CHOP enhancement of gene transcription by interactions with Jun/Fos AP-1 complex proteins

Endoplasmic reticulum stress enhances the expression of TLR3-induced TSLP by airway epithelium

Thymic stromal lymphopoietin (TSLP) is an epithelial-derived pleiotropic cytokine that regulates T-helper 2 (Th2) immune responses in the lung and plays a major role in severe uncontrolled asthma. Emerging evidence suggests a role for endoplasmic reticulum (ER) stress in the pathogenesis of asthma. In this study, we determined if ER stress and the unfolded protein response (UPR) signaling are involved in TSLP induction in the airway epithelium. For this, we treated human bronchial epithelial basal cells and differentiated primary bronchial epithelial cells with ER stress inducers and the TSLP mRNA and protein expression was determined. A series of siRNA gene knockdown experiments were conducted to determine the ER stress-induced TSLP signaling pathways. cDNA collected from asthmatic bronchial biopsies was used to determine the gene correlation between ER stress and TSLP. Our results show that ER stress signaling induces TSLP mRNA expression via the PERK-C/EBP homologous protein (CHOP) signaling pathway. AP-1 transcription factor is important in regulating this ER stress-induced TSLP mRNA induction, though ER stress alone cannot induce TSLP protein production. However, ER stress significantly enhances TLR3-induced TSLP protein secretion in the airway epithelium. TSLP and ER stress (PERK) mRNA expression positively correlates in bronchial biopsies from participants with asthma, particularly in neutrophilic asthma. In conclusion, these results suggest that ER stress primes TSLP that is then enhanced further upon TLR3 activation, which may induce severe asthma exacerbations. Targeting ER stress using pharmacological interventions may provide novel therapeutics for severe uncontrolled asthma.NEW & NOTEWORTHY TSLP is an epithelial-derived cytokine and a key regulator in the pathogenesis of severe uncontrolled asthma. We demonstrate a novel mechanism by which endoplasmic reticulum stress signaling upregulates airway epithelial TSLP mRNA expression via the PERK-CHOP signaling pathway and enhances TLR3-mediated TSLP protein secretion.

SH3RF2 contributes to cisplatin resistance in ovarian cancer cells by promoting RBPMS degradation

Platinum-based chemotherapy remains one of the major choices for treatment of ovarian cancer (OC). However, primary or acquired drug resistance severely impairs their efficiency, thereby causing chemotherapy failure and poor prognosis. SH3 domain containing ring finger 2 (SH3RF2) has been linked to the development of cancer. Here we find higher levels of SH3RF2 in the tumor tissues from cisplatin-resistant OC patients when compared to those from cisplatin-sensitive patients. Similarly, cisplatin-resistant OC cells also express higher levels of SH3RF2 than normal OC cells. Through in vitro and in vivo loss-of-function experiments, SH3RF2 is identified as a driver of cisplatin resistance, as evidenced by increases in cisplatin-induced cell apoptosis and DNA damage and decreases in cell proliferation induced by SH3RF2 depletion. Mechanistically, SH3RF2 can directly bind to the RNA-binding protein mRNA processing factor (RBPMS). RBPMS has been reported as an inhibitor of cisplatin resistance in OC. As a E3 ligase, SH3RF2 promotes the K48-linked ubiquitination of RBPMS to increase its proteasomal degradation and activator protein 1 (AP-1) transactivation. Impairments in RBPMS function reverse the inhibitory effect of SH3RF2 depletion on cisplatin resistance. Collectively, the SH3RF2-RBPMS-AP-1 axis is an important regulator in cisplatin resistance and inhibition of SH3RF2 may be a potential target in preventing cisplatin resistance.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

The Fra-1: Novel role in regulating extensive immune cell states and affecting inflammatory diseases

Fra-1(Fos-related antigen1), a member of transcription factor activator protein (AP-1), plays an important role in cell proliferation, apoptosis, differentiation, inflammation, oncogenesis and tumor metastasis. Accumulating evidence suggest that the malignancy and invasive ability of tumors can be significantly changed by directly targeting Fra-1. Besides, the effects of Fra-1 are gradually revealed in immune and inflammatory settings, such as arthritis, pneumonia, psoriasis and cardiovascular disease. These regulatory mechanisms that orchestrate immune and non-immune cells underlie Fra-1 as a potential therapeutic target for a variety of human diseases. In this review, we focus on the current knowledge of Fra-1 in immune system, highlighting its unique importance in regulating tissue homeostasis. In addition, we also discuss the possible critical intervention strategy in diseases, which also outline future research and development avenues.

Small Molecule 20S Proteasome Enhancer Regulates MYC Protein Stability and Exhibits Antitumor Activity in Multiple Myeloma

Despite the addition of several new agents to the armamentarium for the treatment of multiple myeloma (MM) in the last decade and improvements in outcomes, the refractory and relapsing disease continues to take a great toll, limiting overall survival. Therefore, additional novel approaches are needed to improve outcomes for MM patients. The oncogenic transcription factor MYC drives cell growth, differentiation and tumor development in many cancers. MYC protein levels are tightly regulated by the proteasome and an increase in MYC protein expression is found in more than 70% of all human cancers, including MM. In addition to the ubiquitin-dependent degradation of MYC by the 26S proteasome, MYC levels are also regulated in a ubiquitin-independent manner through the REGγ activation of the 20S proteasome. Here, we demonstrate that a small molecule activator of the 20S proteasome, TCH-165, decreases MYC protein levels, in a manner that parallels REGγ protein-mediated MYC degradation. TCH-165 enhances MYC degradation and reduces cancer cell growth in vitro and in vivo models of multiple myeloma by enhancing apoptotic signaling, as assessed by targeted gene expression analysis of cancer pathways. Furthermore, 20S proteasome enhancement is well tolerated in mice and dogs. These data support the therapeutic potential of small molecule-driven 20S proteasome activation for the treatments of MYC-driven cancers, especially MM.

Pyridaben induces mitochondrial dysfunction and leads to latent male reproductive abnormalities

As an organochloride pesticide, pyridaben (PDB) has been used on various plants, including fruiting plants and other crops. Because of emerging concerns regarding exposure to pesticides, the deleterious effects of PDB, including neuronal disease and reproductive abnormalities, have been determined. However, the intracellular mechanisms that contribute to the effects of PDB on the male reproductive system are still unknown. Therefore, we investigated the effects of PDB on the male reproductive organ, focusing on the testes using mouse testicular cells. We demonstrated that PDB suppressed cellular proliferation of mouse Leydig (TM3) and Sertoli (TM4) cells. Additionally, PDB disturbed calcium homeostasis via mitochondrial dysfunction and activation of endoplasmic reticulum stress. Furthermore, PDB inhibited transcriptional gene expression regarding the cell cycle, as well as steroidogenesis and spermatogenesis, which are the primary functions of TM3 and TM4 cells. Moreover, we verified via western blot analysis that PDB dysregulated the intracellular cell signaling pathways in mitochondrial-associated membranes and the Mapk/Pi3k pathway. Lastly, we confirmed that PDB efficiently suppressed the spheroid formation of TM3 and TM4 cells mimicking an in vivo environment. Collectively, the current results indicate that PDB induces testicular toxicity and male reproductive abnormalities by inducing mitochondrial dysfunction, endoplasmic reticulum stress and calcium imbalance.

CHOP and c-JUN up-regulate the mutant Z α1-antitrypsin, exacerbating its aggregation and liver proteotoxicity

α₁-Antitrypsin (AAT) encoded by the SERPINA1 gene is an acute-phase protein synthesized in the liver and secreted into the circulation. Its primary role is to protect lung tissue by inhibiting neutrophil elastase. The Z allele of SERPINA1 encodes a mutant AAT, named ATZ, that changes the protein structure and leads to its misfolding and polymerization, which cause endoplasmic reticulum (ER) stress and liver disease through a gain-of-function toxic mechanism. Hepatic retention of ATZ results in deficiency of one of the most important circulating proteinase inhibitors and predisposes to early-onset emphysema through a loss-of-function mechanism. The pathogenetic mechanisms underlying the liver disease are not completely understood. C/EBP-homologous protein (CHOP), a transcription factor induced by ER stress, was found among the most up-regulated genes in livers of PiZ mice that express ATZ and in human livers of patients homozygous for the Z allele. Compared with controls, juvenile PiZ/Chop ^-/- mice showed reduced hepatic ATZ and a transcriptional response indicative of decreased ER stress by RNA-Seq analysis. Livers of PiZ/Chop ^-/- mice also showed reduced SERPINA1 mRNA levels. By chromatin immunoprecipitations and luciferase reporter-based transfection assays, CHOP was found to up-regulate SERPINA1 cooperating with c-JUN, which was previously shown to up-regulate SERPINA1, thus aggravating hepatic accumulation of ATZ. Increased CHOP levels were detected in diseased livers of children homozygous for the Z allele. In summary, CHOP and c-JUN up-regulate SERPINA1 transcription and play an important role in hepatic disease by increasing the burden of proteotoxic ATZ, particularly in the pediatric population.

The bZIP Proteins of Oncogenic Viruses

Basic leucine zipper (bZIP) transcription factors (TFs) govern diverse cellular processes and cell fate decisions. The hallmark of the leucine zipper domain is the heptad repeat, with leucine residues at every seventh position in the domain. These leucine residues enable homo- and heterodimerization between ZIP domain α-helices, generating coiled-coil structures that stabilize interactions between adjacent DNA-binding domains and target DNA substrates. Several cancer-causing viruses encode viral bZIP TFs, including human T-cell leukemia virus (HTLV), hepatitis C virus (HCV) and the herpesviruses Marek’s disease virus (MDV), Epstein–Barr virus (EBV) and Kaposi’s sarcoma-associated herpesvirus (KSHV). Here, we provide a comprehensive review of these viral bZIP TFs and their impact on viral replication, host cell responses and cell fate.

Butylated hydroxytoluene induces dysregulation of calcium homeostasis and endoplasmic reticulum stress resulting in mouse Leydig cell death

Butylated hydroxytoluene (BHT) is a synthetic phenolic antioxidant that has been used as an additive for fat- or oil-containing foods. The exposure index value increases with extended usage of the chemical. Further, estimated total amount of BHT could exceed standard regulation, considering dietary intake or another exposure. Although BHT may induce side effects in reproductive systems, adequate research had not yet been performed to confirm them. In this study, we investigated the effects of BHT on mouse Leydig cells (TM3), which are components of testis. Our results indicated that BHT suppressed cellular proliferation and induced cell cycle arrest in TM3 cells. Moreover, BHT hampered cytosolic and mitochondrial calcium homeostasis in TM3 cells. Furthermore, BHT treatment led to endoplasmic reticulum (ER) stress and DNA fragmentation, simultaneously stimulating intrinsic apoptosis signal transduction. To elucidate the mode of action of BHT on Leydig cells, we performed western blot analysis and confirmed the activation of the PI3K/AKT and MAPK pathways. Collectively, our results demonstrated that BHT has toxic effects on mouse Leydig cells via induction of calcium dysregulation and ER-mitochondria dysfunction.

Inflammatory responses to a pathogenic West Nile virus strain

Background

West Nile virus (WNV) circulates across Australia and was referred to historically as Kunjin virus (WNV_KUN). WNV_KUN has been considered more benign than other WNV strains circulating globally. In 2011, a more virulent form of the virus emerged during an outbreak of equine arboviral disease in Australia.

Methods

To better understand the emergence of this virulent phenotype and the mechanism by which pathogenicity is manifested in its host, cells were infected with either the virulent strain (NSW2012), or less pathogenic historical isolates, and their innate immune responses compared by digital immune gene expression profiling. Two different cell systems were used: a neuroblastoma cell line (SK-N-SH cells) and neuronal cells derived from induced pluripotent stem cells (iPSCs).

Results

Significant innate immune gene induction was observed in both systems. The NSW2012 isolate induced higher gene expression of two genes (IL-8 and CCL2) when compared with cells infected with less pathogenic isolates. Pathway analysis of induced inflammation-associated genes also indicated generally higher activation in infected NSW2012 cells. However, this differential response was not paralleled in the neuronal cultures.

Conclusion

NSW2012 may have unique genetic characteristics which contributed to the outbreak. The data herein is consistent with the possibility that the virulence of NSW2012 is underpinned by increased induction of inflammatory genes.

c‑Jun/Ap‑1 is upregulated in an Ang II‑induced abdominal aortic aneurysm formation model and mediates Chop expression in mouse aortic smooth muscle cells

Abdominal aortic aneurysm (AAA) is an asymptomatic, potentially lethal disease whose ruptures have a high mortality rate. An effective pharmacological approach to decrease expansion or prevent the rupture of AAAs in humans remains lacking. Previous studies have suggested that activator protein 1 (c-Jun/AP-1) and C/EBP homologous protein (Chop) are involved in the development of AAA. The purpose of the present study was to investigate whether c-Jun/AP-1 mediates Chop overexpression in AAA. c-Jun/AP-1 and Chop protein levels were determined in an angiotensin II (Ang II)-induced AAA model using apolipoprotein E-deficient mice. Additionally, mouse aortic smooth muscle cells (MOVAS cell line) were treated with Ang II. Apoptosis was evaluated via TUNEL assay, MOVAS cell migration ability was assessed by monolayer wound healing assay and the levels of c-Jun/AP-1 and Chop were determined by western blotting, immunofluorescence and immunocytochemical assays. Following c-Jun silencing using c-Jun-specific small interfering (si)RNA, Chop expression was evaluated. Furthermore, chromatin immunoprecipitation (ChIP) was used to investigate whether c-Jun/Ap-1 binds directly to the DNA damage-inducible transcript 3 protein (Ddit3) promoter. It was observed that c-Jun/AP-1 and Chop were synchronously overexpressed in Ang II-induced AAA and Ang II-treated cells, and that apoptosis and migration were induced by Ang II. In addition, Chop was suppressed when c-Jun was silenced by targeted siRNA. Notably, the ChIP assay demonstrated that the DNA fragments pulled down by primary antibodies against c-Jun/Ap-1 were able to be amplified by (Ddit3) promoter-specific primers. c-Jun/AP-1 may therefore mediate Chop expression in MOVAS cells via Ddit3. These results suggested that c-Jun/AP-1 may be a novel target for AAA therapy.

Inducible Intestine-Specific Expression of krasV12 Triggers Intestinal Tumorigenesis In Transgenic Zebrafish

KRAS mutations are a major risk factor in colorectal cancers. In particular, a point mutation of KRAS of amino acid 12, such as KRAS^V12, renders it stable activity in oncogenesis. We found that kras^V12 promotes intestinal carcinogenesis by generating a transgenic zebrafish line with inducible kras^V12 expression in the intestine, Tg(ifabp:EGFP-kras^V12). The transgenic fish generated exhibited significant increases in the rates of intestinal epithelial outgrowth, proliferation, and cross talk in the active Ras signaling pathway involving in epithelial-mesenchymal transition (EMT). These results provide in vivo evidence of Ras pathway activation via kras^V12 overexpression. Long-term transgenic expression of kras^V12 resulted in enteritis, epithelial hyperplasia, and tubular adenoma in adult fish. This was accompanied by increased levels of the signaling proteins p-Erk and p-Akt and by downregulation of the EMT marker E-cadherin. Furthermore, we also observed a synergistic effect of kras^V12 expression and dextran sodium sulfate treatment to enhance intestinal tumor in zebrafish. Our results demonstrate that kras^V12 overexpression induces intestinal tumorigenesis in zebrafish, which mimics intestinal tumor formation in humans. Thus, our transgenic zebrafish may provide a valuable in vivo platform that can be used to investigate tumor initiation and anticancer drugs for gastrointestinal cancers.

3-Bromopyruvate enhances TRAIL-induced apoptosis in human nasopharyngeal carcinoma cells through CHOP-dependent upregulation of TRAIL-R2

Past reports have shown that the sensitivity of cancer cells to TRAIL-induced apoptosis is related to their expression of TRAIL-death receptors on the cell surface. However, the level of TRAIL-death receptors expression on cancer cells is always low. Our previous research showed that nasopharyngeal carcinoma (NPC) cells have a poor sensitivity to low doses of TRAIL. Here, we evaluated combined treatment with the energy inhibitor 3-bromopyruvate (3BP) and TRAIL as a method to produce an increased apoptotic response in NPC cells. The results showed that 3BP and TRAIL together produced higher cytotoxicity and increased TRAIL-R2 expression in NPC cells compared with the effects of either 3BP or TRAIL alone. These findings led us to hypothesize that 3BP may sensitize NPC cells to TRAIL. 3BP is a metabolic blocker that inhibits hexokinase II activity, suppresses ATP production, and induces endoplasmic reticulum (ER) stress. Our results showed that 3BP also activated AMP-activated protein kinase, which we found to play an important role in the induction of ER stress by 3BP. Furthermore, the induction of TRAIL-R2 expression and the sensitization of the NPC cells to TRAIL by 3BP were reduced when we inhibited the expression of CHOP. Taken together, our results showed that a low dose of 3BP sensitized NPC cells to TRAIL-induced apoptosis by the upregulation of CHOP, which was mediated by the activation of AMP-activated protein kinase and ER stress. The results showed that 3BP is a promising candidate agent for enhancing the therapeutic response to TRAIL in NPC.

Together JUN and DDIT3 (CHOP) control retinal ganglion cell death after axonal injury

BACKGROUND

Optic nerve injury is an important pathological component in neurodegenerative diseases such as traumatic optic neuropathies and glaucoma. The molecular signaling pathway(s) critical for retinal ganglion cell (RGC) death after axonal insult, however, is/are not fully defined. RGC death after axonal injury is known to occur by BAX-dependent apoptosis. Two transcription factors JUN (the canonical target of JNK) and DDIT3 (CHOP; a key mediator of the endoplasmic reticulum stress response) are known to be important apoptotic signaling molecules after axonal injury, including in RGCs. However, neither Jun nor Ddit3 deficiency provide complete protection to RGCs after injury. Since Jun and Ddit3 are important apoptotic signaling molecules, we sought to determine if their combined deficiency might provide additive protection to RGCs after axonal injury.

METHODS

To determine if DDIT3 regulated the expression of JUN after an axonal insult, mice deficient for Ddit3 were examined after optic nerve crush (ONC). In order to critically test the importance of these genes in RGC death after axonal injury, RGC survival was assessed at multiple time-points after ONC (14, 35, 60, and 120 days after injury) in Jun, Ddit3, and combined Jun/Ddit3 deficient mice. Finally, to directly assess the role of JUN and DDIT3 in axonal degeneration, compound actions potentials were recorded from Jun, Ddit3, and Jun/Ddit3 deficient mice after ONC.

RESULTS

Single and combined deficiency of Jun and Ddit3 did not appear to alter gross retinal morphology. Ddit3 deficiency did not alter expression of JUN after axonal injury. Deletion of both Jun and Ddit3 provided significantly greater long-term protection to RGCs as compared to Jun or Ddit3 deficiency alone. Finally, despite the profound protection to RGC somas provided by the deficiency of Jun plus Ddit3, their combined loss did not lessen axonal degeneration.

CONCLUSIONS

These results suggest JUN and DDIT3 are independently regulated pro-death signaling molecules in RGCs and together account for the vast majority of apoptotic signaling in RGCs after axonal injury. Thus, JUN and DDIT3 may represent key molecular hubs that integrate upstream signaling events triggered by axonal injury with downstream transcriptional events that ultimately culminate in RGC apoptosis.

Endoplasmic reticulum stress inhibition attenuates hypertensive chronic kidney disease through reduction in proteinuria

Endoplasmic reticulum (ER) stress is implicated in chronic kidney disease (CKD) development in patients and in animal models. Here we show that ER stress inhibition through 4-phenylbutyric acid (4-PBA) administration decreases blood pressure, albuminuria, and tubular casts in an angiotensin II/deoxycorticosterone acetate/salt murine model of CKD. Lower albuminuria in 4-PBA-treated mice was associated with higher levels of cubilin protein in renal tissue membrane fractions. 4-PBA decreased renal interstitial fibrosis, renal CD3⁺ T-cell and macrophage infiltration, mRNA expression of TGFβ1, Wnt signaling molecules, and ER stress-induced pro-inflammatory genes. CHOP deficient mice that underwent this model of CKD developed hypertension comparable to wild type mice, but had less albuminuria and tubular casts. CHOP deficiency resulted in higher nephrin levels and decreased glomerulosclerosis compared to wild type mice; this effect was accompanied by lower macrophage infiltration and fibrosis. Our findings portray ER stress inhibition as a means to alleviate hypertensive CKD by preserving glomerular barrier integrity and tubular function. These results demonstrate ER stress modulation as a novel target for preserving renal function in hypertensive CKD.

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.

Candida albicans infection leads to barrier breakdown and a MAPK/NF-κB mediated stress response in the intestinal epithelial cell line C2BBe1

Intestinal epithelial cells (IEC) form a tight barrier to the gut lumen. Paracellular permeability of the intestinal barrier is regulated by tight junction proteins and can be modulated by microorganisms and other stimuli. The polymorphic fungus Candida albicans, a frequent commensal of the human mucosa, has the capacity of traversing this barrier and establishing systemic disease within the host. Infection of polarized C2BBe1 IEC with wild-type C. albicans led to a transient increase of transepithelial electric resistance (TEER) before subsequent barrier disruption, accompanied by a strong decline of junctional protein levels and substantial, but considerably delayed cytotoxicity. Time-resolved microarray-based transcriptome analysis of C. albicans challenged IEC revealed a prominent role of NF-κB and MAPK signalling pathways in the response to infection. Hence, we inferred a gene regulatory network based on differentially expressed NF-κB and MAPK pathway components and their predicted transcriptional targets. The network model predicted activation of GDF15 by NF-κB was experimentally validated. Furthermore, inhibition of NF-κB activation in C. albicans infected C2BBe1 cells led to enhanced cytotoxicity in the epithelial cells. Taken together our study identifies NF-κB activation as an important protective signalling pathway in the response of epithelial cells to C. albicans.

Resveratrol via sirtuin-1 downregulates RE1-silencing transcription factor (REST) expression preventing PCB-95-induced neuronal cell death

Resveratrol (3,5,4'-trihydroxystilbene) (RSV), a polyphenol widely present in plants, exerts a neuroprotective function in several neurological conditions; it is an activator of class III histone deacetylase sirtuin1 (SIRT1), a crucial regulator in the pathophysiology of neurodegenerative diseases. By contrast, the RE1-silencing transcription factor (REST) is involved in the neurotoxic effects following exposure to polychlorinated biphenyl (PCB) mixture A1254. The present study investigated the effects of RSV-induced activation of SIRT1 on REST expression in SH-SY5Y cells. Further, we investigated the possible relationship between the non-dioxin-like (NDL) PCB-95 and REST through SIRT1 to regulate neuronal death in rat cortical neurons. Our results revealed that RSV significantly decreased REST gene and protein levels in a dose- and time-dependent manner. Interestingly, overexpression of SIRT1 reduced REST expression, whereas EX-527, an inhibitor of SIRT1, increased REST expression and blocked RSV-induced REST downregulation. These results suggest that RSV downregulates REST through SIRT1. In addition, RSV enhanced activator protein 1 (AP-1) transcription factor c-Jun expression and its binding to the REST promoter gene. Indeed, c-Jun knockdown reverted RSV-induced REST downregulation. Intriguingly, in SH-SY5Y cells and rat cortical neurons the NDL PCB-95 induced necrotic cell death in a concentration-dependent manner by increasing REST mRNA and protein expression. In addition, SIRT1 knockdown blocked RSV-induced neuroprotection in rat cortical neurons treated with PCB-95. Collectively, these results indicate that RSV via SIRT1 activates c-Jun, thereby reducing REST expression in SH-SY5Y cells under physiological conditions and blocks PCB-95-induced neuronal cell death by activating the same SIRT1/c-Jun/REST pathway.

Distinct mechanisms of inadequate erythropoiesis induced by tumor necrosis factor alpha or malarial pigment

The role of infection in erythropoietic dysfunction is poorly understood. In children with P. falciparum malaria, the by-product of hemoglobin digestion in infected red cells (hemozoin) is associated with the severity of anemia which is independent of circulating levels of the inflammatory cytokine tumor necrosis alpha (TNF-α). To gain insight into the common and specific effects of TNF-α and hemozoin on erythropoiesis, we studied the gene expression profile of purified primary erythroid cultures exposed to either TNF-α (10ng/ml) or to hemozoin (12.5μg/ml heme units) for 24 hours. Perturbed gene function was assessed using co-annotation of associated gene ontologies and expression of selected genes representative of the profile observed was confirmed by real time PCR (rtPCR). The changes in gene expression induced by each agent were largely distinct; many of the genes significantly modulated by TNF-α were not affected by hemozoin. The genes modulated by TNF-α were significantly enriched for those encoding proteins involved in the control of type 1 interferon signalling and the immune response to viral infection. In contrast, genes induced by hemozoin were significantly enriched for functional roles in regulation of transcription and apoptosis. Further analyses by rtPCR revealed that hemozoin increases expression of transcription factors that form part of the integrated stress response which is accompanied by reduced expression of genes involved in DNA repair. This study confirms that hemozoin induces cellular stress on erythroblasts that is additional to and distinct from responses to inflammatory cytokines and identifies new genes that may be involved in the pathogenesis of severe malarial anemia. More generally the respective transcription profiles highlight the varied mechanisms through which erythropoiesis may be disrupted during infectious disease.

MAPK signaling triggers transcriptional induction of cFOS during amino acid limitation of HepG2 cells

Amino acid (AA) deprivation in mammalian cells activates a collection of signaling cascades known as the AA response (AAR), which is characterized by transcriptional induction of stress-related genes, including FBJ murine osteosarcoma viral oncogene homolog (cFOS). The present study established that the signaling mechanism underlying the AA-dependent transcriptional regulation of the cFOS gene in HepG2 human hepatocellular carcinoma cells is independent of the classic GCN2-eIF2-ATF4 pathway. Instead, a RAS-RAF-MEK-ERK cascade mediates AAR signaling to the cFOS gene. Increased cFOS transcription is observed from 4-24 h after AAR-activation, exhibiting little or no overlap with the rapid and transient increase triggered by the well-known serum response. Furthermore, serum is not required for the AA-responsiveness of the cFOS gene and no phosphorylation of promoter-bound serum response factor (SRF) is observed. The ERK-phosphorylated transcription factor E-twenty six-like (p-ELK1) is increased in its association with the cFOS promoter after activation of the AAR. This research identified cFOS as a target of the AAR and further highlights the importance of AA-responsive MAPK signaling in HepG2 cells.

Targeting death receptors for TRAIL by agents designed by Mother Nature

Selective killing of cancer cells is one of the major goals of cancer therapy. Although chemotherapeutic agents are being used for cancer treatment, they lack selectivity toward tumor cells. Among the six different death receptors (DRs) identified to date, DR4 and DR5 are selectively expressed on cancer cells. Therefore, unlike chemotherapeutic agents, these receptors can potentially mediate selective killing of tumor cells. In this review we outline various nutraceuticals derived from 'Mother Nature' that can upregulate DRs and thus potentiate apoptosis. These nutraceuticals increase tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of cancer cells through different mechanisms. First, nutraceuticals have been found to induce DRs through the upregulation of various signaling molecules. Second, nutraceuticals can downregulate tumor cell-survival pathways. Third, nutraceuticals alone have been found to activate cell-death pathways. Although both TRAIL and agonistic antibodies against DR4 and DR5 are in clinical trials, combination with nutraceuticals is likely to boost their anticancer potential.

CHOP mediates ASPP2-induced autophagic apoptosis in hepatoma cells by releasing Beclin-1 from Bcl-2 and inducing nuclear translocation of Bcl-2

Apoptosis-stimulating protein of p53-2 (ASPP2) induces apoptosis by promoting the expression of pro-apoptotic genes via binding to p53 or p73; however, the exact mechanisms by which ASPP2 induces apoptotic death in hepatoma cells are still unclear. Here, we show that the transient overexpression of ASPP2 induces autophagic apoptosis in hepatoma cells by promoting p53- or p73-independent C/EBP homologous protein (CHOP) expression. CHOP expression decreases the expression of Bcl-2; this change releases Beclin-1 from cytoplasmic Bcl-2-Beclin-1 complexes and allows it to initiate autophagy. However, transient overexpression of Beclin-1 can induce autophagy but not apoptosis. Our results show that ASPP2 induces the expression of damage-regulated autophagy modulator (DRAM), another critical factor that cooperates with free Beclin-1 to induce autophagic apoptosis. The effect of CHOP on the translocation and sequestration of Bcl-2 in the nucleus, which requires the binding of Bcl-2 to ASPP2, is also critical for ASPP2-induced autophagic apoptosis. Although the role of nuclear ASPP2–Bcl-2 complexes is still unclear, our results suggest that nuclear ASPP2 can prevent the translocation of the remaining Bcl-2 to the cytoplasm by binding to Bcl-2 in a CHOP-dependent manner, and this effect also contributes to Beclin-1-initiated autophagy. Thus, CHOP is critical for mediating ASPP2-induced autophagic apoptosis by decreasing Bcl-2 expression and maintaining nuclear ASPP2–Bcl-2 complexes. Our results, which define a mechanism whereby ASPP2 overexpression induces autophagic apoptosis, open a new avenue for promoting autophagy in treatments to cure hepatocellular carcinoma.

Abnormal chondrocyte apoptosis in the cartilage growth plate is influenced by genetic background and deletion of CHOP in a targeted mouse model of pseudoachondroplasia

Pseudoachondroplasia (PSACH) is an autosomal dominant skeletal dysplasia caused by mutations in cartilage oligomeric matrix protein (COMP) and characterised by short limbed dwarfism and early onset osteoarthritis. Mouse models of PSACH show variable retention of mutant COMP in the ER of chondrocytes, however, in each case a different stress pathway is activated and the underlying disease mechanisms remain largely unknown. T585M COMP mutant mice are a model of moderate PSACH and demonstrate a mild ER stress response. Although mutant COMP is not retained in significant quantities within the ER of chondrocytes, both BiP and the pro-apoptotic ER stress-related transcription factor CHOP are mildly elevated, whilst bcl-2 levels are decreased, resulting in increased and spatially dysregulated chondrocyte apoptosis. To determine whether the abnormal chondrocyte apoptosis observed in the growth plate of mutant mice is CHOP-mediated, we bred T585M COMP mutant mice with CHOP-null mice to homozygosity, and analysed the resulting phenotype. Although abnormal apoptosis was alleviated in the resting zone following CHOP deletion, the mutant growth plates were generally more disorganised. Furthermore, the bone lengths of COMP mutant CHOP null mice were significantly shorter at 9 weeks of age when compared to the COMP mutant mice, including a significant difference in the skull length. Overall, these data demonstrate that CHOP-mediated apoptosis is an early event in the pathobiology of PSACH and suggest that the lack of CHOP, in conjunction with a COMP mutation, may lead to aggravation of the skeletal phenotype via a potentially synergistic effect on endochondral ossification.

Efficient photodynamic therapy on human retinoblastoma cell lines

Photodynamic therapy (PDT) has shown to be a promising technique to treat various forms of malignant neoplasia. The photodynamic eradication of the tumor cells is achieved by applying a photosensitizer either locally or systemically and following local activation through irradiation of the tumor mass with light of a specific wavelength after a certain time of incubation. Due to preferential accumulation of the photosensitizer in tumor cells, this procedure allows a selective inactivation of the malignant tumor while sparing the surrounding tissue to the greatest extent. These features and requirements make the PDT an attractive therapeutic option for the treatment of retinoblastoma, especially when surgical enucleation is a curative option. This extreme solution is still in use in case of tumours that are resistant to conventional chemotherapy or handled too late due to poor access to medical care in less advanced country. In this study we initially conducted in-vitro investigations of the new cationic water-soluble photo sensitizer tetrahydroporphyrin-tetratosylat (THPTS) regarding its photodynamic effect on human Rb-1 and Y79 retinoblastoma cells. We were able to show, that neither the incubation with THPTS without following illumination, nor the sole illumination showed a considerable effect on the proliferation of the retinoblastoma cells, whereas the incubation with THPTS combined with following illumination led to a maximal cytotoxic effect on the tumor cells. Moreover the phototoxicity was lower in normal primary cells from retinal pigmented epithelium demonstrating a higher phototoxic effect of THPTS in cancer cells than in this normal retinal cell type. The results at hand form an encouraging foundation for further in-vivo studies on the therapeutic potential of this promising photosensitizer for the eyeball and vision preserving as well as potentially curative therapy of retinoblastoma.

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

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

Xenobiotic perturbation of ER stress and the unfolded protein response

The proper folding, assembly, and maintenance of cellular proteins is a highly regulated process and is critical for cellular homeostasis. Multiple cellular compartments have adapted their own systems to ensure proper protein folding, and quality control mechanisms are in place to manage stress due to the accumulation of unfolded proteins. When the accumulation of unfolded proteins exceeds the capacity to restore homeostasis, these systems can result in a cell death response. Unfolded protein accumulation in the endoplasmic reticulum (ER) leads to ER stress with activation of the unfolded protein response (UPR) governed by the activating transcription factor 6 (ATF6), inositol requiring enzyme-1 (IRE1), and PKR-like endoplasmic reticulum kinase (PERK) signaling pathways. Many xenobiotics have been shown to influence ER stress and UPR signaling with either pro-survival or pro-death features. The ultimate outcome is dependent on many factors including the mechanism of action of the xenobiotic, concentration of xenobiotic, duration of exposure (acute vs. chronic), cell type affected, nutrient levels, oxidative stress, state of differentiation, and others. Assessing perturbations in activation or inhibition of ER stress and UPR signaling pathways are likely to be informative parameters to measure when analyzing mechanisms of action of xenobiotic-induced toxicity.

Acidosis blocks CCAAT/enhancer-binding protein homologous protein (CHOP)- and c-Jun-mediated induction of p53-upregulated mediator of apoptosis (PUMA) during amino acid starvation

Cancer cells must avoid succumbing to a variety of noxious conditions within their surroundings. Acidosis is one such prominent feature of the tumor microenvironment that surprisingly promotes tumor survival and progression. We recently reported that acidosis prevents apoptosis of starved or stressed lymphoma cells through regulation of several Bcl-2 family members (Ryder et al., JBC, 2012). Mechanistic studies in that work focused on the acid-mediated upregulation of anti-apoptotic Bcl-2 and Bcl-xL, while additionally showing inhibition of glutamine starvation-induced expression of pro-apoptotic PUMA by acidosis. Herein we report that amino acid (AA) starvation elevates PUMA, an effect that is blocked by extracellular acidity. Knockdown studies confirm that PUMA induction during AA starvation requires expression of both CHOP and c-Jun. Interestingly, acidosis strongly attenuates AA starvation-mediated c-Jun expression, which correlates with PUMA repression. As c-Jun exerts a tumor suppressive function in this and other contexts, its inhibition by acidosis has broader implications for survival of cancer cells in the acidic tumor milieu.

Involvement of de novo ceramide synthesis in gamma-tocopherol and gamma-tocotrienol-induced apoptosis in human breast cancer cells

SCOPE

This study further examines mechanisms involved in the pro-apoptotic action of gamma-tocopherol (γT) and gamma-tocotrienol (γT3) in human breast cancer cell lines.

METHODS AND RESULTS

γT upregulates phospho-JNK (pJNK), CCAAT/enhancer-binding protein homologous protein (CHOP), and death receptor-5 (DR5) protein expression as detected by Western blot assays. siRNA knockdown of JNK, CHOP, or DR5 shows that γT-induced apoptosis is JNK/CHOP/DR5 signaling dependent, which is similar to γT3-mediated apoptotic signaling. Furthermore, both γT and γT3 induce increased levels of cellular ceramides and dihydroceramides as determined by LC-MS/MS analyses. Inhibition of de novo ceramide synthesis using chemical inhibitors blocked the ability of γT and γT3 to induce apoptosis as detected by Annexin V-FITC/PI assay and to activate JNK/CHOP/DR5 pro-apoptotic signaling thereby demonstrating the involvement of de novo ceramide synthesis in γT- and γT3-induced apoptosis.

CONCLUSION

Taken together, data show that both γT and γT3 induce apoptosis via de novo ceramide synthesis dependent activation of JNK/CHOP/DR5 pro-apoptotic signaling.

Sensitization of TRAIL-induced cell death by 20(S)-ginsenoside Rg3 via CHOP-mediated DR5 upregulation in human hepatocellular carcinoma cells

The TRAIL pathway is a potential therapeutic target for anticancer drugs due to selective cytotoxicity in cancer cells. Despite considerable promise, TRAIL or TRAIL receptor agonists have been used thus far with limited success in multiple clinical trials, in part due to acquired TRAIL resistance during chemotherapeutic treatment. Hepatocellular carcinoma (HCC) is a common solid tumor and the third leading cause of cancer-related death worldwide. Classical chemotherapy is not effective for HCC treatment and targeted therapy is limited to sorafenib. Isolated from Panax ginseng CA Meyer, 20(S)-ginsenoside Rg3 is a steroidal saponin with high pharmacologic activity that has been shown to sensitize cells to some chemotherapeutic agents. We investigated the sensitizing effect of Rg3 on TRAIL-induced cell death in HCC cells. We show Rg3 is capable of promoting TRAIL-induced apoptosis in a number of HCC cell lines, including HepG2, SK-Hep1, Huh-7, and Hep3B, but not in normal HL-7702 hepatocytes, indicating that Rg3 sensitization to TRAIL may be specific to cancer cells. Mechanistically, we found that Rg3 upregulates DR5 expression at the transcriptional level. DR5 upregulation in this case is mediated by C/EBP homology protein (CHOP), an important endoplasmic reticulum stress responsive protein. Furthermore, Rg3 is well tolerated and enhances the therapeutic efficacy of TRAIL in mouse xenograft models, suggesting that chemosensitization also occurs in vivo. Taken together, our study identifies Rg3 as a novel anticancer therapeutic agent and supports the further development of Rg3 as a chemosensitizer in combined therapy with TRAIL.

Midkine upregulates MICA/B expression in human gastric cancer cells and decreases natural killer cell cytotoxicity

Midkine (MK) is a heparin-binding growth factor overexpressed in various human cancers. In the current study, a positive correlation was observed between MK expression and MICA/B serum levels of gastric cancer patients. In addition, MK transfection significantly increased MICA/B expression in gastric cancer cells. The soluble MICA/B expression was also elevated. Furthermore, MK transfection inhibited CD107a and Granzyme B expression, thereby suppressing the natural killer (NK) cell cytotoxicity in vitro. The phosphorylation of p38 MAPK and its promotion of CHOP expression were also observed after MK treatment and transfection. CHOP was indirectly bound to the MICA/B promoter region by interacting with AP-1, leading to MICA/B transcription. Overall, the current study shows that MK expression in tumor cells indirectly suppresses NK cytotoxicity by inducing MICA/B expression and suppressing NKG2D expression.

CHOP potentially co-operates with FOXO3a in neuronal cells to regulate PUMA and BIM expression in response to ER stress

Endoplasmic reticulum (ER) stress-induced apoptosis has been implicated in various neurodegenerative diseases including Parkinson Disease, Alzheimer Disease and Huntington Disease. PUMA (p53 upregulated modulator of apoptosis) and BIM (BCL2 interacting mediator of cell death), pro-apoptotic BH3 domain-only, BCL2 family members, have previously been shown to regulate ER stress-induced cell death, but the upstream signaling pathways that regulate this response in neuronal cells are incompletely defined. Consistent with previous studies, we show that both PUMA and BIM are induced in response to ER stress in neuronal cells and that transcriptional induction of PUMA regulates ER stress-induced cell death, independent of p53. CHOP (C/EBP homologous protein also known as GADD153; gene name Ddit3), a critical initiator of ER stress-induced apoptosis, was found to regulate both PUMA and BIM expression in response to ER stress. We further show that CHOP knockdown prevents perturbations in the AKT (protein kinase B)/FOXO3a (forkhead box, class O, 3a) pathway in response to ER stress. CHOP co-immunoprecipitated with FOXO3a in tunicamycin treated cells, suggesting that CHOP may also regulate other pro-apoptotic signaling cascades culminating in PUMA and BIM activation and cell death. In summary, CHOP regulates the expression of multiple pro-apoptotic BH3-only molecules through multiple mechanisms, making CHOP an important therapeutic target relevant to a number of neurodegenerative conditions.

Stress-induced C/EBP homology protein (CHOP) represses MyoD transcription to delay myoblast differentiation

When mouse myoblasts or satellite cells differentiate in culture, the expression of myogenic regulatory factor, MyoD, is downregulated in a subset of cells that do not differentiate. The mechanism involved in the repression of MyoD expression remains largely unknown. Here we report that a stress-response pathway repressing MyoD transcription is transiently activated in mouse-derived C2C12 myoblasts growing under differentiation-promoting conditions. We show that phosphorylation of the α subunit of the translation initiation factor 2 (eIF2α) is followed by expression of C/EBP homology protein (CHOP) in some myoblasts. ShRNA-driven knockdown of CHOP expression caused earlier and more robust differentiation, whereas its constitutive expression delayed differentiation relative to wild type myoblasts. Cells expressing CHOP did not express the myogenic regulatory factors MyoD and myogenin. These results indicated that CHOP directly repressed the transcription of the MyoD gene. In support of this view, CHOP associated with upstream regulatory region of the MyoD gene and its activity reduced histone acetylation at the enhancer region of MyoD. CHOP interacted with histone deacetylase 1 (HDAC1) in cells. This protein complex may reduce histone acetylation when bound to MyoD regulatory regions. Overall, our results suggest that the activation of a stress pathway in myoblasts transiently downregulate the myogenic program.

Oncogenic Ras and B-Raf proteins positively regulate death receptor 5 expression through co-activation of ERK and JNK signaling

Oncogenic mutations of ras and B-raf frequently occur in many cancer types and are critical for cell transformation and tumorigenesis. Death receptor 5 (DR5) is a cell surface pro-apoptotic death receptor for tumor necrosis factor-related apoptosis-inducing ligand and has been targeted in cancer therapy. The current study has demonstrated induction of DR5 expression by the oncogenic proteins Ras and B-Raf and revealed the underlying mechanisms. We demonstrated that both Ras and B-Raf induce DR5 expression by enforced expression of oncogenic Ras (e.g. H-Ras12V or K-Ras12V) or B-Raf (i.e. V600E) in cells and by analyzing gene expression array data generated from cancer cell lines and from human cancer tissues. This finding is further supported by our results that knockdown of endogenous K-Ras or B-Raf (V600E) reduced the expression of DR5. Importantly, we have elucidated that Ras induces DR5 expression through co-activation of ERK/RSK and JNK signaling pathways and subsequent cooperative effects among the transcriptional factors CHOP, Elk1, and c-Jun to enhance DR5 gene transcription. Moreover, we found that the majority of cancer cell lines highly sensitive to the DR5 agonistic antibody AMG655 have either Ras or B-Raf mutations. Our findings warrant further study on the biology of DR5 regulation by Ras and B-Raf, which may provide new insight into the biology of Ras and B-Raf, and on the potential impact of Ras or B-Raf mutations on the outcome of DR5-targeted cancer therapy.

Hepatitis E virus ORF2 protein activates the pro-apoptotic gene CHOP and anti-apoptotic heat shock proteins

Background

Hepatitis E virus (HEV) is a non-enveloped plus-strand RNA virus that causes acute hepatitis. The capsid protein open reading frame 2 (ORF2) is known to induce endoplasmic reticulum stress in ORF2 expressing cells.

Methodology/Principal Findings

In this study we found that HEV ORF2 activates the expression of the pro-apoptotic gene C/EBP homologous protein (CHOP). ORF2 stimulates the CHOP promoter mainly through AARE (amino acid response elements) and to a minor extent the ERSE (endoplasmic reticulum stress response elements). Activating transcription factor 4 (ATF4) protein binds and activates the AARE regulatory sites of the CHOP promoter. ORF2 expression also leads to increased phosphorylation of eukaryotic initiation factor 2 alpha (eIF2α) that in turn initiates the translation of ATF4 mRNA. The pro-apoptotic gene CHOP is an important trigger to initiate endoplasmic reticulum stress induced apoptosis. However, the activation of CHOP by ORF2 in this study did not induce apoptosis, nor did BCL2-associated X protein (Bax) translocate to mitochondria. Microarray analysis revealed an ORF2 specific increased expression of chaperones Hsp72, Hsp70B', and co-chaperone Hsp40. Co-immunoprecipitation (Co-IP) and in silico molecular docking analysis suggests that HEV ORF2 interacts with Hsp72. In addition, Hsp72 shows nuclear accumulation in ORF2 expressing cells.

Conclusions/Significance

These data provide new insight into simultaneously occurring counter-acting effects of HEV ORF2 that may be part of a strategy to prevent host suicide before completion of the viral replication cycle.

Gene expression profiling reveals the defining features of the classical, intermediate, and nonclassical human monocyte subsets

New official nomenclature subdivides human monocytes into 3 subsets: the classical (CD14(++)CD16(-)), intermediate (CD14(++)CD16(+)), and nonclassical (CD14(+)CD16(++)) monocytes. This introduces new challenges, as monocyte heterogeneity is mostly understood based on 2 subsets, the CD16(-) and CD16(+) monocytes. Here, we comprehensively defined the 3 circulating human monocyte subsets using microarray, flow cytometry, and cytokine production analysis. We find that intermediate monocytes expressed a large majority (87%) of genes and surface proteins at levels between classical and nonclassical monocytes. This establishes their intermediary nature at the molecular level. We unveil the close relationship between the intermediate and nonclassic monocytes, along with features that separate them. Intermediate monocytes expressed highest levels of major histocompatibility complex class II, GFRα2 and CLEC10A, whereas nonclassic monocytes were distinguished by cytoskeleton rearrangement genes, inflammatory cytokine production, and CD294 and Siglec10 surface expression. In addition, we identify new features for classic monocytes, including AP-1 transcription factor genes, CLEC4D and IL-13Rα1 surface expression. We also find circumstantial evidence supporting the developmental relationship between the 3 subsets, including gradual changes in maturation genes and surface markers. By comprehensively defining the 3 monocyte subsets during healthy conditions, we facilitate target identification and detailed analyses of aberrations that may occur to monocyte subsets during diseases.

Peroxisome proliferator-activated receptor-γ stimulates 11β-hydroxysteroid dehydrogenase type 1 in rat vascular smooth muscle cells

Glucocorticoids are metabolized in vascular tissue by two types of 11β-hydroxysteroid dehydrogenases (11HSD1, 11HSD2) and thus these enzymes are considered to be important factors that modulate the diverse and complex effects of glucocorticoids on cardiovascular function. The present study evaluated the effect of peroxisome proliferator-activated receptor-γ (PPARγ) agonist pioglitazone on 11HSD1 vascular smooth muscle cells (VSMC) and compared the effect with that of corticosterone. Using primary cultures of VSMC derived from rat aorta, we showed that pioglitazone significantly increases 11HSD1 activity and mRNA expression in a dose-dependent manner with EC(50) 243 nM and that this effect is not blocked by RU 486, an antagonist of the glucocorticoid receptor. In contrast, corticosterone had no effect on 11HSD1. Pioglitazone positively regulated transcription of two CCAAT/enhancer-binding proteins (C/EBPs), specifically C/EBPα a potent activator of 11HSD1 gene transcription in some cells types, and C/EBPζ, whereas C/EBPβ and C/EBPδ were not changed. In contrast, corticosterone stimulated the expression of C/EBPβ and C/EBPδ, but the levels of C/EBPα and C/EBPζ were not changed. In conclusion, activation of PPARγ in VSMC up-regulates vascular 11HSD1 and thus reactivates 11-oxo metabolites to biologically active glucocorticoids through a mechanism that seems to involve C/EBPα and C/EBPζ. Our data provide one of the possible explanations for PPARγ agonists' effects on the cardiovascular system.

XB130, a novel adaptor protein, promotes thyroid tumor growth

Adaptor proteins with multimodular structures can participate in the regulation of various cellular functions. We have cloned a novel adaptor protein, XB130, which binds the p85α subunit of phosphatidyl inositol 3-kinase and subsequently mediates signaling through RET/PTC in TPC-1 thyroid cancer cells. In the present study, we sought to determine the role of XB130 in the tumorigenesis in vivo and in related molecular mechanisms. In WRO thyroid cancer cells, knockdown of XB130 using small interfering RNA inhibited G(1)-S phase progression, induced spontaneous apoptosis, and enhanced intrinsic and extrinsic apoptotic stimulus-induced cell death. Growth of tumors in nude mice formed from XB130 shRNA stably transfected WRO cells were significantly reduced, with decreased cell proliferation and increased apoptosis. Microarray analysis identified 246 genes significantly changed in XB130 shRNA transfected cells. Among them, 57 genes are related to cell proliferation or survival, including many transcription regulators. Ingenuity Pathway Analysis showed that the top-ranked disease related to XB130 is cancer, and the top molecular and cellular functions are cellular growth and proliferation and cell cycle. A human thyroid tissue microarray study identified expression of XB130 in normal thyroid tissue as well as in human thyroid carcinomas. These observations suggest that the expression of XB130 in these cancer cells may affect cell proliferation and survival by controlling the expression of multiple genes, especially transcription regulators.

Transcriptional profiling of intrinsic PNS factors in the postnatal mouse

Neurons in the peripheral nervous system (PNS) display a higher capacity to regenerate after injury than those in the central nervous system, suggesting cell specific transcriptional modules underlying axon growth and inhibition. We report a systems biology based search for PNS specific transcription factors (TFs). Messenger RNAs enriched in dorsal root ganglion (DRG) neurons compared to cerebellar granule neurons (CGNs) were identified using subtractive hybridization and DNA microarray approaches. Network and transcription factor binding site enrichment analyses were used to further identify TFs that may be differentially active. Combining these techniques, we identified 32 TFs likely to be enriched and/or active in the PNS. Twenty-five of these TFs were then tested for an ability to promote CNS neurite outgrowth in an overexpression screen. Real-time PCR and immunohistochemical studies confirmed that one representative TF, STAT3, is intrinsic to PNS neurons, and that constitutively active STAT3 is sufficient to promote CGN neurite outgrowth.

Role of endoplasmic reticulum stress in alpha-TEA mediated TRAIL/DR5 death receptor dependent apoptosis

Background

α-TEA (RRR-α-tocopherol ether-linked acetic acid analog), a derivative of RRR-α-tocopherol (vitamin E) exhibits anticancer actions in vitro and in vivo in variety of cancer types. The objective of this study was to obtain additional insights into the mechanisms involved in α-TEA induced apoptosis in human breast cancer cells.

Methodology/Principal Findings

α-TEA induces endoplasmic reticulum (ER) stress as indicated by increased expression of CCAAT/enhancer binding protein homologous protein (CHOP) as well as by enhanced expression or activation of specific markers of ER stress such as glucose regulated protein (GRP78), phosphorylated alpha subunit of eukaryotic initiation factor 2 (peIF-2α), and spliced XBP-1 mRNA. Knockdown studies using siRNAs to TRAIL, DR5, JNK and CHOP as well as chemical inhibitors of ER stress and caspase-8 showed that: i) α-TEA activation of DR5/caspase-8 induces an ER stress mediated JNK/CHOP/DR5 positive amplification loop; ii) α-TEA downregulation of c-FLIP (L) protein levels is mediated by JNK/CHOP/DR5 loop via a JNK dependent Itch E3 ligase ubiquitination that further serves to enhance the JNK/CHOP/DR5 amplification loop by preventing c-FLIP's inhibition of caspase-8; and (iii) α-TEA downregulation of Bcl-2 is mediated by the ER stress dependent JNK/CHOP/DR5 signaling.

Conclusion

Taken together, ER stress plays an important role in α-TEA induced apoptosis by enhancing DR5/caspase-8 pro-apoptotic signaling and suppressing anti-apoptotic factors c-FLIP and Bcl-2 via ER stress mediated JNK/CHOP/DR5/caspase-8 signaling.

TRB3 is stimulated in diabetic kidneys, regulated by the ER stress marker CHOP, and is a suppressor of podocyte MCP-1

The prevalence of diabetic nephropathy continues to rise, highlighting the importance of investigating and discovering novel treatment strategies. TRB3 is a kinase-like molecule that modifies cellular survival and metabolism and interferes with signal transduction pathways. Herein, we report that TRB3 expression is increased in the kidneys of type 1 and type 2 diabetic mice. TRB3 is expressed in conditionally immortalized podocytes; however, it is not stimulated by elevated glucose. The diabetic milieu is associated with increased oxidative stress and circulating free fatty acids (FFA). We show that reactive oxygen species (ROS) such as H(2)O(2) and superoxide anion (via the xanthine/xanthine oxidase reaction) as well as the FFA palmitate augment TRB3 expression in podocytes. C/EBP homologous protein (CHOP) is a transcription factor that is associated with the endoplasmic reticulum stress response. CHOP expression increases in diabetic mouse kidneys and in podocytes treated with ROS and FFA. In podocytes, transfection of CHOP increases TRB3 expression, and ROS augment recruitment of CHOP to the proximal TRB3 promoter. MCP-1/CCL2 is a chemokine that contributes to the inflammatory injury associated with diabetic nephropathy. In these studies, we demonstrate that TRB3 can inhibit basal and stimulated podocyte production of MCP-1. In summary, enhanced ROS and/or FFA associated with the diabetic milieu induce podocyte CHOP and TRB3 expression. Because TRB3 inhibits MCP-1, manipulation of TRB3 expression could provide a novel therapeutic approach in diabetic kidney disease.

CHOP and AP-1 cooperatively mediate PUMA expression during lipoapoptosis

Endoplasmic reticulum (ER) stress-mediated apoptosis is a key feature of hepatocyte cytotoxicity by saturated free fatty acids (FFA). This lipoapoptosis is dependent, in part, on the transcriptional upregulation of the BH3-only protein PUMA (p53 upregulated modulator of apoptosis). Although the activator protein (AP)-1 complex facilitates PUMA expression by saturated FFA, the transcription factor CAAT/enhancer binding homologous protein (CHOP) is also induced by ER stress and promotes apoptosis. To integrate the role of these two transcription factors in ER stress-induced apoptosis, we examined the relative contribution of CHOP and AP-1 in mediating PUMA induction by saturated FFA. Our results demonstrate that short-hairpin RNA-targeted knockdown of CHOP attenuates palmitate-induced apoptosis in Huh-7 cells. Loss of CHOP induction also reduced the increase in PUMA mRNA and protein levels as well as Bax activation by palmitate. No functional CHOP binding sites were identified in the PUMA promoter sequence. Rather, we observed that CHOP physically interacts with the AP-1 complex protein c-Jun upon palmitate treatment, and a CHOP:phosphorylated c-Jun heteromeric complex binds to the AP-1 consensus binding sequence within the PUMA promoter region. Finally, loss of function studies suggest that both transcription factors are necessary for maximal PUMA induction. Collectively, these data suggest that CHOP and AP-1 cooperatively mediate PUMA induction during hepatocyte lipoapoptosis.

DDIT3/CHOP and the sarcoma fusion oncoprotein FUS-DDIT3/TLS-CHOP bind cyclin-dependent kinase 2

Background

The DDIT3 gene encodes a transcription factor belonging to the CCAAT/enhancer binding protein (C/EBP) family. It is normally expressed at very low levels but is activated by cellular stress conditions and induces G1 arrest and, in some cell types, apoptosis. DDIT3 is found as a part of the fusion oncogene FUS-DDIT3 that is causal for the development of myxoid/round-cell liposarcomas (MLS/RCLS).

Results

In the present study, we searched for putative interaction partners of DDIT3 and the oncogenic FUS-DDIT3 among G1 cyclins and cyclin-dependent kinases. We found that FUS-DDIT3 and the normal DDIT3 bind CDK2. In addition, CDK2 showed an increased affinity for cytoskeletal proteins in cells expressing FUS-DDIT3 and DDIT3.

Conclusions

We conclude that DDIT3 binds CDK2 and that many of the observed biological effects of DDIT3 may involve interaction with CDK2.

Age-dependent response of CCAAT/enhancer binding proteins following traumatic brain injury in mice

Exacerbated inflammatory responses have been reported following traumatic injury to the aged brain. The present study was designed to investigate the involvement of the transcription factors belonging to the CCAAT/enhancer binding protein (C/EBP) family that regulate expression of many of the pro-inflammatory genes which show increased expression following injury to the aged brain. Controlled cortical impact injury was induced in adult (5-6 months) and aged (22-24 months) C57/BL6 mice. C/EBP mRNA and protein expression were analyzed in injured cortex at 1, 3, and 7 days post-injury. Expression of C/EBPalpha was reduced relative to baseline at day 1 in both adult and aged mice, whereas, it increased at days 3 and 7 post-injury. No significant differences were observed between adult and aged brain. Upregulation of C/EBPbeta was observed 1 day following injury in both the adult and aged brain, but there were no major age-related differences in mRNA levels. However, there was higher C/EBPbeta protein in the aged brain. C/EBPdelta expression increased beginning 1 day post-injury in both adult and aged brain. In this case, the increase in C/EBPdelta expression was higher in the aged brain than in the adult at all time points studied. Expression of CCAAT/enhancer binding protein homologous protein (CHOP), a transcription factor involved in ER stress and protein unfolding responses, was also up-regulated in response to injury, but CHOP levels were significantly lower in the aged than the adult brain. Based on these results, we conclude that differential expression of C/EBP beta, delta and CHOP might contribute to the hyper-inflammatory response and poor prognosis following traumatic brain injury in the elderly patients. In addition elevated C/EBPdelta levels following TBI in the aged brain may play a role in the link between TBI and Alzheimer's disease.

Transcriptional regulation of the human growth hormone receptor (hGHR) gene V2 promoter by transcriptional activators and repressor

The V2 transcript is the major ubiquitously expressed human GH receptor (hGHR) mRNA in all tissues examined to date. In a previous investigation, we defined the V2 promoter as TATA-less and exhibiting many characteristics of a housekeeping gene promoter. We also demonstrated that its basal activity is determined by several different cis-regulatory regions within both the promoter and the V2 exon. In the present study, we used luciferase-reporter, site-directed mutagenesis, gel shift, chromatin immunoprecipitation, and quantitative RT-PCR assays to investigate the ability of certain transcription factors to regulate hGHR V2 transcription through these regions in mammalian cells, including human adipocytes. Ets1 was found to transactivate the V2 proximal promoter through specific Ets sites. Two CCAAT/enhancer-binding protein (C/EBP) family members [C/EBP-homologous protein (CHOP) and C/EBPbeta] enhanced V2 transcription via different pathways: indirectly, by association with a V2 exon region (CHOP), and directly, using a V2 proximal promoter noncanonical binding site (C/EBPbeta). The Notch signaling mediator, Hes1, potently suppressed V2 promoter activity through interaction with two Hes sites within the V2 exon. We propose that these transcriptional factors regulate hGHR V2 expression by acting as downstream nuclear effectors, linking specific signaling cascades (e.g. MAPK and Notch) triggered by different growth factor-, development-, and nutrition- as well as stress-related stimuli. Our data also suggest that these factors are likely to be important in the differentiation-induced increase in V2 mRNA expression in adipocytes, with Ets1 and CHOP functioning at the preadipocyte stage to prepare the cells for differentiation and increasing C/EBPs and decreasing Hes1 levels contributing during adipocyte maturation.

Zhangfei, a novel regulator of the human nerve growth factor receptor, trkA

The replication of herpes simplex virus (HSV) in epithelial cells, and during reactivation from latency in sensory neurons, depends on a ubiquitous cellular protein called host cell factor (HCF). The HSV transactivator, VP16, which initiates the viral replicative cycle, binds HCF as do some other cellular proteins. Of these, the neuronal transcription factor Zhangfei suppresses the ability of VP16 to initiate the replicative cycle. It also suppresses Luman, another cellular transcription factor that binds HCF. Interactions of nerve growth factor (NGF) and its receptor tropomyosin-related kinase (trkA) appear to be critical for maintaining HSV latency. Because the neuronal transcription factor Brn3a, which regulates trkA expression, has a motif for binding HCF, we investigated if Zhangfei had an effect on its activity. We found that Brn3a required HCF for activating the trkA promoter and Zhangfei suppressed its activity in non-neuronal cells. However, in neuron-like NGF-differentiated PC12 cells, both Brn3a and Zhangfei activated the trkA promoter and induced the expression of endogenous trkA. In addition, capsaicin, a stressor, which activates HSV in in vitro models of latency, decreased levels of Zhangfei and trkA transcripts in NGF-differentiated PC12 cells.