Dimerization of NF-KB2 with RelA(p65) regulates DNA binding, transcriptional activation, and inhibition by an I kappa B-alpha (MAD-3)

Effects of Naturally Occurring Mutations in Bovine Leukemia Virus 5'-LTR and Tax Gene on Viral Transcriptional Activity

Bovine leukemia virus (BLV) is a deltaretrovirus infecting bovine B cells and causing enzootic bovine leucosis (EBL). The long terminal repeat (LTR) plays an indispensable role in viral gene expression. The BLV Tax protein acts as the main transactivator of LTR-driven transcription of BLV viral genes. The aim of this study was to analyze mutations in the BLV LTR region and tax gene to determine their association with transcriptional activity. LTRs were obtained from one hundred and six BLV isolates and analyzed for their genetic variability. Fifteen variants were selected and characterized based on mutations in LTR regulatory elements, and further used for in vitro transcription assays. Reporter vectors containing the luciferase gene under the control of each variant BLV promoter sequence, in addition to variant Tax expression vectors, were constructed. Both types of plasmids were used for cotransfection of HeLa cells and the level of luciferase activity was measured as a proxy of transcriptional activity. Marked differences in LTR promoter activity and Tax transactivation activity were observed amongst BLV variants. These results demonstrate that mutations in both the BLV LTR and tax gene can affect the promoter activity, which may have important consequences on proviral load, viral fitness, and transmissibility in BLV-infected cattle.

Sulforaphane: Its "Coming of Age" as a Clinically Relevant Nutraceutical in the Prevention and Treatment of Chronic Disease

A growing awareness of the mechanisms by which phytochemicals can influence upstream endogenous cellular defence processes has led to intensified research into their potential relevance in the prevention and treatment of disease. Pharmaceutical medicine has historically looked to plants as sources of the starting materials for drug development; however, the focus of nutraceutical medicine is to retain the plant bioactive in as close to its native state as possible. As a consequence, the potency of a nutraceutical concentrate or an extract may be lower than required for significant gene expression. The molecular structure of bioactive phytochemicals to a large extent determines the molecule's bioavailability. Polyphenols are abundant in dietary phytochemicals, and extensive in vitro research has established many of the signalling mechanisms involved in favourably modulating human biochemical pathways. Such pathways are associated with core processes such as redox modulation and immune modulation for infection control and for downregulating the synthesis of inflammatory cytokines. Although the relationship between oxidative stress and chronic disease continues to be affirmed, direct-acting antioxidants such as vitamins A, C, and E, beta-carotene, and others have not yielded the expected preventive or therapeutic responses, even though several large meta-analyses have sought to evaluate the potential benefit of such supplements. Because polyphenols exhibit poor bioavailability, few of their impressive in vitro findings have been replicated in vivo. SFN, an aliphatic isothiocyanate, emerges as a phytochemical with comparatively high bioavailability. A number of clinical trials have demonstrated its ability to produce favourable outcomes in conditions for which there are few satisfactory pharmaceutical solutions, foreshadowing the potential for SFN as a clinically relevant nutraceutical. Although myrosinase-inert broccoli sprout extracts are widely available, there now exist myrosinase-active broccoli sprout supplements that yield sufficient SFN to match the doses used in clinical trials.

Structural basis for reactivating the mutant TERT promoter by cooperative binding of p52 and ETS1

Transcriptional factors ETS1/2 and p52 synergize downstream of non-canonical NF-κB signaling to drive reactivation of the −146C>T mutant TERT promoter in multiple cancer types, but the mechanism underlying this cooperativity remains unknown. Here we report the crystal structure of a ternary p52/ETS1/−146C>T TERT promoter complex. While p52 needs to associate with consensus κB sites on the DNA to function during non-canonical NF-κB signaling, we show that p52 can activate the −146C>T TERT promoter without binding DNA. Instead, p52 interacts with ETS1 to form a heterotetramer, counteracting autoinhibition of ETS1. Analogous to observations with the GABPA/GABPB heterotetramer, the native flanking ETS motifs are required for sustained activation of the −146C>T TERT promoter by the p52/ETS1 heterotetramer. These observations provide a unifying mechanism for transcriptional activation by GABP and ETS1, and suggest that genome-wide targets of non-canonical NF-κB signaling are not limited to those driven by consensus κB sequences.

Incessant telomere synthesis in cancer cells depends on specific mutations in the TERT promoter, enabling its activation by transcription factors ETS1 and p52. Here, the authors elucidate the structural basis for p52/ETS1 binding to mutant TERT, suggesting a general mechanism for TERT reactivation in cancer.

TNF-α Modulation of Intestinal Tight Junction Permeability Is Mediated by NIK/IKK-α Axis Activation of the Canonical NF-κB Pathway

Tumor necrosis factor (TNF)-α, a key mediator of intestinal inflammation, causes an increase in intestinal epithelial tight junction (TJ) permeability by activating myosin light chain kinase (MLCK; official name MYLK3) gene. However, the precise signaling cascades that mediate the TNF-α-induced activation of MLCK gene and increase in TJ permeability remain unclear. Our aims were to delineate the upstream signaling mechanisms that regulate the TNF-α modulation of intestinal TJ barrier function with the use of in vitro and in vivo intestinal epithelial model systems. TNF-α caused a rapid activation of both canonical and noncanonical NF-κB pathway. NF-κB-inducing kinase (NIK) and mitogen-activated protein kinase kinase-1 (MEKK-1) were activated in response to TNF-α. NIK mediated the TNF-α activation of inhibitory κB kinase (IKK)-α, and MEKK1 mediated the activation of IKK complex, including IKK-β. NIK/IKK-α axis regulated the activation of both NF-κB p50/p65 and RelB/p52 pathways. Surprisingly, the siRNA induced knockdown of NIK, but not MEKK-1, prevented the TNF-α activation of both NF-κB p50/p65 and RelB/p52 and the increase in intestinal TJ permeability. Moreover, NIK/IKK-α/NF-κB p50/p65 axis mediated the TNF-α-induced MLCK gene activation and the subsequent MLCK increase in intestinal TJ permeability. In conclusion, our data show that NIK/IKK-α/regulates the activation of NF-κB p50/p65 and plays an integral role in the TNF-α-induced activation of MLCK gene and increase in intestinal TJ permeability.

BAG-1 interacts with the p50-p50 homodimeric NF-κB complex: implications for colorectal carcinogenesis

Understanding the mechanisms that promote aberrant tumour cell survival is critical for the determination of novel strategies to combat colorectal cancer (CRC). We have recently shown that the anti-apoptotic protein BAG-1, highly expressed in pre-malignant and CRC tissue, can potentiate cell survival through regulating NF-κB transcriptional activity. In this study, we identify a novel complex between BAG-1 and the p50-p50 NF-κB homodimers, implicating BAG-1 as a co-regulator of an atypical NF-κB pathway. Importantly, the BAG-1-p50 complex was detected at gene regulatory sequences including the epidermal growth factor receptor (EGFR) and COX-2 (PTGS2) genes. Suppression of BAG-1 expression using small interfering RNA was shown to increase EGFR and suppress COX-2 expression in CRC cells. Furthermore, mouse embryonic fibroblasts derived from the NF-κB1 (p105/p50) knock-out mouse were used to demonstrate that p50 expression was required for BAG-1 to suppress EGFR expression. This was shown to be functionally relevant as attenuation of BAG-1 expression increased ligand activated phosphorylation of EGFR in CRC cells. In summary, this paper identifies a novel role for BAG-1 in modulating gene expression through interaction with the p50-p50 NF-κB complexes. Data presented led us to propose that BAG-1 can act as a selective regulator of p50-p50 NF-κB responsive genes in colorectal tumour cells, potentially important for the promotion of cell survival in the context of the fluctuating tumour microenvironment. As BAG-1 expression is increased in the developing adenoma through to metastatic lesions, understanding the function of the BAG-1-p50 NF-κB complexes may aid in identifying strategies for both the prevention and treatment of CRC.

Suppressed induction of proinflammatory cytokines by a unique metabolite produced by Vibrio cholerae O1 El Tor biotype in cultured host cells

Vibrio cholerae O1 has two biotypes, El Tor and Classical, and the latter is now presumed to be extinct in nature. Under carbohydrate-rich growth conditions, El Tor biotype strains produce the neutral fermentation end product 2,3-butanediol (2,3-BD), which prevents accumulation of organic acids from mixed acid fermentation and thus avoids a lethal decrease in the medium pH, while the Classical biotype strains fail to do the same. In this study, we investigated the inhibitory effect of 2,3-BD on the production of two proinflammatory biomarkers, intreleukin-8 (IL-8) and tumor necrosis factor alpha (TNF-α), in human intestinal epithelial HT29 and alveolar epithelial A549 cells. Cell-free culture supernatants of El Tor strain N16961 grown in LB supplemented with 1% glucose induced a negligible amount of IL-8 or TNF-α, while the Classical O395 strain induced much higher levels of these proinflammatory cytokines. On the other hand, three mutant strains constructed from the N16961 strain with defects in the constitutive 2,3-BD pathway were also able to induce high levels of cytokines. When HT29 and A549 cells were treated with bacterial flagella, known proinflammatory cytokine inducers, and chemically synthesized 2,3-BD at various concentrations, a dose-dependent decrease in IL-8 and TNF-α production was observed, demonstrating the suppressive effect of 2,3-BD on the production of proinflammatory cytokines in epithelial cells. Upon cotreatment with extraneous 2,3-BD, elevated levels of IκBα, the inhibitor of the NF-κB pathway, were detected in both HT29 and A549 cells. Furthermore, treatments containing 2,3-BD elicited lower levels of NF-κB-responsive luciferase activity, demonstrating that the reduced cytokine production is likely through the inhibition of the NF-κB pathway. These results reveal a novel and potential role of 2,3-BD as an immune modulator that might have conferred a superior pathogenic potential of the El Tor over the Classical biotype.

Cross-talk between the p38alpha and JNK MAPK pathways mediated by MAP kinase phosphatase-1 determines cellular sensitivity to UV radiation

MAPK phosphatase-1 (DUSP1/MKP-1) is a mitogen and stress-inducible dual specificity protein phosphatase, which can inactivate all three major classes of MAPK in mammalian cells. DUSP1/MKP-1 is implicated in cellular protection against a variety of genotoxic insults including hydrogen peroxide, ionizing radiation, and cisplatin, but its role in the interplay between different MAPK pathways in determining cell death and survival is not fully understood. We have used pharmacological and genetic tools to demonstrate that DUSP1/MKP-1 is an essential non-redundant regulator of UV-induced cell death in mouse embryo fibroblasts (MEFs). The induction of DUSP1/MKP-1 mRNA and protein in response to UV radiation is mediated by activation of the p38alpha but not the JNK1 or JNK2 MAPK pathways. Furthermore, we identify MSK1 and -2 and their downstream effectors cAMP-response element-binding protein/ATF1 as mediators of UV-induced p38alpha-dependent DUSP1/MKP-1 transcription. Dusp1/Mkp-1 null MEFs display increased signaling through both the p38alpha and JNK MAPK pathways and are acutely sensitive to UV-induced apoptosis. This lethality is rescued by the reintroduction of wild-type DUSP1/MKP-1 and by a mutant of DUSP1/MKP-1, which is unable to bind to either p38alpha or ERK1/2, but retains full activity toward JNK. Importantly, whereas small interfering RNA-mediated knockdown of DUSP1/MKP-1 sensitizes wild-type MEFs to UV radiation, DUSP1/MKP-1 knockdown in MEFS lacking JNK1 and -2 does not result in increased cell death. Our results demonstrate that cross-talk between the p38alpha and JNK pathways mediated by induction of DUSP1/MKP-1 regulates the cellular response to UV radiation.

TAp63 is a transcriptional target of NF-kappaB

The p53 homologue p63 encodes multiple protein isoforms either with (TA) or without (DeltaN) the N-terminal transactivation domain. Accumulating evidence indicates that TAp63 plays an important role in various biological processes, including cell proliferation, differentiation, and apoptosis. However, how TAp63 is regulated remains largely unclear. In this study, we demonstrate that NF-kappaB induces TAp63 gene expression. The responsible elements for NF-kappaB-mediated TAp63 induction are located within the region from -784 to -296 bp in the TAp63 promoter, which contains two NF-kappaB binding sites. Ectopic expression of RelA stimulates TAp63 promoter-driven reporter activity and increases endogenous TAp63 mRNA levels. Inhibition of NF-kappaB by IkappaBalpha super-repressor or with a chemical inhibitor leads to down regulation of TAp63 mRNA expression and activity. In addition, mutations in the critical NF-kappaB-binding sites significantly abolish the effects of NF-kappaB on TAp63. Activation of NF-kappaB by TNFalpha enhances p50/RelA binding to the NF-kappaB binding sites. Furthermore, we show that an Sp1 site adjacent to the NF-kappaB sites plays a role in NF-kappaB-mediated upregulation of TAp63. Taken together, these data reveal that TAp63 is a transcriptional target of NF-kappaB, which may play a role in cell proliferation, differentiation and survival upon NF-kappaB activation by various stimuli.

Kaposi sarcoma-associated herpesvirus latency-associated nuclear antigen inhibits interferon (IFN) beta expression by competing with IFN regulatory factor-3 for binding to IFNB promoter

Host cells respond to viral infections by synthesizing and producing antiviral molecules such as type I interferons (IFN). The Kaposi sarcoma-associated herpesvirus (KSHV) encodes multiple proteins expressed during the lytic replication cycle that alter the antiviral response of the host. Considering that in Kaposi sarcoma lesions and primary effusion lymphoma cells KSHV is latent in the vast majority of cells, we were interested in determining whether latently expressed viral proteins have the ability to modulate IFN synthesis. The latency-associated nuclear antigen (LANA-1) is a large nuclear protein that plays a role in the establishment and maintenance of latent KSHV episome in the nucleus of infected cells. LANA-1 is also described to modulate the cellular transcription. Here, we report that LANA-1 inhibits IFN-beta transcription and synthesis by competing with the binding of interferon regulatory factor-3 (IRF3) to the IFNB promoter. Using mutants of LANA-1, we have identified the central acidic repeated region as the domain essential for interfering with the binding of IRF3 to the positive regulatory domains I-III of the IFNB promoter. In addition, the nuclear localization of LANA-1 proved essential for IFN-beta inhibition. Thus, LANA-1 interferes with the formation of IFN-beta enhanceosome by competing with the fixation of IRF3 and by inhibiting the expression of the CREB-binding protein. The ability of LANA-1 to inhibit IFNB gene expression highlights a new role for this protein in cellular gene modulation and immune evasion strategies.

Old target new approach: an alternate NF-kappaB activation pathway via translation inhibition

Activation of the transcription factor NF-kappaB is a highly regulated multi-level process. The critical step during activation is the release from its inhibitor IkappaB, which as any other protein is under the direct influence of translation regulation. In this review, we summarize in detail the current understanding of the impact of translational regulation on NF-kappaB activation. We illustrate a newly developed mechanism of eIF2alpha kinase-mediated IkappaB depletion and subsequent NF-kappaB activation. We also show that the classical NF-kappaB activation pathways occur simultaneously with, and are complemented by, translational down regulation of the inhibitor molecule IkappaB, the importance of one or the other being shifted in accordance with the type and magnitude of the stressing agent or stimuli.

Nuclear factor-kappaB binds to the Epstein-Barr Virus LMP1 promoter and upregulates its expression

The latent membrane protein 1 (LMP1) oncogene carried by Epstein-Barr virus (EBV) is essential for transformation and maintenance of EBV-immortalized B cells in vitro, and it is expressed in most EBV-associated tumor types. The activation of the NF-kappaB pathway by LMP1 plays a critical role in the upregulation of antiapoptotic proteins. The EBV-encoded EBNA2 transactivator is required for LMP1 activation in latency III, while LMP1 itself appears to be critical for its activation in the latency II gene expression program. In both cases, additional viral and cellular transcription factors are required in mediating transcription activation of the LMP1 promoter. Using DNA affinity purification and chromatin immunoprecipitation assay, we showed here that members of the NF-kappaB transcription factor family bound to the LMP1 promoter in vitro and in vivo. Electrophoretic mobility shift assay analyses indicated the binding of the p50-p50 homodimer and the p65-p50 heterodimer to an NF-kappaB site in the LMP1 promoter. Transient transfections and reporter assays showed that the LMP1 promoter is activated by exogenous expression of NF-kappaB factors in both B cells and epithelial cells. Exogenous expression of NF-kappaB factors in the EBNA2-deficient P3HR1 cell line induced LMP1 protein expression. Overall, our data are consistent with the presence of a positive regulatory circuit between NF-kappaB activation and LMP1 expression.

Negative regulation of the SH2-homology containing protein-tyrosine phosphatase-1 (SHP-1) P2 promoter by the HTLV-1 Tax oncoprotein

Expression of SH(2)-homology-containing protein-tyrosine phosphatase-1 (SHP-1), a candidate tumor suppressor, is repressed in human T-cell leukemia virus type-1 (HTLV-1)-transformed lymphocyte cell lines, adult T-cell leukemia (ATL) cells, and in other hematologic malignancies. However, the mechanisms underlying regulation and repression of SHP-1 remain unclear. Herein, we cloned the putative full-length, hematopoietic cell-specific SHP-1 P2 promoter and identified the "core" promoter regions. HTLV-1 Tax profoundly represses P2 promoter activity and histone deacetylase-1 (HDAC1) potentiates such inhibition. NF-kappaB was implicated as both a rate-limiting factor for basal P2 promoter activity and important for Tax-induced promoter silencing (TIPS). Chromatin immunoprecipitation studies demonstrated that NF-kappaB dissociates from the SHP-1 P2 promoter following the binding of Tax and HDAC1. This is in agreement with coimmunoprecipitation studies where NF-kappaB competed with HDAC1 for association with Tax protein. We propose that in TIPS, Tax recruits HDAC1 to the SHP-1 P2 promoter and forms an inhibitory complex that results in deacetylation and dissociation of NF-kappaB from the promoter and attenuation of SHP-1 expression. TIPS provides a possible first step toward HTLV-1 leukemogenesis through its down-modulation of this key immediate early negative regulator of IL-2 signaling.

Regulation of p53 tumour suppressor target gene expression by the p52 NF-kappaB subunit

The p52/p100 nuclear factor kappa B (NF-kappaB) subunit (NF-kappaB2) is aberrantly expressed in many tumour types and has been implicated as a regulator of cell proliferation. Here, we demonstrate that endogenous p52 is a direct regulator of Cyclin D1 expression. However, stimulation of Cyclin D1 expression alone cannot account for all the cell cycle effects of p52/p100 and we also find that p52 represses expression of the Cyclin-dependent kinase inhibitor p21(WAF/CIP1). Significantly, this latter effect is dependent upon basal levels of the tumour suppressor p53. By contrast, p52 cooperates with p53 to regulate other known p53 target genes such as PUMA, DR5, Gadd45alpha and Chk1. p52 associates directly with these p53-regulated promoters where it regulates coactivator and corepressor binding. Moreover, recruitment of p52 is p53 dependent and does not require p52-DNA-binding activity. These results reveal a complex role for p52 as regulator of cell proliferation and p53 transcriptional activity. Furthermore, they imply that in some cell types, p52 can regulate p53 function and influence p53-regulated decision-making following DNA damage and oncogene activation.

Characterization of COMMD protein-protein interactions in NF-kappaB signalling

COMMD [copper metabolism gene MURR1 (mouse U2af1-rs1 region 1) domain] proteins constitute a recently identified family of NF-kappaB (nuclear factor kappaB)-inhibiting proteins, characterized by the presence of the COMM domain. In the present paper, we report detailed investigation of the role of this protein family, and specifically the role of the COMM domain, in NF-kappaB signalling through characterization of protein-protein interactions involving COMMD proteins. The small ubiquitously expressed COMMD6 consists primarily of the COMM domain. Therefore COMMD1 and COMMD6 were analysed further as prototype members of the COMMD protein family. Using specific antisera, interaction between endogenous COMMD1 and COMMD6 is described. This interaction was verified by independent techniques, appeared to be direct and could be detected throughout the whole cell, including the nucleus. Both proteins inhibit TNF (tumour necrosis factor)-induced NF-kappaB activation in a non-synergistic manner. Mutation of the amino acid residues Trp24 and Pro41 in the COMM domain of COMMD6 completely abolished the inhibitory effect of COMMD6 on TNF-induced NF-kappaB activation, but this was not accompanied by loss of interaction with COMMD1, COMMD6 or the NF-kappaB subunit RelA. In contrast with COMMD1, COMMD6 does not bind to IkappaBalpha (inhibitory kappaBalpha), indicating that both proteins inhibit NF-kappaB in an overlapping, but not completely similar, manner. Taken together, these data support the significance of COMMD protein-protein interactions and provide new mechanistic insight into the function of this protein family in NF-kappaB signalling.

Protein methyltransferase 2 inhibits NF-kappaB function and promotes apoptosis

The protein arginine methyltransferases (PRMTs) include a family of proteins with related putative methyltransferase domains that modify chromatin and regulate cellular transcription. Although some family members, PRMT1 and PRMT4, have been implicated in transcriptional modulation or intracellular signaling, the roles of other PRMTs in diverse cellular processes have not been fully established. Here, we report that PRMT2 inhibits NF-kappaB-dependent transcription and promotes apoptosis. PRMT2 exerted this effect by blocking nuclear export of IkappaB-alpha through a leptomycin-sensitive pathway, increasing nuclear IkappaB-alpha and decreasing NF-kappaB DNA binding. The highly conserved S-adenosylmethionine-binding domain of PRMT2 mediated this effect. PRMT2 also rendered cells susceptible to apoptosis by cytokines or cytotoxic drugs, likely due to its effects on NF-kappaB. Mouse embryo fibroblasts from PRMT2 genetic knockouts showed elevated NF-kappaB activity and decreased susceptibility to apoptosis compared to wild-type or complemented cells. Taken together, these data suggest that PRMT2 inhibits cell activation and promotes programmed cell death through this NF-kappaB-dependent mechanism.

A model for generating circadian rhythm by coupling ultradian oscillators

Background

Organisms ranging from humans to cyanobacteria undergo circadian rhythm, that is, variations in behavior that cycle over a period about 24 hours in length. A fundamental property of circadian rhythm is that it is free-running, and continues with a period close to 24 hours in the absence of light cycles or other external cues. Regulatory networks involving feedback inhibition and feedforward stimulation of mRNA transcription and translation are thought to be critical for many circadian mechanisms, and genes coding for essential components of circadian rhythm have been identified in several organisms. However, it is not clear how such components are organized to generate a circadian oscillation.

Results

We propose a model in which two independent transcriptional-translational oscillators with periods much shorter than 24 hours are coupled to drive a forced oscillator that has a circadian period, using mechanisms and parameters of conventional molecular biology. Furthermore, the resulting circadian oscillator can be entrained by an external light-dark cycle through known mechanisms. We rationalize the mathematical basis for the observed behavior of the model, and show that the behavior is not dependent on the details of the component ultradian oscillators but occurs even if quite generalized basic oscillators are used.

Conclusion

We conclude that coupled, independent, transcriptional-translational oscillators with relatively short periods can be the basis for circadian oscillators. The resulting circadian oscillator can be entrained by 24-hour light-dark cycles, and the model suggests a mechanism for its evolution.

Activation of RelA homodimers by tumour necrosis factor alpha: a possible transcriptional activator in human vascular endothelial cells

In vascular endothelial cells, cytokines induce genes that are expressed in inflammatory lesions partly through the activation of transcription factor NF-kappaB (nuclear factor-kappaB). Among the members of the NF-kappaB/rel protein family, homodimers of the RelA subunit of NF-kappaB can also function as strong transactivators when expressed in cells. However, the functional role of endogenous RelA homodimers has not been clearly elucidated. We investigated whether RelA homodimers are induced in cytokine-treated vascular endothelial cells. Gel mobility-shift and supershift assays revealed that a cytokine TNFalpha (tumour necrosis factor alpha) activated both NF-kappaB1/RelA heterodimers and RelA homodimers that bound to a canonical kappaB sequence, IgkappaB (immunoglobulin kappaB), in SV40 (simian virus 40) immortalized HMEC-1 (human dermal microvascular endothelial cell line 1). In HMEC-1 and HUVEC (human umbilical-vein endothelial cells), TNFalpha also induced RelA homodimers that bound to the sequence 65-2kappaB, which specifically binds to RelA homodimers but not to NF-kappaB1/RelA heterodimers in vitro. Deoxycholic acid, a detergent that can dissociate the NF-kappaB-IkappaB complex (where IkappaB stands for inhibitory kappaB), induced the binding of the RelA homodimers to 65-2kappaB from the cytosolic fraction of resting HMEC-1. Furthermore, TNFalpha induced the transcriptional activity of a reporter gene that was driven by 65-2kappaB in HMEC-1. These results suggest that in addition to NF-kappaB1/RelA heterodimers, TNFalpha also induces RelA homodimers that are functionally active. Thus RelA homodimers may actively participate in cytokine regulation of gene expression in human vascular endothelial cells.

The effects of calpain inhibition on IkB alpha degradation after activation of PBMCs: identification of the calpain cleavage sites

Human peripheral blood mononuclear cells (PBMCs) were activated using anti-CD3/CD28 (HIT3A/CD28.2) resulting in degradation of IkB alpha, an inhibitor of NFkB, relative to unactivated cells. Degradation of IkB alpha began by 30 min and proceeded for at least 5 h. Calpeptin, a calpain inhibitor, inhibited IkB alpha degradation in a time- and dose-dependent manner. Furthermore, calpain inhibition increased IkB alpha levels compared to nonactivated controls. Recombinant IkB alpha was incubated with purified porcine m-calpain in the presence of 0.1% Triton X-100, and the degradation products were monitored by SDS-PAGE and sequenced. Most of the degradation products were peptides derived from calpain, but one was derived from IkB alpha cleaved between amino acids 50 and 51 (glutamine and glutamic acid). The liberated fragment included the entire signal response domain (SRD), a region containing key serine and threonine residues necessary for phosphorylation by the IKKinase complex and sites required for ubiquitination. The results suggest that calpain plays an important role in IkB alpha degradation, a crucial event in T cell activation.

Potentiation of tumor necrosis factor-induced NF-kappa B activation by deacetylase inhibitors is associated with a delayed cytoplasmic reappearance of I kappa B alpha

Previous studies have implicated acetylases and deacetylases in regulating the transcriptional activity of NF-kappa B. Here, we show that inhibitors of deacetylases such as trichostatin A (TSA) and sodium butyrate (NaBut) potentiated TNF-induced expression of several natural NF-kappa B-driven promoters. This transcriptional synergism observed between TNF and TSA (or NaBut) required intact kappa B sites in all promoters tested and was biologically relevant as demonstrated by RNase protection on two instances of endogenous NF-kappa B-regulated gene transcription. Importantly, TSA prolonged both TNF-induced DNA-binding activity and the presence of NF-kappa B in the nucleus. We showed that the p65 subunit of NF-kappa B was acetylated in vivo. However, this acetylation was weak, suggesting that other mechanisms could be implicated in the potentiated binding and transactivation activities of NF-kappa B after TNF plus TSA versus TNF treatment. Western blot and immunofluorescence confocal microscopy experiments revealed a delay in the cytoplasmic reappearance of the I kappa B alpha inhibitor that correlated temporally with the prolonged intranuclear binding and presence of NF-kappa B. This delay was due neither to a defect in I kappa B alpha mRNA production nor to a nuclear retention of I kappa B alpha but was rather due to a persistent proteasome-mediated degradation of I kappa B alpha. A prolongation of I kappa B kinase activity could explain, at least partially, the delayed I kappa B alpha cytoplasmic reappearance observed in presence of TNF plus TSA.

The IkappaB function of NF-kappaB2 p100 controls stimulated osteoclastogenesis

The prototranscription factor p100 represents an intersection of the NF-kappaB and IkappaB families, potentially serving as both the precursor for the active NF-kappaB subunit p52 and as an IkappaB capable of retaining NF-kappaB in the cytoplasm. NF-kappaB-inducing kinase (NIK) controls processing of p100 to generate p52, and thus NIK-deficient mice can be used to examine the biological effects of a failure in such processing. We demonstrate that treatment of wild-type osteoclast precursors with the osteoclastogenic cytokine receptor activator of NF-kappaB ligand (RANKL) increases both expression of p100 and its conversion to p52, resulting in unchanged net levels of p100. In the absence of NIK, p100 expression is increased by RANKL, but its conversion to p52 is blocked, leading to cytosolic accumulation of p100, which, acting as an IkappaB protein, binds NF-kappaB complexes and prevents their nuclear translocation. High levels of unprocessed p100 in osteoclast precursors from NIK-/- mice or a nonprocessable form of the protein in wild-type cells impair RANKL-mediated osteoclastogenesis. Conversely, p100-deficient osteoclast precursors show enhanced sensitivity to RANKL. These data demonstrate a novel, biologically relevant means of regulating NF-kappaB signaling, with upstream control and kinetics distinct from the classical IkappaBalpha pathway.

Activation of human immunodeficiency virus transcription in T cells revisited: NF-kappaB p65 stimulates transcriptional elongation

Human immunodeficiency virus type 1 (HIV-1) is able to establish a persistent latent infection during which the integrated provirus remains transcriptionally silent. Viral transcription is stimulated by NF-kappaB, which is activated following the exposure of infected T cells to antigens or mitogens. Although it is commonly assumed that NF-kappaB stimulates transcriptional initiation alone, we have found using RNase protection assays that, in addition to stimulating initiation, it can also stimulate elongation from the HIV-1 long terminal repeat. When either Jurkat or CCRF/CEM cells were activated by the mitogens phorbol myristate acetate and phytohemagglutinin, elongation, as measured by the proportion of full-length transcripts, increased two- to fourfold, even in the absence of Tat. Transfection of T cells with plasmids carrying the different subunits of NF-kappaB demonstrated that the activation of transcriptional elongation is mediated specifically by the p65 subunit. It seems likely that initiation is activated because of NF-kappaB's ability to disrupt chromatin structures through the recruitment of histone acetyltransferases. To test whether p65 could stimulate elongation under conditions where it did not affect histone acetylation, cells were treated with the histone deacetylase inhibitor trichostatin A. Remarkably, addition of p65 to the trichostatin A-treated cell lines resulted in a dramatic increase in transcription elongation, reaching levels equivalent to those observed in the presence of Tat. We suggest that the activation of elongation by NF-kappaB p65 involves a distinct biochemical mechanism, probably the activation of carboxyl-terminal domain kinases at the promoter.

Involvement of TFIID and USA components in transcriptional activation of the human immunodeficiency virus promoter by NF-kappaB and Sp1

The purified Rel/NF-kappaB (p50/p65) complex and Sp1 markedly activate transcription from the human immunodeficiency virus type 1 (HIV-1) promoter in a highly purified HeLa reconstituted transcription system. Transcriptional activation by NF-kappaB and Sp1 requires both TFIID and the USA fraction. The USA-derived coactivators PC2 and PC4 fully reconstitute the USA coactivator activity, both by repressing the basal level of transcription and by potentiating activator function to yield large increases in the levels of transcription induction. Under limiting concentrations, PC2 and PC4 also show synergistic effects. The C-terminal portion (amino acids 416 to 550) of the p65 subunit of NF-kappaB is a potent activator when assayed as a Gal fusion in the reconstituted transcription system and interacts both with TATA-binding protein (TBP) and with several human TBP-associated factors (TAFs) that include TAFII250. The p65 activation domain mediates transcription activation in the presence of partially reconstituted TFIID species that include a minimal complex containing only TBP and TAFII250. These studies also show that, like USA components, TAFs can serve both to repress TBP-mediated transcription and, following activator interactions, to reverse the repression and effect a net increase in activity. Taken together, these data underscore the importance of both TAFs and specific USA-derived coactivators for optimal activation of the HIV-1 promoter, as well as certain parallels in their overall mechanisms of action.

The 30-base-pair deletion in Chinese variants of the Epstein-Barr virus LMP1 gene is not the major effector of functional differences between variant LMP1 genes in human lymphocytes

One group of sequence variants of Epstein-Barr virus is characterized by a 10-amino-acid deletion within the CTAR-2 functional domain of the latent membrane protein, LMP1. A role for this deletion in enhancing the tumorigenicity of the viral oncogene in rodent fibroblasts was recently demonstrated. We examined the effect of this deletion upon LMP1 function in four human lymphoid cell lines by using three natural variants of LMP1: the prototype B95.8 gene and the CAO and AG876 genes, both of which have codons 343 to 352 of the B95.8-LMP1 deleted. These experiments revealed that LMP1-mediated upregulation of CD40 and CD54 was markedly impaired (by 60 to 90%) with CAO-LMP1 compared with B95.8-LMP1. In contrast, the function of AG876-LMP1 was indistinguishable from that of B95.8-LMP1 in two lines and was only slightly impaired in the other two lines. Activation of NF-kappaB by CAO-LMP1 was not impaired in any of the lines; rather, activation of an NF-kappaB reporter by CAO-LMP1 was consistently about twofold greater than the activation with B95.8- or AG876-LMP1. Therefore, while the CAO-LMP1 is functionally distinct from the prototype B95.8-LMP1 in human lymphocytes, the 10-amino-acid deletion appears not to be directly responsible. This conclusion was confirmed by using a B95.8-LMP1 mutant with codons 343 to 352 deleted and chimerae of CAO- and B95.8-LMP1 in which the CTAR-2 domains of these genes were exchanged. Sequences outside the CTAR-2 domain were implicated in the distinct functional characteristics of CAO-LMP1 in human lymphoid cells.

HIV transcriptional activation by the accessory protein, VPR, is mediated by the p300 co-activator

The accessory protein, Vpr, is a virion-associated protein that is required for HIV-1 replication in macrophages and regulates viral gene expression in T cells. Vpr causes arrest of cell cycle progression at G2/M, presumably through its effect on cyclin B1.Cdc2 activity. Here, we show that the ability of Vpr to activate HIV transcription correlates with its ability to induce G2/M growth arrest, and this effect is mediated by the p300 transcriptional co-activator, which promotes cooperative interactions between the Rel A subunit of NF-kappaB and cyclin B1.Cdc2. Vpr cooperates with p300, which regulates NF-kappaB and the basal transcriptional machinery, to increase HIV gene expression. Similar effects are seen in the absence of Vpr with a kinase-deficient Cdc2, and overexpression of p300 increases levels of HIV Vpr+ replication. Taken together, these data suggest that p300, through its interactions with NF-kappaB, basal transcriptional components, and Cdks, is modulated by Vpr and regulates HIV replication. The regulation of p300 by Vpr provides a mechanism to enhance viral replication in proliferating cells after growth arrest by increasing viral transcription.

NF-kappaB2 is a putative target gene of activated Notch-1 via RBP-Jkappa

NF-kappaB2 (p100/p52), a member of the NF-kappaB/Rel family of transcription factors, is involved in the regulation of a variety of genes important for immune function. Previously, we have shown that the NF-kappaB2 gene is regulated in a positive and a negative manner. Two kappaB elements within the NF-kappaB2 promoter mediate tumor necrosis factor alpha-inducible transactivation. In addition, we have shown that there exists a transcriptional repression in the absence of NF-kappaB. To identify a DNA binding activity responsible for this transcriptional repression, we have partially purified a nuclear complex, named Rep-kappaB. Here we further analyze this putative repressive binding activity. Detailed examination of Rep-kappaB-DNA interaction revealed the sequence requirements for binding to be almost identical to those of recombination signal binding protein Jkappa (RBP-Jkappa), the mammalian homolog of the protein encoded by Drosophila suppressor of hairless [Su(H)]. In addition, in electromobility shift assays, Rep-kappaB binding activity is recognized by an antibody directed against RBP-Jkappa. By performing transient-transfection assays, we show that human RBP-Jkappa represses basal as well as RelA (p65)-stimulated NF-kappaB2 promoter activity. Studies in Drosophila melanogaster have shown that Su(H) is implicated in the Notch signaling pathway regulating cell fate decisions. In transient-transfection assays we show that truncated Notch-1 strongly induces NF-kappaB2 promoter activity. In summary, our data clearly demonstrate that Rep-kappaB is closely related or identical to RBP-Jkappa. RBP-Jkappa is a strong transcriptional repressor of NF-kappaB2. Moreover, this repression can be overcome by activated Notch-1, suggesting that NF-kappaB2 is a novel putative Notch target gene.

Cooperative interaction of ets-1 with USF-1 required for HIV-1 enhancer activity in T cells

The distal enhancer region of the human immunodeficiency virus 1 (HIV-1) long terminal repeat (LTR) is known to be essential for HIV replication and to contain immediately adjacent E-box and Ets binding sites. Based on a yeast one-hybrid screen we have identified the E-box binding protein USF-1 as a direct interaction partner of Ets-1 and found that the complex acts on this enhancer element. The binding surfaces of USF-1 and Ets-1 map to their DNA-binding domains and although these domains are highly conserved, the interaction is very selective within the respective protein family. USF-1 and Ets-1 synergize in specific DNA binding as well as in the transactivation of reporter constructs containing the enhancer element, and mutations of the individual binding sites dramatically reduce reporter activity in T cells. In addition, a dominant negative Ets-1 mutant inhibits both USF-1-mediated transactivation and the activity of the HIV-1 LTR in T cells. The inhibition is independent of Ets DNA-binding sites but requires the Ets binding surface on USF-1, highlighting the importance of the direct protein-protein interaction. Together these results indicate that the interaction between Ets-1 and USF-1 is required for full transcriptional activity of the HIV-1 LTR in T cells.

Sulfasalazine: a potent and specific inhibitor of nuclear factor kappa B

Transcription factors of the NF-kappaB/Rel family are critical for inducible expression of multiple genes involved in inflammatory responses. Sulfasalazine and its salicylate moiety 5-aminosalicylic acid are among the most effective agents for treating inflammatory bowel disease and rheumatoid arthritis. However, the mode of action of these drugs remains unclear. Here we provide evidence that the transcription factor NF-kappaB is a target of sulfasalazine-mediated immunosuppression. Treatment of SW620 colon cells with sulfasalazine inhibited TNFalpha-, LPS-, or phorbol ester- induced NF-kappaB activation. NF-kappaB-dependent transcription was inhibited by sulfasalazine at micro- to millimolar concentrations. In contrast, 5-aminosalicylic acid or sulfapyridine did not block NF-kappaB activation at all doses tested. TNFalpha-induced nuclear translocation of NF-kappaB was prevented by sulfasalazine through inhibition of IkappaBalpha degradation. When blocking proteasome-mediated degradation of IkappaBalpha, we could demonstrate that sulfasalazine interfered with IkappaBalpha phosphorylation, suggesting a direct effect on an IkappaBalpha kinase or on an upstream signal. Inhibition of NF-kappaB activation seems to be specific since other DNA-binding activities such as AP1 were not affected. These results demonstrate that sulfasalazine is a potent and specific inhibitor of NF-kappaB activation, and thus may explain some of the known biological properties of sulfasalazine.

Structure of the human NF-kappaB p52 homodimer-DNA complex at 2.1 A resolution

The crystal structure of human NF-kappaB p52 in its specific complex with the natural kappaB DNA binding site MHC H-2 has been solved at 2.1 A resolution. Whereas the overall structure resembles that of the NF-kappaB p50-DNA complex, pronounced differences are observed within the 'insert region'. This sequence segment differs in length between different Rel proteins. Compared with NF-kappaB p50, the compact alpha-helical insert region element is rotated away from the core of the N-terminal domain, opening up a mainly polar cleft. The insert region presents potential interaction surfaces to other proteins. The high resolution of the structure reveals many water molecules which mediate interactions in the protein-DNA interface. Additional complexity in Rel protein-DNA interaction comes from an extended interfacial water cavity that connects residues at the edge of the dimer interface to the central DNA bases. The observed water network might acount for differences in binding specificity between NF-kappaB p52 and NF-kappaB p50 homodimers.

Gastric hyperplasia and increased proliferative responses of lymphocytes in mice lacking the COOH-terminal ankyrin domain of NF-kappaB2

The nfkb2 gene encodes the p100 precursor which produces the p52 protein after proteolytic cleavage of its COOH-terminal domain. Although the p52 product can act as an alternative subunit of NF-kappaB, the p100 precursor is believed to function as an inhibitor of Rel/NF-kappaB activity by cytoplasmic retention of Rel/NF-kappaB complexes, like other members of the IkappaB family. However, the physiological relevance of the p100 precursor as an IkappaB molecule has not been understood. To assess the role of the precursor in vivo, we generated, by gene targeting, mice lacking p100 but still containing a functional p52 protein. Mice with a homozygous deletion of the COOH-terminal ankyrin repeats of NF-kappaB2 (p100(-/-)) had marked gastric hyperplasia, resulting in early postnatal death. p100(-/-) animals also presented histopathological alterations of hematopoietic tissues, enlarged lymph nodes, increased lymphocyte proliferation in response to several stimuli, and enhanced cytokine production in activated T cells. Dramatic induction of nuclear kappaB-binding activity composed of p52-containing complexes was found in all tissues examined and also in stimulated lymphocytes. Thus, the p100 precursor is essential for the proper regulation of p52-containing Rel/NF-kappaB complexes in various cell types and its absence cannot be efficiently compensated for by other IkappaB proteins.

A new member of the I kappaB protein family, I kappaB epsilon, inhibits RelA (p65)-mediated NF-kappaB transcription

A novel member of the I kappaB family has been identified as a protein that associated with the p50 subunit of NF-kappaB in a yeast two-hybrid screen. Similar to previously known I kappaB proteins, this member, I kappaB epsilon, has six consecutive ankyrin repeats. I kappaB epsilon mRNA is widely expressed in different human tissues, with highest levels in spleen, testis, and lung. I kappaB epsilon interacts with different NF-kappaB proteins, including p65 (RelA), c-Rel, p50, and p52, in vitro and in vivo and inhibits the DNA-binding activity of both p50-p65 and p50-c-Rel complexes effectively. Endogenous and transfected NF-kappaB (RelA-dependent) transcriptional activation is inhibited by I kappaB epsilon. I kappaB epsilon mRNA is expressed at different levels in specific cell types and is synthesized constitutively in transformed B-cell lines. It also displays differential induction in response to tumor necrosis factor alpha, interleukin-1, or phorbol ester stimulation compared to I kappaB alpha in non-B-cell lines. Therefore, I kappaB epsilon represents a novel I kappaB family member which provides an alternative mechanism for regulation of NF-kappaB-dependent transcription.

Induction of nuclear factor kappaB by the CD30 receptor is mediated by TRAF1 and TRAF2

CD30 is a lymphoid cell-specific surface receptor which was originally identified as an antigen expressed on Hodgkin's lymphoma cells. Activation of CD30 induces the nuclear factor kappaB (NF-kappaB) transcription factor. In this study, we define the domains in CD30 which are required for NF-kappaB activation. Two separate elements of the cytoplasmic domain which were capable of inducing NF-kappaB independently of one another were identified. The first domain (domain 1) mapped to a approximately 120-amino-acid sequence in the membrane-proximal region of the CD30 cytoplasmic tail, between residues 410 and 531. A second, more carboxy-terminal region (domain 2) was identified between residues 553 and 595. Domain 2 contains two 5- to 10-amino-acid elements which can mediate the binding of CD30 to members of the tumor necrosis factor receptor-associated factor (TRAF) family of signal transducing proteins. Coexpression of CD30 with TRAF1 or TRAF2 but not TRAF3 augmented NF-kappaB activation through domain 2 but not domain 1. NF-kappaB induction through domain 2 was inhibited by coexpression of either full-length TRAF3 or dominant negative forms of TRAF1 or TRAF2. In contrast, NF-kappaB induction by domain 1 was not affected by alterations in TRAF protein levels. Together, these data support a model in which CD30 can induce NF-kappaB by both TRAF-dependent and -independent mechanisms. TRAF-dependent induction of NF-kappaB appears to be regulated by the relative levels of individual TRAF proteins in the cell.

The nfkb1 promoter is controlled by proteins of the Ets family

The gene encoding NFKB1 is autoregulated, responding to NF-kappa B/Rel activation through NF-kappa B binding sites in its promoter, which also contains putative sites for Ets proteins. One of the Ets sites, which we refer to as EBS4, is located next to an NF-kappa B/Rel binding site, kB3, which is absolutely required for activity of the promoter in Jurkat T cells in response to activation by phorbol 12-myristate 13-acetate (PMA), PMA/ionomycin, or the Tax protein from human T cell leukemia virus type I. We show that EBS4 is, required for the full response of the nfkb1 promoter to PMA or PMA/ionomycin in Jurkat cells. EBS4 is bound by Ets-1, Elf-1, and other species. Overexpression of Ets-1 augments the response to PMA/ionomycin and this is reduced by mutation of EBS4. Elf-1 has less effect in conjunction with PMA/ionomycin, but by itself activates the promoter 12-fold. This activation is only partly affected by mutation of EBS4, and a mutant promoter that binds Ets-1, but not Elf-1, at the EBS4 site responds to PMA/ionomycin as efficiently as the wild-type. Ets proteins may be responsible for fine-tuning the activity of the nfkb1 gene in a cell-type-specific manner.

Differential regulation of NF-kappaB2(p100) processing and control by amino-terminal sequences

Proteolytic degradation of the C-terminal region of NF-(kappa)B precursors to their active DNA binding forms represents an important regulatory step in the activation of NF-(kappa)B. NF-(kappa)B2(p100) is found ubiquitously in the cytoplasm; however, the site and mechanism of processing to p52 have not previously been defined. We show by deletion mapping that processing of NF-(kappa)B2(p100) terminates at alanine 405 to generate p52 and is prevented by specific inhibitors of the multicatalytic proteinase complex. Although the C-terminal I(kappa)B-like domain of NF-(kappa)B2(p100) was constitutively phosphorylated, disruption of this phosphorylation by mutagenesis demonstrated that it was not required as a signal to mediate processing. Mutational analysis further showed that cleavage of NF-(kappa)B2 is not dependent on a specific sequence motif adjacent to alanine 405, the ankyrin repeats, or other C-terminal sequences but is directed by structural determinants amino terminal to the cleavage site, within the Rel homology domain and/or the glycine hinge region. The level of processing of NF-(kappa)B2(p100) was much lower than that of NF-(kappa)B1(p105) and differed from that of I(kappa)B-alpha, suggesting differential control of processing of NF-(kappa)B/I(kappa)B family members.

A cooperative interaction of human T-cell leukemia virus type 1 Tax with the p21 cyclin-dependent kinase inhibitor activates the human immunodeficiency virus type 1 enhancer

Interactions between the Tax transactivator of human T-cell leukemia virus type 1 (HTLV-1) and a cell cycle regulatory protein have been examined. We report cooperative stimulation of human immunodeficiency virus type 1 gene expression by Tax and a regulator of cell cycle progression, the p21 cyclin-dependent kinase inhibitor (CKI). This cooperativity results from the effect of p21 on transcriptional coactivation by Tax-induced NF-kappaB. This effect was abrogated by a mutation in Tax which specifically eliminated NF-kappaB induction, was inhibitable by IkappaB-alpha, and was markedly reduced in human immunodeficiency virus reporter plasmids with mutant kappaB sites. These studies demonstrate that transcriptional activation by Tax is influenced by cell cycle regulatory proteins.

T cell leukemia-associated human Notch/translocation-associated Notch homologue has I kappa B-like activity and physically interacts with nuclear factor-kappa B proteins in T cells

Translocation-associated Notch homologue (TAN-1), a gene originally cloned from the translocation breakpoint of a human T cell leukemia carrying a 9:7(q34.3) translocation, encodes a protein belonging to the Notch/Lin-12/Glp-1 receptor family. These receptors mediate the specification of numerous cell fates during development in invertebrates and vertebrates. The intracellular portion of Notch/TAN-1 contains six ankyrin repeats that are similar to those found in cytoplasmic I kappa B proteins. I kappa B proteins are specific inhibitors of nuclear factor (NF)-kappa B/Rel transcription factors. Here we show that TAN-1 has functional properties of an I kappa B-like regulator with specificity for the NF-kappa B p50 subunit. A recombinant polypeptide corresponding to the cytoplasmic portion of TAN-1 (TAN-1C) specifically inhibited the DNA binding of p50-containing NF-kappa B complexes. When overexpressed in an appropriate cell line, TAN-1C prevented kappa B-dependent transactivation in transient reporter gene assays in a fashion similar to the structurally related protein, Bcl-3. TAN-1C could activate kappa B-dependent gene expression by attenuating the inhibitory effect of an excess of p50 homodimers. Immunoprecipitation experiments showed that the TAN-1 from a T cell line is associated with NF-kappa B containing p50 and p65 subunits. These observations indicate that TAN-1C may directly engage NF-kappa B transcription factors and modulate nuclear gene expression.

Phosphorylation of IkappaBalpha in the C-terminal PEST domain by casein kinase II affects intrinsic protein stability

The NF-kappaB/Rel transcription factors participate in the activation of immune system regulatory genes and viral early genes including the human immunodeficiency virus type 1 long terminal repeat. NF-kappaB/Rel proteins are coupled to inhibitory molecules, collectively termed IkappaB, which are responsible for cytoplasmic retention of NF-kappaB. Cell activation leads to the phosphorylation and degradation of IkappaBalpha, permitting NG-kappaB/Rel translocation to the nucleus and target gene activation. To further characterize the signaling events that contribute to IkappaBalpha phosphorylation, a kinase activity was isolated from Jurkat T cells that specifically interacted with IkappaBalpha in an affinity chromatography step and phosphorylated IkappaBalpha with high specificity in vitro. By using an in-gel kinase assay with recombinant IkappaBalpha as substrate, two forms of the kinase (43 and 38 kDa) were identified. Biochemical criteria and immunological cross-reactivity identified the kinase activity as the alpha catalytic subunit of casein kinase II (CKII). Deletion mutants of IkappaBalpha delta1 to delta4) localized phosphorylation to the C-terminal PEST domain of IkappaBalpha. Point mutation of residues T-291, S-283, and T-299 dramatically reduced phosphorylation of IkappaBalpha by the kinase in vitro. NIH-3T3 cells that stably expressed wild-type IkappaBalpha (wtIkappaB), double-point-mutated IkappaBalpha (T291A, S283A), or triple-point-mutated IkappaBalpha (T291A, S283A, T299A) under the control of the tetracycline-responsive promoter were generated. Constitutive phosphorylation of the triple point mutant was eliminated in vivo, although tumor necrosis factor-inducible IkappaBalpha degradation was unaffected. In cell lines and in transiently transfected cells, mutation of the CKII sites in IkappaBalpha resulted in a protein with increased intrinsic stability. Together with results demonstrating a role for N-terminal sites in inducer-mediated phosphorylation and degradation of IkappaBalpha, these studies indicate that CKII sites in the C-terminal PEST domain are important for constitutive phosphorylation and intrinsic stability of IkappaBalpha.

Rearranged NFKB-2 genes in lymphoid neoplasms code for constitutively active nuclear transactivators

The NFKB-2 gene codes for an NF-kappa B-related transcription factor containing rel-polyG-ankyrin domains. Chromosomal rearrangements of the NFKB-2 locus have been found in various types of lymphoid neoplasms, suggesting that they may contribute to lymphomagenesis. Rearrangements cluster within the 3'-terminal ankyrin-encoding domain of the NFKB-2 gene and lead to the production of C-terminally truncated proteins which, in some cases, are fused to heterologous protein domains. In order to determine the functional consequences of these alterations, we have analyzed the subcellular localization, DNA binding, and transcriptional activity of two representative tumor-associated mutants in which the ankyrin domain is either terminally truncated (NFKB-2p85) or truncated and joined to an out-of-frame immunoglobulin C alpha domain (lyt-10C alpha). Immunofluorescence studies performed on cells transfected with p85 or lyt-10C alpha expression vectors showed that both the abnormal proteins were constitutively localized in the nucleus. Immunoprecipitation analysis of UV-cross-linked DNA-protein adducts showed that p85 can bind kappa B sites in its unprocessed form. Cotransfection of p85 or lyt-10C alpha expression vectors with kappa B-driven reporter plasmids showed that both p85 and lyt-10C alpha have retained the ability to mediate transcriptional activation via heterodimerization with Rel-Ap65 but have lost the transrepression activity associated with homodimeric DNA binding. Furthermore, both p85 and lyt-10C alpha were capable of independent transactivation of kappa B-reporter genes and this activity could not be further stimulated by Bcl-3. These abnormal proteins may contribute to lumphomagenesis by determining a constitutive activation of the NF-kappa B system and, in particular, of NFKB-2 target genes.

Regulation of human immunodeficiency virus type 1 and cytokine gene expression in myeloid cells by NF-kappa B/Rel transcription factors

CD4+ macrophages in tissues such as lung, skin, and lymph nodes, promyelocytic cells in bone marrow, and peripheral blood monocytes serve as important targets and reservoirs for human immunodeficiency virus type 1 (HIV-1) replication. HIV-1-infected myeloid cells are often diminished in their ability to participate in chemotaxis, phagocytosis, and intracellular killing. HIV-1 infection of myeloid cells can lead to the expression of surface receptors associated with cellular activation and/or differentiation that increase the responsiveness of these cells to cytokines secreted by neighboring cells as well as to bacteria or other pathogens. Enhancement of HIV-1 replication is related in part to increased DNA-binding activity of cellular transcription factors such as NF-kappa B. NF-kappa B binds to the HIV-1 enhancer region of the long terminal repeat and contributes to the inducibility of HIV-1 gene expression in response to multiple activating agents. Phosphorylation and degradation of the cytoplasmic inhibitor I kappa B alpha are crucial regulatory events in the activation of NF-kappa B DNA-binding activity. Both N- and C-terminal residues of I kappa B alpha are required for inducer-mediated degradation. Chronic HIV-1 infection of myeloid cells leads to constitutive NF-kappa B DNA-binding activity and provides an intranuclear environment capable of perpetuating HIV-1 replication. Increased intracellular stores of latent NF-kappa B may also result in rapid inducibility of NF-kappa B-dependent cytokine gene expression. In response to secondary pathogenic infections or antigenic challenge, cytokine gene expression is rapidly induced, enhanced, and sustained over prolonged periods in HIV-1-infected myeloid cells compared with uninfected cells. Elevated levels of several inflammatory cytokines have been detected in the sera of HIV-1-infected individuals. Secretion of myeloid cell-derived cytokines may both increase virus production and contribute to AIDS-associated disorders.

Coordinate regulation of the human TAP1 and LMP2 genes from a shared bidirectional promoter

Recently, four genes (TAP1, TAP2, LMP2, LMP7) involved or potentially involved in the processing and transport of major histocompatibility complex class I-associated antigen to the endoplasmic reticulum have been identified. We now report the initial characterization of the bidirectional promoter for the human transporter associated with antigen processing 1 (TAP1) and low molecular mass polypeptide 2 (LMP2) genes. These genes are divergently transcribed from a central promoter region of only 593 bp. Functional analysis using a bidirectional reporter system demonstrates the minimal 593-bp promoter is sufficient for concurrent expression in both directions. There is no TATA box homology at either end but there is a prevalence of GC boxes. Transcription is initiated at multiple sites for each gene without any of the TAP1 transcripts overlapping with the LMP2 transcripts. The region proximal to the TAP1 gene is required for maximal basal level expression of not only TAP1 but also LMP2. Furthermore, this region is necessary for tumor necrosis factor alpha (TNF-alpha) induction of both genes. Site-specific mutations of an NF-kappa B element in the TAP1 proximal region blocked induction by TNF-alpha in both the TAP1 and LMP2 directions. An adjacent GC box was required for basal expression of both genes as well as augmenting the TNF-alpha induction of the distal LMP2 gene. In vivo genomic foot-printing of this region revealed strong protein/DNA interactions at the NF-kappa B and GC box consensus sequences. In vitro binding studies confirmed the capacity of the NF-kappa B site to bind p50/p65 and p52/p65 heterodimers and of the GC box to bind Sp1. Thus, the promoter elements proximal to the TAP1 gene play a significant role in regulating basal and induced expression of both TAP1 and LMP2. The findings presented in this report clearly link LMP2 expression with TAP1 expression and provide additional suggestive evidence linking LMP2 to class I antigen presentation.

Regulation of human retroviral latency by the NF-kappa B/I kappa B family: inhibition of human immunodeficiency virus replication by I kappa B through a Rev-dependent mechanism

The cellular transcription factor NF-kappa B stimulates human immunodeficiency virus type 1 (HIV-1) transcriptional initiation, but its role in the retroviral life cycle has not been fully defined. In this report, we show that I kappa B alpha acts as a cellular inhibitor of human retroviral replication through a discrete mechanism, independent of its effect on HIV transcription. I kappa B alpha inhibited HIV replication and gp160 expression by negatively regulating Rev function, most likely acting through a cellular factor involved in Rev transactivation. A similar effect was observed with human T leukemia virus I, in which I kappa B alpha inhibited Rex function. In contrast, no effect was observed on the replication of a DNA virus, adenovirus type 5. The NF-kappa B/I kappa B regulatory pathway therefore modulates human retroviral replication by regulating a program of cellular gene expression required for several steps in the viral life cycle, including not only viral transcription but also RNA export. This interaction between cellular and viral gene products suggests that NF-kappa B plays a broader role in the regulation of human retroviral replication, providing a previously unrecognized link between two important regulators of HIV gene expression and common NF-kappa B-dependent programs of gene expression used by human retroviruses.

Transcriptional regulation of NF-kappa B2: evidence for kappa B-mediated positive and negative autoregulation

NF-kappa B is an inducible transcription factor complex which regulates the expression of a variety of genes which are involved in the immune, inflammatory, and acute-phase responses. The maintenance of NF-kappa B activity in stimulated cells requires ongoing protein synthesis, suggesting several modes of regulation. In this report, we have characterized the transcriptional regulation of one family member, NF-kappa B2. The genomic structure and sequence of NF-kappa B2 revealed the presence of two promoters and at least four kappa B regulatory elements, which mediate responsiveness to phorbol myristate acetate and tumor necrosis factor alpha. Similar to other NF-kappa B family members, NF-kappa B2 is positively autoregulated. In contrast to other family members, we find that kappa B elements in the NFKB2 promoter can also mediate transcriptional repression in the absence of NF-kappa B. We identified a nuclear complex which binds specifically to a subset of kappa B-related sites but not to the canonical kappa B element. Because of its putative inhibitory or repressive effect, this binding activity has been termed Rep-kappa B. This mechanism of repressing basal NF-kappa B2 transcription in an inactivated state enables the cell to tightly control NF-kappa B2 activity. These data demonstrate that a novel mode of kappa B-dependent regulation is mediated by specific kappa B sites in the NFKB2 promoter.

Transcriptional regulation of NF-kappa B2: evidence for kappa B-mediated positive and negative autoregulation

NF-kappa B is an inducible transcription factor complex which regulates the expression of a variety of genes which are involved in the immune, inflammatory, and acute-phase responses. The maintenance of NF-kappa B activity in stimulated cells requires ongoing protein synthesis, suggesting several modes of regulation. In this report, we have characterized the transcriptional regulation of one family member, NF-kappa B2. The genomic structure and sequence of NF-kappa B2 revealed the presence of two promoters and at least four kappa B regulatory elements, which mediate responsiveness to phorbol myristate acetate and tumor necrosis factor alpha. Similar to other NF-kappa B family members, NF-kappa B2 is positively autoregulated. In contrast to other family members, we find that kappa B elements in the NFKB2 promoter can also mediate transcriptional repression in the absence of NF-kappa B. We identified a nuclear complex which binds specifically to a subset of kappa B-related sites but not to the canonical kappa B element. Because of its putative inhibitory or repressive effect, this binding activity has been termed Rep-kappa B. This mechanism of repressing basal NF-kappa B2 transcription in an inactivated state enables the cell to tightly control NF-kappa B2 activity. These data demonstrate that a novel mode of kappa B-dependent regulation is mediated by specific kappa B sites in the NFKB2 promoter.

An interaction between the DNA-binding domains of RelA(p65) and Sp1 mediates human immunodeficiency virus gene activation

Induction of human immunodeficiency virus type 1 (HIV-1) gene expression in stimulated T cells has been attributed to the activation of the transcription factor NF-kappa B. The twice-repeated kappa B sites within the HIV-1 long terminal repeat are in close proximity to three binding sites for Sp1. We have previously shown that a cooperative interaction of NF-kappa B with Sp1 is required for the efficient stimulation of HIV-1 transcription. In this report, we define the domains of each protein responsible for this effect. Although the transactivation domains seemed likely to mediate this interaction, we find, surprisingly, that this interaction occurs through the putative DNA-binding domains of both proteins. Sp1 specifically interacted with the amino-terminal region of RelA(p65). Similarly, RelA bound directly to the zinc finger region of Sp1. This interaction was specific and resulted in cooperative DNA binding to the kappa B and Sp1 sites in the HIV-1 long terminal repeat. Furthermore, the amino-terminal region of RelA did not associate with several other transcription factors, including MyoD, E12, or Kox15, another zinc finger protein. These findings suggest that the juxtaposition of DNA-binding sites promotes a specific protein interaction between the DNA-binding regions of these transcription factors. This interaction is required for HIV transcriptional activation and may provide a mechanism to allow for selective activation of kappa B-regulated genes.

Transcription factor AP-2 regulates human immunodeficiency virus type 1 gene expression

Human immunodeficiency virus type 1 (HIV-1) gene expression is regulated by an enhancer region composed of multiple potential cis-acting regulatory sites. Here, we describe binding sites for the transcription factor AP-2 in the HIV-1 long terminal repeat which modulate HIV enhancer function. One site is embedded within the two previously described kappa B elements, and a second site is detected further downstream. DNase I footprinting and electrophoretic mobility shift assay experiments demonstrated that AP-2 binds to the site between the kappa B elements. Interestingly, AP-2 and NF-kappa B bind to this region in a mutually exclusive manner. Mutations which disrupt this AP-2-binding site lower basal levels of transcription but do not affect NF-kappa B-mediated induction by tumor necrosis factor alpha in Jurkat T leukemia cells.

An interaction between the DNA-binding domains of RelA(p65) and Sp1 mediates human immunodeficiency virus gene activation

Induction of human immunodeficiency virus type 1 (HIV-1) gene expression in stimulated T cells has been attributed to the activation of the transcription factor NF-kappa B. The twice-repeated kappa B sites within the HIV-1 long terminal repeat are in close proximity to three binding sites for Sp1. We have previously shown that a cooperative interaction of NF-kappa B with Sp1 is required for the efficient stimulation of HIV-1 transcription. In this report, we define the domains of each protein responsible for this effect. Although the transactivation domains seemed likely to mediate this interaction, we find, surprisingly, that this interaction occurs through the putative DNA-binding domains of both proteins. Sp1 specifically interacted with the amino-terminal region of RelA(p65). Similarly, RelA bound directly to the zinc finger region of Sp1. This interaction was specific and resulted in cooperative DNA binding to the kappa B and Sp1 sites in the HIV-1 long terminal repeat. Furthermore, the amino-terminal region of RelA did not associate with several other transcription factors, including MyoD, E12, or Kox15, another zinc finger protein. These findings suggest that the juxtaposition of DNA-binding sites promotes a specific protein interaction between the DNA-binding regions of these transcription factors. This interaction is required for HIV transcriptional activation and may provide a mechanism to allow for selective activation of kappa B-regulated genes.

Function of NF-kappa B/Rel binding sites in the major histocompatibility complex class II invariant chain promoter is dependent on cell-specific binding of different NF-kappa B/Rel subunits

The promoter of the human major histocompatibility complex class II-associated invariant-chain gene (Ii) contains two NF-kappa B/Rel binding sites located at -109 to -118 (Ii kappa B-1) and -163 to -172 (Ii kappa B-2) from the transcription start site. We report here that the differential function of each of these NF-kappa B/Rel sites in several distinct cell types depends on cell-specific binding of NF-kappa B/Rel transcription factors. Ii kappa B-1 is a positive regulatory element in B-cell lines and in the Ii-expressing T-cell line, H9, but acts as a negative regulatory element in myelomonocytic and glia cell lines. In vivo protein-DNA contacts are detectable at Ii kappa B-1 in cell lines in which this site is functional as either a positive or negative regulator. Electrophoretic mobility supershift assays determine that members of the NF-kappa B/Rel family of transcription factors can bind to this site in vitro and that DNA-binding complexes that contain p50, p52, p65, and cRel correlate with positive regulation whereas the presence of p50 correlates with negative regulation. Ii kappa B-2 is a site of positive regulation in B-cell lines and a site of negative regulation in H9 T cells, myelomonocytic, and glial cell lines. In vivo occupancy of this site is observed only in the H9 T-cell line. Again, in vitro supershift studies indicate that the presence of p50, p52, p65, and cRel correlates with positive function whereas the presence of only p50 and p52 correlates with negative function. This differential binding of specific NF-kappa B/Rel subunits is likely to mediate the disparate functions of these two NF-kappa B/Rel binding sites.

Function of NF-kappa B/Rel binding sites in the major histocompatibility complex class II invariant chain promoter is dependent on cell-specific binding of different NF-kappa B/Rel subunits

The promoter of the human major histocompatibility complex class II-associated invariant-chain gene (Ii) contains two NF-kappa B/Rel binding sites located at -109 to -118 (Ii kappa B-1) and -163 to -172 (Ii kappa B-2) from the transcription start site. We report here that the differential function of each of these NF-kappa B/Rel sites in several distinct cell types depends on cell-specific binding of NF-kappa B/Rel transcription factors. Ii kappa B-1 is a positive regulatory element in B-cell lines and in the Ii-expressing T-cell line, H9, but acts as a negative regulatory element in myelomonocytic and glia cell lines. In vivo protein-DNA contacts are detectable at Ii kappa B-1 in cell lines in which this site is functional as either a positive or negative regulator. Electrophoretic mobility supershift assays determine that members of the NF-kappa B/Rel family of transcription factors can bind to this site in vitro and that DNA-binding complexes that contain p50, p52, p65, and cRel correlate with positive regulation whereas the presence of p50 correlates with negative regulation. Ii kappa B-2 is a site of positive regulation in B-cell lines and a site of negative regulation in H9 T cells, myelomonocytic, and glial cell lines. In vivo occupancy of this site is observed only in the H9 T-cell line. Again, in vitro supershift studies indicate that the presence of p50, p52, p65, and cRel correlates with positive function whereas the presence of only p50 and p52 correlates with negative function. This differential binding of specific NF-kappa B/Rel subunits is likely to mediate the disparate functions of these two NF-kappa B/Rel binding sites.

Glucose kinase has a regulatory role in carbon catabolite repression in Streptomyces coelicolor

A glucose kinase (glkA) mutant of Streptomyces coelicolor A3(2) M145 was selected by the ability to grow in the presence of the nonmetabolizable glucose analog 2-deoxyglucose. In this glkA mutant, carbon catabolite repression of glycerol kinase and agarase was relieved on several carbon sources tested, even though most of these carbon sources are not metabolized via glucose kinase. This suggests that catabolite repression is not regulated by the flux through glucose kinase and that the protein itself has a regulatory role in carbon catabolite repression. A 10-fold overproduction of glucose kinase also results in relief of catabolite repression, suggesting that excess glucose kinase can titrate the repressing signal away. This could be achieved directly by competition of excess glucose kinase with its repressing form for binding sites on DNA promoter regions or indirectly by competition for binding of another regulatory protein.

Differential regulation of vascular cell adhesion molecule 1 gene expression by specific NF-kappa B subunits in endothelial and epithelial cells

Vascular cell adhesion molecule 1 (VCAM-1) is expressed in both endothelial and epithelial cell types, where it contributes to lymphocyte migration to sites of inflammation. Its expression is regulated by cytokines, in part through two kappa B-like regulatory elements. Because NF-kappa B can be composed of multiple alternative subunits with differential effects on gene expression, the role of different specific NF-kappa B family members subunits in VCAM-1 regulation is unknown. In this report, we define the contribution of different NF-kappa B family members to VCAM-1 gene regulation. We show that both kappa B sites in the VCAM-1 enhancer are required to optimally stimulate gene expression, but the enhancer is differentially regulated by specific combinations of NF-kappa B subunits. At low concentrations, RelA(p65) acted in concert with the approximately 50-kDa product of p105 NF-kappa B, NF-kappa B1(p50), to stimulate transcription, and at high concentrations, RelA(p65) alone stimulated the VCAM-1 promoter. In contrast, NF-kappa B2 inhibited functional activation of the VCAM reporter by p65. Consistent with this finding, an additional binding complex was detected by using recombinant NF-kappa B2(p49)/RelA(p65) with radiolabeled VCAM kappa B site probes. Interestingly, the human immunodeficiency virus enhancer responded differently to stimulation by NF-kappa B subunits, with optimal response to p49(100)/p65. Analysis of NF-kappa B mRNA in human umbilical vein endothelial cells revealed that nfkb1, nfkb2, and relA NF-kappa B but not c-rel were induced by tumor necrosis factor alpha and lipopolysaccharide, which also induce VCAM-1. These data suggest that specific subunits of NF-kappa B regulate VCAM-1 and differentially activate other genes in these cells.

Differential regulation of vascular cell adhesion molecule 1 gene expression by specific NF-kappa B subunits in endothelial and epithelial cells

Vascular cell adhesion molecule 1 (VCAM-1) is expressed in both endothelial and epithelial cell types, where it contributes to lymphocyte migration to sites of inflammation. Its expression is regulated by cytokines, in part through two kappa B-like regulatory elements. Because NF-kappa B can be composed of multiple alternative subunits with differential effects on gene expression, the role of different specific NF-kappa B family members subunits in VCAM-1 regulation is unknown. In this report, we define the contribution of different NF-kappa B family members to VCAM-1 gene regulation. We show that both kappa B sites in the VCAM-1 enhancer are required to optimally stimulate gene expression, but the enhancer is differentially regulated by specific combinations of NF-kappa B subunits. At low concentrations, RelA(p65) acted in concert with the approximately 50-kDa product of p105 NF-kappa B, NF-kappa B1(p50), to stimulate transcription, and at high concentrations, RelA(p65) alone stimulated the VCAM-1 promoter. In contrast, NF-kappa B2 inhibited functional activation of the VCAM reporter by p65. Consistent with this finding, an additional binding complex was detected by using recombinant NF-kappa B2(p49)/RelA(p65) with radiolabeled VCAM kappa B site probes. Interestingly, the human immunodeficiency virus enhancer responded differently to stimulation by NF-kappa B subunits, with optimal response to p49(100)/p65. Analysis of NF-kappa B mRNA in human umbilical vein endothelial cells revealed that nfkb1, nfkb2, and relA NF-kappa B but not c-rel were induced by tumor necrosis factor alpha and lipopolysaccharide, which also induce VCAM-1. These data suggest that specific subunits of NF-kappa B regulate VCAM-1 and differentially activate other genes in these cells.