Altered expression of activating transcription factor 3 in the hippocampus of patients with mesial temporal lobe epilepsy-hippocampal sclerosis (MTLE-HS)

Aim of the study: Activating Transforming factor 3 (ATF3) is a stress induced gene and closely associated with neuro-inflammation while Transforming growth Factor Beta (TGFβ) signalling is also reported to be involved in neuro-inflammation and hyper-excitability associated with drug resistant epilepsy. Animal model studies indicate the involvement of ATF3 and TGFβ receptors to promote epileptogenesis. Human studies also show that TGFβ signalling is activated in MTLE-HS. However, lack of studies on ATF3 and TGFβRI expression in MTLE-HS patients exists. We hypothesize that ATF3 and TGFβRI might be expressed in hippocampi of patients with MTLE-HS and playing role in epileptogenesis. Materials & methods: Protein expression of ATF3 and TGFβRI was performed by western blotting. Localisation of ATF3 was performed by immunohistochemistry and immunoflorescence. Results: Protein expression of ATF3 and TGFβRI was significantly up-regulated in hippocampi of patients as compared to controls. Also ATF3 IR was significantly expressed in hippocampi of patients and ATF3 was expressed predominantly in cytoplasm as compared to nucleus. No correlation was found between ATF3 expression and epilepsy duration and seizure frequency. Conclusions: ATF3 and TGFβRI are both important players in neuro-inflammation and might potentiate epileptogenesis in these patients.

Co-catalpol alleviates fluoxetine-induced main toxicity: Involvement of ATF3/FSP1 signaling-mediated inhibition of ferroptosis

BACKGROUND

Fluoxetine is often used as a well-known first-line antidepressant. However, it is accompanied with hepatogenic injury as its main organ toxicity, thereby limiting its application despite its superior efficacy. Fluoxetine is commonly traditionally used combined with some Chinese antidepressant prescriptions containing Rehmannia glutinosa (Dihuang) for depression therapy and hepatoprotection. Our previous experiments showed that co-Dihuang can alleviate fluoxetine-induced liver injury while efficiencies, and catalpol may be the key ingredient to characterize the toxicity-reducing and synergistic effects. However, whether co-catalpol can alleviate fluoxetine-induced liver injury and its toxicity-reducing mechanism remain unclear.

PURPOSE

On the basis of the first recognition of the dose and duration at which pre-fluoxetine caused hepatic injury, co-catalpol's alleviation of fluoxetine-induced hepatic injury and its pathway was comprehensively elucidated.

METHOD AND RESULTS

The hepatoprotection of co-catalpol was evaluated by serum biochemical indexes sensitive to hepatic injury and multiple staining techniques for hepatic pathologic analysis. Subsequently, the pathway by which catalpol alleviated fluoxetine-induced hepatic injury was predicted by network pharmacology to be predominantly the inhibition of ferroptosis. These were validated and confirmed in subsequent experiments with key technologies and diagnostic reagents related to ferroptosis. Further molecular docking showed that activating transcription factor 3 (ATF3) and ferroptosis suppressor protein 1 (FSP1) were the the most prospective molecules for catalpol and fluoxetine among many ferroptosis-related molecules. The critical role of ATF3/FSP1 signaling was further observed by surface plasmon resonance, diagnostic reagents, transmission electron microscopy, Western blot, real-time PCR, immunofluorescence, and immunohistochemistry. Results showed that fluoxetine directly bound to ATF3 and FSP1; agonisting ATF3 or blocking FSP1 abolished the alleviation of catalpol on fluoxetine-induced liver injury, and both exacerbated ferroptosis. Moreover, co-catalpol significantly enhanced the antidepressant efficacy of fluoxetine against depressive behaviours in mice.

CONCLUSION

The hepatic impairment properties of fluoxetine were largely dependent on ATF3/FSP1 target-mediated ferroptosis. Co-catalpol alleviated fluoxetine-induced hepatic injury while enhancing its antidepressant efficacy, and that ATF3/FSP1 signaling-mediated inhibition of ferroptosis was involved in its co-administration detoxification mechanism. This study was the first to reveal the hepatotoxicity characteristics, targets, and mechanisms of fluoxetine; provide a detoxification and efficiency regimen by co-catalpol; and elucidate the detoxification mechanism.

Nucleus pulposus cells regulate macrophages in degenerated intervertebral discs via the integrated stress response-mediated CCL2/7-CCR2 signaling pathway

Lower back pain (LBP), which is a primary cause of disability, is largely attributed to intervertebral disc degeneration (IDD). Macrophages (MΦs) in degenerated intervertebral discs (IVDs) form a chronic inflammatory microenvironment, but how MΦs are recruited to degenerative segments and transform into a proinflammatory phenotype remains unclear. We evaluated chemokine expression in degenerated nucleus pulposus cells (NPCs) to clarify the role of NPCs in the establishment of an inflammatory microenvironment in IDD and explored the mechanisms. We found that the production of C-C motif chemokine ligand 2 (CCL2) and C-C motif chemokine ligand 7 (CCL7) was significantly increased in NPCs under inflammatory conditions, and blocking CCL2/7 and their receptor, C-C chemokine receptor type 2(CCR2), inhibited the inductive effects of NPCs on MΦ infiltration and proinflammatory polarization. Moreover, activation of the integrated stress response (ISR) was obvious in IDD, and ISR inhibition reduced the production of CCL2/7 in NPCs. Further investigation revealed that activating Transcription Factor 3 (ATF3) responded to ISR activation, and ChIP-qPCR verified the DNA-binding activity of ATF3 on CCL2/7 promoters. In addition, we found that Toll-like receptor 4 (TLR4) inhibition modulated ISR activation, and TLR4 regulated the accumulation of mitochondrial reactive oxygen species (mtROS) and double-stranded RNA (dsRNA). Downregulating the level of mtROS reduced the amount of dsRNA and ISR activation. Deactivating the ISR or blocking CCL2/7 release alleviated inflammation and the progression of IDD in vivo. Moreover, MΦ infiltration and IDD were inhibited in CCR2-knockout mice. In conclusion, this study highlights the critical role of TLR4/mtROS/dsRNA axis-mediated ISR activation in the production of CCL2/7 and the progression of IDD, which provides promising therapeutic strategies for discogenic LBP.

Apigenin-7-glucoside-loaded nanoparticle alleviates intestinal ischemia-reperfusion by ATF3/SLC7A11-mediated ferroptosis

Intestinal ischemia reperfusion injury (II/R injury) is a common and intractable pathophysiological process in critical patients, for which exploring new treatments and mechanisms is of great importance to improve treatment outcomes. Apigenin-7-O-Glucoside (AGL) is a sugar derivative of apigenin natural product with various pharmacological activities to protect against intestinal diseases. In this study, we synthesized two amphiphilic molecules, namely DTPA-N10-10 and mPEG-TK-DA, which can scavenge free radicals and reactive oxygen species (ROS). They were successfully encapsulated AGL through self-assembly, resulting in the formation of multi-site ROS scavenging nanoparticles called PDN@AGL. In vitro and in vivo experiments demonstrated that PDN@AGL could protect intestinal tissues by reducing lipid peroxidation, lowering ROS levels and inhibiting ferroptosis during II/R injury. Furthermore, our study revealed, for the first time, that the regulation of the ATF3/SLC7A11 pathway by PDN@AGL may play a crucial role in mitigating II/R injury. In conclusion, our study confirmed the beneficial effects of PDN@AGL in combating II/R injury through the ATF3/SLC7A11-mediated regulation of ferroptosis and oxidative stress. These findings lay the groundwork for the potential application of PDN@AGL in the treatment of II/R injury.

Tumor-intrinsic RGS1 potentiates checkpoint blockade response via ATF3-IFNGR1 axis

Background

Non-responsiveness is a major barrier in current cancer immune checkpoint blockade therapies, and the mechanism has not been elucidated yet. Therefore, it is necessary to discover the mechanism and biomarkers of tumor immunotherapeutic resistance.

Methods

Bioinformatics analysis was performed based on CD8+ T cell infiltration in multiple tumor databases to screen out genes related to anti-tumor immunity. Associations between Regulator of G-protein signaling 1 (RGS1) and IFNγ-STAT1 signaling, and MHCI antigen presentation pathway were examined by RT-qPCR, western blotting, and flow cytometry. The modulatory mechanisms of RGS1 were investigated via CHIP-qPCR and dual-luciferase assay. The clinical and therapeutic implications of RGS1 were comprehensively investigated using tumor cell lines, mouse models, and clinical samples receiving immunotherapy.

Results

RGS1 was identified as the highest gene positively correlated with immunogenicity among RGS family. Inhibition of RGS1 in neoplastic cells dampened anti-tumor immune response and elicited resistance to immunotherapy in both renal and lung murine subcutaneous tumors. Mechanistically, RGS1 enhanced the binding of activating transcription factor 3 (ATF3) to the promoter of interferon gamma receptor 1 (IFNGR1), activated STAT1 and the subsequent expression of IFNγ-inducible genes, especially CXCL9 and MHC class I (MHCI), thereby influenced CD8+ T cell infiltration and antigen presentation and processing. Clinically, lower expression level of RGS1 was associated with resistance of PD1 inhibition therapy and shortened progression-free survival among 21 NSCLC patients receiving immunotherapy.

Conclusions

Together, these findings uncover a novel mechanism that elicits immunotherapy resistance and highlight the function of tumor-intrinsic RGS1, which brings new insights for future strategies to sensitize anti-PD1 immunotherapy.

Butyrate enhances erastin-induced ferroptosis of osteosarcoma cells via regulating ATF3/SLC7A11 pathway

Osteosarcoma (OS) is a highly fatal bone tumor characterized by high degree of malignancy and early lung metastasis. Traditional chemotherapy fails in improving the efficacy and survival rate of patients with OS. Butyrate (NaBu) has been reported as a new antitumor drug for inhibiting proliferation and inducing apoptosis in various cancer cells. However, the effect of NaBu on the ferroptosis of OS is still unknown. This study aimed to investigate whether NaBu promotes erastin-induced ferroptosis in OS cells and to uncover the underlying mechanism. Here, we found that NaBu significantly enhanced erastin-induced ferroptosis in vitro and in vivo. Compared with the group that erastin used alonely, pre-treating with NaBu exacerbated erastin-meditated GSH depletion, lipid peroxidation, and mitochondrial morphologic changes in OS cells. In a subcutaneous OS model, NaBu combined with erastin significantly reduced tumor growth and increased the levels of 4-HNE. Mechanistically, NaBu downregulated SLC7A11 transcription via regulating ATF3 expression. Overexpression of ATF3 facilitated erastin to induce ferroptosis, while ATF3 knockdown attenuated NaBu-induced ferroptosis sensitivity. In conclusion, our findings revealed a previously unidentified role of NaBu in erastin-induced ferroptosis by regulating SLC7A11, suggesting that NaBu may be a potential therapeutic agent for OS treatment.

Macrophages originated IL-33/ST2 inhibits ferroptosis in endometriosis via the ATF3/SLC7A11 axis

Endometriosis is a gynecological inflammatory disease that is linked with immune cells, specifically macrophages. IL-33 secreted from macrophages is known to accelerate the progression of endometriosis. The periodic and repeated bleeding that occurs in women with endometriosis leads to excess iron in the microenvironment that is conducive to ferroptosis, a process related to intracellular ROS production, lipid peroxidation and mitochondrial damage. It is suggested that eESCs may specifically be able to inhibit ferroptosis. However, it is currently unclear whether IL-33 directly regulates ferroptosis to influence the disease course in endometriosis. In this study, eESCs co-cultured with macrophages or stimulated with IL-33/ST2 were observed to have increased cell viability and migration. Additionally, IL-33/ST2 decreased intracellular iron levels and lipid peroxidation in eESCs exposed to erastin treatment. Furthermore, IL-33/ST2 treatment resulted in a notable upregulation in SLC7A11 expression in eESCs due to the downregulation of negative transcription factor ATF3, thereby suppressing ferroptosis. The P38/JNK pathway activated by IL-33/ST2 was also found to inhibit the transcription factor ATF3. Therefore, we concluded that IL-33/ST2 inhibits the ATF3-mediated reduction in SLC7A11 transcript levels via the P38/JNK pathway. The findings reveal that macrophage-derived IL-33 upregulates SLC7A11 in eESCs through the p38/JNK/ATF3 pathway, ultimately resulting in protection against ferroptosis in eESCs. Moreover, we conducted an experiment using endometriosis model mice that showed that a combination of IL-33-Ab and erastin treatment alleviated the disease, showing the promise of combining immunotherapy and ferroptosis therapy.

Intracellular Fusobacterium nucleatum infection attenuates antitumor immunity in esophageal squamous cell carcinoma

Currently, the influence of the tumor microbiome on the effectiveness of immunotherapy remains largely unknown. Intratumoural Fusobacterium nucleatum (Fn) functions as an oncogenic bacterium and can promote tumor progression in esophageal squamous cell carcinoma (ESCC). Our previous study revealed that Fn is a facultative intracellular bacterium and that its virulence factor Fn-Dps facilitates the intracellular survival of Fn. In this study, we find that Fn DNA is enriched in the nonresponder (NR) group among ESCC patients receiving PD-1 inhibitor and that the serum antibody level of Fn is significantly higher in the NR group than in the responder (R) group. In addition, Fn infection has an opposite impact on the efficacy of αPD-L1 treatment in animals. Mechanistically, we confirm that Fn can inhibit the proliferation and cytokine secretion of T cells and that Fn-Dps binds to the PD-L1 gene promoter activating transcription factor-3 (ATF3) to transcriptionally upregulate PD-L1 expression. Our results suggest that it may be an important therapeutic strategy to eradicate intratumoral Fn infection before initiating ESCC immunotherapies.

PARPi treatment enhances radiotherapy-induced ferroptosis and antitumor immune responses via the cGAS signaling pathway in colorectal cancer

In cancer cells, poly (ADP-ribose) polymerase (PARP)-1 and PARP2 initiate and regulate DNA repair pathways to protect against DNA damage and cell death caused by radiotherapy or chemotherapy. Radiotherapy and PARP inhibitors (PARPis) have been combined in clinical trials, but their action mechanisms remain unclear. Here, we show that activated by ionizing radiation (IR) generated dsDNA, cyclic GMP-AMP synthase (cGAS) signaling promoted regulated cell death, specifically ferroptosis, via the activating transcription factor 3 (ATF3)-solute carrier family 7 member 11 axis and the antitumor immune response via the interferon-β-CD8⁺ T cell pathway. Niraparib, a widely used PARPi, augmented cGAS-mediated ferroptosis and immune activation. In colorectal cancer models, cGAS knockdown (KD) compromised IR-induced ferroptosis via downregulation of ATF3 (key ferroptosis regulator) expression. cGAS depletion reversed IR-induced infiltration of CD8⁺ T or CD8⁺GZMB⁺ T cells in the cGAS KD group. Survival analysis of paired tumor samples before and after standard radiotherapy revealed that high expression levels of cGAS, ATF3, and PTGS2 and high density of CD8⁺ T cells resulted in a significantly high disease-free survival rate in patients with rectal cancer. Therefore, PARPi treatment increases the cytoplasmic accumulation of dsDNA caused by IR, triggering the cGAS signaling-mediated tumor control in cancer cell lines and mouse xenograft models.

Exercise ameliorates high-fat diet-induced insulin resistance accompanied by changes in protein levels of hepatic ATF3-related signaling in rats

PURPOSE

Exercise is an effective way to alleviate insulin resistance (IR). However, the underlying mechanisms remain to be elucidated. Previous studies demonstrated that cardiolipin synthase 1 (CRLS1)/interferon-regulatory factor-2 binding protein 2 (IRF2bp2)-activating transcription factor 3 (ATF3)-adiponectin receptor 2 (AdipoR2)-adaptor protein containing pH domain, PTB domain and leucine zipper motif 1 (APPL1)-protein kinase B (AKT/PKB)-related signaling was closely associated with obesity-induced IR-related diseases, but the correlation between exercise training alleviating obesity-induced IR and the protein levels of hepatic CRLS1/IRF2bp2-ATF3-AdipoR2-APPL1-AKT-related signaling in rats is unknown. Therefore, We want to investigate the effect of exercise training on IR and the protein levels of hepatic CRLS1/IRF2bp2-ATF3-AdipoR2-APPL1-AKT-related signaling in rat.

METHODS

The male healthy Sprague-Dawley rats were divided into four groups: normal control group (NCG, n = 10), diet-induced obesity-sedentary group (DIO-SG, n = 10), diet-induced obesity-chronic exercise group (DIOCEG, n = 10) received chronic swim exercise training and diet-induced obesity-acute exercise group (DIO-AEG, n = 10) received acute swim exercise training. We measured the levels of IR-related indicators and the protein levels of hepatic CRLS1/IRF2bp2-ATF3-AdipoR2-APPL1-AKT-related signaling in NCG, DIO-SG, DIOCEG and DIO-AEG.

RESULTS

We found that high-fat diet (HFD)-induced obesity decreased insulin sensitivity in rats accompanied by decreased protein levels of hepatic CRLS1, IRF2bp2, AdipoR2, APPL1, p-AKT and increased protein level of hepatic ATF3. The acute exercise and the chronic exercise both increased insulin sensitivity in rats. The chronic exercise decreased hepatic ATF3 protein level and increased CRLS1, IRF2bp2, AdipoR2, APPL1, p-AKT protein levels in HFD-fed rats. The acute exercise decreased hepatic ATF3 protein level and increased hepatic IRF2bp2, APPL1 and p-AKT protein levels in HFD-fed rats. The acute exercise had no significant effect on hepatic CRLS1 and AdipoR2 protein levels in HFD-fed rats.

CONCLUSION

Our current findings indicated that exercise alleviated obesity-induced IR accompanied by changes in protein levels of hepatic ATF3-related signaling in rats. Our results are meaningful for exploring the molecular mechanism of exercise alleviating IR symptoms.

Citrus alkaline extracts prevent endoplasmic reticulum stress in type II alveolar epithelial cells to ameliorate pulmonary fibrosis via the ATF3/PINK1 pathway

BACKGROUND

Idiopathic pulmonary fibrosis is a chronic, progressive, fibrotic disease. Although the pathogenesis remains unclear, the effect of endoplasmic reticulum (ER) stress in type II alveolar epithelial cells (AEC IIs) is increasingly thought to be a critical mechanism.

PURPOSE

We investigated the effects of citrus alkaline extracts (CAE) on AEC IIs and elucidated the underlying mechanism for their possible use in ameliorating pulmonary fibrosis (PF).

METHODS

A bleomycin-induced mouse model of PF, and an in vitro tunicamycin (TM) -induced ER stress model in A549 cells were successfully established. Accumulation of collagen in lung tissues in vivo was assessed using histological analysis and western blotting. The expression levels of the ER-stress marker BiP and other related proteins were assessed by western blotting and immunofluorescence staining. Mitochondrial membrane potential was assessed to evaluate mitochondrial homeostasis.

RESULTS

CAE mitigated collagen deposition to ameliorate PF in vivo. CAE suppressed the bleomycin or TM-induced increases in ER-stress biomarker, BiP, and PERK pathway proteins, resulting in a decrease in ER stress in mouse lung tissues and A549 cells, respectively. Additionally, CAE treatment suppressed the bleomycin or TM-induced increase in the ER-stress downstream proteins, activating ATF3 and increased the levels of PINK1 in AEC IIs, both in vivo and in vitro. The reduced mitochondrial homeostasis induced by TM was restored by CAE-treatment in A549 cells. Furthermore, conditioned media from TM-treated A549 cells increased collagen deposition in MRC5 cells mainly via TGF-β1. The increased collagen deposition was not seen using conditioned media from CAE-treated A549 cells.

CONCLUSION

These results provide novel insights into the potential mechanism of CAE in inhibiting ER stress in AEC IIs, and suggests that it has great potential to ameliorate PF via the ATF3/PINK1 pathway.

Loss of activating transcription factor 3 prevents KRAS-mediated pancreatic cancer

The unfolded protein response (UPR) is activated in pancreatic pathologies and suggested as a target for therapeutic intervention. In this study, we examined activating transcription factor 3 (ATF3), a mediator of the UPR that promotes acinar-to-ductal metaplasia (ADM) in response to pancreatic injury. Since ADM is an initial step in the progression to pancreatic ductal adenocarcinoma (PDAC), we hypothesized that ATF3 is required for initiation and progression of PDAC. We generated mice carrying a germline mutation of Atf3 (Atf3-/-) combined with acinar-specific induction of oncogenic KRAS (Ptf1acreERT/+KrasG12D/+). Atf3-/- mice with (termed APK) and without KRASG12D were exposed to cerulein-induced pancreatitis. In response to recurrent pancreatitis, Atf3-/- mice showed decreased ADM and enhanced regeneration based on morphological and biochemical analysis. Similarly, an absence of ATF3 reduced spontaneous pancreatic intraepithelial neoplasia (PanIN) formation and PDAC in Ptf1acreERT/+KrasG12D/+ mice. In response to injury, KRASG12D bypassed the requirement for ATF3 with a dramatic loss in acinar tissue and PanIN formation observed regardless of ATF3 status. Compared to Ptf1acreERT/+KrasG12D/+ mice, APK mice exhibited a significant decrease in pancreatic and total body weight, did not progress through to PDAC, and showed altered pancreatic fibrosis and immune cell infiltration. These findings suggest a complex, multifaceted role for ATF3 in pancreatic cancer pathology.

Diverse motif ensembles specify non-redundant DNA binding activities of AP-1 family members in macrophages

Mechanisms by which members of the AP-1 family of transcription factors play non-redundant biological roles despite recognizing the same DNA sequence remain poorly understood. To address this question, here we investigate the molecular functions and genome-wide DNA binding patterns of AP-1 family members in primary and immortalized mouse macrophages. ChIP-sequencing shows overlapping and distinct binding profiles for each factor that were remodeled following TLR4 ligation. Development of a machine learning approach that jointly weighs hundreds of DNA recognition elements yields dozens of motifs predicted to drive factor-specific binding profiles. Machine learning-based predictions are confirmed by analysis of the effects of mutations in genetically diverse mice and by loss of function experiments. These findings provide evidence that non-redundant genomic locations of different AP-1 family members in macrophages largely result from collaborative interactions with diverse, locus-specific ensembles of transcription factors and suggest a general mechanism for encoding functional specificities of their common recognition motif.

Characterization of ATF3 induction after ionizing radiation in human skin cells

The epidermis is a physiological barrier that protects an organism against pathogens and chemical or physical damage. The degree of skin injuries caused by radiation influences the subsequent survival from and prognosis of such injuries. Recently, we have identified, using microarray technology, genes regulated by high-dose radiation exposure in normal human epidermal keratinocytes. Our results suggest the possible role of ATF3 in the apoptosis pathway in radiation injuries caused by high-dose radiation exposure in human skin. In the present study, we characterized ATF3 induction after X-ray irradiation in normal human skin cells. Our results showed that the induction of ATF3 mRNA is rapid, transient, and at least in part mediated through a transcriptional mechanism after X-irradiation of normal human keratinocytes. In addition, ATF3 was induced and accumulated in the nuclei of keratinocytes upon treatment with an apoptosis inducer, anisomycin. Our results also suggested that the induction mechanism of ATF3 mRNA by X-irradiation may be different not only between epidermal keratinocytes and dermal fibroblasts, but also between dermal fibroblasts and lung fibroblasts.

Retrograde axonal transport of JNK signaling molecules influence injury induced nuclear changes in p-c-Jun and ATF3 in adult rat sensory neurons

In the present study, we investigated if the previously observed JNK-mediated activation of c-Jun and induction of ATF3 could be ascribed to axonal transport of JNK signaling components, or if axonal transport of the transcription factors themselves contributes to the nuclear changes in injured sensory neurons. We observed retrograde axonal transport of a number of JNK upstream kinases in ligated rat sciatic nerve. In these preparations, axonal transport of JNK/p-JNK, the JNK scaffolding protein JIP, and the transcription factors ATF3 and ATF2/p-ATF2 was also found. No or little retrograde transport of c-Jun and p-c-Jun was found, whereas an anterograde transport of Hsp27, a protein previously reported in the context of p-c-Jun and ATF3, was observed. In separate experiments, we found that in vitro inhibition of axonal transport or axonal inhibition of JNK reduced the number of p-c-Jun- and ATF3-positive neuronal nuclei. The results suggest that retrograde axonal transport of JNK signaling components contributes to the injury induced c-Jun phosphorylation and ATF3 induction.

Induction of activating transcription factor 3 (ATF3) by peripheral nerve compression

Nuclear translocation of activating transcription factor 3 (ATF3), used as a marker for neuronal injury, was studied by immunocytochemistry in sensory neurons in dorsal root ganglia and locally along the sciatic nerve after severe chronic nerve compression in rats. In compressed nerves (application of a narrow silicone tube), ATF3 immunoreactivity was seen in the nucleus of sensory neurons and in Schwann cells below the compression at two and four weeks. Removal of the silicone tube (decompression) at two weeks did not affect the number of ATF3-positive cell nuclei in dorsal root ganglia. No ATF3 immunoreactivity was found in undamaged nerves on the other side. Functional variables (toe spreading and muscle force) were impaired at two weeks, with partial improvement at four weeks. Nerve compression induces nuclear translocation of ATF3, a transcription factor associated with survival and regeneration of sensory neurons. The response is related to duration of compression and partly correlated to function.

Intraneural injection of interleukin-1beta and tumor necrosis factor-alpha into rat sciatic nerve at physiological doses induces signs of neuropathic pain

Proinflammatory cytokines are mediators of inflammatory and neuropathic pain. Here, we investigated pain-related behavior in rats after intraneural injection of different doses of rat recombinant interleukin-1beta (rrIL-1beta) and tumor necrosis factor-alpha (rrTNF) into the sciatic nerve. Doses ranged between 0.25 and 2500pg/ml for rrIL-1beta and 0.25-250pg/ml for rrTNF. Thermal hyperalgesia as measured according to the Hargreaves method was most prominent with 2.5pg/ml of rrIL-1beta or rrTNF. Mechanical allodynia as assessed using von Frey hairs was seen consistently with 2.5pg/ml of rrIL-1beta and 0.25-2.5pg/ml of rrTNF. Higher and lower doses had no significant effect on pain-related behavior. Morphometric analysis of semithin sections of the sciatic nerve 10 days after the injections revealed no significant fiber loss. The fiber size distribution was not significantly altered by any of the treatments. Particularly with injections of rrIL-1beta, an increase of epineurial macrophages was observed at all doses. The immunohistochemical expression of cellular markers of neuronal damage (activating transcription factor 3) or activation (phosphorylated p38 mitogen-activated kinase, NF-kappa B p65) in dorsal root ganglia (DRG) tended to increase with both cytokine injections. However, this did not reflect the extent of behavioral changes. In summary, we found a bell-shaped dose-response curve for the algesic effects of rrIL-1beta and rrTNF, peaking at doses equivalent to those of endogenous cytokines released locally after nerve injury. The absence of corresponding morphological changes in nerves supports the concept of a functional effect of the cytokines at these doses.

Induction of plasminogen activator inhibitor-1 and -2 in dorsal root ganglion neurons after peripheral nerve injury

We have previously found that tissue type and urokinase type plasminogen activators (tPA and uPA) are induced in dorsal root ganglia (DRG) neurons after peripheral axotomy and that tPA plays crucial roles in generating neuropathic pain. Here we examined whether the plasminogen activator inhibitor-1 and -2 (PAI-1 and PAI-2) mRNA, endogenous inhibitors of tPA and uPA, are induced in the DRG following sciatic nerve transection. L4 and L5 DRG sections were examined using in situ hybridization histochemistry. The results showed that both PAI-1 and PAI-2 mRNA were up-regulated in DRG neurons within 1 day, and peaked at 1-3 days, after injury. Reduction of these mRNA was observed from 7 days after injury. The precise expression patterns of PAI-1 and PAI-2 mRNA at 3 days after axotomy revealed that PAI-1 mRNA was observed in predominantly small neurons, while much of the PAI-2 mRNA was expressed in large neurons. Double-labeling analysis of these mRNAs with activated transcription factor 3, known as an injury marker, revealed that most PAI-1 and PAI-2 mRNAs was induced in injured neurons. Co-expression of PAI-1, 2 with tPA and uPA in DRG neurons suggests that these inhibitors may act in an autocrine manner to modulate extracellular proteolytic activity after nerve injury.

Activating transcription factor 3, a stress sensor, activates p53 by blocking its ubiquitination

Activating transcription factor 3 (ATF3) is rapidly induced by diverse environmental insults including genotoxic stress. We report herein that its interaction with p53, enhanced by genotoxic stress, stabilizes the tumor suppressor thereby augmenting functions of the latter. Overexpression of ATF3 (but not a mutated ATF3 protein (Delta102-139) devoid of its p53-binding region) prevents p53 from MDM2-mediated degradation and leads to increased transcription from p53-regulated promoters. ATF3, but not the Delta102-139 protein, binds the p53 carboxy-terminus and diminishes its ubiquitination and nuclear export. Genotoxic-stressed ATF3-null mouse embryonic fibroblasts, or cells in which ATF3 was reduced by small interference RNA, show inefficient p53 induction and impaired apoptosis compared with wild-type cells. ATF3-null cells (but not wild-type cells), which poorly accumulate p53, are transformed by oncogenic Ras. Thus, ATF3 is a novel stress-activated regulator of p53 protein stability/function providing the cell with a means of responding to a wide range of environmental insult, thus maintaining DNA integrity and protecting against cell transformation.

Stress response gene ATF3 is a target of c-myc in serum-induced cell proliferation

The c-myc proto-oncogene encodes a transcription factor that promotes cell cycle progression and cell proliferation, and its deficiency results in severely retarded proliferation rates. The ATF3 stress response gene encodes a transcription factor that plays a role in determining cell fate under stress conditions. Its biological significance in the control of cell proliferation and its crosstalk regulation, however, are not well understood. Here, we report that the serum response of the ATF3 gene expression depends on c-myc gene and that the c-Myc complex at ATF/CREB site of the gene promoter plays a role in mediating the serum response. Intriguingly, ectopic expression of ATF3 promotes proliferation of c-myc-deficient cells, mostly by alleviating the impeded G1-phase progression observed in these cells, whereas ATF3 knockdown significantly suppresses proliferation of wild-type cells. Our study demonstrates that ATF3 is downstream of the c-Myc signaling pathway and plays a role in mediating the cell proliferation function of c-Myc. Our results provide a novel insight into the functional link of the stress response gene ATF3 and the proto-oncogene c-myc.

Transcript profiling of immediate early genes reveals a unique role for activating transcription factor 3 in mediating activation of the glycoprotein hormone alpha-subunit promoter by gonadotropin-releasing hormone

Recent studies profiling immediate early gene responses to GnRH in the LbetaT2 gonadotrope cell model revealed increased expression of numerous genes including activating transcription factor (ATF) 3. The present studies demonstrate similar results with GnRH administration in vivo in ovariectomized mice. In this model, ATF3 mRNA was markedly up-regulated at 20, 40, and 60 min after in vivo administration of a GnRH analog. In alphaT3-1 gonadotrope cells, ATF3 mRNA and protein were induced by GnRH in a manner consistent with in vivo observations. Pharmacological studies implicated a combined role for the activities of protein kinase C isozymes, ERK and c-Jun N-terminal kinase, in modulating ATF3 expression. The role of ATF3 was further investigated in the activation of the human glycoprotein hormone alpha-subunit gene promoter. GnRH induced the alpha-subunit promoter-luciferase reporter approximately 16-fold, and this induction was completely abolished with mutations in the dual cAMP response elements (CREs) or the combined inhibition of GnRH-induced ERK and c-Jun N-terminal kinase. GnRH induced recruitment of ATF3, c-Jun, and c-Fos to the dual CREs. Overexpression and specific knockdown of ATF3 by small inhibitory RNA implicate a functional role for ATF3 in mediating activation of the alpha-subunit gene promoter. These studies provide clear evidence that ATF3 is a key immediate early gene induced by GnRH administration in vivo and in the alphaT3-1 gonadotrope cell model. These studies support the conclusion that the dual CREs of the human alpha-subunit promoter are the target of GnRH-induced MAPK regulation through ATF3.

Blockade of rapid versus prolonged extracellularly regulated kinase 1/2 activation has differential effects on insulin-induced gene expression

In the present work, insulin's regulation of expression of activating transcription factor 3 (ATF-3), the putative transcription factor proline-rich induced protein (Pip)92, and insulin-inducible gene-1 (Insig-1) (an ER resident protein involved in regulation of sterol-responsive element-binding protein 1 activation) have been examined in a liver-derived cell line (rat H4IIE hepatoma cells). We report that: 1) insulin-induced transcription of ATF-3, Pip92, and Insig-1 required MEK-ERK activation; 2) insulin-induced transcription of ATF-3 and Pip92 reached maximum levels within 15 min and was blocked by wortmannin but not LY294002; 3) in contrast, the maximum level of insulin-induced transcription of Insig-1 was delayed and was not blocked by either wortmannin or LY294002; 4) insulin activated ERK1/2 in two distinct phases, a rapid peak and a later plateau; 5) the delayed plateau phase of insulin-induced ERK1/2 activation was partially phosphatidylinositol 3-OH-kinase dependent; and 6) however, the rapid, insulin-induced peak of ERK1/2 activation was blocked by wortmannin but not LY294002.

Expression of damage-induced neuronal endopeptidase (DINE) mRNA in peri-infarct cortical and thalamic neurons following middle cerebral artery occlusion

Damage-induced neuronal endopeptidase (DINE) is a unique nerve-injury associated molecule, which was recently identified in a peripheral nerve injury model. The aim of this study was to determine the expression profiles and distribution of DINE in adult rats after middle cerebral artery (MCA) occlusion. Focal cerebral ischemia induced late-onset and prolonged expression of DINE mRNA in the peri-infarct cortex and specific nuclei of thalamus. Double labeling using immunohistochemistry and in situ hybridization revealed that DINE mRNA was exclusively expressed in cells that were positive to a neuronal marker NeuN. Previously established knowledge on neuroanatomical fiber connection suggests that DINE mRNA was expressed in areas projecting their axons to or through the core region of the infarction. This unique expression profile was similar to that of activating transcription factor-3 (ATF-3), which is a marker of nerve-injured neuron. More than 98% of ATF-3 immunoreactive neurons simultaneously expressed DINE mRNA, suggesting that DINE expression is observed in injured neurons of CNS as well as PNS. Since DINE expression promotes antioxidant activity, our results suggest that DINE may act as a neuroprotective molecule in neurons under ischemic insult.

The anti-invasive activity of cyclooxygenase inhibitors is regulated by the transcription factor ATF3 (activating transcription factor 3)

We previously showed that nonsteroidal anti-inflammatory drugs (NSAID) such as sulindac sulfide, which has chemopreventive activity, modulate the expression of several genes detected by microarray analysis. Activating transcription factor 3 (ATF3) was selected for further study because it is a transcription factor involved in cell proliferation, apoptosis, and invasion, and its expression is repressed in human colorectal tumors as compared with normal adjacent tissue. In this report, we show that ATF3 mRNA and protein expression are up-regulated in HCT-116 human colorectal cancer cells following treatment with NSAIDs, troglitazone, diallyl disulfide, and resveratrol. To ascertain the biological significance of ATF3, we overexpressed full-length ATF3 protein in the sense and antisense orientations. Overexpression of ATF3 in the sense orientation decreased focus formation in vitro and reduced the size of mouse tumor xenografts by 54% in vivo. Conversely, overexpression of antisense ATF3 was protumorigenic in vitro, however, not in vivo. ATF3 in the sense orientation did not modulate apoptosis, indicating another mechanism is involved. With microarray analysis, several genes relating to invasion and metastasis were identified by ATF3 overexpression and were confirmed by real-time reverse transcription-PCR, and several of these genes were modulated by sulindac sulfide, which inhibited invasion in these cells. Furthermore, overexpression of ATF3 inhibited invasion to a similar degree as sulindac sulfide treatment, whereas antisense ATF3 increased invasion. In conclusion, ATF3 represents a novel mechanism in which NSAIDs exert their anti-invasive activity, thereby linking ATF3 and its gene regulatory activity to the biological activity of these compounds.

Upregulation of activating transcription factor 3 (ATF3) by intrinsic CNS neurons regenerating axons into peripheral nerve grafts

The expression of the transcription factor ATF3 in the brain was examined by immunohistochemistry during axonal regeneration induced by the implantation of pieces of peripheral nerve into the thalamus of adult rats. After 3 days, ATF3 immunoreactivity was present in many cells within approximately 500 mum of the graft. In addition, ATF3-positive cell nuclei were found in the thalamic reticular nucleus (TRN) and medial geniculate nuclear complex (MGN), from which most regenerating axons originate. CNS cells with ATF3-positive nuclei were predominantly neurons and did not show signs of apoptosis. The number of ATF3-positive cells had declined by 7 days and further by 1 month after grafting when most ATF3-positive cells were found in the TRN and MGN. 14 days or more after grafting, some ATF3-positive nuclei were distorted and may have been apoptotic. In some experiments of 1 month duration, neurons which had regenerated axons to the distal ends of grafts were retrogradely labeled with DiAsp. ATF3-positive neurons in these animals were located in regions of the TRN and MGN containing retrogradely labeled neurons and the great majority were also labeled with DiAsp. SCG10 and c-Jun were found in neurons in the same regions as retrogradely labeled and ATF3-positive cells. Thus, ATF3 is transiently upregulated by injured CNS neurons, but prolonged expression is part of the pattern of gene expression associated with axonal regeneration. The co-expression of ATF3 with c-jun suggests that interactions between these transcription factors may be important for controlling the program of gene expression necessary for regeneration.

Indole-3-carbinol and 3,3'-diindolylmethane induce expression of NAG-1 in a p53-independent manner

Indole-3-carbinol (I3C), present in cruciferous vegetables, and its major in vivo product 3,3'-diindolylmethane (DIM), have been reported to suppress cancer development. However, the responsible molecular mechanisms are not fully understood. Nonsteroidal anti-inflammatory drug-activated gene-1 (NAG-1) is a TGF-beta superfamily gene associated with pro-apoptotic and anti-tumorigenic activities. The present study was performed to investigate whether I3C and DIM influence NAG-1 expression and to provide the potential molecular mechanism of their effects on anti-tumorigenesis. The I3C repressed cell proliferation and induced NAG-1 expression in a concentration-dependent manner. In addition, DIM increased the expression of NAG-1 as well as activating transcription factor 3 (ATF3), and the induction of ATF3 was earlier than that of NAG-1. The DIM treatment increased luciferase activity of NAG-1 in HCT-116 cells transfected with NAG-1 promoter construct. The results suggest that I3C represses cell proliferation through up-regulation of NAG-1 and that ATF3 may play a pivotal role in DIM-induced NAG-1 expression in human colorectal cancer cells. Furthermore, the mixture of I3C with resveratrol enhances NAG-1 expression, suggesting the synergistic effect of these two unrelated compounds on NAG-1 expression.

Identification of ATF-3, caveolin-1, DLC-1, and NM23-H2 as putative antitumorigenic, progesterone-regulated genes for ovarian cancer cells by gene profiling

Although progesterone (P4) has been implicated to offer protection against ovarian cancer (OCa), little is known of its mechanism of action. The goal of this study was to identify P4-regulated genes that have anti-OCa action. Three immortalized nontumorigenic human ovarian surface epithelial (HOSE) cell lines and three OCa (OVCA) cell lines were subjected to 5 days of P4 treatment. Transcriptional profiling with a cDNA microarray containing approximately 2400 known genes was used to identify genes (1) whose expression was consistently downregulated in OVCA cell lines compared to HOSE cell lines, and (2) whose expression was restored in OCa cell lines by P4 treatment. From the candidates selected, activating transcription factor-3 (ATF-3), caveolin-1, deleted in liver cancer-1 (DLC-1), and nonmetastatic clone 23 (NM23-H2) were chosen for post hoc functional studies based on their previously reported action as tumor suppressors or apoptosis inducers. Semiquantitative RT-PCR analyses confirmed loss of or reduced transcription of these genes in OVCA cells when compared to HOSE cells and their upregulation following P4 treatment. Hormonal specificity was demonstrated by blockade experiments with a progestin antagonist RU 38486. Ectopic expression of caveolin-1, DLC-1, and NM23-H2 caused growth inhibition in OVCA cell cultures, but not in HOSE cell cultures, while forced expression of ATF-3 suppressed growth in both. Overexpression of AFT-3 also enhanced caspase-3 activity in both HOSE and OVCA cells, whereas ectopic expression of caveolin-1 and DLC-1 only activated this enzyme in OCa cells. In contrast, NM23-H2 overexpression was ineffective in activating caspase-3. Overexpression of any of the four genes in OCa cells reduced soft-agar colony formation and cell invasiveness. Taken together, we have identified four new P4-regulated, antitumor genes for OCa. However, their modes of action differ significantly; ATF-3 primarily functions as an apoptosis inducer, NM23-H2 as a suppressor of cell motility, and caveolin-1 and DLC-1 exhibiting features of classical tumor suppressors. To the best of our knowledge, except for NM23-H2, this is the first report linking P4 to the regulation of these tumor suppressor/proapoptotic genes, which could serve as future therapeutic targets.

Gene expression profiling identifies activating transcription factor 3 as a novel contributor to the proapoptotic effect of curcumin

The antitumor effect of curcumin (diferuloylmethane) is well established. However, there have been no unbiased studies to identify novel molecular targets of this compound. We therefore undertook a gene expression profiling study to identify novel targets of curcumin. A cDNA array comprised of 12,625 probes was used to compare total RNA extracted from curcumin-treated and untreated MDA-1986 cells for differential gene expression. We identified 202 up-regulated mRNAs and 505 transcripts decreased > or =2-fold. The proapoptotic activating transcription factor 3 (ATF3) was induced >4-fold. Two negative regulators of growth control [antagonizer of myc transcriptional activity (Mad) and p27kip1] were induced 68- and 3-fold, respectively. Additionally, two dual-activity phosphatases (CL 100 and MKP-5), which inactivate the c-jun-NH2-kinases, showed augmented expression, coinciding with reduced expression of the upstream activators of c-jun-NH2-kinase (MEKK and MKK4). Of the repressed genes, the expression of Frizzled-1 (Wnt receptor) was most strongly attenuated (8-fold). Additionally, two genes implicated in growth control (K-sam, encoding the keratinocyte growth factor receptor, and HER3) as well as the E2F-5 transcription factor, which regulates genes controlling cell proliferation, also showed down-regulated expression. Considering its role in apoptosis, we determined the contribution of ATF3 to the antitumor effect of curcumin. Curcumin-treated MDA-1986 cells showed a rapid, dose-dependent increase in ATF3/mRNA protein. Moreover, expression of an exogenous ATF3 cDNA synergized with curcumin in inducing apoptosis. Thus, we have identified several putative, novel molecular targets of curcumin and showed that one, (ATF3) contributes to the proapoptotic effects of this compound.

Smad3-ATF3 signaling mediates TGF-beta suppression of genes encoding Phase II detoxifying proteins

This study provides evidence that in mammary epithelial cells the pluripotent cytokine TGF-beta1 repressed expression of multiple genes involved in Phase II detoxification. GCLC, the gene that encodes the catalytic subunit of the enzyme glutamate cysteine ligase, the rate-limiting enzyme in the biosynthesis of glutathione, was used as a molecular surrogate for investigating the mechanisms by which TGF-beta suppressed Phase II gene expression. TGF-beta was found to suppress luciferase reporter activity mediated by the human GCLC proximal promoter, as well as reporter activity mediated by the GCLC antioxidant response element, ARE4. TGF-beta downregulated expression of endogenous GCLC mRNA and GCLC protein. TGF-beta suppression of the Phase II genes correlated with a decrease in cellular glutathione and an increase in cellular reactive oxygen species. Ectopic expression of constitutively active Smad3E was sufficient to inhibit both reporters in the absence of TGF-beta, whereas dominant negative Smad3A blocked TGF-beta suppression. Smad3E suppressed Nrf2-mediated activation of the GCLC reporter. We demonstrate that TGF-beta increased ATF3 protein levels, as did transient overexpression of Smad3E. Ectopic expression of ATF3 was sufficient to suppress the GCLC reporter activity, as well as endogenous GCLC expression. These results demonstrate that Smad3-ATF3 signaling mediates TGF-beta repression of ARE-dependent Phase II gene expression and potentially provide critical insight into mechanisms underlying TGF-beta1 function in carcinogenesis, tissue repair, and fibrosis.

Overexpression of activating transcription factor-2 is required for tumor growth and progression in mouse skin tumors

Activating transcription factor (ATF)-2 is a member of the ATF/cyclic AMP-responsive element binding protein family of transcription factors. It has been shown, in vitro, to possess growth factor-independent proliferation and transformation capacity. The information concerning the involvement of ATF-2 in carcinogenesis is rather limited. In a previous report, we showed a progressive increase in the levels of various activator protein (AP)-1 components, including phosphorylated ATF-2, in a series of mouse skin cell lines that represented developmental stages of the mouse skin carcinogenesis system. In the present study, we examined in detail the role of ATF-2 in the development of mouse skin spindle cells A5 and CarB, which correspond to the late and most aggressive stage of the mouse skin carcinogenesis model. To address this issue, we overexpressed a dominant negative form of ATF-2 in the A5 and CarB cell lines and examined their behavior in vitro and in vivo at the molecular and cellular level. The stable transfectants expressed decreased levels of phosphorylated ATF-2 and c-Jun. Subsequently, we observed that dominant negative ATF-2 affected the composition and reduced the activity of AP-1. The above biochemical changes were followed, both in vitro and in vivo in BALB/c severe combined immunodeficient mice, by suppression of the aggressive characteristics of the A5 and CarB mouse skin spindle cells. We attributed this behavior to the significant down-regulation of cyclin D1, cyclin A, and ATF-3, known AP-1 targets implicated in cell cycle control and promotion. In conclusion, our findings underscore a key regulatory role of ATF-2 in tumor growth and progression of mouse skin tumors.

Differential activation of MAPK in injured and uninjured DRG neurons following chronic constriction injury of the sciatic nerve in rats

To investigate the intracellular signal transduction pathways involved in the pathophysiological mechanisms of neuropathic pain after partial nerve injury, we examined the activation of extracellular signal-regulated protein kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) in the dorsal root ganglion (DRG) in the chronic constriction injury (CCI) model. The CCI induced an increase in the phosphorylation of ERK in predominantly injured medium-sized and large-sized DRG neurons and in satellite glial cells. Treatment with the MAPK kinase 1/2 inhibitor, U0126, suppressed CCI-induced mechanical allodynia and partially reversed the increase in neuropeptide Y (NPY) expression in damaged DRG neurons. In contrast, the CCI induced the activation of p38, mainly in uninjured small-to-medium-diameter DRG neurons and in satellite glial cells. The p38 inhibitor, SB203580, reversed the CCI-induced heat hyperalgesia and also the increase in brain-derived neurotrophic factor (BDNF) expression in intact DRG neurons. On the other hand, the nerve growth factor (NGF)-induced increase in BDNF expression in small-to-medium-diameter neurons was reversed by SB203580, whereas the anti-NGF-induced increase in NPY in medium-sized and large-sized neurons was partially blocked by U0126. Taken together, our results demonstrate that the activation of ERK and p38 and also the changes in NPY and BDNF expression may occur in different populations of DRG neurons after CCI, partially through alterations in the target-derived NGF. These changes in injured and intact primary afferents are likely to have a substantial role in pathological states, and MAPK pathways in nociceptors may be potential targets for the development of novel analgesics.

Bone cancer pain: the effects of the bisphosphonate alendronate on pain, skeletal remodeling, tumor growth and tumor necrosis

Patients with metastatic breast, lung or prostate cancer frequently have significant bone cancer pain. In the present report we address, in a single in vivo mouse model, the effects the bisphosphonate alendronate has on bone cancer pain, bone remodeling and tumor growth and necrosis. Following injection and confinement of green fluorescent protein-transfected murine osteolytic tumor cells into the marrow space of the femur of male C3H/HeJ mice, alendronate was administered chronically from the time the tumor was established until the bone cancer pain became severe. Alendronate therapy reduced ongoing and movement-evoked bone cancer pain, bone destruction and the destruction of sensory nerve fibers that innervate the bone. Whereas, alendronate treatment did not change viable tumor burden, both tumor growth and tumor necrosis increased. These data emphasize that it is essential to utilize a model where pain, skeletal remodeling and tumor growth can be simultaneously assessed, as each of these can significantly impact patient quality of life and survival.

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

ATF3 (Activating transcription factor 3), a member of the CREB/ATF family, can be induced by stress and growth factors in mammalian cells, and is thought to play an important role in the cardiovascular system. However, little is currently known about how the induction of ATF3 is regulated, except that the JNK pathway is involved. Here, we investigated the differential roles of the MAPK pathways involved in TNFalpha (tumour necrosis factor alpha)-induced ATF3 expression in vascular endothelial cells. In human umbilical vein endothelial cells, the expression of constitutively active MKK7 (MAPK kinase 7) increased the number of ATF3-positive cells, and dominant negative MKK7 suppressed the TNFalpha-induced expression of ATF3, indicating a requirement for the JNK pathway. In contrast, the expression of constitutively active or dominant negative MEK1/2 (MAPK/ERK kinase 1/2) suppressed or enhanced TNFalpha-mediated induction of ATF3, respectively. In support of this, the MEK1/2 specific inhibitor U0126 enhanced the expression of ATF3 induced by TNFalpha. Furthermore, the ERK pathway inhibits the TNFalpha-mediated induction of ATF3 mRNA, but not its stability, suggesting the involvement of ERK activity in the transcriptional regulation of the ATF3 gene. Our results suggest that TNFalpha-induced ATF3 gene expression is bidirectionally regulated by the JNK and ERK pathways in vascular endothelial cells.

Amino acid deprivation induces the transcription rate of the human asparagine synthetase gene through a timed program of expression and promoter binding of nutrient-responsive basic region/leucine zipper transcription factors as well as localized histone acetylation

Expression of human asparagine synthetase (ASNS), which catalyzes asparagine and glutamate biosynthesis, is transcriptionally induced following amino acid deprivation. Previous overexpression and electrophoresis mobility shift analysis showed the involvement of the transcription factors ATF4, C/EBPbeta, and ATF3-FL through the nutrient-sensing response element-1 (NSRE-1) within the ASNS promoter. Amino acid deprivation caused an elevated mRNA level for ATF4, C/EBPbeta, and ATF3-FL, and the present study established that the nuclear protein content for ATF4 and ATF3-FL were increased during amino acid limitation, whereas C/EBPbeta-LIP declined slightly. The total amount of C/EBPbeta-LAP protein was unchanged, but changes in the distribution among multiple C/EBPbeta-LAP forms were observed. Overexpression studies established that ATF4, ATF3-FL, and C/EBPbeta-LAP could coordinately modulate the transcription from the human ASNS promoter. Chromatin immunoprecipitation demonstrated that amino acid deprivation increased ATF3-FL, ATF4, and C/EBPbeta binding to the ASNS promoter and enhanced promoter association of RNA polymerase II, TATA-binding protein, and TFIIB of the general transcription machinery. A time course revealed a markedly different temporal order of interaction between these transcription factors and the ASNS promoter. During the initial 2 h, there was a 20-fold increase in ATF4 binding and a rapid increase in histone H3 and H4 acetylation, which closely paralleled the increased transcription rate of the ASNS gene, whereas the increase in ATF3-FL and C/EBPbeta binding was considerably slower and more closely correlated with the decline in transcription rate between 2 and 6 h. The data suggest that ATF3-FL and C/EBPbeta act as transcriptional suppressors for the ASNS gene to counterbalance the transcription rate activated by ATF4 following amino acid deprivation.

TLR9 is localized in the endoplasmic reticulum prior to stimulation

In mammals, 10 TLRs recognize conserved pathogen-associated molecular patterns, resulting in the induction of inflammatory innate immune responses. One of these, TLR9, is activated intracellularly by bacterial DNA and synthetic oligodeoxynucleotides (ODN), containing unmethylated CpG dinucleotides. Following treatment with CpG ODN, TLR9 is found in lysosome-associated membrane protein type 1-positive lysosomes, and we asked which intracellular compartment contains TLR9 before CpG exposure. Surprisingly, we found by microscopy and supporting biochemical evidence that both transfected and endogenously expressed human TLR9 is retained in the endoplasmic reticulum. By contrast, human TLR4 trafficked to the cell surface, indicating that endoplasmic reticulum retention is not a property common to all TLRs. Because TLR9 is observed in endocytic vesicles following exposure to CpG ODN, our data indicate that a special mechanism must exist for translocating TLR9 to the signaling compartments that contain the CpG DNA.

Over expression of ATF-3 protects rat hippocampal neurons from in vivo injection of kainic acid

ATF-3 is a member of the ATF superfamily of transcription factors and is strongly associated with episodes of cellular stress. We demonstrate an association between increases in ATF-3 protein and resistance to exitotoxic cell death in vivo. Intra-hippocampal injection of kainic acid elicited a robust increase in endogenous ATF-3 within kainate-resistant cells of the dentate gyrus, while overexpression of exogenous ATF-3 was found to protect vulnerable CA3 neurons from the same insult. These results suggest a positive contribution to neuronal survival in the context of stress-induced death, and support an anti-apoptotic role for ATF-3 in the brain.

Role for activating transcription factor 3 in stress-induced beta-cell apoptosis

Activating transcription factor 3 (ATF3) is a stress-inducible gene and encodes a member of the ATF/CREB family of transcription factors. However, the physiological significance of ATF3 induction by stress signals is not clear. In this report, we describe several lines of evidence supporting a role of ATF3 in stress-induced beta-cell apoptosis. First, ATF3 is induced in beta cells by signals relevant to beta-cell destruction: proinflammatory cytokines, nitric oxide, and high concentrations of glucose and palmitate. Second, induction of ATF3 is mediated in part by the NF-kappaB and Jun N-terminal kinase/stress-activated protein kinase signaling pathways, two stress-induced pathways implicated in both type 1 and type 2 diabetes. Third, transgenic mice expressing ATF3 in beta cells develop abnormal islets and defects secondary to beta-cell deficiency. Fourth, ATF3 knockout islets are partially protected from cytokine- or nitric oxide-induced apoptosis. Fifth, ATF3 is expressed in the islets of patients with type 1 or type 2 diabetes, and in the islets of nonobese diabetic mice that have developed insulitis or diabetes. Taken together, our results suggest ATF3 to be a novel regulator of stress-induced beta-cell apoptosis.

Long term proteasome inhibition does not preferentially afflict motor neurons in organotypical spinal cord cultures

Ubiquitinated inclusions are a constant feature of amyotrophic lateral sclerosis (ALS). It has been hypothesised that these inclusions reflect overload or failure of the ubiquitin-proteasome system, and that this failure contributes to the degeneration of motor neurons. In the present study we have examined the effect of low concentrations of proteasome inhibitors on protein aggregation and viability of neurons in organotypical spinal cord cultures. We found a dose-dependent degeneration of neurons after a one-week exposure to the proteasome inhibitors lactacystin and epoxomicin. Neuronal degeneration was associated with an increase in poly-ubiquitination, consistent with failure of the ubiquitin-proteasome system. Proteasome inhibition caused degeneration of both motor neurons and interneurons, and no difference in survival between motor neurons and interneurons was observed. Since protein aggregation may particularly play a role in ALS patients with superoxide dismutase 1 (SOD1) mutations, we have compared the effect of proteasome inhibition between spinal cord cultures from non-transgenic and SOD1(G93A) transgenic mice. There was no difference between the viability of motor neurons from transgenic and non-transgenic mice.

Interleukin-10 induced activating transcription factor 3 transcriptional suppression of matrix metalloproteinase-2 gene expression in human prostate CPTX-1532 Cells

Aberrant expression of the 72-kDa type IV collagenase [matrix metalloproteinase (MMP)-2] is implicated in the invasion and angiogenesis process of malignant tumors. We investigated the effects of interleukin (IL)-10 on MMP-2 expression in CPTX-1532 human prostate tumor cells. Our results demonstrate that IL-10 significantly inhibited MMP-2 transcription and protein expression induced by a phorbol ester, phorbol 12-myristate 13-acetate. The inhibitory effects of IL-10 on MMP-2 expression correlated with the suppression of MMP-2 promoter activity. To determine the mechanism of IL-10 action, we examined IL-10-dependent promoter activity with luciferase constructs from a 2-kbp promoter region of the human MMP-2 gene. We functionally characterized the promoter fragments by transient transfection experiments with CPTX-1532 cells. The experiments revealed that a cAMP responsive element binding protein (CREB) consensus domain was identified upstream of the 5' transcriptional start site, which was highly responsive to IL-10-dependent down-regulation of promoter luciferase activity. Electrophoretic mobility shift assays combined with antibody "supershift assays" confirmed the data from the luciferase assays. Immunoblot assays of activating transcription factor (ATF) 3 immunoprecipitates with tyrosine specific antibodies revealed that IL-10 stimulated tyrosine phosphorylation of ATF3 to activate binding to the CREB domain and suppress MMP-2 expression. Studies with stable, IL-10 transfected CPTX-1532 subclones further showed that IL-10 failed to suppress MMP-2 expression in ATF3-deficient CPTX-1532 cells, where the ATF3 mRNA was destroyed with a DNAzyme oligonucleotide targeting the 5' region of the mRNA. Finally, reconstitution of ATF3 successfully restored the inhibitory effects of IL-10 on MMP-2 gene expression. Taken together, these data demonstrate the critical role of tyrosine phosphorylated ATF3 and the CREB consensus domain in IL-10 suppression of MMP-2 gene expression in primary human prostate tumor cells.

Decrease of Hsp25 protein expression precedes degeneration of motoneurons in ALS-SOD1 mice

We have investigated the expression of Hsp25, a heat shock protein constitutively expressed in motoneurons, in amyotrophic lateral sclerosis (ALS) mice that express G93A mutant SOD1 (G93A mice). Immunocytochemistry and Western blotting showed that a decrease of Hsp25 protein expression occurred in motoneurons of G93A mice prior to the onset of motoneuron death and muscle weakness. This decrease in Hsp25 expression also preceded the appearance of SOD1 aggregates as identified by cellulose acetate filtration and Western blot analysis. In contrast to Hsp25 protein levels, Hsp25 mRNA as determined by in situ hybridization and RT-PCR, remained unchanged. This suggests that the decrease in Hsp25 protein levels occurs post-transcriptionally. In view of the cytoprotective properties of Hsp25 and the temporal relationship between decreased Hsp25 expression and the onset of motoneuron death, it is feasible that reduced Hsp25 concentration contributes to the degeneration of motoneurons in G93A mice. These data are consistent with the idea that mutant SOD1 may reduce the availability of the protein quality control machinery in motoneurons.

Adenylyl cyclase type VI gene transfer reduces phospholamban expression in cardiac myocytes via activating transcription factor 3

Cardiac-directed expression of adenylyl cyclase type VI (AC(VI)) increases stimulated cAMP production, improves heart function, and increases survival in cardiomyopathy. In contrast, pharmacological agents that increase intracellular levels of cAMP have detrimental effects on cardiac function and survival. We wondered whether effects that are independent of cAMP might be responsible for these salutary outcomes associated with AC(VI) expression. We therefore conducted a series of experiments focused on how gene transcription is influenced by AC(VI) in cultured neonatal rat cardiac myocytes, with a particular focus on genes that might influence cardiac function. We found that overexpression of AC(VI) down-regulated mRNA and protein expression of phospholamban, an inhibitor of the sarcoplasmic reticulum Ca(2+)-ATPase. We determined that the cAMP-responsive-like element in the phospholamban (PLB) promoter was critical for down-regulation by AC(VI). Overexpression of AC(VI) did not alter the expression of CREB, CREM, ATF1, ATF2, or ATF4 proteins. In contrast, overexpression of AC(VI) increased expression of ATF3 protein, a suppressor of transcription. Following AC(VI) gene transfer, when cardiac myocytes were stimulated with isoproterenol or NKH477, a water-soluble forskolin analog that directly stimulates AC, expression of ATF3 protein was increased even more, which correlated with reduced expression of PLB. We then showed that AC(VI)-induced ATF3 protein binds to the cAMP-responsive-like element on the PLB promoter and that overexpression of ATF3 in cardiac myocytes inhibits PLB promoter activity. These findings indicate that AC(VI) has effects on gene transcription that are not directly dependent on cAMP generation.

Nitric oxide inhibits matrix metalloproteinase-2 expression via the induction of activating transcription factor 3 in endothelial cells

Nitric oxide (NO) has been shown to inhibit migration of cells in which various matrix metalloproteinases (MMPs) are involved. The underlying molecular mechanisms of this inhibition remain elusive. Endothelial cells (ECs) constitutively produce MMP-2. The effect of NO on MMP-2 expression was examined. A dose-dependent inhibition of MMP-2 mRNA level was demonstrated in ECs treated with NO. ECs infected with adenovirus carrying endothelial NO synthase (Ade-NOS) reduced MMP-2 expression. The inhibitory effect of NO on MMP-2 expression was a transcriptional event because NO reduced MMP-2 promoter activity. NO treatment of ECs consequently suppressed MMP-2 secretion revealed by zymographic assay. Functional analysis of MMP-2 promoter (1716 base pairs) indicated that the p53-binding site (-1659 to -1629) was crucial for MMP-2 promoter activity. Activating transcription factor 3 (ATF3) has been reported to act as a transcriptional repressor for p53. ECs treated with NO induced ATF3 expression. Consistently, Ade-NOS-infected ECs showed an increase of ATF3 level. Moreover, ECs either over-expressed ATF3 or, when treated with an ATF3 activator (MG-132; carbobenzoxy-l-leucyl-l-leucyl-l-leucinal), resulted in a repression of MMP-2 promoter activity. Because of MMP-2 suppression by NO, ECs treated with NO inhibited endothelial migration, a phenomenon similar to that of ECs treated with MMP-2 antibody or MG-132. These results indicate that NO-attenuating endothelial migration is mediated at least in part by its reduction of MMP-2 expression via the up-regulation of ATF3. This study provides a molecular basis that supports the notion that NO acts as a negative regulator in endothelial migration.

G protein-coupled receptor agonist-stimulated expression of ATF3/LRF-1 and c-myc and comitogenic effects in hepatocytes do not require EGF receptor transactivation

Several agonists acting on G protein-coupled receptors (GPCR) enhance the mitogenic effect of epidermal growth factor (EGF) in rat hepatocytes, through mechanisms that have only partially been clarified. Results in various cells have led to the idea that a major mechanism for GPCR-mediated stimulation of cell growth is transactivation of receptor tyrosine kinases, particularly the EGF receptor (EGFR), leading to rapid phosphorylation of the EGFR and activation of downstream signaling pathways. In the present study cultured rat hepatocytes were exposed to various GPCR agonists, including vasopressin, angiotensin II (Ang.II), norepinephrine, or prostaglandin F(2 alpha) (PGF(2 alpha)). None of these agents increased the phosphorylation of the EGFR or the docking protein Shc. Furthermore, we examined the effect of the GPCR agonists on the expression of two early response genes believed to be involved in growth activation. The GPCR agonists increased the mRNA expression of c-myc, and also of activating transcription factor 3 (ATF3)/liver regeneration factor-1 (LRF-1), which is a novel finding. Finally, the selective EGFR inhibitor AG1478 did not suppress the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) or the induction of c-myc or ATF3/LRF-1 by the GPCR agonists, and did not prevent the comitogenic effects induced by these agents, while it blocked the effect of EGF on these responses. The results suggest that GPCR agonists induce expression of ATF3/LRF-1 and c-myc and exert comitogenic effects through mechanisms that do not require EGFR transactivation.

ATF3 upregulation in glia during Wallerian degeneration: differential expression in peripheral nerves and CNS white matter

BACKGROUND

Many changes in gene expression occur in distal stumps of injured nerves but the transcriptional control of these events is poorly understood. We have examined the expression of the transcription factors ATF3 and c-Jun by non-neuronal cells during Wallerian degeneration following injury to sciatic nerves, dorsal roots and optic nerves of rats and mice, using immunohistochemistry and in situ hybridization.

RESULTS

Following sciatic nerve injury--transection or transection and reanastomosis--ATF3 was strongly upregulated by endoneurial, but not perineurial cells, of the distal stumps of the nerves by 1 day post operation (dpo) and remained strongly expressed in the endoneurium at 30 dpo when axonal regeneration was prevented. Most ATF3+ cells were immunoreactive for the Schwann cell marker, S100. When the nerve was transected and reanastomosed, allowing regeneration of axons, most ATF3 expression had been downregulated by 30 dpo. ATF3 expression was weaker in the proximal stumps of the injured nerves than in the distal stumps and present in fewer cells at all times after injury. ATF3 was upregulated by endoneurial cells in the distal stumps of injured neonatal rat sciatic nerves, but more weakly than in adult animals. ATF3 expression in transected sciatic nerves of mice was similar to that in rats. Following dorsal root injury in adult rats, ATF3 was upregulated in the part of the root between the lesion and the spinal cord (containing Schwann cells), beginning at 1 dpo, but not in the dorsal root entry zone or in the degenerating dorsal column of the spinal cord. Following optic nerve crush in adult rats, ATF3 was found in some cells at the injury site and small numbers of cells within the optic nerve displayed weak immunoreactivity. The pattern of expression of c-Jun in all types of nerve injury was similar to that of ATF3.

CONCLUSION

These findings raise the possibility that ATF3/c-Jun heterodimers may play a role in regulating changes in gene expression necessary for preparing the distal segments of injured peripheral nerves for axonal regeneration. The absence of the ATF3 and c-Jun from CNS glia during Wallerian degeneration may limit their ability to support regeneration.

NGF and GDNF ameliorate the increase in ATF3 expression which occurs in dorsal root ganglion cells in response to peripheral nerve injury

Activating transcription factor-3 (ATF3) is a member of the ATF/CREB transcription factor superfamily and is induced in dorsal root ganglion (DRG) cells after nerve injury. In order to study the regulation of ATF3, we have examined the effect of nerve growth factor (NGF) and glial cell line-derived neurotrophic factor (GDNF) on ATF3 expression. In untreated rats, sciatic nerve transection induced ATF3 immunoreactivity in 82% of L4 DRG cells at 14 days after axotomy. Intrathecal delivery of NGF or GDNF for 2 weeks commencing immediately after injury reduced the ATF3 expression to 35 and 23% of DRG cells, respectively. Cell size analysis indicated that NGF had protected a population of mainly small- to medium-sized cells, but that the GDNF had protected a population of both small and large cells. This effect was confirmed by double labelling for P2X(3), CGRP and 200 kDa neurofilament, markers for small peptide-poor cells, peptide-rich cells and large cells, respectively. Thus GDNF reduced the percentage of ATF3-immunoreactive P2X(3) cells from 70 to 4%, and the percentage of ATF3-immunoreactive neurofilament cells from 63 to 24%. NGF was less effective than GDNF in reducing ATF3 expression in these cell types, but reduced the percentage of ATF3-immunoreactive CGRP cells from 10% to < 1%. These results show that ATF3 expression in specific populations of DRG cells can be modulated by exogenous supplementation of specific trophic factors, and suggest that ATF3 expression may normally be induced by the loss of target-derived NGF and GDNF.

Activating transcription factor 3 is integral to the eukaryotic initiation factor 2 kinase stress response

In response to environmental stress, cells induce a program of gene expression designed to remedy cellular damage or, alternatively, induce apoptosis. In this report, we explore the role of a family of protein kinases that phosphorylate eukaryotic initiation factor 2 (eIF2) in coordinating stress gene responses. We find that expression of activating transcription factor 3 (ATF3), a member of the ATF/CREB subfamily of basic-region leucine zipper (bZIP) proteins, is induced in response to endoplasmic reticulum (ER) stress or amino acid starvation by a mechanism requiring eIF2 kinases PEK (Perk or EIF2AK3) and GCN2 (EIF2AK4), respectively. Increased expression of ATF3 protein occurs early in response to stress by a mechanism requiring the related bZIP transcriptional regulator ATF4. ATF3 contributes to induction of the CHOP transcriptional factor in response to amino acid starvation, and loss of ATF3 function significantly lowers stress-induced expression of GADD34, an eIF2 protein phosphatase regulatory subunit implicated in feedback control of the eIF2 kinase stress response. Overexpression of ATF3 in mouse embryo fibroblasts partially bypasses the requirement for PEK for induction of GADD34 in response to ER stress, further supporting the idea that ATF3 functions directly or indirectly as a transcriptional activator of genes targeted by the eIF2 kinase stress pathway. These results indicate that ATF3 has an integral role in the coordinate gene expression induced by eIF2 kinases. Given that ATF3 is induced by a very large number of environmental insults, this study supports involvement of eIF2 kinases in the coordination of gene expression in response to a more diverse set of stress conditions than previously proposed.

ATF3 enhances c-Jun-mediated neurite sprouting

The AP-1 transcription factor c-Jun is induced in axotomized neurons of the peripheral and central nervous systems, and in both cases upregulation of c-Jun expression has been correlated with axonal regeneration. More recently there has been interest in the c-Jun-related bZIP transcription factor, ATF3, and its function in neurons. ATF3 is also induced in nerve cells in response to axotomy and there is a correlation between increased ATF3 expression and upregulation of c-Jun in surviving neurons. Moreover, c-Jun is able to induce expression of ATF3. We investigated the effect of co-expressing c-Jun and ATF3 in two neuronal-like cell lines to model transcriptional events occurring in axotomized neurons undergoing regeneration. We show that expression of ATF3 with c-Jun significantly enhances c-Jun-mediated neurite sprouting, and that this phenotype is most likely mediated by a physical association of these two transcription factors. Our results suggest that a program of axonal regeneration is initiated when both c-Jun and ATF3 are upregulated in neurons in response to axotomy.

Gene expression analysis in mastocytosis reveals a highly consistent profile with candidate molecular markers

BACKGROUND

Mastocytosis is a rare clonal disorder that might be accompanied by non-mast-cell clonal hematologic disorders, such as myeloproliferative or myelodysplastic syndromes.

OBJECTIVE

Our aim was to further understand the pathologic basis of mastocytosis and to identify novel molecular markers of disease.

METHODS

Microarray analysis was performed on RNA preparations obtained from bone marrow mononuclear cells of patients with mastocytosis. Results were compared with gene expression profiles performed on bone marrow mononuclear cells of healthy subjects.

RESULTS

Analysis of gene expression in neoplastic bone marrow tissues revealed highly consistent profiles. One hundred four genes were significantly upregulated, and 64 genes were significantly downregulated in the bone marrow of patients with mastocytosis. The most prominent differentially expressed gene was alpha-tryptase (44.6-fold increase). Also upregulated were genes involved in cell proliferation, neoplastic transformation, and apoptosis. Both hierarchical and K-means clustering analyses identified an identical group of 10 genes highly coordinately overexpressed in patients with mastocytosis, including genes for the mast-cell-associated enzymes alpha- and beta-tryptase and carboxypeptidase A. The expression level of 3 of these 10 genes (alpha-tryptase, the activating transcription factor type 3, and the muscle aponeurotic fibrosarcoma type F oncogene) was significantly correlated with serum tryptase levels, a surrogate marker of disease.

CONCLUSION

The data presented in this study reveal significant differences in gene expression in the bone marrow of patients with mastocytosis compared with healthy subjects, demonstrate highly coordinated genes that might contribute to pathology, and identify 3 genes as candidate molecular markers for systemic disease.

Recruitment of SWI/SNF to the human immunodeficiency virus type 1 promoter

Following human immunodeficiency virus type 1 (HIV-1) integration into the host cell's genome, the 5' long terminal repeat (LTR) is packaged into a highly specific chromatin structure comprised of an array of nucleosomes positioned with respect to important DNA sequence elements that regulate the transcriptional activity of the provirus. While several host cell factors have been shown to be important for chromatin remodeling and/or basal transcription, no specific mechanism that relieves the transcriptional repression imposed by nuc-1, a positioned nucleosome that impedes the start site of transcription, has been found. Since phorbol esters cause the rapid disruption of nuc-1 and markedly stimulate HIV-1 transcription, we looked for protein factors that associate with this region of the HIV-1 promoter in a phorbol-ester-dependent manner. We report here that ATF-3, JunB, and BRG-1 (the ATPase subunit of the 2-MDa human chromatin remodeling machine SWI/SNF) are recruited to the 3' boundary of nuc-1 following phorbol myristate acetate stimulation in Jurkat T cells. Analysis of the recruitment of BRG-1 in nuclear extracts prepared from Jurkat T cells and reconstitution of an in vitro system with purified components demonstrate that ATF-3 is responsible for targeting human SWI/SNF (hSWI/SNF) to the HIV-1 promoter. Importantly, this recruitment of hSWI/SNF required HMGA1 proteins. Further support for this conclusion comes from immunoprecipitation experiments showing that BRG-1 and ATF-3 can exist together in the same complex. Although ATF-3 clearly plays a role in the specific targeting of BRG-1 to the HIV-1 promoter, the maintenance of a stable association between BRG-1 and chromatin appears to be dependent upon histone acetylation. By adding BRG-1 back into a BRG-1-deficient cell line (C33A cells), we demonstrate that trichostatin A strongly induces the 5'-LTR-driven reporter transcription in a manner that is dependent upon BRG-1 recruitment.