Activating transcription factor 3 up-regulated by c-Jun NH(2)-terminal kinase/c-Jun contributes to apoptosis induced by potassium deprivation in cerebellar granule neurons

Cell type- and region-specific translatomes in an MPTP mouse model of Parkinson's disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder, characterized by the progressive loss of nigrostriatal dopaminergic neurons (DANs), involving the dysregulation of both neurons and glial cells. Cell type- and region-specific gene expression profiles can provide an effective source for revealing the mechanisms of PD. In this study, we adopted the RiboTag approach to obtain cell type (DAN, microglia, astrocytes)- and brain region (substantia nigra, caudate-putamen)-specific translatomes at an early stage in an MPTP-induced mouse model of PD. Through DAN-specific translatome analysis, the glycosphingolipid biosynthetic process was identified as a significantly downregulated pathway in the MPTP-treated mice. ST8Sia6, a key downregulated gene related to glycosphingolipid biosynthesis, was confirmed to be downregulated in nigral DANs from postmortem brains of patients with PD. Specific expression of ST8Sia6 in DANs exerts anti-inflammatory and neuroprotective effects in MPTP-treated mice. Through cell type (microglia vs. astrocyte) and brain region (substantia nigra vs. caudate-putamen) comparisons, nigral microglia showed the most intense immune responses. Microglia and astrocytes in the substantia nigra showed similar levels of activation in interferon-related pathways and interferon gamma (IFNG) was identified as the top upstream regulator in both cell types. This work highlights that the glycosphingolipid metabolism pathway in the DAN is involved in neuroinflammation and neurodegeneration in an MPTP mouse model of PD and provides a new data source for elucidating the pathogenesis of PD.

Dysregulated miRNAs in Progression and Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive degeneration of neurons due to the accumulation of amyloid-β peptide (Aβ) and hyper-phosphorylation of tau protein in the neuronal milieu leading to increased oxidative stress and apoptosis. Numerous factors contribute towards the progression of AD, including miRNA, which are 22-24 nucleotides long sequence which acts as critical regulators of cellular processes by binding to 3' UTR of mRNA, regulating its expression post-transcriptionally. This review aims to determine the miRNA with the most significant dysregulation in the brain and cerebrospinal fluid (CSF) of human patients. A systemized inclusion/exclusion criterion has been utilized based on selected keywords followed by screening of those articles to conclude a list of 8 highly dysregulated miRNAs based on the fold change of AD vs control patients, which could be used in clinical testing as these miRNAs play central role in the pathophysiology of AD. Furthermore, a network study of highly dysregulated miRNA estimated the association of these miRNA in the mediation of Aβ generation and aggregation, inhibition of autophagy, reduction of Aβ clearance, microglial and astrocytic activation, neuro-inflammation, tau hyper-phosphorylation, and synaptic loss.

Transcriptomic changes triggered by ouabain in rat cerebellum granule cells: Role of α3- and α1-Na+,K+-ATPase-mediated signaling

It was shown previously that inhibition of the ubiquitous α1 isoform of Na⁺,K⁺-ATPase by ouabain sharply affects gene expression profile via elevation of intracellular [Na⁺]_i/[K⁺]_i ratio. Unlike other cells, neurons are abundant in the α3 isoform of Na⁺,K⁺-ATPase, whose affinity in rodents to ouabain is 10⁴-fold higher compared to the α1 isoform. With these sharp differences in mind, we compared transcriptomic changes in rat cerebellum granule cells triggered by inhibition of α1- and α3-Na⁺,K⁺-ATPase isoforms. Inhibition of α1- and α3-Na⁺,K⁺-ATPase isoforms by 1 mM ouabain resulted in dissipation of transmembrane Na⁺ and K⁺ gradients and differential expression of 994 transcripts, whereas selective inhibition of α3-Na⁺,K⁺-ATPase isoform by 100 nM ouabain affected expression of 144 transcripts without any impact on the [Na⁺]_i/[K⁺]_i ratio. The list of genes whose expression was affected by 1 mM ouabain by more than 2-fold was abundant in intermediates of intracellular signaling and transcription regulators, including augmented content of Npas4, Fos, Junb, Atf3, and Klf4 mRNAs, whose upregulated expression was demonstrated in neurons subjected to electrical and glutamatergic stimulation. The role [Na⁺]_i/[K⁺]_i-mediated signaling in transcriptomic changes involved in memory formation and storage should be examined further.

Transcriptomic changes triggered by ouabain in rat cerebellum granule cells: Role of α3- and α1-Na+,K+-ATPase-mediated signaling

It was shown previously that inhibition of the ubiquitous α1 isoform of Na+,K+-ATPase by ouabain sharply affects gene expression profile via elevation of intracellular [Na+]i/[K+]i ratio. Unlike other cells, neurons are abundant in the α3 isoform of Na+,K+-ATPase, whose affinity in rodents to ouabain is 104-fold higher compared to the α1 isoform. With these sharp differences in mind, we compared transcriptomic changes in rat cerebellum granule cells triggered by inhibition of α1- and α3-Na+,K+-ATPase isoforms. Inhibition of α1- and α3-Na+,K+-ATPase isoforms by 1 mM ouabain resulted in dissipation of transmembrane Na+ and K+ gradients and differential expression of 994 transcripts, whereas selective inhibition of α3-Na+,K+-ATPase isoform by 100 nM ouabain affected expression of 144 transcripts without any impact on the [Na+]i/[K+]i ratio. The list of genes whose expression was affected by 1 mM ouabain by more than 2-fold was abundant in intermediates of intracellular signaling and transcription regulators, including augmented content of Npas4, Fos, Junb, Atf3, and Klf4 mRNAs, whose upregulated expression was demonstrated in neurons subjected to electrical and glutamatergic stimulation. The role [Na+]i/[K+]i-mediated signaling in transcriptomic changes involved in memory formation and storage should be examined further.

Protective effect of resveratrol against nigrostriatal pathway injury in striatum via JNK pathway

Nigrostriatal pathway injury is one of the traumatic brain injury models that usually lead to neurological dysfunction or neuron necrosis. Resveratrol-induced benefits have recently been demonstrated in several models of neuronal degeneration diseases. However, the protective properties of resveratrol against neurodegeneration have not been explored definitely. Thus, we employ the nigrostriatal pathway injury model to mimic the insults on the brain. Resveratrol decreased the p-ERK expression and increased the p-JNK expression compared to the DMSO group, but not alter the p38 MAPK proteins around the lesion site by Western blot. Prior to the injury, mice were infused with resveratrol intracerebroventricularly with or without JNK-IN-8, a specific c-JNK pathway inhibitor for JNK1, JNK2 and JNK4. The study assessed modified improved neurological function score (mNSS) and beam/walking test, the level of inflammatory cytokines IL-1β, IL-6 and TNF-α, and striatal expression of Bax and Bcl-2 proteins associated with neuronal apoptosis. The results revealed that resveratrol exerted a neuroprotective effect as shown by the improved mNSS and beam latency, anti-inflammatory effects as indicated by the decreased level of IL-1β, TNF-α and IL-6. Furthermore, resveratrol up-regulated the protein expression of p-JNK and Bcl-2, down-regulated the expression of Bax and the number of Fluoro-Jade C (FJC) positive neurons. However, these advantages of resveratrol were abolished by JNK-IN-8 treatment. Overall, we demonstrated that resveratrol treatment attenuates the nigrostriatal pathway injury-induced neuronal apoptosis and inflammation via activation of c-JNK signaling.

14-3-3σ Gene Loss Leads to Activation of the Epithelial to Mesenchymal Transition Due to the Stabilization of c-Jun Protein

Loss of 14-3-3σ has been observed in multiple tumor types; however, the mechanisms by which 14-3-3σ loss leads to tumor progression are not understood. The experiments in this report demonstrate that loss of 14-3-3σ leads to a decrease in the expression of epithelial markers and an increase in the expression of mesenchymal markers, which is indicative of an induction of the epithelial to mesenchymal transition (EMT). The EMT was accompanied by an increase in migration and invasion in the 14-3-3σ(-/-) cells. 14-3-3σ(-/-) cells show increased stabilization of c-Jun, resulting in an increase in the expression of the EMT transcription factor slug. 14-3-3σ induces the ubiquitination and degradation of c-Jun in an FBW7-dependent manner. c-Jun ubiquitination is dependent on the presence of an intact nuclear export pathway as c-Jun is stabilized and localized to the nucleus in the presence of a nuclear export inhibitor. Furthermore, the absence of 14-3-3σ leads to the nuclear accumulation and stabilization of c-Jun, suggesting that 14-3-3σ regulates the subcellular localization of c-Jun. Our results have identified a novel mechanism by which 14-3-3σ maintains the epithelial phenotype by inhibiting EMT and suggest that this property of 14-3-3σ might contribute to its function as a tumor suppressor gene.

TGRL Lipolysis Products Induce Stress Protein ATF3 via the TGF-β Receptor Pathway in Human Aortic Endothelial Cells

Studies have suggested a link between the transforming growth factor beta 1 (TGF-β1) signaling cascade and the stress-inducible activating transcription factor 3 (ATF3). We have demonstrated that triglyceride-rich lipoproteins (TGRL) lipolysis products activate MAP kinase stress associated JNK/c-Jun pathways resulting in up-regulation of ATF3, pro-inflammatory genes and induction of apoptosis in human aortic endothelial cells. Here we demonstrate increased release of active TGF-β at 15 min, phosphorylation of Smad2 and translocation of co-Smad4 from cytosol to nucleus after a 1.5 h treatment with lipolysis products. Activation and translocation of Smad2 and 4 was blocked by addition of SB431542 (10 μM), a specific inhibitor of TGF-β-activin receptor ALKs 4, 5, 7. Both ALK receptor inhibition and anti TGF-β1 antibody prevented lipolysis product induced up-regulation of ATF3 mRNA and protein. ALK inhibition prevented lipolysis product-induced nuclear accumulation of ATF3. ALKs 4, 5, 7 inhibition also prevented phosphorylation of c-Jun and TGRL lipolysis product-induced p53 and caspase-3 protein expression. These findings demonstrate that TGRL lipolysis products cause release of active TGF-β and lipolysis product-induced apoptosis is dependent on TGF-β signaling. Furthermore, signaling through the stress associated JNK/c-Jun pathway is dependent on TGF-β signaling suggesting that TGF-β signaling is necessary for nuclear accumulation of the ATF3/cJun transcription complex and induction of pro-inflammatory responses.

Heroin activates ATF3 and CytC via c-Jun N-terminal kinase pathways to mediate neuronal apoptosis

Background

Drug abuse and addiction has become a major public health problem that impacts all societies. The use of heroin may cause spongiform leukoencephalopathy (SLE).

Material/Methods

Cerebellar granule cells were derived from 7-day-old Sprague-Dawley rat pups.

Neurons were dissociated from freshly dissected cerebella by mechanical disruption in the presence of 0.125% trypsin and DNaseI and then seeded at a density of 4×10⁶ cells/ml in Dulbecco’s modified Eagle’s medium/nutrient mixture F-12 ham’s containing 10% fetal bovine serum and Arc-C(sigma) at concentrations to inhibit glial cell growth inoculated into 6-well plates and a small dish.

Results

We found that heroin induces the apoptosis of primary cultured cerebellar granule cells (CGCS) and that the c-Jun N-terminal kinase (JNK) pathway was activated under heroin treatment and stimulated obvious increases in the levels of C-jun, Cytc, and ATF3mRNA. CYTC and ATF3 were identified as candidate targets of the JNK/c-Jun pathway in this process because the specificity inhibitors SP600125 of JNK/C-jun pathways reduced the levels of C-jun, Cytc, and ATF3mRNA. The results suggested that SP600125 of JNK/C-jun can inhibit heroin-induced apoptosis of neurons.

Conclusions

The present study analyzes our understanding of the critical role of the JNK pathway in the process of neuronal apoptosis induced by heroin, and suggests a new and effective strategy to treat SLE.

A novel missense mutation in CCDC88C activates the JNK pathway and causes a dominant form of spinocerebellar ataxia

Background

Spinocerebellar ataxias (SCAs) are a group of clinically and genetically diverse and autosomal-dominant disorders characterised by neurological deficits in the cerebellum. At present, there is no cure for SCAs. Of the different distinct subtypes of autosomal-dominant SCAs identified to date, causative genes for only a fraction of them are currently known. In this study, we investigated the cause of an autosomal-dominant SCA phenotype in a family that exhibits cerebellar ataxia and pontocerebellar atrophy along with a global reduction in brain volume.

Methods and results

Whole-exome analysis revealed a missense mutation c.G1391A (p.R464H) in the coding region of the coiled-coil domain containing 88C (CCDC88C) gene in all affected individuals. Functional studies showed that the mutant form of CCDC88C activates the c-Jun N-terminal kinase (JNK) pathway, induces caspase 3 cleavage and triggers apoptosis.

Conclusions

This study expands our understanding of the cause of autosomal-dominant SCAs, a group of heterogeneous congenital neurological conditions in humans, and unveils a link between the JNK stress pathway and cerebellar atrophy.

Peripheral expression of MAPK pathways in Alzheimer's and Parkinson's diseases

Alteration of mitogen-activated protein kinase pathways may cause aberrant protein phosphorylation and enhanced apoptosis in Alzheimer's disease (AD) and Parkinson's disease (PD). Increased susceptibility of lymphocytes to apoptosis has been reported in AD. To our knowledge this is the first study to investigate the expression and phosphorylation status of p38 mitogen-activated protein kinase (p38MAPK) and c-Jun N-terminal kinase (JNK) in peripheral blood lymphocytes of 20 AD and 20 PD patients and 20 healthy controls using western blot analysis. Compared with controls, no significant difference of total p38MAPK or JNK levels were observed in AD and PD patients, whereas phosphorylated p38MAPK and phosphorylated JNK levels were significantly increased in the AD and PD groups (p<0.001). However, the increased levels of the two phosphorylated kinases in AD versus PD patients presented no significant difference. Interestingly, phosphorylated p38MAPK and phosphorylated JNK levels were positively correlated with disease duration (r=0.602, p=0.005 and r=0.561, p=0.010, respectively) and negatively correlated with the Mini Mental State Examination score (r=-0.664, p=0.001 and r=-0.578, p=0.008, respectively) in AD patients. No correlations between protein levels and clinical variables were found in PD patients. Investigation of peripheral changes in the expression of p38MAPK and JNK may lead to the development of innovative biomarkers of neurodegenerative diseases, particularly for AD.

JUN regulates early transcriptional responses to axonal injury in retinal ganglion cells

The AP1 family transcription factor JUN is an important molecule in the neuronal response to injury. In retinal ganglion cells (RGCs), JUN is upregulated soon after axonal injury and disrupting JUN activity delays RGC death. JUN is known to participate in the control of many different injury response pathways in neurons, including pathways controlling cell death and axonal regeneration. The role of JUN in regulating genes involved in cell death, ER stress, and regeneration was tested to determine the overall importance of JUN in regulating RGC response to axonal injury. Genes from each of these pathways were transcriptionally controlled following axonal injury and Jun deficiency altered the expression of many of these genes. The differentially expressed genes included, Atf3, Ddit3, Ecel1, Gadd45α, Gal, Hrk, Pten, Socs3, and Sprr1a. Two of these genes, Hrk and Atf3, were tested for importance in RGC death using null alleles of each gene. Disruption of the prodeath Bcl2 family member Hrk did not affect the rate or amount of RGC death after axonal trauma. Deficiency in the ATF/CREB family transcription factor Atf3 did lessen the amount of RGC death after injury, though it did not provide long term protection to RGCs. Since JUN's dimerization partner determines its transcriptional targets, the expression of several candidate AP1 family members were examined. Multiple AP1 family members were induced by axonal injury and had a different expression profile in Jun deficient retinas compared to wildtype retinas (Fosl1, Fosl2 and Jund). Overall, JUN appears to play a multifaceted role in regulating RGC response to axonal injury.

Heroin activates Bim via c-Jun N-terminal kinase/c-Jun pathway to mediate neuronal apoptosis

Heroin is reported to cause spongiform leukoencephalopathy (SLE) in heroin addicts and the exact mechanism has not yet been identified. In the present study, we found that heroin could induce apoptosis of primary cultured cerebellar granule cells (CGCs) and Bim was upregulated both transcriptionally and post transcriptionally during CGCs apoptosis. Upregulated Bim translocated to mitochondria and Bax was activated under heroin treatment. Genetic knockdown of Bim using lentiviruses significantly prevented neuronal apoptosis induced by heroin. Meanwhile, c-Jun N-terminal kinase (JNK)/c-Jun pathway was activated in heroin-induced apoptosis. Bim was demonstrated as a downstream target of JNK/c-Jun pathway in this process because pharmacological inhibition of JNK reduced the levels of Bim mRNA and protein. These results indicate that Bim plays a critical role in the neurotoxic process by heroin and JNK/c-Jun pathway acts upstream of Bim in regulating heroin-induced neuronal death. This represents a detailed mechanism of heroin-induced neuronal apoptosis and may provide a new and effective strategy to treat heroin-induced addiction and SLE.

The JNK- and AKT/GSK3β- signaling pathways converge to regulate Puma induction and neuronal apoptosis induced by trophic factor deprivation

The AKT, GSK3 and JNK family kinases have been implicated in neuronal apoptosis associated with neuronal development and several neurodegenerative conditions. However, the mechanisms by which these kinase pathways regulate apoptosis remain unclear. In this study we have investigated the role of these kinases in neuronal cell death using an established model of trophic factor deprivation induced apoptosis in cerebellar granule neurons. BCL-2 family proteins are known to be central regulators of apoptosis and we have determined that the pro-apoptotic family member Puma is transcriptionally up-regulated in trophic factor deprived neurons and that Puma induction is required for apoptosis in vitro and in vivo. Importantly, we demonstrate that Puma induction is dependent on both JNK activation and AKT inactivation. AKT is known to regulate a number of downstream pathways, however we have determined that PI3K-AKT inactivation induces Puma expression through a GSK3β-dependent mechanism. Finally we demonstrate that the JNK and AKT/GSK3β pathways converge to regulate FoxO3a-mediated transcriptional activation of Puma. In summary we have identified a novel and critical link between the AKT, GSK3β and JNK kinases and the regulation of Puma induction and suggest that this may be pivotal to the regulation of neuronal apoptosis in neurodegenerative conditions.

ATF2, a novel factor promoting epithelial-mesenchymal transition in human pancreatic cancer cells

AIM: To investigate whether ATF2 together with TGF-β1 can induce epithelial-mesenchymal transition (EMT) in human pancreatic cancer cell line Capan2.

METHODS: Capan2 cells were induced with TGF-β1 after transfection with PGEX-ATF2, and the negative control group was treated with DMSO. Cell morphological alternations were examined by phase contrast microscopy. The expression of mesenchymal marker vimentin and epithelial markers E-cadherin and ATF2 were detected by Western blot. Cell migration was determined by Transwell motility assay.

RESULTS: Compare to the negative control group, cells transfected with ATF2 and treated with TGF-β1 showed loss of cell-cell contacts, fibroblastic morphology, decreased expression of E-cadherin, up-regulated expression of vimentin and ATF2, and increased migration ability (P = 0.008).

CONCLUSION: ATF2 together with TGF-β1 can induce EMT in human pancreatic cancer cell line Capan2. ATF2 may be a new molecular target for therapy of pancreatic cancer.

Transforming growth factor β suppresses glutamate-cysteine ligase gene expression and induces oxidative stress in a lung fibrosis model

The concentration of glutathione (GSH), the most abundant intracellular free thiol and an important antioxidant, is decreased in the lung in both fibrotic diseases and experimental fibrosis models. The underlying mechanisms and biological significance of GSH depletion, however, remain unclear. Transforming growth factor β (TGF-β) is the most potent and ubiquitous profibrogenic cytokine and its expression is increased in almost all fibrotic diseases. In this study, we show that increasing TGF-β1 expression in mouse lung to a level comparable to those found in lung fibrotic diseases by intranasal instillation of AdTGF-β1(223/225), an adenovirus expressing constitutively active TGF-β1, suppressed the expression of both catalytic and modifier subunits of glutamate-cysteine ligase (GCL), the rate-limiting enzyme in de novo GSH synthesis, decreased GSH concentration, and increased protein and lipid peroxidation in mouse lung. Furthermore, we show that increasing TGF-β1 expression activated JNK and induced activating transcription factor 3, a transcriptional repressor involved in the regulation of the catalytic subunit of GCL, in mouse lung. Control virus (AdDL70-3) had no significant effect on any of these parameters, compared to saline-treated control. Concurrent with GSH depletion, TGF-β1 induced lung epithelial apoptosis and robust pulmonary fibrosis. Importantly, lung GSH levels returned to normal, whereas fibrosis persisted at least 21 days after TGF-β1 instillation. Together, the data suggest that increased TGF-β1 expression may contribute to the GSH depletion observed in pulmonary fibrosis diseases and that GSH depletion may be an early event in, rather than a consequence of, fibrosis development.

Neuronal c-Jun is required for successful axonal regeneration, but the effects of phosphorylation of its N-terminus are moderate

Although neural c-Jun is essential for successful peripheral nerve regeneration, the cellular basis of this effect and the impact of c-Jun activation are incompletely understood. In the current study, we explored the effects of neuron-selective c-Jun deletion, substitution of serine 63 and 73 phosphoacceptor sites with non-phosphorylatable alanine, and deletion of Jun N-terminal kinases 1, 2 and 3 in mouse facial nerve regeneration. Removal of the floxed c-jun gene in facial motoneurons using cre recombinase under control of a neuron-specific synapsin promoter (junΔS) abolished basal and injury-induced neuronal c-Jun immunoreactivity, as well as most of the molecular responses following facial axotomy. Absence of neuronal Jun reduced the speed of axonal regeneration following crush, and prevented most cut axons from reconnecting to their target, significantly reducing functional recovery. Despite blocking cell death, this was associated with a large number of shrunken neurons. Finally, junΔS mutants also had diminished astrocyte and microglial activation and T-cell influx, suggesting that these non-neuronal responses depend on the release of Jun-dependent signals from neighboring injured motoneurons. The effects of substituting serine 63 and 73 phosphoacceptor sites (junAA), or of global deletion of individual kinases responsible for N-terminal c-Jun phosphorylation were mild. junAA mutants showed decrease in neuronal cell size, a moderate reduction in post-axotomy CD44 levels and slightly increased astrogliosis. Deletion of Jun N-terminal kinase (JNK)1 or JNK3 showed delayed functional recovery; deletion of JNK3 also interfered with T-cell influx, and reduced CD44 levels. Deletion of JNK2 had no effect. Thus, neuronal c-Jun is needed in regeneration, but JNK phosphorylation of the N-terminus mostly appears to not be required for its function.

JDP2 suppresses transforming growth factor-β1-induced epithelial-mesenchymal transition in human pancreatic cancer cell line Panc-1

AIM: To determine the correlation between overexpression of Jun dimerization protein 2 (JDP2) and epithelial-mesenchymal transition (EMT) in human pancreatic cancer cell line Panc-1.

METHODS: Panc-1 cells were divided into three groups: negative control group, JDP2-transfected group, and empty vector-transfected group. The JDP2-transfected group and empty vector-transfected group were transiently transfected with PCEFL-HA-JDP2 vector and pCEFL vector, respectively. Untreated Panc-1 cells were used as normal controls. Forty-eight hours after transfection, cells were treated with TGF-β1 (10 ng/mL). Cell morphological alternations were examined by phase-contrast microscopy. The expression of mesenchymal marker vimentin and epithelial marker E-cadherin was detected by RT-PCR and Western blot. Cell migration was determined by Transwell motility assay.

RESULTS: TGF-β1-induced EMT was inhibited in the JDP2-transfected group. Compare to the negative control group, cells in the JDP2-transfected group showed no fibroblastic morphology and no significant changes in the levels of E-cadherin and vimentin and in migration ability (48.0 ± 5.3 vs 52.0 ± 7.2). However, cells in the vector-transfected group showed loss of cell-cell contacts, fibroblastic morphology, decreased expression of E-cadherin (mRNA: P < 0.01; protein: P < 0.05), increased expression of vimentin (P < 0.01) and migration ability (48.0 ± 5.3 vs 81.0 ± 10.7, P < 0.01) when compared to the negative control group.

CONCLUSION: JDP2 can inhibit TGF-β1-induced EMT in Panc-1 cells and may be a molecular target for pancreatic carcinoma therapy.

Caspase-3 is a target gene of c-Jun:ATF2 heterodimers during apoptosis induced by activity deprivation in cerebellar granule neurons

Caspase-3, a key executor of neuronal apoptosis, is up-regulated and activated during apoptosis induced by activity deprivation in cerebellar granule neurons (CGNs). However, the transcriptional mechanism regulating caspase-3 during CGN apoptosis remains unknown. Here, we show that the caspase-3 gene is transactivated and its induction is preceded by c-Jun NH(2)-terminal kinase (JNK)/c-Jun:ATF2 pathway activation following activity deprivation in CGNs. We observed that caspase-3 induction is abolished by pharmacological inhibition of the JNK/c-Jun:ATF2 pathway. Destroying c-Jun:ATF2 heterodimers with dominant negative mutants of c-Jun and ATF2 or knockdown by small RNA interference reduced caspase-3 promoter activity and mRNA level. Furthermore, chromatin immunoprecipitation showed increased binding of c-Jun:ATF2 heterodimers to the caspase-3 promoter in response to activity deprivation in vivo. Site-directed mutagenesis of the caspase-3 promoter revealed that caspase-3 transcriptional activation depends primarily on an ATF site -233 to -225 nucleotides upstream of the start site. Taken together, these data demonstrate that caspase-3 is a target gene of c-Jun:ATF2 heterodimers during apoptosis induced by activity deprivation in CGNs.

Identification of a c-Jun N-terminal kinase-2-dependent signal amplification cascade that regulates c-Myc levels in ras transformation

Ras is one of the most frequently activated oncogenes in cancer. Two mitogen-activated protein kinases (MAPKs) are important for ras transformation: extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase 2 (JNK2). Here we present a downstream signal amplification cascade that is critical for ras transformation in murine embryonic fibroblasts. This cascade is coordinated by ERK and JNK2 MAPKs, whose Ras-mediated activation leads to the enhanced levels of three oncogenic transcription factors, namely, c-Myc, activating transcription factor 2 (ATF2) and ATF3, all of which are essential for ras transformation. Previous studies show that ERK-mediated serine 62 phosphorylation protects c-Myc from proteasomal degradation. ERK is, however, not alone sufficient to stabilize c-Myc but requires the cooperation of cancerous inhibitor of protein phosphatase 2A (CIP2A), an oncogene that counteracts protein phosphatase 2A-mediated dephosphorylation of c-Myc. Here we show that JNK2 regulates Cip2a transcription via ATF2. ATF2 and c-Myc cooperate to activate the transcription of ATF3. Remarkably, not only ectopic JNK2, but also ectopic ATF2, CIP2A, c-Myc and ATF3 are sufficient to rescue the defective ras transformation of JNK2-deficient cells. Thus, these data identify the key signal converging point of JNK2 and ERK pathways and underline the central role of CIP2A in ras transformation.

Activating transcription factor 3 regulates survivability and migration of vascular smooth muscle cells

Activating transcription factor 3 (ATF3) is a member of the ATF/CREB (CAMP responsive element binding protein) family of transcription factors. The expression and the function of ATF3 in vascular smooth muscle cells (VSMCs) remain unknown. The aim of this work is to determine the expression and possible function of ATF3 in VSMCs. We found that VSMCs expressed ATF3, and expression of ATF3 in VSMCs was induced by a variety of stimuli including serum, angiotensin II, and H(2)O(2). Knockdown of ATF3 induced apoptosis of VSMCs, caspase-3 cleavage, and cytochrome c release. The results suggest that ATF3 regulates survivability of VSMCs. Moreover, we found that overexpression of ATF3 promoted migration of VSMCs and induced expression of matrix metalloproteinase 1, 3, and 13. These results suggest that ATF3 plays a role in regulating migration of VSMCs. In addition, we found that the expression of ATF3 was upregulated in smooth muscle cells in the injured mouse femoral arteries compared with the uninjured control group. These results suggest that ATF3 is relevant to disease physiology.

Activation and function of immediate-early genes in the nervous system

Immediate-early genes have important roles in processes such as brain development, learning, and responses to drug abuse. Further, immediate-early genes play an essential role in cellular responses that contribute to long-term neuronal plasticity. Neuronal plasticity is a characteristic of the nervous system that is not limited to the first stages of brain development but persists in adulthood and seems to be an inherent feature of everyday brain function. The plasticity refers to the neuron's capability of showing short- or long-lasting phenotypic changes in response to different stimuli and cellular scenarios. In this review, we focus on the immediate-early genes encoding transcription factors (AP-1 and Egr) that are relevant for neuronal responses. Our current understanding of the mechanisms involved in the induction of the immediate-early genes is presented.

The potential role of ATF3 on immune response is regulated by BMP10 through Smad dependent pathway

It is hypothesis that ATF3 is a downstream component of BMP10. The possible function of ATF3 on immune response is partially regulated by BMP10 via Smad dependent pathway. BMP10 is highly expressed in blood cells during embryonic development based on our in situ hybridization. The expression of ATF3 is enhanced by BMP10 in overexpression transgenic mice. Both BMP10 and ATF3 can response to stress stimulate, and ATF3 is well understood as a stress inducible gene which possible contributes to immune response. The Smad dependent pathway is well established for BMP10 in regulation expression of downstream targets. It would be interesting for us to determine the relationship between BMP10 and ATF3, especially to understand the mechanism of BMP10 and ATF3 effecting on heart development, as well as immune response exposed to stress stimulates.

Down-expression of PGC-1alpha partially mediated by JNK/c-Jun through binding to CRE site during apoptotic procedure in cerebellar granule neurons

In eukaryotes, mitochondria are critical for cellular bioenergetics and mediating apoptosis. The transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC-1alpha) is an important regulator of mitochondrial biogenesis and function. However, the role of PGC-1alpha in neuronal apoptosis and its regulation by apoptotic pathway are still unknown. We demonstrated that PGC-1alpha expression was down-regulated in cerebellar granule neurons(CGNs) after activation of the JNK/c-Jun pathway by potassium deprivation. Overexpression of PGC-1alpha partially protected CGNs from potassium deprivation-induced apoptosis. JNK-specific inhibitors, SP600125 and CEP11004, partially blocked the inhibitory effects of JNK on PGC-1alpha expression and its promoter activity. Furthermore, ChIP assays revealed that c-Jun was able to bind to the CRE site (-188 to -180) in the PGC-1alpha promoter. In conclusion, these results suggest that down-expression of PGC-1alpha partially mediated by activation of JNK/c-Jun may be through the binding of c-Jun to the CRE site in the PGC-1alpha promoter, and it might be involved in potassium deprivation-induced apoptosis in CGNs.

Thapsigargin induces expression of activating transcription factor 3 in human keratinocytes involving Ca2+ ions and c-Jun N-terminal protein kinase

Thapsigargin is a specific inhibitor of the sarco/endoplasmic reticulum Ca(2+) ATPase of the endoplasmic reticulum. Here, we show that stimulation of human HaCaT keratinocytes with nanomolar concentrations of thapsigargin triggers expression of activating transcription factor (ATF) 3, a basic-region leucin zipper transcription factor. ATF3 expression was also up-regulated in thapsigargin-stimulated glioma cells, hepatoma cells, retinal pigment epithelial cells, and airway epithelial cells. Thapsigargin-induced up-regulation of ATF3 expression in keratinocytes was attenuated by BAPTA-acetoxymethyl ester or by expression of the Ca(2+)-binding protein parvalbumin in the cytosol of HaCaT cells but not by a panel of pharmacological agents that chelate extracellular Ca(2+) (EGTA) or inhibit either ryanodine receptors (dantrolene) or voltage-gated Ca(2+) channels (nifedipine). Hence, elevated levels of intracellular Ca(2+), released from intracellular stores, are essential for the effect of thapsigargin on the biosynthesis of ATF3. The thapsigargin-induced signaling pathway was blocked by expression of either mitogen-activated protein kinase phosphatase-1 or -5. Experiments involving pharmacological and genetic tools revealed the importance of c-Jun N-terminal protein kinase (JNK) within the signaling cascade, whereas inhibition of extracellular signal-regulated protein kinase or p38 protein kinase did not attenuate thapsigargin-induced expression of ATF3. Functional studies showed that treatment of HaCaT keratinocytes with thapsigargin led to a 2-fold induction of caspase-3/7 activity. The up-regulation of caspase-3/7 activity in thapsigargin-stimulated HaCaT cells was attenuated by inhibition of JNK. Together, these data show that stimulation of HaCaT cells with thapsigargin induces a specific signaling pathway in keratinocytes involving activation of JNK, biosynthesis of ATF3, and up-regulation of caspase-3/7 activity.

The expression of mitogen-activated protein kinases and brain-derived neurotrophic factor in inferior colliculi after acoustic trauma

Acoustic trauma is well known to cause peripheral damage with subsequent effects in the central auditory system. The inferior colliculus (IC) is a major auditory center for the integration of ascending and descending information and is involved in noise-induced tinnitus and central hyperactivity. Here we show that the early effects of acoustic trauma, that eventually result in permanent damage to auditory system, lead to a transient activation of BDNF and mitogen-activated protein kinases (MAPK) including extracellular signal-regulated kinase (ERK), c-jun N-terminal kinase (JNK), and p38 in the IC. In contrast, the early effects of acoustic trauma that result in a temporary damage produced a reversible activation only of p38. The transient activation of MAPK and BDNF in the IC after permanent acoustic trauma is attributed to the plastic changes triggered by a decreased signal input from the damaged periphery. The pattern of MAPK and BDNF activation in the IC is different from that previously described for the cochlea from this laboratory. The differences in the pattern of MAPK and BDNF expression in the IC highlight unique molecular mechanisms underlying temporary and permanent acoustic damage to the central auditory system.

Activating transcription factor 3 is a positive regulator of human IFNG gene expression

IL-12 and IL-18 are essential for Th1 differentiation, whereas the role of IFN-alpha in Th1 development is less understood. In this microarray-based study, we searched for genes that are regulated by IFN-alpha, IL-12, or the combination of IL-12 plus IL-18 during the early differentiation of human umbilical cord blood CD4(+) Th cells. Twenty-six genes were similarly regulated in response to treatment with IL-12, IFN-alpha, or the combination of IL-12 plus IL-18. These genes could therefore play a role in Th1 lineage decision. Transcription factor activating transcription factor (ATF) 3 was upregulated by these cytokines and selected for further study. Ectopic expression of ATF3 in CD4(+) T cells enhanced the production of IFN-gamma, the hallmark cytokine of Th1 cells, whereas small interfering RNA knockdown of ATF3 reduced IFN-gamma production. Furthermore, ATF3 formed an endogenous complex with JUN in CD4(+) T cells induced to Th1. Chromatin immunoprecipitation and luciferase reporter assays showed that both ATF3 and JUN are recruited to and transactivate the IFNG promoter during early Th1 differentiation. Collectively, these data indicate that ATF3 promotes human Th1 differentiation.

Role of activating transcription factor 3 (ATF3) in sublytic C5b-9-induced glomerular mesangial cell apoptosis

Sublytic complement C5b-9 complexes can cause cell apoptosis, but the mechanism of glomerular mesangial cell (GMC) apoptosis mediated by these complexes has not been well defined. The activating transcription factor 3 (ATF3) gene is an immediate early gene for the cell to cope with a variety of stress signals and can promote apoptosis of some cells. In this study, ATF3 expression and cell apoptosis in GMCs induced by sublytic C5b-9 were measured, and then the effects of ATF3 gene over-expression or knockdown on GMC apoptosis induced by sublytic C5b-9 were examined at a fixed time. The results showed that both ATF3 expression and GMC apoptosis were markedly increased and ATF3 over-expression obviously increased sublytic C5b-9-induced GMC apoptosis, whereas ATF3 gene silencing had a significant opposite effect. Collectively, these findings indicate that upregulation of ATF3 gene expression is involved in regulating GMC apoptosis induced by sublytic C5b-9 complexes.

Interstitial flow induces MMP-1 expression and vascular SMC migration in collagen I gels via an ERK1/2-dependent and c-Jun-mediated mechanism

The migration of vascular smooth muscle cells (SMCs) and fibroblasts into the intima after vascular injury is a central process in vascular lesion formation. The elevation of transmural interstitial flow is also observed after damage to the vascular endothelium. We have previously shown that interstitial flow upregulates matrix metalloproteinase-1 (MMP-1) expression, which in turn promotes SMC and fibroblast migration in collagen I gels. In this study, we investigated further the mechanism of flow-induced MMP-1 expression. An ERK1/2 inhibitor PD-98059 completely abolished interstitial flow-induced SMC migration and MMP-1 expression. Interstitial flow promoted ERK1/2 phosphorylation, whereas PD-98059 abolished flow-induced activation. Silencing ERK1/2 completely abolished MMP-1 expression and SMC migration. In addition, interstitial flow increased the expression of activator protein-1 transcription factors (c-Jun and c-Fos), whereas PD-98059 attenuated flow-induced expression. Knocking down c-jun completely abolished flow-induced MMP-1 expression, whereas silencing c-fos did not affect MMP-1 expression. Taken together, our data indicate that interstitial flow induces MMP-1 expression and SMC migration in collagen I gels via an ERK1/2-dependent and c-Jun-mediated mechanism and suggest that interstitial flow, ERK1/2 MAPK, c-Jun, and MMP-1 may play important roles in SMC migration and neointima formation after vascular injury.

Cell volume decrease as a link between azaspiracid-induced cytotoxicity and c-Jun-N-terminal kinase activation in cultured neurons

Azaspiracids (AZAs) are a group of marine toxins recently described that currently includes 20 members. Not much is known about their mechanism of action, although the predominant analog in nature, AZA-1 targets several organs in vivo, including the central nervous system, and exhibits high neurotoxicity in vitro. AZA distribution is increasing globally with mussels being most widely implicated in AZA-related food poisoning events, with human poisoning by AZAs emerging as an increasing worldwide problem in recent years. We used pharmacological tools to inhibit the cytotoxic effect of the toxin in primary cultured neurons. Several targets for AZA-induced neurotoxicity were evaluated. AZA-1 elicited a concentration-dependent hyperpolarization in cerebellar granule cells of 2-3 days in vitro; however, it did not modify membrane potential in mature neurons. Furthermore, in immature cells, AZA-1 decreased the membrane depolarization evoked by exposure of the neurons to 50mM K(+). Preincubation of the neurons with 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), 4-acetamido-4'-isothiocyanato-2,2'-stilbenedisulfonic acid (SITS), 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), amiloride, or ouabain before addition of AZA-1 decreased the AZA-1-induced neurotoxicity and the increase in phosphorylated c-Jun-N-terminal kinase (JNK) caused by the toxin, indicating that disruption in ion fluxes was involved in the neurotoxic effect of AZA-1. Furthermore, short exposures of cultured neurons to AZA-1 caused a significant decrease in neuronal volume that was reverted by preincubation of the neurons with DIDS or amiloride before addition of the toxin. The results presented here indicate that the JNK activation induced by AZA-1 is secondary to the decrease in cellular volume elicited by the toxin.

Does elevated intraocular pressure reduce retinal TRKB-mediated survival signaling in experimental glaucoma?

Reduced retrograde transport of neurotrophins (NT) and their receptors has been hypothesized to contribute directly to retinal ganglion cell (RGC) loss in glaucoma. However, strategies of supplementing NT and NT receptors have failed to avert ultimate RGC death in experimental glaucoma. This study examines the response of major components of the NT system and their interacting proteins in a rat glaucoma model. Unilateral chronic intraocular pressure (IOP) elevation was produced by episcleral vein injection of hypertonic saline (N = 99). Retinas were collected and grouped by extent of optic nerve injury. Quantitative reverse transcription PCR, western blot analysis and immunohistochemistry were used to determine mRNA and protein levels and protein localization. Out of three RGC-specific Brn3 proteins (Brn3a, b, and c), only Brn3a was significantly downregulated at the message level to 35 +/- 4% of fellow values with the severest nerve injury. With IOP elevation, no significant alterations were found in retinal mRNA levels for BDNF, NGF, NT-4/5 or NT-3. The abundance of mature retinal BDNF protein was not significantly affected by elevated IOP, while proBDNF protein decreased linearly with increasing injury grade (r(2) = 0.50). In retinas with the severest nerve injury, TrkB and TrkC receptor mRNA levels significantly declined to 67 +/- 9% and 44 +/- 5% of fellow values, respectively. However, the levels of TRKB protein and its phosphorylated form were unchanged. Message level for p75(NTR) was linearly upregulated up to 219 +/- 26% with increasing injury (r(2) = 0.46), but no alteration was detected at protein level. The mRNA expression of p75(NTR) apoptosis adaptor proteins NADE, NRIF, and Lingo1 were significantly downregulated in retinas with the greatest nerve injury. A positive correlation was found between injury extent and message levels for Jun (r(2) = 0.23) as well as Junb (r(2) = 0.27), and RGC labeling of activated JUN protein increased. Atf3 mRNA levels demonstrated a positive linear correlation to the extent of injury (r(2) = 0.53), resulting in a nearly five-fold increase (482 +/- 76%) in eyes with the greatest nerve damage. Among downstream pro-survival signaling components, Erk5 mRNA expression was linearly upregulated (r(2) = 0.32) up to 157 +/- 15% of fellow values in retinas with the severest nerve injury (p < 0.01). A slight positive correlation was found between NF-kappaB message levels and injury extent (r(2) = 0.12). Bcl-xl mRNA levels in the most severely injured retinas were significantly reduced to 83 +/- 7% by elevated IOP exposure. Message levels for Erk1/2, Akt1-3 or Bcl2 appeared unaffected. Elevated IOP did not alter mRNA levels of pro-apoptotic Bim, Bax, or p53. This study demonstrates that elevated IOP exposure does not result in a dramatic decrease in retinal levels of either BDNF or its receptor, TrkB. It shows that the responses of NT pathways to elevated IOP are complex, particularly with regard to the role of p75(NTR) and Atf3. A better understanding of the roles of these proteins in IOP-induced injury is likely to suggest informed strategies for neuroprotection in glaucoma.

Opposing roles for ATF2 and c-Fos in c-Jun-mediated neuronal apoptosis

The activator protein 1 (AP-1) transcription factor c-Jun is crucial for neuronal apoptosis. However, c-Jun dimerization partners and the regulation of these proteins in neuronal apoptosis remain unknown. Here we report that c-Jun-mediated neuronal apoptosis requires the concomitant activation of activating transcription factor-2 (ATF2) and downregulation of c-Fos. Furthermore, we have observed that c-Jun predominantly heterodimerizes with ATF2 and that the c-Jun/ATF2 complex promotes apoptosis by triggering ATF activity. Inhibition of c-Jun/ATF2 heterodimerization using dominant negative mutants, small hairpin RNAs, or decoy oligonucleotides was able to rescue neurons from apoptosis, whereas constitutively active ATF2 and c-Jun mutants were found to synergistically stimulate apoptosis. Bimolecular fluorescence complementation analysis confirmed that, in living neurons, c-Fos downregulation facilitates c-Jun/ATF2 heterodimerization. A chromatin immunoprecipitation assay also revealed that c-Fos expression prevents the binding of c-Jun/ATF2 heterodimers to conserved ATF sites. Moreover, the presence of c-Fos is able to suppress the expression of c-Jun/ATF2-mediated target genes and, therefore, apoptosis. Taken together, our findings provide evidence that potassium deprivation-induced neuronal apoptosis is mediated by concurrent upregulation of c-Jun/ATF2 heterodimerization and downregulation of c-Fos expression. This paradigm demonstrates opposing roles for ATF2 and c-Fos in c-Jun-mediated neuronal apoptosis.

JNK signaling in apoptosis

Jun N-terminal kinases or JNKs play a critical role in death receptor-initiated extrinsic as well as mitochondrial intrinsic apoptotic pathways. JNKs activate apoptotic signaling by the upregulation of pro-apoptotic genes through the transactivation of specific transcription factors or by directly modulating the activities of mitochondrial pro- and antiapoptotic proteins through distinct phosphorylation events. This review analyses our present understanding of the role of JNK in apoptotic signaling and the various mechanisms by which JNK promotes apoptosis.

c-Jun expression, activation and function in neural cell death, inflammation and repair

Up-regulation of c-Jun is a common event in the developing, adult as well as in injured nervous system that serves as a model of transcriptional control of brain function. Functional studies employing in vivo strategies using gene deletion, targeted expression of dominant negative isoforms and pharmacological inhibitors all suggest a three pronged role of c-Jun action, exercising control over neural cell death and degeneration, in gliosis and inflammation as well as in plasticity and repair. In vitro, structural and molecular studies reveal several non-overlapping activation cascades via N-terminal c-Jun phosphorylation at serine 63 and 73 (Ser63, Ser73), and threonine 91 and 93 (Thr91, Thr93) residues, the dephosphorylation at Thr239, the p300-mediated lysine acetylation of the near C-terminal region (Lys268, Lys271, Lys 273), as well as the Jun-independent activities of the Jun N-terminal family of serine/threonine kinases, that regulate the different and disparate cellular responses. A better understanding of these non-overlapping roles in vivo could considerably increase the potential of pharmacological agents to improve neurological outcome following trauma, neonatal encephalopathy and stroke, as well as in neurodegenerative disease.