain management. In this review article, we provide evidence from animal models for the potential role of SGK1 in the regulation of pathological pain caused by inflammation, nerve injury, psychiatric disorders, and chronic opioid exposure.

Renal Inflammation Induces Salt Sensitivity in Male db/db Mice through Dysregulation of ENaC

BACKGROUND

Hypertension is considered a major risk factor for the progression of diabetic kidney disease. Type 2 diabetes is associated with increased renal sodium reabsorption and salt-sensitive hypertension. Clinical studies show that men have higher risk than premenopausal women for the development of diabetic kidney disease. However, the renal mechanisms that predispose to salt sensitivity during diabetes and whether sexual dimorphism is associated with these mechanisms remains unknown.

METHODS

Female and male db/db mice exposed to a high-salt diet were used to analyze the progression of diabetic kidney disease and the development of hypertension.

RESULTS

Male, 34-week-old, db/db mice display hypertension when exposed to a 4-week high-salt treatment, whereas equivalently treated female db/db mice remain normotensive. Salt-sensitive hypertension in male mice was associated with no suppression of the epithelial sodium channel (ENaC) in response to a high-salt diet, despite downregulation of several components of the intrarenal renin-angiotensin system. Male db/db mice show higher levels of proinflammatory cytokines and more immune-cell infiltration in the kidney than do female db/db mice. Blocking inflammation, with either mycophenolate mofetil or by reducing IL-6 levels with a neutralizing anti-IL-6 antibody, prevented the development of salt sensitivity in male db/db mice.

CONCLUSIONS

The inflammatory response observed in male, but not in female, db/db mice induces salt-sensitive hypertension by impairing ENaC downregulation in response to high salt. These data provide a mechanistic explanation for the sexual dimorphism associated with the development of diabetic kidney disease and salt sensitivity.

Cutaneous and hepatic vascular lesions due to a recurrent somatic GJA4 mutation reveal a pathway for vascular malformation

The term “cavernous hemangioma” has been used to describe vascular anomalies with histology featuring dilated vascular spaces, vessel walls consisting mainly of fibrous stromal bands lined by a layer of flattened endothelial cells, and an irregular outer rim of interrupted smooth muscle cells. Hepatic hemangiomas (HHs) and cutaneous venous malformations (VMs) share this histologic pattern, and we examined lesions in both tissues to identify genetic drivers. Paired whole-exome sequencing (WES) of lesional tissue and normal liver in HH subjects revealed a recurrent GJA4 c.121G>T (p.Gly41Cys) somatic mutation in four of five unrelated individuals, and targeted sequencing in paired tissue from 9 additional HH individuals identified the same mutation in 8. In cutaneous lesions, paired targeted sequencing in 5 VMs and normal epidermis found the same GJA4 c.121G>T (p.Gly41Cys) somatic mutation in three. GJA4 encodes gap junction protein alpha 4, also called connexin 37 (Cx37), and the p.Gly41Cys mutation falls within the first transmembrane domain at a residue highly conserved among vertebrates. We interrogated the impact of the Cx37 mutant via lentiviral transduction of primary human endothelial cells. We found that the mutant induced changes in cell morphology and activated serum/glucocorticoid-regulated kinase 1 (SGK1), a serine/threonine kinase known to regulate cell proliferation and apoptosis, via non-canonical activation. Treatment with spironolactone, an inhibitor of angiogenesis, suppressed mutant SGK1 activation and reversed changes in cell morphology. These findings identify a recurrent somatic GJA4 c.121G>T mutation as a driver of hepatic and cutaneous VMs, revealing a new pathway for vascular anomalies, with spironolactone a potential pathogenesis-based therapy.

Serum and Glucocorticoid-Inducible Kinase 1 (SGK1) in NSCLC Therapy

Non-small cell lung cancer (NSCLC) remains the most prevalent and one of the deadliest cancers worldwide. Despite recent success, there is still an urgent need for new therapeutic strategies. It is also becoming increasingly evident that combinatorial approaches are more effective than single modality treatments. This review proposes that the serum and glucocorticoid-inducible kinase 1 (SGK1) may represent an attractive target for therapy of NSCLC. Although ubiquitously expressed, SGK1 deletion in mice causes only mild defects of ion physiology. The frequent overexpression of SGK1 in tumors is likely stress-induced and provides a therapeutic window to spare normal tissues. SGK1 appears to promote oncogenic signaling aimed at preserving the survival and fitness of cancer cells. Most importantly, recent investigations have revealed the ability of SGK1 to skew immune-cell differentiation toward pro-tumorigenic phenotypes. Future studies are needed to fully evaluate the potential of SGK1 as a therapeutic target in combinatorial treatments of NSCLC. However, based on what is currently known, SGK1 inactivation can result in anti-oncogenic effects both on tumor cells and on the immune microenvironment. A first generation of small molecules to inactivate SGK1 has already been already produced.

Lack of PPARβ/δ-Inactivated SGK-1 Is Implicated in Liver Carcinogenesis

Objective

The present study examined the role of PPARβ/δ in hepatocellular carcinoma (HCC).

Methods

The effect of PPARβ/δ on HCC development was analyzed using PPARβ/δ-overexpressed liver cancer cells and PPARβ/δ-knockout mouse models.

Results

PPARβ/δ^(-/-) mice were susceptible to diethylnitrosamine- (DEN-) induced HCC (87.5% vs. 37.5%, p < 0.05). In addition, PPARβ/δ-overexpressed HepG2 cells had reduced proliferation, migration, and invasion capabilities accompanied by increased apoptosis and cell cycle arrest at the G0/G1 phase. Moreover, differential gene expression profiling uncovered that the levels of serine/threonine-protein kinase (SGK-1) mRNA and its encoded protein were reduced in PPARβ/δ-overexpressed HepG2 cells. Consistently, elevated SGK-1 levels were found in PPARβ/δ^(-/-) mouse livers as well as PPARβ/δ-knockdown human SMMC-7721 HCC cells. Chromatin immunoprecipitation (ChIP) assays followed by real-time quantitative polymerase chain reaction (qPCR) assays further revealed the binding of PPARβ/δ to the SGK-1 regulatory region in HepG2 cells.

Conclusions

Due to the known tumor-promoting effect of SGK1, the present data suggest that PPARβ/δ-deactivated SGK1 is a novel pathway for inhibiting liver carcinogenesis.

The PI3K-AKT-mTOR Pathway and Prostate Cancer: At the Crossroads of AR, MAPK, and WNT Signaling

Oncogenic activation of the phosphatidylinositol-3-kinase (PI3K), protein kinase B (PKB/AKT), and mammalian target of rapamycin (mTOR) pathway is a frequent event in prostate cancer that facilitates tumor formation, disease progression and therapeutic resistance. Recent discoveries indicate that the complex crosstalk between the PI3K-AKT-mTOR pathway and multiple interacting cell signaling cascades can further promote prostate cancer progression and influence the sensitivity of prostate cancer cells to PI3K-AKT-mTOR-targeted therapies being explored in the clinic, as well as standard treatment approaches such as androgen-deprivation therapy (ADT). However, the full extent of the PI3K-AKT-mTOR signaling network during prostate tumorigenesis, invasive progression and disease recurrence remains to be determined. In this review, we outline the emerging diversity of the genetic alterations that lead to activated PI3K-AKT-mTOR signaling in prostate cancer, and discuss new mechanistic insights into the interplay between the PI3K-AKT-mTOR pathway and several key interacting oncogenic signaling cascades that can cooperate to facilitate prostate cancer growth and drug-resistance, specifically the androgen receptor (AR), mitogen-activated protein kinase (MAPK), and WNT signaling cascades. Ultimately, deepening our understanding of the broader PI3K-AKT-mTOR signaling network is crucial to aid patient stratification for PI3K-AKT-mTOR pathway-directed therapies, and to discover new therapeutic approaches for prostate cancer that improve patient outcome.

SGK1 Mediates Hypoxic Pulmonary Hypertension through Promoting Macrophage Infiltration and Activation

Inflammation plays a pivotal role in the development of pulmonary arterial hypertension (PAH). Meanwhile, serum glucocorticoid-regulated kinase-1 (SGK1) has been considered to be an important factor in the regulation of inflammation in some vascular disease. However, the role of SGK1 in hypoxia-induced inflammation and PAH is still unknown. WT and SGK1^−/− mice were exposed to chronic hypoxia to induce PAH. The quantitative PCR and immunohistochemistry were used to determine the expression of SGK1. The right ventricular hypertrophy index (RVHI), RV/BW ratio, right ventricle systolic pressure (RVSP), and percentage of muscularised vessels and medical wall thickness were measured to evaluate PAH development. The infiltration of macrophages and localization of SGK1 on cells were examined by histological analysis. The effects of SGK1 on macrophage function and cytokine expression were assessed by comparing WT and SGK1^−/− macrophages in vitro. SGK1 has high expression in hypoxia-induced PAH. Deficiency of SGK1 prevented the development of hypoxia-induced PAH and inhibited macrophage infiltration in the lung. In addition, SGK1 knockout inhibited the expression of proinflammatory cytokines in macrophages. SGK1-induced macrophage activation and proinflammatory response contributes to the development of PAH in hypoxia-treated mice. Thus, SGK1 might be considered a promising target for PAH treatment.

Bradykinin contributes to immune liver injury via B2R receptor-mediated pathways in trichloroethylene sensitized mice: A role in Kupffer cell activation

We have previously shown trichloroethylene (TCE) induced occupational medicamentosa-like dermatitis due to TCE (OMLDT) with immune liver injury, and kallikrein-kinin system (KKS) activation as a probably mechanism underlying the immune damage. Bradykinin (BK) is an important active component of KKS system function, but the specific role of BK in the immune liver injury has never been examined. The present study aimed to explore the important role of BK and mechanisms of action in immune liver injury induced by TCE. TCE sensitization significantly increased the expression of BK receptor (B2R) in the liver. Compared to blank and vehicle control group, TCE sensitization positive mice developed exacerbated liver injury evidenced by elevated AST, ALT levels and hepatocyte damage. TCE sensitization also stimulated MAPK and STAT3 activation in liver tissue. B2R antagonist HOE140 ameliorated these changes. Kupffer cells (KCs) of the liver were also activated following TCE sensitization; both CD68⁺ KCs and CD16/CD32⁺ M1 type KCs were increased in TCE positive group. Further experiments isolated the KCs from the liver in each group and showed that TCE sensitization resulted activation of MAPK signal pathway which in turn caused release of the pro-inflammatory cytokines, IL-1β, IL-6, TNF-α, in KCs; the antagonist HOE140 again decreased these changes in KCs. These results uncover a novel role of BK and B2R cross-talk in KCs activation in TCE sensitized mice, mediated by pro-inflammatory cytokine release via MAPK and STAT3 activation, contributing to the immune liver injury.

Sodium Chloride Aggravates Arthritis via Th17 Polarization

PURPOSE

Sodium chloride (NaCl) has been proposed as a driving factor in autoimmune diseases through the induction of pathogenic CD4⁺ T helper cells that produce interleukin-17 (Th17 cells). This study investigated the effects of NaCl on inflammatory arthritis in mice and humans.

MATERIALS AND METHODS

Collagen-induced arthritis (CIA) mice were fed a normal or high-salt diet ad libitum, and clinical and histologic features of arthritis were evaluated. The proportion of Th17 cells in the spleens of CIA mice fed a normal or high-salt diet was evaluated by flow cytometry, and the expression of IL-17 in joints and intestines was determined by immunohistochemical staining. We also analyzed the effect of NaCl on Th17 differentiation from peripheral blood monocytes of patients with rheumatoid arthritis (RA) and osteoarthritis (OA) and evaluated the contents of sodium and IL-17 in the synovial fluid of RA and OA patients.

RESULTS

NaCl increased murine and human Th17 cell differentiation in a dose-dependent manner. Clinical and histological arthritis was more severe in the high-salt-fed CIA mice, compared to control CIA mice. The proportion of Th17 cells among splenocytes was higher in CIA mice fed a high-salt diet. Expression of synovial and intestinal IL-17 was also higher in high-salt-fed CIA mice. Comparison of synovial fluid between RA patients and OA patients revealed that Na⁺ and IL-17 were more abundant in RA synovial fluid.

CONCLUSION

This study suggests that NaCl can aggravate arthritis by affecting Th17 differentiation. Accordingly, limiting salt intake may be helpful for treating inflammatory arthritis, such as RA.

miR-17-92 cluster promotes cholangiocarcinoma growth: evidence for PTEN as downstream target and IL-6/Stat3 as upstream activator

miR-17-92 is an oncogenic miRNA cluster implicated in the development of several cancers; however, it remains unknown whether the miR-17-92 cluster is able to regulate cholangiocarcinogenesis. This study was designed to investigate the biological functions and molecular mechanisms of the miR-17-92 cluster in cholangiocarcinoma. In situ hybridization and quantitative RT-PCR analysis showed that the miR-17-92 cluster is highly expressed in human cholangiocarcinoma cells compared with the nonneoplastic biliary epithelial cells. Forced overexpression of the miR-17-92 cluster or its members, miR-92a and miR-19a, in cultured human cholangiocarcinoma cells enhanced tumor cell proliferation, colony formation, and invasiveness, in vitro. Overexpression of the miR-17-92 cluster or miR-92a also enhanced cholangiocarcinoma growth in vivo in hairless outbred mice with severe combined immunodeficiency (SHO-Prkdc(scid)Hr(hr)). The tumor-suppressor, phosphatase and tensin homolog deleted on chromosome 10 (PTEN), was identified as a bona fide target of both miR-92a and miR-19a in cholangiocarcinoma cells via sequence prediction, 3' untranslated region luciferase activity assay, and Western blot analysis. Accordingly, overexpression of the PTEN open reading frame protein (devoid of 3' untranslated region) prevented miR-92a- or miR-19a-induced cholangiocarcinoma cell growth. Microarray analysis revealed additional targets of the miR-17-92 cluster in human cholangiocarcinoma cells, including APAF-1 and PRDM2. Moreover, we observed that the expression of the miR-17-92 cluster is regulated by IL-6/Stat3, a key oncogenic signaling pathway pivotal in cholangiocarcinogenesis. Taken together, our findings disclose a novel IL-6/Stat3-miR-17-92 cluster-PTEN signaling axis that is crucial for cholangiocarcinogenesis and tumor progression.

Significance of Interleukin-6 in Papillary Thyroid Carcinoma

This study sought to reveal the significance of IL-6 in papillary thyroid carcinoma by determining its circulating levels, tumoral protein, and mRNA expressions. As compared to the healthy individuals, serum IL-6 was significantly higher in patients with benign thyroid diseases and PTC. Further, its level was significantly higher in PTC patients as compared to patients with benign thyroid diseases. ROC curves also confirmed a good discriminatory efficacy of serum IL-6 between healthy individuals and patients with benign thyroid diseases and PTC. The circulating IL-6 was significantly associated with poor overall survival in PTC patients. IL-6 immunoreactivity was significantly high in PTC patients as compared to the benign thyroid disease patients. Significantly higher IL-6 mRNA expression was also observed in the primary tumour tissues of PTC patients than the adjacent normal tissues. The protein expression of IL-6 at both the circulating and tissue level correlated with disease aggressiveness in PTC patients. Moreover, a significant positive correlation was observed between the IL-6 protein and mRNA expression in the primary tumours of PTC patients. Finally in conclusion, IL-6 has an important role in thyroid cancer progression. Thus targeting IL-6 signalling can help in clinical management of thyroid carcinoma patients.

Serum-glucocorticoid regulated kinase 1 regulates macrophage recruitment and activation contributing to monocrotaline-induced pulmonary arterial hypertension

Sustained inflammation is associated with pulmonary vascular remodeling and arterial hypertension (PAH). Serum-glucocorticoid regulated kinase 1 (SGK1) has been shown to participate in vascular remodeling, but its role in inflammation-associated PAH remains unknown. In this study, the importance of SGK1 expression and activation was investigated on monocrotaline (MCT)-induced PAH, an inflammation-associated experimental model of PAH used in mice and rats. The expression of SGK1 in the lungs of rats with MCT-induced PAH was significantly increased. Furthermore, SGK1 knockout mice were resistant to MCT-induced PAH and showed less elevation of right ventricular systolic pressure and right ventricular hypertrophy and showed reduced pulmonary vascular remodeling in response to MCT injection. Administering the SGK1 inhibitor, EMD638683, to rats also prevented the development of MCT-induced PAH. The expression of SGK1 was shown to take place primarily in alveolar macrophages. EMD638683 treatment suppressed macrophage infiltration and inhibited the proliferation of pulmonary arterial smooth muscle cells (PASMCs) in the lungs of rats with MCT-induced PAH. Co-culture of bone marrow-derived macrophages (BMDMs) from wild-type (WT) mice promoted proliferation of PASMC in vitro, whereas BMDMs from either SGK1 knockout mice or WT mice with EMD638683 treatment failed to induce this response. Collectively, the present results demonstrated that SGK1 is important to the regulation of macrophage activation that contributes to the development of PAH; thus, SGK1 may be a potential therapeutic target for the treatment of PAH.

Increased expression and activation of serum- and glucocorticoid-inducible kinase-1 (SGK1) by cadmium in HK-2 renal proximal tubular epithelial cells

In HK-2 cells exposed to cadmium chloride (CdCl2), the level of serum- and glucocorticoid-inducible kinase-1 (SGK1) protein is increased, but the levels of SGK2 and SGK3 proteins are not. Phosphorylation of SGK1 protein is also observed. Treatment with actinomycin D abolished CdCl2-induced elevation of SGK1 mRNA level. Treatment with actinomycin D or cycloheximide suppressed SGK1 protein levels in cells exposed to CdCl2. Treatment with SGK1 inhibitor EMD638683 or knockdown of SGK1 with siRNA suppressed CdCl2-induced phosphorylation of N-Myc downstream-regulated kinase 1 (NDRG1). These results indicate that cadmium induces the transcriptional upregulation of SGK1 expression and regulates NDRG1 in HK-2 cells.

Systemic and targeted therapy for biliary tract tumors and primary liver tumors

Tumors of the biliary tract and hepatocellular carcinoma (HCC) are complex tumors with heterogeneous carcinogenic mechanisms. Patients with hepatobiliary cancer have advances disease and need systematic therapy to palliate symptoms and extend survival. Development of effective systematic therapy is a significant unmet medical need. It is hoped that current and future clinical trials will identify additional effective systemic agents, combination systemic therapies, and combined modality options. The HCC community needs validated biomarkers to help identify the patients who will benefit most from emerging treatment options.

Knockdown of astrocyte elevated gene-1 inhibits growth through suppression of IL-6 secretion in HepG2 human hepatoma cells

Astrocyte-elevated gene-1 (AEG-1) has been reported to be associated with cancer progression in various types of human cancers, including liver cancer. However, to date, the molecular mechanism of AEG-1 action on the growth of liver cancer cells has been poorly elucidated. The present study aimed to investigate the effect of AEG-1 on the proliferation and apoptosis of liver cancer cells and the role of IL-6 in this process using the HepG2 human hepatoma cell line. shRNAs targeting AEG-1 were used to silence the expression of AEG-1. The effects on cell growth were detected by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, colony formation and cell cycle assays. Apoptosis was analyzed by flow cytometry. The expression of IL-6 was examined by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay, and the phosphorylation of Stat3 was detected by western blotting. AEG-1 knockdown was observed to induce cell proliferation inhibition and apoptosis through the suppression of IL-6 secretion. Stat3, a downstream target of IL-6 signaling, was suppressed in the AEG-1-silenced cells and target genes, including Bcl-2 and crystalin, αB, which are associated with cell survival, were downregulated. Overall, the findings suggest that aberrant AEG-1 expression promotes the growth of HepG2 liver cancer cells, contributing to the progression of liver cancer, which may partly be mediated by IL-6 signaling.

TGFβ1 and SGK1-sensitive store-operated Ca2+ entry and Orai1 expression in endometrial Ishikawa cells

The serum-and-glucocorticoid-inducible-kinase-1 (SGK1) is ubiquitously expressed and under genomic control by cell stress, hormones and further mediators. A most powerful stimulator of SGK1 expression is transforming growth factor TGFβ1. SGK1 is activated by insulin and growth factors via phosphatidylinositol-3-kinase and the 3-phosphoinositide-dependent kinase PDK1. As shown recently, SGK1 increases the store-operated Ca(2+) entry (SOCE), which is accomplished by the pore-forming ion channel unit Orai. Most recent observations further revealed that SGK1 plays a critical role in the regulation of fertility. SGK1 is up-regulated in the luminal epithelium of women with unexplained infertility but down-regulated in decidualizing stromal cells of patients with recurrent pregnancy loss. The present study explored whether Orai1 is expressed in endometrium and sensitive to regulation by SGK1 and/or TGFβ1. To this end, Orai1 protein abundance was determined by western blotting and SOCE by fura-2 fluorescence. As a result, Orai1 was expressed in human endometrium and in human endometrial Ishikawa cells. Orai1 expression and SOCE in Ishikawa cells were increased by transfection with constitutively active (S422D)SGK1 but not by transfection with inactive (K127N)SGK1. The difference of SOCE between (S422D)SGK1 and (K127N)SGK1-transfected cells was virtually abrogated in the presence of Orai1 inhibitor 2-aminoethoxydiphenyl borate (2-APB, 50 µM). Similar to (S422D)SGK1 transfection TGFβ1 treatment up-regulated both Orai1 protein abundance and SOCE. In conclusion, Orai1 is expressed in the human endometrium and is up-regulated by SGK1 and TGFβ1. The present observations thus uncover a novel element in SGK1-sensitive regulation of endometrial cells.

High-glucose-based peritoneal dialysis solution induces the upregulation of VEGF expression in human peritoneal mesothelial cells: The role of pleiotrophin

The aim of the present study was to investigate the effect of a high-glucose-based peritoneal dialysis solution (HGPDS) on the expression of pleiotrophin (PTN) and vascular endothelial growth factor (VEGF) in human peritoneal mesothelial cells (HPMCs) and the mechanisms through which fluvastatin (Flu) protects the peritoneal membrane in continuous ambulatory peritoneal dialysis (CAPD). HPMCs were cultured with HGPDS, Flu (10-8‑10-6 mol/l) and PTN (10‑30 nmol/l). The expression of PTN and VEGF was examined at the mRNA and protein level. To define the role of PTN in the regulation of VEGF expression, HPMCs were cultured with HGPDS in the presence or absence of the blocking peptide of PTN. The signaling pathways involved in PTN synthesis induced by HGPDS were also characterized. The phenotypic characteristics of HPMCs were observed under a light microscope. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetry and the mRNA and protein expression of PTN, VEGF and ERK1/2 was assessed by RT‑PCR and the western blot analysis, respectively. Following incubation with HGPDS for 48 h, the morphology of the HPMCs changed from a typical cobblestone‑like appearance to a fibroblast‑like phenotype. The same alteration in the morphology of the HPMCs also occurred following incubation with 20 nmol/l PTN. Flu (10-6 mol/l), GSK650394 [a competitive inhibitor of serum/glucocorticoid-regulated kinase 1 (SGK1), 10-5 mol/l] and PD98059 (a competitive inhibitor of ERK1/2, 10-5 mol/l) improved the negative changes in cell morphology induced by HGPDS. The results of MTT assay revealed that the reduction in HPMC viability occurred in the groups treated with HGPDS and this reduction was partially restored by Flu, GSK650394 and PD98059. A significant improvement in cell viability, which had been decreased by HGPDS, was observed following treatment with Flu (10-6 mol/l), PD98059 (10-5 mol/l) or GSK650394 (10-5 mol/l) (P<0.05). Compared with the control, the mRNA and protein expression of PTN and VEGF significantly increased in the HPMCs treated with HGPDS (P<0.05). GSK650394 and PD98059 significantly decreased the high mRNA and protein expression levels of PTN and VEGF induced by HGPDS (P<0.05) and Flu had the same inhibitory effect as GSK650394 and PD98059 in a dose‑dependent manner (P<0.05). The mRNA and protein expression of VEGF increased following the incubation of HPMCs with 20 nmol/l PTN. By contrast, the mRNA and protein expression levels of VEGF in the HPMCs decreased in the presence of the blocking peptide of PTN. The results from the present study indicated that HGPDS increased the expression of PTN and VEGF in the HPMCs, and this increase was attenuated by Flu, GSK650394 and PD98059. The protein expression of phosphorylated ERK1/2 (p-ERK1/2) was decreased by GSK650394 in the HPMCs treated with HGPDS. Taken together, the protective effects of Flu in HPMCs may be partially achieved through the SGK1‑ERK1/2 signaling pathway.

Therapeutic potential of serum and glucocorticoid inducible kinase inhibition

INTRODUCTION

Expression of serum-and-glucocorticoid-inducible kinase-1 (SGK1) is low in most cells, but dramatically increases under certain pathophysiological conditions, such as glucocorticoid or mineralocorticoid excess, inflammation with TGFβ release, hyperglycemia, cell shrinkage and ischemia. SGK1 is activated by insulin and growth factors via phosphatidylinositide-3-kinase, 3-phosphoinositide-dependent kinase and mammalian target of rapamycin. SGK1 sensitive functions include activation of ion channels (including epithelial Na(+) channel ENaC, voltage gated Na(+) channel SCN5A transient receptor potential channels TRPV4 - 6, Ca(2+) release activated Ca(2+) channel Orai1/STIM1, renal outer medullary K(+) channel ROMK, voltage gated K(+) channels KCNE1/KCNQ1, kainate receptor GluR6, cystic fibrosis transmembrane regulator CFTR), carriers (including Na(+),Cl(-) symport NCC, Na(+),K(+),2Cl(-) symport NKCC, Na(+)/H(+) exchangers NHE1 and NHE3, Na(+), glucose symport SGLT1, several amino acid transporters), and Na(+)/K(+)-ATPase. SGK1 regulates several enzymes (e.g., glycogen synthase kinase-3, ubiquitin-ligase Nedd4-2) and transcription factors (e.g., forkhead transcription factor 3a, β-catenin, nuclear factor kappa B).

AREAS COVERED

The phenotype of SGK1 knockout mice is mild and SGK1 is apparently dispensible for basic functions. Excessive SGK1 expression and activity, however, contributes to the pathophysiology of several disorders, including hypertension, obesity, diabetes, thrombosis, stroke, fibrosing disease, infertility and tumor growth. A SGK1 gene variant (prevalence ∼ 3 - 5% in Caucasians and ∼ 10% in Africans) is associated with hypertension, stroke, obesity and type 2 diabetes. SGK1 inhibitors have been developed and shown to reduce blood pressure of hyperinsulinemic mice and to counteract tumor cell survival.

EXPERT OPINION

Targeting SGK1 may be a therapeutic option in several clinical conditions, including metabolic syndrome and tumor growth.

The plant-derived glucocorticoid receptor agonist Endiandrin A acts as co-stimulator of colonic epithelial sodium channels (ENaC) via SGK-1 and MAPKs

In a search for secondary plant compounds that bind to the glucocorticoid receptor (GR), the cyclobutane lignan endiandrin A was discovered from the rainforest tree Endiandra anthropophagorum Domin. Our present study aims to characterize the effect of endiandrin A on GR-dependent induction of colonic sodium transport. The effect of endiandrin A was analyzed in GR-expressing colonic HT-29/B6 cells (HT-29/B6-GR). GR transactivation and subcellular localization were investigated by reporter gene assay and immunofluorescence. Epithelial sodium channel (ENaC) was analyzed by qRT-PCR and by measuring amiloride-sensitive short-circuit current (I_sc) in Ussing chambers. Endiandrin A (End A) has been identified as GR receptor binder. However, it did not cause significant GR transactivation as pGRE-luciferase activity was only 7% of that of the maximum effect of dexamethasone. Interestingly, endiandrin A had a significant impact on dexamethasone-dependent sodium absorption in cells co-exposed to tumor necrosis factor (TNF)-α. This was in part due to up-regulation of β- and γ-ENaC subunit expression. Endiandrin A potentiated GR-mediated transcription by increasing GR protein expression and phosphorylation. It inhibited c-Jun N-terminal kinase (JNK) activation induced by dexamethasone and/or TNF-α and increased levels of GR localized to the nucleus. Additionally, endiandrin A increased the serum- and glucocorticoid-induced kinase (sgk)-1 via activation of p38. Finally, the regulation of ENaC function by endiandrin A was confirmed in rat native colon. In conclusion, endiandrin A potentiates glucocorticoid-driven activation of colonic epithelial sodium channels via JNK inhibition and p38 activation due to transcriptional up-regulation of β- and γ-ENaC-subunits along with induction of sgk-1.

Serum/glucocorticoid-regulated kinase 1 (SGK1) is a prominent target gene of the transcriptional response to cytokines in multiple myeloma and supports the growth of myeloma cells

Multiple myeloma (MM) is a paradigm for a malignant disease that exploits external stimuli of the microenvironment for growth and survival. A thorough understanding of the complex interactions between malignant plasma cells and their surrounding requires a detailed analysis of the transcriptional response of myeloma cells to environmental signals. We determined the changes in gene expression induced by interleukin (IL)-6, tumor necrosis factor-α, IL-21 or co-culture with bone marrow stromal cells in myeloma cell lines. Among a limited set of genes that were consistently activated in response to growth factors, a prominent transcriptional target of cytokine-induced signaling in myeloma cells was the gene encoding the serine/threonine kinase serum/glucocorticoid-regulated kinase 1 (SGK1), which is a down-stream effector of PI3-kinase. We could demonstrate a rapid, strong and sustained induction of SGK1 in the cell lines INA-6, ANBL-6, IH-1, OH-2 and MM.1S as well as in primary myeloma cells. Pharmacologic inhibition of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway abolished STAT3 phosphorylation and SGK1 induction. In addition, small hairpin RNA (shRNA)-mediated knock-down of STAT3 reduced basal and induced SGK1 levels. Furthermore, downregulation of SGK1 by shRNAs resulted in decreased proliferation of myeloma cell lines and reduced cell numbers. On the molecular level, this was reflected by the induction of cell cycle inhibitory genes, for example, CDKNA1/p21, whereas positively acting factors such as CDK6 and RBL2/p130 were downregulated. Our results indicate that SGK1 is a highly cytokine-responsive gene in myeloma cells promoting their malignant growth.

Tristetraprolin-dependent post-transcriptional regulation of inflammatory cytokine mRNA expression by apolipoprotein A-I: role of ATP-binding membrane cassette transporter A1 and signal transducer and activator of transcription 3

Atherosclerosis is an inflammatory disease characterized by the accumulation of macrophages in the arterial intima. The activated macrophages secreted more pro-inflammatory cytokines, such as tumor necrosis factor (TNF)-α, which promote the development of the disease. Apolipoprotein A-I (apoA-I), the major component of high density lipoprotein, is involved in reverse cholesterol transport of lipid metabolism. Recently, it has been found that apoA-I suppresses inflammation via repression of inflammatory cytokine expression; the mechanisms of the apoA-I-suppressive action, however, are not yet well characterized. In this study, we have for the first time found that apoA-I suppresses the expression of some inflammatory cytokines induced by lipopolysaccharide via a specific post-transcriptional regulation process, namely mRNA destabilization, in macrophages. Our further studies have also shown that AU-rich elements in the 3'-untranslated region of TNF-α mRNA are responsive to the apoA-I-mediated mRNA destabilization. The apoA-I-induced inflammatory cytokine mRNA destabilization was associated with increased expression of mRNA-destabilizing protein tristetraprolin through a JAK2/STAT3 signaling pathway-dependent manner. When blocking interaction of apoA-I with ATP-binding membrane cassette transporter A1 (ABCA1), a major receptor for apoA-I in macrophages, it would almost totally abolish the effect of apoA-I on tristetraprolin expression. These results present not only a novel mechanism for the apoA-I-mediated inflammation suppression in macrophages but also provide new insights for developing strategies for modulating vascular inflammation and atherosclerosis.

Leptin and acetaldehyde synergistically promotes αSMA expression in hepatic stellate cells by an interleukin 6-dependent mechanism

BACKGROUND

The mechanisms whereby patients with obesity/overweight are more susceptible to alcohol-associated liver fibrosis are unclear. Leptin, a peptide hormone secreted by white adipose tissue is increased in association with overweight/obesity and is recognized as mediator of liver fibrosis. We sought to assess whether leptin contributes to alcoholic liver fibrosis by in vitro studies in hepatic stellate cells (HSC).

METHODS

Rat HSCs in second or third passage were utilised. Leptin, Acetaldehyde or combination with leptin and acetaldehyde were incubated for specific periods in cultured HSCs. Profibrogenic gene and protein expression were determined and associated-signalling pathways were assessed. Interleukin 6 (IL-6) antibody neutralization was used to evaluate the role of IL-6.

RESULTS

Leptin did not promote acetaldehyde-induced gene expression of collagen I, transforming growth factor β1 (TGFβ1) and tissue inhibitor of metalloproteinase 1 (TIMP1) in vitro. However, combined treatment of leptin with acetaldehyde synergistically enhanced the protein expression of smooth muscle actin (αSMA), an activation marker of HSCs, and of Interleukin-6 (IL-6). The combination of leptin and acetaldehyde also augmented MAPK/p38 and MAPK/ERK1/2 phosphoprotein expression. IL-6 neutralization down-regulated protein expression of pp38, pERK1/2 and αSMA, while exogenous rat recombinant IL-6 administration up-regulated αSMA. Similarly, MAPK/p38 and MAPK/ERK1/2 inhibition attenuated αSMA expression. H(2)O(2) induction by acetaldehyde was not potentiated by co-treatment with leptin nor did IL-6 neutralization reduce acetaldehyde-induced H(2)O(2) production.

CONCLUSIONS

We conclude that leptin potentiates acetaldehyde-induced HSC activation and αSMA expression by an IL-6-dependent mechanism.

Targeting the IL-6 dependent phenotype can identify novel therapies for cholangiocarcinoma

Background

The need for new therapies for cholangiocarcinoma is highlighted by their poor prognosis and refractoriness to chemotherapy. Increased production of Interleukin-6 promotes cholangiocarcinoma growth and contributes to chemoresistance by activating cell survival mechanisms. We sought to identify biologically active compounds capable of ameliorating the phenotypic effects of IL-6 expression and to explore their potential therapeutic use for cholangiocarcinoma.

Methodology

A genomic signature associated with Interleukin-6 expression in Mz-ChA-1 human malignant cholangiocytes was derived. Computational bioinformatics analysis was performed to identify compounds that induced inverse gene changes to the signature. The effect of these compounds on cholangiocarcinoma growth was then experimentally verified in vitro and in vivo. Interactions with other therapeutic agents were evaluated using median effects analysis.

Principal Findings

A group of structurally related compounds, nitrendipine, nifedipine and felodipine was identified. All three compounds were cytotoxic to Mz-ChA-1 cells with an IC50 for felodipine of 26 µM, nitrendipine, 44 µM and nifedipine, 15 µM. Similar results were observed in KMCH-1, CC-LP-1 and TFK-1 cholangiocarcinoma cell lines. At a fractional effect of 0.5, all three agents were synergistic with either camptothecin or gemcitabine in Mz-ChA-1 cells in vitro. Co-administration of felodipine and gemcitabine decreased the growth of Mz-ChA-1 cell xenografts in nude athymic mice.

Conclusions

Computational bioinformatics analysis of phenotype-based genomic expression can be used to identify therapeutic agents. Using this drug discovery approach based on targeting a defined tumor associated phenotype, we identified compounds with the potential for therapeutic use in cholangiocarcinoma.

Second AKT: the rise of SGK in cancer signalling

The serum and glucocorticoid kinase (SGK) family of serine/threonine kinases consists of three isoforms, SGK-1, SGK-2 and SGK-3. This family of kinases is highly homologous to the AKT kinase family, sharing similar upstream activators and downstream targets. SGKs have been implicated in the regulation of cell growth, proliferation, survival and migration: cellular processes that are dysregulated in cancer. Furthermore, SGKs lie downstream of phosphoinositide-3-kinase (PI3Kinase) signalling and interact at various levels with RAS/RAF/ERK signalling, two pathways that are involved in promoting tumorigenesis. Recent evidence suggests that mutant PI3Kinase can induce tumorigenesis through an AKT-independent but SGK3-dependent mechanism, thus implicating SGKs as potential players in malignant transformation. Here, we will review the current state of knowledge on the regulation of the SGKs and their role in normal cell physiology and transformation with a particular focus on SGK3.

NDRG2 is one of novel intrinsic factors for regulation of IL-10 production in human myeloid cell

N-myc downstream-regulated gene 2 (NDRG2) implicated in cellular growth and differentiation was previously reported as it is specifically expressed in primary and in vitro-differentiated dendritic cells (DCs) from monocytes and CD34(+) progenitor cells. However, its function has yet to be investigated in DCs. Here, the novel NDRG2 function about modulation of cytokines in DC was observed in this study. The secretion of IL-10 was not found in the monocyte-derived DC cells with high level of NDRG2 expression, but IL-10 was abundantly secreted up to 1ng/ml in the monocyte-derived macrophages with low level of NDRG2 expression, and further confirmed that the expression of IL-10 was dramatically increased in NDRG2-silenced DCs under presence of LPS, and significantly reduced in the NDRG2-overexpressed U937 cells under stimulation of PMA. The secretion of IL-12p70 was significantly reduced in the siNDRG2 introduced DC cells. The intracellular signaling of IL-10 secretion was markedly inhibited by SB203580, inhibitor of p38 MAPK, in the LPS-activated DCs and phosphorylation of p38 MAPK was decreased in the NDRG2 introduced U937 cells under PMA-stimulation. Taken together, NDRG2 might have a pivotal role as one of intrinsic factors for the modulation of p38 MAPK phosphorylation, and subsequently involve in controlling of IL-10 production.

Increased expression of serum- and glucocorticoid-regulated kinase-1 in the duodenal mucosa of children with coeliac disease

OBJECTIVES

Enterocyte apoptosis induced by activated intraepithelial lymphocytes is increased in coeliac disease (CD). Serum- and glucocorticoid-regulated kinase-1 (SGK1) is a serine/threonine protein kinase that may inhibit apoptosis and compensate for the excessive death of surface epithelial cells. The significance of SGK1 in CD is elusive so far. The aim of this study was to characterise the expression and localisation of SGK1 in duodenal biopsy samples taken from children with untreated CD, children with treated CD, and controls.

PATIENTS AND METHODS

Duodenal biopsy specimens were collected from 16 children with untreated CD, 9 children with treated CD, and 10 controls. The mRNA expression of SGK1 was determined by real-time reverse transcription-polymerase chain reaction. SGK1 and phosphorylated (P)-SGK1 protein levels and their localisation were determined by Western blot and immunofluorescent staining, respectively.

RESULTS

We found increased SGK1-mRNA expression as well as higher SGK1 and P-SGK1 protein levels in the duodenal mucosa of children with untreated CD compared with controls. In the duodenal mucosa of children with treated CD, SGK1-mRNA expression was decreased and SGK1 and P-SGK1 protein levels were lower than in untreated CD. SGK1 and P-SGK1 staining intensity was stronger in duodenal villous enterocytes of children with untreated CD compared with treated CD.

CONCLUSIONS

Our results of increased expression of SGK1 in untreated CD may suggest its contribution to the enterocyte survival in this disease.

Translation initiation: a critical signalling node in cancer

Mammalian target of rapamycin (mTOR) is a master regulator of translation initiation that controls the recruitment of ribosomes to mRNA templates in response to intracellular and extracellular cues. Evidence suggests that mTOR and its direct downstream targets, S6K and eIF4E/4E-BP, play significant roles in oncogenesis, and that inhibiting this pathway holds promise as an anti-proliferative approach. Recent genome-wide analyses of mutations in human cancers indicate that transformed cells activate a handful of processes and signalling pathways that are major contributors to their phenotype. Here we review the current literature implicating mTOR and translation initiation downstream of many of these various signalling pathways and processes usurped in human cancers. This review highlights the widespread activation of mTOR/eIF4E following acquisition of oncogenic lesions and its implication in promoting the transformation phenotype and indicates that targeting the control of translation initiation makes logical sense as a broad-acting therapeutic approach.

The physiological impact of the serum and glucocorticoid-inducible kinase SGK1

PURPOSE OF REVIEW

The role of serum and glucocorticoid-inducible kinase 1 (SGK1) in renal physiology and pathophysiology is reviewed with particular emphasis on recent advances.

RECENT FINDINGS

The mammalian target of rapamycin complex 2 has been shown to phosphorylate SGK1 at Ser422 (the so-called hydrophobic motif). Ser397 and Ser401 are two additional SGK1-phosphorylation sites required for maximal SGK1 activity. A 5' variant alternate transcript of human Sgk1 has been identified that is widely expressed and shows improved stability, enhanced membrane association, and greater stimulation of epithelial Na+ transport. SGK1 is essential for optimal processing of the epithelial sodium channel and also regulates the expression of the Na+-Cl- cotransporter. With regard to pathophysiology, SGK1 participates in the stimulation of renal tubular glucose transport in diabetes, the renal profibrotic effect of both angiotensin II and aldosterone, and in fetal programing of arterial hypertension.

SUMMARY

The outlined recent findings advanced our understanding of the molecular regulation of SGK1 as well as the role of the kinase in renal physiology and the pathophysiology of renal disease and hypertension. Future studies using pharmacological inhibitors of SGK1 will reveal the utility of the kinase as a new therapeutic target.

Relative resistance of SGK1 knockout mice against chemical carcinogenesis

The serum and glucocorticoid inducible kinase SGK1 was originally cloned from mammary tumor cells. SGK1 was found to be up-regulated in a variety of tumors, but down-regulated in several distinct tumors. Thus, evidence for a role of SGK1 in tumor growth remained conflicting. According to in vitro observations, SGK1 is up-regulated by the oncogene beta-catenin and negatively regulates the proapoptotic transcription factor FOXO3a, which in turn stimulates transcription of the Bcl2-interacting mediator BIM. This study aimed to define the role of SGK1 in colon carcinoma in vivo. SGK1 knockout mice (sgk1(-/-)) and their wild type littermates (sgk1(+/+)) were subjected to chemical cancerogenesis (intraperitoneal injection of 20 mg/kg 1,2-dimethylhydrazine followed by three cycles of 30 g/L synthetic dextran sulfate sodium for 7 days). Moreover, SGK1 was silenced in HEK293 cells. FOXO3a and BIM protein abundance was determined by Western blotting and immunohistochemistry. Following chemical cancerogenesis, sgk1(-/-)mice developed significantly less colonic tumors than sgk1(+/+)mice. According to Western blotting and immunohistochemistry, SGK1 deficiency enhanced the expression of FOXO3a and BIM both, in vitro and in vivo. SGK1 deficiency counteracts the development of colonic tumors, an effect at least in part due to up-regulation of FOXO3a and BIM.

A novel defense mechanism that is activated on amyloid-beta insult to mediate cell survival: role of SGK1-STAT1/STAT2 signaling

Amyloid-beta (Abeta) is known to induce apoptotic cell death and its underlying mechanism has been studied extensively, but the endogenous protection mechanism that results from Abeta insult is less known. In this study, we have found that Abeta(1-42) produced a dose-dependent decrease in cell viability and dose-dependent increase in apoptotic cell death in PC12 cells. Meanwhile, Abeta(1-42) (0.1 muM) increased the phosphorylation of serum- and glucocorticoid-inducible kinase1 (SGK1) at Ser-78 specifically. A parallel increase in ERK1/2, STAT1 and STAT2 phosphorylation and the anti-apoptotic gene Mcl-1 expression was also observed. Transfection of rat siRNAs against ERK1/2, SGK1, STAT1 and STAT2 abolished these effects of Abeta. Transfection of sgkS78D, the constitutively active SGK1, dose-dependently protected against Abeta-induced apoptosis and dose-dependently increased the expression of Mcl-1. SGK1 activation further phosphorylates STAT1 at Tyr-701 and Ser-727 directly, and activates STAT2 at Tyr-690 indirectly. Phosphorylation of STAT1/STAT2 upregulated Mcl-1 expression which in turn protected against Abeta-induced apoptosis. But Mcl-1 siRNA transfection enhanced Abeta-induced apoptosis. Mutation of SGK1 at Ser-78 blocked the effect of Abeta on STAT1/STAT2 phosphorylation and Mcl-1 expression. Further, mutation of STAT1/STAT2 prevented the effect of both Abeta and SGK1 on Mcl-1 expression. These results together showed a novel endogenous protection mechanism that is activated on Abeta insult to mediate cell survival.

WNT signaling in lung disease: a failure or a regeneration signal?

The WNT family of signaling proteins is essential to organ development in general and lung morphogenesis in particular. Originally identified as a developmentally active signaling pathway, the WNT pathway has recently been linked to the pathogenesis of important lung diseases, in particular lung cancer and pulmonary fibrosis. This review summarizes our current understanding about WNT signaling in lung development and disease, and is structured into three chapters. The first chapter presents an introduction to WNT signaling, outlining WNT proteins, their receptors and signaling intermediates, as well as the regulation of this complex pathway. The second chapter focuses on the role of WNT signaling in the normal embryonic and adult lung, and highlights recent findings of altered WNT signaling in lung diseases, such as lung cancer, pulmonary fibrosis, or pulmonary arterial hypertension. In the last chapter, we will discuss novel data and ideas about the biological effects of WNT signaling on the cellular level, highlighting pleiotropic effects induced by WNT ligands on distinct cell types, and how these cellular effects may be relevant to the pathogenesis of the aforementioned diseases.

SGK1-sensitive renal tubular glucose reabsorption in diabetes

The hyperglycemia of diabetes mellitus increases the filtered glucose load beyond the maximal tubular transport rate and thus leads to glucosuria. Sustained hyperglycemia, however, may gradually increase the maximal renal tubular transport rate and thereby blunt the increase of urinary glucose excretion. The mechanisms accounting for the increase of renal tubular glucose transport have remained ill-defined. A candidate is the serum- and glucocorticoid-inducible kinase SGK1. The kinase has been shown to stimulate Na(+)-coupled glucose transport in vitro and mediate the stimulation of electrogenic intestinal glucose transport by glucocorticoids in vivo. SGK1 expression is confined to glomerula and distal nephron in intact kidneys but may extend to the proximal tubule in diabetic nephropathy. To explore whether SGK1 modifies glucose transport in diabetic kidneys, Akita mice (akita(+/-)), which develop spontaneous diabetes, have been crossbred with gene-targeted mice lacking SGK1 on one allele (sgk1(+/-)) to eventually generate either akita(+/-)/sgk1(-/-) or akita(+/-)/sgk1(+/+) mice. Both akita(+/-)/sgk1(-/-) and akita(+/-)/sgk1(+/+) mice developed profound hyperglycemia (>20 mM) within approximately 6 wk. Body weight and plasma glucose concentrations were not significantly different between these two genotypes. However, urinary excretion of glucose and urinary excretion of fluid, Na(+), and K(+), as well as plasma aldosterone concentrations, were significantly higher in akita(+/-)/sgk1(-/-) than in akita(+/-)/sgk1(+/+) mice. Studies in isolated perfused proximal tubules revealed that the electrogenic glucose transport was significantly lower in akita(+/-)/sgk1(-/-) than in akita(+/-)/sgk1(+/+) mice. The data provide the first evidence that SGK1 participates in the stimulation of renal tubular glucose transport in diabetic kidneys.

SGK1 phosphorylation of IkappaB Kinase alpha and p300 Up-regulates NF-kappaB activity and increases N-Methyl-D-aspartate receptor NR2A and NR2B expression

Serum- and glucocorticoid-inducible kinase 1 (SGK1) is a downstream target of phosphatidylinositol 3-kinase signaling, and it regulates various cellular and physiological functions, but the SGK1 substrate proteins and genes regulated by SGK1 are less known. Here we have identified IkappaB kinase alpha (IKKalpha) as a novel substrate of SGK1 by using biochemical and bioinformatic approaches. SGK1 directly phosphorylates IKKalpha at Thr-23 and indirectly activates IKKalpha at Ser-180. Furthermore, SGK1 enhanced nuclear factor kappaB (NF-kappaB) activity and up-regulated N-methyl-d-aspartate receptor NR2A and NR2B expression through activation of IKKalpha at Thr-23 and Ser-180, and these two residues play an equally important role in mediating these effects of SGK1. Although SGK1 does not phosphorylate IKKbeta, IKKbeta activity is still required for IKK complex activation and for SGK1 phosphorylation and activation of NF-kappaB. In addition, SGK1 increased the acetylation of NF-kappaB through phosphorylation of p300 at Ser-1834, and this also leads to NF-kappaB activation and NR2A and NR2B expression. Moreover, an endogenous stimulus of SGK1, insulin, increased IKKalpha and NF-kappaB phosphorylation as well as NF-kappaB acetylation and NF-kappaB activity, but SGK1 small interfering RNA transfection blocked these effects of insulin. In examination of the functional significance of the SGK1-IKKalpha-NF-kappaB signaling pathway, we found that transfection of the IKKalpha double mutant (IKKalphaT23A/S180A) to rat hippocampus antagonized SGK-1-mediated spatial memory facilitation. Our results together demonstrated novel substrate proteins of SGK1 and novel SGK1 signaling pathways. Activation of these signaling pathways enhances NR2A and NR2B expression that is implicated in neuronal plasticity.

Induction of serum- and glucocorticoid-induced kinase-1 (SGK1) by cAMP regulates increases in alpha-ENaC

Alpha-ENaC expression and activity is regulated by a variety of hormones including beta-adrenergic agonists via the second messenger cAMP. We evaluated the early intermediate pathways involved in the up-regulation of SGK1 by DbcAMP and whether SGK1 is a prerequisite for induction of alpha-ENaC expression. Submandibular gland epithelial (SMG-C6) cells treated with DbcAMP (1 mM) induced both SGK1 mRNA and protein expression. DbcAMP-stimulated SGK1 mRNA expression was decreased by actinomycin D and mRNA and protein expressions were attenuated by PKA inhibitors (H-89 and KT5720). Inhibition of PI3-K with either LY294002 or dominant negative PI3-K reduced DbcAMP-stimulated SGK1 protein and mRNA levels, attenuated the phosphorylation of CREB (a cAMP-activated transcription factor) and decreased alpha-ENaC protein levels and Na(+) transport. In addition, the combination of PKA inhibitors with dominant negative PI3-K synergistically inhibited DbcAMP-induced Na(+) transport. Inhibition of SGK1 expression by siRNA decreased but did not obliterate DbcAMP-induced alpha-ENaC expression. Thus, in a cell line which endogenously exhibits minimal alpha-ENaC expression, induction of SGK1 by DbcAMP occurs via the PI3-K and PKA pathways. Increased alpha-ENaC levels and function are partly dependent upon the early induction of SGK1 expression.

Regulation of epithelial Na+ channels by aldosterone: role of Sgk1

1. The epithelial sodium channel (ENaC) is tightly regulated by hormonal and humoral factors, including cytosolic ion concentration and glucocorticoid and mineralocorticoid hormones. Many of these regulators of ENaC control its activity by regulating its surface expression via neural precursor cell-expressed developmentally downregulated (gene 4) protein (Nedd4-2). 2. During the early phase of aldosterone action, Nedd4-2-dependent downregulation of ENaC is inhibited by the serum- and glucocorticoid-induced kinase 1 (Sgk1). 3. Sgk1 phosphorylates Nedd4-2. Subsequently, phosphorylated Nedd4-2 binds to the 14-3-3 protein and, hence, reduces binding of Nedd4-2 to ENaC. 4. Nedd4-2 is also phosphorylated by protein kinase B (Akt1). Both Sgk1 and Akt1 are part of the insulin signalling pathway that increases transepithelial Na(+) absorption by inhibiting Nedd4-2 and activating ENaC.

Role of mitogen-activated protein kinases in aryl hydrocarbon receptor signaling

Human populations are increasingly exposed to a number of environmental pollutants such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls and dioxins. These compounds are activators of the aryl hydrocarbon receptor (AhR) that controls the expression of many genes including those for detoxification enzymes. The regulatory mechanisms of AhR are multi-factorial and include phosphorylation by various protein kinases. Significant progress in the research of mitogen-activated protein kinases (MAPKs) has been achieved in the last decade. Isolated reports have been published on the role of MAPKs in AhR functions and vice versa, with activation of MAPKs by AhR ligands. This mini-review summarizes current knowledge on the mutual interactions between MAPKs and AhR. The majority of studies has been done on cancer-derived cell lines that have impaired cell cycle regulation and lacks the complete detoxification apparatus. We emphasize the importance of the future studies that should be done on non-transformed cells to distinguish the role of MAPKs in cancer and normal cells. Primary cultures of human or rodent hepatocytes that are equipped with a fully functional biotransformation battery or xenobiotics-metabolizing extra-hepatic tissues should be the models of choice, as the results in our experiments confirm.

Differential regulation of serum- and glucocorticoid-inducible kinase 1 (SGK1) splice variants based on alternative initiation of transcription

The serum- and glucocorticoid-inducible kinase 1 (SGK1) is a key-regulator of transport, cell volume and cell survival. SGK1 transcription is under genomic control of a wide variety of hormones and cell stressors. Little is known, however, about sequence variation in SGK1 transcripts. Thus, we took an in silico approach to determine sequence variations in the N-terminal region of SGK1, which is considered particularly important for subcellular SGK1 localization. Expressed Sequence Tag analysis revealed two novel phylogenetically highly conserved SGK1 mRNAs with different promoter sites based on alternative initiation of transcription at -2981, -850 upstream of the transcription initiation site (+1) of the reference mRNA. RT-PCR in various human cell lines and tissues confirmed the expression of the 3 alternative splice variants, which differed exclusively in their first exons. The two novel variants were devoid of the localization and degradation signal with otherwise unchanged and intact open reading frames. Spatial distribution of transcription factor binding sites among the three promoter sites indicated common responsiveness to glucocorticoids but different responsiveness to hypoxia and cellular differentiation. Differential expression under those conditions was confirmed for all variants in cultured myoblasts and myotubes. p53 and ETF-1 binding sites were overrepresented at the promoter site of the reference sequence variant SGK1(+1). Transcript levels were 4.1-fold [SGK1(+1)] and 3.1-fold [SGK1(-850)] higher in renal clear cell carcinoma than in remote tissue. The transcript levels were 42-fold [SGK1(+1)], 26-fold [SGK1(-850)] and 17-fold [SGK1(-2981)] higher in highly malignant human glioma cells than in non-neoplastic brain tissue. SGK1 transcript levels were differentially increased by differentiation or hypoxia (treatment with CoCl(2)). In conclusion, the present observations disclose the transcription of three distinct SGK1 splice variants, which are all markedly upregulated in tumor tissue but differentially upregulated following differentiation or hypoxia.

Epigenetic regulation of microRNA-370 by interleukin-6 in malignant human cholangiocytes

Interleukin-6 (IL-6) is overexpressed and contributes to tumor cell growth in cholangiocarcinoma. Enforced IL-6 production can alter the expression of specific microRNAs (miRNAs) involved in tumor growth, and moreover can modulate expression of methylation-dependent genes. Thus, we assessed the methylation-dependent regulation of miRNA expression in human malignant cholangiocytes stably transfected to overexpress IL-6. The expression of the methyltransferases DNA methyltransferase enzyme-1 and HASJ4442 was increased by IL-6 overexpression, but was decreased by the methylation inhibitor 5-aza-2'-deoxycytidine (5-aza-CdR). Expression profiling identified seven miRNAs that were significantly downregulated by IL-6 overexpression (<0.4-fold) and upregulated (>2-fold) by 5-aza-CdR. One of these, miR-370, is embedded in a CpG island. Although 5-aza-CdR increased miR-370 expression by 2.1-fold in malignant cells, the expression in nonmalignant cells was unchanged. The oncogene mitogen-activated protein kinase kinase kinase 8 (MAP3K8) was identified as a target of miR-370, and its expression was decreased by 5-aza-CdR in cholangiocarcinoma cells. Overexpression of IL-6 reduced miR-370 expression and reinstated MAP3K8 expression in vitro as well as in tumor cell xenografts in vivo. Thus, IL-6 may contribute to tumor growth by modulation of expression of selected miRNAs, such as miR-370. These studies define a mechanism by which inflammation-associated cytokines can epigenetically modulate gene expression and directly contribute to tumor biology.

Interleukin-6 stimulates alpha-MG uptake in renal proximal tubule cells: involvement of STAT3, PI3K/Akt, MAPKs, and NF-kappaB

Recent studies have shown that interleukin 6 (IL-6) acts on the cellular proliferation-activating transduction signals during cellular regeneration. Therefore, this study examined the effect of IL-6 on the activation of Na(+)/glucose cotransporters (SGLTs) and its related signaling pathways in primary cultured renal proximal tubule cells (PTCs). IL-6 increased the level of alpha-methyl-d-[(14)C]glucopyranoside (alpha-MG) uptake in time- and dose-dependent manners. IL-6 also increased SGLT1 plus SGLT2 mRNA and protein expression level. The IL-6 receptors (IL-6Ralpha and gp 130) were expressed in PTCs. In addition, genistein and herbimycin A completely blocked the IL-6-induced increases in alpha-MG uptake and the protein expression level of SGLTs. On the other hand, IL-6 increased the level of 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate-sensitive cellular reactive oxygen species (ROS), and IL-6-induced increases in alpha-MG uptake and the protein expression level of SGLTs were blocked by ascorbic acid or taurine (antioxidants). IL-6 also increased the phosphorylation of signal transducer and activator of transcription-3 (STAT3), phosphoinositide-3 kinase (PI3K)/Akt, and mitogen-activated protein kinases (MAPKs) in a time-dependent manner. A pretreatment with STAT3 inhibitor LY 294002, an Akt inhibitor, or MAPK inhibitors significantly blocked the IL-6-induced increase in alpha-MG uptake. In addition, IL-6 increased the level of nuclear factor-kappaB (NF-kappaB) phosphorylation. A pretreatment with SN50 or BAY 11-7082 also blocked the IL-6-induced increase in alpha-MG uptake. In conclusion, IL-6 increases the SGLT activity through ROS, and its action in renal PTCs is associated with the STAT3, PI3K/Akt, MAPKs, and NF-kappaB signaling pathways.

Serum- and glucocorticoid-inducible kinase1 enhances contextual fear memory formation through down-regulation of the expression of Hes5

Mitogen-activated protein kinase/extracellular signal-regulated kinase plays an important role in memory formation and directly phosphorylates serum- and glucocorticoid-inducible kinase1 (SGK1) at Ser78. In this study, we examined the role and mechanism of SGK1 Ser78 activation involved in contextual fear memory formation in rats. Results revealed that SGK1 Ser78 phosphorylation was increased 30 min, 1 h and 3 h after training. Transient transfection of the dominant negative mutant of sgk, sgkS78A, to hippocampal neurons impaired, whereas transfection of the constitutively active sgk, sgkS78D, enhanced fear retention. Microarray analysis identified 14 genes that showed more than threefold alteration in their gene expression in sgkS78A-transfected animals 6 h after training. One of them is Hairy and Enhancer of split 5 (Hes5). The expression level of Hes5 is approximately 4.4-fold higher in sgkS78A-transfected animals. Further analyses revealed that Hes5 level is markedly decreased after training in control animals, but sgkS78A markedly increased Hes5 level after training. RNA interference experiment showed that shHes5 dose-dependently enhanced fear retention, whereas over-expression of Hes5 impaired fear retention. Moreover, shHes5 at a lower concentration completely blocked the memory-impairing effect of sgkS78A. These results together suggest that Hes5 negatively regulates contextual fear memory formation and SGK activation down-regulates Hes5 expression to enhance fear retention.

Serum and glucocorticoid-regulated protein kinases: variations on a theme

The phosphatidylinositol 3' kinase (PI3K)-signaling pathway plays a critical role in a variety of cellular responses such as modulation of cell survival, glucose homeostasis, cell division, and cell growth. PI3K generates important lipid second messengers-phosphatidylinositides that are phosphorylated at the 3' position of their inositol ring head-group. These membrane restricted lipids act by binding with high affinity to specific protein domains such as the pleckstrin homology (PH) domain. Effectors of PI3K include molecules that harbor such domains such as phosphoinositide-dependent kinase (PDK1) and protein kinase B (PKB), also termed Akt. The mammalian genome encodes three different PKB genes (alpha, beta, and gamma; Akt1, 2, and 3, respectively) and each is an attractive target for therapeutic intervention in diseases such as glioblastoma and breast cancer. A second family of three protein kinases, termed serum and glucocorticoid-regulated protein kinases (SGKs), is structurally related to the PKB family including regulation by PI3K but lack a PH domain. However, in addition to PH domains, a second class of 3' phosphorylated inositol phospholipid-binding domains exists that is termed Phox homology (PX) domain: this domain is found in one of the SGKs (SGK3). Here, we summarize knowledge of the three SGK isoforms and compare and contrast them to PKB with respect to their possible importance in cellular regulation and potential as therapeutic targets.