Mycobacterium tuberculosis (Mtb) uses maltose-1-phosphate to synthesize α-glucans that make up the major component of its outer capsular layer. Maltose kinase (MaK) catalyzes phosphorylation of maltose. The molecular basis for this phosphorylation is currently not understood. Here, we describe the first crystal structure of MtbMaK refined to 2.4 Å resolution. The bi-modular architecture of MtbMaK reveals a remarkably unique N-lobe. An extended sheet protrudes into ligand binding pocket of an adjacent monomer and contributes residues critical for kinase activity. Structure of the complex of MtbMaK bound with maltose reveals that maltose binds in a shallow cavity of the C-lobe. Structural constraints permit phosphorylation of α-maltose only. Surprisingly, instead of a Gly-rich loop, MtbMaK employs ‘EQS’ loop to tether ATP. Notably, this loop is conserved across all MaK homologues. Structures of MtbMaK presented here unveil features that are markedly different from other kinases and support the scaffolding role proposed for this kinase.
Engineered nanoparticles are widely used in commercial products, and yet due to the paucity of safety information, there are concerns surrounding potential adverse health effects, especially from inhaled nanoparticles and their putative contribution to allergic airway disease. The objective of this study was to investigate whether size or surface chemistry of engineered nanoparticles can influence the immune enhancing properties of these agents on antigen-specific T cell responses. Ovalbumin (OVA)-derived peptides were presented to T cells by either spleen-derived endogenous antigen presenting cells or a mouse dendritic cell (DC) line, DC2.4. In all models, interferon (IFN)-γ and interleukin (IL)-2 production by CD8+ or CD4+ T cells in response to peptide OVA257–264 or OVA323–339, respectively, was measured by flow cytometry. To address the study objective, silica nanoparticles (SNPs) were modified with alkyne-terminated surfaces and appended with polyethylene glycol chains via “click” chemistry. These modified SNPs were resistant to agglomerate in in vitro culture media, suggesting that their modulation of T cell responses is the result of true nanoscale-mediated effects. Under conditions of suboptimal T-cell activation, modified SNPs (up to 10 μg/ml) enhanced the proportion of CD8+, but not CD4+, T cells producing IFN-γ and IL-2. Various functional groups (–COOH, –NH2 and –OH) on modified SNPs enhanced IFN-γ and IL-2 production to different levels, with –COOH SNPs being the most effective. Furthermore, 51 nm –COOH SNPs exhibited a greater enhancing effect on the CD8+ T cell response than other sized particles. Collectively, our results show that modified SNPs can enhance antigen-specific CD8+ T cell responses, suggesting that certain modified SNPs exhibit potential adjuvant-like properties.
Silica nanoparticles; cytokines; T cells; ovalbumin antigens; adjuvant
The development of a series of potent and highly selective casein kinase 1δ/ε (CK1δ/ε) inhibitors is described. Starting from a purine scaffold inhibitor (SR-653234) identified by high throughput screening, we developed a series of potent and highly kinase selective inhibitors, including SR-2890 and SR-3029, which have IC50 ≤ 50 nM versus CK1δ. The two lead compounds have ≤ 100 nM EC50 values in MTT assays against the human A375 melanoma cell line and have physical, in vitro and in vivo PK properties suitable for use in proof of principle animal xenograft studies against human cancer cell lines.
Casein kinase 1δ/ε inhibitor; Selective CK1δ/ε inhibitor; Purine scaffold kinase inhibitor; Antiproliferative agent; Potent growth inhibitor of A375 melanoma; cell line
Tumor suppressor p53 maintains genome stability by differentially activating target genes that control diverse cellular responses, such as the antioxidant response, cell cycle arrest and apoptosis. Despite the fact that many p53 downstream genes have been well characterized, novel p53 target genes are continuously being identified. Here, we report that Tpt1 is a direct target gene of p53. We found that p53 upregulates the transcription of Tpt1 and identified a p53-responsive element in the promoter of the mouse Tpt1 gene. Furthermore, p53-dependent induction of Tpt1 was able to reduce oxidative stress, minimize apoptosis, and promote cell survival in response to H2O2 challenge. In addition, a positive correlation between the expression of p53 and Tpt1 only existed in normal lung tissues, not in lung tumors. Such positive correlation was also found in lung cell lines that contain wild-type p53, but not mutated p53. Based on the important role of Tpt1 in cancer development, chemoresistance, and cancer reversion, identification of Tpt1 as a direct target gene of p53 not only adds to the complexity of the p53 network, but may also open up a new avenue for cancer prevention and intervention.
p53; Tpt1; TCTP; cancer
Δ9-tetrahydrocannabinol (Δ9-THC) has potent immune modulatory properties and can impair pathogen-induced immune defenses, which in part have been attributed to ligation of the cannabinoid receptors 1 (CB1) and 2 (CB2). Most recently, dendritic cells (DC) were identified for their potential to enhance influenza-induced immunopathology in mice lacking CB1 and CB2 (CB1
−/−). This study focused on the modulation of the inflammatory immune response to influenza by Δ9-THC and the role of CB1 and/or CB2 as receptor targets for Δ9-THC. C57Bl/6 (wild type) and CB1
−/− mice were administered Δ9-THC (75mg/kg) surrounding the intranasal instillation of A/PR/8/34 influenza virus. Three days post infection (dpi), Δ9-THC broadly decreased expression levels of mRNA induced by the innate immune response to influenza, suppressed the percentage of interferon-gamma (IFN-γ)–producing CD4+ and interleukin-17–producing NK1.1+ cells, and reduced the influx of antigen-presenting cells (APC), including inflammatory myeloid cells and monocytes/macrophages, into the lung in a CB1- and/or CB2-dependent manner. Δ9-THC had little effect on the expression of CD86, major histocompatibility complex I (MHC I), and MHC II by APC isolated from the lung. In vitro studies demonstrated that lipopolysaccharide (LPS)–induced maturation was suppressed by Δ9-THC in bone marrow–derived DC (bmDC). Furthermore, antigen-specific IFN-γ production by CD8+ T cells after coculture was reduced by Δ9-THC treatment of bmDC in a CB1- and/or CB2-dependent manner. Collectively, these studies suggest that Δ9-THC potently suppresses myeloid cell immune function, in a manner involving CB1 and/or CB2, thereby impairing immune responses to influenza infection.
Δ9-tetrahydrocannabinol; cannabinoid receptors; immune modulation; antigen-presenting cells; influenza.
In response to oxidative stress, the transcription factor Nrf2 is upregulated and controls activation of many genes that work in concert to defend cells from damages and to maintain cellular redox homeostasis. p53 has been regarded as the guardian of the genome through its pro-oxidant and antioxidant functions. Under low levels of reactive oxygen species (ROS), “normal” amounts of p53 upregulates expression of antioxidant genes, protecting macromolecules from ROS-induced damage. However, at high levels or extended exposure of ROS, p53 expression is enhanced, activating pro-oxidant genes and resulting in p53-dependent apoptosis. We observed a two-phase Nrf2 expression controlled by p53. (i) The induction phase: when p53 expression is relatively low, p53 enhances the protein level of Nrf2 and its target genes to promote cell survival in a p21-dependent manner. (ii) The repression phase: when p53 expression is high, the Nrf2-mediated survival response is inhibited by p53. Our observation leads to the hypothesis that the p53-mediated biphasic regulation of Nrf2 may be key for the tumor-suppressor function of p53 by coordinating cell survival and death pathways. Antioxid. Redox Signal. 17, 1670–1675.
Arthrobacter sp. strain FB24 is a species in the genus Arthrobacter Conn and Dimmick 1947, in the family Micrococcaceae and class Actinobacteria. A number of Arthrobacter genome sequences have been completed because of their important role in soil, especially bioremediation. This isolate is of special interest because it is tolerant to multiple metals and it is extremely resistant to elevated concentrations of chromate. The genome consists of a 4,698,945 bp circular chromosome and three plasmids (96,488, 115,507, and 159,536 bp, a total of 5,070,478 bp), coding 4,536 proteins of which 1,257 are without known function. This genome was sequenced as part of the DOE Joint Genome Institute Program.
With the increase in production and use of engineered nanoparticles (NP; ≤ 100 nm), safety concerns have risen about the potential health effects of occupational or environmental NP exposure. Results of animal toxicology studies suggest that inhalation of NP may cause pulmonary injury with subsequent acute or chronic inflammation. People with chronic respiratory diseases like asthma or allergic rhinitis may be even more susceptible to toxic effects of inhaled NP. Few studies, however, have investigated adverse effects of inhaled NP that may enhance the development of allergic airway disease.
We investigated the potential of polyethylene glycol coated amorphous silica NP (SNP; 90 nm diameter) to promote allergic airway disease when co-exposed during sensitization with an allergen. BALB/c mice were sensitized by intranasal instillation with 0.02% ovalbumin (OVA; allergen) or saline (control), and co-exposed to 0, 10, 100, or 400 μg of SNP. OVA-sensitized mice were then challenged intranasally with 0.5% OVA 14 and 15 days after sensitization, and all animals were sacrificed a day after the last OVA challenge. Blood and bronchoalveolar lavage fluid (BALF) were collected, and pulmonary tissue was processed for histopathology and biochemical and molecular analyses.
Co-exposure to SNP during OVA sensitization caused a dose-dependent enhancement of allergic airway disease upon challenge with OVA alone. This adjuvant-like effect was manifested by significantly greater OVA-specific serum IgE, airway eosinophil infiltration, mucous cell metaplasia, and Th2 and Th17 cytokine gene and protein expression, as compared to mice that were sensitized to OVA without SNP. In saline controls, SNP exposure did cause a moderate increase in airway neutrophils at the highest doses.
These results suggest that airway exposure to engineered SNP could enhance allergen sensitization and foster greater manifestation of allergic airway disease upon secondary allergen exposures. Whereas SNP caused innate immune responses at high doses in non-allergic mice, the adjuvant effects of SNP were found at lower doses in allergic mice and were Th2/Th17 related. In conclusion, these findings in mice suggest that individuals exposed to SNP might be more prone to manifest allergic airway disease, due to adjuvant-like properties of SNP.
Silica nanoparticles; Adjuvant potential; Allergic airway disease; Th2/Th17 response; Murine ovalbumin model
Recombination processes in GaP/GaNP core/shell nanowires (NWs) grown on Si are studied by employing temperature-dependent continuous wave and time-resolved photoluminescence (PL) spectroscopies. The NWs exhibit bright PL emissions due to radiative carrier recombination in the GaNP shell. Though the radiative efficiency of the NWs is found to decrease with increasing temperature, the PL emission remains intense even at room temperature. Two thermal quenching processes of the PL emission are found to be responsible for the degradation of the PL intensity at elevated temperatures: (a) thermal activation of the localized excitons from the N-related localized states and (b) activation of a competing non-radiative recombination (NRR) process. The activation energy of the latter process is determined as being around 180 meV. NRR is also found to cause a significant decrease of carrier lifetime.
Nanowires; III-V semiconductors; Photoluminescence; 68.65.La; 78.55.Cr; 61.72.-y
Previously, CD8+ T cells were found to be a sensitive target for suppression by Δ9-tetrahydrocannabinol (Δ9-THC) in a murine model of influenza infection. To study the effect of Δ9-THC on CD8+ cytotoxic T lymphocytes (CTL), an allogeneic model of MHC I mismatch was used to elicit CTL. In addition, to determine the requirement for the cannabinoid receptors 1 (CB1) and 2 (CB2) in Δ9-THC-mediated CTL response modulation, mice null for both receptors were used (CB1
−/−). Δ9-THC suppressed CTL function independent of CB1 and CB2 as evidenced by reduction of 51Cr release by CTL generated from CB1
−/− mice. Furthermore, viability in CD4+ and CD8+ cells was reduced in a concentration-dependent manner with Δ9-THC, independent of CB1 and CB2, but no effect of Δ9-THC on proliferation was observed, suggesting that Δ9-THC decreases the number of T cells initially activated. Δ9-THC increased expression of the activation markers, CD69 in CD8+ cells and CD25 in CD4+ cells in a concentration-dependent manner in cells derived from WT and CB1
−/− mice. Furthermore, Δ9-THC synergized with the calcium ionophore, ionomycin, to increase CD69 expression on both CD4+ and CD8+ cells. In addition, without stimulation, Δ9-THC increased CD69 expression in CD8+ cells from CB1
−/− and WT mice. Overall, these results suggest that CB1 and CB2 are dispensable for Δ9-THC-mediated suppression and that perturbation of Ca2+ signals during Tcell activation plays an important role in the mechanism by which Δ9-THC suppresses CTL function.
Δ9-tetrahydrocannabinol; Cannabinoid receptors; Cytotoxic T lymphocytes; Immune modulation; Ca2+; T cell activation
Mesorhizobium alhagi strain CCNWXJ12-2T is a novel species of soil-dwelling, nitrogen-fixing bacteria that can form symbiotic root nodules with Alhagi sparsifolia. Moreover, the strain has high resistance to salt and alkali. Here we report the draft genome sequence of Mesorhizobium alhagi strain CCNWXJ12-2T. A large number of osmotic regulation-related genes have been identified.
The design and synthesis of a novel series of c-jun N-terminal kinase (JNK) inhibitors is described. The development of the 4-(pyrazol-3-yl)-pyridine series was discovered from an earlier pyrimidine series of JNK inhibitors. Through the optimization of the scaffold 2, several potent compounds with good in vivo profiles were discovered.
There are currently no drugs to treat neurodegeneration in Parkinson’s disease (PD) and all existing medications only treat symptoms, lose efficacy over time, and produce untoward side effects. In the current work, we report the first highly selective, orally bioavailable, c-jun-N-terminal kinase (JNK) inhibitor for protection of dopaminergic neurons in vitro and in vivo. At 300 nM this compound showed statistically significant protection of primary dopaminergic neurons exposed to 1-methyl-4-phenylpyridinium (MPP+), had pharmacokinetic properties in rodents consistent with twice daily (b.i.d.) dosing, and was orally efficacious at 30 mg/kg in a mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson’s disease. Moreover, a dose-dependent target modulation of c-jun phosphorylation served as a biomarker for demonstrating on-target inhibition of JNK as the mechanism of action for this compound. Collectively these results suggest that this JNK inhibitor could be a promising therapeutic neuroprotective agent in the treatment of Parkinson’s disease.
There are currently no drugs to treat neurodegeneration in Parkinson’s disease (PD), and all existing medications only treat symptoms, lose efficacy over time, and produce untoward side effects. In the current work, we report the first highly selective, orally bioavailable c-jun-N-terminal kinase (JNK) inhibitor for protection of dopaminergic neurons in vitro and in vivo. At 300 nM, this compound showed statistically significant protection of primary dopaminergic neurons exposed to 1-methyl-4-phenylpyridinium (MPP+), had pharmacokinetic properties in rodents consistent with twice daily (b.i.d.) dosing, and was orally efficacious at 30 mg/kg in a mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson’s disease. Moreover, a dose-dependent target modulation of c-jun phosphorylation served as a biomarker for demonstrating on-target inhibition of JNK as the mechanism of action for this compound. Collectively, these results suggest that this JNK inhibitor could be a promising therapeutic neuroprotective agent in the treatment of Parkinson’s disease.
JNK; MPTP; neuroprotection; Parkinsonʼs disease
Given the significant body of data supporting an essential role for c-jun-N-terminal kinase (JNK) in neurodegenerative disorders, we set out to develop highly selective JNK inhibitors, with good cell potency, and good brain penetration properties. The structure activity relationships (SAR) around a series of aminopyrimidines was evaluated utilizing biochemical and cell- based assays to measure JNK inhibition, and brain penetration in mice. Microsomal stability in three species, P450 inhibition, inhibition of generation of reactive oxygen species (ROS), and pharmacokinetics in rats were also measured. Compounds 9g, 9i, 9j, and 9l had greater than 135-fold selectivity over p38, and cell-based IC50 values < 100 nM. Moreover, compound 9l showed an IC50= 0.8 nM for inhibition of ROS and had good pharmacokinetic properties in rat, along with a brain-to-plasma ratio of 0.75. These results suggest that biaryl substituted aminopyrimidines represented by compound 9l may serve as the first small molecule inhibitors to test efficacy of JNK inhibitors in neurodegenerative disorders.
The transcription factor Nrf2 has emerged as a master regulator for the endogenous antioxidant response, which is critical in defending cells against environmental insults and in maintaining intracellular redox balance. However, whether Nrf2 has any role in neuronal cell differentiation is largely unknown. In this report, we have examined the effects of Nrf2 on cell differentiation using a neuroblastoma cell line, SH-SY5Y. Retinoic acid (RA) and 12-O-tetradecanoylphorbol-13-acetate (TPA), two well-studied inducers for neuronal differentiation, are able to induce Nrf2 and its target gene NAD(P)H quinone oxidoreductase 1 (NQO1) in a dose- and time- dependent manner. RA-induced Nrf2 up-regulation is accompanied by neurite outgrowth and an induction of two neuronal differentiation markers, neurofilament-M (NF-M) and microtubule-associated protein 2 (MAP-2). Overexpression of Nrf2 in SH-SY5Y cells promotes neuronal differentiation whereas inhibition of endogenous Nrf2 expression inhibited neuronal differentiation. More remarkably, the positive role of Nrf2 in neuronal differentiation was verified ex vivo in primary neuron culture. Primary neurons isolated from Nrf2-null mice showed a retarded progress in differentiation, compared to that from wild-type mice. Collectively, our data demonstrate a novel role for Nrf2 in promoting neuronal cell differentiation, which will open new perspectives for therapeutic uses of Nrf2 activators in patients with neurodegenerative diseases.
Nrf2; Keap1; Oxidative Stress; Neuronal differentiation; SH-SY5Y; NQO1
In response to oxidative stress, Nrf2 and p21 Cip1/WAF1 are both upregulated to protect cells from oxidative damage. Nrf2 is constantly ubiquitinated by a Keap1 dimer that interacts with a weak-binding 29DLG motif and a strong-binding 79ETGE motif in Nrf2, resulting in degradation of Nrf2. Modification of the redox-sensitive cysteine residues on Keap1 disrupts the Keap1-29DLG binding, leading to diminished Nrf2 ubiquitination and activation of the antioxidant response. However, the underlying mechanism by which p21 protects cells from oxidative damage remains unclear. Here, we present molecular and genetic evidence suggesting that the antioxidant function of p21 is mediated through activation of Nrf2 by stabilizing the Nrf2 protein. The 154KRR motif in p21 directly interacts with the 29DLG and 79ETGE motifs in Nrf2, and thus, competes with Keap1 for Nrf2 binding, compromising ubiquitination of Nrf2. Furthermore, the physiological significance of our findings was demonstrated in vivo using p21-deficient mice.
Although many self-reactive T cells are eliminated by negative selection in the thymus, some of these cells escape into the periphery, where they must be controlled by additional mechanisms. However, the molecular mechanisms underlying peripheral T cell tolerance and its maintenance remain largely undefined. In this study, we report that sirtuin 1 (Sirt1), a type III histone deacetylase, negatively regulates T cell activation and plays a major role in clonal T cell anergy in mice. In vivo, we found that loss of Sirt1 function resulted in abnormally increased T cell activation and a breakdown of CD4+ T cell tolerance. Conversely, upregulation of Sirt1 expression led to T cell anergy, in which the activity of the transcription factor AP-1 was substantially diminished. Furthermore, Sirt1 interacted with and deacetylated c-Jun, yielding an inactive AP-1 factor. In addition, Sirt1-deficient mice were unable to maintain T cell tolerance and developed severe experimental allergic encephalomyelitis as well as spontaneous autoimmunity. These findings provide insight into the molecular mechanisms of T cell activation and anergy, and we suggest that activators of Sirt1 may be useful as therapeutic agents for the treatment and/or prevention of autoimmune diseases.
Drinking water contaminated with arsenic, a human carcinogen, is a worldwide health issue. An understanding of cellular signaling events in response to arsenic exposure and rational designing of strategies to reduce arsenic damages by modulating signaling events are important to fight against arsenic-induced diseases. Previously, we reported that activation of the Nrf2-mediated cellular defense pathway confers protection against toxic effects induced by sodium arsenite [As(III)] or monomethylarsonous acid [MMA(III)]. Paradoxically, arsenic has been reported to induce the Nrf2-dependent signaling pathway. Here, we report the unique mechanism of Nrf2 induction by arsenic. Similar to tert-butylhydroquinone (tBHQ) or sulforaphane (SF), arsenic induced the Nrf2-dependent response through enhancing Nrf2 protein levels by inhibiting Nrf2 ubiquitination and degradation. However, the detailed action of arsenic in Nrf2 induction is different from that of tBHQ or SF. Arsenic markedly enhanced the interaction between Keap1 and Cul3, subunits of the E3 ubiquitin ligase for Nrf2, which led to impaired dynamic assembly/disassembly of the E3 ubiquitin ligase and thus decreased its ligase activity. Furthermore, induction of Nrf2 by arsenic is independent of the previously identified C151 residue in Keap1 that is required for Nrf2 activation by tBHQ or SF. Distinct mechanisms of Nrf2 activation by seemingly harmful and beneficial reagents provide a molecular basis to design Nrf2-activating agents for therapeutic intervention.
Drug resistance during chemotherapy is the major obstacle to the successful treatment of many cancers. Here, we report that inhibition of NF-E2-related factor 2 (Nrf2) may be a promising strategy to combat chemoresistance. Nrf2 is a critical transcription factor regulating a cellular protective response that defends cells against toxic insults from a broad spectrum of chemicals. Under normal conditions, the low constitutive amount of Nrf2 protein is maintained by the Kelch-like ECH-associated protein1 (Keap1)-mediated ubiquitination and proteasomal degradation system. Upon activation, this Keap1-dependent Nrf2 degradation mechanism is quickly inactivated, resulting in accumulation and activation of the antioxidant response element (ARE)-dependent cytoprotective genes. Since its discovery, Nrf2 has been viewed as a ‘good’ transcription factor that protects us from many diseases. In this study, we demonstrate the dark side of Nrf2: stable overexpression of Nrf2 resulted in enhanced resistance of cancer cells to chemotherapeutic agents including cisplatin, doxorubicin and etoposide. Inversely, downregulation of the Nrf2-dependent response by overexpression of Keap1 or transient transfection of Nrf2–small interfering RNA (siRNA) rendered cancer cells more susceptible to these drugs. Upregulation of Nrf2 by the small chemical tert-butylhydroquinone (tBHQ) also enhanced the resistance of cancer cells, indicating the feasibility of using small chemical inhibitors of Nrf2 as adjuvants to chemotherapy to increase the efficacy of chemotherapeutic agents. Furthermore, we provide evidence that the strategy of using Nrf2 inhibitors to increase efficacy of chemotherapeutic agents is not limited to certain cancer types or anticancer drugs and thus can be applied during the course of chemotherapy to treat many cancer types.
A near-infrared spectrometer based on novel MOEMS grating light modulators is proposed. The spectrum detection method that combines a grating light modulator array with a single near-infrared detector has been applied. Firstly, optics theory has been used to analyze the essential principles of the proposed spectroscopic sensor. Secondly, the grating light modulators have been designed and fabricated by micro-machining technology. Finally, the principles of this spectroscopic sensor have been validated and its key parameters have been tested by experiments. The result shows that the spectral resolution is better than 10 nm, the wavelength deviation is less than 1 nm, the deviation of the intensity of peak wavelength is no more than 0.5%, the driving voltage of grating light modulators array device is below 25 V and the response frequency of it is about 5 kHz. With low cost, satisfactory precision, portability and other advantages, the spectrometer should find potential applications in food safety and quality monitoring, pharmaceutical identification and agriculture product quality classification.
MOEMS; Near-infrared; Spectrometer; Grating light modulator
Arsenic is widely spread in our living environment and imposes a big challenge on human health worldwide. Arsenic damages biological systems through multiple mechanisms including the generation of reactive oxygen species. The transcription factor Nrf2 regulates the cellular antioxidant response that protects cells from various insults. In this study, the protective role of Nrf2 in arsenic toxicity was investigated in a human bladder urothelial cell line, UROtsa. Using an UROtsa cell line stably infected with Nrf2-siRNA, we clearly demonstrate that compromised Nrf2 expression sensitized the cells to As(III)- and MMA(III)-induced toxicity. On the other hand, the activation of the Nrf2 pathway by tert-butylhydroquinone (tBHQ) and sulforaphane (SF), the known Nrf2-inducers, rendered UROtsa cells more resistant to As(III)- and MMA(III). Furthermore, the wild type mouse embryo fibroblast (WT-MEF) cells were protected from As(III)- and MMA(III)-induced toxicity following Nrf2 activation by tBHQ or SF whereas neither tBHQ nor SF conferred protection in the Nrf2−/−-MEF cells, demonstrating that tBHQ- or SF-mediated protection against As(III)- and MMA(III)-induced toxicity depends on Nrf2 activation. These results, obtained by both loss of function and gain of function analyses, clearly demonstrate the protective role of Nrf2 in arsenic-induced toxicity. The current work lays the groundwork for using Nrf2 activators for therapeutic and dietary interventions against adverse effects of arsenic.
Nrf2; Keap1; arsenic; arsenite; MMA(III); UROtsa
The persistent environmental contaminant and immunotoxicant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), markedly suppresses humoral immune responses. We recently reported impaired down-regulation of paired box 5 (Pax5), a repressor of B cell differentiation and concomitant suppression of the immunoglobulin M (IgM) response by TCDD in the murine CH12.LX B cell line. The objectives of the current study were to determine the impact of TCDD treatment on molecular outcomes characteristic of terminal B cell differentiation and to assess the role that Pax5 isoforms play in the suppression of B cell differentiation by TCDD. Here we show the highly abundant full-length Pax5 isoform, Pax5a, and at least two additional modestly expressed Pax5 isoforms were expressed in CH12.LX and splenic B cells. In LPS-activated B cells, all of the identified Pax5 isoforms were synchronously down-regulated and in the presence of TCDD co-treatment were abnormally and synchronously elevated, suggesting a common mechanism of regulation. Furthermore, B cell differentiation markers x-box protein 1 and major histocompatibility complex class II showed that the levels to which Pax5 was de-repressed by TCDD were sufficient to impair B cell differentiation and immunoglobulin gene expression. Confirming the involvement of Pax5, ectopic expression of Pax5a in the LPS-activated CH12.LX cells closely mimicked the suppression of the IgM response by TCDD. In summary, our results demonstrate a critical role by Pax5a in the TCDD-mediated impairment of B cell differentiation and the suppression of the humoral immune response.
Groundwater contaminated with arsenic imposes a big challenge to human health worldwide. Using natural compounds to subvert the detrimental effects of arsenic represents an attractive strategy. The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) is a critical regulator of the cellular antioxidant response and xenobiotic metabolism. Recently, activation of the Nrf2 signaling pathway has been reported to confer protection against arsenic-induced toxicity in a cell culture model.
The goal of the present work was to identify a potent Nrf2 activator from plants as a chemopreventive compound and to demonstrate the efficacy of the compound in battling arsenic-induced toxicity.
Oridonin activated the Nrf2 signaling pathway at a low subtoxic dose and was able to stabilize Nrf2 by blocking Nrf2 ubiquitination and degradation, leading to accumulation of the Nrf2 protein and activation of the Nrf2-dependent cytoprotective response. Pretreatment of UROtsa cells with 1.4 μM oridonin significantly enhanced the cellular redox capacity, reduced formation of reactive oxygen species (ROS), and improved cell survival after arsenic challenge.
We identified oridonin as representing a novel class of Nrf2 activators and illustrated the mechanism by which the Nrf2 pathway is activated. Furthermore, we demonstrated the feasibility of using natural compounds targeting Nrf2 as a therapeutic approach to protect humans from various environmental insults that may occur daily.
antioxidant responsive element; antitumor; ARE; arsenic; chemoprevention; diterpenoid; Keap1; Nrf2; oridonin; oxidative stress; rubescensin