Rel-associated pp40: an inhibitor of the rel family of transcription factors

Lost and Found: The Family of NF-κB Inhibitors Is Larger than Assumed in Salmonid Fish

NF-κB signalling is largely controlled by the family of 'inhibitors of NF-κB' (IκB). The relevant databases indicate that the genome of rainbow trout contains multiple gene copies coding for iκbα (nfkbia), iκbε (nfkbie), iκbδ (nkfbid), iκbζ (nfkbiz), and bcl3, but it lacks iκbβ (nfkbib) and iκbη (ankrd42). Strikingly, three nfkbia paralogs are apparently present in salmonid fish, two of which share a high sequence identity, while the third putative nfkbia gene is significantly less like its two paralogs. This particular nfkbia gene product, iκbα, clusters with the human IκBβ in a phylogenetic analysis, while the other two iκbα proteins from trout associate with their human IκBα counterpart. The transcript concentrations were significantly higher for the structurally more closely related nfkbia paralogs than for the structurally less similar paralog, suggesting that iκbβ probably has not been lost from the salmonid genomes but has been incorrectly designated as iκbα. In the present study, two gene variants coding for iκbα (nfkbia) and iκbε (nfkbie) were prominently expressed in the immune tissues and, particularly, in a cell fraction enriched with granulocytes, monocytes/macrophages, and dendritic cells from the head kidney of rainbow trout. Stimulation of salmonid CHSE-214 cells with zymosan significantly upregulated the iκbα-encoding gene while elevating the copy numbers of the inflammatory markers interleukin-1-beta and interleukin-8. Overexpression of iκbα and iκbε in CHSE-214 cells dose-dependently quenched both the basal and stimulated activity of an NF-κB promoter suggesting their involvement in immune-regulatory processes. This study provides the first functional data on iκbε-versus the well-researched iκbα factor-in a non-mammalian model species.

Identification of a NFKBIA polymorphism associated with lower NFKBIA protein levels and poor survival outcomes in patients with glioblastoma multiforme

The aberrant constitutive activation of nuclear factor-κB (NF-κB) has been observed in glioblastomas, while NF-κB inhibitor alpha (NFKBIA) inhibits the NF-κB signaling pathway under several physiological processes. However, the contribution of NFKBIA to glioblastomas is poorly understood. In the present study, using gene sequencing, we identified rs1957106 as a novel single nucleotide polymorphism (SNP) in NFKBIA in glioblastoma and found that it was more frequently present in glioblastoma patients. In addition, we examined the association between different genotypes of the rs1957106 SNP of NFKBIA and the gene copy number, mRNA level and protein expression of NFKBIA. The SNP rs1957106 CT and TT genotypes were found to be associated with lower NFKBIA protein levels and a poor prognosis of pateints with glioblastoma. Hence, by identifying rs1957106 as a novel SNP in NFKBIA in glioblastoma patients, we provide a new platform for further investigating the function of NFKBIA in the pathobiology of glioblastoma.

Atypical IκB proteins - nuclear modulators of NF-κB signaling

Nuclear factor κB (NF-κB) controls a multitude of physiological processes such as cell differentiation, cytokine expression, survival and proliferation. Since NF-κB governs embryogenesis, tissue homeostasis and the functions of innate and adaptive immune cells it represents one of the most important and versatile signaling networks known. Its activity is regulated via the inhibitors of NF-κB signaling, the IκB proteins. Classical IκBs, like the prototypical protein IκBα, sequester NF-κB transcription factors in the cytoplasm by masking of their nuclear localization signals (NLS). Thus, binding of NF-κB to the DNA is inhibited. The accessibility of the NLS is controlled via the degradation of IκBα. Phosphorylation of the conserved serine residues 32 and 36 leads to polyubiquitination and subsequent proteasomal degradation. This process marks the central event of canonical NF-κB activation. Once their NLS is accessible, NF-κB transcription factors translocate into the nucleus, bind to the DNA and regulate the transcription of their respective target genes. Several studies described a distinct group of atypical IκB proteins, referred to as the BCL-3 subfamily. Those atypical IκBs show entirely different sub-cellular localizations, activation kinetics and an unexpected functional diversity. First of all, their interaction with NF-κB transcription factors takes place in the nucleus in contrast to classical IκBs, whose binding to NF-κB predominantly occurs in the cytoplasm. Secondly, atypical IκBs are strongly induced after NF-κB activation, for example by LPS and IL-1β stimulation or triggering of B cell and T cell antigen receptors, but are not degraded in the first place like their conventional relatives. Finally, the interaction of atypical IκBs with DNA-associated NF-κB transcription factors can further enhance or diminish their transcriptional activity. Thus, they do not exclusively act as inhibitors of NF-κB activity. The capacity to modulate NF-κB transcription either positively or negatively, represents their most important and unique mechanistic difference to classical IκBs. Several reports revealed the importance of atypical IκB proteins for immune homeostasis and the severe consequences following their loss of function. This review summarizes insights into the physiological processes regulated by this protein class and the relevance of atypical IκB functioning.

Regulation of IkappaBalpha function and NF-kappaB signaling: AEBP1 is a novel proinflammatory mediator in macrophages

NF-κB comprises a family of transcription factors that are critically involved in various inflammatory processes. In this paper, the role of NF-κB in inflammation and atherosclerosis and the regulation of the NF-κB signaling pathway are summarized. The structure, function, and regulation of the NF-κB inhibitors, IκBα and IκBβ, are reviewed. The regulation of NF-κB activity by glucocorticoid receptor (GR) signaling and IκBα sumoylation is also discussed. This paper focuses on the recently reported regulatory function that adipocyte enhancer-binding protein 1 (AEBP1) exerts on NF-κB transcriptional activity in macrophages, in which AEBP1 manifests itself as a potent modulator of NF-κB via physical interaction with IκBα and a critical mediator of inflammation. Finally, we summarize the regulatory roles that recently identified IκBα-interacting proteins play in NF-κB signaling. Based on its proinflammatory roles in macrophages, AEBP1 is anticipated to serve as a therapeutic target towards the treatment of various inflammatory conditions and disorders.

Control of NF-κB activity by proteolysis

NF-κB transcription factors are critical regulators of many biological processes such as innate and adaptive immune responses, inflammation, cell proliferation and programmed cell death. This versatility necessitates a highly complex and tightly coordinated control of the signaling pathways leading to their activation. Here, we review the role of proteolysis in the regulation of NF-κB activity, more specifically the contribution of the well-known ubiquitin-proteasome system and the involvement of proteolytic activity of caspases and calpains.

Structural basis of HIV-1 activation by NF-kappaB--a higher-order complex of p50:RelA bound to the HIV-1 LTR

The activation and latency of human immunodeficiency virus type 1 (HIV-1) are tightly controlled by the transcriptional activity of its long terminal repeat (LTR) region. The LTR is regulated by viral proteins as well as host factors, including the nuclear factor kappaB (NF-kappaB) that becomes activated in virus-infected cells. The two tandem NF-kappaB sites of the LTR are among the most highly conserved sequence elements of the HIV-1 genome. Puzzlingly, these sites are arranged in a manner that seems to preclude simultaneous binding of both sites by NF-kappaB, although previous biochemical work suggests otherwise. Here, we have determined the crystal structure of p50:RelA bound to the tandem kappaB element of the HIV-1 LTR as a dimeric dimer, providing direct structural evidence that NF-kappaB can occupy both sites simultaneously. The two p50:RelA dimers bind the adjacent kappaB sites and interact through a protein contact that is accommodated by DNA bending. The two dimers clamp DNA from opposite faces of the double helix and form a topological trap of the bound DNA. Consistent with these structural features, our biochemical analyses indicate that p50:RelA binds the HIV-1 LTR tandem kappaB sites with an apparent anti-cooperativity but enhanced kinetic stability. The slow on and off rates we observe may be relevant to viral latency because viral activation requires sustained NF-kappaB activation. Furthermore, our work demonstrates that the specific arrangement of the two kappaB sites on the HIV-1 LTR can modulate the assembly kinetics of the higher-order NF-kappaB complex on the viral promoter. This phenomenon is unlikely restricted to the HIV-1 LTR but probably represents a general mechanism for the function of composite DNA elements in transcription.

The 22.5 kDa spectrin-binding domain of ankyrinR binds spectrin with high affinity and changes the spectrin distribution in cells in vivo

It was previously shown that ankyrins play a crucial role in the membrane skeleton arrangement. Purifying ankyrinR obtained from erythrocytes is a time-consuming process. Therefore, cloned and bacterially expressed ankyrinR-spectrin-binding domain (AnkSBD) is a demanded tool for studying spectrin-ankyrin interactions. In this communication, we report on the cloning and purification of AnkSBD and describe the results of binding experiments, in which we showed high-affinity interactions between the AnkSBD construct and isolated erythrocyte or non-erythroid spectrins. pEGFP-AnkSBD-transfected cells co-localised with non-erythroid spectrin in HeLa cells. The functional interactions of the AnkSBD construct in vivo and in vitro open many possibilities to study the structure and function of this domain, which has not yet been as extensively studied when compared to the aminoterminal domain of this protein.

Sustained induction of NF-kappa B is required for efficient expression of latent human immunodeficiency virus type 1

Cells harboring infectious, but transcriptionally latent, human immunodeficiency virus type 1 (HIV-1) proviruses currently pose an insurmountable barrier to viral eradication in infected patients. To better understand the molecular basis for HIV-1 latency, we used the J-Lat model of postintegration HIV-1 latency to assess the kinetic relationship between the induction of NF-kappaB and the activation of latent HIV-1 gene expression. Chromatin immunoprecipitation analyses revealed an oscillating pattern of RelA recruitment to the HIV-1 long terminal repeat (LTR) during continuous tumor necrosis factor alpha (TNF-alpha) stimulation. RNA polymerase II (Pol II) recruitment to the HIV-1 LTR closely mirrored RelA binding. Transient stimulation of cells with TNF-alpha for 15 min induced only a single round of RelA and RNA Pol II binding and failed to induce robust expression of latent HIV-1. Efficient formation of elongated HIV-1 transcripts required sustained induction by NF-kappaB, which promoted de novo synthesis of Tat. Cyclin-dependent kinase 9 (CDK9) and serine-2-phosphorylated RNA Pol II were rapidly recruited to the HIV-1 LTR after NF-kappaB induction; however, these elongating polymerase complexes were progressively dephosphorylated in the absence of Tat. Okadaic acid promoted sustained serine-2 phosphorylation of the C-terminal domain of RNA Pol II and stimulated efficient transcriptional elongation and HIV-1 expression in the absence of Tat. These findings underscore important differences between NF-kappaB and Tat stimulation of RNA Pol II elongation. While NF-kappaB binding to the HIV-1 LTR induces serial waves of efficient RNA Pol II initiation, elongation is impaired by the action of an okadaic acid-sensitive phosphatase that dephosphorylates the C-terminal domain of RNA Pol II. Conversely, the action of this phosphatase is overcome in the presence of Tat, promoting very efficient RNA Pol II elongation.

Therapeutic effect of arsenious acid combined with recombinant adenovirus Ad-IκBαM on hepatocellur carcinoma

AIM: To observe the inhibitory effect of recombinant adenovirus Ad-IκBαM on the activation of nuclear factor kappa B (NF-κB) as well as the enhancing effect of arsenious acid on the apoptosis of hepatocellular carcinoma cells.

METHODS: Hepatocellular carcinoma cell lines BEL-7402 and SMMC-7721 were treated with different concentrations of arsenious acid, respectively. The recombinant adenoviruses were prepared to transfect BEL-7402 and SMMC-7721 cells received or not received arsenious acid treatment. MTT assay and TUNEL method were used to observe the growth and apoptosis of the cells, respectively. Electrophoretic mobility shift assay (EMSA) and Western blot were performed to detect the activation of NF-κB and its inhibition after Ad-IκBαM transfection, respectively.

RESULTS: MTT indicated that the proliferations of BEL-7402 and SMMC-7721 cells were significantly suppressed after treatment of arsenious acid with different concentrations (P < 0.05). Western blot and EMSA showed that arsenious acid markedly inhibited the growth of liver cancer cells, and promoted the activation of NF-κB. After transfection with Ad-IκBαM, the activation of NF-κB induced by arsenious acid was dramatically inhibited. The apoptosis rates were 66.47% and 36.67% in SMMC-7721 cells transfected with Ad-IκBαM and Ad-IκBa, respectively, and they were 74.5% and 32.37% in Bel-7402 cells transfected with Ad-IκBαM and Ad-IκBa, respectively.

CONCLUSION: Arsenious acid has obvious effect in the treatment of hepatocarcinoma, but it promotes the activation of NF-κB at the same time. Recombinant adenovirus Ad-IκBαM can inhibit NF-κB activation while increase the effect of Arsenious acid effectively.

Adenosine and cAMP are potent inhibitors of the NF-kappa B pathway downstream of immunoreceptors

Anergic B lymphocytes exert compromised signal transduction towards the activation of NF-kappa B in response to B cell antigen receptor (BCR) triggering, whereas activation of the ERK pathway appears normal. How this differential down-regulation of the NF-kappa B pathway is regulated remains still elusive. Here, we demonstrate that stimuli known to enhance 3',5'-cyclic adenosine monophosphate (cAMP) are capable of selectively suppressing the activation both of NF-kappa B downstream of the BCR and Toll-like receptor 4 in splenic B lymphocytes and of the high-affinity receptor for IgE in BM-derived mast cells. This suppression is accomplished by blocking phosphorylation and subsequent degradation of the inhibitor of NF-kappa B. A cAMP-dependent protein kinase (PKA) inhibitor reverses this suppressive effect, indicating that PKA is a downstream effector of cAMP in this process. Importantly, not only drugs that artificially elevate intracellular cAMP levels, but also the nucleoside adenosine, which is known to be a mediator of cellular distress, inhibit the NF-kappa B pathway. This suggests that adenosine-mediated signals represent an important step in the molecular decision process controlling inflammation versus anergic immune responses.

Positive and negative regulation of nuclear factor-kappaB-mediated transcription by IkappaB-zeta, an inducible nuclear protein

IkappaB-zeta is an inducible nuclear protein that interacts with nuclear factor-kappaB (NF-kappaB) via its carboxyl-terminal ankyrin-repeats. Previous studies using an NF-kappaB reporter have shown that IkappaB-zeta inhibits the activity of NF-kappaB. In the present study, we dissected the amino-terminal region of IkappaB-zeta, which shows no homology to any other proteins. Indirect immunofluorescence studies demonstrated the presence of a bipartite nuclear localization signal spanning amino acids 163-178. Using GAL4 fusion proteins, we found that internal fragments containing amino acids 329-402 possessed intrinsic transcriptional activation activity. Interestingly, the activity was not detected in GAL4 fusion proteins of the full-length IkappaB-zeta. On the other hand, the GAL4-dependent transcriptional activity was generated by co-expression of the GAL4-NF-kappaB p50 subunit fusion protein and the full-length IkappaB-zeta, neither of which exhibited the activity on their own. A new splicing variant, IkappaB-zeta(D), with a deletion of amino acids 236-429, was found to lack transactivation activity. Forced expression of IkappaB-zeta, but not IkappaB-zeta(D), augmented interleukin-6 production, indicating the functional significance of the transactivation activity. In contrast, tumor necrosis factor-alpha production was inhibited by expression of IkappaB-zeta, highlighting the dual functions of this molecule. These results indicate that IkappaB-zeta harbors latent transcriptional activation activity, and that the activity is expressed upon interaction with the NF-kappaB p50 subunit. In addition to the inhibitory activity on NF-kappaB-mediated transcription, the transcriptional activation activity of IkappaB-zeta should be crucial for the regulation of inflammation.

Expanded nuclear roles for IkappaBs

I kappa B (IkappaB) was initially identified as a factor that inhibits DNA binding and nuclear translocation of the transcription factor nuclear factor kappa B (NF-kappaB). Recently, however, IkappaB family members have demonstrated direct nuclear roles in regulating NF-kappaB-dependent transcription. Some IkappaB proteins, including IkappaBalpha and IkappaBbeta, can regulate transcription by modulating the concentration of active NF-kappaB complexes within the nucleus. Others, such as IkappaBzeta and Bcl-3, can directly activate transcription by forming transcriptional complexes at gene promoters. Thus, IkappaB proteins play important nuclear roles in regulating NF-kappaB-dependent transcription after stimulation with various extracellular signals.

The ANK repeat: a ubiquitous motif involved in macromolecular recognition

Many proteins rely on stable, noncovalent interactions with other macromolecules to perform their function. The identification of a repeated sequence motif, the ANK repeat, in diverse proteins whose common function involves binding to other proteins indicates one way nature may achieve a wide range of protein-protein interactions. In this article, we describe evidence that these ANK repeats are involved in the specific recognition of proteins and possibly DNA, and present a model for the folding of the motif.

Differential regulation of the inhibitor of apoptosis ch-IAP1 by v-rel and the proto-oncogene c-rel

The v-rel oncogene encoded by reticuloendotheliosis virus is the acutely transforming member of the Rel/NF-kappaB family of transcription factors. v-Rel is a truncated and mutated form of c-Rel and transforms cells by inducing the aberrant expression of genes regulated by Rel/NF-kappaB proteins. The expression of ch-IAP1, a member of the inhibitor-of-apoptosis family, is highly elevated in cells expressing v-Rel and contributes to the immortalization of cells transformed by this oncoprotein. In this study we demonstrate that the elevated expression of ch-IAP1 in v-Rel-expressing cells is due to an increased rate of transcription. The ch-IAP1 promoter was isolated, and four Rel/NF-kappaB binding sites were identified upstream of the transcription start site. Two kappaB sites proximal to the transcription start site were required for v-Rel to activate the ch-IAP1 promoter. While c-Rel also utilized these sites, a third more-distal kappaB site was required for its full activation of the ch-IAP1 promoter. Differences in the transactivation domains of v-Rel and c-Rel are responsible for their different abilities to utilize these sites and account for their differential activation of the ch-IAP1 promoter. Although c-Rel was a more potent activator of the ch-IAP1 promoter than v-Rel in transient reporter assays, cells stably overexpressing c-Rel failed to maintain high levels of ch-IAP1 expression. The reduction of ch-IAP1 expression in these cells correlated with the efficient regulation of c-Rel by IkappaBalpha. The ability of v-Rel to escape IkappaBalpha regulation allows for the gradual and sustained elevation of ch-IAP1 expression directly contributing to the transforming properties of v-Rel.

Identification of polymorphisms of the IkappaBalpha gene associated with an increased risk of multiple myeloma

When NF-kappaB proteins are bound to IkappaBalpha, they remain in the cytosol, and are unable to act as transcription factors. Phosphorylation of IkappaBalpha at Serine32 and Serine36 has been shown to stimulate ubiquitination followed by proteasome-mediated degradation of IkappaBalpha, resulting in the release of active NF-kappaB. NF-kappaB activity is associated with bone loss and B cell growth as well as chemotherapy resistance. Because previous studies have shown abnormalities of the IkappaBalpha gene in patients with lymphoma, we determined whether alterations of this gene also occur in multiple myeloma (MM). We determined the DNA sequence of the IkappaBalpha gene from bone marrow mononuclear cells from 18 MM patients and 24 healthy subjects as well as two MM cell-lines. We identified eight polymorphisms. Statistically, the prevalence of three polymorphisms, one in exon 1 and two in exon 6, were significantly higher in MM patients (alpha>1) compared with samples from control subjects. Six of eight polymorphisms in myeloma samples have also been identified in previous studies of IkappaBalpha sequences derived from lymphoma samples. In addition, we detected two polymorphisms in the IkappaBalpha gene that have not been previously reported. Together, these results provide the basis for future evaluation the IkappaBalpha/NF-kappaB pathway in MM patients.

Mutational analysis of the v-Rel dimerization interface reveals a critical role for v-Rel homodimers in transformation

The v-rel oncogene encoded by reticuloendotheliosis virus strain T is the acutely transforming member of the Rel/NF-kappaB family of transcription factors. In v-Rel-transformed cells, v-Rel exists as homodimers or heterodimers with the endogenous Rel/NF-kappaB proteins c-Rel, NF-kappaB1, NF-kappaB2, and RelA. To examine the contribution of these complexes to v-Rel-mediated transformation, mutations were introduced into the dimerization interface of v-Rel to generate v-Rel mutants with selective dimerization properties. Nine mutants are described in this study that are defective in homodimer and/or heterodimer formation with specific Rel/NF-kappaB family members. Viruses expressing mutants that failed to homodimerize but were able to form heterodimeric complexes were unable to transform splenic lymphocytes in vitro, indicating that the dimerization of v-Rel with endogenously expressed Rel/NF-kappaB proteins is not in itself sufficient for transformation. In addition, two partially transforming mutants were identified that exhibited an impaired ability to form homodimers. Sequence analysis of the proviral DNA from cells transformed by these mutants revealed the presence of multiple secondary mutations in sequences responsible for dimerization and DNA binding. Two of these mutations either enhanced or restored the ability of these proteins to bind DNA as a homodimer. Viruses expressing these proteins transformed cells at levels comparable to or slightly less than v-Rel, suggesting that a threshold level of DNA binding by v-Rel homodimers is required for transformation.

[The Rel/NF-kappa-B transcription factors: complex role in cell regulation]

The transcription factor NF-kappa B has attracted widespread attention among researchers. NF-kappa B displays some original characteristics including rapid regulation, the wide range of genes that it controls and its probable involvement in several diseases. In resting cells, NF-kappa B is kept in an inactive form in the cytoplasm where it is bound to a member of the I kappa B family of inhibitory proteins. NF-kappa B can be activated by exposure of cells to physiological as well as non physiological stimuli. Upon cell activation, the inhibitors are modified through site specific phosphorylations which target them for subsequent ubiquitination and proteolytic degradation by the proteasome. Removal of the inhibitor unmasks the nuclear localization signals on subunits of NF-kappa B. Free NF-kappa B moves to the nucleus where it binds to target DNA elements and activate transcription of genes encoding proteins involved in immune responses, inflammation or cell proliferation. NF-kappa B could be considered as a co-ordinating element in the body's responses to situations of stress, infection or inflammation. A tight regulation of NF-kappa B seems to be crucial since a dysfunction could promote pathogenic processes including AIDS (acquired immunodeficiency syndrome), rheumatoid arthritis and cancer. Additionally, it will be important to understand the exact roles for NF-kappa B in regulating apoptosis. NF-kappa B is now regarded as a good therapeutic target and the development of specific inhibitors should lead in the next future to novel therapeutics.

Degradation of IkappaBalpha is limited by a postphosphorylation/ubiquitination event

Regulation of IkappaBalpha during activation was examined using EGFP. Single cell analysis showed that both localisation- and cytokine-induced degradation of IkappaBalpha are dependent on expression levels. Cells expressing higher levels of the inhibitor demonstrated an increase in nuclear IkappaBalphaEGFP with a pronounced enhancement in the nuclear/cytoplasmic ratio. Enhancing the levels of the endogenous IkappaBalpha by relA transfection caused significant reduction in IL-1-mediated degradation of the fusion protein. Similarly, IkappaBalphaEGFP-transfected cells showed an inverse correlation between the level of the fusion protein and IL-1-mediateddegradation. Comparing absolute levels demonstrated a biphasic response, with reduction in cells expressing over 15-fold that of endogenous levels. Further experiments using Western analysis showed a positive correlation between both phosphorylation and ubiquitination of IkappaBalphaEGFP, and the level the inhibitor. In contrast, and in agreement with the singlecell analysis, while IL-1 stimulation caused the expected degradation at lower levels of the fusion protein,breakdown of IkappaBalphaEGFP was totally inhibited at the higher transfection levels. The data show that turnover of IkappaBalpha is saturable and suggest that limitation of the pathway by enhanced inhibitor expression is regulated through a post phosphorylation/ubiquitination event, at the level of degradation.

The N-terminal nuclear export sequence of IkappaBalpha is required for RanGTP-dependent binding to CRM1

Nuclear export of IkappaBalpha is mediated by the CRM1 nuclear export receptor. However, the identity of the nuclear export sequences NES(s) in IkappaBalpha that are responsible for binding of IkappaBalpha to CRM1 is controversial. Both a N-terminal NES-like region (amino acids 45-54) and a C-terminal NES-like region (amino acids 265-280) have, in a number of reports from different laboratories, been implicated in CRM1-dependent nuclear export of IkappaBalpha. We now demonstrate that the N-terminal NES-like region, but not the C-terminal NES-like region, is required for RanGTP-dependent binding of IkappaBalpha to CRM1. IkappaBalpha is a relatively weak substrate for CRM1, with an affinity for CRM1 that is 100-fold less than the minute virus of mice NS2 protein, a high affinity cargo protein for CRM1. We also demonstrate that IkappaBalpha functions as a physical adaptor between CRM1 and NFkappaB/Rel proteins. Both free IkappaBalpha and Rel-associated IkappaBalpha have comparable affinities for CRM1, suggesting that CRM1 does not discriminate between free IkappaBalpha and Rel-associated IkappaBalpha. Nuclear export of c-Rel by IkappaBalpha requires the N-terminal NES-like sequence of IkappaBalpha but is not affected by alanine substitutions within the C-terminal NES-like sequence of IkappaBalpha. In contrast, nuclear export of the v-Rel oncoprotein by IkappaBalpha is disrupted by alanine substitutions within either the N-terminal or the C-terminal NES-like sequences. However, alanine substitutions within the C-terminal NES-like sequence significantly reduce the affinity of IkappaBalpha for v-Rel, suggesting that loss of export function for this mutant is secondary to reduced association between IkappaBalpha and v-Rel. Taken together, our results demonstrate that the N-terminal NES-like sequence in IkappaBalpha is required for RanGTP-dependent binding of both free IkappaBalpha and NFkappaB/Rel-associated IkappaBalpha proteins to CRM1.

Two waves of nuclear factor kappaB recruitment to target promoters

Proinflammatory stimuli induce the rapid and transient translocation of nuclear factor (NF)-kappaB to the nucleus, where it activates transcription from several genes, including those encoding inflammatory cytokines and chemokines, adhesion molecules, and cytoprotective proteins. Using chromatin immunoprecipitation, we show that after an acute stimulation two distinct waves of NF-kappaB recruitment to target promoters occur: a fast recruitment to constitutively and immediately accessible (CIA) promoters and a late recruitment to promoters requiring stimulus-dependent modifications in chromatin structure to make NF-kappaB sites accessible (promoters with regulated and late accessibility [RLA]). Our results suggest that a mechanism of specificity in NF-kappaB-dependent transcriptional responses relies on the ability of individual stimuli to make RLA promoters accessible to NF-kappaB before its rapid extrusion from the nucleus.

Integrin involvement in glioblastoma multiforme: possible regulation by NF-kappaB

Glioblastoma multiforme (GBM) is the most malignant astroglial-derived tumors which has the propensity to aggressively infiltrate normal regions of the brain surrounding the tumor. The interaction of tumor cells with the extracellular matrix (ECM) is an integral step in the process of tumorigenesis and may play a role in the local invasion of the GBM cells. Our study investigated the role of the nuclear transcription factor NF-kappaB on GBM integrin expression and cell attachment. Our results show that treatment of GBM cell lines, SNB-19 and T98G with PMA, an inducer of NF-kappaB, increased the expression of fibronectin and vitronectin genes. Accordingly, ectopic over-expression of NFkappaB subunits in GBM cells elevated the levels of fibronectin gene expression, providing direct evidence for a regulatory role for NF-kappaB in ECM protein production. Cell attachment to the ECM proteins including fibronectin, vitronectin and laminin was increased in GBM and normal astrocytic cells. Interestingly, treatment of cells with PMA augmented attachment of SNB-19 and T98G cells to fibronectin and vitronectin, however it had no effect on attachment of normal astrocytes. Addition of the tripeptide arginine-glycine-asparatic acid (RGD), the recognition site for many integrins, significantly inhibited SNB-19 and T98G cell attachment to fibronectin and vitronectin. Finally, activation of NFkappaB upon treatment of SNB cells with PMA led to an increase in the levels of mRNA for the beta3 and the alphav integrin subunits. Collectively, these data demonstrate a possible role for NF-kappaB in glioma cell attachment.

Role and regulation of Rel/NF-kappaB activity in anti-immunoglobulin-induced apoptosis in WEHI-231 B lymphoma cells

In WEHI-231 cells, anti-immunoglobulin (anti-Ig) treatment leads to both a decrease in the DNA-binding activity of p50/c-Rel/p53 protein complexes and a transient enhancement in the DNA-binding activity of p50 homodimeric complexes. These cells subsequently undergo apoptosis. Because IkappaB-alpha plays a pivotal role in the regulation of Rel/NF-kappaB activity, we have characterized both the nature and kinetics of the expression of IkappaB-alpha following anti-Ig-induced apoptosis in WEHI-231 cells. Anti-Ig treatment of WEHI-231 cells decreased the steady-state level of IkappaB-alpha mRNA, but enhanced the stability of IkappaB-alpha, leading to an accumulation of IkappaB-alpha in both the cytosol and nucleus. Concomitant with the increase in IkappaB-alpha expression there was a gradual decline in the nuclear expression of c-Rel. Because c-Rel plays an important role in the survival of WEHI-231 cells, these results suggest that post-transcriptional regulation of IkappaB-alpha expression might play a role in the anti-Ig-induced apoptosis in WEHI-231 cells.

Nuclear import of IkappaBalpha is accomplished by a ran-independent transport pathway

The inhibitor of kappa B alpha (IkappaBalpha) protein is able to shuttle between the cytoplasm and the nucleus. We have utilized a combination of in vivo and in vitro approaches to provide mechanistic insight into nucleocytoplasmic shuttling by IkappaBalpha. IkappaBalpha contains multiple functional domains that contribute to shuttling of IkappaBalpha between the cytoplasm and the nucleus. Nuclear import of IkappaBalpha is mediated by the central ankyrin repeat domain. Similar to previously described nuclear import pathways, nuclear import of IkappaBalpha is temperature and ATP dependent and is blocked by a dominant-negative mutant of importin beta. However, in contrast to classical nuclear import pathways, nuclear import of IkappaBalpha is independent of soluble cytosolic factors and is not blocked by the dominant-negative RanQ69L protein. Nuclear export of IkappaBalpha is mediated by an N-terminal nuclear export sequence. Nuclear export of IkappaBalpha requires the CRM1 nuclear export receptor and is blocked by the dominant-negative RanQ69L protein. Our results are consistent with a model in which nuclear import of IkappaBalpha is mediated through direct interactions with components of the nuclear pore complex, while nuclear export of IkappaBalpha is mediated via a CRM1-dependent pathway.

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

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

Common pathway for the ubiquitination of IkappaBalpha, IkappaBbeta, and IkappaBepsilon mediated by the F-box protein FWD1

FWD1 (the mouse homolog of Drosophila Slimb and Xenopus betaTrCP, a member of the F-box- and WD40 repeat-containing family of proteins, and a component of the SCF ubiquitin ligase complex) was recently shown to interact with IkappaBalpha and thereby to promote its ubiquitination and degradation. This protein has now been shown also to bind to IkappaBbeta and IkappaBepsilon as well as to induce their ubiquitination and proteolysis. FWD1 was shown to recognize the conserved DSGPsiXS motif (where Psi represents the hydrophobic residue) present in the NH(2)-terminal regions of these three IkappaB proteins only when the component serine residues are phosphorylated. However, in contrast to IkappaBalpha and IkappaBbeta, the recognition site in IkappaBepsilon for FWD1 is not restricted to the DSGPsiXS motif; FWD1 also interacts with other sites in the NH(2)-terminal region of IkappaBepsilon. Substitution of the critical serine residues in the NH(2)-terminal regions of IkappaBalpha, IkappaBbeta, and IkappaBepsilon with alanines also markedly reduced the extent of FWD1-mediated ubiquitination of these proteins and increased their stability. These data indicate that the three IkappaB proteins, despite their substantial structural and functional differences, all undergo ubiquitination mediated by the SCF(FWD1) complex. FWD1 may thus play an important role in NF-kappaB signal transduction through regulation of the stability of multiple IkappaB proteins.

The nuclear transcription factor NF-kappaB mediates interleukin-1beta-induced expression of cyclooxygenase-2 in human myometrial cells

OBJECTIVE

Up-regulation of prostaglandin production by gestational tissues in the setting of intrauterine infection has been implicated as an important contributor to preterm labor and parturition. In this study we investigated the possible role of the nuclear transcription factor NF-kappaB in interleukin-1 signaling, leading to the expression of cyclooxygenase 2 and prostaglandin production in human myometrial cell cultures.

STUDY DESIGN

Human myometrial smooth muscle cells from an immortalized line were used as a model system between passages 20 and 35. Growth-arrested cell cultures were stimulated with human recombinant interleukin 1, and the activation of NF-kappaB was assessed by the degradation of the inhibitory protein IkappaB-alpha (Western analysis), as well as by nuclear binding of NF-kappaB by using an electrophoretic mobility shift assay. The abundance of cyclooxygenase-2 messenger ribonucleic acid and protein was measured by Northern and Western analyses, whereas prostaglandin (prostaglandin I(2 ) and prostaglandin E(2 )) production was determined by specific radioimmunoassays.

RESULTS

Within 15 minutes of stimulation with interleukin 1, 90% of IkappaB-alpha was degraded. This was temporally associated with nuclear translocation and binding of NF-kappaB. Within 30 minutes, cyclooxygenase 2 messenger ribonucleic acid appeared, with steady-state levels increasing up to 4 hours. This was followed by an up to 80-fold increase in cyclooxygenase 2 protein and a corresponding time-dependent increase in prostaglandin production. When IkappaB-alpha degradation was blocked with calpain I inhibitor, NF-kappaB translocation, cyclooxygenase 2 messenger ribonucleic acid and protein expression, and prostaglandin synthesis were also inhibited.

CONCLUSION

Stimulation of human myometrial cells with interleukin 1 leads to rapid activation of the transcription factor NF-kappaB, which is functionally linked to the expression of cyclooxygenase 2 messenger ribonucleic acid, protein, and prostaglandin synthesis.

Functional characterization of a purified, recombinant NF-kappaB/IkappaB complex

The NF-kappaB signal transduction pathway involves the interaction of several NF-kappaB and IkappaB family members that are activated by a diverse range of extracellular signals and that stimulate many different cellular responses. The biochemical regulation of this cascade can be studied by establishing a cell-free system using purified proteins. As a first step toward establishing an in vitro model incorporating multiple combinations of NF-kappaB and IkappaB proteins, we produced purified human p65 (RelA) and human IkappaBalpha proteins and tested their functionality. Full-length RelA and IkappaBalpha proteins were overproduced by coinfection of TN5-JE cells with two recombinant baculoviruses. RelA and IkappaBalpha formed a stable complex that could be purified to >95% homogeneity. Protein-protein interactions, protein-DNA binding, and protein phosphorylation were similar to the native proteins.

Structure of an IkappaBalpha/NF-kappaB complex

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

c-Rel is essential for B lymphocyte survival and cell cycle progression

c-Rel is a lymphoid-specific member of the NF-kappaB/Rel family of transcriptional factors. To investigate the role of c-Rel in B lymphocyte function, we generated a c-Rel(-/-) mouse via a gene targeting approach. Although early lymphocyte development is normal in c-Rel(-/-) mice, there are significantly fewer B cells displaying a memory (IgM/IgD-) phenotype. Upon immunization, c-Rel(-/-) mice generate fewer B cells with a germinal center (PNAhi) phenotype. In vitro, c-Rel(-/-) B cells proliferate poorly upon ligation of their surface IgM or CD40 receptors or when stimulated with either lipopolysaccharide (LPS) or T cell help. Early molecular events that precede proliferation, such as increases in RNA synthesis as well as IL-2 receptor alpha chain expression, are greatly diminished in c-Rel(-/-) B cells. Furthermore, c-Rel(-/-) B cells are impaired in the ability to receive survival signals generated by anti-IgM or LPS. In contrast, CD40-mediated cell survival is normal in c-Rel(-/-) B cells, suggesting the involvement of a survival-signaling pathway that is independent of c-Rel. When c-Rel (-/-) B cells are co-stimulated with either anti-IgM and CD40 or LPS and CD40, they are rendered capable of progressing through the cell cycle. Finally, co-culture experiments suggest that the defects observed in c-Rel(-/-) B cells are intrinsic to the cell and can not be rescued through either cell-cell contact or addition of soluble factors. Thus, c-Rel is requisite for differentiation to the germinal center and memory B cells in vivo and is required for the transduction of survival and cell cycle progression signals mediated by anti-IgM and LPS in vitro. Furthermore, while c-Rel is involved in CD40-induced proliferation, it is apparently dispensable for the survival signals transduced by CD40.

Regulation of serum amyloid A protein expression during the acute-phase response

The acute-phase (AP) serum amyloid A proteins (A-SAA) are multifunctional apolipoproteins which are involved in cholesterol transport and metabolism, and in modulating numerous immunological responses during inflammation and the AP response to infection, trauma or stress. During the AP response the hepatic biosynthesis of A-SAA is up-regulated by pro-inflammatory cytokines, and circulating concentrations can increase by up to 1000-fold. Chronically elevated A-SAA concentrations are a prerequisite for the pathogenesis of secondary amyloidosis, a progressive and fatal disease characterized by the deposition in major organs of insoluble plaques composed principally of proteolytically cleaved A-SAA, and may also contribute to physiological processes that lead to atherosclerosis. There is therefore a requirement for both positive and negative control mechanisms that permit the rapid induction of A-SAA expression until it has fulfilled its host-protective function(s) and subsequently ensure that its expression can be rapidly returned to baseline. These mechanisms include modulation of promoter activity involving, for example, the inducer nuclear factor kappaB (NF-kappaB) and its inhibitor IkappaB, up-regulatory transcription factors of the nuclear factor for interleukin-6 (NF-IL6) family and transcriptional repressors such as yin and yang 1 (YY1). Post-transcriptional modulation involving changes in mRNA stability and translation efficiency permit further up- and down-regulatory control of A-SAA protein synthesis to be achieved. In the later stages of the AP response, A-SAA expression is effectively down-regulated via the increased production of cytokine antagonists such as the interleukin-1 receptor antagonist (IL-1Ra) and of soluble cytokine receptors, resulting in less signal transduction driven by pro-inflammatory cytokines.

Loss of IkappaB alpha-mediated control over nuclear import and DNA binding enables oncogenic activation of c-Rel

The IkappaB alpha protein is able both to inhibit nuclear import of Rel/NF-kappaB proteins and to mediate the export of Rel/NF-kappaB proteins from the nucleus. We now demonstrate that the c-Rel-IkappaB alpha complex is stably retained in the cytoplasm in the presence of leptomycin B, a specific inhibitor of Crm1-mediated nuclear export. In contrast, leptomycin B treatment results in the rapid and complete relocalization of the v-Rel-IkappaB alpha complex from the cytoplasm to the nucleus. IkappaB alpha also mediates the rapid nuclear shuttling of v-Rel in an interspecies heterokaryon assay. Thus, continuous nuclear export is required for cytoplasmic retention of the v-Rel-IkappaB alpha complex. Furthermore, although IkappaB alpha is able to mask the c-Rel-derived nuclear localization sequence (NLS), IkappaB alpha is unable to mask the v-Rel-derived NLS in the context of the v-Rel-IkappaB alpha complex. Taken together, our results demonstrate that IkappaB alpha is unable to inhibit nuclear import of v-Rel. We have identified two amino acid differences between c-Rel and v-Rel (Y286S and L302P) which link the failure of IkappaB alpha to inhibit nuclear import and DNA binding of a mutant c-Rel protein to oncogenesis. Our results support a model in which loss of IkappaB alpha-mediated control over c-Rel leads to oncogenic activation of c-Rel.

The cloning and developmental regulation of murine diacylglycerol kinase zeta

Diacylglycerol kinases (DGKs) regulate the key signaling intermediates diacylglycerol (DAG) and phosphatidic acid (PA). We isolated cDNA clones of mouse diacylglycerol kinase zeta (mDGKzeta) and found that it shares 88% identity at the nucleic acid level and 95.5% identity at the amino acid level with human DGKzeta (hDGKzeta). Murine DGKzeta protein rose gradually during embryonic development, and was abundant in newborn and adult brains. By RNA whole-mount in situ hybridization, mDGKzeta was shown to be expressed in spinal ganglia and limb buds at low level in E11.5 embryos and at higher level in E12.5 embryos. In E13.5 embryos, DGKzeta mRNA was highly expressed in vibrissa follicles, in spinal ganglia, and in the interdigital regions of the developing limbs. Northern blotting showed that DGKzeta expression was limited to specific anatomical regions of the brain. Thus, the expression of DGKzeta is regulated temporally and spatially during mammalian development and correlates with the development of sensory neurons and regions undergoing apoptosis.

NF-kappa B and Rel proteins: evolutionarily conserved mediators of immune responses

The transcription factor NF-kappa B, more than a decade after its discovery, remains an exciting and active area of study. The involvement of NF-kappa B in the expression of numerous cytokines and adhesion molecules has supported its role as an evolutionarily conserved coordinating element in the organism's response to situations of infection, stress, and injury. Recently, significant advances have been made in elucidating the details of the pathways through which signals are transmitted to the NF-kappa B:I kappa B complex in the cytosol. The field now awaits the discovery and characterization of the kinase responsible for the inducible phosphorylation of I kappa B proteins. Another exciting development has been the demonstration that in certain situations NF-kappa B acts as an anti-apoptotic protein; therefore, elucidation of the mechanism by which NF-kappa B protects against cell death is an important goal. Finally, the generation of knockouts of members of the NF-kappa B/I kappa B family has allowed the study of the roles of these proteins in normal development and physiology. In this review, we discuss some of these recent findings and their implications for the study of NF-kappa B.

Dominant Signals Leading to Inhibitor κB Protein Degradation Mediate CD40 Ligand Rescue of WEHI 231 Immature B Cells from Receptor-Mediated Apoptosis

Recently, we demonstrated maintenance of nuclear factor (NF)-κB/Rel factors plays a major role in B cell survival. Treatment of WEHI 231 immature B cells with an Ab against the surface IgM protein (anti-IgM) induces apoptosis that can be rescued by engagement of CD40 receptor. The dramatic decrease in high basal levels of NF-κB/Rel activity induced by anti-IgM treatment led to cell death. CD40 ligand (CD40L) treatment prevented the drop in NF-κB/Rel factor binding by inducing a sustained decrease in inhibitor (I) κB-α and transient decrease in IκB-β protein levels. In this study, we have investigated the regulation of these NF-κB/Rel-inhibitory proteins. In exponentially growing WEHI 231 cells, the IκB-α and IκB-β proteins decayed with an approximate t1/2 of 38 and 76 min, respectively, which was blocked effectively upon addition of the proteasome-specific inhibitor (benzylcarbonyl)-Leu-Leu-phenylalaninal (Z-LLF-CHO). Anti-IgM treatment stabilized IκB-α and IκB-β proteins. CD40L treatment resulted in a dramatic decrease in t1/2 (&lt;5 min) for both IκB molecules, which was inhibited by addition of Z-LLF-CHO. CD40L treatment also caused a delayed increase in IκB-β mRNA levels, most likely contributing to the observed recovery of IκB-β levels. Microinjection of IκB-α-glutathione S-transferase fusion protein into nuclei of WEHI 231 cells ablated protection by CD40L from receptor-mediated killing. Furthermore, CD40L rescued apoptosis induced upon microinjection of a vector expressing wild-type IκB-α, but not a 32A/36A mutant form of IκB-α, unable to be phosphorylated and hence degraded. Thus, control of turnover of IκB proteins by CD40L plays a major role in maintenance of NF-κB/Rel and resultant rescue of WEHI 231 cells from apoptosis.

Nuclear localization of IkappaB alpha is mediated by the second ankyrin repeat: the IkappaB alpha ankyrin repeats define a novel class of cis-acting nuclear import sequences

The ability of the IkappaB alpha protein to sequester dimeric NF-kappaB/Rel proteins in the cytoplasm provides an effective mechanism for regulating the potent transcriptional activation properties of NF-kappaB/Rel family members. IkappaB alpha can also act in the nucleus as a postinduction repressor of NF-kappaB/Rel proteins. The mechanism by which IkappaB alpha enters the nucleus is not known, as IkappaB alpha lacks a discernible classical nuclear localization sequence (NLS). We now report that nuclear localization of IkappaB alpha is mediated by a novel nuclear import sequence within the second ankyrin repeat. Deletion of the second ankyrin repeat or alanine substitution of hydrophobic residues within the second ankyrin repeat disrupts nuclear localization of IkappaB alpha. Furthermore, a region encompassing the second ankyrin repeat of IkappaB alpha is able to function as a discrete nuclear import sequence. The presence of a discrete nuclear import sequence in IkappaB alpha suggests that cytoplasmic sequestration of the NF-kappaB/Rel-IkappaB alpha complex is a consequence of the mutual masking of the NLS within NF-kappaB/Rel proteins and the import sequence within IkappaB alpha. Nuclear import may be a conserved property of ankyrin repeat domains (ARDs), as the ARDs from two other ARD-containing proteins, 53BP2 and GABPbeta, are also able to function as nuclear import sequences. We propose that the IkappaB alpha ankyrin repeats define a novel class of cis-acting nuclear import sequences.

Distinct domains of IkappaBalpha regulate c-Rel in the cytoplasm and in the nucleus

IkappaBalpha is a critical regulator of Rel/NF-KB-mediated gene activation. It controls the induction of NF-KB factors by retaining them in the cytoplasm and also functions in the nucleus to terminate the induction process. In this study, we show that IkappaBalpha regulates the transcriptional activity of c-Rel in the nuclear compartment. We also demonstrate that discrete functional domains of IkappaBalpha are responsible for the cytoplasmic and nuclear regulation of c-Rel. We show that the determinants for the cytoplasmic regulation of c-Rel reside in the N-terminal and central ankyrin regions of IkappaBalpha and that the N-terminal domain of IkappaBalpha is required to mask the c-Rel nuclear localization signal. Importantly, IkappaBalpha sequences necessary to regulate c-Rel in the nucleus map to its central ankyrin domain and to a few negatively charged amino acids that immediately follow in the C-terminal IkappaBalpha PEST domain. The mapping of the IkappaBalpha determinants that control the cytoplasmic and nuclear activities of c-Rel to specific regions of the molecule suggests that IkappaBalpha inhibitors could be designed to antagonize Rel/NF-kappaB activity in different subcellular compartments or at defined stages of activation.

Inhibition of nuclear factor kappaB activation by a virus-encoded IkappaB-like protein

Certain viruses have evolved mechanisms to counteract innate immunity, a host response in which nuclear factor kappaB (NF-kappaB) transcription factors play a central role. African swine fever virus encodes a protein of 28.2 kDa containing ankyrin repeats similar to those of cellular IkappaB proteins, which are inhibitors of NF-kappaB. Transfection of the African swine fever virus IkappaB gene inhibited tumor necrosis factor- or phorbol ester-induced activation of kappaB- but not AP-1-driven reporter genes. Moreover, African swine fever virus IkappaB co-immunoprecipitated with p65 NF-kappaB, and the purified recombinant protein prevented the binding of p65-p50 NF-kappaB proteins to their target sequences in the DNA. NF-kappaB activation induced by tumor necrosis factor, as detected by mobility shift assays or by transfection of kappaB-driven reporter genes, is impaired in African swine fever virus-infected cells. These results indicate that the African swine fever virus IkappaB gene homologue interferes with NF-kappaB activation, likely representing a new mechanism to evade the immune response during viral infection.

ch-IAP1, a member of the inhibitor-of-apoptosis protein family, is a mediator of the antiapoptotic activity of the v-Rel oncoprotein

The oncoprotein v-Rel, a member of the Rel/NF-kappaB family of transcription factors, induces neoplasias and inhibits apoptosis. To identify differentially regulated cellular genes and to evaluate their relevance to transformation and apoptosis in v-Rel-transformed cells, mRNA differential display has been used. One of the recovered cDNAs corresponds to a gene that was highly expressed in v-Rel-transformed fibroblasts. Analysis of the isolated full-length cDNA of a chicken inhibitor-of-apoptosis protein (ch-IAP1) revealed that it encodes a 68-kDa protein that is highly homologous to members of the IAP family, such as human c-LAP1. Like other IAPs, ch-IAP1 contains the N-terminal baculovirus IAP repeats and C-terminal RING finger motifs. Northern blot analysis identified a 3.3-kb ch-IAP1 transcript expressed at relatively high levels in the spleen, thymus, bursa, intestine, and lungs. Expression of v-Rel in fibroblasts, a B-cell line, and spleen cells up-regulated the expression of ch-IAP1. In contrast, ch-IAP1 expression levels were low in chicken cell lines transformed by several other unrelated tumor viruses. ch-IAP1 was expressed predominantly in the cytoplasm of the v-Rel-transformed cells. ch-IAP1 suppressed mammalian cell apoptosis induced by the overexpression of the interleukin-1-converting enzyme. Expression of exogenous ch-IAP1 in temperature-sensitive v-Rel transformed spleen cells inhibited apoptosis of these cells at the nonpermissive temperature. Collectively, these results suggest that ch-IAP1 is induced during the v-Rel-mediated transformation process and functions as a suppressor of apoptosis in v-Rel-transformed cells.

I kappaB alpha-independent downregulation of NF-kappaB activity by glucocorticoid receptor

I kappaB alpha is an inhibitor protein that prevents nuclear transport-and activation of the transcription factor NF-kappaB. In acute inflammation, NF-kappaB is activated and increases the expression of several pro-inflammatory cytokine and chemokine genes. Glucocorticoids counteract this process. It has been proposed that the glucocorticoid-dependent inhibition of NF-kappaB activity is mediated by increased synthesis of I kappaB alpha which should then sequester NF-kappaB in an inactive cytoplasmic form. Here, we show by the use of a mutant glucocorticoid receptor and steroidal ligands that hormone-induced I kappaB alpha synthesis and inhibition of NF-kappaB activity are separable biochemical processes. A dimerization-defective glucocorticoid receptor mutant that does not enhance the I kappaB alpha level is still able to repress NF-kappaB activity. Conversely, glucocorticoid analogues competent in enhancing I kappaB alpha synthesis do not repress NF-kappaB activity. These results demonstrate that increased synthesis of I kappaB alpha is neither required nor sufficient for the hormone-mediated downmodulation of NF-kappaB activity.

Regulation of IkappaB beta in WEHI 231 mature B cells

Constitutive activation of NF-kappaB in WEHI 231 early mature B cells resembles the persistent activation of NF-kappaB that is observed upon prolonged stimulation of other cells. In both cases, NF-kappaB DNA binding complexes are found in the nucleus, despite the abundance of cytosolic IkappaB alpha. Recently, we have shown that prolonged activation of 70Z/3 cells with lipopolysaccharide results in the degradation of IkappaB beta, followed by its subsequent resynthesis as a hypophosphorylated protein. This protein was shown to facilitate transport of a portion of NF-kappaB to the nucleus in a manner that protects it from cytosolic IkappaB alpha. We now demonstrate that the most abundant form of IkappaB beta in WEHI 231 cells is a hypophosphorylated protein. This hypophosphorylated IkappaB beta is found in a stable complex with NF-kappaB in the cytosol and is also detected in NF-kappaB DNA binding complexes in the nucleus. It is likely that hypophosphorylated IkappaB beta in WEHI 231 cells also protects NF-kappaB from IkappaB alpha, thus leading to the continuous nuclear import of this transcription factor.

Hypoxia, but not reoxygenation, induces interleukin 6 gene expression through NF-kappa B activation

Interleukin (IL) 6 is one of major mediators of inflammation, and IL-6 gene activation during hypoxia/reoxygenation has been implicated in the pathogenesis of ischemia/reperfusion injury. However, molecular events involved in IL-6 gene expression during hypoxia/reoxygenation remain to be identified. We have previously shown that NF-kappa B plays an essential and indispensable role in the transcriptional activation of the IL-6 gene induced by various stimuli, including IL-1 and tumor necrosis factor-alpha. We show here that hypoxia, but not reoxygenation, induces the activation of NF-kappa B through the degradation of a major inhibitor of NF-kappa B, I kappa B alpha. This hypoxia-induced NF-kappa B activation resulted in the kappa B-dependent transcriptional activation of the IL-6 gene. Interestingly, the time course of hypoxia-induced NF-kappa B activation was rather slow as compared with those of NF-kappa B activation induced by other stimuli, such as IL-1: a significant NF-kappa B activation was not observed before 1 hr of hypoxia treatment and persisted for up to 7 hr of hypoxia treatment. However, hypoxia-induced NF-kappa B activation was not inhibited by cycloheximide, which indicates that hypoxia directly triggers NF-kappa B activation. Furthermore, while hypoxia is unlikely to generate reactive oxygen intermediates, pretreatment of cells with antioxidants such as N-acetyl cysteine and alpha-tocopherol inhibited NF-kappa B activation induced by hypoxia. Thus, we discuss possible implications of these results for a postulated role of reactive oxygen intermediates in NF-kappa B activation.

Inhibition of NFkappaB activity through maintenance of IkappaBalpha levels contributes to dihydrotestosterone-mediated repression of the interleukin-6 promoter

Androgens repress expression of many genes, yet the mechanism of this activity has remained elusive. The cytokine, interleukin-6, is active in a variety of biological systems, and its expression is repressed by androgens. Accordingly we dissected the mechanism of androgen's ability to inhibit interleukin-6 expression at the molecular level. In a series of co-transfection assays, we found that 5alpha-dihydrotestosterone, through the androgen receptor, repressed activation of the interleukin-6 promoter, in part, by inhibiting NFkappaB activity. It did not appear that 5alpha-dihydrotestosterone inhibited NFkappaB by activating the androgen receptor to compete for the NFkappaB response element as we could not detect androgen receptor binding to the IL-6 promoter by DNase I footprinting assay. However, by electrophoretic mobility shift assay we found that 5alpha-dihydrotestosterone repressed formation of NFkappaB middle dotNFkappaB response element complex formation. In LNCaP prostate carcinoma cells, 5alpha-dihydrotestosterone achieved this effect through maintenance of IkappaBalpha protein levels in the face of phorbol ester, a stimulus that results in IkappaBalpha degradation. Finally, we confirmed that IkappaBalpha inhibits NFkappaB-mediated activation of the interleukin-6 promoter. These data suggest that maintenance of IkappaBalpha levels may represent the first identified mechanism for androgen-mediated repression of a natural androgen-regulated gene.

In vivo and in vitro expression of a non-mammalian cyclooxygenase-1

Unlike cyclooxygenase 2 (COX-2), COX-1 has never been identified, purified or cloned in a non-mammalian species. Here we report the RT-PCR cloning of a chicken cDNA that encodes the amphipathic membrane binding region and parts of the dimerization and catalytic domains of COX-1-like enzyme. Sequence comparison showed this putative COX-1 to be evolutionarily less conserved than COX-2. Furthermore, whereas COX-1 in mammals is broadly expressed in tissues as a constitutive enzyme, the mRNA detected by our clone in chicken was almost absent in tissues and embryo fibroblasts (CEF). Highest expression was in brain and seminal vesicle. This transcript was not detectable during chick embryogenesis and, as is the case for mammalian COX-1, was not induced above background by mitogen stimulation. The identification of an avian COX-1 shows that COX-1 and COX-2 existed as separate catalysts for prostaglandin synthesis before the divergence of birds and mammals.