Mechanism of oxidative stress-induced GADD153 gene expression in vascular smooth muscle cells

Activation of Epstein-Barr Virus' Lytic Cycle in Nasopharyngeal Carcinoma Cells by NEO212, a Conjugate of Perillyl Alcohol and Temozolomide

The Epstein-Barr virus (EBV) is accepted as a primary risk factor for certain nasopharyngeal carcinoma (NPC) subtypes, where the virus persists in a latent stage which is thought to contribute to tumorigenesis. Current treatments are sub-optimal, and recurrence occurs in many cases. An alternative therapeutic concept is aimed at triggering the lytic cycle of EBV selectively in tumor cells as a means to add clinical benefit. While compounds able to stimulate the lytic cascade have been identified, their clinical application so far has been limited. We are developing a novel anticancer molecule, NEO212, that was generated by covalent conjugation of the alkylating agent temozolomide (TMZ) to the naturally occurring monoterpene perillyl alcohol (POH). In the current study, we investigated its potential to trigger the lytic cycle of EBV in NPC cells in vitro and in vivo. We used the established C666.1 cell line and primary patient cells derived from the brain metastasis of a patient with NPC, both of which harbored latent EBV. Upon treatment with NEO212, there was an increase in EBV proteins Zta and Ea-D, key markers of the lytic cycle, along with increased levels of CCAAT/enhancer-binding protein homologous protein (CHOP), a marker of endoplasmic reticulum (ER) stress, followed by the activation of caspases. These effects could also be confirmed in tumor tissue from mice implanted with C666.1 cells. Towards a mechanistic understanding of these events, we used siRNA-mediated knockdown of CHOP and inclusion of anti-oxidant compounds. Both approaches blocked lytic cycle induction by NEO212. Therefore, we established a sequence of events, where NEO212 caused reactive oxygen species (ROS) production, which triggered ER stress and elevated the levels of CHOP, which was required to stimulate the lytic cascade of EBV. Inclusion of the antiviral agent ganciclovir synergistically enhanced the cytotoxic impact of NEO212, pointing to a potential combination treatment for EBV-positive cancers which should be explored further. Overall, our study establishes NEO212 as a novel agent able to stimulate EBV's lytic cycle in NPC tumors, with implications for other virus-associated cancers.

Identification of genomic binding sites and direct target genes for the transcription factor DDIT3/CHOP

DDIT3 is a tightly regulated basic leucine zipper (bZIP) transcription factor and key regulator in cellular stress responses. It is involved in a variety of pathological conditions and may cause cell cycle block and apoptosis. It is also implicated in differentiation of some specialized cell types and as an oncogene in several types of cancer. DDIT3 was originally believed to act as a dominant-negative inhibitor by forming heterodimers with other bZIP transcription factors, preventing their DNA binding and transactivating functions. DDIT3 has, however, been reported to bind DNA and regulate target genes. Here, we employed ChIP sequencing combined with microarray-based expression analysis to identify direct binding motifs and target genes of DDIT3. The results reveal DDIT3 binding to motifs similar to other bZIP transcription factors, known to form heterodimers with DDIT3. Binding to a class III satellite DNA repeat sequence was also detected. DDIT3 acted as a DNA-binding transcription factor and bound mainly to the promotor region of regulated genes. ChIP sequencing analysis of histone H3K27 methylation and acetylation showed a strong overlap between H3K27-acetylated marks and DDIT3 binding. These results support a role for DDIT3 as a transcriptional regulator of H3K27ac-marked genes in transcriptionally active chromatin.

DDIT3 antagonizes innate immune response to promote bovine alphaherpesvirus 1 replication via the DDIT3-SQSTM1-STING pathway

DNA damage-inducible transcript 3 (DDIT3), a transcription factor, is typically involved in virus replication control. We are the first to report that DDIT3 promotes the replication of bovine viral diarrhea virus, an RNA virus, by inhibiting innate immunity. However, whether the DDIT3 gene participates in DNA virus replication by regulating innate immunity remains unclear. This study reported that DDIT3 suppressed the innate immune response caused by DNA viruses to promote bovine herpesvirus 1 (BoHV-1) replication. After BoHV-1 infection of Madin-Darby bovine kidney (MDBK) cells, upregulated expression of DDIT3 induced SQSTM1-mediated autophagy and promoted STING degradation. Overexpression of the SQSTM1 protein effectively reduced STING protein levels, whereas SQSTM1 knockdown increased STING protein levels. Coimmunoprecipitation experiments and confocal laser scanning microscopy revealed that the SQSTM1 protein interacts with and colocalizes with STING. Knockdown of SQSTM1 expression in DDIT3-overexpressing cell lines restored STING protein levels. Moreover, a dual-luciferase reporter assay revealed that DDIT3 directly binds to the bovine SQSTM1 promoter and induces SQSTM1 transcription. Overexpression of SQSTM1 promoted BoHV-1 replication by inhibiting IFN-β and IFN-stimulated genes (ISGs) production; silencing of SQSTM1 promoted the expression of IFN-β and ISGs to inhibit BoHV-1 replication. In conclusion, DDIT3 targets STING via SQSTM1-mediated autophagy to promote BoHV-1 replication. These results suggest a novel mechanism by which DDIT3 regulates DNA virus replication by targeting innate immunity. DDIT3 antagonizes the innate immune response to promote bovine alphaherpesvirus 1 replication via the DDIT3-SQSTM1-STING pathway.

DNA damage and repair, oxidative stress and metabolism biomarker responses in lungs of rats exposed to ambient atmospheric 1-nitropyrene

1-Nitropyrene (1-NP) is a mutagenic and carcinogenic pollutant very widespread in the environment. However, the relative investigations on genotoxicity, oxidative stress and metabolic enzymes in lungs of mammalian caused by 1-NP have not been fully established. In this study, the 1-NP solutions at 3 dosages (1.0×10^-5, 4.0×10^-5 and 1.6×10^-4mg/kg body weight) were respectively given to rats by the intratracheal instillation. The responses of 1-NP on DNA damage and repair, oxidative stress and metabolism biomarkers in rat lungs after exposure to 1-NP were measured. The results showed 1-NP at three dosages induced obvious DNA strand breaks, 8-OH-dG formation and DNA-protein cross-link in rat lungs compared with the control. Higher dosage 1-NP (4.0×10^-5 and 1.6×10^-4mg/kg body weight) greatly activated DNA repair gene OGG1 and inhibited MTH1 and XRCC1 expressions, and they significantly elevated the levels of GADD153, heme oxygenase-1 and malondialdehyde and decreased SOD activity, accompanied by the increases of CYP450, CYP1A1, CYP1A2 and GST levels. These results suggested the genotoxicity of 1-NP might rely on 1-NP-caused DNA damage and its combined effects on the suppression of DNA repair and the enhancement of oxidative stress and metabolic enzyme activity.

Effects of ambient PM2.5 and 9-nitroanthracene on DNA damage and repair, oxidative stress and metabolic enzymes in the lungs of rats

Ambient fine particulate matter (PM2.5) is a complex mixture associated with lung cancer risk. PM2.5-bound nitro-polycyclic aromatic hydrocarbons (NPAHs) have been demonstrated to possess mutagenicity and carcinogenicity. Previous studies showed that PM2.5 induced DNA damage, whereas there is little knowledge of whether 9-nitroanthracene (9-NA), a typical compound of NPAHs in PM2.5, causes DNA damage. Also, the regulating mechanisms of PM2.5 and 9-NA in DNA damage and repair are not yet fully established. Here we sought to investigate the molecular mechanisms of DNA damage and repair in the lungs of male Wistar rats exposed to PM2.5 (1.5 mg per kg body weight) or three different dosages of 9-NA. And then DNA strand breaks, 8-OH-dG formation, DNA-protein crosslink and DNA repair gene expressions in rat lungs were analyzed. In addition, alteration in oxidative stress factors and metabolic enzymes were detected. The results showed that (1) PM2.5 and higher dosage 9-NA (4.0 × 10-5 and 1.2 × 10-4 mg per kg body weight) significantly caused lung DNA damage, accompanied by increasing OGG1 expression while inhibiting MTH1 and XRCC1 expression, elevating the levels of GADD153, hemeoxygenase-1 and malondialdehyde, and promoting the activities of CYP450 isozymes and glutathione S-transferase. (2) 1.3 × 10-5 mg kg-1 9-NA exposure couldn't cause DNA damage and oxidative stress. (3) At the approximately equivalent dose level, PM2.5-induced DNA damage effects were more obvious than 9-NA with positive correlation. It suggests that DNA damage caused by PM2.5 and 9-NA may be mediated partially through influencing the DNA repair capacity and enhancing oxidative stress and biotransformation, and this negative effect of 9-NA might be related to the PM2.5-induced lung genotoxicity.

Piperlongumine induces cell death through ROS-mediated CHOP activation and potentiates TRAIL-induced cell death in breast cancer cells

PURPOSE

Piperlongumine (PL) has been shown to selectively induce apoptotic cell death in cancer cells via reactive oxygen species (ROS) accumulation. In this study, we characterized a molecular mechanism for PL-induced cell death.

METHODS

Cell viability and cell death were assessed by MTT assay and Annexin V-FITC/PI staining, respectively. ROS generation was measured using the H2DCFDA. Small interfering RNA (siRNA) was used for suppressing gene expression. The mRNA and protein expression were analyzed by RT-PCR and Western blot analysis, respectively.

RESULTS

We found that PL promotes C/EBP homologous protein (CHOP) induction, which leads to the up-regulation of its targets Bim and DR5. Pretreatment with the ROS scavenger N-acetyl-cysteine abolishes the PL-induced up-regulation of CHOP and its target genes, suggesting an essential role for ROS in PL-induced CHOP activation. The down-regulation of CHOP or Bim with siRNA efficiently attenuates PL-induced cell death, suggesting a critical role for CHOP in this cell death. Furthermore, PL potentiates TRAIL-induced cytotoxicity in breast cancer cells by upregulating DR5, as DR5 knockdown abolished the sensitizing effect of PL on TRAIL responses.

CONCLUSIONS

Overall, our data suggest a new mechanism for the PL-induced cell death in which ROS mediates CHOP activation, and combination treatment with PL and TRAIL could be a potential strategy for breast cancer therapy.

Expression of endoplasmic reticulum stress markers GRP78 and CHOP induced by oxidative stress in blue light-mediated damage of A2E-containing retinal pigment epithelium cells

AIMS

Age-related lipofuscin N-retinylidene-N-retinylethanolamine (A2E) accumulated in human retinal pigment epithelium (RPE) cells confers susceptibility to blue light-mediated damage, which represents one pathogenesis of age-related macular degeneration. This study investigated the expression of 2 best-characterized endoplasmic reticulum (ER) stress markers, glucose-related protein 78 (GRP78) and C/EBP homologous protein (CHOP), as well as their regulation by oxidative stress after blue light-mediated damage of A2E-containing RPE cells.

METHODS

ARPE-19 cells were incubated with A2E (10, 25, 50 μM) for 2 h and exposed to blue light for 20 min. A2E distributions in RPE cells were assessed via laser scanning confocal microscope and liquid chromatography-mass spectrometry. Cell viability was measured by a Cell Titer 96 Aqueous One Solution cell proliferation assay. The quantity of intracellular reactive oxygen species (ROS) was detected by dihydroethidium fluorescence using flow cytometry. Expressions of GRP78 and CHOP were measured at both mRNA and protein levels. To examine the role of oxidative stress in regulating GRP78 and CHOP expression, RPE cells were pretreated with the antioxidant N-acetylcysteine (NAC) for 2 h. RNA interference of GRP78 performed by short hairpin RNA was used to evaluate the effect of GRP78 in blue light-mediated damage of RPE cells.

RESULTS

After blue light exposure, A2E-treated RPE cells showed a gradual decrease in cell viability and a particular increase in ROS levels. Meanwhile, the expressions of GRP78 and CHOP in A2E-treated RPE cells were significantly increased at different time points after illumination. Pretreatment with NAC attenuated the expression of 2 ER stress markers, especially CHOP in A2E and blue light-treated RPE cells. Silencing of GRP78 by RNA interference upregulated CHOP and caspase-12 expression as well as aggravated the blue light-mediated damage of A2E-laden RPE cells.

CONCLUSION

RPE cells exhibited ROS accumulation and subsequent elevation of GRP78 and CHOP expression after A2E and blue light-induced damage. The ROS scavenger NAC diminished ER stress protein expression, suggesting a connection between ER and oxidative stress in blue light-mediated damage of A2E-containing RPE cells. Besides, GRP78 may play a protective role in it.

Quercetin enhances apoptotic effect of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in ovarian cancer cells through reactive oxygen species (ROS) mediated CCAAT enhancer-binding protein homologous protein (CHOP)-death receptor 5 pathway

Although tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has shown efficacy in a phase 2 clinical trial, development of resistance to TRAIL by tumor cells is a major roadblock. We investigated whether quercetin, a flavonoid, can sensitize human ovarian cancer cells to TRAIL. Results indicate that quercetin sensitized cancer cells to TRAIL. The quercetin induced expression of death receptor DR5 but did not affect expression of DR4 in cancer cells. The induction of DR5 was mediated through activation of JNK and through upregulation of a transcription factor CCAAT enhancer-binding protein homologous protein (CHOP); as silencing of these signaling molecules abrogated the effect of quercetin. Upregulation of DR5 was mediated through the generation of reactive oxygen species (ROS), as ROS scavengers reduced the effect of quercetin on JNK activation, CHOP upregulation, DR induction, TRAIL sensitization, downregulated the expression of cell survival proteins and upregulated the proapoptotic proteins. Furthermore, quercetin enhances TRAIL mediated inhibition of tumor growth of human SKOV-3 xenograft was associated with induction of apoptosis, activation of caspase-3, CHOP and DR5. Overall, our data suggest that quercetin enhances apoptotic death of ovarian cancer cells to TRAIL through upregulation of CHOP-induced DR5 expression following ROS mediated endoplasmic reticulum-stress.

C/EBP homologous protein deficiency aggravates acute pancreatitis and associated lung injury

AIM: To investigate the pathophysiological role of C/EBP homologous protein (CHOP) in severe acute pancreatitis and associated lung injury.

METHODS: A severe acute pancreatitis model was induced with 6 injections of cerulein (Cn, 50 μg/kg) at 1-h intervals, then intraperitoneal injection of lipopolysaccharide (LPS, 7.5 mg/kg) in CHOP-deficient (Chop^-/-) mice and wild-type (WT) mice. Animals were sacrificed under anesthesia, 3 h or 18 h after LPS injection. Serum amylase, lipase, and cytokines [interleukin (IL)-6 and tumor necrosis factor (TNF)-α], pathological changes, acute lung injury, and apoptosis in the pancreas were evaluated. Serum amylase and lipase activities were detected using a medical automatic chemical analyzer. Enzyme-linked immunosorbent assay kits were used to evaluate TNF-α and IL-6 levels in mouse serum and lung tissue homogenates. Apoptotic cells in sections of pancreatic tissues were determined by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) analysis. The mouse carotid arteries were cannulated and arterial blood samples were collected for PaO₂ analysis. The oxygenation index was expressed as PaO₂/FiO₂.

RESULTS: Administration of Cn and LPS for 9 and 24 h induced severe acute pancreatitis in Chop^-/- and WT mice. When comparing Chop^-/- mice and WT mice, we observed that CHOP-deficient mice had greater increases in serum TNF-α (214.40 ± 19.52 pg/mL vs 150.40 ± 16.70 pg/mL; P = 0.037), amylase (4236.40 ± 646.32 U/L vs 2535.30 ± 81.83 U/L; P = 0.041), lipase (1678.20 ± 170.57 U/L vs 1046.21 ± 35.37 U/L; P = 0.008), and IL-6 (2054.44 ± 293.81 pg/mL vs 1316.10 ± 108.74 pg/mL; P = 0.046) than WT mice. The histopathological changes in the pancreases and lungs, decreased PaO₂/FiO₂ ratio, and increased TNF-α and IL-6 levels in the lungs were greater in Chop^-/- mice than in WT mice (pancreas: Chop^-/-vs WT mice, hemorrhage, P = 0.005; edema, P = 0.005; inflammatory cells infiltration, P = 0.005; total scores, P = 0.006; lung: hemorrhage, P = 0.017; edema, P = 0.017; congestion, P = 0.017; neutrophil infiltration, P = 0.005, total scores, P = 0.001; PaO₂/FiO₂ ratio: 393 ± 17.65 vs 453.8, P = 0.041; TNF-α: P = 0.043; IL-6, P = 0.040). Results from TUNEL analysis indicated increased acinar cell apoptosis in mice following the induction of acute pancreatitis. However, Chop^-/- mice displayed significantly reduced pancreatic apoptosis compared with the WT mice (201.50 ± 31.43 vs 367.00 ± 47.88, P = 0.016).

CONCLUSION: These results suggest that CHOP can exert protective effects against acute pancreatitis and limit the spread of inflammatory damage to the lungs.

Increased endoplasmic reticulum stress response is involved in clopidogrel-induced apoptosis of gastric epithelial cells

Background

The widespread use of clopidogrel alone or in combination with aspirin may result in gastrointestinal mucosal injury, clinically represented as recurrent ulceration and bleeding complications. Our recent work suggested that clopidogrel significantly induced human gastric epithelial cell (GES-1) apoptosis and disrupted gastric mucosal barrier, and that a p38 MAPK inhibitor could attenuate such injury. However, their exact mechanisms are largely unknown.

Methods

The GES-1 cells were used as a model system, the effects of clopidogrel on the whole gene expression profile were evaluated by human gene expression microarray and gene ontology analysis, changes of the mRNA and protein expression were determined by real-time PCR and Western blot analysis, and cell viability and apoptosis were measured by MTT assay and flow cytometry analysis, respectively.

Results

Gene microarray analysis identified 79 genes that were differentially expressed (P<0.05 and fold-change >3) when cells were treated with or without clopidogrel. Gene ontology analysis revealed that response to stress and cell apoptosis dysfunction were ranked in the top 10 cellular events being affected, and that the major components of endoplasmic reticulum stress-mediated apoptosis pathway – CHOP and TRIB3– were up-regulated in a concentration- and time-dependent manner when cells were treated with clopidogrel. Pathway analysis demonstrated that multiple MAPK kinases were phosphorylated in clopidogrel-treated GES-1 cells, but that only SB-203580 (a p38-specific MAPK inhibitor) attenuated cell apoptosis and CHOP over-expression, both of which were induced by clopidogrel.

Conclusions

Increased endoplasmic reticulum stress response is involved in clopidogrel-induced gastric mucosal injury, acting through p38 MAPK activation.

Inorganic phosphate accelerates the migration of vascular smooth muscle cells: evidence for the involvement of miR-223

Backgound

An elevated serum inorganic phosphate (Pi) level is a major risk factor for kidney disease and downstream vascular complications. We focused on the effect of Pi levels on human aortic vascular smooth muscle cells (VSMCs), with an emphasis on the role of microRNAs (miRNAs).

Methodology/Principal Findings

Exposure of human primary VSMCs in vitro to pathological levels of Pi increased calcification, migration rate and concomitantly reduced cell proliferation and the amount of the actin cytoskeleton. These changes were evidenced by significant downregulation of miRNA-143 (miR-143) and miR-145 and concomitant upregulation of their targets and key markers in synthetic VSMCs, such as Krüppel-like factors−4 and −5 and versican. Interestingly, we also found that miR-223 (a marker of muscle damage and a key factor in osteoclast differentiation) is expressed in VSMCs and is significantly upregulated in Pi-treated cells. Over-expressing miR-223 in VSMCs increased proliferation and markedly enhanced VSMC migration. Additionally, we found that the expression of two of the known miR-223 targets, Mef2c and RhoB, was highly reduced in Pi treated as well as miR-223 over-expressing VSMCs. To complement these in vitro findings, we also observed significant downregulation of miR-143 and miR-145 and upregulation of miR-223 in aorta samples collected from ApoE knock-out mice, which display vascular calcification.

Conclusions/Significance

Our results suggest that (i) high levels of Pi increase VSMC migration and calcification, (ii) altered expression levels of miR-223 could play a part in this process and (iii) miR-223 is a potential new biomarker of VSMC damage.

Distinct cytoplasmic and nuclear functions of the stress induced protein DDIT3/CHOP/GADD153

DDIT3, also known as GADD153 or CHOP, encodes a basic leucine zipper transcription factor of the dimer forming C/EBP family. DDIT3 is known as a key regulator of cellular stress response, but its target genes and functions are not well characterized. Here, we applied a genome wide microarray based expression analysis to identify DDIT3 target genes and functions. By analyzing cells carrying tamoxifen inducible DDIT3 expression constructs we show distinct gene expression profiles for cells with cytoplasmic and nuclear localized DDIT3. Of 175 target genes identified only 3 were regulated by DDIT3 in both cellular localizations. More than two thirds of the genes were downregulated, supporting a role for DDIT3 as a dominant negative factor that could act by either cytoplasmic or nuclear sequestration of dimer forming transcription factor partners. Functional annotation of target genes showed cell migration, proliferation and apoptosis/survival as the most affected categories. Cytoplasmic DDIT3 affected more migration associated genes, while nuclear DDIT3 regulated more cell cycle controlling genes. Cell culture experiments confirmed that cytoplasmic DDIT3 inhibited migration, while nuclear DDIT3 caused a G1 cell cycle arrest. Promoters of target genes showed no common sequence motifs, reflecting that DDIT3 forms heterodimers with several alternative transcription factors that bind to different motifs. We conclude that expression of cytoplasmic DDIT3 regulated 94 genes. Nuclear translocation of DDIT3 regulated 81 additional genes linked to functions already affected by cytoplasmic DDIT3. Characterization of DDIT3 regulated functions helps understanding its role in stress response and involvement in cancer and degenerative disorders.

Activation of the unfolded protein response enhances motor recovery after spinal cord injury

Spinal cord injury (SCI) is a major cause of paralysis, and involves multiple cellular and tissular responses including demyelination, inflammation, cell death and axonal degeneration. Recent evidence suggests that perturbation on the homeostasis of the endoplasmic reticulum (ER) is observed in different SCI models; however, the functional contribution of this pathway to this pathology is not known. Here we demonstrate that SCI triggers a fast ER stress reaction (1–3 h) involving the upregulation of key components of the unfolded protein response (UPR), a process that propagates through the spinal cord. Ablation of X-box-binding protein 1 (XBP1) or activating transcription factor 4 (ATF4) expression, two major UPR transcription factors, leads to a reduced locomotor recovery after experimental SCI. The effects of UPR inactivation were associated with a significant increase in the number of damaged axons and reduced amount of oligodendrocytes surrounding the injury zone. In addition, altered microglial activation and pro-inflammatory cytokine expression were observed in ATF4 deficient mice after SCI. Local expression of active XBP1 into the spinal cord using adeno-associated viruses enhanced locomotor recovery after SCI, and was associated with an increased number of oligodendrocytes. Altogether, our results demonstrate a functional role of the UPR in SCI, offering novel therapeutic targets to treat this invalidating condition.

CHOP-independent apoptosis and pathway-selective induction of the UPR in developing plasma cells

Upon antigen stimulation, B lymphocytes differentiate into antibody secreting cells (ASC), most of which undergo apoptosis after a few days of intense Ig production. Differentiation entails expansion of the endoplasmic reticulum (ER) and requires XBP1 but not other elements of the unfolded protein response, like PERK. Moreover, normal and malignant ASC are exquisitely sensitive to proteasome inhibitors, but the underlying mechanisms are poorly understood. Here we analyze the role of C/EBP homologous protein (CHOP), a transcription factor mediating apoptosis in many cell types that experience high levels of ER stress. CHOP is transiently induced early upon B cell stimulation: covalent IgM aggregates form more readily and IgM secretion is slower in chop(-/-) cells. Despite these subtle changes, ASC differentiation and lifespan are normal in chop(-/-) mice. Unlike fibroblasts and other cell types, chop(-/-) ASC are equally or slightly more sensitive to proteasome inhibitors and ER stressors, implying tissue-specific roles for CHOP in differentiation and stress.

Involvement of GADD153 and cardiac ankyrin repeat protein in cardiac ischemia-reperfusion injury

Oxidative stress is critical for causing cardiac injuries during ischemia-reperfusion (IR), yet the molecular mechanism for this remains unclear. In the present study, we observe that hypoxia and reoxygenation, a component of ischemia, effectively induces apoptosis in the cardiac myocytes from neonatal rats and it concomitantly leads to induction of GADD153, an apoptosis-related gene. Furthermore, IR injury of rat heart showed a GADD153 overexpression in the ischemic area where the TUNEL reaction was positive. A downregulation of cardiac ankyrin repeat protein (CARP) was also observed in this ischemic area. Promoter deletion and reporter analysis revealed that hypoxia transcriptionally activates a GADD153 promoter through the AP-1 element in neonatal cardiomyocytes. Ectopic overexpression of GADD153 resulted in the downregulation of CARP expression. Accordingly, the induction of GADD153 mRNA were followed by the CARP down-regulation in an in vivo rat coronary ischemia/reperfusion injury model. These results suggest that GADD153 over-expression and the resulting downregulation of CARP may have causative roles in apoptotic cell death during cardiac IR injury.

Mouse pancreatic islets are resistant to indoleamine 2,3 dioxygenase-induced general control nonderepressible-2 kinase stress pathway and maintain normal viability and function

Islet transplantation is a promising treatment for diabetes. However, it faces several challenges including requirement of systemic immunosuppression. Indoleamine 2,3-dioxygenase (IDO), a tryptophan degrading enzyme, is a potent immunomodulatory factor. Local expression of IDO in bystander fibroblasts suppresses islet allogeneic immune response in vitro. The aim of the present study was to investigate the impact of IDO on viability and function of mouse islets embedded within IDO-expressing fibroblast-populated collagen scaffold. Mouse islets were embedded within collagen matrix populated with IDO adenovector-transduced or control fibroblasts. Proliferation, insulin content, glucose responsiveness, and activation of general control nonderepressible-2 kinase stress-responsive pathway were then measured in IDO-exposed islets. In vivo viabilities of composite islet grafts were also tested in a syngeneic diabetic animal model. No reduction in islet cells proliferation was detected in both IDO-expressing and control composites compared to the baseline rates. Islet functional studies showed normal insulin content and secretion in both preparations. In contrast to lymphocytes, general control nonderepressible-2 kinase pathway was not activated in islets cocultured with IDO-expressing fibroblasts. When transplanted to diabetic mice, syngeneic IDO-expressing composite islet grafts were functional up to 100 days tested. These findings collectively confirm normal viability and functionality of islets cocultured with IDO-expressing cells and indicate the feasibility of development of a functional nonrejectable islet graft.

The role of CHOP messenger RNA expression in the link between oxidative stress and apoptosis

Low expression of antioxidant enzymes makes pancreatic beta-cells susceptible to cell damage by oxidative stress. Pancreatic beta-cell loss caused by endoplasmic reticulum stress is associated with the onset of diabetes mellitus. The present studies were undertaken to investigate a possible involvement of proapoptotic gene CHOP in pancreatic beta-cells damage by oxidative stress. The induction of CHOP messenger RNA and apoptosis were investigated in betaHC-9 cells after the oxidative stress by hydrogen peroxide and ribose. Latter was examined after the suppression of CHOP by small interfering RNA. For in vivo study, the pancreatic beta-cells were examined in CHOP-knockout (KO) mice after multiple low-dose streptozotocin (MLDS) administration. In betaHC-9 cells, both hydrogen peroxide and ribose obviously increased apoptotic cells, accompanied with enhanced CHOP messenger RNA expression. However, the number of apoptotic cells by those stimulations was significantly reduced by the addition of small interfering RNA against CHOP. In vivo study also showed that CHOP-KO mice were less susceptible to diabetes after MLDS administration. Although the oxidative stress marker level was similar to that of MLDS-treated wild type, the pancreatic beta-cell area was maintained in CHOP-KO mice. The present studies showed that CHOP should be important in pancreatic beta-cell injury by oxidative stress and indicate that CHOP may play a role in the development of pancreatic beta-cell damage on the onset of diabetes mellitus.

Immunolocalization and biochemical evidence of pregnancy-associated plasma protein A in the intervertebral disc

STUDY DESIGN

Studies were approved by the authors' Human Subjects Institutional Review Board and Institutional Animal Care and Use Committee. Anulus tissue was used in studies of the immunocytochemical localization of pregnancy-associated plasma protein A (PAPP-A) in disc tissue from the sand rat and from human disc surgical specimens and specimens from control donors. Cultured human disc cells were also tested for production of PAPP-A.

OBJECTIVES

(1) To determine the immunohistochemical localization of PAPP-A in human and sand rat discs; (2) To test for gene expression of PAPP-A in the human disc in vivo and in vitro production by cultured cells; and (3) To test for expression of insulin-like growth factor binding proteins (IGFBP)-2, -4, and -5 in vivo and in vitro by human disc cells.

SUMMARY OF BACKGROUND DATA

PAPP-A is a metalloproteinase expressed by several cell types, including fibroblasts, osteoblasts, and smooth muscle cells. PAPP-A has an extremely important role because it cleaves IGFBP-2, -4, and -5 in the extracellular matrix, thereby increasing the bioavailability of IGF to nearby cells. METHODS.: Specimens of human disc tissue and lumbar discs from sand rats were assessed for immunocytochemical localization of PAPP-A, and the percentage of positive cells determined. Human disc cells in three-dimensional culture were assessed for production of PAPP-A using an enzyme linked immunosorbent assay. Molecular gene expression studies were carried out using microarray analysis.

RESULTS

Positive cytoplasmic immunolocalization of PAPP-A was present in the majority of cells of the human and sand rat outer anulus (OA). In the human outer anulus, the percentage of cells positive for PAPP-A localization did not differ in Grades I-II discs vs. Grades III-V discs (OA: 77.4% +/- 10.5 vs. 75.1% +/- 7.4 [mean +/- SEM] respectively). In the inner anulus, however, the percentage of cells positive for PAPP-A localization in more degenerate discs was significantly greater than the percentage in healthier discs (60.7% +/- 10.1 vs. 15.6 +/- 5.4, P = 0.024). % positive cells in the inner anulus correlated significantly with disc grade (r = 0.579; P = 0.01). Over a 5-day three-dimensional culture period, human anulus cells produced and secreted abundant PAPP-A into the culture media. Molecular studies confirmed the expression of IGFBP-2, -4, and -5 both in vivo and in vitro.

CONCLUSIONS

Data provide important new insights into disc cell expression of PAPP-A at the translational level. The presence of a significantly greater proportion of cells positive for PAPP-A in the inner anulus of more degenerate Grade III-V discs compared with healthier Grade I-II discs supports our previous observation of increased gene expression of PAPP-A in more degenerated discs. Biochemical data shown here documented production of PAPP-A by disc cells in vitro. Production of PAPP-A by disc cells is important since PAPP-A cleaves IGF-binding proteins, and makes IGF-I, a potent mitogen and antiapoptotic agent, available to cells. Future studies are indicated to further investigate PAPP-A and IGF-BP function in the disc.

The molecular regulation of GADD153 in apoptosis of cultured vascular smooth muscle cells by cyclic mechanical stretch

AIMS

The expression of GADD153 (growth arrest and DNA damage-inducible gene 153), an apoptosis-regulated gene, increases during endoplasmic reticulum (ER) stress. How mechanical stretch affects the regulation of GADD153 in vascular smooth muscle cells (VSMCs) during apoptosis is not fully understood. We aimed to test the hypothesis that mechanical stretch induces GADD153 expression in VSMCs undergoing apoptosis.

METHODS AND RESULTS

Rat VSMCs grown on a flexible membrane base were stretched by vacuum to 20% of maximum elongation, at 60 cycles/min. An in vivo model of aorta-caval shunt in adult rats was used to investigate GADD153 expression. Cyclic stretch significantly increased GADD153 protein and mRNA expression after 18 h of stretch. Addition of c-jun N-terminal kinase (JNK) inhibitor SP600125, JNK siRNA, tumour necrosis factor-alpha (TNF-alpha) and TNF-alpha receptor antibody 30 min before stretch inhibited the induction of GADD153 protein. Gel shift assay showed that DNA-binding activity of activating factor 1 (AP-1) increased after stretch. SP600125, JNK siRNA and TNF-alpha antibody abolished the binding activity induced by stretch. Stretch increased while GADD153-Mut plasmid, SP600125, and c-jun antibody abolished the promoter activity. Both conditioned media from stretched VSMCs and exogenous administration of TNF-alpha recombinant protein to the non-stretched VSMCs increased GADD153 protein expression similar to that seen after stretch. An in vivo model of aorta-caval shunt in adult rats also demonstrated the increased GADD153 protein expression in the aorta.

CONCLUSION

Cyclic stretch enhanced GADD153 expression in cultured rat VSMCs. The stretch-induced GADD153 is mediated by TNF-alpha, at least in part, through the JNK and AP-1 pathway. These findings suggest that GADD153 plays a role in stretch-induced VSMC apoptosis.

Differential regulation of CHOP-10/GADD153 gene expression by MAPK signaling in pancreatic beta-cells

CHOP-10 (GADD153/DDIT-3) is a bZIP protein involved in differentiation and apoptosis. Its expression is induced in response to stresses such as nutrient deprivation, perturbation of the endoplasmic reticulum, redox imbalance, and UV exposure. Here we show that CHOP expression is induced in cultured pancreatic beta-cells maintained in a basal glucose concentration of 5.5 mM and repressed by stimulatory glucose (>or=11 mM). Both induction and repression of CHOP are dependent on the MAPKs ERK1 and ERK2. Two regulatory composite sites containing overlapping MafA response elements (MARE) and CAAT enhancer binding (CEB) elements regulate transcription in an ERK1/2-dependent manner. One site (MARE-CEB), from -320 to -300 bp in the promoter, represses transcription. The other site (CEB-MARE), from +2,628 to +2,641 bp in the first intron of the CHOP gene, activates it. MafA can influence transcription of both sites. The MARE-CEB is repressed by MafA, whereas the CEB-MARE site, which is homologous to the A2C1 component of the glucose-sensitive RIPE3b region of the insulin gene promoter, is activated by MafA. These results indicate that ERK1/2 have dual roles in regulating CHOP gene expression via both promoter and intronic regions, depending on environmental and metabolic stresses imposed on pancreatic beta-cells.

Complex formation with plasmid DNA increases the cytotoxicity of cationic liposomes

Cationic liposomes (CL) are one of the most widely studied non-viral vectors for gene delivery. It is well-known that CL induces cytotoxicity following lipofection. However, little is known regarding the mechanism involved in the cytotoxicity. In this study, the in vitro cytotoxicity of CL and its complex with pDNA (lipoplex) was investigated, and a part of the mechanism of induction as well. While free pDNA did not show any cytotoxicity, pDNA increased the cytotoxicity of CL via the formation of lipoplex. In addition, the lipoplex-induced cytotoxicity increased in a lipoplex dose-dependent manner, irrespective of the type of pDNA, cell line and the absence or presence of serum. An assay showed that apoptosis was largely induced by treatment with the lipoplex (lipofection), but not with CL alone, in the tested range of concentration of CL and pDNA. Furthermore, following treatment with lipoplexes, the cells exhibited the morphological features of apoptosis and DNA fragmentation. A cDNA microarray study showed that the lipofection up-regulated 45 genes related to apoptosis, transcription regulation and immune response. These results clearly indicate that pDNA in the lipoplex increases the cytotoxicity of CL as a result of inducing apoptosis. The fundamental principle for gene therapy is to deliver gene-based therapeutics to target cells for specific gene targeting with minimal cytotoxicity. Our results suggest the possibility that cytotoxicity induced by lipofection, accompanied by gene changes, could intrinsically exacerbate, attenuate or even mask the desired effects of gene-based therapy.

Induction of transcription factor CEBP homology protein mediates hypoglycaemia-induced necrotic cell death in human neuroblastoma cells

Oxygen and glucose deprivation are direct consequences of tissue ischaemia. We explored the interaction of hypoxia and hypoglycaemia on cell survival and gene expression in the absence of glutamatergic signalling using human SH-SY5Y neuroblastoma cells as a model. In agreement with previous investigations in non-neural cells, prolonged hypoxia (0.5% O(2)) failed to induce significant cell death in this system. In contrast, exposure to hypoglycaemia induced significant necrotic cell death (> 80% after 72 h). Interestingly, hypoglycaemia-induced cell death was completely abrogated by simultaneous exposure to hypoxia, suggesting strong cytoprotective effects of hypoxia. Subsequent microarray analysis of the underlying transcriptional responses revealed that the transcription factor CEBP homology protein (CHOP) was strongly induced by hypoglycaemia, and suppressed by simultaneous hypoxia. RNA interference against CHOP significantly protected cells from glucose deprivation-induced cell death. Hypoxia-induced vascular endothelial growth factor (VEGF) activation also protected cells against hypoglycaemia-induced cell death, but VEGF failed to modify hypoglycaemia-induced CHOP induction. Our data suggest that hypoglycaemia-induced necrotic cell death of neuroblastoma cells is an active process mediated via the induction of the transcription factor CHOP, and that hypoxia counteracts this cell death via at least two distinct mechanisms: repression of CHOP and induction of VEGF.

ROS mediates 4HPR-induced posttranscriptional expression of the Gadd153 gene

All-trans-N-(4-hydroxyphenyl)retinamide (4HPR) is a synthetic retinoid that can induce apoptosis in many cancer cell lines. The cytotoxicity of 4HPR is dependent on the production of ROS but the underlying reasons are not entirely certain. We have investigated the role of 4HPR-induced production of ROS in mediating the expression of the recently identified 4HPR-responsive gene Gadd153. In 4HPR-treated cells, the elevation of Gadd153 protein level was prevented by vitamin C, which had no effect on the activation of the Gadd153 gene promoter. The 4HPR-induced elevation of Gadd153 mRNA level persisted even after transcription was blocked with actinomycin D, but declined rapidly upon the addition of antioxidants to the transcription-arrested cells. The mRNA expressed from the full-length Gadd153 cDNA was degraded constitutively in cells in the absence but not in the presence of 4HPR. Such an inhibitory effect of 4HPR was abolished by antioxidants and by inhibitors of 12-lipoxygenase, baicalein (specific) and esculetin (panspecific). The inhibition of 4HPR-induced expression of Gadd153 protein by vitamin C was independent of intracellular proteasome activity and vitamin C had no effect on the intracellular decay of Gadd153 protein. Our data provide the first evidence that the posttranscriptional expression of the Gadd153 gene can be regulated by ROS produced by 4HPR.

Involvement of GADD153 and Cardiac Ankyrin Repeat Protein in Hypoxia-induced Apoptosis of H9c2 Cells

Oxidative stress is the main cause of cardiac injury during ischemia/reperfusion but the molecular mechanism for this process is unclear. In this study, it was found that hypoxia induces apoptosis in rat embryonic heart-derived H9c2 cells leading to the induction of GADD153, which is an apoptosis-related gene. Therefore, this study addressed the molecular role of GADD153 in hypoxia-induced apoptosis. The stable or inducible overexpression of GADD153 sensitized the H9c2 cells to apoptotic cell death. The results suggest that the transactivation domain of the GADD153 might be responsible for this cell execution and play a role in the nucleoplasmic localization of GADD153. The cells transiently transfected with the antisense GADD153 were more resistant to hypoxia-induced apoptosis than the vector control cells. Furthermore, GADD153 transcriptionally down-regulated the expression of the cardiac ankyrin repeat protein gene (CARP), which is a nuclear transcriptional co-factor that negatively regulates the expression of the cardiac gene. The ectopic expression of CARP in H9c2 cells increased the resistance to hypoxia-induced apoptosis. These results suggest that GADD153 overexpression and the concomitant down-regulation of CARP might have a causative role in the apoptotic cell injury of hypoxic H9c2 cells.

Hydrogen peroxide induces GADD153 in Jurkat cells through the protein kinase C-dependent pathway

Growth arrest and DNA damage-inducible gene 153 (GADD153) is a CCAAT/enhancer binding protein (C/EBP) related gene and is induced in response to various stimuli including DNA damaging agents, UV irradiation, and serum starvation. In this study, we investigated which intracellular signals contribute to the expression of GADD153 mRNA in Jurkat cells in response to oxidative stress using several kinds of kinase inhibitors. GADD153 mRNA expression was immediately enhanced following hydrogen peroxide exposure and was significantly inhibited by treatment with H-7, staurosporin, and Ro-31-8220. In particular, rottlerin, a PKCdelta specific inhibitor, markedly attenuated hydrogen peroxide-induced GADD153 mRNA expression even at 1 microM. Treatment with a potent PKC activator, phorbol-12-myristate-13-acetate (PMA), augmented GADD153 mRNA in Jurkat cells in the presence of hydrogen peroxide, although PMA alone induced GADD153 mRNA marginally. Hydrogen peroxide significantly enhanced the AP-1 binding activity of the nuclear extract from Jurkat cells to the GADD153 AP-1 binding site. AP-1 binding activity was suppressed by rottlerin treatment. These findings indicate that PKC, especially PKCdelta, plays an important role in the induction of GADD153 mRNA following oxidative stress.

Expression profile of genes regulated by activity of the Na-H exchanger NHE1

BACKGROUND

In mammalian cells changes in intracellular pH (pHi), which are predominantly controlled by activity of plasma membrane ion exchangers, regulate a diverse range of normal and pathological cellular processes. How changes in pHi affect distinct cellular processes has primarily been determined by evaluating protein activities and we know little about how pHi regulates gene expression.

RESULTS

A global profile of genes regulated in mammalian fibroblasts by decreased pHi induced by impaired activity of the plasma membrane Na-H exchanger NHE1 was characterized by using cDNA microarrays. Analysis of selected genes by quantitative RT-PCR, TaqMan, and immunoblot analyses confirmed results obtained from cDNA arrays. Consistent with established roles of pHi and NHE1 activity in cell proliferation and oncogenic transformation, grouping regulated genes into functional categories and biological pathways indicated a predominant number of genes with altered expression were associated with growth factor signaling, oncogenesis, and cell cycle progression.

CONCLUSION

A comprehensive analysis of genes selectively regulated by pHi provides insight on candidate targets that might mediate established effects of pHi on a number of normal and pathological cell functions.

Early aldosterone up-regulated genes: new pathways for renal disease?

BACKGROUND

The use of aldosterone antagonists has important beneficial effects on the progression of renal and cardiac disease reflected in a decrease of cardiovascular mortality and renal failure. Nevertheless, the incidence of heart and end-stage renal failure continues to increase. This leads to the conclusion that mechanisms independent of the classical aldosterone/mineralocorticoid receptor system may contribute to the pathogenesis of cardiac and renal disease.

METHODS

The mRNA expression profile of human renal epithelial cells in response to aldosterone was characterized using cDNA arrays covering approximately 1430 genes. Differentially expressed genes were further evaluated by quantitative reverse transcription-polymerase chain reaction (RT-PCR), Northern blotting, and estimating the gene products by Western blotting.

RESULTS

Aldosterone treatment of cells resulted in significant up-regulation of several genes within 1 hour, with sgk, p21/waf1, gadd45, and gadd153 being the most significant ones. Long-term treatment (>4 hours) with aldosterone induced the mRNA expression of pparalpha and puralpha. The mineralocorticoid receptor inhibitor spironolactone decreased the mRNA levels of sgk, p21/waf1, and gadd45, whereas the glucocorticoid receptor inhibitor RU 486 reduced the mRNA level of sgk and p21/waf1. Gadd153 was not affected by any of the inhibitors, probably indicating regulation by nonclassic mechanisms.

CONCLUSION

Among the early genes investigated in this study, one transcript has been identified that is not suppressed by antagonists of either glucocorticoid or mineralocorticoid receptor. Further studies should be able to identify other genes regulated in a similar manner that could explain the inefficacy of spironolactone in some cases of aldosterone-mediated kidney disease.

Inducing cancer cell death by targeting transcription factors

We review the biological significance of transcription factors such as p53, Myc, E2F family and AP-1 (Jun/Fos) in anticancer drug-induced apoptosis. It is likely that the functional role of these transcription factors is complex in response to DNA damage depending on cancer cell type. Regulation of apoptosis following DNA damage is mediated by cell cycle arrest for DNA repair and subsequent signal transduction pathways leading to apoptosis, which is associated with mitochondrial dysfunction. Activation of transcription factors following anticancer drugs is located upstream of signal transduction pathways, thereby the downstream pathway is promoted, which is connected to activation or suppression of apoptosis-related proteins. Switching on apoptotic signals by anticancer drugs is amplified in mitochondria by releasing cytochrome from the ion channel to activate the caspase cascade, which is regulated by Bcl-2 families in the central gate for drug-induced apoptosis. Activation of transcription factors targeting downstream genes, some of which are apoptosis-related genes, can play a critical role in promoting apoptosis following treatment with anticancer drugs. The strategy of identification of downstream target proteins or transcription factors involved in apoptosis will be necessary for the development of an effective transcription factor-targeted chemotherapy for cancer.