c-Fos phosphorylation induced by H2O2 prevents proteasomal degradation of c-Fos in cardiomyocytes

UDCA for Drug-Induced Liver Disease: Clinical and Pathophysiological Basis

Drug-induced liver injury (DILI) is an adverse reaction to medications and other xenobiotics that leads to liver dysfunction. Based on differential clinical patterns of injury, DILI is classified into hepatocellular, cholestatic, and mixed types; although hepatocellular DILI is associated with inflammation, necrosis, and apoptosis, cholestatic DILI is associated with bile plugs and bile duct paucity. Ursodeoxycholic acid (UDCA) has been empirically used as a supportive drug mainly in cholestatic DILI, but both curative and prophylactic beneficial effects have been observed for hepatocellular DILI as well, according to preliminary clinical studies. This could reflect the fact that UDCA has a plethora of beneficial effects potentially useful to treat the wide range of injuries with different etiologies and pathomechanisms occurring in both types of DILI, including anticholestatic, antioxidant, anti-inflammatory, antiapoptotic, antinecrotic, mitoprotective, endoplasmic reticulum stress alleviating, and immunomodulatory properties. In this review, a revision of the literature has been performed to evaluate the efficacy of UDCA across the whole DILI spectrum, and these findings were associated with the multiple mechanisms of UDCA hepatoprotection. This should help better rationalize and systematize the use of this versatile and safe hepatoprotector in each type of DILI scenarios.

How does NFAT3 regulate the occurrence of cardiac hypertrophy?

Cardiac hypertrophy is initially an adaptive response to physiological and pathological stimuli. Although pathological myocardial hypertrophy is the main cause of morbidity and mortality, our understanding of its mechanism is still weak. NFAT3 (nuclear factor of activated T-cell-3) is a member of the nuclear factor of the activated T cells (NFAT) family. NFAT3 plays a critical role in regulating the expression of cardiac hypertrophy genes by inducing their transcription. Recently, accumulating evidence has indicated that NFAT3 is a potent regulator of the progression of cardiac hypertrophy. This review, for the first time, summarizes the current studies on NFAT3 in cardiac hypertrophy, including the pathophysiological processes and the underlying pathological mechanism, focusing on the nuclear translocation and transcriptional function of NFAT3. This review will provide deep insight into the pathogenesis of cardiac hypertrophy and a theoretical basis for identifying new therapeutic targets in the NFAT3 network.

Design, synthesis, biological evaluation of 3,5-diaryl-4,5-dihydro-1H-pyrazole carbaldehydes as non-purine xanthine oxidase inhibitors: Tracing the anticancer mechanism via xanthine oxidase inhibition

Xanthine oxidase (XO) has been primarily targeted for the development of anti-hyperuriciemic /anti-gout agents as it catalyzes the conversion of xanthine and hypoxanthine into uric acid. XO overexpression in various cancer is very well correlated due to reactive oxygen species (ROS) production and metabolic activation of carcinogenic substances during the catalysis. Herein, we report the design and synthesis of a series of 3,5-diaryl-4,5-dihydro-1H-pyrazole carbaldehyde derivatives (2a-2x) as xanthine oxidase inhibitors (XOIs). A docking model was developed for the prediction of XO inhibitory activity of our novel compounds. Furthermore, our compounds anticancer activity results in low XO expression and XO-harboring cancer cells both in 2D and 3D-culture models are presented and discussed. Among the array of synthesized compounds, 2b and 2m emerged as potent XO inhibitors having IC₅₀ values of 9.32 ± 0.45 µM and 10.03 ± 0.43 µM, respectively. Both compounds induced apoptosis, halted the cell cycle progression at the G1 phase, elevated ROS levels, altered mitochondrial membrane potential, and inhibited antioxidant enzymes. The levels of miRNA and expression of redox sensors in cells were also altered due to increase oxidative stress induced by our compounds. Compounds 2b and 2m hold a great promise for further development of XOIs for the treatment of XO-harboring tumors.

Histone deacetylase inhibitors prevent H2O2 from inducing stress granule formation

Reactive Oxygen Species (ROS) are generated as by-products of aerobic metabolism. The production of ROS increases during xenobiotic stress and under multiple pathological conditions. Although ROS are considered harmful historically, mounting evidence recently indicates a signaling function of ROS, preceding to and regulating transcriptional or post-transcriptional events, contributing to cell death or cell survival and adaptation. Among the cellular defense mechanisms activated by ROS is formation of stress granules (SGs). The stalled translational apparatus, together with mRNA, aggregates into microscopically detectable and molecularly dynamic granules. We found that with H2O2, the dose most potent for inducing SGs in HeLa cells is 400-600 μM. With 200 μM H2O2, 2 h treatment induced the highest percentage of cells containing SGs. Whether ROS signaling pathways regulate the formation of SGs was tested using pharmacological inhibitors. We probed the potential role of PI3K, MAPKs, PKC or histone deacetylation in SG formation. Using deferoxamine as a positive control, we found a lack of inhibitory effect of wortmannin, LY-294002, JNK-I, SB-202190, PD-98059, or H89 when the percentage of cells containing SGs was counted. About 35% inhibition was observed with HDAC6 inhibitor Tubastatin A, whereas general HDAC inhibitor Trichostatin A provided a complete inhibition of SG formation. Our data point to the need of investigating the role of HDACs in SG formation during oxidative stress.

Glucolipotoxicity diminishes cardiomyocyte TFEB and inhibits lysosomal autophagy during obesity and diabetes

Impaired cardiac metabolism in the obese and diabetic heart leads to glucolipotoxicity and ensuing cardiomyopathy. Glucolipotoxicity causes cardiomyocyte injury by increasing energy insufficiency, impairing proteasomal-mediated protein degradation and inducing apoptosis. Proteasome-evading proteins are degraded by autophagy in the lysosome, whose metabolism and function are regulated by master regulator transcription factor EB (TFEB). Limited studies have examined the impact of glucolipotoxicity on intra-lysosomal signaling proteins and their regulators. By utilizing a mouse model of diet-induced obesity, type-1 diabetes (Akita) and ex-vivo model of glucolipotoxicity (H9C2 cells and NRCM, neonatal rat cardiomyocyte), we examined whether glucolipotoxicity negatively targets TFEB and lysosomal proteins to dysregulate autophagy and cause cardiac injury. Despite differential effects of obesity and diabetes on LC3B-II, expression of proteins facilitating autophagosomal clearance such as TFEB, LAMP-2A, Hsc70 and Hsp90 were decreased in the obese and diabetic heart. In-vivo data was recapitulated in H9C2 and NRCM cells, which exhibited impaired autophagic flux and reduced TFEB content when exposed to a glucolipotoxic milieu. Notably, overloading myocytes with a saturated fatty acid (palmitate) but not an unsaturated fatty acid (oleate) depleted cellular TFEB and suppressed autophagy, suggesting a fatty acid specific regulation of TFEB and autophagy in the cardiomyocyte. The effect of glucolipotoxicity to reduce TFEB content was also confirmed in heart tissue from patients with Class-I obesity. Therefore, during glucolipotoxicity, suppression of lysosomal autophagy was associated with reduced lysosomal content, decreased cathepsin-B activity and diminished cellular TFEB content likely rendering myocytes susceptible to cardiac injury.

α₁ adrenoceptor activation by norepinephrine inhibits LPS-induced cardiomyocyte TNF-α production via modulating ERK1/2 and NF-κB pathway

Cardiomyocyte tumour necrosis factor α (TNF-α) production contributes to myocardial depression during sepsis. This study was designed to observe the effect of norepinephrine (NE) on lipopolysaccharide (LPS)-induced cardiomyocyte TNF-α expression and to further investigate the underlying mechanisms in neonatal rat cardiomyocytes and endotoxaemic mice. In cultured neonatal rat cardiomyocytes, NE inhibited LPS-induced TNF-α production in a dose-dependent manner. α₁- adrenoceptor (AR) antagonist (prazosin), but neither β₁- nor β₂-AR antagonist, abrogated the inhibitory effect of NE on LPS-stimulated TNF-α production. Furthermore, phenylephrine (PE), an α₁-AR agonist, also suppressed LPS-induced TNF-α production. NE inhibited p38 phosphorylation and NF-κB activation, but enhanced extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation and c-Fos expression in LPS-treated cardiomyocytes, all of which were reversed by prazosin pre-treatment. To determine whether ERK1/2 regulates c-Fos expression, p38 phosphorylation, NF-κB activation and TNF-α production, cardiomyocytes were also treated with U0126, a selective ERK1/2 inhibitor. Treatment with U0126 reversed the effects of NE on c-Fos expression, p38 mitogen-activated protein kinase (MAPK) phosphorylation and TNF-α production, but not NF-κB activation in LPS-challenged cardiomyocytes. In addition, pre-treatment with SB202190, a p38 MAPK inhibitor, partly inhibited LPS-induced TNF-α production in cardiomyocytes. In endotoxaemic mice, PE promoted myocardial ERK1/2 phosphorylation and c-Fos expression, inhibited p38 phosphorylation and IκBα degradation, reduced myocardial TNF-α production and prevented LPS-provoked cardiac dysfunction. Altogether, these findings indicate that activation of α₁-AR by NE suppresses LPS-induced cardiomyocyte TNF-α expression and improves cardiac dysfunction during endotoxaemia via promoting myocardial ERK phosphorylation and suppressing NF-κB activation.

Expression of glucocorticoid-induced leucine zipper (GILZ) in cardiomyocytes

Glucocorticoids (GCs) are frequently prescribed pharmacological agents most notably for their immunosuppressive effects. Endogenous GCs mediate biological processes such as energy metabolism and tissue development. At the cellular level, GCs bind to the glucocorticoid receptor (GR), a cytosolic protein that translocates to the nuclei and functions to alter transcription upon ligand binding. Among a long list of genes activated by GCs is the glucocorticoid-induced leucine zipper (GILZ). GC-induced GILZ expression has been well established in lymphocytes and mediates GC-induced apoptosis. Unlike lymphocytes, cardiomyocytes respond to GCs by gaining resistance against apoptosis. We determined GILZ expression in cardiomyocytes in vivo and in vitro. Expression of GILZ in mouse hearts as a result of GC administration was confirmed by Western blot analyses. GCs induced dose- and time-dependent elevation of GILZ expression in primary cultured rat cardiomyocytes, with dexamethasone (Dex) as low as 0.1 μM being effective. Time course analysis indicated that GILZ protein levels increased at 8 h and peaked at 48 h after exposure to 1 μM Dex. H9c2(2-1) cell line showed a similar response of GILZ induction by Dex as primary cultured rat cardiomyocytes, providing a convenient model for studying the biological significance of GILZ expression. With corticosterone (CT), an endogenous form of corticosteroids in rodents, 0.1-2.5 μM was found to induce GILZ in H9c2(2-1) cells. Time course analysis with 1 μM CT indicated induction of GILZ at 6 h with peak expression at 18 h. Inhibition of the GR by mifepristone led to blunting of GILZ induction by GCs. Our data demonstrate GILZ induction in cardiomyocytes both in vivo and in vitro by GCs, pointing to H9c2(2-1) cells as a valid model for studying the biological function of GILZ in cardiomyocytes.

GnRH increases c-Fos half-life contributing to higher FSHβ induction

GnRH is a potent hypothalamic regulator of gonadotropin hormones, LH and FSH, which are both expressed within the pituitary gonadotrope and are necessary for the stimulation of gametogenesis and steroidogenesis in the gonads. Differential regulation of LH and FSH, which is essential for reproductive fitness, is achieved, in part, through the varying of GnRH pulse frequency. However, the mechanism controlling the increase in FSH during the periods of low GnRH has not been elucidated. Here, we uncover another level of regulation by GnRH that contributes to differential expression of the gonadotropins and may play an important role for the generation of the secondary rise of FSH that stimulates folliculogenesis. GnRH stimulates LHβ and FSHβ subunit transcription via induction of the immediate early genes, Egr1 and c-Fos, respectively. Here, we determined that GnRH induces rapidly both Egr1 and c-Fos, but specifically decreases the rate of c-Fos degradation. In particular, GnRH modulates the rate of c-Fos protein turnover by inducing c-Fos phosphorylation through the ERK1/2 pathway. This extends the half-life of c-Fos, which is normally rapidly degraded. Confirming the role of phosphorylation in promoting increased protein activity, we show that a c-Fos mutant that cannot be phosphorylated by GnRH induces lower expression of the FHSβ promoter than wild-type c-Fos. Our studies expand upon the role of GnRH in the regulation of gonadotropin gene expression by highlighting the role of c-Fos posttranslational modification that may cause higher levels of FSH during the time of low GnRH pulse frequency to stimulate follicular growth.

Knockout of SOD1 alters murine hepatic glycolysis, gluconeogenesis, and lipogenesis

We previously observed a stronger effect of knockout of Cu,Zn-superoxide dismutase (SOD1) than that of Se-dependent glutathione peroxidase 1 (GPX1) on murine body weight and glucose homeostasis. Two experiments were conducted to determine how hepatic lipid profiles and key metabolic regulators were correlated with this difference. SOD1(-/-) and GPX1(-/-) mice and their respective wild-type (WT) littermates (n=6 or 7/group, male) were fed a Se-adequate Torula yeast-sucrose diet and killed at 6 months of age to collect liver samples. In Experiment 1, fasted SOD1(-/-) mice displayed pyruvate intolerance and a 61% decrease (P<0.05) in liver glycogen compared with their WT littermates. The former had lower (P<0.05) activities of phosphoenolpyruvate carboxykinase, total protein phosphatase, and protein phosphatase 2A, but a higher (P<0.05) activity of glucokinase in the liver than the latter. In contrast, hepatic concentrations of total cholesterol, triglycerides, and nonesterified fatty acids were increased by 11 to 100% (P<0.05) in the SOD1(-/-) mice. Meanwhile, these mice had elevated (P<0.05) hepatic protein levels of sterol-regulatory element binding proteins 1 and 2, p53 MAPK, total and phosphorylated AMP-activated protein kinase α1 protein, protein tyrosine phosphatase 1B, and protein phosphatase 2B. In Experiment 2, GPX1(-/-) mice and their WT littermates were compared, but showed no difference in any of the measures. In conclusion, knockout of SOD1, but not GPX1, led to a decreased liver glycogen storage synchronized with pyruvate intolerance and elevated hepatic lipid profiles in adult mice. This striking comparison was possibly due to unique impacts of these two knockouts on intracellular tone of H(2)O(2) and key regulators of liver gluconeogenesis, glycolysis, and lipogenesis.

IKKα contributes to UVB-induced VEGF expression by regulating AP-1 transactivation

Exposure to ultraviolet B (UVB) irradiation from sunlight induces the upregulation of VEGF, a potent angiogenic factor that is critical for mediating angiogenesis-associated photodamage. However, the molecular mechanisms related to UVB-induced VEGF expression have not been fully defined. Here, we demonstrate that one of the catalytic subunits of the IκB kinase complex (IKK), IKKα, plays a critical role in mediating UVB-induced VEGF expression in mouse embryonic fibroblasts (MEFs), which requires IKKα kinase activity but is independent of IKKβ, IKKγ and the transactivation of NF-κB. We further show that the transcriptional factor AP-1 functions as the downstream target of IKKα that is responsible for VEGF induction under UVB exposure. Both the accumulation of AP-1 component, c-Fos and the transactivation of AP-1 by UVB require the activated IKKα located within the nucleus. Moreover, nuclear IKKα can associate with c-Fos and recruit to the vegf promoter regions containing AP-1-responsive element and then trigger phosphorylation of the promoter-bound histone H3. Thus, our results have revealed a novel independent role for IKKα in controlling VEGF expression during the cellular UVB response by regulating the induction of the AP-1 component and phosphorylating histone H3 to facilitate AP-1 transactivation. Targeting IKKα shows promise for the prevention of UVB-induced angiogenesis and the associated photodamage.

Y-box binding protein-1 mediates profibrotic effects of calcineurin inhibitors in the kidney

The immunosuppressive calcineurin inhibitors (CNIs) cyclosporine A (CsA) and tacrolimus are widely used in transplant organ recipients, but in the kidney allograft, they may cause tubulointerstitial as well as mesangial fibrosis, with TGF-β believed to be a central inductor. In this study, we report that the cold-shock protein Y-box binding protein-1 (YB-1) is a TGF-β independent downstream effector in CsA- as well as in tacrolimus- but not in rapamycin-mediated activation of rat mesangial cells (rMCs). Intracellular content of YB-1 is several-fold increased in MCs following CNI treatment in vitro and in vivo in mice. This effect ensues in a time-dependent manner, and the operative concentration range encompasses therapeutically relevant doses for CNIs. The effect of CNI on cellular YB-1 content is abrogated by specific blockade of translation, whereas retarding the transcription remains ineffective. The activation of rMCs by CNIs is accomplished by generation of reactive oxygen species. In contrast to TGF-β-triggered reactive oxygen species generation, hydrogen peroxide especially could be identified as a potent inductor of YB-1 accumulation. In line with this, hindering TGF-β did not influence CNI-induced YB-1 upregulation, whereas ERK/Akt pathways are involved in CNI-mediated YB-1 expression. CsA-induced YB-1 accumulation results in mRNA stabilization and subsequent generation of collagen. Our results provide strong evidence for a CNI-dependent induction of YB-1 in MCs that contributes to renal fibrosis via regulation of its own and collagen translation.

Cadmium induces phosphorylation and stabilization of c-Fos in HK-2 renal proximal tubular cells

We examined the effects of cadmium chloride (CdCl₂) exposure on the expression and phosphorylation status of members of the Fos family, components of the activator protein-1 transcription factor, in HK-2 human renal proximal tubular cells. Following the exposure to CdCl₂, the expression of c-fos, fosB, fra-1, and fra-2 increased markedly, with different magnitudes and time courses. The levels of Fos family proteins (c-Fos, FosB, Fra-1, and Fra-2) also increased in response to CdCl₂ exposure. Although the elevation of c-fos transcripts was transient, c-Fos protein levels increased progressively with lower electrophoretic mobility, suggesting stabilization of c-Fos through post-translational modifications. Consistently, we observed phosphorylation of c-Fos at Ser362 and Ser374 in HK-2 cells treated with CdCl₂. Phosphorylated forms of mitogen-activated protein kinases (MAPKs)-including extracellular signal-regulated protein kinase (ERK), c-Jun NH₂-terminal kinase, and p38-increased after CdCl₂ exposure, whereas treatment with the MAPK/ERK kinase inhibitor U0126 and the p38 inhibitor SB203580 suppressed the accumulation and phosphorylation of c-Fos. We mutated Ser362 to alanine (S362A), Ser374 to alanine (S374A), and both residues to alanines (S362A/S374A) to inhibit potential phosphorylation of c-Fos at these sites. S374A or double S362A/S374A mutations reduced c-Fos level markedly, but S362A mutation did not. On the other hand, S362A/S374A mutations induced a more pronounced reduction in c-Fos DNA-binding activity than S374A mutation. These results suggest that while Ser374 phosphorylation seems to play a role in c-Fos stabilization, phosphorylation at two C-terminal serine residues is required for the transcriptional activation of c-Fos in HK-2 cells treated with CdCl₂.

Immunomodulatory and therapeutic activity of curcumin

Inflammation is a disease of vigorous uncontrolled activated immune responses. Overwhelming reports have suggested that the modulation of immune responses by curcumin plays a dominant role in the treatment of inflammation and metabolic diseases. Observations from both in-vitro and in-vivo studies have provided strong evidence towards the therapeutic potential of curcumin. These studies have also identified a plethora of biological targets and intricate mechanisms of action that characterize curcumin as a potent 'drug' for numerous ailments. During inflammation the functional influence of lymphocytes and the related cross-talk can be modulated by curcumin to achieve the desired immune status against diseases. This review describes the regulation of immune responses by curcumin and effectiveness of curcumin in treatment of diseases of diverse nature.

Oxidative stress modulates PPAR gamma in vascular endothelial cells

The peroxisome proliferator-activated receptor gamma (PPAR gamma) plays an important role in vascular regulation. However, the impact of oxidative stress on PPAR gamma expression and activity has not been clearly defined. Human umbilical vein endothelial cells (HUVECs) were exposed to graded concentrations of H(2)O(2) for 0.5-72h, or bovine aortic endothelial cells (BAECs) were exposed to alterations in extracellular thiol/disulfide redox potential (E(h)) of the cysteine/cystine couple. Within 2h, H(2)O(2) reduced HUVEC PPAR gamma mRNA and activity and reduced the expression of two PPAR gamma-regulated genes without altering PPAR gamma protein levels. After 4h H(2)O(2) exposure, mRNA levels remained reduced, whereas PPAR gamma activity returned to control levels. PPAR gamma mRNA levels remained depressed for up to 72 h after exposure to H(2)O(2), without any change in PPAR gamma activity. Catalase prevented H(2)O(2)-induced reductions in PPAR gamma mRNA and activity. H(2)O(2) (1) reduced luciferase expression in HUVECs transiently transfected with a human PPAR gamma promoter reporter, (2) failed to alter PPAR gamma mRNA half-life, and (3) transiently increased expression and activity of c-Fos and phospho-c-Jun. Treatment with the AP1 inhibitor curcumin prevented H(2)O(2)-mediated reductions in PPAR gamma expression. In addition, medium having an oxidized E(h) reduced BAEC PPAR gamma mRNA and activity. These findings demonstrate that oxidative stress, potentially through activation of inhibitory redox-regulated transcription factors, attenuates PPAR gamma expression and activity in vascular endothelial cells through suppression of PPAR gamma transcription.

Breviscapine ameliorates hypertrophy of cardiomyocytes induced by high glucose in diabetic rats via the PKC signaling pathway

AIM

To investigate the influence of breviscapine on high glucose-induced hypertrophy of cardiomyocytes and the relevant mechanism in vitro and in vivo.

METHODS

Cultured neonatal cardiomyocytes were divided into i) control; ii) high glucose concentrations; iii) high glucose+PKC inhibitor Ro-31-8220; iv) high glucose+breviscapine; or v) high glucose+NF-kappaB inhibitor BAY11-7082. Cellular contraction frequency and volumes were measured; the expression of protein kinase C (PKC), NF-kappaB, TNF-alpha, and c-fos were assessed by Western blot or reverse transcription-polymerase chain reaction (RT-PCR). Diabetic rats were induced by a single intraperitoneal injection of streptozotocin, and randomly divided into i) control rats; ii) diabetic rats; or iii) diabetic rats administered with breviscapine (10 or 25 mg x kg(-1) x d(-1)). After treatment with breviscapine for six weeks, the echocardiographic parameters were measured. All rats were then sacrificed and heart tissue was obtained for microscopy. The expression patterns of PKC, NF-kappaB, TNF-alpha, and c-fos were measured by Western blot or RT-PCR.

RESULTS

Cardiomyocytes cultured in a high concentration of glucose showed an increased pulsatile frequency and cellular volume, as well as a higher expression of PKC, NF-kappaB, TNF-alpha, and c-fos compared with the control group. Breviscapine could partly prevent these changes. Diabetic rats showed relative cardiac hypertrophy and a higher expression of PKC, NF-kappaB, TNF-alpha, and c-fos; treatment with breviscapine could ameliorate these changes in diabetic cardiomyopathy.

CONCLUSION

Breviscapine prevented cardiac hypertrophy in diabetic rats by inhibiting the expression of PKC, which may have a protective effect in the pathogenesis of diabetic cardiomyopathy via the PKC/NF-kappaB/c-fos signal transduction pathway.

Calcineurin activates cytoglobin transcription in hypoxic myocytes

Cardiac hypertrophy develops in response to a variety of cardiovascular stresses and results in activation of numerous signaling cascades and proteins. In the present study, we demonstrate that cytoglobin is a stress-responsive hemoprotein in the hypoxia-induced hypertrophic myocardium and it is transcriptionally regulated by calcineurin-dependent transcription factors. The cytoglobin transcript level is abundantly expressed in the adult heart and in response to hypoxia cytoglobin expression is markedly up-regulated within the hypoxia-induced hypertrophic heart. To define the molecular mechanism resulting in the induction of cytoglobin, we undertook a transcriptional analysis of the 5' upstream regulatory region of the cytoglobin gene. Evolutionarily conserved binding elements for transcription factors HIF-1, AP-1, and NFAT are located within the upstream region of the cytoglobin gene. Transcriptional assays demonstrated that calcineurin activity modulates cytoglobin transcription. Increased calcineurin activity enhances the ability of NFAT and AP-1 to bind to the putative cytoglobin promoter, especially under hypoxic conditions. In addition, inhibition of calcineurin, NFAT, and/or AP-1 activities decreases endogenous cytoglobin transcript and protein levels. Thus, the regulation of cytoglobin transcription by calcineurin-dependent transcription factors suggests that cytoglobin may have a functional role in calcium-dependent events accompanying cardiac remodeling.

The signal transduction pathway of PKC/NF-kappa B/c-fos may be involved in the influence of high glucose on the cardiomyocytes of neonatal rats

Background

High glucose could induce structure and function change in cardiomyocytes, PKC plays a core effect in the onset and progression of diabetic cardiomyopathy, but its underlying downstream signal transduction pathway is still not completely understood.

Objectives

To study the influence of high glucose on the structure, function and signal transduction pathway of PKC (Protein Kinase C)/NF-κB(Nuclear factor-κB)/c-fos in cultured cardiomyocytes.

Methods

Using cultured cardiomyocytes of neonatal Sprague-Dawley rats as a model, groups were divided into: control group (glucose: 5 mmol/L); high glucose group (glucose: 10 mmol/L, 15 mmol/L, 20 mmol/L, 25.5 mmol/L); equimolar mannital group (5 mmol/L glucose + 20.5 mmol/L maninital); high glucose(25.5 mmol/L) add PKC inhibitor (Ro-31-8220, 50 nmol/L); high glucose (25.5 mmol/L) add NF-κB inhibitor (BAY11-7082, 5 μmol/L). The cellular contracting frequency and volumes were measured and the expression of PKC-α, PKC-β2, p-PKC-α, p-PKC-β2, NF-κB, p-NF-κB, TNF-α (tumor necrosis factor-α) and c-fos were measured by western blot or RT-PCR.

Results

Cardiomyocytes cultured in high glucose level, but not iso-osmotic mannital, showed an increased pulsatile frequency and higher cellular volumes consistent with the increased glucose levels, and also higher expression of PKC-α, PKC-β2, p-PKC-α, p-PKC-β2, NF-κB, p-NF-κB, TNF-α and c-fos. The addition of Ro-31-8220 and BAY11-7082 could partly reverse these changes induced by high glucose level.

Conclusion

High glucose significantly increased the pulsatile frequency and cellular volumes of cultured cardiomyocytes via PKC/NF-κB/c-fos pathway, which might lead to diabetic cardiomyopathy.

Genomic and proteomic profiling of oxidative stress response in human diploid fibroblasts

A number of lines of evidence suggest that senescence of normal human diploid fibroblasts (HDFs) in culture is relevant to the process of aging in vivo. Using normal human skin diploid fibroblasts, we examine the changes in genes and proteins following treatment with a mild dose of H2O2, which induces premature senescence. Multidimensional Protein Identification Technology (MudPIT) in combination with mass spectrometry analyses of whole cell lysates from HDFs detected 65 proteins in control group, 48 proteins in H2O2-treated cells and 109 proteins common in both groups. In contrast, cDNA microarray analyses show 173 genes up-regulated and 179 genes down-regulated upon H2O2 treatment. Both MudPIT and cDNA microarray analyses indicate that H2O2 treatment caused elevated levels of thioredoxin reductase 1. Semi-quantitative RT-PCR and Western-blot were able to verify the finding. Out of a large number of genes or proteins detected, only a small fraction shows the overlap between the outcomes of microarray versus proteomics. The low overlap suggests the importance of considering proteins instead of transcripts when investigating the gene expression profile altered by oxidative stress.

Corticosteroids induce cyclooxygenase 1 expression in cardiomyocytes: role of glucocorticoid receptor and Sp3 transcription factor

Cyclooxygenase (COX) encodes a rate-limiting enzyme in the biosynthesis of prostanoids. Although COX-1 is constitutively expressed in many tissues, we found that glucocorticoids cause elevated expression of COX-1 gene in cardiomyocytes. Corticosterone (CT) at physiologically relevant doses (0.05-1 microm) induces transcriptional activation of COX-1 gene as shown by nuclear run-on and promoter reporter assays. An antagonist of glucocorticoid receptor (GR), mifepristone, prevented CT from inducing COX-1. COX-1 gene promoter deletion and mutation studies indicate a role of Sp transcription factors in CT-induced COX-1 gene. EMSAs or chromatin immunoprecipitation assays suggest that GR and Sp3 transcription factor bind to the promoter of COX-1 gene. Coimmunoprecipitation assays found an association of GR with Sp3. Silencing Sp3 protein with small interfering RNA suppressed CT-induced COX-1 promoter activation. Our data suggest that activated GR interacts with Sp3 transcription factor in binding to COX-1 promoter to enhance COX-1 gene expression in cardiomyocytes.

Inhibitors of GSK-3 prevent corticosterone from inducing COX-1 expression in cardiomyocytes

Our recent study has demonstrated that glucocorticoids (GCs) induce cyclooxygenase-1 (COX-1) gene expression in rat cardiomyocytes. While investigating the mechanism underlying corticosterone (CT) induced COX-1, we found that three structurally and mechanistically distinct GSK-3 inhibitors, LiCl, SB216763, and (2'Z,3'E)-6-Bromoindirubin-3'-oxime (BIO), inhibited COX-1 transcription and protein induction. A genetic approach of expressing wild type GSK-3beta increased COX-1 promoter activity, which was abolished by LiCl. LiCl increased inhibitory GSK-3alpha/beta phosphorylation at Ser21/Ser9, while BIO or SB216763 prevented stimulatory phosphorylation at Tyr279/Tyr216 of GSK-3alpha/beta. GSK inhibitors failed to block nuclear translocation of glucocorticoid receptor (GR) or activation of glucocorticoid response element (GRE) by CT treatment. While Sp3 transcription factor mediates CT induced COX-1 expression, GSK inhibitors did not change the level of Sp3 protein or binding of Sp3 transcription factor to COX-1 promoter. The observed effect of GSK-3 inhibitors appears to be unique to COX-1 since LiCl or BIO does not prevent CT from inducing COX-2 gene. We conclude that GSK-3 inhibitors block CT from inducing COX-1 gene expression via a mechanism beyond GR and Sp3 transcription factor.

Ubiquitin-independent degradation of proteins by the proteasome

The proteasome is the main proteolytic machinery of the cell and constitutes a recognized drugable target, in particular for treating cancer. It is involved in the elimination of misfolded, altered or aged proteins as well as in the generation of antigenic peptides presented by MHC class I molecules. It is also responsible for the proteolytic maturation of diverse polypeptide precursors and for the spatial and temporal regulation of the degradation of many key cell regulators whose destruction is necessary for progression through essential processes, such as cell division, differentiation and, more generally, adaptation to environmental signals. It is generally believed that proteins must undergo prior modification by polyubiquitin chains to be addressed to, and recognized by, the proteasome. In reality, however, there is accumulating evidence that ubiquitin-independent proteasomal degradation may have been largely underestimated. In particular, a number of proto-oncoproteins and oncosuppressive proteins are privileged ubiquitin-independent proteasomal substrates, the altered degradation of which may have tumorigenic consequences. The identification of ubiquitin-independent mechanisms for proteasomal degradation also poses the paramount question of the multiplicity of catabolic pathways targeting each protein substrate. As this may help design novel therapeutic strategies, the underlying mechanisms are critically reviewed here.

LY294002 inhibits glucocorticoid-induced COX-2 gene expression in cardiomyocytes through a phosphatidylinositol 3 kinase-independent mechanism

Glucocorticoids induce COX-2 expression in rat cardiomyocytes. While investigating whether phosphatidylinositol 3 kinase (PI3K) plays a role in corticosterone (CT)-induced COX-2, we found that LY294002 (LY29) but not wortmannin (WM) attenuates CT from inducing COX-2 gene expression. Expression of a dominant-negative mutant of p85 subunit of PI3K failed to inhibit CT from inducing COX-2 expression. CT did not activate PI3K/AKT signaling pathway whereas LY29 and WM decreased the activity of PI3K. LY303511 (LY30), a structural analogue and a negative control for PI3K inhibitory activity of LY29, also suppressed COX-2 induction. These data suggest PI3K-independent mechanisms in regulating CT-induced COX-2 expression. LY29 and LY30 do not inhibit glucocorticoid receptor transactivity. Both compounds have been reported to inhibit Casein Kinase 2 activity and modulate potassium and calcium levels independent of PI3K, while LY29 has been reported to inhibit mammalian Target of Rapamycin (mTOR), and DNA-dependent Protein Kinase (DNA-PK). Inhibitor of Casein Kinase 2 (CK2), mTOR or DNA-PK failed to prevent CT from inducing COX-2 expression. Tetraethylammonium (TEA), a potassium channel blocker, and nimodipine, a calcium channel blocker, both attenuated CT from inducing COX-2 gene expression. CT was found to increase intracellular Ca(2+) concentration, which can be inhibited by LY29, TEA or nimodipine. These data suggest a possible role of calcium instead of PI3K in CT-induced COX-2 expression in cardiomyocytes.

FP prostanoid receptor-mediated induction of the expression of early growth response factor-1 by activation of a Ras/Raf/mitogen-activated protein kinase signaling cascade

FP prostanoid receptors are G-protein-coupled receptors whose physiological activator is prostaglandin-F(2alpha) (PGF(2alpha)). PGF(2alpha) has been implicated in wound healing and cardiac hypertrophy, which are both known to involve the induction of the immediate-early response gene, early growth response factor-1 (EGR-1). We hypothesized that activation of the human FP receptor by PGF(2alpha) could induce the expression of EGR-1 and found that 1 muM PGF(2alpha) produced a time-dependent induction of both mRNA and protein expression for EGR-1. This FP receptor-mediated induction of EGR-1 expression involved activation of the small GTPase Ras followed by activation of C-Raf and the mitogen-activated protein (MAP) kinase kinases 1 and 2 (MEK1/2). Thus, induction of EGR-1 expression by PGF(2alpha) was blocked using dominant-negative constructs of Ras and C-Raf and the Raf kinase inhibitor 4-(4-(3-(4-chloro-3-trifluoromethylphenyl)ureido)phenoxy)-pyridine-2-carboxyllic acid methyamide-4-methylbenzenesulfonate (BAY43-9006). Likewise, the MEK1/2 inhibitor 2'-amino-3'-methoxyflavone (PD98059) blocked the induction of EGR-1 expression by PGF(2alpha). FP receptor stimulation by PGF(2alpha) induced the phosphorylation of C-Raf, MEK1/2, and extracellular signal-regulated kinases 1 and 2, consistent with the activation of a MAP kinase signaling cascade. PGF(2alpha) was also found to induce the expression of EGR-1 in rat cardiomyocytes through the activation of endogenous FP receptors. This induction of EGR-1 expression in cardiomyocytes also involved the activation of Raf and MAP kinase signaling and was dependent on the activation of protein kinase C. This is the first report to show the regulation of EGR-1 expression after PGF(2alpha) activation of FP receptors and suggests that this could be an early event involved in wound healing and cardiac hypertrophy.

Translational control of nrf2 protein in activation of antioxidant response by oxidants

Nf-E2 related factor-2 (Nrf2) is a basic leucine zipper transcription factor that binds and activates the antioxidant response element (ARE) in the promoters of many antioxidant and detoxification genes. We found that H(2)O(2) treatment caused a rapid increase in endogenous Nrf2 protein level in rat cardiomyocytes. Semiquantitative or real-time reverse transcription-polymerase chain reaction failed to show an increase of Nrf2 mRNA level by H(2)O(2) treatment. Measurements of Nrf2 protein stability excluded the possibility of Nrf2 protein stabilization. Although inhibiting protein synthesis with cycloheximide prevented H(2)O(2) from elevating Nrf2 protein level, RNA synthesis inhibition with actinomycin D failed to do so. Measurements of new protein synthesis with [(35)S]methionine incorporation confirmed that H(2)O(2) increased the translation of Nrf2 protein. Inhibitors of phosphoinositide 3-kinase were able to abolish the induction of Nrf2 protein by H(2)O(2). Although H(2)O(2) increased phosphorylation of p70 S6 kinase, rapamycin failed to inhibit H(2)O(2) from elevating Nrf2 protein. H(2)O(2) also induced phosphorylation of eukaryotic translation initiation factor (eIF) 4E and eIF2alpha within 30 and 10 min, respectively. Inhibiting eIF4E with small interfering siRNA or increasing eIF2alpha phosphorylation with salubrinal did not affect Nrf2 elevation by H(2)O(2). Our data present a novel phenomenon of quick onset of the antioxidant/detoxification response via increased translation of Nrf2 by oxidants. The mechanism underlying such stress-induced de novo protein translation may involve multiple components of translational machinery.

Alternative splicing of c-fos pre-mRNA: contribution of the rates of synthesis and degradation to the copy number of each transcript isoform and detection of a truncated c-Fos immunoreactive species

Background

Alternative splicing is a widespread mechanism of gene expression regulation. Previous analyses based on conventional RT-PCR reported the presence of an unspliced c-fos transcript in several mammalian systems. Compared to the well-defined knowledge on the alternative splicing of fosB, the physiological relevance of the unspliced c-fos transcript in regulating c-fos expression remains largely unknown. This work aimed to investigate the functional significance of the alternative splicing c-fos pre-mRNA.

Results

A set of primers was designed to demonstrate that, whereas introns 1 and 2 are regularly spliced from primary c-fos transcript, intron 3 remains unspliced in part of total transcript molecules. Here, the two species are referred to as c-fos-2 (+ intron 3) and spliced c-fos (- intron 3) transcripts. Then, we used a quantitatively rigorous approach based on real-time PCR to provide, for the first time, the actual steady-state copy numbers of the two c-fos transcripts. We tested how the mouse-organ context and mouse-gestational age, the synthesis and turnover rates of the investigated transcripts, and the serum stimulation of quiescent cells modulate their absolute-expression profiles. Intron 3 generates an in-frame premature termination codon that predicts the synthesis of a truncated c-Fos protein. This prediction was evaluated by immunoaffinity chromatography purification of c-Fos proteins.

Conclusion

We demonstrate that: (i) The c-fos-2 transcript is ubiquitously synthesized either in vivo or in vitro, in amounts that are higher or similar to those of mRNAs coding for other Fos family members, like FosB, ΔFosB, Fra-1 or Fra-2. (ii) Intron 3 confers to c-fos-2 an outstanding destabilizing effect of about 6-fold. (iii) Major determinant of c-fos-2 steady-state levels in cultured cells is its remarkably high rate of synthesis. (iv) Rapid changes in the synthesis and/or degradation rates of both c-fos transcripts in serum-stimulated cells give rise to rapid and transient changes in their relative proportions. Taken as a whole, these findings suggest a co-ordinated fine-tune of the two c-fos transcript species, supporting the notion that the alternative processing of the precursor mRNA might be physiologically relevant. Moreover, we detected a c-Fos immunoreactive species corresponding in mobility to the predicted truncated variant.

MLN3897, a novel CCR1 inhibitor, impairs osteoclastogenesis and inhibits the interaction of multiple myeloma cells and osteoclasts

The interaction between osteoclasts (OCs) and multiple myeloma (MM) cells plays a key role in the pathogenesis of MM-related osteolytic bone disease (OBD). MM cells promote OC formation and, in turn, OCs enhance MM cell proliferation. Chemokines are mediators of MM effects on bone and vice versa; in particular, CCL3 enhances OC formation and promotes MM cell migration and survival. Here, we characterize the effects of MLN3897, a novel specific antagonist of the chemokine receptor CCR1, on both OC formation and OC-MM cell interactions. MLN3897 demonstrates significant impairment of OC formation (by 40%) and function (by 70%), associated with decreased precursor cell multinucleation and down-regulation of c-fos signaling. OCs secrete high levels of CCL3, which triggers MM cell migration; conversely, MLN3897 abrogates its effects by inhibiting Akt signaling. Moreover, MM cell-to-OC adhesion was abrogated by MLN3897, thereby inhibiting MM cell survival and proliferation. Our results therefore show novel biologic sequelae of CCL3 and its inhibition in both osteoclastogenesis and MM cell growth, providing the preclinical rationale for clinical trials of MLN3897 to treat OBD in MM.

Sustained Hydrogen Peroxide Induces Iron Uptake by Transferrin Receptor-1 Independent of the Iron Regulatory Protein/Iron-responsive Element Network

Local and systemic inflammatory conditions are characterized by the intracellular deposition of excess iron, which may promote tissue damage via Fenton chemistry. Because the Fenton reactant H(2)O(2) is continuously released by inflammatory cells, a tight regulation of iron homeostasis is required. Here, we show that exposure of cultured cells to sustained low levels of H(2)O(2) that mimic its release by inflammatory cells leads to up-regulation of transferrin receptor 1 (TfR1), the major iron uptake protein. The increase in TfR1 results in increased transferrin-mediated iron uptake and cellular accumulation of the metal. Although iron regulatory protein 1 is transiently activated by H(2)O(2), this response is not sufficient to stabilize TfR1 mRNA and to repress the synthesis of the iron storage protein ferritin. The induction of TfR1 is also independent of transcriptional activation via hypoxia-inducible factor 1alpha or significant protein stabilization. In contrast, pulse experiments with (35)S-labeled methionine/cysteine revealed an increased rate of TfR1 synthesis in cells exposed to sustained low H(2)O(2) levels. Our results suggest a novel mechanism of iron accumulation by sustained H(2)O(2), based on the translational activation of TfR1, which could provide an important (patho) physiological link between iron metabolism and inflammation.

Sequential actions of ERK1/2 on the AP‐1 transcription factor allow temporal integration of metabolic signals in pancreatic β cells

The AP-1 transcription factor composed of fos and jun gene products mediates transcriptional responses to hormonal and metabolic stimulations of pancreatic beta cells. Here, we investigated the mechanisms that dynamically control expression of AP-1 subunit proteins. In MIN6 cells, glucose and GLP-1 raised c-FOS protein with biphasic kinetics, an initial peak being followed by a plateau that persisted as long as stimuli were maintained. ERK1/2 activation paralleled c-FOS expression. Whereas initial induction of c-FOS protein required ERK1/2-dependent activation of c-fos transcription and de novo protein synthesis, persistent accumulation of c-FOS under sustained stimulation did not. Indeed, dependent on ERK1/2 activation, c-FOS accumulated in its hyperphosphorylated form protected from degradation through the proteasome pathway. The implication of ERK1/2 in the accumulation of c-FOS protein was confirmed in rat primary beta cells, and the functional consequences of this mechanism were demonstrated with DNA-binding and reporter assays. Altogether these findings reveal a sequential regulation of AP-1 by ERK1/2, which initially increases transcription of c-fos and, if stimulation persists, stabilizes freshly synthesized c-FOS protein to efficiently activate the transcription of AP-1-regulated genes. This ERK1/2-AP-1 module can function as a temporal integrator converting metabolic stimuli of different durations into differential transcriptional outputs.

Dullard promotes degradation and dephosphorylation of BMP receptors and is required for neural induction

Bone morphogenetic proteins (BMPs) regulate multiple biological processes, including cellular proliferation, adhesion, differentiation, and early development. In Xenopus development, inhibition of the BMP pathway is essential for neural induction. Here, we report that dullard, a gene involved in neural development, functions as a negative regulator of BMP signaling. We show that Dullard promotes the ubiquitin-mediated proteosomal degradation of BMP receptors (BMPRs). Dullard preferentially complexes with the BMP type II receptor (BMPRII) and partially colocalizes with the caveolin-1-positive compartment, suggesting that Dullard promotes BMPR degradation via the lipid raft-caveolar pathway. Dullard also associates with BMP type I receptors and represses the BMP-dependent phosphorylation of the BMP type I receptor. The phosphatase activity of Dullard is essential for the degradation of BMP receptors and neural induction in Xenopus. Together, these observations suggest that Dullard is an essential inhibitor of BMP receptor activation during Xenopus neuralization.

Predominant Effect of A-Type Natriuretic Peptide on Reduction of Oxidative Stress During the Treatment of Patients With Heart Failure

BACKGROUND

Oxidative stress plays an important role in the pathogenesis of heart failure and was investigated in the present study of the role of exogenous A-type natriuretic peptide (ANP) in the patients with heart failure and in cultured neonatal rat cardiomyocytes.

METHODS AND RESULTS

The first protocol was to examine if an infusion of human ANP (carperitide) changed serum levels of TRX (thioredoxin) during the treatment of patients with heart failure compared with conventional therapy using furosemide. Protocol 2 investigated whether ANP had a direct antioxidant action on the failing heart by measuring TRX gene expression and reactive oxygen species (ROS) production in cultured neonatal rat cardiomyocytes. In Protocol 1, 8 patients were treated with only an intravenous bolus of furosemide and 11 patients with only an intravenous infusion of carperitide for 24 h. Serum TRX levels significantly decreased at 4 h (p<0.03) and at 24 h (p<0.05) in the carperitide group, whereas they decreased slightly but were not significantly different in the furosemide group. In Protocol 2, it was found that a low dose of exogenous ANP of 10(-9) mol/L significantly suppressed TRX expression and ROS production in cardiomyocytes.

CONCLUSION

Carperitide infusion has a predominantly antioxidant action, in addition to improving the hemodynamics of patients with acute heart failure. Furthermore, carperitide infusion should have a direct antioxidant effect on the failing heart.

Endostatin down-regulates soluble guanylate cyclase (sGC) in endothelial cells in vivo: influence of endostatin on vascular endothelial growth factor (VEGF) signaling

Endostatin was suggested to be an antiangiogenic agent with the potential for clinical use in cancer therapy. Unfortunately, up to now no antiangiogenic effect was seen in clinical trials using this substance. The lack of response might be caused by an incomplete understanding of endostatin signaling. Endostatin is known to influence the vascular endothelial growth factor (VEGF) signaling pathway. It has been reported to bind to the VEGF receptor KDR directly and to decrease the phosphorylation of endothelial nitric oxide synthase (eNOS) at Ser1177 via the protein phosphatase 2A (PP2A). But so far no details of endostatin signaling with regard to NO downstream effectors have been revealed. In the present work the authors demonstrate that endostatin down-regulates the protein level of soluble guanylate cyclase (sGC) in endothelial cells of newly formed blood vessels in 5 day-old wounds (control: 62.5 +/- 33 vessels/mm2, endostatin: 9.2 +/- 3.2 vessels/mm2). This was confirmed in experiments with endothelial tubes of embryoid bodies and endothelial cells derived from embryonic stem cells (eESCs; control: 126 +/- 20, endostatin: 58 +/- 10). The decrease of sGC protein levels in response to endostatin was abolished after preincubation with the PP2A inhibitor okadaic acid. No alterations of sGC mRNA levels could be found under endostatin treatment in eESC. The authors conclude that endostatin affects VEGF signaling in endothelial cells by a post-transcriptional PP2A-dependent down-regulation of sGC protein levels.

N-Terminal c-Fos tyrosine phosphorylation regulates c-Fos/ER association and c-Fos-dependent phospholipid synthesis activation

c-Fos dephosphorylated on tyrosine (c-Fos), a component of the activator protein-1 (AP-1) family of transcription factors, is expressed at very low levels in resting cells. However, its expression is rapidly upregulated in cells undergoing G(0) to S phase transition leading to AP-1-dependent gene transcription responses. In addition, cytoplasmic c-Fos associates to the endoplasmic reticulum (ER) membranes and activates phospholipid synthesis during cell growth and differentiation. Herein, it is shown that in T98G cells, c-Fos/ER association and consequently phospholipid synthesis activation is regulated by the phosphorylated state of c-Fos tyrosine (tyr) residues. The small amount of c-Fos present in quiescent T98G cells is tyr-phosphorylated and not ER-membrane bound. In growing cells, it is dephosphorylated, associated to ER membranes and promotes phospholipid synthesis activation. Impairing tyr-dephosphorylation abrogates phospholipid synthesis activation and reduces proliferation rates to those of quiescent cells. Substitution of tyr residues 10, 30, 106 and 337 evidence tyr 10 and 30 as relevant for this regulatory phenomenon. It is concluded that phosphorylation of tyr residues 10 and 30 of c-Fos regulate the rate of synthesis of phospholipids by regulating c-Fos/ER association.

Involvement of oxidants and AP-1 in angiotensin II-activated NFAT3 transcription factor

Cardiomyocyte hypertrophy is associated with multiple pathophysiological cardiovascular conditions. Recent studies have substantiated the finding that oxidants may contribute to the development of cardiomyocyte hypertrophy. Activation of the nuclear factor of activated T cells-3 (NFAT3) transcription factor has been shown to result from endocrine inducers of cardiomyocyte hypertrophy such as angiotensin II (ANG II) and serves as an important molecular regulator of cardiomyocyte hypertrophy. In this study, we found that antioxidant enzyme catalase and antioxidants N-acetyl-l-cysteine, alpha-phenyl-N-tert-butylnitrone, and lipoic acid prevent ANG II from activating NFAT3 promoter-luciferase. H(2)O(2) induces a time- and dose-dependent activation of NFAT3 transcription factor. A dominant negative form of NFAT3 transcription factor inhibited H(2)O(2) from activating NFAT3 promoter. An inhibitor of ERKs, but not phosphoinositide 3-kinase or p38 MAPKs, blocked NFAT3 activation by H(2)O(2). The NFAT3 binding site in the promoters of most genes contains a weak activator protein-1 (AP-1) binding site adjacent to the core consensus NFAT binding sequence. ERK inhibitor PD98059 was found previously to inhibit AP-1 activation by H(2)O(2). Inactivation of AP-1 transcription factor by cotransfection of a dominant negative c-Jun, TAM67, prevented H(2)O(2) or ANG II from activating NFAT3 promoter. NFAT3 promoter containing the core NFAT cis-element without AP-1 binding site failed to show activation by H(2)O(2) treatment. Our data suggest that hypertrophy inducers ANG II and H(2)O(2) may activate NFAT3 in cardiomyocyte through an AP-1 transcription factor-dependent mechanism.

Induction of antioxidant and detoxification response by oxidants in cardiomyocytes: evidence from gene expression profiling and activation of Nrf2 transcription factor

Mild or low doses of oxidants are known to prime cells towards resistance against further damage. In cardiomyocytes, we found that pretreatment with 100 microM H(2)O(2) prevents the cells from apoptosis induced by doxorubicin (Dox). Affymetrix microarray analyses of 28,000 genes reveal that H(2)O(2) treated cells reduced expression of genes encoding cytochrome c, mitochondrial complex I, III, IV and V and several contractile proteins. Elevated expression of antioxidant and detoxification genes appears as a dominant feature of the gene expression profile of H(2)O(2) treated cells. Most of the genes in this category contain an Antioxidant Response Element (ARE) in their promoters. Measurements of ARE promoter-reporter gene activity indicate a dose- and time-dependent activation of the ARE by H(2)O(2). Since the Nrf2 transcription factor regulates ARE-mediated gene expression, we overexpressed Nrf2 to test whether activation of Nrf2 is sufficient to induce cytoprotection. High levels of Nrf2 expression were achieved via adenovirus mediated gene delivery. Transduced Nrf2 was present in the nuclei and caused an increase in the expression of NAD(P)H:quinone oxidoreductase 1 (NQO1), a representative downstream target of Nrf2. Unlike H(2)O(2) pretreated cells, the cells expressing high levels of Nrf2 were not resistant to Dox-induced apoptosis. Therefore, the cytoprotective effect of H(2)O(2) pretreatment is not reliant upon Nrf2 activation alone as measured by resistance against Dox-induced apoptosis.

A comprehensive map of the toll-like receptor signaling network

Recognition of pathogen-associated molecular signatures is critically important in proper activation of the immune system. The toll-like receptor (TLR) signaling network is responsible for innate immune response. In mammalians, there are 11 TLRs that recognize a variety of ligands from pathogens to trigger immunological responses. In this paper, we present a comprehensive map of TLRs and interleukin 1 receptor signaling networks based on papers published so far. The map illustrates the possible existence of a main network subsystem that has a bow-tie structure in which myeloid differentiation primary response gene 88 (MyD88) is a nonredundant core element, two collateral subsystems with small GTPase and phosphatidylinositol signaling, and MyD88-independent pathway. There is extensive crosstalk between the main bow-tie network and subsystems, as well as feedback and feedforward controls. One obvious feature of this network is the fragility against removal of the nonredundant core element, which is MyD88, and involvement of collateral subsystems for generating different reactions and gene expressions for different stimuli.

Mitogen activated protein kinase-dependent activation of c-Jun and c-Fos is required for neuronal differentiation but not for growth and stress response in PC12 cells

MAPK-dependent activation of AP-1 protein c-Jun is involved in PC12 cell differentiation and apoptosis. However, the role of other AP-1 proteins and their connection to MAPKs during growth, differentiation and apoptosis has remained elusive. Here we studied the activation of AP-1 proteins in response to ERK, JNK, and p38 signaling upon NGF, EGF and anisomycin exposures. All treatments caused different kinetics and strength of MAPK and AP-1 activities. NGF induced persistent ERK and AP-1 activities, whereas upon EGF and anisomycin exposures, their activities were only weakly and transiently induced. The sustained AP-1 activity was associated with concomitant c-Fos and c-Jun expression and phoshorylation, which were JNK and ERK dependent. While inhibition of the ERK, JNK, and p38 activities partially prevented AP-1 activity and suppressed differentiation, none of them was required for anisomycin-induced apoptosis. The importance of c-Fos and c-Jun as mediators of differentiation was demonstrated by the findings that the corresponding siRNAs suppressed NGF-induced neurite outgrowth. However, the capacity of c-Fos to promote differentiation required cooperation with Jun proteins. In contrast, Fra-2 expression was not required for the differentiation response. Together, the results show that sustained c-Jun and c-Fos activities mediate MAPK signaling and are essential for differentiation of PC12 cells.

c-Fos degradation by the ubiquitin-proteasome proteolytic pathway in osteoclast progenitors

c-Fos is an immediate early gene type proto-oncogene that belongs to the AP (activator protein)-1 transcription factor family. Gene knockout experiments have demonstrated that, among the Fos family, only c-Fos is indispensable for osteoclast differentiation but that c-Fos can be substituted for by other Fos family members including FosB/DeltaFosB, Fra-1 and Fra-2, in most other tissues and cells. To further understand a unique role of c-Fos in osteoclastogenesis, we investigated the temporal profile and regulatory mode of expression of c-Fos during the course of osteoclast differentiation. The results indicated that c-Fos protein gradually increased in preosteoclasts during differentiation to a greater extent than that of mRNA induction. We then determined the proteolytic pathway of c-Fos conferring unstable nature on c-Fos protein in a preosteoclastic cell line, RAW264.7. Proteasome inhibitors including MG132 and Z-LLF caused a rapid increase in c-Fos protein expression in these cells within several hours, but other inhibitors of cysteine protease (E-64), lysosome (chloroquine) and calpain (ALLM) did not. Moreover, the proteasome inhibitors caused an extensive accumulation of ubiquitinated c-Fos protein and an approximately three-fold extension of the c-Fos protein half-life. We therefore conclude that the ubiquitin-proteasome system is the major proteolytic pathway conferring instability on c-Fos protein in preosteoclasts. Our results further imply that c-Fos stabilization due to dynamic changes in the ubiquitin-proteasome-dependent degradation may be involved in the accumulation of c-Fos protein in differentiating preosteoclasts.

NFkappaB and AP-1 differentially contribute to the induction of Mn-SOD and eNOS during the development of oxidant tolerance

Exposure of cardiac myocytes to anoxia/reoxygenation (A/R) increases myocyte oxidant stress and converts the myocytes to a proinflammatory phenotype. These oxidant-induced effects are prevented by pretreatment of the myocytes with an oxidant stress (A/R or H2O2) 24 h earlier (oxidant tolerance). Although NF-kappaB and AP-1 (nuclear signaling) and Mn-SOD and eNOS (effector enzymes) have been implicated in the development oxidant tolerance, the precise relationship between the nuclear transcription factors and the effector enzymes in the development of oxidant tolerance has not been defined. Herein, we show that an initial A/R challenge results in nuclear accumulation of both NF-kappaB and AP-1 (EMSA). In addition, blockade of nuclear translocation of NF-kappaB (SN50) or AP-1 (decoy oligonucleotide) prevents the development of oxidant tolerance, i.e., the second A/R challenge produces the same quantitative effects as the initial A/R challenge. In this model, nuclear translocation of both NF-kappaB and AP-1 is required for induction of Mn-SOD, while nuclear translocation of AP-1, but not NF-kappaB, is a prerequisite for induction of eNOS. Collectively, our findings indicate that NF-kappaB and AP-1 work in concert to ensure the induction eNOS and Mn-SOD, which in turn are important for the development of oxidant tolerance.

Corticosteroids inhibit cell death induced by doxorubicin in cardiomyocytes: induction of antiapoptosis, antioxidant, and detoxification genes

Psychological or physical stress induces an elevation of corticosteroids in the circulating system. We report here that corticosterone (CT) protects cardiomyocytes from apoptotic cell death induced by doxorubicin (Dox), an antineoplastic drug known to induce cardiomyopathy possibly through reactive oxygen species production. The cytoprotection induced by CT is within the range of physiologically relevant doses. The lowest dose tested, 0.1 microM (or 3.5 microg/dl), inhibited apoptosis by approximately 25% as determined by caspase activity. With 1 microM CT, cardiomyocytes gain a cytoprotective effect after 8 h of incubation and remain protected for at least 72 h. Hydrocortisone, cortisone, dexamethasone, and aldosterone but not androstenedione or cholesterol also induced cytoprotection. Analyses of 20,000 gene expression sequences using Affymetrix high-density oligonucleotide array found that CT caused up-regulation of 140 genes and down-regulation of 108 genes over 1.5-fold. Among the up-regulated genes are bcl-xL, metallothioneins, glutathione peroxidase-3, and glutathione S-transferases. Western blot analyses revealed that CT induced an elevation of bcl-xL but not bcl-2 or proapoptotic factors bax, bak, and bad. Inhibiting the expression of bcl-xL reduced the cytoprotective effect of CT. Our data suggest that CT induces a cytoprotective effect on cardiomyocytes in association with reprogramming gene expression and induction of bcl-xL gene.

A comprehensive pathway map of epidermal growth factor receptor signaling

The epidermal growth factor receptor (EGFR) signaling pathway is one of the most important pathways that regulate growth, survival, proliferation, and differentiation in mammalian cells. Reflecting this importance, it is one of the best-investigated signaling systems, both experimentally and computationally, and several computational models have been developed for dynamic analysis. A map of molecular interactions of the EGFR signaling system is a valuable resource for research in this area. In this paper, we present a comprehensive pathway map of EGFR signaling and other related pathways. The map reveals that the overall architecture of the pathway is a bow-tie (or hourglass) structure with several feedback loops. The map is created using CellDesigner software that enables us to graphically represent interactions using a well-defined and consistent graphical notation, and to store it in Systems Biology Markup Language (SBML).

Epidermal growth factor receptor-dependent and -independent pathways in hydrogen peroxide-induced mitogen-activated protein kinase activation in cardiomyocytes and heart fibroblasts

Mild doses of oxidative stress in the heart correlate with the induction of apoptosis or hypertrophy in cardiomyocytes (CMCs) and fibrosis or proliferation of fibroblasts. Three branches of mitogen-activated protein kinases (MAPKs), i.e., c-Jun N-terminal kinases (JNKs), extracellular signal-related kinases 1 and 2 (ERK1/2), and p38, are activated by oxidants in a variety of cell types, including CMCs. However, the initiation process of these signaling pathways remains unsolved. We explored the role of the epidermal growth factor (EGF) receptor in H(2)O(2)-induced MAPK activation using two different cell types from the same organ: CMCs and heart fibroblasts (HFs). Pretreatment of each cell type with EGF revealed differences in how CMCs and HFs responded to subsequent treatment with H(2)O(2): in CMCs, the second treatment resulted in little further activation of JNKs and ERK1/2, whereas HFs retained the full response of JNKs and ERK1/2 activation by H(2)O(2) regardless of EGF pretreatment. AG-1478 [4-(3'-chloroanilino)-6,7-dimethoxy-quinazoline], a pharmacologic inhibitor of the EGF receptor tyrosine kinase, inhibited JNK and ERK1/2 activations but not p38 in both cell types. The data using the Src inhibitor PP2 [4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine] resemble those found when using AG-1478 in either cell type. Pharmacologic inhibitors of matrix metalloproteinases (MMPs) further illustrated the difference between the two cell types. In HFs, MMP inhibitors GM6001 [N-[(2R)-2-(hydroxamidocarbonylmethyl)-4-methylpentanoyl]-l-tryptophan methylamide] and BB2516 [[2S-[N4(R(*)),2R(*),3S(*)]]-N4-[2,2-dimethyl-1-[(methylamino)carbonyl]propyl]-N1,2-dihydroxy-3-(2-methylpropyl)butanediamide, marimastat] inhibited JNKs and ERK1/2 activation without affecting p38 activation by H(2)O(2) inhibitors. In contrast, these MMP failed to significantly inhibit the activation of JNKs, ERKs, or p38 in CMCs. These data suggest the complexity of the cell type-dependent signaling web initiated by oxidants in the heart.

Cleavage and proteasome-mediated degradation of the basal transcription factor TFIIA

The transcription factor TFIIA is encoded by two genes, TFIIAalphabeta and TFIIAgamma. In higher eukaryotes, the TFIIAalphabeta is translated as a precursor and undergoes proteolytic cleavage; the regulation and biological implications of the cleavage have remained elusive. We determined by Edman degradation that the TFIIAbeta subunit starts at Asp 278. We found that a cleavage recognition site (CRS), a string of amino acids QVDG at positions -6 to -3 from Asp 278, is essential for cleavage. Mutations in the CRS that prevent cleavage significantly prolong the half-life of TFIIA. Consistently, the cleaved TFIIA is a substrate for the ubiquitin pathway and proteasome-mediated degradation. We show that mutations in the putative phosphorylation sites of TFIIAbeta greatly affect degradation of the beta-subunit. We propose that cleavage and subsequent degradation fine-tune the amount of TFIIA in the cell and consequently the level of transcription.