The RxxRxRxxC motif conserved in all Rel/kappa B proteins is essential for the DNA-binding activity and redox regulation of the v-Rel oncoprotein

Psiadin and plectranthone selectively inhibit colorectal carcinoma cells proliferation via modulating cyclins signaling and apoptotic pathways

Three scarce terpenes, psiadin, plectranthone and saudinolide, were obtained after chromatographic isolation and purification from the aerial parts of the respective plants. Their identities were established based on their spectral data. Their anticancer effects against two human colorectal carcinoma cell lines, CCL233 and CCL235, along with the potential molecular mechanisms of action, were explored. Psiadin and plectranthone exhibited marked growth inhibition on both cell lines in a time- and dose-dependent manner with minimal cytotoxicity against normal breast cells (HB2). The terpenes even showed superior activities to the tested standards. Flow cytometry showed apoptosis induction and alteration in the cell cycle in colorectal cancer cells treated with both compounds. Nevertheless, it was also found that both compounds inhibited NF-κB transcriptional activity, induced mitochondrial membrane potential depolarization and increased the percentage of reactive oxygen species in the treated cancer cells in a dose-dependent manner as well. Since the anticancer effect of psiadin on cancer cells was higher than that produced by plectranthone, only psiadin was tested to determine its possible targets. The results suggested a high degree of specificity of action affecting particular cellular processes in both cancer cells. In conclusion, both terpenes, in particular psiadin, showed significant discriminative therapeutic potential between cancer and normal cells, a value that is missing in current chemotherapies.

Intestinal Epithelial Cells Respond to Chronic Inflammation and Dysbiosis by Synthesizing H2O2

The microbes in the gastrointestinal tract are separated from the host by a single layer of intestinal epithelial cells (IECs) that plays pivotal roles in maintaining homeostasis by absorbing nutrients and providing a physical and immunological barrier to potential pathogens. Preservation of homeostasis requires the crosstalk between the epithelium and the microbial environment. One epithelial-driven innate immune mechanism that participates in host-microbe communication involves the release of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂), toward the lumen. Phagocytes produce high amounts of ROS which is critical for microbicidal functions; the functional contribution of epithelial ROS, however, has been hindered by the lack of methodologies to reliably quantify extracellular release of ROS. Here, we used a modified Amplex Red assay to investigate the inflammatory and microbial regulation of IEC-generated H₂O₂ and the potential role of Duox2, a NADPH oxidase that is an important source of H₂O₂. We found that colonoids respond to interferon-γ and flagellin by enhancing production of H₂O₂ in a Duox2-mediated fashion. To extend these findings, we analyzed ex vivo production of H₂O₂ by IECs after acute and chronic inflammation, as well as after exposure to dysbiotic microbiota. While acute inflammation did not induce a significant increase in epithelial-driven H₂O₂, chronic inflammation caused IECs to release higher levels of H₂O₂. Furthermore, colonization of germ-free mice with dysbiotic microbiota from mice or patients with IBD resulted in increased H₂O₂ production compared with healthy controls. Collectively, these data suggest that IECs are capable of H₂O₂ production during chronic inflammation and dysbiotic states. Our results provide insight into luminal production of H₂O₂ by IECs as a read-out of innate defense by the mucosa.

Emerging role of alpha-lipoic acid in the prevention and treatment of bone loss

Osteoporosis is a chronic disease associated with decreased bone density that afflicts millions of people worldwide. Current pharmacological treatments are limited, costly, and linked to several negative side effects. These factors are driving current interest in the clinical use of naturally occurring bioactive compounds to mitigate bone loss. Alpha-lipoic acid, a potent antioxidant and essential member of mitochondrial dehydrogenases, has shown considerable promise as an antiosteoclastogenic agent due to its potent reactive oxygen species-scavenging capabilities along with a proven clinical safety record. Collectively, current data indicate that alpha-lipoic acid protects from bone loss via a 2-pronged mechanism involving inhibition of osteoclastogenic reactive oxygen species generation and upregulation of redox gene expression.

Regulation of cell survival and death by pyridine nucleotides

Pyridine nucleotides (PNs), such as NAD(H) and NADP(H), mediate electron transfer in many catabolic and anabolic processes. In general, NAD(+) and NADP(+) receive electrons to become NADH and NADPH by coupling with catabolic processes. These electrons are utilized for biologically essential reactions such as ATP production, anabolism and cellular oxidation-reduction (redox) regulation. Thus, in addition to ATP, NADH and NADPH could be defined as high-energy intermediates and "molecular units of currency" in energy transfer. We discuss the significance of PNs as energy/electron transporters and signal transducers, in regulating cell death and/or survival processes. In the first part of this review, we describe the role of NADH and NADPH as electron donors for NADPH oxidases (Noxs), glutathione (GSH), and thioredoxin (Trx) systems in cellular redox regulation. Noxs produce superoxide/hydrogen peroxide yielding oxidative environment, whereas GSH and Trx systems protect against oxidative stress. We then describe the role of NAD(+) and NADH as signal transducers through NAD(+)-dependent enzymes such as PARP-1 and Sirt1. PARP-1 is activated by damaged DNA in order to repair the DNA, which attenuates energy production through NAD(+) consumption; Sirt1 is activated by an increased NAD(+)/NADH ratio to facilitate signal transduction for metabolic adaption as well as stress responses. We conclude that PNs serve as an important interface for distinct cellular responses, including stress response, energy metabolism, and cell survival/death.

The sedoheptulose kinase CARKL directs macrophage polarization through control of glucose metabolism

Immune cells are somewhat unique in that activation responses can alter quantitative phenotypes upwards of 100,000-fold. To date little is known about the metabolic adaptations necessary to mount such dramatic phenotypic shifts. Screening for novel regulators of macrophage activation, we found nonprotein kinases of glucose metabolism among the most enriched classes of candidate immune modulators. We find that one of these, the carbohydrate kinase-like protein CARKL, is rapidly downregulated in vitro and in vivo upon LPS stimulation in both mice and humans. Interestingly, CARKL catalyzes an orphan reaction in the pentose phosphate pathway, refocusing cellular metabolism to a high-redox state upon physiological or artificial downregulation. We find that CARKL-dependent metabolic reprogramming is required for proper M1- and M2-like macrophage polarization and uncover a rate-limiting requirement for appropriate glucose flux in macrophage polarization.

Anti-inflammatory properties of phenolic compounds and crude extract from Porphyra dentata

ETHNOPHARMACOLOGICAL RELEVANCE

Porphyra dentata, a red edible seaweed, has long been used worldwide in folk medicine for the treatment of inflammatory diseases such as hypersensitivity, lymphadenitis, bronchitis.

AIMS OF STUDY

To clarify the anti-inflammatory role of Porphyra dentata crude extract and its identified phenolic compounds by investigating their effect on the nitric oxide (NO)/inducible nitric oxide synthase (iNOS) transcription pathway in macrophage RAW 264.7 cells.

MATERIALS AND METHODS

Porphyra dentata crude extract was prepared with methanol. High performance liquid chromatography (HPLC) hyphenated to electrospray ionization mass spectrometry (ESI-MS) and UV detection were utilized to analyze the extract fingerprints. Nitrite measurement, iNOS promoter activity and nuclear factor-kappaB (NF-kappaB) enhancer activity were used to assess the anti-inflammatory effect in lipopolysaccharide (LPS) challenged mouse RAW 264.7 cell line.

RESULTS

Phenolic compounds (catechol, rutin and hesperidin) were identified in the crude extract of Porphyra dentata. The crude extract and the phenolic compounds inhibited the production of NO in LPS-stimulated RAW 264.7 cells. Catechol was a more potent suppressor of the up-regulation of iNOS promoter and NF-kappaB enhancer than rutin and yet, hesperidin alone failed to inhibit either activity.

CONCLUSION

Our results indicate that catechol and rutin, but not hesperidin, are primary bioactive phenolic compounds in the crude extract to suppress NO production in LPS-stimulated macrophages via NF-kappaB-dependent iNOS gene transcription. The data also explain the anti-inflammatory use and possible mechanism of Porphyra dentata in iNOS implicated diseases.

Two alleles of NF-kappaB in the sea anemone Nematostella vectensis are widely dispersed in nature and encode proteins with distinct activities

Background

NF-κB is an evolutionarily conserved transcription factor that controls the expression of genes involved in many key organismal processes, including innate immunity, development, and stress responses. NF-κB proteins contain a highly conserved DNA-binding/dimerization domain called the Rel homology domain.

Methods/Principal Findings

We characterized two NF-κB alleles in the sea anemone Nematostella vectensis that differ at nineteen single-nucleotide polymorphisms (SNPs). Ten of these SNPs result in amino acid substitutions, including six within the Rel homology domain. Both alleles are found in natural populations of Nematostella. The relative abundance of the two NF-κB alleles differs between populations, and departures from Hardy-Weinberg equilibrium within populations indicate that the locus may be under selection. The proteins encoded by the two Nv-NF-κB alleles have different molecular properties, in part due to a Cys/Ser polymorphism at residue 67, which resides within the DNA recognition loop. In nearly all previously characterized NF-κB proteins, the analogous residue is fixed for Cys, and conversion of human RHD proteins from Cys to Ser at this site has been shown to increase DNA-binding ability and increase resistance to inhibition by thiol-reactive compounds. However, the naturally-occurring Nematostella variant with Cys at position 67 binds DNA with a higher affinity than the Ser variant. On the other hand, the Ser variant activates transcription in reporter gene assays more effectively, and it is more resistant to inhibition by a thiol-reactive compound. Reciprocal Cys<->Ser mutations at residue 67 of the native Nv-NF-κB proteins affect DNA binding as in human NF-κB proteins, e.g., a Cys->Ser mutation increases DNA binding of the native Cys variant.

Conclusions/Significance

These results are the first demonstration of a naturally occurring and functionally significant polymorphism in NF-κB in any species. The functional differences between these alleles and their uneven distribution in the wild suggest that different genotypes could be favored in different environments, perhaps environments that vary in their levels of peroxides or thiol-reactive compounds.

P-glycoprotein: so many ways to turn it on

Expression of the ABC transporter P-glycoprotein (P-gp or ABCB1) is associated with resistance to chemotherapy in cancer. However, early investigations into the regulation of ABCB1 expression revealed that the process is not a classical induction as observed for certain metabolizing enzymes. The process involves the cellular stress response pathway initiated by either inflicted (e.g., chemotherapy damage) or endogenous (e.g., hypoxia) factors. However, ABCB1 is also expressed in a number of noncancerous tissues. In particular, the protein is found at tissues providing a barrier or secretory function. The localization of ABCB1 in normal tissues will impact significantly on drug pharmacokinetics, in particular the absorption and elimination processes. This review also describes the mechanism underlying ABCB1 expression in noncancerous tissue, a process that does not involve the stress response.

Ethyl caffeate suppresses NF-kappaB activation and its downstream inflammatory mediators, iNOS, COX-2, and PGE2 in vitro or in mouse skin

Ethyl caffeate, a natural phenolic compound, was isolated from Bidens pilosa, a medicinal plant popularly used for treating certain inflammatory syndromes. The purpose of this study was to investigate the structural activity, and the anti-inflammatory functions and mechanism(s) of ethyl caffeate. Ethyl caffeate was found to markedly suppress the lipopolysaccharide (LPS)-induced nitric oxide (NO) production (IC(50) = 5.5 microg ml(-1)), mRNA and protein expressions of inducible nitric oxide synthase (iNOS), and prostaglandin E(2) (PGE(2)) production in RAW 264.7 macrophages. Transient gene expression assays using human cox-2 promoter construct revealed that ethyl caffeate exerted an inhibitory effect on cox-2 transcriptional activity in 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated MCF-7 cells. Immunohistochemical studies of mouse skin demonstrated that TPA-induced COX-2 expression was significantly inhibited by ethyl caffeate with a superior effect to that of celecoxib, a nonsteroidal anti-inflammatory drug. The phosphorylation and degradation of inhibitor kappaB (IkappaB) and the translocation of nuclear transcription factor-kappaB (NF-kappaB) into the nucleus, as well as the activation of mitogen-activated protein kinases (MAPKs) induced by LPS in macrophages, were not affected by ethyl caffeate. Ethyl caffeate, however, could inhibit NF-kappaB activation by impairing the binding of NF-kappaB to its cis-acting element. These results suggest that ethyl caffeate suppresses iNOS and COX-2 expressions partly through the inhibition of the NF-kappaB.DNA complex formation. Structure-activity relationship analyses suggested that the catechol moiety and alpha,beta-unsaturated ester group in ethyl caffeate are important and essential structural features for preventing NF-kappaB.DNA complex formation. This study provides an insight into the probable mechanism(s) underlying the anti-inflammatory and therapeutic properties of ethyl caffeate.

Induction of apoptotic cell death by 2'-hydroxycinnamaldehyde is involved with ERK-dependent inactivation of NF-kappaB in TNF-alpha-treated SW620 colon cancer cells

2'-Hydroxycinnamaldehyde (HCA) inhibits cell growth of several human cancer cells with unknown mechanisms. We investigated the inhibitory effect of HCA on TNF-alpha-induced cell growth and possible signal pathway in SW620 colon cancer cells. HCA inhibited TNF-alpha-induced SW620 colon cell growth in time- and dose-dependent manner through induction of apoptotic cell death. Parallel with inhibitory effect on cell growth, HCA dose dependency inhibited TNF-alpha-induced activation of NF-kappaB accompanied with inhibition of the translocation of p50. HCA also induced expression of caspase-3 and Bax, but decreased Bcl-2. HCA furthermore activated ERK pathway, and ERK inhibitor reversed inhibitory effect of HCA on cell growth and transcriptional activation of NF-kappaB. These results demonstrate that HCA inhibits cell growth through induction of apoptotic cell death by ERK pathway-dependent NF-kappaB inactivation.

Molecular recognition of 15-deoxy-Δ12,14-prostaglandin J2 by nuclear factor-kappa B and other cellular proteins

15-Deoxy-delta(12,14)-prostaglandin J2 (15d-PGJ2), a dehydration product of prostaglandin D2, is an important pharmacological molecule, which with the virtue of its electrophilicity, has been reported to covalently modify some cellular proteins (such as nuclear factor-kappa B (NF-kappaB), AP-1, p53, and thioredoxin) and elicit its physiological effects. The aim of the present computational study is to understand the role molecular recognition plays in the association of 15d-PGJ2 with NF-kappaB and other proteins. Another aim is to characterize whether p53 is a direct target for covalent modification by 15d-PGJ2. A docking strategy is applied along with calculation of ab initio electrostatic potential maps to analyze the mode of binding of prostaglandin molecule with critical cysteine-containing sites in each protein. The results provide identification of important sites in the target proteins, which provide recognition and stability to the prostaglandin molecule. Fit of shape and complementarity of electrostatic interactions are derived as significant determinants of molecular recognition of 15d-PGJ2. Further, comparative results indicate that p53 protein may also be a target for direct modification by 15d-PGJ2. The molecular models obtained should allow the rational design of more specific analogs of 15d-PGJ2.

Characterization of the genomic structure of the mouse limbic system-associated membrane protein (Lsamp) gene

The Lsamp gene encodes the limbic system-associated membrane protein (LAMP) an immunoglobulin (Ig) superfamily member with three Ig domains and a glycosylphosphatidylinositol anchor. LAMP is expressed by neurons composing the limbic system, is highly conserved between rodents and human, and has structural and functional properties that substantiate its role in the formation of limbic circuits. We report here the genomic organization of the Lsamp gene. The Lsamp gene is composed of 11 exons distributed over 2.2 megabases (Mb). Two exons 1 are separated by approximately 1.6 Mb and contribute to the unusual large size of the gene. Alternative spliced Lsamp mRNAs are generated from distinct promoter regions associated with the two exons 1 that encode distinct signal peptides and thus generate identical native mature polypetides. Additional diversity is created by the use of two small exons to include an insertion of 23 amino acids within the polypeptide C-terminal region of the mature protein. The genomic features of the Lsamp gene described here indicate an intricate mechanism of gene expression regulation that may be relevant in the context of human neuropsychiatric and neurological disorders, where LAMP expression may be altered.

Inhibition of lipopolysaccharide-induced inducible nitric oxide synthase expression by a novel compound, mercaptopyrazine, through suppression of nuclear factor-kappaB binding to DNA

Macrophage cells in response to cytokines and endotoxins produced a large amount of nitric oxide (NO) by expression of inducible nitric oxide synthase (iNOS), resulting in acute or chronic inflammatory disorders including septic hypotension and atherosclerosis. In the present study, we investigated the effect and the mechanism of mercaptopyrazine (MP) in the induction of iNOS and NO production as a culminating factor for several inflammatory disorders. Pretreatment of MP alleviated the mortality of endotoxemic mice receiving a lethal bolus of lipopolysaccharide (LPS), which was associated with the reduced levels of serum nitrite/nitrate and IL-1beta. In RAW264.7 mouse macrophage cells, MP (300microM) inhibited both protein and mRNA levels of iNOS stimulated by LPS/interferon-gamma (IFNgamma) up to 50%. The nuclear factor-kappa B (NF-kappaB)-driven transactivation was also suppressed by MP to the same degree. Treatment of MP reduced the binding of NF-kappaB to the oligonucleotides containing NF-kappaB consensus sequence, while it did not affect the translocation of NF-kappaB to nuclear. Suppression of NF-kappaB activity by MP was completely reversed by a reducing agent, dithiothreitol, implying that MP might oxidize the sulfhydryl group(s) of DNA binding domain of NF-kappaB. In conclusion, MP would be one of interesting candidates or chemical moieties of iNOS expression inhibitor via specific suppression of NF-kappaB binding to DNA, and be useful as a chemopreventive agent or a therapeutic against iNOS-associated inflammatory diseases.

Role of cysteine residues of p65/NF-κB on the inhibition by the sesquiterpene lactone parthenolide and N-ethyl maleimide, and on its transactivating potential

Sesquiterpene lactones (SLs) are potent anti-inflammatory substances. It was previously shown that the anti-inflammatory effect could be partly explained by the inhibition of the transcription factor NF-kappaB. Whether they inhibit the DNA binding of NF-kappaB, the activation of the IkappaB-kinase, or both is still a matter of debate. The data supporting these hypotheses were obtained using different cell systems. In this contribution we analyzed the mechanism of the sesquiterpene lactone-mediated inhibition using different cell systems, and showed that in all the cell lines analyzed, SLs inhibited both NF-kappaB binding and the IkappaB-kinase, but that the former played a more preponderant role in the inhibition. These results again confirm the importance of cysteine 38 in the inhibition and regulation of NF-kappaB's function. Moreover, we compared the selectivity of the SL parthenolide with that of N-ethyl maleimide (NEM). We showed that NEM directly alkylated p65 as well as p50 of NF-kappaB, whereas SLs possess a selectivity towards p65. Finally, we studied the transactivating properties of various p65 mutants, to analyze the effect of exchanged cysteine residues in the DNA binding domain of NF-kappaB/p65 on its function and demonstrated that the transactivating potential of the mutants did not correlate with their DNA binding strenght.

Discreet mutations from c-Rel to v-Rel alter kappaB DNA recognition, IkappaBalpha binding, and dimerization: implications for v-Rel oncogenicity

The avian Rev-T retrovirus encodes the oncoprotein v-Rel, a member of the Rel/nuclear factor (NF)-kappaB transcription factor family. The aggressive oncogenic potential of v-Rel has arisen from multiple mutations within the coding sequence of the avian cellular protein c-Rel. In this study, using quantitative biochemical experiments, we have tested the role of a limited set of alterations between v-Rel and c-Rel located within the Rel homology region (RHR) of the family that might confer functional differences. Our results show that only a set of six mutations within the RHR of v-Rel are responsible for its ability to bind to a broad spectrum of kappaB-DNA that are normally regulated by distinct NF-kappaB dimers. We also observe that both v-Rel homodimer and p50/v-Rel heterodimer bind IkappaBalpha weakly compared to other cellular Rel/NF-kappaB dimers with transcription activation potential. We suggest that the ability of v-Rel homodimer to deregulate subunit-specific gene expression and its ability to evade IkappaB inhibition are crucial to its strong oncogenic potential.

Divergent C-terminal transactivation domains of Rel/NF-κB proteins are critical determinants of their oncogenic potential in lymphocytes

rel/nf-kappaB genes are amplified, overexpressed, or constitutively activated in many human hematopoietic tumors; however, the molecular mechanisms by which they contribute to tumorigenesis remain to be determined. Here, we explored the oncogenic potential of cellular Rel/NF-kappaB proteins in vitro and in vivo. We show that overexpression of wild-type mouse and human c-rel genes suffices to malignantly transform primary spleen cells in stringent soft agar assays and produce fatal tumors in vivo. In contrast relA and a constitutively active form of IKKbeta did not. Importantly, a hybrid RelA protein with its C-terminal transactivation domain substituted by that of v-Rel was potently oncogenic in vitro and in vivo. The transactivation domain of v-Rel selectively conferred an oncogenic phenotype upon the Rel homology domain (RHD) of RelA, but not to the more divergent RHDs of p50/NF-kappaB1, p52/NF-kappaB2, or RelB. Collectively, our results highlight important differences in the intrinsic oncogenic activity of mammalian c-Rel and RelA proteins, and indicate that critical determinants of their differential oncogenicity reside in their divergent transactivation domains. These findings provide experimental evidence for a role of mammalian Rel/NF-kappaB factors in leukemia/lymphomagenesis in an in vivo animal model, and are consistent with the implication of c-rel in many human lymphomas.

PC-SPES: A Potent Inhibitor of Nuclear Factor-κB Rescues Mice from Lipopolysaccharide-Induced Septic Shock

Septic shock is the most common cause of death in intensive care units, and no effective treatment is available at present. Lipopolysaccharide (LPS) is the primary mediator of Gram-negative sepsis by inducing the production of macrophage-derived proinflammatory cytokines, in which activation of nuclear factor-kappaB (NF-kappaB) plays an important role. PC-SPES is an eight-herb mixture active against a variety of malignancies, including prostate cancer and leukemia. In this study, we demonstrated that PC-SPES inhibited the LPS-induced NF-kappaB reporter activity in RAW264.7 macrophages. Electrophoretic mobility shift assay showed that PC-SPES inhibited the binding of NF-kappaB to specific DNA sequences; however, it did not affect either degradation of inhibitory kappaBalpha or nuclear translocation of NF-kappaB. Also, we explored the effect of PCSPES on LPS-induced mitogen-activated protein (MAP) kinase signaling; PC-SPES did not affect LPS-induced phosphorylation of MAP kinases, including c-Jun NH2-terminal kinase, p38, and extracellular signal-regulated kinase 1/2. Moreover, PC-SPES decreased the production of proinflammatory cytokines and inducible enzymes, such as tumor necrosis factor (TNF) alpha, interleukin (IL)-1beta, IL-6, cyclooxygenase-2, as well as inducible nitric-oxide synthase in RAW264.7 macrophages and peritoneal macrophages from C57BL/6 mice after the cells were stimulated by either LPS or LPS and interferon-gamma. Furthermore, PC-SPES rescued C57BL/6 mice from death caused by LPS-induced septic shock in conjunction with decreased serum levels of TNFalpha and IL-1beta. Together, PC-SPES is a potent inhibitor of NF-kappaB and might be useful for the treatment of sepsis and inflammatory diseases.

Selenium regulates transcription factor NF-kappaB activation during the acute phase reaction

BACKGROUND

We reported a reciprocal relationship between reduced serum selenium (Se) and elevated serum C-reactive protein (CRP) in various pathological conditions in comparison with the levels in 141 healthy subjects. To clarify the implications of these observations, the effect of Se on nuclear factor (NF)-kappaB, which upregulates the CRP synthesis in the liver, was examined.

METHODS

Human hepatoma cell line HuH-7 was cultured in medium with 2% fetal calf serum (FCS) for 3 days for the Se deprivation, followed by another 3 days in the same medium containing sodium selenite prior to stimulation of the cells with either monocyte-conditioned medium (MoCM) or tumor necrosis factor-alpha (TNF-alpha). NF-kappaB activation and the synthesis of CRP in hepatocytes were examined by a non-radioisotope (non-RI) gel shift assay for the nuclear extract from the cells and by a highly sensitive ELISA for the cellular extract, respectively.

RESULTS

The NF-kappaB activation induced by MoCM and TNF-alpha were inhibited by Se at the physiological levels. The maximum activation of NF-kappaB was induced by TNF-alpha or MoCM at a Se concentration (0.5 approximately 1 micromol/l) which was half the level of the serum Se in healthy subjects and was equivalent to level in subjects with pathological conditions together with high serum CRP values. Under the same conditions, the hepatocytes synthesized maximal amounts of CRP.

CONCLUSIONS

Selenium at physiological levels mediates inhibition of the activation of the transcription factor NF-kappaB which regulates genes that encode inflammatory cytokines, and that conversely, the reduction of selenium induces the synthesis of CRP by hepatocytes during the acute phase response.

Mutations within a conserved protein kinase A recognition sequence confer temperature-sensitive and partially defective activities onto mouse c-Rel

We have created two mutants of mouse transcription factor c-Rel (c-G29E and c-R266H) that are analogous to mutants previously shown to have temperature-sensitive (ts) functions for the homologous Drosophila protein Dorsal and the retroviral oncoprotein v-Rel. In vitro, c-R266H shows both a ts and a concentration-dependent ability to bind DNA, suggesting that the lesion affects the ability of c-Rel to form homodimers. In contrast, the ability of mouse c-G29E to bind DNA in vitro is not ts. c-Rel mutant c-R266H also shows a ts ability to activate transcription from a kappaB-site reporter plasmid, whereas c-G29E activates transcription well above control levels at both 33 and 39 degrees C. Insertion of two amino acids (Pro-Trp) between amino acids 266 and 267 in mouse c-Rel (mutant c-SPW) also creates a c-Rel protein with distinct properties: mutant c-SPW is partially defective in that it cannot form DNA-binding homodimers but can form DNA-binding heterodimers with p50. Interestingly, the mutations in c-Rel that affect homodimer formation (c-R266H and c-SPW) fall within a consensus protein kinase A recognition sequence but are not predicted to lie in the dimer interface. Conditional and partially defective mutants such as those described herein may be useful for identifying physiological responses and genes regulated by specific Rel/NF-kappaB family members.

Natural ligands of PPARgamma: are prostaglandin J(2) derivatives really playing the part?

The peroxisome proliferator-activated receptor (PPAR) family was discovered from an orphan nuclear receptor approach, and thereafter, three subtypes were identified, namely PPARalpha, PPARbeta or PPARgamma and PPARgamma. The two former seem to regulate lipid homeostasis, whereas the latter is involved, among others, in glucose homeostasis and adipocyte differentiation. PPARs were pharmacologically characterised first using peroxisome proliferators such as clofibrates, which demonstrate moderate affinity (efficiency at micromolar concentrations) and low PPARalpha/delta versus PPARgamma specificity. Hence, several laboratories have started the search for potent and subtype-specific natural PPAR activators. In this respect, prostaglandin (PG)-related compounds were identified as good PPARgamma agonists with varying specificity, the most notable PPAR ligand being 15-deoxy-Delta12-14-PGJ2 (15d-PGJ2). Recently, an oxidized phosphatidylcholine was identified as a potent alternative (patho)physiological natural ligand of PPARgamma. In the present review, we discuss the different PPARgamma-dependent and -independent biological effects of the PG PPARgamma ligands and the concern about their low potency in molecular models as compared with thiazolidinediones (TZDs), a family of potent (nanomolar) synthetic PPARgamma ligands. Finally, the oxidized lipids are presented as a novel and interesting alternative for discovering potent PPARgamma activators in order to understand more in details the implications of PPARgamma in various pathophysiological conditions.

Kaurane diterpene, kamebakaurin, inhibits NF-kappa B by directly targeting the DNA-binding activity of p50 and blocks the expression of antiapoptotic NF-kappa B target genes

Kaurane diterpenes have been identified from numerous medicinal plants, which have been used for treatment of inflammation and cancer, however, their molecular mechanism of action remains unclear. We have previously shown that kamebakaurin and other three kaurane diterpenes selectively inhibit activation of transcription factor NF-kappaB, a central mediator of apoptosis and immune responses. We here demonstrate that kamebakaurin is a potent inhibitor of NF-kappaB activation by directly targeting DNA-binding activity of p50. Kamebakaurin prevented the activation of NF-kappaB by different stimuli in various cell types. Kamebakaurin did not prevent either stimuli-induced degradation of IkappaB-alpha or nuclear translocation of NF-kappaB, however, it significantly interfered DNA binding activity of activated NF-kappaB in cell and in vitro and preferentially prevented p50-mediated DNA-binding activity of NF-kappaB rather than that of RelA as measured using in vitro translated p50 and RelA proteins. Moreover, a p50 mutant with a Cys-62 --> Ser mutation was not inhibited with kamebakaurin, indicating that the effect of kamebakaurin was probably due to its interaction with cysteine 62 in p50. The covalent modification of p50 by kamebakaurin was further demonstrated by mass spectrometry analysis that showed an increase in the molecular mass of kamebakaurin-treated p50, and this modification was not reverted by addition of dithiothreitol. These results suggested that kamebakaurin exhibited its inhibitory activity by a direct covalent modification of cysteine 62 in the p50. Also, treatment of cells with kamebakaurin prevented the tumor necrosis factor-alpha (TNF-alpha)-induced expression of antiapoptotic NF-kappaB target genes encoding c-IAP1 (hiap-2) and c-IAP2 (hiap-1), members of the inhibitor of apoptosis family, and Bfl-1/A1, a prosurvival Bcl-2 homologue, and augmented the TNF-alpha-induced caspase 8 activity, thereby resulting in sensitizing MCF-7 cells to TNF-alpha-induced apoptosis. Taken together, kamebakaurin is a valuable candidate for the intervention of NF-kappaB-dependent pathological conditions such as inflammation and cancer.

Free radicals in the physiological control of cell function

At high concentrations, free radicals and radical-derived, nonradical reactive species are hazardous for living organisms and damage all major cellular constituents. At moderate concentrations, however, nitric oxide (NO), superoxide anion, and related reactive oxygen species (ROS) play an important role as regulatory mediators in signaling processes. Many of the ROS-mediated responses actually protect the cells against oxidative stress and reestablish "redox homeostasis." Higher organisms, however, have evolved the use of NO and ROS also as signaling molecules for other physiological functions. These include regulation of vascular tone, monitoring of oxygen tension in the control of ventilation and erythropoietin production, and signal transduction from membrane receptors in various physiological processes. NO and ROS are typically generated in these cases by tightly regulated enzymes such as NO synthase (NOS) and NAD(P)H oxidase isoforms, respectively. In a given signaling protein, oxidative attack induces either a loss of function, a gain of function, or a switch to a different function. Excessive amounts of ROS may arise either from excessive stimulation of NAD(P)H oxidases or from less well-regulated sources such as the mitochondrial electron-transport chain. In mitochondria, ROS are generated as undesirable side products of the oxidative energy metabolism. An excessive and/or sustained increase in ROS production has been implicated in the pathogenesis of cancer, diabetes mellitus, atherosclerosis, neurodegenerative diseases, rheumatoid arthritis, ischemia/reperfusion injury, obstructive sleep apnea, and other diseases. In addition, free radicals have been implicated in the mechanism of senescence. That the process of aging may result, at least in part, from radical-mediated oxidative damage was proposed more than 40 years ago by Harman (J Gerontol 11: 298-300, 1956). There is growing evidence that aging involves, in addition, progressive changes in free radical-mediated regulatory processes that result in altered gene expression.

Cysteine 38 in p65/NF-kappaB plays a crucial role in DNA binding inhibition by sesquiterpene lactones

Sesquiterpene lactones (SLs) have potent anti-inflammatory properties. We have shown previously that they exert this effect in part by inhibiting activation of the transcription factor NF-kappaB, a central regulator of the immune response. We have proposed a molecular mechanism for this inhibition based on computer molecular modeling data. In this model, SLs directly alkylate the p65 subunit of NF-kappaB, thereby inhibiting DNA binding. Nevertheless, an experimental evidence for the proposed mechanism was lacking. Moreover, based on experiments using the SL parthenolide, an alternative mode of action has been proposed by other authors in which SLs inhibit IkappaB-alpha degradation. Here we report the construction of p65/NF-kappaB point mutants that lack the cysteine residues alkylated by SLs in our model. In contrast to wild type p65, DNA-binding of the Cys(38) --> Ser and Cys(38,120) --> Ser mutants is no longer inhibited by SLs. In addition, we provide evidence that parthenolide uses a similar mechanism to other SLs in inhibiting NF-kappaB. Contrary to previous reports, we show that parthenolide, like other SLs, inhibits NF-kappaB most probably by alkylating p65 at Cys(38). Although a slight inhibition of IkappaB degradation was detected for all SLs, the amount of remaining IkappaB was too low to explain the observed NF-kappaB inhibition.

Activation of nuclear factor-kappa b transcriptional activity in airway epithelial cells by thioredoxin but not by N-acetyl-cysteine and glutathione

Increasing evidence indicates that intracellular redox status modulates the activity of various transcriptional factors, including nuclear factor (NF)-kappa B and activator protein-1. Our laboratory has been interested in characterizing the role thioredoxin (TRX) plays in regulating cellular redox status in airway epithelium. TRX is a small, ubiquitous protein with two redox-active half-cysteine residues, -Cys-Gly-Pro-Cys, in its active center. Using primary passage-1 human tracheobronchial epithelial cell cultures and an immortalized human bronchial epithelial cell line, HBE1, we observed that tumor necrosis factor (TNF)-alpha enhanced NF-kappa B transcriptional activity. This observation was based on gel mobility shift assays and interleukin (IL)-8 promoter-reporter gene transfection studies. TNF-alpha activation coincided with translocation of NF-kappa B p65 from the cytoplasm to the nucleus. Pretreatment with N-acetyl-cysteine (NAC) (1 to 10 mM) or glutathione (1 to 10 mM) inhibited TNF-alpha-induced activation of NF-kappa B transcriptional activity and IL-8 promoter-mediated reporter gene expression. In contrast, elevated TRX protein levels in cells enhanced TNF-alpha-dependent NF-kappa B transcriptional activity and IL-8 promoter activity. This observation was independent of the manner in which TRX was elevated in cells (e.g., by cotransfection with a FLAG-TRX expression clone, or by direct exposure to commercially available human TRX protein). Localization of TRX protein by anti-TRX antibody indicated an accumulation of TRX protein in the nucleus after TNF-alpha treatment. The nuclear localization phenomenon was different from the major cytosolic accumulation of glutathione and NAC. This is the first known report demonstrating movement of TRX into the nucleus of airway epithelial cells after an inflammatory stress. These results suggest a compartment effect of thiol chemicals in the regulation of redox-dependent transcriptional activity.

Resolution, detection, and characterization of redox conformers of human HSF1

We describe here an experimental protocol for the resolution, detection, and quantitation of the reduced and oxidized conformers of human heat shock factor 1 (hHSF1) and report on the effects in vitro and in vivo of redox-active agents on the redox status, structure, and function of hHSF1. We showed that diamide, a reagent that promotes disulfide bond formation, caused a loss of immunorecognition of the monomeric hHSF1 protein in a standard Western blot detection procedure. Modification of the Western blot procedure to include dithiothreitol in the equilibration and transfer buffers after gel electrophoresis allowed for the detection of a compact, intramolecularly disulfide cross-linked oxidized hHSF1 (ox-hHSF1) in the diamide-treated sample. The effect of diamide was blocked by pretreatment with N-ethylmaleimide and was reversed by dithiothreitol added to the sample prior to gel electrophoresis. Incubation with nitrosoglutathione at 42 degrees C also promoted the conversion of HSF1 to ox-HSF1; at 25 degrees C, however, nitrosoglutathione was by itself without effect but blocked the formation of ox-hHSF1 in the presence of diamide. The disulfide cross-linked ox-hHSF1 was monomeric and resistant to the in vitro heat-induced trimerization and activation. The possibility that ox-HSF1 may occur in oxidatively stressed cells was evaluated. Treatment of HeLa cells with 2 mm l-buthionine sulfoximine promoted the formation of ox-HSF1 and blocked the heat-induced activation of HSF DNA binding activity. Our result suggests that hHSF1 may have integrated redox chemistry of cysteine sulfhydryl into its functional responses.

Mercuric ion attenuates nuclear factor-kappaB activation and DNA binding in normal rat kidney epithelial cells: implications for mercury-induced nephrotoxicity

Mercuric ion (Hg(2+)), one of the strongest thiol-binding agents known, mediates the toxicity associated with elemental, inorganic, and organic mercurial compounds. Studies of cellular events associated with Hg(2+) toxicity have focused largely on disruption of cell membranes and impairment of mitochondrial functions. In contrast, few studies have sought to define the specific molecular mechanisms through which Hg(2+) might affect toxicity via alteration of thiol-dependent signal transduction pathways that regulate cell proliferation and survival. Of particular interest in this regard is the effect of Hg(2+) on nuclear factor-kappaB (NF-kappaB), a pleiotropic transcriptional factor that is known to require reduced cysteine moieties at critical steps of activation and DNA binding. Here, we evaluated the effects of Hg(2+) on the expression of NF-kappaB in normal rat kidney epithelial (NRK52E) cells, a principal target of Hg(2+) toxicity. The lipopolysaccharide (LPS)-inducible form of NF-kappaB was readily detected in kidney cells and has been characterized as the p50p65 heterodimer. NF-kappaB-DNA binding was prevented in a dose-related manner by Hg(2+) (0-55 microM) in vitro when added to DNA binding reactions containing the nonthiol reducing agent Tris(2-carboxyethyl)phosphine hydrochloride (TCEP). Similarly, Hg(2+) at the same concentrations prevented DNA binding of a human recombinant wild-type p50p50 homodimer in binding reactions, and this effect was attenuated using a mutant form of the p50 protein containing a cys(62)-->ser(62) mutation. The inhibition of p50-DNA binding by Hg(2+) was reversible in a dose-related manner in vitro by competitive thiols DTT, GSH, and l-cysteine in binding reactions. In contrast, competitive thiols added to nuclear binding reactions were unable to reverse attenuation of LPS-mediated NF-kappaB-DNA binding affinity when cells were pretreated in vivo with Hg(2+) at concentrations as low as 2 microM prior to LPS administration. Immunoblot analyses indicted that Hg(2+) pretreatment of kidney cells substantially diminished, in a dose-related manner, the concentration of p65 translocated into the nucleus following LPS administration. Additionally, Hg(2+) pretreatment impaired both the phosphorylation and degradation of IkappaBalpha, suggesting a specific effect on NF-kappaB activation at the level of IkappaBalpha proteolysis. Finally, Hg(2+) at concentrations as low as 5 microM significantly diminished NF-kappaB-mediated transcriptional activity when administered to kidney cells transiently transfected with an NF-kappaB-driven luciferase reporter gene (pLuc-4xNF-kappaB) prior to LPS treatment. These findings demonstrate that Hg(2+), at low cellular concentrations, attenuates NF-kappaB activation at sites associated with IkappaBalpha phosphorylation and degradation, nuclear translocation of the p50p65 heterodimer, and association of p50-cys(62) with the DNA kappaB binding site. Attenuation of NF-kappaB activation by Hg(2+) through these mechanisms may underlie apoptotic or other cytotoxic responses that are known to be associated with low level Hg(2+) exposure in kidney epithelial cells.

Activation and repression by the C-terminal domain of Dorsal

In the Drosophila embryo, Dorsal, a maternally expressed Rel family transcription factor, regulates dorsoventral pattern formation by activating and repressing zygotically active fate-determining genes. Dorsal is distributed in a ventral-to-dorsal nuclear concentration gradient in the embryo, the formation of which depends upon the spatially regulated inhibition of Dorsal nuclear uptake by Cactus. Using maternally expressed Gal4/Dorsal fusion proteins, we have explored the mechanism of activation and repression by Dorsal. We find that a fusion protein containing the Gal4 DNA-binding domain fused to full-length Dorsal is distributed in a nuclear concentration gradient that is similar to that of endogenous Dorsal, despite the presence of a constitutively active nuclear localization signal in the Gal4 domain. Whether this fusion protein activates or represses reporter genes depends upon the context of the Gal4-binding sites in the reporter. A Gal4/Dorsal fusion protein lacking the conserved Rel homology domain of Dorsal, but containing the non-conserved C-terminal domain also mediates both activation and repression, depending upon Gal4-binding site context. A region close to the C-terminal end of the C-terminal domain has homology to a repression motif in Engrailed - the eh1 motif. Deletion analysis indicates that this region mediates transcriptional repression and binding to Groucho, a co-repressor known to be required for Dorsal-mediated repression. As has previously been shown for repression by Dorsal, we find that activation by Dorsal, in particular by the C-terminal domain, is modulated by the maternal terminal pattern-forming system.

Cyclopentenone prostaglandins: new insights on biological activities and cellular targets

The cyclopentenone prostaglandins PGA2, PGA1, and PGJ2 are formed by dehydration within the cyclopentane ring of PGE2, PGE1, and PGD2. PGJ2 is metabolized further to yield Delta(12)-PGJ(2) and 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)). Various compounds within the cyclopentenone prostaglandin family possess potent anti-inflammatory, anti-neoplastic, and anti-viral activity. Most actions of the cyclopentenone prostaglandins do not appear to be mediated by binding to G-protein coupled prostanoid receptors. Rather, the bioactivity of these compounds results from their interaction with other cellular target proteins. 15-deoxy-Delta(12,14)-PGJ(2) is a high affinity ligand for the nuclear receptor PPARgamma and modulates gene transcription by binding to this receptor. Other activities of the cyclopentenone prostaglandins are mediated by the reactive alpha,beta-unsaturated carbonyl group located in the cyclopentenone ring. The transcription factor NF-kappaB and its activating kinase are key targets for the anti-inflammatory activity of 15d-PGJ2, which inhibits NF-kappaB-mediated transcriptional activation by PPARgamma-dependent and independent molecular mechanisms. Other cyclopentenone prostaglandins, such as Delta(7)-PGA1 and Delta(12)-PGJ2, have strong anti-tumor activity. These compounds induce cell cycle arrest or apoptosis of tumor cells depending on the cell type and treatment conditions. We review here recent progress in understanding the mechanisms of action of the cyclopentenone prostaglandins and their possible use as therapeutic agents.

Oxidant stress and endothelial cell dysfunction

Reactive oxygen species (ROS) are generated at sites of inflammation and injury, and at low levels, ROS can function as signaling molecules participating as signaling intermediates in regulation of fundamental cell activities such as cell growth and cell adaptation responses, whereas at higher concentrations, ROS can cause cellular injury and death. The vascular endothelium, which regulates the passage of macromolecules and circulating cells from blood to tissues, is a major target of oxidant stress, playing a critical role in the pathophysiology of several vascular diseases and disorders. Specifically, oxidant stress increases vascular endothelial permeability and promotes leukocyte adhesion, which are coupled with alterations in endothelial signal transduction and redox-regulated transcription factors such as activator protein-1 and nuclear factor-kappaB. This review discusses recent findings on the cellular and molecular mechanisms by which ROS signal events leading to impairment of endothelial barrier function and promotion of leukocyte adhesion. Particular emphasis is placed on the regulation of cell-cell and cell-surface adhesion molecules, the actin cytoskeleton, key protein kinases, and signal transduction events.

Cellular thiols and redox-regulated signal transduction

In contrast to the conventional notion that reactive oxygen is mostly a trigger for oxidative damage of biological structures, now we know that low physiologically relevant concentrations of ROS can regulate a variety of key molecular mechanisms that may be linked with important cell functions (Fig. 4). Redox-based regulation of gene expression has emerged as a fundamental regulatory mechanism in cell biology. Several proteins, with apparent redox-sensing activity, have been described. Electron flow through side-chain functional CH2-SH groups of conserved cysteinyl residues in these proteins account for the redox-sensing properties. Protein thiol groups with high thiol-disulfide oxidation potentials are likely to be redox-sensitive. The ubiquitous endogenous thiols thioredoxin and glutathione are of central importance in redox signaling. Signals are transduced from the cell surface to the nucleus through phosphorylation and dephosphorylation chain reactions of cellular proteins at tyrosine and serine/threonine. Protein phosphorylation, one of the most fundamental mediators of cell signaling, is redox-sensitive. DNA-binding proteins are involved in the regulation of cellular processes such as replication, recombination, viral integration and transcription. Several studies show that the interaction of certain transcription regulatory proteins with their respective cognate DNA sites is also redox-regulated. Changes in the concentration of Ca2+i control a wide variety of cellular functions, including transcription and gene expression; Ca(2+)-driven protein phosphorylation and proteolytic processing of proteins are two major intracellular events that are implicated in signal transduction from the cell surface to the nucleus. Intracellular calcium homeostasis is regulated by the redox state of cellular thiols, and it is evident that cell calcium may play a critical role in the activation of the redox-sensitive transcription factor NF-kappa B. Among the several thiol agents tested for their efficacy in modulating cellular redox status, N-acetyl-L-cysteine and alpha-lipoic acid hold most promise for human use. A strong therapeutic potential of strategies that would modulate the cellular thioredoxin system has been also evident.

Inhibition of nuclear factor-kappab activation in mouse macrophages and the RAW 264.7 cell line by a synthetic adenyl carbocyclic nucleoside

Adenyl carbocyclic nucleosides have potent anti-inflammatory effects on a number of cell types. Notable in this regard is their ability to inhibit the production of tumor necrosis factor-alpha (TNF-alpha) by mouse macrophages that have been activated with bacterial lipopolysaccharide (LPS). Because the transcriptional activation of the mouse TNF-alpha gene is highly dependent on kappaB enhancers, the present study determined whether the synthetic carbocyclic nucleoside 9-[(1S,3R)-cis-cyclopentan-3-ol]adenine (cPA) inhibited LPS-induced nuclear factor-kappaB (NF-kappaB) activation in these cells. Stimulation of either mouse peritoneal macrophages or RAW 264. 7 macrophage-like cells with LPS led to the appearance of four distinct kappaB-binding nucleoprotein complexes detected by gel mobility shift assays. Cells treated with 100 microM cPA showed significantly reduced levels of NF-kappaB activation as evidenced by measurements of nucleoprotein kappaB-binding activity and diminished kappaB-dependent transcriptional activation. However, both the LPS-induced degradation of the cytoplasmic NF-kappaB inhibitor IkappaBalpha and the nuclear translocation of the NF-kappaB p50, p65, and c-Rel peptides were unaffected by treatment of the cells with the nucleoside. These findings suggest that certain adenyl carbocyclic nucleosides inhibit the activation of NF-kappaB/Rel complexes by a novel mechanism that results in an inhibition of their DNA-binding activities, without blocking their dissociation from IkappaBalpha or their nuclear translocation.

N-acetylcysteine suppresses TNF-induced NF-kappaB activation through inhibition of IkappaB kinases

Here, we used a reductant, N-acetyl-L-cysteine (NAC), to investigate the redox-sensitive step(s) in the signalling pathway from the tumor necrosis factor (TNF) receptor to nuclear factor kappaB (NF-kappaB). We found that NAC suppressed NF-kappaB activation triggered by TNF or by overexpression of either the TNF receptor-associated death domain protein, TNF receptor-associated factor 2, NF-kappaB-inducing kinase (NIK), or IkappaB kinases (IKKalpha and IKKbeta). NAC also suppressed the TNF-induced activation of IKKalpha and IKKbeta, phosphorylation and degradation of IkappaB, and nuclear translocation of NF-kappaB. Furthermore, NAC suppressed the activation of IKKalpha and IKKbeta triggered by the overexpression of NIK. These results indicate that IKKalpha and IKKbeta are subject to redox regulation in the cells, and that NAC inhibits NF-kappaB activation through the suppression of these kinases.

Inhibition of NF-kappaB-DNA binding by mercuric ion: utility of the non-thiol reductant, tris(2-carboxyethyl)phosphine hydrochloride (TCEP), on detection of impaired NF-kappaB-DNA binding by thiol-directed agents

Mercuric ion (Hg(2+)), a potent thiol inhibitor, prevents expression of nuclear factor kappaB (NF-kappaB) by mercaptide bond formation with a critical cysteine moiety (cys(62)) on the p50 subunit required for DNA binding. NF-kappaB-DNA binding is typically measured in reaction mixtures in which dithiothreitol (DTT) or other thiol reductants are used to maintain cys(62) in the reduced state. However, the presence of thiol reductants prevents accurate assessment of the Hg(2+) concentration required to prevent NF-kappaB-DNA binding because of competitive mercaptide bond formation. In the present studies we evaluated the efficacy of tris(2-carboxyethyl)phosphine-HCl (TCEP), a non-thiol reducing agent which does not bind Hg(2+), on NF-kappaB-DNA binding in vitro, using recombinant p50 protein and a (32)P-labelled kappaB oligonucleotide. We also measured the minimal Hg(2+) concentration required to prevent this interaction in the presence of either reagent. DTT promoted NF-kappaB-DNA binding in concentrations from 0.25 to 2.6mM in binding reactions. However, in the presence of 0.25mM DTT, inhibition of NF-kappaB binding was seen only at Hg(2+) concentrations greater than 100 microM and results were highly variable. In contrast, TCEP promoted NF-kappaB-DNA binding in a dose-related manner in concentrations from 0.25 to 6mM. In the presence of even 6mM TCEP, Hg(2+) prevented NF-kappaB-DNA binding at concentrations as low as 20 microM in binding reactions. Similar findings were observed with regard to the thiol alkylating agent N-ethylmaleimide (NEM). These findings demonstrate the utility of TCEP as reductant in nuclear binding reaction assays involving the interaction of thiol constituents. They also demonstrate inhibition of NF-kappaB-DNA binding at Hg(2+) concentrations comparable to those known to initiate toxicity and apoptotic cell death in vivo.

Multiple mutations contribute to the oncogenicity of the retroviral oncoprotein v-Rel

The avian Rev-T retrovirus encodes the v-Rel oncoprotein, which is a member of the Rel/NF-kappaB transcription factor family. v-Rel induces a rapidly fatal lymphoma/leukemia in young birds, and v-Rel can transform and immortalize a variety of avian cell types in vitro. Although Rel/NF-kappaB transcription factors have been associated with oncogenesis in mammals, v-Rel is the only member of this family that is frankly oncogenic in animal model systems. The potent oncogenicity of v-Rel is the consequence of a number of mutations that have altered its activity and regulation: for example, certain mutations decrease its ability to be regulated by IkappaBalpha, change its DNA-binding site specificity, and endow it with new transactivation properties. The study of v-Rel will continue to increase our knowledge of how cellular Rel proteins contribute to oncogenesis by affecting cell growth, altering cell-cycle regulation, and blocking apoptosis. This review will discuss biological and molecular activities of v-Rel, with particular attention to how these activities relate to structure - function aspects of the Rel/NF-kappaB transcription factors.

Acrolein causes inhibitor kappaB-independent decreases in nuclear factor kappaB activation in human lung adenocarcinoma (A549) cells

Acrolein is a highly electrophilic alpha,beta-unsaturated aldehyde to which humans are exposed in various situations. In the present study, the effects of sublethal doses of acrolein on nuclear factor kappaB (NF-kappaB) activation in A549 human lung adenocarcinoma cells were investigated. Immediately following a 30-min exposure to 45 fmol of acrolein/cell, glutathione (GSH) and DNA synthesis and NF-kappaB binding were reduced by more than 80%. All parameters returned to normal or supranormal levels by 8 h post-treatment. Pretreatment with acrolein completely blocked 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced activation of NF-kappaB. Cells treated for 1 h with 1 mM diethyl maleate (DEM) showed a 34 and 53% decrease in GSH and DNA synthesis, respectively. DEM also reduced NF-kappaB activation by 64% at 2 h post-treatment, with recovery to within 22% of control at 8 h. Both acrolein and DEM decreased NF-kappaB function approximately 50% at 2 h after treatment with TPA, as shown by a secreted alkaline phosphatase reporter assay. GSH returned to control levels by 8 h after DEM treatment, but proliferation remained significantly depressed for 24 h. Interestingly, DEM caused a profound decrease in NF-kappaB binding, even at doses as low as 0.125 mM that had little effect on GSH. Neither acrolein nor DEM had any effect on the levels of phosphorylated or nonphosphorylated inhibitor kappaB-alpha (IkappaB-alpha). Furthermore, acrolein decreased NF-kappaB activation in cells depleted of IkappaB-alpha by TPA stimulation in the presence of cycloheximide, demonstrating that the decrease in NF-kappaB activation was not the result of increased binding by the inhibitory protein. This conclusion was further supported by the finding that acrolein modified NF-kappaB in the cytosol prior to chemical dissociation from IkappaB with detergent. Together, these data support the conclusion that the inhibition of NF-kappaB activation by acrolein and DEM is IkappaB-independent. The mechanism appears to be related to direct modification of thiol groups in the NF-kappaB subunits.

Tumor promotion by hydrogen peroxide in rat liver epithelial cells

Reactive oxygen species, including H2O2, play an important role in the tumor promotion process. Using an in vitro model of tumor promotion involving the rat liver epithelial oval cell line T51B, the tumor promoting activity of H2O2 in N-methyl-N'-nitro-N-nitrosoguanidine-initiated cells was studied. In this assay system, the promoting effect of H2O2 is evidenced by the formation of colonies in soft agar, appearance of foci in monolayer culture, disruption of gap junction communication (GJC) in foci areas and growth at higher saturation densities. H2O2 preferentially induced the expression of c-fos, c-jun, c-myc and egr-1, while JunB and JunD levels remained almost unchanged. H2O2 also induced hyperphosphorylation of Cx43 and disruption of GJC. The effects of H2O2 on tumor promotion, induction of immediate early (IE) genes and disruption of GJC are blocked by antioxidants. These results suggest that H2O2 acts as a tumor promoter in rat liver non-neoplastic epithelial cells and that the induction of IE genes and disruption of GJC are two possible targets of H2O2 during the tumor promotion process.

Two isoforms of protein disulfide isomerase alter the dimerization status of E2A proteins by a redox mechanism

We have shown previously that E2A helix-loop-helix proteins spontaneously form an intermolecular disulfide cross-link that is required for stable homodimer binding to DNA (Benezra, R. (1994) Cell 79, 1057-1067). These homodimers are important for the development of B lymphocytes but are not present in other cell lineages. We have purified two proteins that are capable of regulating the formation of this disulfide bond and found them to be members of the protein disulfide isomerase (PDI) family. By regulating the formation of the disulfide cross-link, these proteins are capable of regulating the dimerization state of E proteins. PDI-mediated reduction appears to dissociate E protein homodimers and favors heterodimer formation with other basic helix-loop-helix proteins in both a purified protein system and in cellular extracts. These studies suggest that PDI may play an important role in the regulation of E2A transcription factor dimerization and the development of the B lymphocyte lineage.

Plant extracts from stinging nettle (Urtica dioica), an antirheumatic remedy, inhibit the proinflammatory transcription factor NF-kappaB

Activation of transcription factor NF-kappaB is elevated in several chronic inflammatory diseases and is responsible for the enhanced expression of many proinflammatory gene products. Extracts from leaves of stinging nettle (Urtica dioica) are used as antiinflammatory remedies in rheumatoid arthritis. Standardized preparations of these extracts (IDS23) suppress cytokine production, but their mode of action remains unclear. Here we demonstrate that treatment of different cells with IDS23 potently inhibits NF-kappaB activation. An inhibitory effect was observed in response to several stimuli, suggesting that IDS23 suppressed a common NF-kappaB pathway. Inhibition of NF-kappaB activation by IDS23 was not mediated by a direct modification of DNA binding, but rather by preventing degradation of its inhibitory subunit IkappaB-alpha. Our results suggests that part of the antiinflammatory effect of Urtica extract may be ascribed to its inhibitory effect on NF-kappaB activation.

Redox regulation of cellular signalling

Extracellular stimuli elicit a variety of responses, such as cell proliferation and differentiation, through the cellular signalling system. Binding of growth factors to the respective receptor leads to the activation of receptor tyrosine kinases, which in turn stimulate downstream signalling systems such as mitogen-activated protein (MAP) kinases, phospholipase Cgamma (PLCgamma) and phosphatidylinositol 3-kinase. These biochemical reactions finally reach the nucleus, resulting in gene expression mediated by the activation of several transcription factors. Recent studies have revealed that cellular signalling pathways are regulated by the intracellular redox state. Generation of reactive oxygen species (ROS), such as H2O2, leads to the activation of protein tyrosine kinases followed by the stimulation of downstream signalling systems including MAP kinase and PLCgamma. The activation of PLCgamma by oxidative radical stress elevates the cellular Ca2+ levels by flux from the intracellular Ca2+ pool and from the extracellular space. Such reactions in the upstream signalling cascade, in concert, result in the activation of several transcription factors. On the other hand, reductants generally suppress the upstream signalling cascade resulting in the suppression of transcription factors. However, it is well known that cysteine residues in a reduced state are essential for the activity of many transcription factors. In fact, in vitro, oxidation of NFkappaB results in its activation, whereas reductants promote its activity. Thus, cellular signalling pathways are generally subjected to dual redox regulation in which redox has opposite effects on upstream signalling systems and downstream transcription factors. Not only are the cellular signalling pathways subjected to redox regulation, but also the signalling systems regulate the cellular redox state. When cells are activated by extracellular stimuli, the cells produce ROS, which in turn stimulate other cellular signalling pathways, indicating that ROS act as second messengers. It is thus evident that there is cross talk between the cellular signalling system and the cellular redox state. Cell death and life also are subjected to such dual redox regulation and cross talk. Death signals induce apoptosis through the activation of caspases in the cells. Oxidative radical stress induces the activation of caspases, whereas the oxidation of caspases results in their inactivation. Furthermore, some cell-death signals induce the production of ROS in the cells, and the ROS produced in turn stimulate the cell-death machinery. All this evidence shows that the cell's fate is determined by cross talk between the cellular signalling pathways and the cellular redox state through a complicated regulation mechanism.

The anti-inflammatory sesquiterpene lactone helenalin inhibits the transcription factor NF-kappaB by directly targeting p65

The sesquiterpene lactone helenalin is a potent anti-inflammatory drug whose molecular mechanism of action remains unclear despite numerous investigations. We have previously shown that helenalin and other sesquiterpene lactones selectively inhibit activation of the transcription factor NF-kappaB, a central mediator of the human immune response. These drugs must target a central step in NF-kappaB pathway, since they inhibit NF-kappaB induction by four different stimuli. It has previously been reported that sesquiterpene lactones exert their effect by inhibiting degradation of IkappaB, the inhibitory subunit of NF-kappaB. These data contradicted our report that IkappaB is not detectable in helenalin-treated, ocadaic acid-stimulated cells. Here we use confocal laser scanning microscopy to demonstrate the presence of IkappaB-released, nuclear NF-kappaB in helenalin-treated, tumor necrosis factor-alpha stimulated cells. These data show that neither IkappaB degradation nor NF-kappaB nuclear translocation are inhibited by helenalin. Rather, we provide evidence that helenalin selectively alkylates the p65 subunit of NF-kappaB. This sesquiterpene lactone is the first anti-inflammatory agent shown to exert its effect by directly modifying NF-kappaB.

Structure of an IkappaBalpha/NF-kappaB complex

The inhibitory protein, IkappaBalpha, sequesters the transcription factor, NF-kappaB, as an inactive complex in the cytoplasm. The structure of the IkappaBalpha ankyrin repeat domain, bound to a partially truncated NF-kappaB heterodimer (p50/ p65), has been determined by X-ray crystallography at 2.7 A resolution. It shows a stack of six IkappaBalpha ankyrin repeats facing the C-terminal domains of the NF-kappaB Rel homology regions. Contacts occur in discontinuous patches, suggesting a combinatorial quality for ankyrin repeat specificity. The first two repeats cover an alpha helically ordered segment containing the p65 nuclear localization signal. The position of the sixth ankyrin repeat shows that full-length IkappaBalpha will occlude the NF-kappaB DNA-binding cleft. The orientation of IkappaBalpha in the complex places its N- and C-terminal regions in appropriate locations for their known regulatory functions.

Redox signaling and the emerging therapeutic potential of thiol antioxidants

Oxidation-reduction (redox) based regulation of signal transduction and gene expression is emerging as a fundamental regulatory mechanism in cell biology. Electron flow through side chain functional CH2-SH groups of conserved cysteinyl residues in proteins account for their redox-sensing properties. Because in most intracellular proteins thiol groups are strongly "buffered" against oxidation by the highly reduced environment inside the cell, only accessible protein thiol groups with high thiol-disulfide oxidation potentials are likely to be redox sensitive. The list of redox-sensitive signal transduction pathways is steadily growing, and current information suggests that manipulation of the cell redox state may prove to be an important strategy for the management of AIDS and some forms of cancer. The endogenous thioredoxin and glutathione systems are of central importance in redox signaling. Among the thiol agents tested for their efficacy to modulate cellular redox status, N-acetyl-L-cysteine (NAC) and alpha-lipoic acid hold promise for clinical use. A unique advantage of lipoate is that it is able to utilize cellular reducing equivalents, and thus it harnesses the metabolic power of the cell to continuously regenerate its reductive vicinal dithiol form. Because lipoate can be readily recycled in the cell, it has an advantage over N-acetyl-L-cysteine on a concentration:effect basis. Our current knowledge of redox regulated signal transduction has led to the unfolding of the remarkable therapeutic potential of cellular thiol modulating agents.

Structural requirements for DNA binding of GCM proteins

Members of the GCM family of transcription factors contain a DNA binding domain unrelated to any other known DNA binding domain and bind to a DNA sequence motif not recognized by any other known transcription factor. Here we show that positions 2, 3, 6 and 7 of the 5'-ATGCGGGT-3' motif are particularly important for DNA binding and that methylation of several G residues on the upper strand, but not on the lower strand, interfered with binding of GCM proteins. No differences were detected between the DNA binding of Drosophila GCM and mammalian mGCMa. Alanine scan mutagenesis of the DNA binding domain of mGCMa identified the three conserved amino acids K74, C76 and C125 as being essential for DNA binding. Conserved cysteine residues were also found to be important for maintaining the overall integrity of the DNA binding domain and for mediating redox sensitivity of DNA binding. These cysteine residues are arranged in a symmetrical structure that bears no resemblance to other cysteine-containing structures, such as zinc fingers. In agreement with this, DNA binding of mGCMa was not dependent on zinc ions. Our results give insights into the exact nature of the GCM binding sites expected in target genes and point to a role for redox regulation in the function of GCM proteins.

Induction of the differentiation of HL-60 promyelocytic leukemia cells by nonsteroidal anti-inflammatory agents in combination with low levels of vitamin D3

Previous experiments have shown that a variety of agents that interfere with the activity of the transcription factor NF-kB significantly enhanced the differentiation of HL-60 leukemia cells when combined with low levels of the monocytic/macrophagic differentiating agent vitamin D3. These include an antisense phosphorothioate oligonucleotide to the Rel A subunit of NF-kB, vitamin E and other antioxidants, and curcumin. Acetylsalicylic acid and other nonsteroidal anti-inflammatory agents represent another group of agents that have been reported to inhibit NF-kB at serum levels approximating those obtained during long-term therapy of chronic inflammatory states. To determine whether nonsteroidal anti-inflammatory agents also were capable of enhancing the differentiation of HL-60 leukemia cells produced by vitamin D3, we measured the effects of a variety of nonsteroidal anti-inflammatory agents on the maturation of HL-60 cells produced by low levels of vitamin D3. Acetylsalicylic acid by itself had no significant effect on the differentiation of HL-60 cells; however, this agent markedly increased the degree of differentiation produced by low levels of vitamin D3. Furthermore, a variety of other nonsteroidal anti-inflammatory agents of different chemical classes exhibited similar enhancements of the maturation of HL-60 cells when combined with vitamin D3. An analogous increase in the differentiation of HL-60 cells was also obtained by combination of several nonsteroidal anti-inflammatory agents with the granulocytic inducing agent, retinoic acid, but not with dimethylsulfoxide. The nonsteroidal anti-inflammatory agents also enhanced the differentiation of HL-60 cells when combined with vitamin D analogs which share the receptor binding properties of vitamin D3; however, a vitamin D analog which caused significant calcium mobilization, but was less effective in receptor binding than vitamin D3, did not induce the differentiation of HL-60 cells in the presence or absence of anti-inflammatory agents. The findings suggest that the nonsteroidal anti-inflammatory agents may have utility in the treatment of acute promyelocytic leukemia when used with the D vitamins or retinoic acid.

Modulation of transcription factor NF-kappaB by enantiomers of the nonsteroidal drug ibuprofen

1. The nonsteroidal drug ibuprofen exists as an R(-)- and S(+)-enantiomer. Only the S(+)-enantiomer is an effective cyclo-oxygenase inhibitor, while the R(-)-enantiomer is inactive in this respect. Thus the molecular mechanism by which R(-)-ibuprofen exerts its anti-inflammatory and antinociceptive effects remains unknown. 2. In this study the effects of the enantiomers of ibuprofen on modulation of transcription factors have been examined with electrophoretic mobility-shift assay (EMSA), transient transfection experiments, confocal immunofluorescence and nuclear import experiments, to determine their selectivity and potency as inhibitors of the activation of transcription factor nuclear factor-kappaB (NF-kappaB). 3. R(-)-ibuprofen (IC50: 121.8 microM) as well as the S(+)-enantiomer (IC50: 61.7 microM) inhibited the activation of NF-kappaB in response to T-cell stimulation. The effect of ibuprofen was specific because, at concentrations up to 10 mM, ibuprofen did not affect the heat shock transcription factor (HSF) and the activation of NF-kappaB by prostaglandin E2 (PGE2). Very high concentrations of ibuprofen (20 mM) did not prevent NF-kappaB binding to DNA in vitro. Immunofluorescence and nuclear import experiments indicate that the site of ibuprofen action appeared to be upstream of the dissociation of the NF-kappaB-IkappaB-complex. 4. Our data raise the possibility that R(-)-ibuprofen exerts some of its effects by inhibition of NF-kappaB activation.