Calcium ionophore A23187 induces expression of the growth arrest and DNA damage inducible CCAAT/enhancer-binding protein (C/EBP)-related gene, gadd153. Ca2+ increases transcriptional activity and mRNA stability

Lnc-17Rik promotes the immunosuppressive function of Myeloid-Derived suppressive cells in esophageal cancer

Myeloid-derived suppressor cells (MDSCs) are a population of immature bone marrow cells that accumulate in large numbers in the spleen, peripheral blood, bone marrow, lymph nodes, and local and metastatic foci of tumors. C/EBP homologous protein (CHOP) and CCAAT/enhancer binding protein β (C/EBPβ) play key roles in regulating the immunosuppressive function and differentiation of MDSCs. Our study revealed that the long noncoding RNA Lnc-17Rik was able to promote immunosuppression in tumors by facilitating the activation and expression of key genes involved in MDSC differentiation. Lnc-17Rik was shown to directly interact with CHOP and C/EBPβ LIP to facilitate their dissociation from the transcriptional repressor complex involving C/EBP LAP/LIP/CHOP. Moreover, Lnc-17Rik increased the association of WD repeat-containing protein 5 (WDR5) with C/EBP LAP, promoting H3K4me3 enrichment in the promoter regions of arginase 1 (Arg-1), cyclooxygenase 2 (COX2), nitric oxide synthase 2 (NOS2) and NADPH oxidase 2 (NOX2) to enhance the expression of these genes. Furthermore, using a CD45 chimeric model we confirmed that Lnc-17Rik promoted the differentiation of monocytic (M)-MDSCs in vivo with the introduction of Lnc-17Rik-overexpressing MDSCs shown to promote tumor growth as a result of enhancing their immunosuppressive function. Notably, human Lnc-17Rik is highly homologous to mouse Lnc-17Rik and fulfills similar functions in human MDSC-like cells. In addition, we also found a high level of Lnc-17Rik in peripheral blood MDSC of patients with esophageal cancer. These findings suggest that Lnc-17Rik plays an important role in controlling the immunosuppressive function of MDSCs in the tumor environment and may further serve as a potential therapeutic target for patients with esophageal cancer.

Mycoplasma hyopneumoniae Inhibits Porcine Beta-Defensin 2 Production by Blocking the Unfolded Protein Response To Facilitate Epithelial Adhesion and Infection

Mycoplasma hyopneumoniae causes the disease porcine enzootic pneumonia, a highly contagious and chronic disease affecting pigs. Understanding the molecular mechanisms of its pathogenicity is critical for developing effective interventions to control this swine respiratory disease. Here, we describe a novel virulence mechanism by which M. hyopneumoniae interferes with the host unfolded protein response (UPR) and eventually facilitates bacterial adhesion and infection. We observed that M. hyopneumoniae infection suppressed the UPR target molecules GRP78 and CHOP by reducing PKR-like endoplasmic reticulum kinase/eukaryotic initiation factor 2 alpha (PERK/eIF2α) phosphorylation, ATF6 cleavage, and X-box binding protein 1 (XBP1) splicing. Interestingly, further analyses revealed that host UPR inhibition subsequently suppressed the NF-κB pathway, leading to the reduced production of porcine beta-defensin 2 (PBD-2), thus facilitating M. hyopneumoniae adherence and infection. This study provides new insights into the molecular pathogenesis of M. hyopneumoniae and sheds light upon its interactions with the host.

Endoplasmic reticulum stress: New insights into the pathogenesis and treatment of retinal degenerative diseases

Physiological equilibrium in the retina depends on coordinated work between rod and cone photoreceptors and can be compromised by the expression of mutant proteins leading to inherited retinal degeneration (IRD). IRD is a diverse group of retinal dystrophies with multifaceted molecular mechanisms that are not fully understood. In this review, we focus on the contribution of chronically activated unfolded protein response (UPR) to inherited retinal pathogenesis, placing special emphasis on studies employing genetically modified animal models. As constitutively active UPR in degenerating retinas may activate pro-apoptotic programs associated with oxidative stress, pro-inflammatory signaling, dysfunctional autophagy, free cytosolic Ca²⁺ overload, and altered protein synthesis rate in the retina, we focus on the regulatory mechanisms of translational attenuation and approaches to overcoming translational attenuation in degenerating retinas. We also discuss current research on the role of the UPR mediator PERK and its downstream targets in degenerating retinas and highlight the therapeutic benefits of reprogramming PERK signaling in preclinical animal models of IRD. Finally, we describe pharmacological approaches targeting UPR in ocular diseases and consider their potential applications to IRD.

Lnc-chop Promotes Immunosuppressive Function of Myeloid-Derived Suppressor Cells in Tumor and Inflammatory Environments

Myeloid-derived suppressor cells (MDSCs) are major regulators of immune responses in cancer. Both C/EBP homologous protein (CHOP) and C/EBPβ play a critical role in regulating immunosuppressive function of MDSCs. In this study, we identified a novel long noncoding RNA termed as lnc-chop in MDSCs, which may interact with CHOP and the C/EBPβ isoform liver-enriched inhibitory protein. The binding of lnc-chop with both CHOP and the C/EBPβ isoform liver-enriched inhibitory protein promoted the activation of C/EBPβ and upregulated the expression of arginase-1, NO synthase 2, NADPH oxidase 2, and cyclooxygenase-2, which are related to the immunosuppressive function of MDSCs in inflammatory and tumor environments. Additionally, lnc-chop also promoted the enrichment of H3K4me3 on the promoter region of arginase-1, NO synthase 2, NADPH oxidase 2, and cyclooxygenase-2. These findings suggest an important role of lnc-chop in controlling immunosuppressive function of MDSCs in the tumor environment.

Palmitate-induced C/EBP homologous protein activation leads to NF-κB-mediated increase in BACE1 activity and amyloid beta genesis

The etiology of Alzheimer's disease (AD) is egregiously comprehended, but epidemiological studies have posited that diets rich in the saturated fatty acid palmitic acid (palmitate) are a significant risk factor. The production and accumulation of amyloid beta peptide (Aβ) is considered the core pathological molecular event in the pathogenesis of AD. The rate-limiting step in Aβ genesis from amyloid-β precursor protein (AβPP) is catalyzed by the enzyme β-site amyloid precursor protein cleaving enzyme 1 (BACE1), the expression and enzymatic activity of which is significantly up-regulated in the AD brain. In this study, we determined the molecular mechanisms that potentially underlie the palmitate-induced up-regulation in BACE1 expression and augmented Aβ production. We demonstrate that a palmitate-enriched diet and exogenous palmitate treatment evoke an increase in BACE1 expression and activity leading to enhanced Aβ genesis in the mouse brain and SH-SY5Y-APPSwe cells, respectively, through the activation of the transcription factor NF-κB. Chromatin immunoprecipitation (ChIP) assays and luciferase reporter assays revealed that palmitate enhances BACE1 expression by increasing the binding of NF-κB in the BACE1 promoter followed by an enhancement in the transactivation of the BACE1 promoter. Elucidation and delineation of upstream molecular events unveiled a critical role of the endoplasmic reticulum stress-associated transcription factor, C/EBP homologous protein (CHOP) in the palmitate-induced NF-κB activation, as CHOP knock-down cells and Chop-/- mice do not exhibit the same degree of NF-κB activation in response to the palmitate challenge. Our study delineates a novel CHOP-NF-κB signaling pathway that mediates palmitate-induced up-regulation of BACE1 expression and Aβ genesis.

The neuroprotective effect of hesperidin in NMDA-induced retinal injury acts by suppressing oxidative stress and excessive calpain activation

We found that hesperidin, a plant-derived bioflavonoid, may be a candidate agent for neuroprotective treatment in the retina, after screening 41 materials for anti-oxidative properties in a primary retinal cell culture under oxidative stress. We found that the intravitreal injection of hesperidin in mice prevented reductions in markers of the retinal ganglion cells (RGCs) and RGC death after N-methyl-D-aspartate (NMDA)-induced excitotoxicity. Hesperidin treatment also reduced calpain activation, reactive oxygen species generation and TNF-α gene expression. Finally, hesperidin treatment improved electrophysiological function, measured with visual evoked potential, and visual function, measured with optomotry. Thus, we found that hesperidin suppressed a number of cytotoxic factors associated with NMDA-induced cell death signaling, such as oxidative stress, over-activation of calpain, and inflammation, thereby protecting the RGCs in mice. Therefore, hesperidin may have potential as a therapeutic supplement for protecting the retina against the damage associated with excitotoxic injury, such as occurs in glaucoma and diabetic retinopathy.

Molecular Mechanisms of IRE1α-ASK1 Pathway Reactions to Unfolded Protein Response in DRN Neurons of Post-Traumatic Stress Disorder Rats

The goal of this study was to further elucidate the molecular mechanisms of post-traumatic stress disorder (PTSD) pathogenesis and to provide experimental evidence for new drug targets for effective PTSD treatment. Expression changes of IRE1α, ASK1, and other downstream molecules of the IRE1α-ASK1 endoplasmic reticulum stress (ERS) signaling pathway were investigated. JNK, P38, CHOP, Bcl-2, and Bax were analyzed at both protein and mRNA levels of dorsal raphe nucleus (DRN) neurons of PTSD rats. The rat PTSD model was established via the single-prolonged stress (SPS) method. Animals were randomly divided into five groups: a normal control group, a 1-day SPS group, a 4-days SPS group, a 7-day SPS group, and a 14-day SPS group. Spatial memory and learning ability of rats were evaluated subsequent to SPS using the Morris water maze test. Changes of IRE1α expression in the control and SPS groups were detected via immunohistochemistry (IHC). Protein and mRNA expressions of IRE1α, ASK1, JNK, P38, CHOP, Bcl-2, and Bax in the control and SPS groups were detected via Western blot and RT-PCR, respectively. The Morris water maze test revealed significantly longer average escape latencies in all SPS groups compared to the control group. In the spatial probe test, the percentage of time spent in the target quadrant was significantly lower in the SPS groups compared to control. IHC revealed increased positive expression of IRE1α subsequent to SPS challenge, reaching maximal levels on days four and seven (P < 0.01), while significantly decreasing on day 14 (P < 0.01). Western blot and RT-PCR revealed that protein and mRNA expressions of IRE1α, ASK1, JNK, CHOP, and P38 were significantly increased compared to control, peaking on days one, four, and seven post-SPS before returning to previous levels. Compared to control, expressions of Bcl-2 and Bax presented an initial increasing tendency followed by a decrease. A peak of Bcl-2 expression appeared early on day one following SPS, then decreased to a steady level. Bax expression in the SPS groups remained constant during early stages after SPS (days one to three) compared to control; however, expression significantly increased on day four and maintained a high level. In summary, 1) SPS challenge significantly activated the IRE1α-ASK1-JNK and IRE1α-ASK1-P38 apoptosis-signaling pathways in DRN neurons of PTSD rats. This resulted in a cascade of downstream reactions and ultimately apoptosis of DRN neurons. 2) Increased expression of apoptosis-associated molecules Bcl-2 and Bax in DRN neurons following SPS challenge was revealed as a central mechanism, inducing apoptosis of DRN neurons in PTSD rats.

Palmitate-induced Endoplasmic Reticulum stress and subsequent C/EBPα Homologous Protein activation attenuates leptin and Insulin-like growth factor 1 expression in the brain

The peptide hormones Insulin-like growth factor-1 (IGF1) and leptin mediate a myriad of biological effects - both in the peripheral and central nervous systems. The transcription of these two hormones is regulated by the transcription factor C/EBPα, which in turn is negatively regulated by the transcription factor C/EBP Homologous Protein (CHOP), a specific marker of endoplasmic reticulum (ER) stress. In the peripheral system, disturbances in leptin and IGF-1 levels are implicated in a variety of metabolic diseases including obesity, diabetes, atherosclerosis and cardiovascular diseases. Current research suggests a positive correlation between consumption of diets rich in saturated free fatty acids (sFFA) and metabolic diseases. Induction of ER stress and subsequent dysregulation in the expression levels of leptin and IGF-1 have been shown to mediate sFFA-induced metabolic diseases in the peripheral system. Palmitic acid (palmitate), the most commonly consumed sFFA, has been shown to be up-taken by the brain, where it may promote neurodegeneration. However, the extent to which palmitate induces ER stress in the brain and attenuates leptin and IGF1 expression has not been determined. We fed C57BL/6J mice a palmitate-enriched diet and determined effects on the expression levels of leptin and IGF1 in the hippocampus and cortex. We further determined the extent to which ER stress and subsequent CHOP activation mediate the palmitate effects on the transcription of leptin and IGF1. We demonstrate that palmitate induces ER stress and decreases leptin and IGF1 expression by inducing the expression of CHOP. The molecular chaperone 4-phenylbutyric acid (4-PBA), an inhibitor of ER stress, precludes the palmitate-evoked down-regulation of leptin and IGF1 expression. Furthermore, the activation of CHOP in response to ER stress is pivotal in the attenuation of leptin and IGF1 expression as knocking-down CHOP in mice or in SH-SY5Y and Neuro-2a (N2a) cells rescues the palmitate-induced mitigation in leptin and IGF1 expression. Our study implicates for the first time ER stress-induced CHOP activation in the brain as a mechanistic link in the palmitate-induced negative regulation of leptin and IGF1, two neurotrophic cytokines that play an indispensable role in the mammalian brain.

The effect of bovine rotavirus and its nonstructural protein 4 on ER stress-mediated apoptosis in HeLa and HT-29 cells

Endoplasmic reticulum (ER) plays important roles in multiple cellular processes as well as cell survival and apoptosis. Perturbation of ER functions leads to ER stress and unfolded protein response (UPR). The primary goal of this response is cell survival, but severe ER stress can trigger apoptosis signaling. In tumor cells, chronically activated UPR response provides tumor growth. So, apoptosis induced by the ER stress has been the target for anti-cancer therapy. In this in vitro study, we examined the apoptotic effect associated with ER stress of bovine rotavirus and its nonstructural protein 4 (NSP4) alone in two cancer cell lines. The plasmid pcDNA3.1 encoding NSP4 protein of bovine rotavirus transfected with lipofectamine 2000 into the HeLa and HT-29 cells for protein production. MTT, flow cytometry, and Western blot were used to evaluate the cell viability, apoptosis, and expression level of C/EBP-homologous protein (CHOP) and activated caspase-4. In parallel, the apoptotic effect of the bovine rotavirus associated with ER stress in the infected cells was examined too. The cytotoxic and apoptotic effect of NSP4 protein on the cells were statistically significant compared to the control groups. However, Western blot showed that the expression of the NSP4 protein by recombinant plasmid did not lead to high expression of CHOP and activation of caspase-4. Interestingly, rotavirus not only induced significant apoptosis but also caused an increase in CHOP expression and caspase-4 activation in the infected cells compared to control. As a result, NSP4 protein and bovine rotavirus can be considered a potential novel bio-therapeutic strategy for cancer treatment.

Legionella suppresses the host unfolded protein response via multiple mechanisms

The intracellular pathogen, Legionella pneumophila, secretes ∼300 effector proteins to modulate the host environment. Given the intimate interaction between L. pneumophila and the endoplasmic reticulum, we investigated the role of the host unfolded protein response (UPR) during L. pneumophila infection. Interestingly, we show that the host identifies L. pneumophila infection as a form of endoplasmic reticulum stress and the sensor pATF6 is processed to generate pATF6(N), a transcriptional activator of downstream UPR genes. However, L. pneumophila is able to suppress the UPR and block the translation of prototypical UPR genes, BiP and CHOP. Furthermore, biochemical studies reveal that L. pneumophila uses two effectors (Lgt1 and Lgt2) to inhibit the splicing of XBP1u mRNA to spliced XBP1 (XBP1s), an UPR response regulator. Thus, we demonstrate that L. pneumophila is able to inhibit the UPR by multiple mechanisms including blocking XBP1u splicing and causing translational repression. This observation highlights the utility of L. pneumophila as a powerful tool for studying a critical protein homeostasis regulator.

The bacterium Legionella pneumophila, a causative agent of severe pneumonia, replicates inside an endoplasmic reticulum-like organelle in the host cells. Here, Treacy-Abarca and Mukherjee show that the pathogen dampens the host's unfolded protein response (UPR) pathway by multiple mechanisms.

The unfolded protein response as a target for cancer therapy

Various physiological and pathological conditions generate an accumulation of misfolded proteins in the endoplasmic reticulum (ER). This results in ER stress followed by a cellular response to cope with this stress and restore homeostasis: the unfolded protein response (UPR). Overall, the UPR leads to general translational arrest and the induction of specific factors to ensure cell survival or to mediate cell death if the stress is too severe. In multiple cancers, components of the UPR are overexpressed, indicating increased dependence on the UPR. In addition, the UPR can confer resistance to anti-cancer treatment. Therefore, modification of the UPR should be explored for its anti-cancer properties. This review discusses factors associated with the UPR that represent potential therapeutic targets.

The role of calcium in VDAC1 oligomerization and mitochondria-mediated apoptosis

The voltage-dependent anion channel (VDAC), located at the outer mitochondria membrane (OMM), mediates interactions between mitochondria and other parts of the cell by transporting anions, cations, ATP, Ca(2+), and metabolites. Substantial evidence points to VDAC1 as being a key player in apoptosis, regulating the release of apoptogenic proteins from mitochondria, such as cytochrome c, and interacting with anti-apoptotic proteins. Recently, we demonstrated that VDAC1 oligomerization is a general mechanism common to numerous apoptogens acting via different initiating cascades and proposed that a protein-conducting channel formed within a VDAC1 homo/hetero oligomer mediates cytochrome c release. However, the molecular mechanism responsible for VDAC1 oligomerization remains unclear. Several studies have shown that mitochondrial Ca(2+) is involved in apoptosis induction and that VDAC1 possesses Ca(2+)-binding sites and mediates Ca(2+) transport across the OMM. Here, the relationship between the cellular Ca(2+) level, [Ca(2+)]i, VDAC1 oligomerization and apoptosis was studied. Decreasing [Ca(2+)]i using the cell-permeable Ca(2+) chelating reagent BAPTA-AM was found to inhibit VDAC1 oligomerization and apoptosis, while increasing [Ca(2+)]i using Ca(2+) ionophore resulted in VDAC1 oligomerization and apoptosis induction in the absence of apoptotic stimuli. Moreover, induction of apoptosis elevated [Ca(2+)]i, concomitantly with VDAC1 oligomerization. AzRu-mediated inhibition of mitochondrial Ca(2+) transport decreased VDAC1 oligomerization, suggesting that mitochondrial Ca(2+) is required for VDAC1 oligomerization. In addition, increased [Ca(2+)]i levels up-regulate VDAC1 expression. These results suggest that Ca(2+) promotes VDAC1 oligomerization via activation of a yet unknown signaling pathway or by increasing VDAC1 expression, leading to apoptosis. This article is part of a Special Issue entitled: 12th European Symposium on Calcium.

Defective trafficking of cone photoreceptor CNG channels induces the unfolded protein response and ER-stress-associated cell death

Mutations that perturb the function of photoreceptor CNG (cyclic nucleotide-gated) channels are associated with several human retinal disorders, but the molecular and cellular mechanisms leading to photoreceptor dysfunction and degeneration remain unclear. Many loss-of-function mutations result in intracellular accumulation of CNG channel subunits. Accumulation of proteins in the ER (endoplasmic reticulum) is known to cause ER stress and trigger the UPR (unfolded protein response), an evolutionarily conserved cellular programme that results in either adaptation via increased protein processing capacity or apoptotic cell death. We hypothesize that defective trafficking of cone photoreceptor CNG channels can induce UPR-mediated cell death. To test this idea, CNGA3 subunits bearing the R563H and Q655X mutations were expressed in photoreceptor-derived 661W cells with CNGB3 subunits. Compared with wild-type, R563H and Q655X subunits displayed altered degradation rates and/or were retained in the ER. ER retention was associated with increased expression of UPR-related markers of ER stress and with decreased cell viability. Chemical and pharmacological chaperones {TUDCA (tauroursodeoxycholate sodium salt), 4-PBA (sodium 4-phenylbutyrate) and the cGMP analogue CPT-cGMP [8-(4-chlorophenylthio)-cGMP]} differentially reduced degradation and/or promoted plasma-membrane localization of defective subunits. Improved subunit maturation was concordant with reduced expression of ER-stress markers and improved viability of cells expressing localization-defective channels. These results indicate that ER stress can arise from expression of localization-defective CNG channels, and may represent a contributing factor for photoreceptor degeneration.

Endoplasmic reticulum stress-induced CHOP activation mediates the down-regulation of leptin in human neuroblastoma SH-SY5Y cells treated with the oxysterol 27-hydroxycholesterol

Epidemiological studies have suggested an inverse relationship between the adipocytokine leptin and the onset of Alzheimer's disease (AD), and leptin supplementation decreases amyloid-β (Aβ) production and tau phosphorylation (p-tau), two major biochemical events that play a key role in the pathogenesis of AD. We have previously shown that the cholesterol oxidized product 27-hydroxycholesterol (27-OHC) inhibits leptin expression, an effect that correlated with increased levels of Aβ and p-tau. We have also shown that 27-OHC induces endoplasmic reticulum (ER) stress, a cellular response that is implicated in AD and confers leptin resistance. However the extent to which ER stress is involved in 27-OHC-induced attenuation in leptin expression has not been determined. In this study we determined the involvement of ER stress in the 27-OHC-induced attenuation of leptin expression in SH-SY5Y human neuroblastoma cells. We demonstrate that 27-OHC-induced ER stress attenuates leptin expression by activating C/EBP Homologous Protein (CHOP) which negatively regulates C/EBPα, a transcription factor required for leptin expression. The molecular chaperone 4-phenylbutyric acid (4-PBA) precludes 27-OHC-evoked ER stress and down-regulation of leptin. Furthermore, we demonstrate that the activation of the transcription factor CHOP in response to ER stress is pivotal in the attenuation of leptin expression as knocking-down CHOP alleviates the attenuation in leptin expression. Our study implicates ER stress as the mechanistic link in the 27-OHC-induced negative regulation of leptin, a hormone that has potential therapeutic effects in AD by reducing Aβ and phosphorylated tau accumulation.

C/EBPzeta (CHOP/Gadd153) is a negative regulator of LPS-induced IL-6 expression in B cells

C/EBPzeta was originally identified as a gene induced upon DNA damage and growth arrest. It has been shown to be involved in the cellular response to endoplasmic reticulum stress. Because of sequence divergence from other C/EBP family members in its DNA-binding domain and its consequent inability to bind the C/EBP consensus-binding motif, C/EBPzeta can act as a dominant negative inhibitor of other C/EBPs. C/EBP transactivators are essential to the expression of many proinflammatory cytokines and acute phase proteins, but a role for C/EBPzeta in regulating their expression has not been described. We found that expression of C/EBPzeta is induced in response to LPS treatment of B cells at both the mRNA and protein levels. Correlating with the highest levels of C/EBPzeta expression at 48 h after LPS treatment, there is an increased association of C/EBPzeta with C/EBPbeta, and both the abundance of C/EBP DNA-binding species and IL-6 expression are downregulated. Furthermore, ectopic expression of C/EBPzeta inhibited C/EBPbeta-dependent IL-6 expression from both the endogenous IL-6 gene and an IL-6 promoter-reporter. These results suggest that C/EBPzeta functions as negative regulator of IL-6 expression in B cells and that it contributes to the transitory expression of IL-6 that is observed after LPS treatment.

Transforming growth factor-beta1 expression is up-regulated in maturation-stage enamel organ and may induce ameloblast apoptosis

Transforming growth factor-beta1 (TGF-beta1) regulates a variety of cellular responses that are dependent on the developmental stage and on the origins of the cell or the tissue. In mature tissues, and especially in tissues of epithelial origin, TGF-beta1 is generally considered to be a growth inhibitor that may also promote apoptosis. The ameloblast cells of the enamel organ epithelium are adjacent to and responsible for the developing enamel layer on unerupted teeth. Once the enamel layer reaches its full thickness, the tall columnar secretory-stage ameloblasts shorten, and a portion of these maturation-stage ameloblasts become apoptotic. Here we investigate whether TGF-beta1 plays a role in apoptosis of the maturation-stage ameloblasts. We demonstrate in vitro that ameloblast lineage cells are highly susceptible to TGF-beta1-mediated growth arrest and are prone to TGF-beta1-mediated cell death/apoptosis. We also demonstrate in vivo that TGF-beta1 is expressed in the maturation-stage enamel organ at significantly higher levels than in the earlier secretory-stage enamel organ. This increased expression of TGF-beta1 correlates with an increase in expression of the enamel organ immediate-early stress-response gene and with a decrease in the anti-apoptotic Bcl2 : Bax expression ratio. We conclude that TGF-beta1 may play an important role in ameloblast apoptosis during the maturation stage of enamel development.

Calcium signaling-induced Smad3 nuclear accumulation induces acetylcholinesterase transcription in apoptotic HeLa cells

Recently, acetylcholinesterase (AChE) has been studied as an important apoptosis regulator. We previously showed that cellular calcium mobilization upregulated AChE expression by modulating promoter activity and mRNA stability. In this study, we have identified a potential Smad3/4 binding element, TGCCAGACA, located within the -601 to -571 bp fragment of the AChE promoter, as an important calcium response motif. Smad2/3 and Smad4 were shown to bind this element. Overexpression of human Smad3 increased AChE transcription activity in a dose-dependent manner in HeLa cells, whereas dominant-negative Smad3 blocked this activation. Upon A23187 and thapsigargin treatment, nuclear Smad3 accumulation was observed, an effect that was blocked by the intracellular Ca(2+) chelator BAPTA-AM. Calcium-induced AChE transcriptional activation was significantly blocked when the nuclear localization signal of Smad3 was destroyed. Taken together, our data suggest Smad3 can regulate AChE transcriptional activation following calcium-induced nuclear accumulation.

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.

Regulation of interleukin-8 gene at a distinct site of its promoter by CCAAT enhancer-binding protein homologous protein in prostaglandin E2-treated human T cells

For a long period of time, the transcription factor CCAAT/enhancer-binding protein homologous protein (CHOP) has been thought to inhibit transcriptional activity for its ability to interact with CCAAT enhancer-binding protein family factors, thus preventing their binding to DNA. We have previously shown that in human T lymphocytes the CHOP phosphorylation induced by prostaglandin E(2) (PGE(2))-increased interleukin-8 (IL-8) gene expression. Given the CHOP positive role in the regulation of transcription, here we have investigated the molecular mechanism(s) by which CHOP increases IL-8 gene activity under PGE(2) stimulus. Transfection experiments with mutants showed both that the CHOP transactivation domain is essential for IL-8 transcription and that the IL-8/activator protein 1 (AP-1) promoter mutated in NF-kappaB and NF-IL-6, but not in the AP-1 site, harbors essential CHOP-responsive elements. CHOP silencing confirmed its role in the IL-8 transcriptional regulation and protein production, whereas c-Jun small interfering RNA experiments showed that the PGE(2)-induced activation of IL-8 promoter is mainly c-Jun-independent. Moreover, PGE(2) induced CHOP-DNA complexes only when the entire IL-8/AP-1 promoter or the wild type sequences encompassing the AP-1 upstream region were employed. Mutations introduced in these sequences prevented the DNA-CHOP complex formation. The IL-8/AP-1 mutant promoter lacking the sequence immediately upstream the AP-1 site is PGE(2)-unresponsive. Finally, chromatin immunoprecipitation data confirmed in vivo that PGE(2) induces CHOP binding to the IL-8 promoter. Taken together, our results suggest that the increased expression of CHOP in response to PGE(2) exerts a positive transcriptional regulation of the IL-8 promoter mediated by direct binding to a novel consensus site.

Coupling endoplasmic reticulum stress to the cell death program in mouse melanoma cells: effect of curcumin

The microenvironment of cancerous cells includes endoplasmic reticulum (ER) stress the resistance to which is required for the survival and growth of tumors. Acute ER stress triggers the induction of a family of ER stress proteins that promotes survival and/or growth of the cancer cells, and also confers resistance to radiation and chemotherapy. Prolonged or severe ER stress, however, may ultimately overwhelm the cellular protective mechanisms, triggering cell death through specific programmed cell death (pcd) pathways. Thus, downregulation of the protective stress proteins may offer a new therapeutic approach to cancer treatment. In this regard, recent reports have demonstrated the roles of the phytochemical curcumin in the inhibition of proteasomal activity and triggering the accumulation of cytosolic Ca(2+) by inhibiting the Ca(2+)-ATPase pump, both of which enhance ER stress. Using a mouse melanoma cell line, we investigated the possibility that curcumin may trigger ER stress leading to programmed cell death. Our studies demonstrate that curcumin triggers ER stress and the activation of specific cell death pathways that feature caspase cleavage and activation, p23 cleavage, and downregulation of the anti-apoptotic Mcl-1 protein.

The amyloid precursor protein potentiates CHOP induction and cell death in response to ER Ca2+ depletion

Here we investigated the role of the amyloid precursor protein (APP) in regulation of Ca(2+) store depletion-induced neural cell death. Ca(2+) store depletion from the endoplasmic reticulum (ER) was induced by the SERCA (Sarco/Endoplasmic Reticulum Calcium ATPase) inhibitor thapsigargin which led to a rapid induction of the unfolded protein response (UPR) and a delayed activation of executioner caspases in the cultures. Overexpression of APP potently enhanced cytosolic Ca(2+) levels and cell death after ER Ca(2+) store depletion in comparison to vector-transfected controls. GeneChip and RT-PCR analysis revealed that the expression of classical UPR chaperone genes was not altered by overexpression of APP. Interestingly, the induction of the ER stress-responsive pro-apoptotic transcription factor CHOP was significantly upregulated in APP-overexpressing cells in comparison to vector-transfected controls. Chelation of intracellular Ca(2+) with BAPTA-AM revealed that enhanced CHOP expression after store depletion occurred in a Ca(2+)-dependent manner in APP-overexpressing cells. Prevention of CHOP induction by BAPTA-AM and by RNA interference was also able to abrogate the potentiating effect of APP on thapsigargin-induced apoptosis. Application of the store-operated channel (SOC)-inhibitors SK & F96365 and 2-APB downmodulated APP-triggered potentiation of cytosolic Ca(2+) levels and apoptosis after treatment with thapsigargin. Our data demonstrate that APP significantly modulates Ca(2+) store depletion-induced cell death in a SOC- and CHOP-dependent manner, but independent of the UPR.

Neuregulin 1-Beta cytoprotective role in AML 12 mouse hepatocytes exposed to pentachlorophenol

Neuregulins are a family of growth factor domain proteins that are structurally related to the epidermal growth factor. Accumulating evidence has shown that neuregulins have cyto- and neuroprotective properties in various cell types. In particular, the neuregulin-1 Beta (NRG1-Beta) isoform is well documented for its antiinflammatory properties in rat brain after acute stroke episodes. Pentachlorophenol (PCP) is an organochlorine compound that has been widely used as a biocide in several industrial, agricultural, and domestic applications. Previous investigations from our laboratory have demonstrated that PCP exerts both cytotoxic and mitogenic effects in human liver carcinoma (HepG2) cells, primary catfish hepatocytes and AML 12 mouse hepatocytes. We have also shown that in HepG2 cells, PCP has the ability to induce stress genes that may play a role in the molecular events leading to toxicity and tumorigenesis. In the present study, we hypothesize that NRG1-Beta will exert its cytoprotective effects in PCP-treated AML 12 mouse hepatocytes by its ability to suppress the toxic effects of PCP. To test this hypothesis, we performed the MTT-cell respiration assay to assess cell viability, and Western-blot analysis to assess stress-related proteins as a consequence of PCP exposure. Data obtained from 48 h-viability studies demonstrated a biphasic response; showing a dose-dependent increase in cell viability within the range of 0 to 3.87 microg/mL, and a gradual decrease within the concentration range of 7.75 to 31.0 microg/mL in concomitant treatments of NRG1-Beta+PCP and PCP. Cell viability percentages indicated that NRG1-Beta+PCPtreated cells were not significantly impaired, while PCP-treated cells were appreciably affected; suggesting that NRG1-Beta has the ability to suppress the toxic effects of PCP. Western Blot analysis demonstrated the potential of PCP to induce oxidative stress and inflammatory response (c-fos), growth arrest and DNA damage (GADD153), proteotoxic effects (HSP70), cell cycle arrest as consequence of DNA damage (p53), mitogenic response (cyclin- D1), and apoptosis (caspase-3). NRG1-Beta exposure attenuated stress-related protein expression in PCP-treated AML 12 mouse hepatocytes. Here we provide clear evidence that NRG1-Beta exerts cytoprotective effects in AML 12 mouse hepatocytes exposed to PCP.

Regulation of acetylcholinesterase expression by calcium signaling during calcium ionophore A23187- and thapsigargin-induced apoptosis

We have recently reported that acetylcholinesterase expression was induced during apoptosis in various cell types. In the current study we provide evidence to suggest that the induction of acetylcholinesterase expression during apoptosis is regulated by the mobilization of intracellular Ca(2+). During apoptosis, treatment of HeLa and MDA-MB-435s cells with the calcium ionophore A23187 resulted in a significant increase in acetylcholinesterase mRNA and protein levels. Chelation of intracellular Ca(2+) by BAPTA-AM (1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester), an intracellular Ca(2+) chelator, inhibited acetylcholinesterase expression. A23187 also enhanced the stability of acetylcholinesterase mRNA and increased the activity of acetylcholinesterase promoter, effects that were blocked by BAPTA-AM. Perturbations of cellular Ca(2+) homeostasis by thapsigargin resulted in the increase of acetylcholinesterase expression as well as acetylcholinesterase promoter activity during thapsigargin induced apoptosis in HeLa and MDA-MB-435s cells, effects that were also inhibited by BAPTA-AM. We further demonstrated that the transactivation of the human acetylcholinesterase promoter by A23187 and thapsigargin was partially mediated by a CCAAT motif within the -1270 to -1248 fragment of the human acetylcholinesterase promoter. This motif was able to bind to CCAAT binding factor (CBF/NF-Y). These results strongly suggest that cytosolic Ca(2+) plays a key role in acetylcholinesterase regulation during apoptosis induced by A23187 and thapsigargin.

Enhancement of neuroprotection and heat shock protein induction by combined prostaglandin A1 and lithium in rodent models of focal ischemia

Both prostaglandin A(1) (PGA(1)) and lithium have been reported to protect neurons against excitotoxic and ischemic injury. The present study was undertaken to examine the effects of lithium and PGA1 on heat shock proteins (HSP) and the growth arrest and DNA-damage-inducible gene (GADD153) and to evaluate if lithium could potentiate PGA(1)'s neuroprotective effects against cerebral ischemia. Rats were pretreated with a subcutaneous injection of lithium for 2 days and a single intracerebral ventricle administration of PGA(1) 15 min before ischemic insult. Brain ischemia was induced by a permanent middle cerebral artery occlusion. The infarct volume, motor behavior deficits and brain edema were analyzed 24 h after ischemic insult. The result showed that PGA(1) significantly reduced infarct volume, neurological deficits and brain edema. Except for neurological deficit, lithium enhanced PGA(1)'s neuroprotection. The neuroprotective effects of PGA(1) were associated with an up-regulation of cytoprotective heat shock proteins HSP70 and GRP78 in the ischemic brain hemisphere as determined by immunoblotting and immunofluorescence. The induction of HSP70 and GRP78 was enhanced by lithium. However, although the expression of GADD153 was enhanced significantly after pMCAO, it was not influenced by either PGA(1) or lithium or their combination. These studies suggest that lithium can potentiate PGA(1)'s neuroprotective effects and thus may have potential clinical value for the treatment of stroke in combination with other neuroprotective agents.

Free radical biology and medicine: it's a gas, man!

We review gases that can affect oxidative stress and that themselves may be radicals. We discuss O(2) toxicity, invoking superoxide, hydrogen peroxide, and the hydroxyl radical. We also discuss superoxide dismutase (SOD) and both ground-state, triplet oxygen ((3)O(2)), and the more energetic, reactive singlet oxygen ((1)O(2)). Nitric oxide ((*)NO) is a free radical with cell signaling functions. Besides its role as a vasorelaxant, (*)NO and related species have other functions. Other endogenously produced gases include carbon monoxide (CO), carbon dioxide (CO(2)), and hydrogen sulfide (H(2)S). Like (*)NO, these species impact free radical biochemistry. The coordinated regulation of these species suggests that they all are used in cell signaling. Nitric oxide, nitrogen dioxide, and the carbonate radical (CO(3)(*-)) react selectively at moderate rates with nonradicals, but react fast with a second radical. These reactions establish "cross talk" between reactive oxygen (ROS) and reactive nitrogen species (RNS). Some of these species can react to produce nitrated proteins and nitrolipids. It has been suggested that ozone is formed in vivo. However, the biomarkers that were used to probe for ozone reactions may be formed by non-ozone-dependent reactions. We discuss this fascinating problem in the section on ozone. Very low levels of ROS or RNS may be mitogenic, but very high levels cause an oxidative stress that can result in growth arrest (transient or permanent), apoptosis, or necrosis. Between these extremes, many of the gasses discussed in this review will induce transient adaptive responses in gene expression that enable cells and tissues to survive. Such adaptive mechanisms are thought to be of evolutionary importance.

CHOP plays a pivotal role in the astrocyte death induced by oxygen and glucose deprivation

Ischemia has different consequences on the survival of astrocytes and neurons. Thus, astrocytes show a remarkable resistance to short periods of ischemia that are well known to cause neuronal death. We have used a cell culture model of stroke, oxygen, and glucose deprivation (OGD), to clarify the mechanisms responsible for the exclusive resistance of astrocytes to ischemia. The expression of genes implicated in both ischemia-induced astrocyte death and post-ischemic survival was analysed by the RNA differential display technique. Our study revealed that the expression of the CEBP homologous protein (CHOP)-coding gene is promptly an intensely upregulated following astrocyte oxygen and glucose deprivation. CHOP mRNA induction was accompanied by the activation of other genes (grp78, grp95) that, alike CHOP, are involved in the endoplasmic reticulum (ER) stress response. In addition, drugs that cause ER calcium depletion or protein N-glycosylation inhibition mimicked the effects of OGD on astrocyte survival, further supporting the involvement of ER in the astrocyte responses to OGD. Our experiments also demonstrated that upregulation of CHOP during the ER stress response is required for ischemia to cause astrocyte death. Not only the levels of CHOP mRNA and protein correlate perfectly with the degree of OGD-triggered cell injury, but also astrocyte death induced by OGD is significantly overcome by CHOP antisense oligonucleotide treatment. Nevertheless, we observed that astrocytes undergo apoptosis only when CHOP is permanently upregulated, and not when CHOP increases are transient. Finally, we found that the extent of CHOP induction is determined by the length of the ischemic stimulus. Taken together, our results indicate that permanent upregulation of CHOP is decisive for the induction of astrocyte death by OGD.

Degradation of C/EBPβ in cultured myotubes is calpain-dependent

Members of the C/EBP transcription factor family regulate cell differentiation and multiple other cellular functions. The cellular levels of C/EBPalpha, gamma, delta, epsilon, and Gadd153/CHOP are regulated in part by proteasome-dependent degradation. In contrast, mechanisms regulating the degradation of C/EBPbeta are poorly understood. We tested the hypothesis that the degradation of C/EBPbeta is calpain-dependent. Studies were performed in cultured L6 myotubes (a rat skeletal muscle cell line) because we have found previously that C/EBPbeta may be involved in the regulation of muscle proteolysis. Treatment of cultured L6 myotubes with the calpain inhibitors calpeptin and Calpain Inhibitor I and II resulted in increased C/EBPbeta concentrations but did not influence cellular levels of the other C/EBP transcription factor family members. Transfection of myoblasts with a plasmid expressing the endogenous calpain inhibitor calpastatin resulted in increased cellular levels of C/EBPbeta whereas the opposite result was observed in myoblasts overexpressing micro- or m-calpain. Co-immunoprecipitation provided evidence for protein-protein interaction between C/EBPbeta and micro- and m-calpain suggesting that C/EBPbeta may be a calpain substrate. This notion was supported by experiments in which immunoprecipitated C/EBPbeta was incubated with purified micro-calpain in a cell-free system. The increase in C/EBPbeta levels caused by inhibition of calpain activity was accompanied by increased C/EBPbeta DNA-binding and gene activation. The present results suggest that C/EBPbeta is degraded by a calpain-dependent mechanism in skeletal muscle cells and that the role of calpains is specific for C/EBPbeta among different members of the C/EBP transcription factor family.

Involvement of endoplasmic reticulum stress in hereditary tyrosinemia type I

Hereditary tyrosinemia type I (HTI) is the most severe disease of the tyrosine degradation pathway. HTI is caused by a deficiency of fumarylacetoacetate hydrolase (FAH), the enzyme responsible for the hydrolysis of fumarylacetoacetate (FAA). As a result, there is an accumulation of metabolites such as maleylacetoacetate, succinylacetone, and FAA. The latter was shown to display mutagenic, cytostatic, and apoptogenic activities and to cause chromosomal instability. Herein, we demonstrate that FAA also causes a cellular insult leading to the endoplasmic reticulum (ER) stress signaling. Treatment of V79 Chinese hamster lung cells with an apoptogenic dose of FAA (100 mum) causes an early induction of the ER resident chaperone GRP78/BiP and a simultaneous phosphorylation of the eIF2alpha. FAA treatment also causes a subsequent induction of the proapoptotic CHOP (CEBP homologous protein) transcription factor as well as a late activation of caspase-12. Data obtained from fah(-/-) mice taken off the therapeutic 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3 cyclohexanedione drug are similar. However, in this mouse model, there is also an increase in proteasome activity indicative of ER-associated degradation. This difference observed between the two models may be due to the fact that the murine model measures the effects of all metabolites accumulating in hereditary tyrosinemia type I as opposed to the cellular model that only measures the effects of exogenous FAA.

Novel aspects on the regulation of muscle wasting in sepsis

Muscle wasting in sepsis is associated with increased expression of messenger RNA for several genes in the ubiquitin-proteasome proteolytic pathway, indicating that increased gene transcription is involved in the development of muscle atrophy. Here we review the influence of sepsis on the expression and activity of the transcription factors activator protein-1, nuclear factor-kappaB (NF-kappaB), and CCAAT/enhancer binding protein, as well as the nuclear cofactor p300. These transcription factors may be important for sepsis-induced muscle wasting because several of the genes in the ubiquitin-proteasome proteolytic pathway have multiple binding sites for activating protein-1, nuclear factor-kappaB, and CCAAT/enhancer binding protein in their promoter regions. In addition, the potential role of increased muscle calcium levels for sepsis-induced muscle atrophy is reviewed. Calcium may regulate several mechanisms and factors involved in muscle wasting, including the expression and activity of the calpain-calpastatin system, proteasome activity, CCAAT/enhancer binding protein transcription factors, apoptosis and glucocorticoid-mediated muscle protein breakdown. Because muscle wasting is commonly seen in patients with sepsis and has severe clinical consequences, a better understanding of mechanisms regulating sepsis-induced muscle wasting may help improve the care of patients with sepsis and other muscle-wasting conditions as well.

Oncogenic Ras-mediated downregulation of Gadd153/CHOP is required for Ras-induced cellular transformation

Oncogenic Ras proteins transform cells via multiple downstream signaling cascades that are important for cell proliferation and survival. Gadd153, also known as CHOP, is a growth inhibitory and proapoptotic protein and its expression is upregulated by many agents that induce apoptosis. Here, we report our novel findings that oncogenic Ras downregulates Gadd153 expression at both protein and mRNA levels and that such downregulation occurs, at least in part, via decreases in GADD153 mRNA stability. Gadd153 downregulation is specific to oncogenic Ras since another oncogenic family member R-Ras2/TC21 does not downregulate Gadd153. We further demonstrate that the expression of exogenous Gadd153 interferes with Ras-induced oncogenic transformation, which suggests that downregulation of Gadd153 appears to be an important mechanism by which oncogenic Ras promotes cellular transformation. Thus, oncogenic Ras-mediated cellular transformation also involves downmodulation of important molecules such as Gadd153 that negatively regulate cell growth and survival.

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.

Fluoride induces endoplasmic reticulum stress in ameloblasts responsible for dental enamel formation

The mechanism of how fluoride causes fluorosis remains unknown. Exposure to fluoride can inhibit protein synthesis, and this may also occur by agents that cause endoplasmic reticulum (ER) stress. When translated proteins fail to fold properly or become misfolded, ER stress response genes are induced that together comprise the unfolded protein response. Because ameloblasts are responsible for dental enamel formation, we used an ameloblast-derived cell line (LS8) to characterize specific responses to fluoride treatment. LS8 cells were growth-inhibited by as little as 1.9-3.8 ppm fluoride, whereas higher doses induced ER stress and caspase-mediated DNA fragmentation. Growth arrest and DNA damage-inducible proteins (GADD153/CHOP, GADD45alpha), binding protein (BiP/glucose-responsive protein 78 (GRP78), the non-secreted form of carbonic anhydrase VI (CA-VI), and active X-box-binding protein-1 (Xbp-1) were all induced significantly after exposure to 38 ppm fluoride. Unexpectedly, DNA fragmentation increased when GADD153 expression was inhibited by short interfering RNA treatment but remained unaffected by transient GADD153 overexpression. Analysis of control and GADD153(-/-) embryonic fibroblasts demonstrated that caspase-3 mediated the increased DNA fragmentation observed in the GADD153 null cells. We also demonstrate that mouse incisor ameloblasts are sensitive to the toxic effects of high dose fluoride in drinking water. Activated Ire1 initiates an ER stress response pathway, and mouse ameloblasts were shown to express activated Ire1. Ire1 levels appeared induced by fluoride treatment, indicating that ER stress may play a role in dental fluorosis. Low dose fluoride, such as that present in fluoridated drinking water, did not induce ER stress.

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.

Induction of CCAAT/Enhancer-binding Protein (C/EBP)-homologous Protein/Growth Arrest and DNA Damage-inducible Protein 153 Expression during Inhibition of Phosphatidylcholine Synthesis Is Mediated via Activation of a C/EBP-activating Transcription Factor-responsive Element

The gene for the proapoptotic transcription factor CCAAT/enhancer-binding protein (C/EBP)-homologous protein/growth arrest and DNA damage-inducible protein 153 (CHOP/GADD153) is induced by various cellular stresses. Previously, we described that inhibition of phosphatidylcholine (PC) synthesis in MT58 cells, which contain a temperature-sensitive mutation in CTP:phosphocholine cytidylyltransferase (CT), results in apoptosis preceded by the induction of CHOP. Here we report that prevention of CHOP induction, by expression of antisense CHOP, delays the PC depletion-induced apoptotic process. By mutational analysis of the conserved region in the promoter of the CHOP gene, we provide evidence that the C/EBP-ATF composite site, but not the ER stress-responsive element or the activator protein-1 site, is required for the increased expression of CHOP during PC depletion. Inhibition of PC synthesis in MT58 cells also led to an increase in phosphorylation of the stress-related transcription factor ATF2 and the stress kinase JNK after 8 and 16 h, respectively. In contrast, no phosphorylation of p38 MAPK was observed in MT58 cultured at the nonpermissive temperature. Treatment of MT58 cells with the JNK inhibitor SP600125 could rescue the cells from apoptosis but did not inhibit the phosphorylation of ATF2 or the induction of CHOP. Taken together, our results suggest that increased expression of CHOP during PC depletion depends on a C/EBP-ATF element in its promoter and might be mediated by binding of ATF2 to this element.

Liver-enriched transcription factors in liver function and development. Part II: the C/EBPs and D site-binding protein in cell cycle control, carcinogenesis, circadian gene regulation, liver regeneration, apoptosis, and liver-specific gene regulation

In the first part of our review (see Pharmacol Rev 2002;54:129-158), we discussed the basic principles of gene transcription and the complex interactions within the network of hepatocyte nuclear factors, coactivators, ligands, and corepressors in targeted liver-specific gene expression. Now we summarize the role of basic region/leucine zipper protein family members and particularly the albumin D site-binding protein (DBP) and the CAAT/enhancer-binding proteins (C/EBPs) for their importance in liver-specific gene expression and their role in liver function and development. Specifically, regulatory networks and molecular interactions were examined in detail, and the experimental findings summarized in this review point to pivotal roles of DBP and C/EBPs in cell cycle control, carcinogenesis, circadian gene regulation, liver regeneration, apoptosis, and liver-specific gene regulation. These regulatory proteins are therefore of great importance in liver physiology, liver disease, and liver development. Furthermore, interpretation of the vast data generated by novel genomic platform technologies requires a thorough understanding of regulatory networks and particularly the hierarchies that govern transcription and translation of proteins as well as intracellular protein modifications. Thus, this review aims to stimulate discussions on directions of future research and particularly the identification of molecular targets for pharmacological intervention of liver disease.

African swine fever virus inhibits induction of the stress-induced proapoptotic transcription factor CHOP/GADD153

Stress signaling from mitochondria and the endoplasmic reticulum (ER) leads to the induction of the proapoptotic transcription factor CHOP/GADD153. Many viruses use the ER as a site of replication and/or envelopment, and this activity can lead to the activation of ER stress and apoptosis. African swine fever virus (ASFV) is assembled on the cytoplasmic face of the ER and ultimately enveloped by ER membrane cisternae. The virus also recruits mitochondria to sites of viral replication and induces the mitochondrial stress protein hsp60. Here we studied the effects of ASFV on the induction of CHOP/GADD153 in infected cells. Interestingly, unlike other ER-tropic viruses, ASFV did not activate CHOP and was able to inhibit the induction of CHOP/GADD153 by a number of exogenous stimuli.

Roles of CHOP/GADD153 in endoplasmic reticulum stress

Endoplasmic reticulum (ER) is the site of synthesis and folding of secretory proteins. Perturbations of ER homeostasis affect protein folding and cause ER stress. ER can sense the stress and respond to it through translational attenuation, upregulation of the genes for ER chaperones and related proteins, and degradation of unfolded proteins by a quality-control system. However, when the ER function is severely impaired, the organelle elicits apoptotic signals. ER stress has been implicated in a variety of common diseases such as diabetes, ischemia and neurodegenerative disorders. One of the components of the ER stress-mediated apoptosis pathway is C/EBP homologous protein (CHOP), also known as growth arrest- and DNA damage-inducible gene 153 (GADD153). Here, we summarize the current understanding of the roles of CHOP/GADD153 in ER stress-mediated apoptosis and in diseases including diabetes, brain ischemia and neurodegenerative disease.

Activation of endoplasmic reticulum stress signaling pathway is associated with neuronal degeneration in MoMuLV-ts1-induced spongiform encephalomyelopathy

Temperature-sensitive mutant of Moloney murine leukemia virus-TB (MoMuLV-ts1)-mediated neuronal death in mice is likely due to both loss of glial support and release of cytokines and neurotoxins from ts1-infected glial cells. Cytotoxic mediators present in ts1-induced spongiform lesions may generate endoplasmic reticulum (ER) stress, which has been implicated in the pathogenesis of a variety of neurodegenerative diseases. We investigated whether ER stress signaling is involved in ts1-mediated neuronal loss in the brain of infected mice. ts1-infected brainstems were found to show significant increases in phosphorylation of the double-stranded RNA-dependent protein kinase-like ER kinase and eukaryotic initiation factor 2-alpha. In addition, increased expression of growth arrest DNA damage 153 (GADD153), glucose-regulated protein 78, and caspase-12 were accompanied by increases in processing of caspase-12 and its downstream target, caspase-3. All of these events are markers of ER stress. We observed that GADD153 and cleaved caspase-3 were present in degenerative neurons in the lesions of infected mice, but not in uninfected controls. Phosphorylated calmodulin-dependent protein kinase II-alpha was significantly increased, and was coexpressed with GADD153 in a large proportion of neurons undergoing early and advanced degenerative changes. Finally, neuronal degeneration in spongiform lesions was associated with increase in calcium (Ca(2+)) accumulation in mitochondria. Together, these results suggest that ts1 infection-mediated neuronal degeneration in mice may result from activation of ER stress signaling pathways, presumably initiated by perturbation of Ca(2+) homeostasis. Our findings highlight the importance of the ER stress signaling pathway in ts1 infection-induced neuronal degeneration and death.

Regulation of Involucrin Gene Expression

The epidermis is a dynamic renewing structure that provides life-sustaining protection from the environment. The major cell type of the epidermis, the epidermal keratinocyte, undergoes a carefully choreographed program of differentiation. Alteration of these events results in a variety of debilitating and life-threatening diseases. Understanding how this process is regulated is an important current goal in biology. In this review, we summarize the literature regarding regulation of involucrin, an important marker gene that serves as a model for understanding the mechanisms that regulate the differentiation process. Current knowledge describing the role of transcription factors and signaling cascades in regulating involucrin gene expression are presented. These studies describe a signaling cascade that includes the novel protein kinase C isoforms, Ras, MEKK1, MEK3, and a p38delta-extracellular signal regulated kinase 1/2 complex. This cascade regulates activator protein one, Sp1, and CCATT/enhancer-binding protein transcription factor DNA binding to two discrete involucrin promoter regions, the distal- and proximal-regulatory regions, to regulate involucrin gene expression.

Green tea polyphenol and curcumin inversely regulate human involucrin promoter activity via opposing effects on CCAAT/enhancer-binding protein function

Antioxidants are important candidate agents for the prevention of disease. However, the possibility that different antioxidants may produce opposing effects in tissues has not been adequately explored. We have reported previously that (-)-epigallocatechin-3-gallate (EGCG), a green tea polyphenol antioxidant, stimulates expression of the keratinocyte differentiation marker, involucrin (hINV), via a Ras, MEKK1, MEK3, p38delta signaling cascade (Balasubramanian, S., Efimova, T., and Eckert, R. L. (2002) J. Biol. Chem. 277, 1828-1836). We now show that EGCG activation of this pathway results in increased CCAAT/enhancer-binding protein (C/EBPalpha and C/EBPbeta) factor level and increased complex formation at the hINV promoter C/EBP DNA binding site. This binding is associated with increased promoter activity. Mutation of the hINV promoter C/EBP binding site eliminates the regulation as does expression of GADD153, a dominant-negative C/EBP factor. In contrast, a second antioxidant, curcumin, inhibits the EGCG-dependent promoter activation. This is associated with inhibition of the EGCG-dependent increase in C/EBP factor level and C/EBP factor binding to the hINV promoter. Curcumin also inhibits the EGCG-dependent increase in endogenous hINV levels. The curcumin-dependent suppression of C/EBP factor level is inhibited by treatment with the proteasome inhibitor MG132, suggesting that the proteasome function is required for curcumin action. We conclude that curcumin and EGCG produce opposing effects on involucrin gene expression via regulation of C/EBP factor function. The observation that two antioxidants can produce opposite effects is an important consideration in the context of therapeutic antioxidant use.

Transcriptional regulation of the human transferrin gene by GADD153 in hepatoma cells

The transcription factor CHOP/GADD153 is reportedly induced by cellular stresses such as UV light, genotoxic agents, and protein misfolding in the endoplasmic reticulum. However, the mechanism whereby induction of the GADD153 gene is linked to a downstream pathway is still unclear. Previously, we observed that a synthetic retinoid N-(4-hydroxyphenyl)retinamide (4HPR) effectively impaired cell growth and survival (induction of growth arrest and apoptosis) in human hepatoma cells, which was accompanied by over expression of GADD153. Furthermore, GADD153-transfected Hep 3B cells were growth arrested and were sensitized to drug-induced apoptosis. Thus, in this study, we used suppression subtractive hybridization (SSH) to identify GADD153 target genes that were up-regulated or down-regulated in the GADD153 transfectants. We screened 614 sequence-verified clones by Northern blotting, of which 42 genes were scored as over expressed and 17 genes as under expressed in GADD153 transfectants compared with control vector transfectants. Of those genes, 49 corresponded to known genes in public databases. Among them, we further verified that the expression of transferrin (Tf), which is a negative acute-phase protein and is essential to cell survival as a growth factor, was highly modulated by drug-induced GADD153 over expression or by in vitro transfection. GADD153 significantly antagonized the C/EBP (C/EBP-alpha, -beta, and -delta)-mediated transcriptional activation of the Tf gene. In conclusion, Tf and other target genes identified may play a functional role in the downstream pathway of GADD153.

Isoliquiritigenin inhibits the growth of prostate cancer

OBJECTIVE

Isoliquiritigenin, one of the components in the root of Glycyrrhiza glabra L., is a member of the flavonoids, which are known to have an anti-tumor activity in vitro and in vivo. In this study, we investigated the anti-tumor effect of isoliquiritigenin on prostate cancer in vitro.

METHODS

DU145 and LNCaP prostate cancer cell lines were used as targets. We examined the effects of isoliquiritigenin on cell proliferation, cell cycle regulation and cell cycle-regulating gene expression. Further, we investigated the effects of isoliquiritigenin on the GADD153 mRNA and protein expression, and promoter activity.

RESULTS

Isoliquiritigenin significantly inhibited the proliferation of prostate cancer cell lines in a dose-dependent and time-dependent manner. Fluorescence-activated cell sorting (FACS) analysis indicated that isoliquiritigenin induced S and G2/M phase arrest. Isoliquiritigenin enhanced the expression of GADD153 mRNA and protein associated with cell cycle arrest. Further, isoliquiritigenin stimulated transcriptional activity of GADD153 promoter dose-dependently.

CONCLUSION

These findings suggest that isoliquiritigenin is a candidate agent for the treatment of prostate cancer and GADD153 may play an important role in isoliquiritigenin-induced cell cycle arrest and cell growth inhibition.

C/EBP homologous protein (CHOP) up-regulates IL-6 transcription by trapping negative regulating NF-IL6 isoform

Interleukin-6 (IL-6) production is up-regulated by several stimuli through the activation of transcription factors. We have previously demonstrated that CCAAT/enhancer binding protein homologous protein (CHOP) positively regulates IL-6 production at the transcriptional level in the human melanoma cell line A375. In this study, we provide evidence that CHOP up-regulates the IL-6 transcription without binding to the IL-6 promoter. CHOP dimerized more preferentially with an inhibitory isoform of nuclear factor for IL-6 expression (LIP (liver-enriched inhibitory protein)) than with a positively acting isoform (LAP, liver-enriched activator protein). These results indicate that CHOP plays an important role in IL-6 production without binding to its promoter, probably by trapping protein(s) such as LIP, which would otherwise inhibit IL-6 transcription.

GADD153-mediated anticancer effects of N-(4-hydroxyphenyl)retinamide on human hepatoma cells

The anticancer effects of N-(4-hydroxyphenyl)retinamide (4HPR), a potential chemopreventive or chemotherapeutic retinamide, are thought to be derived from its ability to induce apoptosis. However, the mechanism of apoptosis induced by 4HPR remains unclear. Thus, this study was designed to identify the gene(s) responsible for induction of apoptosis by 4HPR. Apoptosis was effectively induced by 4HPR in human hepatoma cells. Using the differential display-PCR method, a gene involved in the response to 4HPR was identified, and cells in which the expression of that gene was modulated were analyzed for survival, induction of apoptosis, and cell cycle. GADD153, a gene involved in growth arrest and apoptosis, was preferentially expressed in human hepatoma cells as well as in other cancer cells during 4HPR-induced apoptosis. 4HPR regulates GADD153 expression at the post-transcriptional level in Hep 3B cells and at the transcriptional and post-transcriptional levels in SK-HEP-1 cells, when assayed by in vitro transfection and mRNA stability experiments. To determine the role of the GADD153 protein overexpression that is induced by 4HPR, Hep 3B cells with ectopic overexpression of GADD153 were found to be growth-arrested (at G(1)) and readily underwent apoptosis following treatment with 4HPR or even when they reached confluence. N-Acetyl-l-cysteine or GADD153 antisense significantly protected the cells from 4HPR-induced apoptosis, accompanying by the inhibition of GADD153 overexpression. Parthenolide-mediated overexpression of GADD153 resulted in enhanced 4HPR-induced apoptosis. These results suggest that GADD153 overexpression induced by 4HPR may contribute to the anticancer effects (induction of apoptosis and growth arrest) of 4HPR on cancer cells.

Novel protein kinase C isoforms regulate human keratinocyte differentiation by activating a p38 delta mitogen-activated protein kinase cascade that targets CCAAT/enhancer-binding protein alpha

The novel protein kinase C (nPKC) isoforms are important regulators of human involucrin (hINV) gene expression during keratinocyte differentiation (Efimova, T., and Eckert, R. L. (2000) J. Biol. Chem. 275, 1601-1607). Although the regulatory mechanism involves mitogen-activated protein kinase (MAPK) activation, the role of individual MAPK isoforms has not been elucidated. We therefore examined the effects of individual nPKCs on MAPK activation. We observe unique changes whereby nPKC expression simultaneously increases p38 activity and decreases ERK1 and ERK2 activity. Although p38 alpha, p38 beta, and p38 delta are expressed in keratinocytes, only a single isoform, p38 delta, accounts for the increased p38 activity. Parallel studies indicate that this isoform is also activated by treatment with the keratinocyte regulatory agents, 12-O-tetradecanoylphorbol-13-acetate, calcium, and okadaic acid. These changes in MAPK activity are associated with increased C/EBP alpha transcription factor expression and DNA binding to the hINV promoter and increased hINV gene expression. Expression of PKC delta, PKC epsilon, or PKC eta causes a 10-fold increase in hINV promoter activity, whereas C/EBP alpha expression produces a 25-fold increase. However, simultaneous expression of both proteins causes a synergistic 100-fold increase in promoter activity. These responses are eliminated by the dominant-negative C/EBP isoform, GADD153, and are also inhibited by dominant-negative forms of Ras, MEKK1, MEK3, and p38. These results suggest that the nPKC isoforms produce a unique shift in MAPK activity via a Ras, MEKK1, MEK3 pathway, to increase p38 delta and inhibit ERK1/2 and ultimately increase C/EBP alpha binding to the hINV promoter and hINV gene expression.