Achieving transcriptional specificity with NF-kappa B

Epstein-Barr virus-encoded latent infection membrane protein 1 regulates the processing of p100 NF-kappaB2 to p52 via an IKKgamma/NEMO-independent signalling pathway

The oncogenic Epstein-Barr virus (EBV)-encoded latent infection membrane protein 1 (LMP1) constitutively activates the 'canonical' NF-kappaB pathway that involves the phosphorylation and degradation of IkappaBalpha downstream of the IkappaB kinases (IKKs). In this study, we show that LMP1 also promotes the proteasome-mediated proteolysis of p100 NF-kappaB2 resulting in the generation of active p52, which translocates to the nucleus in complex with the p65 and RelB NF-kappaB subunits. LMP1-induced NF-kappaB transactivation is reduced in nf-kb2(-/-) mouse embryo fibroblasts, suggesting that p100 processing contributes to LMP1-mediated NF-kappaB transcriptional effects. This pathway is likely to operate in vivo, as the expression of LMP1 in primary EBV-positive Hodgkin's lymphoma and nasopharyngeal carcinoma biopsies correlates with the nuclear accumulation of p52. Interestingly, while the ability of LMP1 to activate the canonical NF-kappaB pathway is impaired in cells lacking IKKgamma/NEMO, the regulatory subunit of the IKK complex, p100 processing remains unaffected. As a result, nuclear translocation of p52, but not p65, occurs in the absence of IKKgamma. These data point to the existence of a novel signalling pathway that regulates NF-kappaB in LMP1-expressing cells, and may thereby play a role in both oncogenic transformation and the establishment of persistent EBV infection.

Transcriptional coactivation of nuclear factor-kappaB-dependent gene expression by p300 is regulated by poly(ADP)-ribose polymerase-1

Nuclear factor kappaB (NF-kappaB) plays an important role in the transcriptional regulation of genes involved in inflammation and cell survival. In this study, we demonstrated that NF-kappaB-dependent gene expression was inhibited by E1A in poly(ADP)-ribose polymerase-1 knock out (PARP-1 (-/-)) cells complemented with wild type PARP-1 after tumor necrosis factor alpha (TNFalpha) or lipopolysaccharide (LPS) treatment. PARP-1 and p300 synergistically coactivated NF-kappaB-dependent gene expression in response to TNFalpha and LPS. Furthermore, PARP-1 interacted directly with p300 and enhanced the interaction of NF-kappaB1/p50 to p300. The C terminus, harboring the catalytic domain of PARP-1 but not its enzymatic activity, was required for complete transcriptional coactivation of NF-kappaB by p300 in response to TNFalpha and LPS. Together, these results indicate that PARP-1 acts synergistically with p300 and plays an essential regulatory role in NF-kappaB-dependent gene expression.

The interplay between the glucocorticoid receptor and nuclear factor-kappaB or activator protein-1: molecular mechanisms for gene repression

The inflammatory response is a highly regulated physiological process that is critically important for homeostasis. A precise physiological control of inflammation allows a timely reaction to invading pathogens or to other insults without causing overreaction liable to damage the host. The cellular signaling pathways identified as important regulators of inflammation are the signal transduction cascades mediated by the nuclear factor-kappaB and the activator protein-1, which can both be modulated by glucocorticoids. Their use in the clinic includes treatment of rheumatoid arthritis, asthma, allograft rejection, and allergic skin diseases. Although glucocorticoids have been widely used since the late 1940s, the molecular mechanisms responsible for their antiinflammatory activity are still under investigation. The various molecular pathways proposed so far are discussed in more detail.

NF-kappaB is involved in regulation of CD40 ligand expression on Mycobacterium bovis bacillus Calmette-Guérin-activated human T cells

Interaction between CD40L (CD154) on activated T cells and its receptor CD40 on antigen-presenting cells has been reported to be important in the resolution of infection by mycobacteria. However, the mechanism(s) by which Mycobacterium bovis bacillus Calmette-Guérin (BCG) up-regulates membrane expression of CD40L molecules is poorly understood. This study was done to investigate the role of the nuclear factor kappaB (NF-kappaB) signaling pathway in the regulation of CD40L expression in human CD4(+) T cells stimulated with BCG. Specific pharmacologic inhibition of the NF-kappaB pathway revealed that this signaling cascade was required in the regulation of CD40L expression on the surface of BCG-activated CD4(+) T cells. These results were further supported by the fact that treatment of BCG-activated CD4(+) T cells with these pharmacological inhibitors significantly down-regulated CD40L mRNA. In this study, inhibitor kappaBalpha (IkappaBalpha) and IkappaBbeta protein production was not affected by the chemical protease inhibitors and, more importantly, BCG led to the rapid but transient induction of NF-kappaB activity. Our results also indicated that CD40L expression on BCG-activated CD4(+) T cells resulted from transcriptional up-regulation of the CD40L gene by a mechanism which is independent of de novo protein synthesis. Interestingly, BCG-induced activation of NF-kappaB and the increased CD40L cell surface expression were blocked by the protein kinase C (PKC) inhibitors 1-[5-isoquinolinesulfonyl]-2-methylpiperazine and salicylate, both of which block phosphorylation of IkappaB. Moreover, rottlerin a Ca(2+)-independent PKC isoform inhibitor, significantly down-regulated CD40L mRNA in BCG-activated CD4(+) T cells. These data strongly suggest that CD40L expression by BCG-activated CD4(+) T cells is regulated via the PKC pathway and by NF-kappaB DNA binding activity.

Diminished NF-kappaB activation and PDGF-B expression in glomerular endothelial cells subjected to chronic shear stress

We tested the hypothesis that in endothelial cells, chronic arterial shear stress represses both the transactivator nuclear factor-kappaB (NF-kappaB) and subsequent platelet-derived growth factor (PDGF)-B gene transcription. Bovine aortic endothelial (BAE) and glomerular capillary endothelial (GEN) cells were subjected to chronic (9 days) arterial shear stress (10 dyne/cm(2)). Chronic shear stress reduced PDGF-B transcripts in BAE cells by 59 +/- 23% compared to controls, and by 70 +/- 14% in GEN cells. While PDGF-B mRNA levels were not significantly changed in BAE cells subjected to acute (4 h) shear stress, in GEN cells PDGF-B transcript abundance fell by 59 +/- 3%. PDGF-B mRNA stability was unchanged. We investigated the possibility that these effects were due to decreased nuclear NF-kappaB. NF-kappaB levels were much lower in nuclei of chronic shear stress-treated cells compared to controls. This represents classical inactivation of NF-kappaB since cytoplasmic NF-kappaB/I-kappaB (the inhibitory protein of NF-kappaB) levels were elevated in shear stress-treated cells. Further supporting NF-kappaB regulation of PDGF-B, activation of NF-kappaB by interleukin (IL)-1beta resulted in increased PDGF-B transcript levels. Treatment of cells with MG-132, an inhibitor of NF-kappaB activation, resulted in a dramatic decrease in basal PDGF-B transcript levels, and essentially abrogated the response to IL-1beta. Thus, repression of NF-kappaB activation in endothelial cells by shear stress decreases PDGF-B gene expression, while activators of NF-kappaB increase PDGF-B transcription.

Role of nuclear factor-kappa B activation in acute ischaemia-reperfusion injury in myocardium

(1) Our aims were to characterize activation of the transcription factor, nuclear factor kappa-B(NF-kappaB), during myocardial ischaemia-reperfusion and to assess its functional role in the evolution of acute ischaemia-reperfusion injury in intact myocardium in vivo. (2) Under pentobarbitone anaesthesia, rabbits underwent sham operation, 30 min left coronary artery occlusion followed by 0, 10 or 180 min reperfusion. Saline or NF-kappaB inhibitor diethyldithiocarbamic acid (DDTC, 50, 100 or 200 mg kg(-1)) was given intravenously 5 min prior to reperfusion. (3) Electromobility shift assay revealed that 30 min ischaemia alone did not activate NF-kappaB compared to time-matched sham-operated controls (85+/-13% vs 100+/-28%, respectively). However, ischaemia plus 10 min reperfusion markedly increased activation of NF-kappaB (295+/-77%). DDTC 50 mg kg(-1) did not inhibit NF-kappaB activation (278+/-67%) but at the higher doses complete inhibition was observed (54+/-20%, 31+/-16%, respectively). (4) Infarct to risk ratio was determined by triphenyltetrazolium chloride staining after 30 min ischaemia and 180 min reperfusion. DDTC 50 or 100 mg kg(-1) significantly reduced infarct size compared to the saline-treated control group (34.9+/-5.2%, 37.1+/-5.9%, vs 51.3+/-3.6%, P<0.05, respectively), whereas there was no protection with 200 mg kg(-1) (45.6+/-5.3%). (5) We conclude that ischaemia alone does not activate NF-kappaB, but post-ischaemic reperfusion robustly activates NF-kappaB in the myocardium. DDTC limited irreversible injury at low doses, but this effect appears to be dissociated from inhibition of NF-kappaB. Thus, activation of NF-kappaB during reperfusion does not appear to play a role in the evolution of myocardial infarction during the early phase of reperfusion.

Capsaicin inhibits growth of adult T-cell leukemia cells

Human T-cell leukemia virus type 1 (HTLV-1)-associated adult T-cell leukemia (ATL) is resistant to conventional chemotherapy. We examined the in vitro effects of capsaicin, the principal ingredients of red pepper, on three ATL cell lines. Capsaicin treatment inhibited the growth of ATL cells both in dose- and time-dependent manner. The inhibitory effect was mainly due to the induction of cell cycle arrest and apoptosis. Capsaicin treatment also induced the degradation of Tax and up-regulation of I kappa-B alpha, resulting in the decrease of nuclear factor (NF)-kappa B/p65 DNA binding activity. In addition, the Bcl-2 level was found to be decreased. Based on these findings, capsaicin may be considered for chemoprevention of ATL.

Regulation of c-Rel nuclear localization by binding of Ca2+/calmodulin

The NF-kappa B/Rel family of transcription factors participates in the control of a wide array of genes, including genes involved in embryonic development and regulation of immune, inflammation, and stress responses. In most cells, inhibitory I kappa B proteins sequester NF-kappa B/Rel in the cytoplasm. Cellular stimulation results in the degradation of I kappa B and modification of NF-kappa B/Rel proteins, allowing NF-kappa B/Rel to translocate to the nucleus and act on its target genes. Calmodulin (CaM) is a highly conserved, ubiquitously expressed Ca(2+) binding protein that serves as a key mediator of intracellular Ca(2+) signals. Here we report that two members of the NF-kappa B/Rel family, c-Rel and RelA, interact directly with Ca(2+)-loaded CaM. The interaction with CaM is greatly enhanced by cell stimulation, and this enhancement is blocked by addition of I kappa B. c-Rel and RelA interact with CaM through a similar sequence near the nuclear localization signal. Compared to the wild-type protein, CaM binding-deficient mutants of c-Rel exhibit increases in both nuclear accumulation and transcriptional activity on the interleukin 2 and granulocyte macrophage colony-stimulating factor promoters in the presence of a Ca(2+) signal. Conversely, for RelA neither nuclear accumulation nor transcriptional activity on these promoters is increased by mutation of the sequence interacting with CaM. Our results suggest that CaM binds c-Rel and RelA after their release from I kappa B and can inhibit nuclear import of c-Rel while letting RelA translocate to the nucleus and act on its target genes. CaM can therefore differentially regulate the activation of NF-kappa B/Rel proteins following stimulation.

Regulation of RelA (p65) function by the large subunit of replication factor C

The RelA (p65) subunit of NF-kappaB is an important regulator of inflammation, proliferation, and apoptosis. We have discovered that the large subunit, p140, of replication factor C (RFC) can function as a regulator of RelA. RFC is a clamp loader, facilitating the addition and removal of proliferating-cell nuclear antigen from DNA during replication and repair but can also interact directly with the retinoblastoma tumor suppressor protein and the transcription factor C/EBPalpha. We find that RFC (p140) interacts with RelA both in vitro and in vivo and stimulates RelA transactivation. In contrast, coexpression of fragments of RFC (p140) that mediate the interaction with RelA results in transcriptional inhibition. The significance of this regulation was confirmed by using short interfering RNA oligonucleotides targeted to RFC (p140). Down regulation of endogenous RFC (p140) inhibits expression from a chromosomally integrated reporter plasmid induced by endogenous, TNF-alpha-activated NF-kappaB. Dominant negative fragments of RFC (p140) also cooperate with overexpressed RelA to induce cell death. Interestingly, RFC (p140) also interacts with the tumor suppressor p53. Taken together, these observations suggest that, in addition to its previously described function in DNA replication and repair, RFC (p140) has an important role as a regulator of transcription and NF-kappaB activity.

Codelivery of NF-kappaB decoy-related oligodeoxynucleotide improves LPD-mediated systemic gene transfer

A systemic gene delivery vector for LPD (cationic liposome-polycation-DNA) has been reported previously to transfect the pulmonary endothelium and holds promise for treating pulmonary diseases. However, the uptake of LPD by immune cells triggers a strong inflammatory response that is toxic to animals and limits transgene expression. In this study, LPD was used to codeliver phosphorothioate oligodeoxynucleotides (ODNs) containing an NF-kappaB consensus binding sequence with plasmid DNA carrying a reporter gene. Codelivery of a single-stranded kappaB ODN inhibited TNF-alpha induction by LPD-plasmid delivery and increased transgene expression in the lung in a dose-dependent manner. A similar effect was observed with the double-stranded ODN of the same sequence at twice the dose, and the complementary ODN (antisense) had no effect. Sequence mutation study suggested that the effect was sequence specific and these ODNs may achieve their effect through interaction with NF-kappaB family proteins in a decoy manner. In addition to enhancing gene transfer, these single-stranded ODNs formulated in LPD may be explored as anti-inflammatory agents.

A novel form of the RelA nuclear factor kappaB subunit is induced by and forms a complex with the proto-oncogene c-Myc

Members of both Myc and nuclear factor kappaB (NF-kappaB) families of transcription factors are found overexpressed or inappropriately activated in many forms of human cancer. Furthermore, NF-kappaB can induce c-Myc gene expression, suggesting that the activities of these factors are functionally linked. We have discovered that both c-Myc and v-Myc can induce a previously undescribed, truncated form of the RelA(p65) NF-kappaB subunit, RelA(p37). RelA(p37) encodes the N-terminal DNA binding and dimerization domain of RelA(p65) and would be expected to function as a trans-dominant negative inhibitor of NF-kappaB. Surprisingly, we found that RelA(p37) no longer binds to kappaB elements. This result is explained, however, by the observation that RelA(p37), but not RelA(p65), forms a high-molecular-mass complex with c-Myc. These results demonstrate a previously unknown functional and physical interaction between RelA and c-Myc with many significant implications for our understanding of the role that both proteins play in the molecular events underlying tumourigenesis.

Opposing roles for NF-kappa B/Rel factors p65 and c-Rel in the modulation of neuron survival elicited by glutamate and interleukin-1beta

The nuclear transcription factors NF-kappaB/Rel have been shown to function as key regulators of either cell death or survival in neuronal cells. Here, we investigated whether selective activation of diverse NF-kappaB/Rel family members might lead to distinct effects on neuron viability. In both cultured rat cerebellar granule cells and mouse hippocampal slices, we examined NF-kappaB/Rel activation induced by two opposing modulators of cell viability: 1) interleukin-1beta (IL-1beta), which promotes neuron survival and 2) glutamate, which can elicit toxicity. IL-1beta produced a prolonged stimulation of NF-kappaB/Rel factors by inducing both IkappaBalpha and IkappaBbeta degradation. Glutamate produced a delayed and transient activation of NF-kappaB/Rel, which was associated with a brief loss of IkappaBalpha. Moreover, IL-1beta activated the p50, p65, and c-Rel subunits of NF-kappaB/Rel, whereas glutamate activated only the p50 and p65 proteins. The inhibition of NF-kappaB/Rel protein expression by antisense oligonucleotides in cerebellar granule cells showed that p65 was involved in glutamate-mediated cell death, whereas c-Rel was essential for IL-1beta-preserved cell survival. Furthermore, the depletion of c-Rel in cultured neurons as well as in the hippocampus from the c-Rel(-/-) mouse converted the IL-1beta effect into toxicity. These findings suggest that, within a single neuron, the balance between cell death and survival in response to external stimuli may rely on the activation of distinct NF-kappaB/Rel proteins.

Identification of a NF-kappaB site in the negative regulatory element (epsilon-NRAII) of human epsilon-globin gene and its binding protein NF-kappaB p50 in the nuclei of K562 cells

The developmental control of the human epsilon-globin gene expression is mediated by transcription regulatory elements in the 5' flanking DNA of this gene. Sequence analysis has revealed a DNA motif (GGGGAATTTGCT) similar to NF-kappaB consensus sequence resides in the negative regulatory element (-3028bp approximately -2902bp, termed e-NRAII) 5' to the cap site of this gene. NRF DNA fragment (-3010bp approximately -2986bp) containing the NF-kappaB motif similar sequence was synthesized and used in electrophoresis mobility shift assay (EMSA) and competitive analysis. Data showed that a protein factor from nuclear extracts of K562 cells specifically interacted with NRF DNA fragment. The synthetic NF DNA fragment (containing NF-kappaB consensus sequence) could competed for the protein binding, but MNF DNA fragment (mutated NF-kappaB motif) could not, suggesting that the binding protein is a member of NF-kappaB/Rel family. Western blot assay demonstrated that the molecular weight of NF-kappaB protein in the nuclei of K562 cells is 50ku. We suggested that NF-kappaB p50 may play an important role in the regulation of human epsilon-globin gene expression.

Enhancement of nuclear factor-kappa B acetylation by coactivator p300 and HIV-1 Tat proteins

Nuclear factor (NF)-kappaB transcription factors are involved in the control of a large number of normal cellular and organismal processes, such as immune and inflammatory responses, developmental processes, cellular growth, and apoptosis. Transcription of the human immunodeficiency virus type 1 (HIV-1) genome depends on the intracellular environment where the integrate viral DNA is regulated by a complex interplay among viral regulatory proteins, such as Tat, and host cellular transcription factors, such as NF-kappaB, interacting with the viral long terminal repeat region. CBP (CREB-binding protein) and p300, containing an intrinsic histone acetyltransferase (HAT) activity, have emerged as coactivators for various DNA-binding transcription factors. Here, we show that the p50 subunit as well as the p50/p65 of NF-kappaB, and not other factors such as SP1, TFIIB, polymerase II, TFIIA, or p65, can be acetylated by CBP/p300 HAT domain. Acetylation of p50 was completely dependent on the presence of both HAT domain and Tat proteins, implying that Tat influences the transcription machinery by aiding CBP/p300 to acquire new partners and increase its functional repertoire. Three lysines, Lys-431, Lys-440, and Lys-441 in p50 were all acetylated in vitro, and a sequence similarity among p50, p53, Tat, and activin receptor type I on these particular lysines was observed. All proteins have been shown to be acetylated by the CBP/p300 HAT domain. Acetylated p50 increases its DNA binding properties, as evident by streptavidin/biotin pull-down assays when using labeled NF-kappaB oligonucleotides. Increased DNA binding on HIV-1 long terminal repeat coincided with increases in the rate of transcription. Therefore, we propose that acetylation of the DNA binding domain of NF-kappaB aids in nuclear translocation and enhanced transcription and also suggest that the substrate specificity of CBP/p300 can be altered by small peptide molecules, such as HIV-encoded Tat.

Increased cytochrome P-450 2E1 expression sensitizes hepatocytes to c-Jun-mediated cell death from TNF-alpha

The mechanisms underlying hepatocyte sensitization to tumor necrosis factor-alpha (TNF-alpha)-mediated cell death remain unclear. Increases in hepatocellular oxidant stress such as those that occur with hepatic overexpression of cytochrome P-450 2E1 (CYP2E1) may promote TNF-alpha death. TNF-alpha treatment of hepatocyte cell lines with differential CYP2E1 expression demonstrated that overexpression of CYP2E1 converted the hepatocyte TNF-alpha response from proliferation to apoptotic and necrotic cell death. Death occurred despite the presence of increased levels of nuclear factor-kappaB transcriptional activity and was associated with increased lipid peroxidation and GSH depletion. CYP2E1-overexpressing hepatocytes had increased basal and TNF-alpha-induced levels of c-Jun NH(2)-terminal kinase (JNK) activity, as well as prolonged JNK activation after TNF-alpha stimulation. Sensitization to TNF-alpha-induced cell death by CYP2E1 overexpression was inhibited by antioxidants or adenoviral expression of a dominant-negative c-Jun. Increased CYP2E1 expression sensitized hepatocytes to TNF-alpha toxicity mediated by c-Jun and overwhelming oxidative stress. The chronic increase in intracellular oxidant stress created by CYP2E1 overexpression may serve as a mechanism by which hepatocytes are sensitized to TNF-alpha toxicity in liver disease.

1alpha,25-dihydroxyvitamin D3 stimulates phosphorylation of IkappaBalpha and synergizes with TPA to induce nuclear translocation of NFkappaB during monocytic differentiation of NB4 leukemia cells

Treatment of NB4 acute promyelocytic leukemia cells with 1,25-dihydroxyvitamin D3 (1,25D3) or analogs 20-epi-22-oxa-24a,26a,27a-trihomo-1alpha,25-dihydroxyvitamin D3, 1,24-dihydroxy-22-ene-24-cyclopropylvitamin D3, 1alpha,25-dihydroxylumisterol3, or 1alpha,25(OH)2-d5-previtamin D3 in combination with TPA induces monocytic differentiation. The role of 1,25D3 in the induction of maturation has been shown to be a priming effect. Differentiation in response to these agents requires VDR-independent signaling of 1,25D3, PKC signaling, intracellular calcium, and calpain activity. In this study we identify the NFkappaB/IkappaB signaling pathway as a target of 1,25D3 and TPA action. One of the priming effects of 1,25D3 appears to be the rapid phosphorylation of serine residues on IkappaBalpha. On their own, 1,25D3, its analogs, and TPA do not alter IkappaBalpha expression; however, combinations of analogs with TPA result in a synergistic decrease in IkappaBalpha expression. Decreased expression of IkappaBalpha likely results from enhanced degradation, which allows the observed subsequent nuclear translocation of NFkappaB subunit p65. Since nuclear-localized NFkappaB was observed only in combination-treated cells, it is proposed that nuclear targets of NFkappaB are required for monocytic differentiation. Intracellular calcium and proteolytic activity are both necessary for the induction of IkappaB regulation and translocation of NFkappaB and are critical components of the nongenomic signaling cascades of the 1,25D3-induced differentiation pathway.

The enzymatic and DNA binding activity of PARP-1 are not required for NF-kappa B coactivator function

Poly(ADP-ribose) polymerase 1 (PARP-1)-deficient mice are protected against septic shock, diabetes type I, stroke, and inflammation. We report that primary cells from PARP-1(-/-) animals are impaired in kappa B-dependent transcriptional activation induced by different stimuli involved in inflammatory and genotoxic stress signaling. PARP-1 was also required for p65-mediated transcriptional activation. PARP-1 enzymatic inhibitors did not inhibit the transcriptional activation of a kappa B-dependent reporter gene in wild type cells. Remarkably, neither the enzymatic activity nor the DNA binding activity of PARP-1 was required for kappa B-dependent transcriptional activation in PARP-1(-/-) cells complemented with different PARP-1 mutants. However, PARP-1 interacted in vitro directly with both subunits of NF-kappa B (p50 and p65), and mapping of the interaction domains revealed that both subunits bind to different PARP-1 domains. Furthermore, a PARP-1 mutant lacking the enzymatic and DNA binding activity interacted comparably to the wild type PARP-1 with p65 or p50. Finally, we showed that PARP-1 is activating the natural inducible nitric-oxide synthase and P-selectin promoter in a kappa B-dependent manner upon stimulation of the cells with inflammatory stimuli or cotransfection of p65. Our results provide evidence that neither the DNA binding nor the enzymatic activity of PARP-1 but its direct protein-protein interaction with both subunits of NF-kappa B is required for its coactivator function, thus expanding the role of PARP-1 as an essential and novel classical transcriptional coactivator for kappa B-dependent gene expression in vivo.

SNIP1 inhibits NF-kappa B signaling by competing for its binding to the C/H1 domain of CBP/p300 transcriptional co-activators

SNIP1 is a 396-amino acid nuclear protein shown to be an inhibitor of the TGF-beta signal transduction pathway and to be important in suppressing transcriptional activation dependent on the co-activators CBP and p300. In this report we show that SNIP1 potently inhibits the activity of NF-kappa B, which binds the C/H1 domain of CBP/p300, but does not interfere with the activity of transcription factors such as p53, which bind to other domains of p300, or factors such as VP16, which are independent of these co-activators. Inhibition of NF-kappa B activity is a function of the N-terminal domain of SNIP1 and involves competition of SNIP1 and the NF-kappa B subunit, RelA/p65, for binding to p300, similar to the mechanism of inhibition of Smad signaling by SNIP1. Immunohistochemical staining shows that expression of SNIP1 is strictly regulated in development and that it colocalizes, in certain tissues, with nuclear staining for RelA/p65 and for p300, suggesting that they may regulate NF-kappa B activity in vivo in a spatially and temporally controlled manner. These data led us to suggest that SNIP1 may be an inhibitor of multiple transcriptional pathways that require the C/H1 domain of CBP/p300.

The functional genomic response of developing embryonic submandibular glands to NF-kappa B inhibition

BACKGROUND

The proper balance between epithelial cell proliferation, quiescence, and apoptosis during development is mediated by the specific temporal and spatial appearance of transcription factors, growth factors, cytokines, caspases, etc. Since our prior studies suggest the importance of transcription factor NF-kappaB during embryonic submandibular salivary gland (SMG) development, we attempted to delineate the emergent dynamics of a cognate signaling network by studying the molecular patterns and phenotypic outcomes of interrupted NF-kappaB signaling in embryonic SMG explants.

RESULTS

SN50-mediated inhibition of NF-kappaB nuclear translocation in E15 SMG explants cultured for 2 days results in a highly significant increase in apoptosis and decrease in cell proliferation. Probabilistic Neural Network (PNN) analyses of transcriptomic and proteomic assays identify specific transcripts and proteins with altered expression that best discriminate control from SN50-treated SMGs. These include PCNA, GR, BMP1, BMP3b, Chk1, Caspase 6, E2F1, c-Raf, ERK1/2 and JNK-1, as well as several others of lesser importance. Increased expression of signaling pathway components is not necessarily probative of pathway activity; however, as confirmation we found a significant increase in activated (phosphorylated/cleaved) ERK 1/2, Caspase 3, and PARP in SN50-treated explants. This increased activity of proapoptotic (caspase3/PARP) and compensatory antiapoptotic (ERK1/2) pathways is consistent with the dramatic cell death seen in SN50-treated SMGs.

CONCLUSIONS

Our morphological and functional genomic analyses indicate that the primary and secondary effects of NF-kappaB-mediated transcription are critical to embryonic SMG developmental homeostasis. Relative to understanding complex genetic networks and organogenesis, our results illustrate the importance of evaluating the gene, protein, and activated protein expression of multiple components from multiple pathways within broad functional categories.

Sp3 represses the Sp1-mediated transactivation of the human COL2A1 gene in primary and de-differentiated chondrocytes

Sp1 and Sp3 effects on the transcription of the human alpha1(II) procollagen gene (COL2A1) were investigated in both differentiated and de-differentiated rabbit articular chondrocytes. Transient transfection with constructs of deleted COL2A1 promoter sequences driving the luciferase reporter gene revealed that the region spanning -266 to +121 base pairs showed Sp1-enhancing effects, whatever the differentiation state. In contrast, Sp3 did not influence COL2A1 gene transcription. Concomitant overexpression of the two Sp proteins demonstrated that Sp3 blocked the Sp1 induction of COL2A1 promoter activity. Moreover, inhibition of Sp1/Sp3 binding to their target DNA sequence decreased both COL2A1 gene transcription and Sp1-enhancing effects. DNase I footprinting and gel retardation assays revealed that Sp1 and Sp3 bind specifically to cis-sequences of the COL2A1 gene promoter whereby they exert their transcriptional effects. Sp1 and Sp3 levels were found to be reduced in de-differentiated chondrocytes, as revealed by DNA-binding and immunochemical study. Sp1 specifically activated collagen neosynthesis whatever the differentiation state of chondrocytes, suggesting that this factor exerts a major role in the expression of collagen type II. However, our data indicate that type II collagen-specific expression in chondrocytes depend on both the Sp1/Sp3 ratio and cooperation of Sp1 with other transcription factors, the amounts of which are also modulated by phenotype alteration.

Binding of nerve growth factor to its p75 receptor in stressed cells induces selective IkappaB-beta degradation and NF-kappaB nuclear translocation

Nerve growth factor (NGF) regulates the activity of the transcription factor NF-kappaB (nuclear factor-kappaB) through its low affinity receptor, p75. In the present study we found that NGF binding to p75 induces nuclear translocation of p65 and increases NF-kappaB binding activity in a cell line overexpressing p75, but only after the cells have been subjected to a previous stress. Under physiological conditions, in the absence of stress, NGF is unable to alter p65 nuclear levels. Tumor necrosis factor-alpha (TNF-alpha) induces a down-regulation of IkappaB-alpha, -beta and -epsilon both in physiological and in stress, i.e. serum-free, conditions. In contrast, NGF only induces the specific degradation of IkappaB-beta after serum withdrawal, without affecting IkappaB-alpha or -epsilon either in the presence or in the absence of stress. IkappaB-beta consists of several isoforms, whose relative abundance is regulated by serum withdrawal. NGF does not target all the IkappaB-beta isoforms with the same potency, being more effective in reducing the levels of the isoforms up-regulated by serum withdrawal. TRAF-6 is expressed at the same level under both physiological and stress conditions. These results indicate that NGF is able to induce NF-kappaB nuclear translocation by a mechanism that involves specific IkappaB-beta degradation only after the cells have been subjected to a severe stress.

The contribution of NF-kappa B activity to spontaneous proliferation and resistance to apoptosis in human T-cell leukemia virus type 1 Tax-induced tumors

Human T-cell leukemia virus type I is the etiologic agent of adult T-cell leukemia/lymphoma. The Tax protein of this virus is thought to contribute to cellular transformation and tumor development. In this report, we have used a Tax transgenic mouse model of tumorigenesis to study the contribution of nuclear factor (NF)-kappa B activity to spontaneous tumor cell proliferation and resistance to apoptosis. We have demonstrated elevated expression levels of NF-kappa B--inducible cytokines, including interleukin (IL)-6, IL-10, IL-15, and interferon (IFN)-gamma, in freshly isolated primary tumors from Tax transgenic mice. Inhibitors of NF-kappa B activity, sodium salicylate and cyclopentenone prostaglandins (prostaglandin A(1) and 15-deoxy-Delta(12,14)-prostaglandin J(2)), blocked spontaneous proliferation of Tax transgenic mouse spleen cells. In addition, Tax-induced tumor cells, which are resistant to irradiation-induced apoptosis, became sensitive to apoptosis in the presence of sodium salicylate and prostaglandins. These results strongly suggest that Tax-mediated induction of NF-kappa B activity contributes to tumorigenesis in vivo. (Blood. 2001;98:1200-1208)

Pharmacologic modulators of nitric oxide exacerbate tubulointerstitial inflammation in proteinuric rats

Nitric oxide (NO) regulates inflammatory responses partly by cell-specific inhibition of the transcription factor nuclear factor kappaB (NF-kappaB). This study investigated the effect of continuous oral administration of an NO donor (molsidomine [Mol]), NO precursor (L-arginine [L-arg]), or selective inhibitors of inducible NO synthase (iNOS; aminoguanidine [AG], L-N(6)-(1-iminoethyl)lysine [L-NIL]) on the progression of tubulointerstitial inflammation and NF-kappaB activation in a non-immune model of chronic glomerular disease (Adriamycin nephropathy [AN]), from day 8 until day 30 after disease induction. On day 30, rats with AN had heavy proteinuria, reduced creatinine clearance, and tubulointerstitial disease. Treatment with both AG and L-NIL exacerbated the progression of AN as evidenced by (1) increased renal cortical malondialdehyde; (2) reduced creatinine clearance; and (3) increased tubular atrophy, interstitial volume, and monocyte infiltration. Unexpectedly, Mol also increased renal malondialdehyde and worsened tubular injury, whereas L-arg had no effect. The increase in renal cortical NF-kappaB activation in AN was not altered by AG, L-NIL, or Mol, but the mRNA expression of monocyte chemoattractant protein-1, interleukin-10, and osteopontin were elevated in these groups. Nitrite release from kidney slices reduced in AN. Treatment with Mol restored renal nitrite release to normal, whereas neither L-arg nor the NOS inhibitors had an effect. It is concluded that endogenous iNOS-derived NO has a protective role against tubulointerstitial injury and cytokine production in AN. However, the pro-oxidant activity of NO donors may limit their potential benefit in proteinuric renal disease.

Transactivation by the p65 subunit of NF-kappaB in response to interleukin-1 (IL-1) involves MyD88, IL-1 receptor-associated kinase 1, TRAF-6, and Rac1

We have examined the involvement of components of the interleukin-1 (IL-1) signaling pathway in the transactivation of gene expression by the p65 subunit of NF-kappaB. Transient transfection of cells with plasmids encoding wild-type MyD88, IL-1 receptor-associated kinase 1 (IRAK-1), and TRAF-6 drove p65-mediated transactivation. In addition, dominant negative forms of MyD88, IRAK-1, and TRAF-6 inhibited the IL-1-induced response. In cells lacking MyD88 or IRAK-1, no effect of IL-1 was observed. Together, these results indicate that MyD88, IRAK-1, and TRAF-6 are important downstream regulators of IL-1-mediated p65 transactivation. We have previously shown that the low-molecular-weight G protein Rac1 is involved in this response. Constitutively active RacV12-mediated transactivation was not inhibited by dominant negative MyD88, while dominant negative RacN17 inhibited the MyD88-driven response, placing Rac1 downstream of MyD88 on this pathway. Dominant negative RacN17 inhibited wild-type IRAK-1- and TRAF-6-induced transactivation, and in turn, dominant negative IRAK-1 and TRAF-6 inhibited the RacV12-driven response, suggesting a mutual codependence of Rac1, IRAK-1, and TRAF-6 in regulating this pathway. Finally, Rac1 was found to associate with the receptor complex via interactions with both MyD88 and the IL-1 receptor accessory protein. A pathway emanating from MyD88 and involving IRAK-1, TRAF-6, and Rac1 is therefore involved in transactivation of gene expression by the p65 subunit of NF-kappaB in response to IL-1.

Embryonic mouse submandibular salivary gland morphogenesis and the TNF/TNF-R1 signal transduction pathway

TNF is a pleiotropic cytokine that modulates cell proliferation and apoptosis. The objective of the present study was to investigate the possible function(s) of the TNF/TNF-R1 signaling pathway in embryonic mouse submandibular salivary gland (SMG) morphogenesis. After characterizing in vivo mRNA and protein expression of various constituents of this pathway, we utilized in vitro experiments to investigate the phenotypic outcomes of enhanced and deficient ligand. The results of these experiments indicate that the TNF/TNF-R1 signal transduction pathway plays an important role in balancing cell proliferation and apoptosis during SMG duct and presumptive acini formation.

Inhibition of c-Myc expression sensitizes hepatocytes to tumor necrosis factor-induced apoptosis and necrosis

The typical proliferative response of hepatocytes to tumor necrosis factor (TNF) can be converted to a cytotoxic one by transcriptional arrest. Although NF-kappaB activation is critical for hepatocyte resistance to TNF toxicity, the contribution of other TNF-inducible transcription factors remains unknown. To determine the function of c-Myc in hepatocyte sensitivity to TNF, stable transfectants of the rat hepatocyte cell line RALA255-10G containing sense and antisense c-myc expression vectors were isolated with increased (S-Myc cells) and decreased (AN-Myc cells) c-Myc transcriptional activity. While S-Myc cells proliferated in response to TNF treatment, AN-Myc cells underwent 32% cell death within 6 h. Fluorescent microscopic studies indicated that TNF induced apoptosis and necrosis in AN-Myc cells. Cell death was associated with DNA hypoploidy and poly(ADP-ribose) polymerase cleavage but occurred in the absence of detectable caspase-3, -7, or -8 activation. TNF-induced, AN-Myc cell death was dependent on Fas-associated protein with death domain and partially blocked by caspase inhibitors. AN-Myc cells had decreased levels of NF-kappaB transcriptional activity, but S-Myc cells maintained resistance to TNF despite NF-kappaB inactivation, suggesting that c-Myc and NF-kappaB independently mediate TNF resistance. Thus, in the absence of sufficient c-Myc expression, hepatocytes are sensitized to TNF-induced apoptosis and necrosis. These findings demonstrate that hepatocyte resistance to TNF is regulated by multiple transcriptional activators.

Biochemistry of cyclooxygenase (COX)-2 inhibitors and molecular pathology of COX-2 in neoplasia

Several types of human tumors overexpress cyclooxygenase (COX) -2 but not COX-1, and gene knockout transfection experiments demonstrate a central role of COX-2 in experimental tumorigenesis. COX-2 produces prostaglandins that inhibit apoptosis and stimulate angiogenesis and invasiveness. Selective COX-2 inhibitors reduce prostaglandin synthesis, restore apoptosis, and inhibit cancer cell proliferation. In animal studies they limit carcinogen-induced tumorigenesis. In contrast, aspirin-like nonselective NSAIDs such as sulindac and indomethacin inhibit not only the enzymatic action of the highly inducible, proinflammatory COX-2 but the constitutively expressed, cytoprotective COX-1 as well. Consequently, nonselective NSAIDs can cause platelet dysfunction, gastrointestinal ulceration, and kidney damage. For that reason, selective inhibition of COX-2 to treat neoplastic proliferation is preferable to nonselective inhibition. Selective COX-2 inhibitors, such as meloxicam, celecoxib (SC-58635), and rofecoxib (MK-0966), are NSAIDs that have been modified chemically to preferentially inhibit COX-2 but not COX-1. For instance, meloxicam inhibits the growth of cultured colon cancer cells (HCA-7 and Moser-S) that express COX-2 but has no effect on HCT-116 tumor cells that do not express COX-2. NS-398 induces apoptosis in COX-2 expressing LNCaP prostate cancer cells and, surprisingly, in colon cancer S/KS cells that does not express COX-2. This effect may due to induction of apoptosis through uncoupling of oxidative phosphorylation and down-regulation of Bcl-2, as has been demonstrated for some nonselective NSAIDs, for instance, flurbiprofen. COX-2 mRNA and COX-2 protein is constitutively expressed in the kidney, brain, spinal cord, and ductus deferens, and in the uterus during implantation. In addition, COX-2 is constitutively and dominantly expressed in the pancreatic islet cells. These findings might somewhat limit the use of presently available selective COX-2 inhibitors in cancer prevention but will probably not deter their successful application for the treatment of human cancers.

The Rel/NF-kappa B family: friend and foe

The members of the Rel/NF-kappa B family of transcription factors form one of the first lines of defense against infectious diseases and cellular stress. These proteins initiate a highly coordinated response in multiple cell types that effectively counteracts the threat to the health of the organism. Conversely, disruption of the regulatory mechanisms that control the specificity and extent of this response, which results in aberrant activation of NF-kappa B, can be one of the primary causes of a wide range of human diseases. Thus, targeting NF-kappa B might lead to the development of new pharmaceutical reagents that could provide novel treatments for many inflammatory diseases and cancer.

Sp1 increases expression of cyclooxygenase-2 in hypoxic vascular endothelium. Implications for the mechanisms of aortic aneurysm and heart failure

Cyclooxygenase-2 (COX-2) catalyzes prostaglandin synthesis from arachidonic acid and is expressed locally in aortic aneurysm and heart failure. Cellular hypoxia is also found in these conditions. We have previously shown that cox-2 is transcriptionally regulated by hypoxia in human umbilical vein endothelial cells (HUVEC) in culture via the transactivation factor NF-kappaB p65, leading to increased production of prostaglandin E(2), an inhibitor of vascular smooth muscle cell proliferation. Sp1 is a transactivation factor known to be important in the regulation of cytokine expression in association with NF-kappaB. We hypothesized that Sp1 is involved in the induction of cox-2 in hypoxic HUVEC. Electrophoretic mobility shift assays with hypoxic HUVEC nuclear protein showed that both Sp1 and the related protein Sp3 specifically bound to the cox-2 promoter. Immunoblotting demonstrated that hypoxia increased the nuclear localization of Sp1 but did not change the Sp3 content in HUVEC. Overexpression of Sp1 through transfection of HUVEC enhanced cox-2 promoter activity as measured by reporter gene expression and by the production of COX-2. The specificity of the results was confirmed by mutation of the Sp1-binding site in the cox-2 promoter construct and by reproducibility in an Sp-deficient Drosophila SL2 cell line. The regulatory role of Sp1 discovered in this work supports the concept that a mechanistic link exists between vascular cellular hypoxia and mediators of inflammation associated with aortic aneurysm and heart failure.

Cloning and characterization of the gene encoding mouse IkappaBbeta

IkappaBbeta is a member of the IkappaB family of structurally related proteins that are important regulators of the inducible transcription factor NF-kappaB. In the present study, the mouse IkappaBbeta gene was cloned and sequenced, and its structure determined. The mouse IkappaBbeta gene contains six exons and five introns that span 7435 nucleotides. A single major transcription initiation site is located 59 nucleotides upstream of the initiating methionine. A translation termination codon and a single polyadenylation signal are found within exon 6. The exon/intron structure of IkappaBbeta and IkappaBalpha genes were compared and found to be very similar, with individual ankyrin repeats being maintained on corresponding exons. This suggests a close evolutionary relationship between these two IkappaB isoforms. The significance of this evolutionary relationship is discussed.

NFkappaB decoy oligodeoxynucleotides reduce monocyte infiltration in renal allografts

Monocyte influx secondary to ischemia-reperfusion conditions the renal allograft to rejection by presentation of antigens and production of cytokines. Monocyte influx depends on NFkappaB-dependent transcription of genes encoding adhesion molecules and chemokines. Here we demonstrate that cationic liposomes containing phosphorothioated oligodeoxynucleotides (ODN) with the kappaB binding site serving as competitive binding decoy, can prevent TNF-alpha-induced NFkappaB activity in endothelial cells in vitro. In an allogenic rat kidney transplantation model (BN to LEW), we show that perfusing the renal allograft with this decoy prior to transplantation abolishes nuclear NFkappaB activity in vivo and inhibits VCAM-1 expression in the donor endothelium (P<0.05). At 24 h postreperfusion, periarterial infiltration of monocytes/macrophages was significantly reduced in decoy ODN-treated allografts compared to control allografts (3.7+/-0.7 vs. 9.2+/-1.2 macrophages/vessel; P<0.01). At 72 h, there was a reduction of tubulointerstitial macrophage infiltration in decoy ODN-treated kidneys compared to controls (75.6+/-13.9 vs. 120.0+/-11.2 macrophages/tubulointerstitial area; P<0.05). In conclusion, perfusion of the renal allograft with NFkappaB decoy ODN prior to transplantation decreases the initial inflammatory response in a stringent, nonimmunosuppressed allogenic transplantation model. Therefore, the NFkappaB decoy approach may be useful to explore the role of endothelium and macrophages in graft rejection and may be developed into a graft-specific immunosuppressive strategy allowing reduction of systemic immunosuppression on organ transplantation.

Inhibition of the RelA(p65) NF-kappaB subunit by Egr-1

Induction of transcription from the human immunodeficiency virus 1 long terminal repeat by the RelA (p65) NF-kappaB subunit has been shown to be dependent upon an interaction with the zinc finger DNA-binding domain of Sp1. It was unknown, however, whether NF-kappaB could also interact with other zinc finger-containing transcription factors. In this study we demonstrate that the early growth response transcription factor Egr-1, whose DNA-binding domain shares a high degree of homology with that of Sp1, can also interact with RelA in vitro and regulate NF-kappaB transcriptional activity in vivo. Similar to the interaction with Sp1, the Rel homology domain of RelA interacts with the zinc finger domain of Egr-1. Surprisingly, and in contrast to Sp1, Egr-1 specifically represses RelA transcriptional activity through its zinc finger domain. Moreover, the interaction between RelA and the Egr-1 zinc fingers is mutually exclusive with DNA binding suggesting a model in which Egr-1 directly sequesters NF-kappaB from its target promoters. Because Egr-1 is induced by many of the same stimuli that activate NF-kappaB, this novel transcriptional regulatory mechanism has many implications for the involvement of both factors in cellular processes such as apoptosis and the response to stress and infection.

Cell type-specific regulation of fibrinogen expression in lung epithelial cells by dexamethasone and interleukin-1beta

Our recent studies demonstrating the expression of fibrinogen (FBG) by an alveolar type II cell line stimulated with proinflammatory mediators and also in the inflamed pulmonary epithelium of animals with Pneumocystis carinii pneumonia suggest that extrahepatic FBG participates in the local acute phase response (APR) to infection and subsequent wound repair. However, the mechanisms that regulate extrahepatic FBG expression are poorly understood. This study compares the regulation of hepatic and pulmonary FBG expression by mediators of the APR, interleukin (IL)-6, IL-1beta, and dexamethasone (DEX), a synthetic glucocorticoid. Northern blotting and metabolic labeling studies revealed that IL-6 with or without DEX upregulates gammaFBG messenger RNA and protein, whereas IL-1beta inhibits gammaFBG expression in human lung (A549) and liver (HepG2) epithelial cells. In contrast, the addition of DEX relieved the IL-1beta-mediated inhibition of FBG expression in lung epithelial cells only; this response is termed "DEX rescue." Studies with cycloheximide indicate that only DEX rescue required de novo protein synthesis. Nuclear run-on analysis revealed no increase in gammaFBG transcription by DEX treatment. Although DEX treatment alone increased the stability of gammaFBG transcripts in lung cells, this effect was not observed in the presence of IL-1beta. Together, these results suggest that pre-existing transcription factors mediate the effects of IL-6 with or without DEX, DEX, and IL-1beta on gammaFBG gene expression in lung and liver cells. Also, the data suggest that DEX induces new protein synthesis of an inhibitor of IL-1beta signal transduction to effectively "rescue" FBG production in lung but not liver epithelial cells. This cell type-specific stimulation of FBG production by glucocorticoids to overcome IL-1beta inhibition may promote pulmonary wound repair mechanisms.

STAT3 and NFkappaB activation precedes glial reactivity in the excitotoxically injured young cortex but not in the corresponding distal thalamic nuclei

In this study we evaluated the activation of the cytokine and growth factor responsive transcription factors signal transducer and activator of transcription 3 (STAT3) and nuclear factor kappa B (NFkappaB) after different grades of neural damage in the immature rat brain using double immunocytochemical techniques and electron microscopy. Following neocortical N-methyl-D-aspartate induced excitotoxic cell death, both these transcription factors are mainly activated in astrocytes, although microglia, endothelial cells, and neurons show transient activation at specific times and locations. Interestingly, activation of both transcription factors is only observed in cortical areas affected by severe tissue damage, neuronal degeneration, and blood-brain barrier (BBB) disruption. In contrast, the milder glial response occurring in the distal thalamus is not preceded by immunocytochemically detectable STAT3 and NFkappaB activation, although microglial response, astroglial hypertrophy, and glial fibrillary acidic protein (GFAP) overexpression do occur. In the cortex, astrocytes show STAT3 and NFkappaB activation already at 2 to 4 hours post-lesion, preceding cell hypertrophy and GFAP upregulation, and being maintained in the long-term formed glial scar. STAT3 and NFkappaB activation in microglial cells is protracted and observed at 10 to 24 hours post-lesion. The early activation of both transcription factors in astroglial cells could contribute to the changes in gene expression leading to astrogliosis and the release of signalling molecules which may contribute to the subsequent activation of these transcription factors in microglial cells.

Roles of Intracellular Calcium and NF-κB in the Clostridium difficile Toxin A-Induced Up-Regulation and Secretion of IL-8 from Human Monocytes

Clostridium difficile causes an intense inflammatory colitis through the actions of two large exotoxins, toxin A and toxin B. IL-8 is believed to play an important role in the pathophysiology of C. difficile-mediated colitis, although the mechanism whereby the toxins up-regulate the release of IL-8 from target cells is not well understood. In this study, we investigated the mechanisms through which toxin A induces IL-8 secretion in human monocytes. We found that cellular uptake of toxin A is required for the up-regulation of IL-8, an effect that is not duplicated by a recombinant toxin fragment comprising the cell-binding domain alone. Toxin A induced IL-8 expression at the level of gene transcription and this effect occurred through a mechanism requiring intracellular calcium and calmodulin activation. Additionally, the effects of toxin A were inhibited by the protein tyrosine kinase inhibitor genistein, but were unaffected by inhibitors of protein kinase C and phosphatidylinositol-3 kinase. We determined that toxin A activates nuclear translocation of the transcription factors NF-κB and AP-1, but not NF-IL-6. NF-κB inhibitors blocked the ability of toxin A to induce IL-8 secretion, and supershift analysis indicated that the major isoform of NF-κB activated by the toxin is a p50-p65 heterodimer. This study is the first to identify intracellular signaling pathways and transcription factors involved in the C. difficile toxin-mediated up-regulation of IL-8 synthesis and release by target cells. This information should increase our understanding of the pathogenesis of C. difficile colitis and the nature of IL-8 gene regulation as well.

c-Rel and p65 trans-activate the monocyte chemoattractant protein-1 gene in interleukin-1 stimulated mesangial cells

BACKGROUND

The chemokine monocyte chemoattractant protein-1 (MCP-1) is secreted by human glomerular mesangial cells in response to interleukin-1 (IL-1) and has a central role in amplifying the inflammatory response during glomerulonephritis. However, the mechanism by which IL-1 regulates its transcription is not understood. Specific members of the nuclear factor kappaB/rel (NF-kappaB) proteins may regulate MCP-1 expression in a stimulus- and tissue-specific manner.

METHODS

Electrophoretic mobility shift assays and Western blot analysis characterized the members of the NF-kappaB family that bound the two NF-kappaB sites of the MCP-1 enhancer (A1 and A2) in vitro. Trans-activation of the MCP-1 gene was investigated by transfer of the MCP-1 enhancer DNA to mesangial cells.

RESULTS

Primary human mesangial cells contained in addition to p50 (NF-kappaB1) and p65 (Rel A) NF-kappaB proteins, the oncoprotein c-rel, and Rel B, but not p52 (NF-kappaB2). IL-1 induced c-rel to form a complex with p65, which bound the MCP-1 A2 site but not the A1 or IL-6 NF-kappaB sites in vitro. IL-1 up-regulated transfected MCP-1 enhancer activity. Cotransfer of the MCP-1 enhancer together with individual members of the NF-kappaB family showed that the heterodimer c-relp65 or (p65)2 can selectively trans-activate the MCP-1 gene via its A1 and A2 sites in mesangial cells.

CONCLUSIONS

This study demonstrates for the first time that the c-rel oncoprotein can enhance MCP-1 transcription in mesangial cells and suggests that it may have an important role in amplifying gene expression in the inflamed glomerulus.

Transcriptional cross talk between NF-kappaB and p53

Many cellular stimuli result in the induction of both the tumor suppressor p53 and NF-kappaB. In contrast to activation of p53, which is associated with the induction of apoptosis, stimulation of NF-kappaB has been shown to promote resistance to programmed cell death. These observations suggest that a regulatory mechanism must exist to integrate these opposing outcomes and coordinate this critical cellular decision-making event. Here we show that both p53 and NF-kappaB inhibit each other's ability to stimulate gene expression and that this process is controlled by the relative levels of each transcription factor. Expression of either wild-type p53 or the RelA(p65) NF-kappaB subunit suppresses stimulation of transcription by the other factor from a reporter plasmid in vivo. Moreover, endogenous, tumor necrosis factor alpha-activated NF-kappaB will inhibit endogenous wild-type p53 transactivation. Following exposure to UV light, however, the converse is observed, with p53 downregulating NF-kappaB-mediated transcriptional activation. Both p53 and RelA(p65) interact with the transcriptional coactivator proteins p300 and CREB-binding protein (CBP), and we demonstrate that these results are consistent with competition for a limiting pool of p300/CBP complexes in vivo. These observations have many implications for regulation of the transcriptional decision-making mechanisms that govern cellular processes such as apoptosis. Furthermore, they suggest a previously unrealized mechanism through which dysregulated NF-kappaB can contribute to tumorigenesis and disease.