TNFalpha-induced ATF3 expression is bidirectionally regulated by the JNK and ERK pathways in vascular endothelial cells

Arbitrary Ca2+ regulation for endothelial nitric oxide, NFAT and NF-κB activities by an optogenetic approach

Modern western dietary habits and low physical activity cause metabolic abnormalities and abnormally elevated levels of metabolites such as low-density lipoprotein, which can lead to immune cell activation, and inflammatory reactions, and atherosclerosis. Appropriate stimulation of vascular endothelial cells can confer protective responses against inflammatory reactions and atherosclerotic conditions. This study aims to determine whether a designed optogenetic approach is capable of affecting functional changes in vascular endothelial cells and to evaluate its potential for therapeutic regulation of vascular inflammatory responses in vitro. We employed a genetically engineered, blue light-activated Ca²⁺ channel switch molecule that utilizes an endogenous store-operated calcium entry system and induces intracellular Ca²⁺ influx through blue light irradiation and observed an increase in intracellular Ca²⁺ in vascular endothelial cells. Ca²⁺-dependent activation of the nuclear factor of activated T cells and nitric oxide production were also detected. Microarray analysis of Ca²⁺-induced changes in vascular endothelial cells explored several genes involved in cellular contractility and inflammatory responses. Indeed, there was an increase in the gene expression of molecules related to anti-inflammatory and vasorelaxant effects. Thus, a combination of human blue light-activated Ca²⁺ channel switch 2 (hBACCS2) and blue light possibly attenuates TNFα-induced inflammatory NF-κB activity. We propose that extrinsic cellular Ca²⁺ regulation could be a novel approach against vascular inflammation.

Emerging roles of activating transcription factor (ATF) family members in tumourigenesis and immunity: Implications in cancer immunotherapy

Activating transcription factors, ATFs, are a group of bZIP transcription factors that act as homodimers or heterodimers with a range of other bZIP factors. In general, ATFs respond to extracellular signals, indicating their important roles in maintaining homeostasis. The ATF family includes ATF1, ATF2, ATF3, ATF4, ATF5, ATF6, and ATF7. Consistent with the diversity of cellular processes reported to be regulated by ATFs, the functions of ATFs are also diverse. ATFs play an important role in cell proliferation, apoptosis, differentiation and inflammation-related pathological processes. The expression and phosphorylation status of ATFs are also related to neurodegenerative diseases and polycystic kidney disease. Various miRNAs target ATFs to regulate cancer proliferation, apoptosis, autophagy, sensitivity and resistance to radiotherapy and chemotherapy. Moreover, ATFs are necessary to maintain cell redox homeostasis. Therefore, deepening our understanding of the regulation and function of ATFs will provide insights into the basic regulatory mechanisms that influence how cells integrate extracellular and intracellular signals into genomic responses through transcription factors. Under pathological conditions, especially in cancer biology and response to treatment, the characterization of ATF dysfunction is important for understanding how to therapeutically utilize ATF2 or other pathways controlled by transcription factors. In this review, we will demonstrate how ATF1, ATF2, ATF3, ATF4, ATF5, ATF6, and ATF7 function in promoting or suppressing cancer development and identify their roles in tumour immunotherapy.

Strategies for Improving Photodynamic Therapy Through Pharmacological Modulation of the Immediate Early Stress Response

Photodynamic therapy (PDT) is a minimally to noninvasive treatment modality that has emerged as a promising alternative to conventional cancer treatments. PDT induces hyperoxidative stress and disrupts cellular homeostasis in photosensitized cancer cells, resulting in cell death and ultimately removal of the tumor. However, various survival pathways can be activated in sublethally afflicted cancer cells following PDT. The acute stress response is one of the known survival pathways in PDT, which is activated by reactive oxygen species and signals via ASK-1 (directly) or via TNFR (indirectly). The acute stress response can activate various other survival pathways that may entail antioxidant, pro-inflammatory, angiogenic, and proteotoxic stress responses that culminate in the cancer cell's ability to cope with redox stress and oxidative damage. This review provides an overview of the immediate early stress response in the context of PDT, mechanisms of activation by PDT, and molecular intervention strategies aimed at inhibiting survival signaling and improving PDT outcome.

Ferroptosis Promotes Cyst Growth in Autosomal Dominant Polycystic Kidney Disease Mouse Models

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD), the most common inherited kidney disease, is regulated by different forms of cell death, including apoptosis and autophagy. However, the role in ADPKD of ferroptosis, a recently discovered form of cell death mediated by iron and lipid metabolism, remains elusive.

METHODS

To determine a pathophysiologic role of ferroptosis in ADPKD, we investigated whether the absence of Pkd1 (encoding polycystin-1) affected the expression of key factors involved in the process of ferroptosis, using Western blot and qRT-PCR analysis in Pkd1 mutant renal cells and tissues. We also examined whether treatment with erastin, a ferroptosis inducer, and ferrostain-1, a ferroptosis inhibitor, affected cyst growth in Pkd1 mutant mouse models.

RESULTS

We found that kidney cells and tissues lacking Pkd1 exhibit extensive metabolic abnormalities, including reduced expression of the system Xc- amino acid antiporter (critical for import of cystine), of iron exporter (ferroportin), and of GPX4 (a key and negative regulator of ferroptosis). The abnormalities also include increased expression of iron importers (TfR1, DMT1) and HO-1, which in turn result in high iron levels, low GSH and GPX4 activity, increased lipid peroxidation, and propensity to ferroptosis. We further found that erastin increased, and ferrostatin-1 inhibited ferroptotic cell death and proliferation of Pkd1-deficient cells in kidneys from Pkd1 mutant mice. A lipid peroxidation product increased in Pkd1-deficient cells, 4HNE, promoted the proliferation of survived Pkd1 mutant cells via activation of Akt, S6, Stat3, and Rb during the ferroptotic process, contributing to cyst growth.

CONCLUSION

These findings indicate that ferroptosis contributes to ADPKD progression and management of ferroptosis may be a novel strategy for ADPKD treatment.

Late gestational testosterone exposure causes glucose deregulation and elevated cardiac VCAM-1 and DPP-4 activity in rats

CONTEXT

Increased vascular cell adhesion molecule-1 (VCAM-1) has been reported to be a critical link between obesity and atherosclerotic cardiovascular diseases while dipeptidyl peptidase-4 (DPP-4) has been implicated in the development of disrupted glucose regulation and inflammation.

OBJECTIVE

This study aimed to investigate the effect of gestational testosterone exposure on glucose metabolism, atherogenic dyslipidemia, as well as circulating and cardiac VCAM-1, oxidative stress biomarkers and DPP-4 activity in pregnant rats.

METHODS

Pregnant Wistar rats received either vehicle or testosterone (0.5 mg/kg; sc) between gestational days 14 and 19.

RESULTS

Gestational testosterone exposure caused impaired glucose homeostasis that was accompanied with atherogenic dyslipidemia, elevated circulating and cardiac levels of VCAM-1, uric acid, malondialdehyde as well as increased DPP-4 activity. However, nitric oxide levels were decreased.

CONCLUSION

This study shows that gestational testosterone exposure causes glucose deregulation and atherogenic dyslipidemia that is accompanied by increased circulating and cardiac VCAM-1 and DPP-4 activity.

ATF3 induces RAB7 to govern autodegradation in paligenosis, a conserved cell plasticity program

Differentiated cells across multiple species and organs can re-enter the cell cycle to aid in injury-induced tissue regeneration by a cellular program called paligenosis. Here, we show that activating transcription factor 3 (ATF3) is induced early during paligenosis in multiple cellular contexts, transcriptionally activating the lysosomal trafficking gene Rab7b. ATF3 and RAB7B are upregulated in gastric and pancreatic digestive-enzyme-secreting cells at the onset of paligenosis Stage 1, when cells massively induce autophagic and lysosomal machinery to dismantle differentiated cell morphological features. Their expression later ebbs before cells enter mitosis during Stage 3. Atf3-/- mice fail to induce RAB7-positive autophagic and lysosomal vesicles, eventually causing increased death of cells en route to Stage 3. Finally, we observe that ATF3 is expressed in human gastric metaplasia and during paligenotic injury across multiple other organs and species. Thus, our findings indicate ATF3 is an evolutionarily conserved gene orchestrating the early paligenotic autodegradative events that must occur before cells are poised to proliferate and contribute to tissue repair.

Gene Expression Analysis of the Activating Factor 3/Nuclear Protein 1 Axis in a Non-alcoholic Steatohepatitis Mouse Model

Background

Nonalcoholic fatty liver disease/steatohepatitis (NAFLD/NASH) is a chronic liver disease related to metabolic syndrome that can progress to liver cirrhosis. The involvement of the endoplasmic reticulum (ER) stress response in NAFLD progression and the roles played by activating factor 3 (ATF3) and the downstream nuclear protein 1 (NUPR1) are poorly understood. The aim of this study was to determine the gene expression profiles around the ATF3/NUPR1 axis in relation to the development of NAFLD using novel mouse models.

Methods

Fatty liver Shionogi (FLS) mice (n = 12) as a NAFLD model and FLS-ob/ob mice (n = 28) as a NASH model were fed a standard diet. The FLS mice were sacrificed at 24 weeks of age as a control, whereas the FLS-ob/ob mice were sacrificed at 24, 36, and 48 weeks of age. Hepatic steatosis, inflammation, and fibrosis were evaluated by biochemical, histological, and gene expression analyses. The expression levels of the ER-stress related genes Jun proto-oncogene (C-jun), Atf3, Nupr1, and C/EBP homologous protein (Chop) were measured in liver tissue. Apoptosis was evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining.

Results

Control mice demonstrated hepatic steatosis alone without apparent fibrosis. On the other hand, FLS-ob/ob mice showed severe steatohepatitis at both 24 and 36 weeks of age and severe fibrosis at both 36 and 48 weeks of age. The expression levels of Atf3, Nupr-1, and C-jun significantly increased from 24 to 48 weeks of age in FLS-ob/ob mice compared with control mice. The expression level of Chop was already high in FLS mice and maintained similar levels in FLS-ob/ob mice; the expression level was consistent with the percentage of TUNEL-positive cells.

Conclusion

The ATF3/NUPR1 axis plays a pivotal role in NASH progression in association with C-jun and Chop and appears to induce apoptosis from early steatosis in the NASH model mice.

Role of activating transcription factor 3 and its interacting proteins under physiological and pathological conditions

Activating transcription factor 3 (ATF3) is a stress-responsive factor that belongs to the activator protein 1 (AP-1) family of transcription factors. ATF3 expression is stimulated by various factors such as hypoxia, cytokines, and chemotherapeutic and DNA damaging agents. Upon stimulation, ATF3 can form homodimers or heterodimers with other members of the AP-1 family to repress or activate transcription. Under physiological conditions, ATF3 expression is transient and plays a pivotal role in controlling the expression of cell-cycle regulators and tumor suppressor, DNA repair, and apoptosis genes. However, under pathological conditions such as those during breast cancer, a sustained and prolonged expression of ATF3 has been observed. In this review, the structure and function of ATF3, its posttranslational modifications (PTM), and its interacting proteins are discussed with a special emphasis on breast cancer metastasis.

Activating transcription factor 3 in cardiovascular diseases: a potential therapeutic target

Cardiovascular diseases (CVDs) are the primary causes of death worldwide. Among the numerous signaling molecules involved in CVDs, transcriptional factors directly influence gene expression and play a critical role in regulating cell function and the development of diseases. Activating transcription factor (ATF) 3 is an adaptive-response gene in the ATF/cAMP responsive element-binding (CREB) protein family of transcription factors that acts as either a repressor or an activator of transcription via the formation of homodimers or heterodimers with other ATF/CREB members. A appropriate ATF3 expression is important for the normal physiology of cells, and dysfunction of ATF3 is associated with various pathophysiological responses such as inflammation, apoptosis, oxidative stress and endoplasmic reticulum stress, and diseases, including CVDs. This review focuses on the role of ATF3 in cardiac hypertrophy, heart failure, atherosclerosis, ischemic heart diseases, hypertension and diabetes mellitus to provide a novel therapeutic target for CVDs.

Temporal regulation of extracellular signal-regulated kinase 1/2 phosphorylation, heat shock protein 70 and activating transcription factor 3 during prostaglandin F-induced luteal regression in pseudopregnant rats following heat stress

The aim of the present study was to investigate the effects of heat stress on heat shock protein (HSP) 70 expression and mitogen-activated protein kinase (MAPK) and protein kinase (PK) B signalling during prostaglandin F (PGF)-induced luteal regression. During pseudopregnancy, rats were exposed to heat stress (HS, 40°C, 2h) for 7 days and treated with PGF or physiological saline on Day 7; serum and ovaries were collected 0, 1, 2, 8 or 24h after PGF treatment. The early inhibitory effect of PGF on progesterone was reduced in HS rats. HSP70 expression in response to PGF was significantly enhanced in HS rats. PGF-induced phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 was significantly greater in the HS group; however, HS rats exhibited elevated basal levels of phosphorylation of p38 MAPK, but not ERK1/2. PGF treatment increased expression of activating transcription factor (ATF) 3 at 2h, which was inhibited by heat stress. Evaluating PKB signalling revealed that phosphorylation of p-Akt (Thr³⁰⁸ and Ser⁴⁷³) was reduced at 8 and 24h after PGF treatment in both non-heat stress (NHS) and HS groups, but there were no significant differences between the HS and NHS groups at any of the time points. In conclusion, the present study provides further evidence that heat stress may enhance HSP70 and affect ERK1/2 and ATF3 expression, but not Akt activation, during PGF-induced luteal regression in pseudopregnant rats.

The stress response gene ATF3 is a direct target of the Wnt/β-catenin pathway and inhibits the invasion and migration of HCT116 human colorectal cancer cells

Aberrant Wnt/β-catenin signaling is implicated in tumorigenesis and the progression of human colorectal cancers, and mutations in the components of the Wnt/β-catenin signaling pathway are observed in the majority of patients. Therefore, extensive studies on the Wnt signaling pathway and its target genes are crucial to understand the molecular events of tumorigenesis and develop an efficacious therapy. In this study, we showed that the stress response gene ATF3 is transcriptionally activated by the binding of β-catenin and TCF4 to the redundant TCF4 site at the proximal promoter region of the ATF3 gene, indicating that ATF3 is a direct target of the Wnt/β-catenin pathway. The loss of function or overexpression studies showed that ATF3 inhibited the migration or invasion of HCT116 cells. The expression of some MMP and TIMP genes and the ratio of MMP2/9 to TIMP3/4 mRNAs was differentially regulated by ATF3. Therefore, though ATF3 is activated downstream of the Wnt/β-catenin pathway, it acts as a negative regulator of the migration and invasion of HCT116 human colon cancer cells exhibiting aberrant Wnt/β-catenin activity. ATF3 is a candidate biomarker and target for human colorectal cancer treatment and prevention.

Anti-hypoglycemic and hepatocyte-protective effects of hyperoside from Zanthoxylum bungeanum leaves in mice with high-carbohydrate/high-fat diet and alloxan-induced diabetes

The development of diabetes mellitus (DM) is accompanied by hyperglycemia-induced oxidative stress. Hyperoside is a major bioactive component in Zanthoxylum bungeanum leaves (HZL) and is a natural antioxidant. However, the effects of HZL on DM and its mechanisms of action remain undefined. The present study evaluated the anti-hypoglycemic and hepatocyte-protective effects of HZL in mice with diabetes induced by a high-carbohydrate/high-fat diet (HFD) and alloxan. We also aimed to eludicate the underlying mechanisms. Our resutls demonstrated that the administration of HZL significantly reduced body weight gain, serum glucose levels and insulin levels in diabetic mice compared with the vehicle-treated mice. In addition, the levels of dyslipidemia markers including total cholesterol, triglyceride and low-density lipoprotein cholesterol in the HFD-treated mice were markedly decreased. Further experiments using hepatocytes from mice revealed that HZL significantly attenuated liver injury associated with DM compared with vehicle treatment, as evidenced by lower levels of alanine aminotransferase and aspartate aminotransferase in serum and by lower levels of lipid peroxidation, nitric oxide content and inducible nitric oxide synthase activity in liver tissues. Nuclear factor-κB (NF-κB) and mitogen-associated protein kinase (MAPK) signaling pathways were investigated to elucidate the molecular mechanisms responsible for the protective effects of HZL against diabetic liver injury. The results indicated that HZL inhibited the phosphorylation of p65/NF-κB, MAPK (including p38, JNK and ERK1/2) and activating transcription factor 3 protein expression, with an additional suppression of Bax, cytochrome c, caspase-9 and caspase-3 in the liver tissues of diabetic mice. Taken together, our findings suggest that HZL, which was effective in inhibiting oxidative stress-related pathways may be beneficial for use in the treatment of DM.

Triglyceride-rich lipoprotein lipolysis products increase blood-brain barrier transfer coefficient and induce astrocyte lipid droplets and cell stress

Elevation of blood triglycerides, primarily as triglyceride-rich lipoproteins (TGRL), has been linked to cerebrovascular inflammation, vascular dementia, and Alzheimer's disease (AD). Brain microvascular endothelial cells and astrocytes, two cell components of the neurovascular unit, participate in controlling blood-brain barrier (BBB) permeability and regulating neurovascular unit homeostasis. Our studies showed that infusion of high physiological concentrations of TGRL lipolysis products (TGRL + lipoprotein lipase) activate and injure brain endothelial cells and transiently increase the BBB transfer coefficient (K_i = permeability × surface area/volume) in vivo. However, little is known about how blood lipids affect astrocyte lipid accumulation and inflammation. To address this, we first demonstrated TGRL lipolysis products increased lipid droplet formation in cultured normal human astrocytes. We then evaluated the transcriptional pathways activated in astrocytes by TGRL lipolysis products and found upregulated stress and inflammatory-related genes including activating transcription factor 3 (ATF3), macrophage inflammatory protein-3α (MIP-3α), growth differentiation factor-15 (GDF15), and prostaglandin-endoperoxide synthase 2 (COX2). TGRL lipolysis products also activated the JNK/cJUN/ATF3 pathway, induced endoplasmic reticulum stress protein C/EBP homologous protein (CHOP), and the NF-κB pathway, while increasing secretion of MIP-3α, GDF15, and IL-8. Thus our results demonstrate TGRL lipolysis products increase the BBB transfer coefficient (K_i), induce astrocyte lipid droplet formation, activate cell stress pathways, and induce secretion of inflammatory cytokines. Our observations are consistent with evidence for lipid-induced neurovascular injury and inflammation, and we, therefore, speculate that lipid-induced astrocyte injury could play a role in cognitive decline.

Paternal smoking and germ cell death: A mechanistic link to the effects of cigarette smoke on spermatogenesis and possible long-term sequelae in offspring

Paternal exposure to constituents of cigarette smoke (CS) is reportedly associated with infertility, birth defects and childhood cancers even though the mechanism behind this relationship is still unclear. Chronic cigarette smoking by men leads to poor sperm quality and quantity mainly through oxidative stress and also direct assault by CS metabolites. Among several carcinogenic and teratogenic components of cigarette smoke condensate (CSC), polycyclic aromatic hydrocarbons (PAHs) display a preeminent role in accelerating germ cell death via the cytoplasmic transcription factor, aryl hydrocarbon receptor (AHR) that is present across all stages of spermatogenesis. Activation of AHR by growth factors though benefits normal cellular functions, its mediation by CSC in a spermatocyte cell line [Gc2(spd)ts] adversely affects the expression of a battery of genes associated with antioxidant mechanisms, cell proliferation and apoptosis, and cell cycle progress. Besides, the CSC-mediated cross talk either between AHR and NRF2 or AHR-NRF2 and MAPKs pathways inhibits normal proliferation of the spermatogenic GC-2spd(ts) cells in vitro and cell death of spermatocytes in vivo. Pharmacological inactivation of CSC-induced AHR but not its genetic manipulation seems preventing DNA and cell membrane damage in Gc2(spd)ts. Data from recent reports suggest that the cigarette smoke affects both the genomic and epigenomic components of the sperm and attributes any associated changes to developmental defects in the offspring. Thus, the studies discussed here in this review shed light on possible mechanistic factors that could probably be responsible for the paternally mediated birth defects in the offspring following exposure to the toxic constituents of cigarette smoke.

Lipotoxic brain microvascular injury is mediated by activating transcription factor 3-dependent inflammatory and oxidative stress pathways

Dysfunction of the cerebrovasculature plays an important role in vascular cognitive impairment (VCI). Lipotoxic injury of the systemic endothelium in response to hydrolyzed triglyceride-rich lipoproteins (TGRLs; TGRL lipolysis products) or a high-fat Western diet (WD) suggests similar mechanisms may be present in brain microvascular endothelium. We investigated the hypothesis that TGRL lipolysis products cause lipotoxic injury to brain microvascular endothelium by generating increased mitochondrial superoxide radical generation, upregulation of activating transcription factor 3 (ATF3)-dependent inflammatory pathways, and activation of cellular oxidative stress and apoptotic pathways. Human brain microvascular endothelial cells were treated with human TGRL lipolysis products that induced intracellular lipid droplet formation, mitochondrial superoxide generation, ATF3-dependent transcription of proinflammatory, stress response, and oxidative stress genes, as well as activation of proapoptotic cascades. Male apoE knockout mice were fed a high-fat/high-cholesterol WD for 2 months, and brain microvessels were isolated by laser capture microdissection. ATF3 gene transcription was elevated 8-fold in the hippocampus and cerebellar brain region of the WD-fed animals compared with chow-fed control animals. The microvascular injury phenotypes observed in vitro and in vivo were similar. ATF3 plays an important role in mediating brain microvascular responses to acute and chronic lipotoxic injury and may be an important preventative and therapeutic target for endothelial dysfunction in VCI.

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.

Prostaglandin F2α induces expression of activating transcription factor 3 (ATF3) and activates MAPK signaling in the rat corpus luteum

The current study was conducted to evaluate the expression of ATF3, in association with the activation of mitogen-activated protein kinases (MAPK) during prostaglandin F2α analog (PGF)-induced luteal regression in rats. A sequential PMSG/hCG treatment paradigm was used to obtain a single, well-defined generation of corpora lutea (CL) in rats. Rats were treated with PGF for 0-4h on day 7 of pseudopregnancy. Results showed that serum progesterone (P4) concentrations declined in a time dependent manner. Western blot results revealed that ATF3 increased within 2h post-PGF injection. Phosphorylated ERK1/2 (p-ERK) and JNK (p-JNK) increased within 30min and then were gradually reduced in response to PGF. In contrast, the levels of phosphorylated p38 MAPK (p-p38) were not significantly altered. The immunostaining density for p-ERK decreased from the periphery to the center of the corpus luteum following treatment with PGF, while ATF3 was expressed uniformly in the nuclei of luteal steroidogenic cells. These results indicated that treatment with PGF in vivo could induce increases in MAPK phosphorylation, especially in p-ERK, which might be correlated with the increases in ATF3 expression and the decline in P4 concentrations. To our knowledge, this is the first study to provide evidence for temporal relationships between MAPK activation and ATF3 expression during PGF-induced luteal regression in the rat.

TRPM7 regulates vascular endothelial cell adhesion and tube formation

Transient receptor potential melastatin 7 (TRPM7) is a nonselective cation channel with an α-kinase domain in its COOH terminal, known to play a role in diverse physiological and pathological processes such as Mg2+ homeostasis, cell proliferation, and hypoxic neuronal injury. Increasing evidence suggests that TRPM7 contributes to the physiology/pathology of vascular systems. For example, we recently demonstrated that silencing TRPM7 promotes growth and proliferation and protects against hyperglycemia-induced injury in human umbilical vein endothelial cells (HUVECs). Here we investigated the potential effects of TRPM7 on morphology, adhesion, migration, and tube formation of vascular endothelial cells and the potential underlying mechanism. We showed that inhibition of TRPM7 function in HUVECs by silencing TRPM7 decreases the density of TRPM7-like current and cell surface area and inhibits cell adhesion to Matrigel. Silencing TRPM7 also promotes cell migration, wound healing, and tube formation. Further studies showed that the extracellular signal-regulated kinase (ERK) pathway is involved in the change of cell morphology and the increase in HUVEC migration induced by TRPM7 silencing. We also demonstrated that silencing TRPM7 enhances the phosphorylation of myosin light chain (MLC) in HUVECs, which might be involved in the enhancement of cell contractility and motility. Collectively, our data suggest that the TRPM7 channel negatively regulates the function of vascular endothelial cells. Further studies on the underlying mechanism may facilitate the development of the TRPM7 channel as a target for the therapeutic intervention of vascular diseases.

Extracellular signal-regulated kinase-5: Novel mediator of insulin and tumor necrosis factor α-stimulated vascular cell adhesion molecule-1 expression in vascular cells

BACKGROUND

Atherosclerosis may be stimulated by the increased presence of insulin and tumor necrosis-factor-α (TNFα) with subsequent expression of vascular cell adhesion molecule-1 (VCAM-1). We hypothesized that extracellular signal-regulated kinase-5 (ERK5) plays an important role in insulin and TNFα-stimulated total and cell surface VCAM-1 expression.

METHODS

Rat aorta vascular endothelial cells were first transfected with either no inhibitory RNA, inactive (scrambled) inhibitory ERK5 RNA (scERK5) or active inhibitory ERK5 RNA (siERK5) and then treated with either (i) no analog; (ii) insulin (1 nM), or TNFα (1 ng/mL) alone, or (iii) insulin plus TNFα for 6 h. Thereafter either total VCAM-1 protein or surface VCAM-1 protein was determined.

RESULTS

Genetic inhibition of ERK5 decreased TNFα-stimulated total VCAM-1 expression by 57% and surface expression by 27%. In contrast, genetic inhibition of ERK5 did not significantly decrease insulin-stimulated total or surface VCAM-1 expression. Interestingly, genetic inhibition of ERK5 did not significantly decrease insulin plus TNFα-stimulated total VCAM-1 expression, but significantly (P < 0.05) decreased insulin plus TNFα-stimulated surface VCAM-1 expression 41%.

CONCLUSIONS

We report here that ERK5 plays a minor role in insulin-stimulation of VCAM-1, but plays a significant role in TNFα-stimulation of both total and cell surface VCAM-1 protein expression. Taken together, these results demonstrate that not only does ERK5 have differential mediation of insulin and TNFα-stimulated VCAM-1 expression, but also has differential regulation of insulin plus TNFα-stimulated total and surface VCAM-1 expression, suggesting that other intermediates of the insulin and TNFα intracellular pathways are contributing to atherogenesis.

Characterization of the regulatory mechanisms of activating transcription factor 3 by hypertrophic stimuli in rat cardiomyocytes

Aims

Activating transcription factor 3 (ATF3) is a stress-activated immediate early gene suggested to have both detrimental and cardioprotective role in the heart. Here we studied the mechanisms of ATF3 activation by hypertrophic stimuli and ATF3 downstream targets in rat cardiomyocytes.

Methods and Results

When neonatal rat cardiomyocytes were exposed to endothelin-1 (ET-1, 100 nM) and mechanical stretching in vitro, maximal increase in ATF3 expression occurred at 1 hour. Inhibition of extracellular signal-regulated kinase (ERK) by PD98059 decreased ET-1– and stretch–induced increase of ATF3 protein but not ATF3 mRNA levels, whereas protein kinase A (PKA) inhibitor H89 attenuated both ATF3 mRNA transcription and protein expression in response to ET-1 and stretch. To characterize further the regulatory mechanisms upstream of ATF3, p38 mitogen-activated protein kinase (MAPK) signaling was investigated using a gain-of-function approach. Adenoviral overexpression of p38α, but not p38β, increased ATF3 mRNA and protein levels as well as DNA binding activity. To investigate the role of ATF3 in hypertrophic process, we overexpressed ATF3 by adenovirus-mediated gene transfer. In vitro, ATF3 gene delivery attenuated the mRNA transcription of interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1), and enhanced nuclear factor-κB (NF-κB) and Nkx-2.5 DNA binding activities. Reduced PAI-1 expression was also detected in vivo in adult rat heart by direct intramyocardial adenovirus-mediated ATF3 gene delivery.

Conclusions

These data demonstrate that ATF3 activation by ET-1 and mechanical stretch is partly mediated through ERK and cAMP-PKA pathways, whereas p38 MAPK pathway is involved in ATF3 activation exclusively through p38α isoform. ATF3 activation caused induction of modulators of the inflammatory response NF-κB and Nkx-2.5, as well as attenuation of pro-fibrotic and pro-inflammatory proteins IL-6 and PAI-1, suggesting cardioprotective role for ATF3 in the heart.

A systems biology analysis of brain microvascular endothelial cell lipotoxicity

Background

Neurovascular inflammation is associated with a number of neurological diseases including vascular dementia and Alzheimer’s disease, which are increasingly important causes of morbidity and mortality around the world. Lipotoxicity is a metabolic disorder that results from accumulation of lipids, particularly fatty acids, in non-adipose tissue leading to cellular dysfunction, lipid droplet formation, and cell death.

Results

Our studies indicate for the first time that the neurovascular circulation also can manifest lipotoxicity, which could have major effects on cognitive function. The penetration of integrative systems biology approaches is limited in this area of research, which reduces our capacity to gain an objective insight into the signal transduction and regulation dynamics at a systems level. To address this question, we treated human microvascular endothelial cells with triglyceride-rich lipoprotein (TGRL) lipolysis products and then we used genome-wide transcriptional profiling to obtain transcript abundances over four conditions. We then identified regulatory genes and their targets that have been differentially expressed through analysis of the datasets with various statistical methods. We created a functional gene network by exploiting co-expression observations through a guilt-by-association assumption. Concomitantly, we used various network inference algorithms to identify putative regulatory interactions and we integrated all predictions to construct a consensus gene regulatory network that is TGRL lipolysis product specific.

Conclusion

System biology analysis has led to the validation of putative lipid-related targets and the discovery of several genes that may be implicated in lipotoxic-related brain microvascular endothelial cell responses. Here, we report that activating transcription factors 3 (ATF3) is a principal regulator of TGRL lipolysis products-induced gene expression in human brain microvascular endothelial cell.

Role of TRPM7 channels in hyperglycemia-mediated injury of vascular endothelial cells

This study investigated the change of transient receptor potential melastatin 7 (TRPM7) expression by high glucose and its role in hyperglycemia induced injury of vascular endothelial cells. Human umbilical vein endothelial cells (HUVECs) were incubated in the presence or absence of high concentrations of D-glucose (HG) for 72h. RT-PCR, Real-time PCR, Western blotting, Immunofluorescence staining and whole-cell patch-clamp recordings showed that TRPM7 mRNA, TRPM7 protein expression and TRPM7-like currents were increased in HUVECs following exposure to HG. In contrast to D-glucose, exposure of HUVECs to high concentrations of L-glucose had no effect. HG increased reactive oxygen species (ROS) generation, cytotoxicity and decreased endothelial nitric oxide synthase protein expression, which could be attenuated by knockdown of TRPM7 with TRPM7 siRNA. The protective effect of silencing TRPM7 against HG induced endothelial injury was abolished by U0126, an inhibitor of the extracellular signal-regulated kinase signaling pathway. These observations suggest that TRPM7 channels play an important role in hyperglycemia-induced injury of vascular endothelial cells.

ERK pathway is activated in bare-FeNPs-induced autophagy

Iron oxide nanoparticles (FeNPs) are known to be one of the most biocompatible and safe nanoparticles. However, their long-term persistence remains a problem, and macrophages play as an important mediator in continuous stimulation of the immune system due to biopersistence of nanoparticles. In the present study, we identified the mechanisms underlying the uptake and toxicity of bare-FeNPs using RAW264.7 cells, a mouse peritoneal macrophage cell line. The bare-FeNPs penetrated the cell membrane through electrostatic interactions together with the general phagocytic pathway. At 24 h after exposure, they distributed freely in the cytosol or within autophagosome-like vacuoles. Bare-FeNPs induced decrease in the cell viability along with the cell cycle arrest in G1 phase. In addition, they increased the generation of ROS and the secretion of NO and TNF alpha as well as the expression of SOD-1 and SOD-2 proteins, which are an antioxidant. While the mitochondrial calcium level, the intensity of labeled mitochondria, and ATP production decreased, the levels of autophagy-related proteins such as p62, beclin 1, ATG5, and LC3B increased in a dose-dependent manner together with the levels of ATF 3, p-EGFR, and p-ERK proteins. However, the level of p-JNK protein clearly decreased. TEM images also showed that damaged organelle exist within autophagosome-like vacuoles with bare-FeNPs. On the basis of these results, we suggest that bare-FeNPs induce autophagy by initiating oxidative stress in RAW264.7 cells. Furthermore, ERK, but not JNK, pathway is activated in bare-FeNPs-induced autophagy.

Systemic administration of an alpha-7 nicotinic acetylcholine agonist reverses neuropathic pain in male Sprague Dawley rats

Alpha-7 nicotinic acetylcholine receptor (α7 nAChR) agonists attenuate pain and inflammation in preclinical models. This study tested whether systemic delivery of an α7 nAChR agonist attenuates neuropathic pain and associated immune-mediated pro-inflammation. Hind paw response thresholds to mechanical stimuli in male Sprague Dawley rats were assessed before and after sciatic chronic constriction injury (CCI) or sham surgery. Osmotic mini-pumps containing TC-7020, an α7 nAChR selective agonist, were implanted 10 to 14 days after surgery. TC-7020 (1, 3, and 10 mg/kg/d; s.c.) significantly attenuated CCI-induced allodynia, which lasted through 2 weeks of test compound administration. Spinal cords were collected after 2 weeks and processed for microglial and astrocyte activation markers within the ipsilateral L4-L6 dorsal horn. In addition, ipsilateral L4-5 dorsal root ganglia (DRGs) were processed for neuronal injury and satellite cell activation markers. CCI-induced central glial cell activation markers were not suppressed by TC-7020, even though TC-7020 is mildly blood-brain barrier permeable. However, TC-7020 downregulated the integrated density of activation transcription factor 3 (ATF3) but not the number of ATF positive cells. TC-7020 also downregulated phosphorylated extracellular signal kinase (p-ERK) and satellite cell activation in the CCI-affected DRGs. Therefore, systemic α7 nAChR agonist may be effective in treating neuropathic pain via reducing neuronal injury and immune cells activation occurring in the periphery.

PERSPECTIVE

These studies demonstrated that TC-7020, an alpha7 nicotinic acetylcholine receptor agonist with partial blood-brain barrier permeability, reversed neuropathic pain in rats, likely via attenuation of inflammation in the DRG and/or the site of sciatic injury.

Development of a new in vitro skin sensitization assay (Epidermal Sensitization Assay; EpiSensA) using reconstructed human epidermis

Recent changes in regulatory requirements and social views on animal testing have accelerated the development of reliable alternative tests for predicting skin sensitizing potential of chemicals. In this study, we aimed to develop a new in vitro skin sensitization assay using reconstructed human epidermis, RhE model, which is expected to have broader applicability domain rather than existing in vitro assays. Microarray analysis revealed that the expression of five genes (ATF3, DNAJB4, GCLM, HSPA6 and HSPH1) related to cellular stress response were significantly up-regulated in RhE model after 6h treatment with representative skin sensitizers, 1-fluoro-2,4-dinitrobenzene and oxazolone, but not a non-sensitizer, benzalkonium chloride. The predictive performance of five genes was examined with eight skin sensitizers (e.g., cinnamic aldehyde), four non-sensitizers (e.g., sodium lauryl sulfate) and four pre-/pro-haptens (e.g., p-phenylenediamine, isoeugenol). When the positive criteria were set to obtain the highest accuracy with the animal testing (LLNA), ATF3, DNAJB4 and GCLM exhibited a high predictive accuracy (100%, 93.8% and 87.5%, respectively). All tested pre-/pro-haptens were correctly predicted by both ATF3 and DNAJB4. These results suggested that the RhE-based assay, termed epidermal sensitization assay (EpiSensA), could be an useful skin sensitization assay with a broad applicability domain including pre-/pro-haptens.

Signalling mechanisms involved in renal pathological changes during cisplatin-induced nephropathy

CONTEXT

Cisplatin, a coordination platinum complex, is used as a potential anti-neoplastic agent, having well recognized DNA-damaging property that triggers cell-cycle arrest and cell death in cancer therapy. Beneficial chemotherapeutic actions of cisplatin can be detrimental for kidneys.

BACKGROUND

Unbound cisplatin gets accumulated in renal tubular cells, leading to cell injury and death. This liable action of cisplatin on kidneys is mediated by altered intracellular signalling pathways such as mitogen-activated protein kinase (MAPK), extracellular regulated kinase (ERK), or C- Jun N terminal kinase/stress-activated protein kinase (JNK/SAPK). Further, these signalling alterations are responsible for release and activation of tumour necrosis factor (TNF-α), mitochondrial dysfunction, and apoptosis, which ultimately cause the renal pathogenic process. Cisplatin itself enhances the generation of reactive oxygen species (ROS) and activation of nuclear factor-κB (NF-κB), inflammation, and mitochondrial dysfunction, which further leads to renal apoptosis. Cisplatin-induced nephropathy is also mediated through the p53 and protein kinase-Cδ (PKCδ) signalling pathways.

OBJECTIVE

This review explores these signalling alterations and their possible role in the pathogenesis of cisplatin-induced renal injury.

Induction of ATF3 gene network by triglyceride-rich lipoprotein lipolysis products increases vascular apoptosis and inflammation

OBJECTIVE

Elevation of triglyceride-rich lipoproteins (TGRLs) contributes to the risk of atherosclerotic cardiovascular disease. Our work has shown that TGRL lipolysis products in high physiological to pathophysiological concentrations cause endothelial cell injury; however, the mechanisms remain to be delineated.

APPROACH AND RESULTS

We analyzed the transcriptional signaling networks in arterial endothelial cells exposed to TGRL lipolysis products. When human aortic endothelial cells in culture were exposed to TGRL lipolysis products, activating transcription factor 3 (ATF3) was identified as a principal response gene. Induction of ATF3 mRNA and protein was confirmed by quantitative reverse-transcription polymerase chain reaction and Western blot respectively. Immunofluorescence analysis showed that ATF3 accumulated in the nuclei of cells treated with lipolysis products. Nuclear expression of phosphorylated c-Jun N-terminal kinase (JNK), previously shown to be an initiator of the ATF3 signaling cascade, also was demonstrated. Small interfering RNA (siRNA)-mediated inhibition of ATF3 blocked lipolysis products-induced transcription of E-selectin and interleukin-8, but not interleukin-6 or nuclear factor-κB. c-Jun, a downstream protein in the JNK pathway, was phosphorylated, whereas expression of nuclear factor-κB-dependent JunB was downregulated. Additionally, JNK siRNA suppressed ATF3 and p-c-Jun protein expression, suggesting that JNK is upstream of the ATF3 signaling pathway. In vivo studies demonstrated that infusion of TGRL lipolysis products into wild-type mice induced nuclear ATF3 accumulation in carotid artery endothelium. ATF3(-/-) mice were resistant to vascular apoptosis precipitated by treatment with TGRL lipolysis products. Also peripheral blood monocytes isolated from postprandial humans had increased ATF3 expression as compared with fasting monocytes.

CONCLUSIONS

This study demonstrates that TGRL lipolysis products activate ATF3-JNK transcription factor networks and induce endothelial cells inflammatory response.

In vivo RNAi screen for BMI1 targets identifies TGF-β/BMP-ER stress pathways as key regulators of neural- and malignant glioma-stem cell homeostasis

In mouse and human neural progenitor and glioblastoma "stem-like" cells, we identified key targets of the Polycomb-group protein BMI1 by combining ChIP-seq with in vivo RNAi screening. We discovered that Bmi1 is important in the cellular response to the transforming growth factor-β/bone morphogenetic protein (TGF-β/BMP) and endoplasmic reticulum (ER) stress pathways, in part converging on the Atf3 transcriptional repressor. We show that Atf3 is a tumor-suppressor gene inactivated in human glioblastoma multiforme together with Cbx7 and a few other candidates. Acting downstream of the ER stress and BMP pathways, ATF3 binds to cell-type-specific accessible chromatin preloaded with AP1 and participates in the inhibition of critical oncogenic networks. Our data support the feasibility of combining ChIP-seq and RNAi screens in solid tumors and highlight multiple p16(INK4a)/p19(ARF)-independent functions for Bmi1 in development and 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.

Insulin augments tumor necrosis factor-alpha stimulated expression of vascular cell adhesion molecule-1 in vascular endothelial cells

BACKGROUND

Atherosclerosis is an inflammatory disease that is marked by increased presence of Tumor Necrosis Factor-alpha (TNFα), increased expression of Vascular Cell Adhesion Molecule-1 (VCAM-1), increased presence of serum monocytes and activation of the canonical inflammatory molecule, Nuclear Factor Kappa-B (NFκB). Hyperinsulinemia is a hallmark of insulin resistance and may play a key role in this inflammatory process.

METHODS

Using Western blot analysis, immunocytochemistry, flow cytometry and biochemical inhibitors, we measured changes in VCAM-1 protein expression and NFκB translocation in vascular endothelial cells in the presence of TNFα and/or hyperinsulinemia and in the absence or presence of kinase pathway inhibitors.

RESULTS

We report that hyperinsulinemia augmented TNFα stimulated increases in VCAM-1 protein greater than seen with TNFα alone and decreased the time in which VCAM-1 translocated to the cell surface. We also observed that in the presence of Wortmannin, a biochemical inhibitor of phosphatidylinositol 3-kinase (a hallmark of insulin resistance), VCAM-1 expression was greater in the presence of TNFα plus insulin as compared to that seen with insulin or TNFα alone. Additionally, nuclear import of NFκB occurred sooner in the presence of insulin and TNFα together as compared to each alone, and in the presence of Wortmannin, nuclear import of NFκB was greater than that seen with insulin and TNFα alone.

CONCLUSIONS

hyperinsulinemia and insulin resistance appear to augment the inflammatory effects of TNFα on VCAM-1 expression and NFκB translocation, both of which are markers of inflammation in the vasculature.

Activating transcription factor 3 deficiency promotes cardiac hypertrophy, dysfunction, and fibrosis induced by pressure overload

Activating transcription factor 3 (ATF3), which is encoded by an adaptive-response gene induced by various stimuli, plays an important role in the cardiovascular system. However, the effect of ATF3 on cardiac hypertrophy induced by a pathological stimulus has not been determined. Here, we investigated the effects of ATF3 deficiency on cardiac hypertrophy using in vitro and in vivo models. Aortic banding (AB) was performed to induce cardiac hypertrophy in mice. Cardiac hypertrophy was estimated by echocardiographic and hemodynamic measurements and by pathological and molecular analysis. ATF3 deficiency promoted cardiac hypertrophy, dysfunction and fibrosis after 4 weeks of AB compared to the wild type (WT) mice. Furthermore, enhanced activation of the MEK-ERK1/2 and JNK pathways was found in ATF3-knockout (KO) mice compared to WT mice. In vitro studies performed in cultured neonatal mouse cardiomyocytes confirmed that ATF3 deficiency promotes cardiomyocyte hypertrophy induced by angiotensin II, which was associated with the amplification of MEK-ERK1/2 and JNK signaling. Our results suggested that ATF3 plays a crucial role in the development of cardiac hypertrophy via negative regulation of the MEK-ERK1/2 and JNK pathways.

Hyperoxia-induced activation of the integrated stress response in the newborn rat lung

Diverse environmental stresses stimulate eukaryotic translation initiation factor 2α (eIF2α) phosphorylation, leading to a stress-resistant state characterized by global attenuation of protein synthesis and induction of cytoprotective genes. The signal transduction network culminating in these effects is referred to as the integrated stress response (ISR) or, when initiated by misfolded proteins within the endoplasmic reticulum (ER), the unfolded protein response (UPR). Given that we previously reported that exposure of 4-day-old Sprague-Dawley rats to 95% O(2) (Ox) diminishes global pulmonary protein synthesis and increases eIF2α phosphorylation, we conducted the current study to determine whether Ox activates the ISR or UPR. We found that Ox-induced alterations in ER morphology of alveolar type II cells and interstitial fibroblasts were not associated with activation of the UPR sensors PERK or activating transcription factor (ATF) 6 or with X-box binding protein-1 mRNA splicing in whole lung extracts. Exposure to Ox enhanced ATF4 immunoreactivity and nuclear protein content, followed by a 2- and 5-fold increase in ATF3 protein and mRNA expression, respectively. The accumulation of nuclear ATF4 protein coincided with induction of glutamate-cysteine ligase catalytic subunit, an ISR-responsive gene. Immunohistochemistry revealed that changes in ATF3/4 expression were prominent in the alveolus, whereas primary cell culture implicated epithelial and endothelial cells as targets. Finally, induction of ISR intermediates in the intact lung occurred in the absence of the phosphorylation of PKR, JNK, ERK1/2, and p38 MAPK. These findings demonstrate that Ox activates the ISR within the newborn lung and highlight regional and cell-specific alterations in the expression ISR transcription factors that regulate redox balance.

Neuronal injury marker ATF-3 is induced in primary afferent neurons of monoarthritic rats

Activating transcription factor 3 (ATF-3) expression has been associated with several signaling pathways implicated in cellular stress response in many cell types and is usually regarded as a neuronal damage marker in dorsal root ganglia (DRG). We investigated ATF-3 expression in primary afferents in the monoarthritic (MA) model of chronic inflammatory joint pain. Immunohistochemistry revealed that ATF-3 is highly induced mainly in small and medium neurons, especially at 2 and 4 days of MA in L(5) DRGs. Colocalization with calcitonin gene-related peptide (CGRP) and isolectin B4 (IB4) demonstrated that ATF-3-immunoreactive cells are mainly peptidergic. The lack of significant differences in ATF-3 and pAkt colocalization indicated that ATF-3 is probably not involved in a pAkt-mediated survival pathway. Anti-inflammatory (ketoprofen) administration failed to reverse ATF-3 induction in MA rats, but significantly increased CGRP expression. These data suggest that ATF-3 expression is definitely involved in MA, actually marking injured neurons. Some degree of neuronal damage seems to occur right from the first days of disease, mainly affecting small-to-medium peptidergic neurons. The intra-articular injection of complete Freund's adjuvant and the generation of a neuroinflammatory environment seem to be the plausible explanation for the local nerve damage.

Organelle stress-induced activating transcription factor-3 downregulates low-density lipoprotein receptor expression in Sk-Hep1 human liver cells

The low-density lipoprotein receptor (LDLR) plays a central role in cholesterol homeostasis. Here, we provide evidence that an increase in endoplasmic reticulum (ER) stress response or a disturbance of mitochondrial function inhibits LDLR expression in human liver Sk-Hep1 cells. Both organelle stresses triggered activation of activating transcription factor-3 (ATF3), which subsequently reduced LDLR expression. Serial deletion studies revealed that the LDLR promoter region within -234 bp was involved in the repression of LDLR by ATF3. In addition, we identified the region between -8 and -3 of LDLR promoter region as a putative binding site for ATF3 by using deletion construct lacking 6 bp nucleotide corresponding to this region. Transfection of ATF3-specific siRNA rescued LDLR expression under organelle stress, indicating that ATF3 was mainly responsible for the repression of LDLR by these stressors. Additionally, chromatin immunoprecipitation revealed that ATF3 directly binds to the LDLR promoter in a stress-dependent manner. The unique sterol-independent LDLR repression by organelle stress via ATF3 demonstrated here could be involved in obesity-related hypercholesterolemia, which can lead to insulin resistance and type 2 diabetes.

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.

CREB downregulation in vascular disease: a common response to cardiovascular risk

OBJECTIVE

To examine the impact of low-density lipoprotein (LDL), an established mediator of atherosclerosis, on the transcription factor cAMP-response element-binding protein (CREB), which is a regulator of vascular smooth muscle cell (VSMC) quiescence.

METHODS AND RESULTS

VSMC CREB content is diminished in rodent models of diabetes and pulmonary hypertension. We examined aortic CREB content in rodent models of aging, hypertension, and insulin resistance, and we determined nuclear CREB protein in the medial VSMC of high-fat-fed LDL receptor-null mice. There was significant loss of CREB protein in all models. In vitro, primary culture rat aortic VSMC exposed to LDL and oxidized LDL exhibited a rapid, transient increase in CREB phosphorylation and transient phosphorylation/activation of Akt, ERK, JNK, ans p38 MAPK. Exposure to oxidized LDL, but not to LDL, for 24 to 48 hours decreased CREB protein in a dose-dependent fashion and led to nuclear exclusion of CREB. Pharmacological reactive oxygen species scavengers and inhibition of ERK activation blocked oxidized LDL-mediated CREB downregulation.

CONCLUSIONS

These data support a model wherein loss of VSMC CREB protein, which renders these cells more susceptible to activation and apoptosis, is a common pathological response to vascular injury and potentially contributes to plaque progression.

Zinc-induced neurotoxicity mediated by transient receptor potential melastatin 7 channels

Transient receptor potential melastatin 7 (TRPM7) channels are novel Ca(2+)-permeable non-selective cation channels ubiquitously expressed. Activation of TRPM7 channels has been shown to be involved in cellular Mg(2+) homeostasis, diseases caused by abnormal magnesium absorption, and in Ca(2+)-mediated neuronal injury under ischemic conditions. Here we show strong evidence suggesting that TRPM7 channels also play an important role in cellular Zn(2+) homeostasis and in Zn(2+)-mediated neuronal injury. Using a combination of fluorescent Zn(2+) imaging, small interfering RNA, pharmacological analysis, and cell injury assays, we show that activation of TRPM7 channels augmented Zn(2+)-induced injury of cultured mouse cortical neurons. The Zn(2+)-mediated neurotoxicity was inhibited by nonspecific TRPM7 blockers Gd(3+) or 2-aminoethoxydiphenyl borate, and by knockdown of TRPM7 channels with small interfering RNA. In addition, Zn(2+)-mediated neuronal injury under oxygen-glucose deprivation conditions was also diminished by silencing TRPM7. Furthermore, we show that overexpression of TRPM7 channels in HEK293 cells increased intracellular Zn(2+) accumulation and Zn(2+)-induced cell injury, while silencing TRPM7 by small interfering RNA attenuated the Zn(2+)-mediated cell toxicity. Thus, TRPM7 channels may represent a novel target for neurological disorders where Zn(2+) toxicity plays an important role.

ATF3, a hub of the cellular adaptive-response network, in the pathogenesis of diseases: is modulation of inflammation a unifying component?

Activating transcription factor 3 (ATF3) gene encodes a member of the ATF family of transcription factors and is induced by various stress signals. All members of this family share the basic region-leucine zipper (bZip) DNA binding motif and bind to the consensus sequence TGACGTCA in vitro. Previous reviews and an Internet source have covered the following topics: the nomenclature of ATF proteins, the history of their discovery, the potential interplays between ATFs and other bZip proteins, ATF3-interacting proteins, ATF3 target genes, and the emerging roles of ATF3 in cancer and immunity (see footnote 1). In this review, we present evidence and clues that prompted us to put forth the idea that ATF3 functions as a "hub" of the cellular adaptive-response network. We will then focus on the roles of ATF3 in modulating inflammatory response. Inflammation is increasingly recognized to play an important role for the development of many diseases. Putting this in the context of the hub idea, we propose that modulation of inflammation by ATF3 is a unifying theme for the potential involvement of ATF3 in various diseases.

Expression of stress-response ATF3 is mediated by Nrf2 in astrocytes

Activating Transcription Factor 3 (ATF3), a member of the ATF/CREB family, is induced rapidly by various stresses. Its induction mechanism and role in response to changes in cellular redox status, however, have not been elucidated. Here, we found that NF-E2-related factor 2 (Nrf2), a transcription factor known to bind to antioxidant response element (ARE) in promoters, transcriptionally upregulated ATF3 expression in astrocytes. Treatment with Nrf2 activators and oxidants provoked ATF3 induction in astrocytes, whereas its expression was reduced in Nrf2-depleted cells. We further demonstrated that the consensus ARE in the ATF3 promoter is critical for Nrf2-mediation by promoter analyses using an ATF3 promoter-driven luciferase construct and a chromatin immunoprecipitation assay. In addition, we found that Nrf2-dependent ATF3 induction contributed to the antioxidative and cytoprotective functions of Nrf2 in astrocytes. Taken together, our findings suggest that ATF3 is a new target for Nrf2 and has a cytoprotective function in astrocytes.

Potential of deoxynivalenol to induce transcription factors in human hepatoma cells

To assess the hepatotoxicity of deoxynivalenol (DON), human hepatoma cells (Hep-G2) were used as an in vitro model. After exposing Hep-G2 cells to low (1 mciroM) and high dose (10 mciroM), gene expression profiles were analysed by microarray. More than 5% of genes were up-regulated, most of them being involved in transcriptional regulation. By real-time RT-PCR, elevated expression of transcription factors, commonly induced by activation of MAPK-pathway, was demonstrated for Hep-G2 cells on mRNA and protein level. Further studies, involving U937 human monocytes, showed that effects of DON treatment on mRNA and protein level were concentration-dependent and cell-specific. An inverse relation was noticed for the level of DON induced expression of transcription factors (JUN, FOS, EGR1 and ATF3) and the susceptibility of the cell lines towards the mycotoxin. This is the first report giving evidence that on a molecular level the mild hepatotoxic effects of DON are probably caused by the induction of transcription factors which are known to be associated with injury-induced liver regeneration processes. With ATF3, a novel downstream target gene was identified in DON-related cell signalling suggesting a potential linkage between molecular action and biological effects like reduction of glycogen storage in liver tissue.

Silencing TRPM7 promotes growth/proliferation and nitric oxide production of vascular endothelial cells via the ERK pathway

AIMS

The presence and potential function of transient receptor potential melastatin 7 (TRPM7), a Ca2+-permeable non-selective cation channel of the TRP channel superfamily in human vascular endothelial cells, were examined.

METHODS AND RESULTS

Whole-cell patch-clamp recordings showed outward-rectifying currents in human umbilical vein endothelial cells (HUVECs), which was potentiated by removing the extracellular Ca2+ and Mg2+, but inhibited by non-specific TRPM7 blocker Gd3+ or 2-aminoethoxydiphenyl borate (2-APB). TRPM7 mRNA was detected in HUVECs by RT-PCR, but TRPM6, its closest homologue, was not. Silencing TRPM7 by small interfering RNA (siRNA) decreased the level of TRPM7 mRNA and the TRPM7-like current. Interestingly, knockdown of TRPM7 with siRNA or inhibition of TRPM7 function with 2-APB increased the phosphorylation of extracellular signal-regulated kinase (ERK) and enhanced growth/proliferation of HUVECs. This enhanced cell growth/proliferation was abolished by an inhibitor of the ERK signalling pathway. In addition to cell growth/proliferation, silencing TRPM7 also increased expression of nitric oxide synthase and nitric oxide production in an ERK pathway-dependent manner.

CONCLUSION

These observations suggest that TRPM7 channels may play an important role in the function of vascular endothelial cells.

Apoptosis-related genes change their expression with age and hearing loss in the mouse cochlea

To understand possible causative roles of apoptosis gene regulation in age-related hearing loss (presbycusis), apoptotic gene expression patterns in the CBA mouse cochlea of four different age and hearing loss groups were compared, using GeneChip and real-time (qPCR) microarrays. GeneChip transcriptional expression patterns of 318 apoptosis-related genes were analyzed. Thirty eight probes (35 genes) showed significant differences in expression. The significant gene families include Caspases, B-cell leukemia/lymphoma2 family, P53, Calpains, Mitogen activated protein kinase family, Jun oncogene, Nuclear factor of kappa light chain gene enhancer in B-cells inhibitor-related and tumor necrosis factor-related genes. The GeneChip results of 31 genes were validated using the new TaqMan Low Density Array (TLDA). Eight genes showed highly correlated results with the GeneChip data. These genes are: activating transcription factor3, B-cell leukemia/lymphoma2, Bcl2-like1, caspase4 apoptosis-related cysteine protease 4, Calpain2, dual specificity phosphatase9, tumor necrosis factor receptor superfamily member12a, and Tumor necrosis factor superfamily member13b, suggesting they may play critical roles in inner ear aging.

Expression of the transcriptional repressor ATF3 in gonadotrophs is regulated by Egr-1, CREB, and ATF2 after gonadotropin-releasing hormone receptor stimulation

Stimulation of GnRH receptors enhances expression of activating transcription factor (ATF) 3 in a pituitary gonadotroph cell line. The signaling pathway requires elevated cytosolic Ca2+ levels and activation of ERK and c-Jun N-terminal protein kinase. The signaling cascade was blocked by overexpression of either MAPK phosphatase (MKP)-1 or MAPK phosphatase-5 that dephosphorylate nuclear ERK and c-Jun N-terminal protein kinase. In addition, ATF3 biosynthesis was impaired after lentiviral-mediated expression of a constitutively active mutant of calcineurin A. Thus, MKP-1, MKP-5, and calcineurin may function as shut-off devices for GnRH receptor signaling. Expression of dominant-negative mutants of early growth response protein (Egr)-1, cAMP response element binding protein (CREB), and ATF2 blocked the biosynthesis of ATF3, indicating that these transcription factors connect the intracellular signaling cascade elicited by activation of GnRH receptors with transcription of the ATF3 gene. This view was corroborated by chromatin immunoprecipitation experiments revealing that Egr-1 and the phosphorylated forms of CREB and ATF2 bound to the 5'-upstream region of the ATF3 gene in buserelin-stimulated gonadotrophs. Together the data indicate that the ATF3 gene is a bona fide target gene of Egr-1, CREB, and ATF2 in gonadotrophs. Moreover, we show that in gonadotrophs ATF3 bound to its own promoter under physiological conditions. The analysis of a lentiviral-transmitted ATF3 promoter/luciferase reporter gene, embedded into the chromatin of the cells, revealed that ATF3 blocked the activity of its own promoter. We additionally identified the chromogranin B gene as bona fide target gene of ATF3 in gonadotrophs.

Inhibition of inducible nitric oxide synthase expression by a novel small molecule activator of the unfolded protein response

The transcription of inducible nitric oxide synthase (iNOS) is activated by a network of proinflammatory signaling pathways. Here we describe the identification of a small molecule that downregulates the expression of iNOS mRNA and protein in cytokine-activated cells and suppresses nitric oxide production in vivo. Mechanistic analysis suggests that this small molecule, erstressin, also activates the unfolded protein response (UPR), a signaling pathway triggered by endoplasmic reticulum stress. Erstressin induces rapid phosphorylation of eIF2α and the alternative splicing of XBP-1, hallmark initiating events of the UPR. Further, erstressin activates the transcription of multiple genes involved in the UPR. These data suggest an inverse relationship between UPR activation and iNOS mRNA and protein expression under proinflammatory conditions.

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

Cerebellar granule neurons (CGNs) depend on potassium depolarization for survival and undergo apoptosis when deprived of depolarizing concentration of potassium. Activating transcription factor 3 (ATF3), a stress-inducible protein, belongs to the ATF/CREB family of transcription factors family and is involved in cell growth and apoptosis. However, the role of ATF3 in neuronal apoptosis remains unknown. Here, we showed that ATF3 was up-regulated under potassium deprivation in CGNs, and this induction was preceded by a rapid and sustained activation of c-Jun NH(2)-terminal kinase/c-Jun signaling pathway, which plays a fundamental role in neuronal apoptosis. Furthermore, ATF3 up-regulation was abolished by inhibition of JNK or knockdown of c-Jun. Finally, knockdown of ATF3 by RNA interference protected CGNs from potassium deprivation-induced apoptosis. Taken together, our results indicate that ATF3 is a downstream target of JNK/c-Jun pathway and contributes to apoptosis induced by potassium deprivation in rat CGNs.

Coxsackievirus B3 modulates cell death by downregulating activating transcription factor 3 in HeLa cells

Activating transcription factor 3 (ATF3) is an early-induced gene involved in diverse cellular functions in response to various stresses including viral infection. Here we observed marked reduction of ATF3 by coxsackievirus B3 (CVB3) infection and investigated the regulation and functional role of ATF3 in HeLa cells for the understanding of biological significance of ATF3 downregulation. CVB3 infection markedly reduced ATF3 expression at mRNA and protein levels in parallel with p53 degradation, and preservation of p53 expression rescued CVB3 infection-induced ATF3 downregulation. ATF3 overexpression stimulated apoptotic cell death following CVB3 infection, accompanying with augmentation of CVB3 infection-induced eIF2alpha phosphorylation. However, ATF3 overexpression did not affect viral protein production but promoted virus progeny release. Taken together, our results suggest that ATF3 is under control of p53 in part and that the ATF3 downregulation via p53 degradation may contribute to effective viral production as a modulation mechanism of CVB3 infection-induced cell death.