The oncoprotein Bcl-3 directly transactivates through kappa B motifs via association with DNA-binding p50B homodimers

Thymic microenvironments for T-cell repertoire formation

Functionally competent immune system includes a functionally competent T-cell repertoire that is reactive to foreign antigens but is tolerant to self-antigens. The repertoire of T cells is primarily formed in the thymus through positive and negative selection of developing thymocytes. Immature thymocytes that undergo V(D)J recombination of T-cell antigen receptor (TCR) genes and that express the virgin repertoire of TCRs are generated in thymic cortex. The recent discovery of thymoproteasomes, a molecular complex specifically expressed in cortical thymic epithelial cells (cTEC), has revealed a unique role of cTEC in cuing the further development of immature thymocytes in thymic cortex, possibly by displaying unique self-peptides that induce positive selection. Cortical thymocytes that receive TCR-mediated positive selection signals are destined to survive for further differentiation and are induced to express CCR7, a chemokine receptor. Being attracted to CCR7 ligands expressed by medullary thymic epithelial cells (mTEC), CCR7-expressing positively selected thymocytes relocate to thymic medulla. The medullary microenvironment displays another set of unique self-peptides for trimming positively selected T-cell repertoire to establish self-tolerance, via promiscuous expression of tissue-specific antigens by mTEC and efficient antigen presentation by dendritic cells. Recent results demonstrate that tumor necrosis factor (TNF) superfamily ligands, including receptor activating NF-kappaB ligand (RANKL), CD40L, and lymphotoxin, are produced by positively selected thymocytes and pivotally regulate mTEC development and thymic medulla formation.

Abnormal tumor necrosis factor receptor I cell surface expression and NF-kappaB activation in tumor necrosis factor receptor-associated periodic syndrome

OBJECTIVE

Tumor necrosis factor receptor-associated periodic syndrome (TRAPS) is an autosomal-dominant autoinflammatory condition caused by mutations in the TNFRSF1A gene. The cellular mechanisms by which mutations in this gene trigger inflammation are currently unclear. Because NF-kappaB is the major intracellular signaling component inducing secretion of proinflammatory cytokines, we sought to determine whether differences in the clinical phenotype of patients with TRAPS may be attributable to variable effects of TNFRSF1A mutations on TNFRI expression, localization, or NF-kappaB activity.

METHODS

Peripheral blood mononuclear cells were obtained from patients (following informed consent), and cellular nuclear and cytosolic fractions were generated by subcellular fractionation. Localization of IkappaBalpha and NF-kappaB was determined by Western blotting of the resultant fractions. NF-kappaB subunit activity was determined by enzyme-linked immunosorbent assay analysis and confirmed by electrophoretic mobility shift assay. Subcellular localization of TNFRI was determined by immunofluorescence confocal microscopy or by immunoblotting following affinity isolation of plasma membrane by subcellular fractionation.

RESULTS

Cells from patients with the fully penetrant C73R mutation had marked activation of the proinflammatory p65 subunit of NF-kappaB. In contrast, cells from patients with the low-penetrant R92Q mutation displayed high levels of DNA binding by the p50 subunit, an interaction previously linked to repression of inflammation. Interestingly, although cells from patients with the C73R mutation have no TNFRI shedding defect, there was nonetheless an unusually high concentration of functional TNFRI at the plasma membrane.

CONCLUSION

High levels of TNFRI at the cell surface in patients with the C73R mutation hypersensitizes cells to stimulation by TNF, leading to increased NF-kappaB p65 subunit activation and an exaggerated proinflammatory response.

Expression of nuclear factor-kappaB family proteins in hepatocellular carcinomas

PURPOSE

Nuclear factor-kappaB (NF-kappaB) has been shown to be abnormally activated in some human hepatocellular carcinomas (HCCs), but most studies of NF-kappaB in patient samples have focused on the p65 subunit. Recent information has implicated IkappaB family members (e.g. Bcl-3) as possible mediators of NF-kappaB activation. Therefore, we examined the expression of all NF-kappaB family members and downstream targets in HCC.

STUDY DESIGN

Archived HCCs from 30 patients were evaluated by immunohistochemistry for NF-kappaB family proteins, Bcl-3 and targets of NF-kappaB/IkappaB function. Results were validated by Western blotting in frozen paired HCC and adjacent normal tissue in a subset of cases.

RESULTS

NF-kappaB p50 and p52 subunits were frequently localized to tumor cell nuclei (40 and 48%), whereas p65 positivity was infrequent. Bcl-3 was overexpressed in 90% of tumor cell nuclei compared with 26% of adjacent non-neoplastic liver (p < 0.001).

CONCLUSIONS

Aberrant Bcl-3 nuclear expression occurs in the vast majority of HCCs compared with adjacent normal or cirrhotic liver tissue. Bcl-3 is known to interact with NF-kappaB p50 and p52 homodimers, and our study demonstrates very frequent nuclear colocalization of Bcl-3 and p50/p52, suggesting that the Bcl-3/p50 or Bcl-3/p52 interactions are important in HCC pathogenesis.

The latent membrane protein 1 (LMP1) encoded by Epstein-Barr virus induces expression of the putative oncogene Bcl-3 through activation of the nuclear factor-kappaB

The Epstein-Barr virus (EBV)-encoded oncoprotein latent membrane protein 1 (LMP1) has an essential role in B-lymphocyte transformation by the virus and is expressed in certain EBV-associated tumors and lymphoproliferative disorders. By using the Flp-In/TREx-inducible expression system, we introduced LMP1 into two human cell lines, Jurkat and HEK-293, and found that in both of them the putative cellular oncogene Bcl-3 is rapidly induced following the expression of LMP1. Bcl-3 was also induced in Ramos cells after in vitro EBV infection and after transfection with an LMP1 expression vector. This LMP1-induced Bcl-3 expression is considered to be mediated by the transcription factor NF-kappaB, because (1) deletion of a critical NF-kappaB-binding site in the Bcl-3 promoter abolished its responsiveness to LMP1, (2) an IkappaB mutant that specifically inhibits NF-kappaB activity suppressed the LMP1-induced activation of the Bcl-3 promoter, and (3) an LMP1 mutant lacking its effector domain CTAR2, required for the activation of NF-kappaB, is severely impaired in its ability to induce Bcl-3. Western blot analyses showed that all EBV-infected and LMP1-expressing lymphoid cell lines express Bcl-3. These results suggest the possibility that Bcl-3 is involved in the pathogenesis of certain EBV-associated malignancies and lymphoproliferative disorders.

Induction of epidermal growth factor receptor expression by Epstein-Barr virus latent membrane protein 1 C-terminal-activating region 1 is mediated by NF-kappaB p50 homodimer/Bcl-3 complexes

The Epstein-Barr virus (EBV) is associated with the development of numerous malignancies, including the epithelial malignancy nasopharyngeal carcinoma (NPC). The viral oncoprotein latent membrane protein 1 (LMP1) is expressed in almost all EBV-associated malignancies and has profound effects on gene expression. LMP1 acts as a constitutively active tumor necrosis factor receptor and activates multiple forms of the NF-kappaB family of transcription factors. LMP1 has two domains that both activate NF-kappaB. In epithelial cells, LMP1 C-terminal activating region 1 (CTAR1) uniquely activates p50/p50-, p50/p52-, and p65-containing complexes while CTAR2 activates canonical p50/p65 complexes. CTAR1 also uniquely upregulates the epidermal growth factor receptor (EGFR). In NPC, NF-kappaB p50/p50 homodimers and the transactivator Bcl-3 were detected on the EGFR promoter. In this study, the role of NF-kappaB p50 and Bcl-3 in LMP1-mediated upregulation of EGFR was analyzed. In LMP1-CTAR1-expressing cells, chromatin immunoprecipitation detected p50 and Bcl-3 on the NF-kappaB consensus sites within the egfr promoter. Transient overexpression of p50 and Bcl-3 increased EGFR expression, confirming the regulation of EGFR by these factors. Treatment with p105/p50 siRNA effectively reduced p105/p50 levels but unexpectedly increased Bcl-3 expression and levels of p50/Bcl-3 complexes, resulting in increased EGFR expression. These data suggest that induction of p50/p50/Bcl-3 complexes by LMP1 CTAR1 mediates LMP1-induced EGFR upregulation and that formation of the p50/p50/Bcl-3 complex is negatively regulated by the p105 precursor. The distinct forms of NF-kappaB that are induced by LMP1 CTAR1 likely activate distinct cellular genes.

NF-kappa B p50/p65 affects the frequency of Ly49 gene expression by NK cells

In mice, acquisition of Ly49 receptors characterizes one of the developmental stages of NK cells. We previously described a novel Ly49 promoter, Pro1, involved in Ly49 gene regulation in immature NK cells. Pro1 transcriptional activity requires a NF-kappaB binding site; however, only NF-kappaB/p50 binding to this element was observed. Cotransfection of NF-kappaB/p65 with Ly49g Pro1 in LNK cells induced a decrease in the transcriptional activity of the core promoter. Moreover, decreasing NF-kappaB/p65 protein expression by RNA interference increases Pro1 transcriptional activity. A high rate of NF-kappaB/p65 degradation in LNK cells correlates with Pro1 activity, since treatment with the proteasome inhibitor MG132 increased levels of NF-kappaB/p65 protein and decreased Pro1 activity. In addition, analysis of the Ly49 repertoire in NF-kappaB/p50 null mice reveals a decrease in the proportion of NK cells expressing a given Ly49 molecule. The defect in Ly49 expression is observed in the bone marrow and the spleen with a similar altered pattern of developmental stages in each tissue. The frequency of Ly49 expression in NF-kappaB/p52 null mice is slightly increased, indicating the specific role of NF-kappaB/p50 in Ly49 gene activation. These results suggest that NF-kappaB p50/p65 plays a major role in the initiation of Ly49 gene expression in NK cells.

Despite inhibition of nuclear localization of NF-kappa B p65, c-Rel, and RelB, 17-beta estradiol up-regulates NF-kappa B signaling in mouse splenocytes: the potential role of Bcl-3

NF-kappaB plays a major role in regulating the immune system. Therefore, alterations in NF-kappaB activity have profound effects on many immunopathologies, including inflammation, autoimmunity, and lymphoid neoplasia. We investigated the effects of estrogen (17beta-estradiol) on NF-kappaB in C57BL/6 mice since estrogen is a natural immunomodulator and we have recently reported that estrogen up-regulates several NF-kappaB-regulated proteins (inducible NO synthase, IFN-gamma, and MCP-1). We found that in vivo estrogen treatment had differential effects on NF-kappaB family members. Estrogen profoundly blocked the nuclear translocation of p65, c-Rel, and Rel-B, partially blocked p52, but permitted translocation of p50. Despite blockade of both the classical (p65/p50) and alternative (RelB/p52) NF-kappaB activation pathways, estrogen induced constitutive NF-kappaB activity and increased the levels of cytokines regulated by NF-kappaB (IL-1 alpha, IL-1 beta, IL-10, and IFN-gamma). Studies involving a NF-kappaB inhibitor confirmed a positive regulatory role of NF-kappaB on these cytokines. Remarkably, estrogen selectively induced B cell lymphoma 3 (Bcl-3), which is known to associate with p50 to confer transactivation capabilities, thereby providing a potential link between observed p50 DNA-binding activity and estrogen up-regulation of NF-kappaB transcriptional activity. Chromatin immunoprecipitation assays confirmed that Bcl-3 bound to the promoter of the NF-kappaB-regulated inducible NO synthase gene in cells from estrogen-treated mice. Estrogen appeared to act at the posttranscriptional level to up-regulate Bcl-3 because mRNA levels in splenocytes from placebo- and estrogen-treated mice were comparable. The novel findings of differential regulation of NF-kappaB proteins by estrogen provide fresh insight into potential mechanisms by which estrogen can regulate NF-kappaB-dependent immunological events.

A role for the IkappaB family member Bcl-3 in the control of central immunologic tolerance

Bcl-3 is a member of the family of IkappaB inhibitors. Unlike the classical, cytoplasmic IkappaBs, Bcl-3 does not inhibit RelA- or c-Rel-containing NF-kappaB transcription factor dimers. Instead, Bcl-3 can enter the nucleus and modulate NF-kappaB activity, although the underlying mechanism and physiologic function remain largely unknown. Here we identified Bcl-3 as a regulator of immunologic tolerance to self. In parallel with NF-kappaB2, Bcl-3 functions within stroma to generate medullary thymic epithelial cells, which are essential for negative selection of autoreactive T cells. Loss of both NF-kappaB2 and Bcl-3, but not either one alone, led to a profound breakdown in central tolerance resulting in rapid and fatal multiorgan inflammation. These data reveal extensive utilization of the NF-kappaB system to promote central tolerance in the thymus, in apparent contrast with the well-known roles of NF-kappaB to promote inflammation and autoimmunity in the periphery.

Crucial roles of binding sites for NF-kappaB and C/EBPs in IkappaB-zeta-mediated transcriptional activation

IkappaB-zeta [inhibitor of NF-kappaB (nuclear factor kappaB) zeta] is a nuclear protein that is induced upon stimulation of TLRs (Toll-like receptors) and IL (interleukin)-1 receptor. IkappaB-zeta harbours C-terminal ankyrin repeats that interact with NF-kappaB. Our recent studies have shown that, upon stimulation, IkappaB-zeta is essential for the induction of a subset of inflammatory genes, represented by IL-6, whereas it inhibits the expression of TNF (tumour necrosis factor)-alpha. In the present study, we investigated mechanisms that determine the different functions of IkappaB-zeta. We found that co-expression of IkappaB-zeta and the NF-kappaB subunits synergistically activates transcription of the hBD-2 (human beta-defensin 2) and NGAL (neutrophil gelatinase-associated lipocalin) genes, whereas it inhibits transcription of E-selectin. Reporter analyses indicated that, in addition to an NF-kappaB-binding site, a flanking C/EBP (CCAAT/enhancer-binding protein)-binding site in the promoters is essential for the IkappaB-zeta-mediated transcriptional activation. Using an artificial promoter consisting of the NF-kappaB- and C/EBP-binding sites, transcriptional activation was observed upon co-transfection with IkappaB-zeta and NF-kappaB, indicating that these sequences are minimal elements that confer the IkappaB-zeta-mediated transcriptional activation. Chromatin immunoprecipitation assays and knockdown experiments showed that both IkappaB-zeta and the NF-kappaB subunits were recruited to the NGAL promoter and were essential for the transcriptional activation of the hBD-2 and NGAL promoters on stimulation with IL-1beta. The activation of the NGAL promoter by transfection of IkappaB-zeta and NF-kappaB was suppressed in C/EBPbeta-depleted cells. Thus IkappaB-zeta acts as an essential transcriptional activator by forming a complex with NF-kappaB on promoters harbouring the NF-kappaB- and C/EBP-binding sites, upon stimulation of TLRs or IL-1 receptor.

Transcriptional regulation of parathyroid hormone-related protein promoter P2 by NF-kappaB in adult T-cell leukemia/lymphoma

Parathyroid hormone-related protein (PTHrP) plays a primary role in the development of humoral hypercalcemia of malignancy (HHM) that occurs in the majority of patients with adult T-cell leukemia/lymphoma (ATLL) due to human T-cell lymphotropic virus type-1 (HTLV-1) infection. We previously showed that ATLL cells constitutively express high levels of PTHrP via activation of promoters P2 and P3, resulting in HHM. In this study, we characterized a nuclear factor-kappaB (NF-kappaB) binding site in the P2 promoter of human PTHrP. Using electrophoretic mobility shift assays, we detected a specific complex in Tax-expressing human T cells composed of p50/c-Rel, and two distinct complexes in ATLL cells consisting of p50/p50 homodimers and a second unidentified protein(s). Chromatin immunoprecipitation assays confirmed in vivo binding of p50 and c-Rel on the PTHrP P2 promoter. Using transient co-transfection with NF-kappaB expression plasmids and PTHrP P2 luciferase reporter-plasmid, we showed that NF-kappaB p50/p50 alone and p50/c-Rel or p50/Bcl-3 cooperatively upregulated the PTHrP P2 promoter. Furthermore, inhibition of NF-kappaB activity by Bay 11-7082 reduced PTHrP P2 promoter-initiated transcripts in HTLV-1-infected T cells. In summary, the data demonstrated that transcriptional regulation of PTHrP in ATLL cells can be controlled by NF-kappaB activation and also suggest a Tax-independent mechanism of activation of PTHrP in ATLL.

BCL3 acts as a negative regulator of transcription from the human T-cell leukemia virus type 1 long terminal repeat through interactions with TORC3

By associating with cyclic AMP-responsive element-binding protein (CREB), the human T-cell leukemia virus type 1 (HTLV-1) Tax protein activates transcription from the HTLV-1 long terminal repeat (LTR), which contains multiple cyclic AMP-responsive elements. The transducers of regulated CREB activity (TORCs) were a recently identified family of CREB co-activators that bind to CREB to enhance CRE-mediated transcription. TORC3, a TORC family protein, dramatically enhances Tax-mediated transcription from the LTR. In this study, we performed a yeast two-hybrid screen using the N-terminal region of TORC3 as bait and identified B-cell chronic lymphatic leukemia protein 3 (BCL3) as a protein interacting with TORC3. This interaction was confirmed by glutathione S-transferase pulldown assays and co-immunoprecipitation experiments with detection by Western blotting. The ankyrin repeat domain of BCL3 interacted with TORC3. By using a luciferase assay, we determined that BCL3 inhibited transcription from the HTLV-1 LTR in a manner dependent on TORC3. Knockdown of endogenous BCL3 using RNA interference enhanced transcriptional activation of CRE. Treatment with trichostatin A, a potent inhibitor of the transcriptional co-repressor HDAC, partially reversed the inhibitory effect of BCL3. These results suggest that BCL3 functions as a repressor of HTLV-1 LTR-mediated transcription through interactions with TORC3. In addition to stimulating transcription from the HTLV-1 LTR, Tax also enhances BCL3 expression; thus, transcription from the LTR is regulated by both positive and negative feedback mechanisms.

Bortezomib induces apoptosis of Epstein-Barr virus (EBV)-transformed B cells and prolongs survival of mice inoculated with EBV-transformed B cells

Bortezomib, an inhibitor of the 26S proteasome, is currently approved for treatment of multiple myeloma and is being studied for therapy of non-Hodgkin's lymphoma. We found that Epstein-Barr virus (EBV)-positive B cells with type III latency were more susceptible to killing by bortezomib than those with type I latency. Bortezomib induced apoptosis of EBV lymphoblastoid cell lines (LCLs) by inducing cleavage of caspases 8 and 9; apoptosis was inhibited by pretreatment with a pan-caspase inhibitor. Bortezomib reduced the levels of the p50 and p65 components of the canonical NF-kappaB pathway and reduced the level of p52 in the noncanonical NF-kappaB pathway, which is induced by EBV LMP1. Bortezomib inhibited expression of cIAP-1, cIAP-2, and XIAP, which are regulated by NF-kappaB and function as inhibitors of apoptosis. Bortezomib did not inhibit expression of several other antiapoptotic proteins, including Bcl-2 and Bcl-XL. Finally, bortezomib significantly prolonged the survival of severe combined immunodeficiency mice inoculated with LCLs. These findings suggest that bortezomib may represent a novel strategy for the treatment of certain EBV-associated lymphomas.

Alteration of NF-kappaB activity leads to mitochondrial apoptosis after infection with pathological prion protein

Nuclear factor kappa B (NF-kappaB) is a key regulator of the immune response, but in almost the same manner it is involved in induction of inflammation, proliferation and regulation of apoptosis. In the central nervous system activated NF-kappaB plays a neuroprotective role. While in some neurodegenerative disorders the role of NF-kappaB is well characterized, there is poor knowledge on the role of NF-kappaB in prion disease. We found binding but no transcriptional activity of the transcription factor in vitro. Characterizing the mechanism of cell death after infection with pathological prion protein increased caspase-9 and caspase-3 activity was detected and the lack of NF-kappaB activity resulted in the inability to activate target genes that usually play an important role in neuroprotection. Additionally, we investigated the role of NF-kappaB after prion infection of Nfkb1(-/-), Nfkb2(-/-) and Bcl3(-/-) mice and central nervous system-specific p65-deleted mice revealing an accelerated prion disease in NF-kappaB2- and Bcl-3-deficient mice, which is in line with a reduced neuroprotective activity in prion infection. Based on our findings, we propose a model whereby the alteration of NF-kappaB activity at the early stages of infection with pathological prion protein leads to neuronal cell death mediated by mitochondrial apoptosis.

Diversity and regulation in the NF-kappaB system

The nuclear factor (NF)-kappaB family of transcription factors is a key participant in multiple biological processes, most notably in the immune and inflammatory response. Five proteins make up the NF-kappaB family, and these proteins can hetero- and homo-dimerize, giving rise to diversity. Recently, it has been shown that certain members can also interact directly with other transcription factors such as signal transducers of activated transcription, interferon regulatory factor family members and p53, providing further diversity. We propose that this promiscuity might help explain the many of roles of NF-kappaB in specialized cell function and fate. Furthermore, the state of a cell and its cellular background in addition to overall promoter structure and variations in the kappaB target sequence will all define the composition and activity of multimeric NF-kappaB complexes.

NF-kappa B as a therapeutic target in neurodegenerative diseases

NF-kappaB is a transcription factor that regulates numerous physiological functions, and that is involved in the pathogenesis of various diseases. In the nervous system there is evidence supporting a dual role of NF-kappaB in neurodegenerative diseases; activation of NF-kappaB in neurons promotes their survival, whereas activation in glial and immune cells mediates pathological inflammatory processes. The reason for such a dichotomy lies in the complexity of the NF-kappaB system. Emerging research has begun to dissect the pathways leading to the activation of the different NF-kappaB proteins, and the gene targets of NF-kappaB, in cells of the nervous system. In this article the authors discuss recent findings concerning the roles of NF-kappaB in the pathogenesis of several neurodegenerative disorders, and its potential as a pharmaceutical target for these disorders.

NF-kappaB activation in development and progression of cancer

Nuclear factor-kappaBeta (NF-kappaB) binds specifically to NF-kappaB-binding sites (kappaB sites, 5'-GGGRNNYYCC-3'; R, purine; Y, pyrimidine; N, any nucleotide) present in enhancer regions of various genes. Binding of various cytokines, growth factors and pathogen-associated molecular patterns to specific receptors activates NF-kappaB and expression of genes that play critical roles in inflammation, innate and acquired immunity, bone remodeling and generation of skin appendices. Activation of NF-kappaB is also involved in cancer development and progression. NF-kappaB is activated in cells that become malignant tumors and in cells that are recruited to and constitute the tumor microenvironment. In the latter scenario, the TLR-TRAF6-NF-kB pathways seem to play major roles, and NF-kappaB activation results in production of cytokines, which in turn induce NF-kappaB activation in premalignant cells, leading to expression of genes involved abnormal growth and malignancy. Furthermore, NF-kappaB activation is involved in bone metastasis. Osteoclasts, whose generation requires the RANK-TRAF6-NF-kappaB pathways, release various growth factors stored in bone, which results in creation of microenvironment suitable for proliferation and colonization of cancer cells. Therefore, NF-kappaB and molecules involved its activation, such as TRAF6, are attractive targets for therapeutic strategies against cancer.

mTOR-dependent synthesis of Bcl-3 controls the retraction of fibrin clots by activated human platelets

New activities of human platelets continue to emerge. One unexpected response is new synthesis of proteins from previously transcribed RNAs in response to activating signals. We previously reported that activated human platelets synthesize B-cell lymphoma-3 (Bcl-3) under translational control by mammalian target of rapamycin (mTOR). Characterization of the ontogeny and distribution of the mTOR signaling pathway in CD34+ stem cell-derived megakaryocytes now demonstrates that they transfer this regulatory system to developing proplatelets. We also found that Bcl-3 is required for condensation of fibrin by activated platelets, demonstrating functional significance for mTOR-regulated synthesis of the protein. Inhibition of mTOR by rapamycin blocks clot retraction by human platelets. Platelets from wild-type mice synthesize Bcl-3 in response to activation, as do human platelets, and platelets from mice with targeted deletion of Bcl-3 have defective retraction of fibrin in platelet-fibrin clots mimicking treatment of human platelets with rapamycin. In contrast, overexpression of Bcl-3 in a surrogate cell line enhanced clot retraction. These studies identify new features of post-transcriptional gene regulation and signal-dependant protein synthesis in activated platelets that may contribute to thrombus and wound remodeling and suggest that posttranscriptional pathways are targets for molecular intervention in thrombotic disorders.

Salicylate-based anti-inflammatory drugs inhibit the early lesion of diabetic retinopathy

It has been previously reported that aspirin inhibited the development of diabetic retinopathy in diabetic animals, raising the possibility that anti-inflammatory drugs may have beneficial effects on diabetic retinopathy. To further explore this, we compared effects of oral consumption of three different salicylate-based drugs (aspirin, sodium salicylate, and sulfasalazine) on the development of early stages of diabetic retinopathy in rats. These three drugs differ in their ability to inhibit cyclooxygenase but share an ability to inhibit nuclear factor-kappaB (NF-kappaB). Diabetes of 9-10 months duration significantly increased the number of TUNEL (transferase-mediated dUTP nick-end labeling)-positive capillary cells and acellular (degenerate) capillaries in the retinal vasculature, and all three salicylate-based drugs inhibited this cell death and formation of acellular capillaries without altering the severity of hyperglycemia. In short-term diabetes (2-4 months), all three salicylates inhibited the diabetes-induced loss of neuronal cells from the ganglion cell layer. Oral aspirin (as a representative of the salicylate family) inhibited diabetes-induced increase in NF-kappaB DNA-binding affinity in electrophoretic mobility shift assay and transcription factor array in nuclear extract isolated from whole retina. All three salicylates inhibited the diabetes-induced translocation of p50 (a subunit of NF-kappaB) into nuclei of retinal vascular endothelial cells of the isolated retinal vasculature, as well as of p50 and p65 into nuclei of cells in the ganglion cell layer and inner nuclear layer on whole-retinal sections. Sulfasalazine (also as a representative of the salicylates) inhibited the diabetes-induced upregulation of several inflammatory gene products, which are regulated by NF-kappaB, including vascular cell adhesion molecule, intracellular adhesion molecule-1, inducible nitric oxide synthase, and cyclooxygenase-2 in whole-retinal lysate. Salicylates, in doses administrated in our experiments, inhibited NF-kappaB and perhaps other transcription factors in the retina, were well tolerated, and offered new tools to investigate and inhibit the development of diabetic retinopathy.

p50 nuclear factor-kappaB overexpression in tumor-associated macrophages inhibits M1 inflammatory responses and antitumor resistance

Tumor-associated macrophages (TAM) are a major inflammatory infiltrate in tumors and a major component of the protumor function of inflammation. TAM in established tumors generally have an M2 phenotype with defective production of interleukin-12 (IL-12) and high IL-10. Here, we report that defective responsiveness of TAM from a murine fibrosarcoma and human ovarian carcinoma to M1 activation signals was associated with a massive nuclear localization of the p50 nuclear factor-kappaB (NF-kappaB) inhibitory homodimer. p50 overexpression inhibited IL-12 expression in normal macrophages. TAM isolated from p50(-/-) mice showed normal production of M1 cytokines, associated with reduced growth of transplanted tumors. Bone marrow chimeras showed that p50 inactivation in hematopoietic cells was sufficient to result in reduced tumor growth. Thus, p50 NF-kappaB overexpression accounts for the inability of TAM to mount an effective M1 antitumor response capable of inhibiting tumor growth.

NFkappaB1/p50 is not required for tumor necrosis factor-stimulated growth of primary mammary epithelial cells: implications for NFkappaB2/p52 and RelB

Nuclear factor kappaB (NFkappaB) plays an important role in mammary gland development and breast cancer. We previously demonstrated that TNF stimulates growth of mammary epithelial cells (MEC) in a physiologically relevant three-dimensional primary culture system, accompanied by enhanced DNA-binding of the NFkappaB p50 homodimer. To further understand the mechanism of TNF-stimulated growth of primary MEC, the requirement for NFkappaB1/p50, and the role of cyclin D1 in TNF-stimulated growth were examined. TNF induced the formation of DNA-binding complexes of p50 and p52 with their coactivator bcl3 in MEC nuclear extracts. Concomitantly, TNF increased the binding of NFkappaB proteins to the kappaB site on the cyclin D1 promoter, and increased expression of cyclin D1 mRNA and protein. Using MEC from p50 null mice, we found that p50 was not required for TNF-induced growth nor for up-regulation of cyclin D1. However, TNF induced a p52/RelB NFkappaB DNA-binding complex in p50 null MEC nuclear extracts. In addition, we found that in wild-type MEC, TNF stimulated the occupancy of p52 and RelB on the cyclin D1 promoter kappaB site, whereas p50 was present constitutively. These data suggest that in wild-type MEC, TNF stimulates the interaction of bcl3 with p50 and p52, and the binding of p52, as well as RelB, to cyclin D1 promoter kappaB sites, and as a consequence, stimulates the growth of MEC. In the absence of p50, p52 and RelB can compensate for p50 in TNF-stimulated growth and cyclin D1 induction in MEC.

Two novel transcripts encoding two Ankyrin repeat containing proteins have preponderant expression during the mouse spermatogenesis

The clone 4921537P18 expressed preponderantly in mouse testis was identified by screening the Riken cDNA database, and two new full-length isoforms of this clone, which were named gsarp1 (Gonad Specific Ankyrin Repeat (ANK) Protein 1) and gsarp2, were found and isolated from mouse testis in the course of the research. Both of the GSARP1 and GSARP2 contain an ANK region circular composed by seven ANKs, and their structural feature is very similar to that of the IkappaB family proteins, while IkappaB proteins associate with the transcription factor NF-kappaB via their ANKs in the NF-kappaB pathway. We investigated the expression pattern at the mRNA level by Reverse transcription PCR. The gsarp1 has high expression level in mouse testis, while has low expression level in the ovary, and the gsarp2 is only expressed in mouse testis. The gsarp1 and gsarp2 begin to be detected at the early and later pachytene stage of meiosis separately, while both have high-expression level at the stage of MI and MII. The result of in situ hybridization reveals that the gsarp1 is primarily expressed in spermatocytes, while gsarp2 is expressed in spermatocytes and spermatids. In view of the structural feature and expression pattern of the GSARP1 and GSARP2, we speculate that they may play a certain role in a signal pathway of meiosis.

Mutations in the NF-kappaB signaling pathway: implications for human disease

The nuclear factor-kappa B (NF-kappaB) signaling pathway is a multi-component pathway that regulates the expression of hundreds of genes that are involved in diverse and key cellular and organismal processes, including cell proliferation, cell survival, the cellular stress response, innate immunity and inflammation. Not surprisingly, mis-regulation of the NF-kappaB pathway, either by mutation or epigenetic mechanisms, is involved in many human and animal diseases, especially ones associated with chronic inflammation, immunodeficiency or cancer. This review describes human diseases in which mutations in the components of the core NF-kappaB signaling pathway have been implicated and discusses the molecular mechanisms by which these alterations in NF-kappaB signaling are likely to contribute to the disease pathology. These mutations can be germline or somatic and include gene amplification (e.g., REL), point mutations and deletions (REL, NFKB2, IKBA, CYLD, NEMO) and chromosomal translocations (BCL-3). In addition, human genetic diseases are briefly described wherein mutations affect protein modifiers or transducers of NF-kappaB signaling or disrupt NF-kappaB-binding sites in promoters/enhancers.

Regulation and function of IKK and IKK-related kinases

Members of the nuclear factor kappa B (NF-kappaB) family of dimeric transcription factors (TFs) regulate expression of a large number of genes involved in immune responses, inflammation, cell survival, and cancer. NF-kappaB TFs are rapidly activated in response to various stimuli, including cytokines, infectious agents, and radiation-induced DNA double-strand breaks. In nonstimulated cells, some NF-kappaB TFs are bound to inhibitory IkappaB proteins and are thereby sequestered in the cytoplasm. Activation leads to phosphorylation of IkappaB proteins and their subsequent recognition by ubiquitinating enzymes. The resulting proteasomal degradation of IkappaB proteins liberates IkappaB-bound NF-kappaB TFs, which translocate to the nucleus to drive expression of target genes. Two protein kinases with a high degree of sequence similarity, IKKalpha and IKKbeta, mediate phosphorylation of IkappaB proteins and represent a convergence point for most signal transduction pathways leading to NF-kappaB activation. Most of the IKKalpha and IKKbeta molecules in the cell are part of IKK complexes that also contain a regulatory subunit called IKKgamma or NEMO. Despite extensive sequence similarity, IKKalpha and IKKbeta have largely distinct functions, due to their different substrate specificities and modes of regulation. IKKbeta (and IKKgamma) are essential for rapid NF-kappaB activation by proinflammatory signaling cascades, such as those triggered by tumor necrosis factor alpha (TNFalpha) or lipopolysaccharide (LPS). In contrast, IKKalpha functions in the activation of a specific form of NF-kappaB in response to a subset of TNF family members and may also serve to attenuate IKKbeta-driven NF-kappaB activation. Moreover, IKKalpha is involved in keratinocyte differentiation, but this function is independent of its kinase activity. Several years ago, two protein kinases, one called IKKepsilon or IKK-i and one variously named TBK1 (TANK-binding kinase), NAK (NF-kappaB-activated kinase), or T2K (TRAF2-associated kinase), were identified that exhibit structural similarity to IKKalpha and IKKbeta. These protein kinases are important for the activation of interferon response factor 3 (IRF3) and IRF7, TFs that play key roles in the induction of type I interferon (IFN-I). Together, the IKKs and IKK-related kinases are instrumental for activation of the host defense system. This Review focuses on the functions of IKK and IKK-related kinases and the molecular mechanisms that regulate their activities.

IkappaB kinase epsilon interacts with p52 and promotes transactivation via p65

The members of the NF-kappaB transcription factor family are key regulators of gene expression in the immune response. Different combinations of NF-kappaB subunits not only diverge in timing to induce transcription but also recognize varying sequences of the NF-kappaB-binding site of their target genes. The p52 subunit is generated as a result of processing of NF-kappaB2 p100. Here, we demonstrate that the non-canonical IkappaB kinase epsilon (IKKepsilon) directly interacts with p100. In a transactivation assay, IKKepsilon promoted the ability of p52 to transactivate gene expression. This effect was indirect, requiring p65, which was shown to be part of the IKKepsilon-p52 complex and to be phosphorylated by IKKepsilon. These novel interactions reveal a hitherto unknown function of IKKepsilon in the regulation of the alternative NF-kappaB activation pathway involving p52 and p65.

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.

The alternative NF-kappaB pathway from biochemistry to biology: pitfalls and promises for future drug development

The past two decades have led to a tremendous work on the transcription factor NF-kappaB and its molecular mechanisms of activation. The nuclear translocation of NF-kappaB is controlled by two main pathways: the classical and the alternative NF-kappaB pathways. The classical NF-kappaB pathway activates the IKK complex that controls the inducible degradation of most IkappaB family members that are IkappaBalpha, IkappaBbeta, IkappaBvarepsilon and p105. The alternative NF-kappaB pathway induces p100 processing and p52 generation through the activation of at least two kinases, which are NIK and IKKalpha. Genetic studies have shown that IKKgamma is dispensable for the alternative pathway, which suggests the existence of an alternative IKKalpha-containing complex. It is noteworthy that activation of particular p52 heterodimers like p52/RelB requires solely the alternative pathway while activation of p52/p65 or p52/c-Rel involves a "hybrid pathway". Among others, LTbetaR, BAFF-R, CD40 and RANK have the ability to induce the alternative pathway. The latter plays some roles in biological functions controlled by these receptors, which are the development of secondary lymphoid organs, the proliferation, survival and maturation of B cell, and the osteoclastogenesis. Exacerbated activation of the alternative pathway is potentially associated to a wide range of disorders like rheumatoid arthritis, ulcerative colitis or B cell lymphomas. Therefore, inhibitors of the alternative pathway could be valuable tools for the treatment of inflammatory disorders and cancers.

Extending the nuclear roles of IkappaB kinase subunits

The transcription factor NF-kappaB plays a key role in a wide variety of cellular processes such as innate and adaptive immunity, cellular proliferation, apoptosis and development. In unstimulated cells, NF-kappaB is sequestered in the cytoplasm through its tight association with inhibitory proteins called IkappaBs, comprising notably IkappaBalpha. A key step in NF-kappaB activation is the phosphorylation of IkappaBalpha by the so-called IkappaB kinase (IKK) complex, which targets the inhibitory protein for proteasomal degradation and allows the freed NF-kappaB to enter the nucleus where it can transactivate its target genes. The IKK complex is composed of two catalytic subunits called IKKalpha and IKKbeta, and a regulatory subunit called NEMO/IKKgamma. Despite their key role in mediating IkappaBalpha phosphorylation in the cytoplasm, recent works have provided evidence that IKK subunits also translocate into the nucleus to regulate NF-kappaB-dependent and -independent gene expression, paving the way of a novel and exciting field of research. In this review, we will describe the current knowledge in that research area.

Deregulated NF-kappaB activity in haematological malignancies

The NF-kappaB family of transcription factors plays key roles in the control of cell proliferation and apoptosis. Constitutive NF-kappaB activation is a common feature for most haematological malignancies and is therefore believed to be a crucial event for enhanced proliferation and survival of these malignant cells. In this review, we will describe the molecular mechanisms underlying NF-kappaB deregulation in haematological malignancies and will highlight what is still unclear in this field, 20 years after the discovery of this transcription factor.

Cyld inhibits tumor cell proliferation by blocking Bcl-3-dependent NF-kappaB signaling

Mutations in the CYLD gene cause tumors of hair-follicle keratinocytes. The CYLD gene encodes a deubiquitinase that removes lysine 63-linked ubiquitin chains from TRAF2 and inhibits p65/p50 NF-kappaB activation. Here we show that mice lacking Cyld are highly susceptible to chemically induced skin tumors. Cyld-/- tumors and keratinocytes treated with 12-O-tetradecanoylphorbol-13 acetate (TPA) or UV light are hyperproliferative and have elevated cyclin D1 levels. The cyclin D1 elevation is caused not by increased p65/p50 action but rather by increased nuclear activity of Bcl-3-associated NF-kappaB p50 and p52. In Cyld+/+ keratinocytes, TPA or UV light triggers the translocation of Cyld from the cytoplasm to the perinuclear region, where Cyld binds and deubiquitinates Bcl-3, thereby preventing nuclear accumulation of Bcl-3 and p50/Bcl-3- or p52/Bcl-3-dependent proliferation. These data indicate that, depending on the external signals, Cyld can negatively regulate different NF-kappaB pathways; inactivation of TRAF2 controls survival and inflammation, while inhibition of Bcl-3 controls proliferation and tumor growth.

BCL3 is induced by IL-6 via Stat3 binding to intronic enhancer HS4 and represses its own transcription

BCL3 is a proto-oncogene affected by chromosomal translocations in some patients with chronic lymphocytic leukemia. It is an IkappaB family protein that is involved in transcriptional regulation of a number of NF-kappaB target genes. In this study, interleukin (IL)-6-induced BCL3 expression and its effect on survival of multiple myeloma (MM) cells were examined. We demonstrate the upregulation of BCL3 by IL-6 in INA-6 and other MM cell lines. Sequence analysis of the BCL3 gene locus revealed four potential signal transducer and activator of transcription (Stat) binding sites within two conserved intronic enhancers regions: one located within enhancer HS3 and three within HS4. Chromatin immunoprecipitation experiments showed increased Stat3 binding to both enhancers upon IL-6 stimulation. Silencing Stat3 expression by small interfering RNA (siRNA) abrogated BCL3 expression by IL-6. Using reporter gene assays, we demonstrate that BCL3 transcription depends on HS4. Mutation of the Stat motifs within HS4 abolished IL-6-dependent BCL3 induction. Furthermore, BCL3 transcription was inhibited by its own gene product. This repressive feedback is mediated by NF-kappaB sites within the promoter and HS3. Finally, we show that overexpression of BCL3 increases apoptosis, whereas BCL3-specific siRNA does not affect the viability of INA-6 cells suggesting that BCL3 is not essential for the survival of these cells.

NF-kappaB modulation and ionizing radiation: mechanisms and future directions for cancer treatment

NF-kappaB transcription factor regulates important cellular processes ranging from establishment of the immune and inflammatory responses to regulation of cell proliferation or apoptosis, through the induction of a large array of target genes. NF-kappaB is now considered as an important actor in the tumorigenic process mainly because it exerts strong anti-apoptotic functions in cancer cells. NF-kappaB is triggered by chimio- and radio-therapeutic strategies that are intended to eliminate cancerous cells through induction of apoptosis. Numerous studies have demonstrated that inhibition of NF-kappaB by different means increased sensitivity of cancer cells to the apoptotic action of diverses effectors such as TNFalpha or chemo- or radio-therapies. From these studies as emerged the concept that NF-kappaB blockade could be associated to conventional therapies in order to increase their efficiency. This review focuses on the current knowledge on NF-kappaB regulation and discusses the therapeutic potential of targeting NF-kappaB in cancer in particular during radiotherapy.

A novel member of the IkappaB family, human IkappaB-zeta, inhibits transactivation of p65 and its DNA binding

A novel member of the IkappaB family, human IkappaB-zeta, was identified by a differential screening approach of apoptosis-sensitive and -resistant tumor cells. The protein consists of 6 ankyrin repeats at its COOH terminus and shares about 30% identity with other IkappaB members. IkappaB-zeta associates with both the p65 and p50 subunit of NF-kappaB and inhibits the transcriptional activity as well as the DNA binding of the transcription factor. Interestingly, IkappaB-zeta is localized in the nucleus where it aggregates in matrix-associated deacetylase bodies, indicating that IkappaB-zeta regulates nuclear NF-kappaB activity rather than its nuclear translocation from the cytoplasm. IkappaB-zeta expression itself was regulated by NF-kappaB, suggesting that its activity is controlled in a negative feedback loop. Unlike classical IkappaB proteins, IkappaB-zeta was not degraded upon cell stimulation. Treatment with tumor necrosis factor-alpha, interleukin-1beta, and lipopolysaccharide induced a strong induction of IkappaB-zeta transcripts. Expression of IkappaB-zeta was detected in different tissues including lung, liver, and in leukocytes but not in the brain. Suppression of endogenous IkappaB-zeta by RNA interference rendered cells more resistant to apoptosis, whereas overexpression of IkappaB-zeta was sufficient to induce cell death. Our results, therefore, suggest that IkappaB-zeta functions as an additional regulator of NF-kappaB activity and, hence, provides another control level for the activation of NF-kappaB-dependent target genes.

Expression of the Bcl-3 proto-oncogene suppresses p53 activation

While Bcl-3 expression in cancer was originally thought to be limited to B-cell lymphomas with a 14;19 chromosomal translocation, more recent evidence indicates that expression of this presumptive oncoprotein is significantly more widespread in cancer. However, an oncogenic role for Bcl-3 has not been clearly identified. Experiments presented here indicate that Bcl-3 is inducible by DNA damage and is required for the induction of Hdm2 gene expression and the suppression of persistent p53 activity. Furthermore, constitutive expression of Bcl-3 suppresses DNA damage-induced p53 activation and inhibits p53-induced apoptosis through a mechanism that is at least partly dependent on the up-regulation of Hdm2. The results provide insight into a mechanism whereby altered expression of Bcl-3 leads to tumorigenic potential. Since Bcl-3 is required for germinal center formation, these results suggest functional similarities with the unrelated Bcl-6 oncoprotein in suppressing potential p53-dependent cell cycle arrest and apoptosis in response to somatic hypermutation and class switch recombination.

Notch1 augments NF-kappaB activity by facilitating its nuclear retention

Notch1 specifically upregulates expression of the cytokine interferon-gamma in peripheral T cells through activation of NF-kappaB. However, how Notch mediates NF-kappaB activation remains unclear. Here, we examined the temporal relationship between Notch signaling and NF-kappaB induction during T-cell activation. NF-kappaB activation occurs within minutes of T-cell receptor (TCR) engagement and this activation is sustained for at least 48 h following TCR signaling. We used gamma-secretase inhibitor (GSI) to prevent the cleavage and subsequent activation of Notch family members. We demonstrate that GSI blocked the later, sustained NF-kappaB activation, but did not affect the initial activation of NF-kappaB. Using biochemical approaches, as well as confocal microscopy, we show that the intracellular domain of Notch1 (N1IC) directly interacts with NF-kappaB and competes with IkappaBalpha, leading to retention of NF-kappaB in the nucleus. Additionally, we show that N1IC can directly regulate IFN-gamma expression through complexes formed on the IFN-gamma promoter. Taken together, these data suggest that there are two 'waves' of NF-kappaB activation: an initial, Notch-independent phase, and a later, sustained activation of NF-kappaB, which is Notch dependent.

Reappraisal of BCL3 as a Molecular Marker of Anaplastic Large Cell Lymphoma

The BCL3 gene was initially discovered through its involvement in a recurring translocation, t(14;19)(q32;q13), which is found in some patients with B-cell chronic lymphocytic leukemia (B-CLL). The translocation leads to the juxtaposition of BCL3 to the immunoglobulin heavy chain gene locus, resulting in high-level expression of the BCL3 transcript. The Bcl-3 protein includes 7 tandem copies of the ankyrin repeat element in the central domain, a structure that is characteristic of the IkappaB family of inhibitors of the nuclear factor kappaB transcription factors. Anaplastic large cell lymphoma (ALCL) is a subtype of aggressive non-Hodgkin's lymphoma that is characterized by expression of CD30 and the NPM/ALK chimeric protein, which is generated by t(2;5)(p23;q35). We compared the gene expression profiles of ALCL with those of another CD30+ neoplasm, Hodgkin's disease (HD), and found that BCL3 is expressed at higher levels in ALCL than in HD. A comparison by real-time polymerase chain reaction assay revealed that t(2;5)+ ALCL expresses a high level of BCL3 messenger RNA relative to the levels expressed in other hematologic tumors, and the level in ALCL is comparable to or even higher than that in t(14;19)+ B-CLL. An immunohistochemical analysis of ALCL tumor tissues showed that the lymphoma cells exhibited strong nuclear staining by a monoclonal antibody against Bcl-3. We suggest that Bcl-3 sequestrates the (p50)2 homodimer to the nucleus and that the kappaB sites are occupied by the (p50)2/Bcl-3 ternary complex. Future studies should identify the relationships among the 3 independent molecules (ie, NPM/ALK, CD30, and Bcl-3) that are activated in t(2;5)+ ALCL.

Regulation of Bcl-3 through interaction with the Lck tyrosine kinase

bcl-3 is a protooncogene which undergoes chromosomal translocation in a subset of chronic B-cell lymphocytic leukemia cells. Bcl-3 is a unique IkappaB family protein that regulates transcription of a number of NF-kappaB target genes through interactions with NF-kappaB dimers. Based on previous studies, suggesting that Bcl-3 interacts with the Fyn tyrosine kinase in platelets, we investigated possible interactions of Bcl-3 with Lck, a related tyrosine kinase important in lymphoid cells. Protein-protein interactions between Bcl-3 and the Lck tyrosine kinase were identified both in vitro and in vivo. Lck enhanced Bcl-3-mediated activation of a p52/Bcl-3-responsive promoter in reporter gene assays independent of its tyrosine kinase activity, but requiring the Lck SH3 protein interaction domain. These studies suggest that Bcl-3 might participate in oncogenic pathways involving Lck.

The IκB Protein Bcl-3 Negatively Regulates Transcription of theIL-10Gene in Macrophages

NF-kappaB/Rel transcription factors, implicated in inflammatory and immune responses against pathogens, are regulated by IkappaB proteins. The physiological and molecular function of the IkappaB family member Bcl-3 is understood only poorly. In this study, the role of Bcl-3 in an innate immune response was examined by gene targeting. We demonstrate that Bcl-3(-/-) mice are highly susceptible to Listeria monocytogenes infection. This correlates with diminished production of IL-12 p70 and IFN-gamma in vivo, which is mainly due to elevated synthesis of IL-10. Isolated peritoneal macrophages from Bcl-3(-/-) mice also produce elevated amounts of IL-10, which inhibit IL-12 p70 synthesis in an autocrine fashion. Thus, these data establish Bcl-3 as an inhibitor of IL-10 expression in macrophages. Furthermore, we show that Bcl-3 is not implicated in IL-10 mRNA stabilization but regulates the initiation of IL-10 transcription. Taken together, our results show that an essential function of Bcl-3 during an innate immune response against bacteria is to inhibit transcription of the IL-10 gene in macrophages.

Elevated NF-kappaB p50 complex formation and Bcl-3 expression in classical Hodgkin, anaplastic large-cell, and other peripheral T-cell lymphomas

Transcription factor nuclear factor kappa B (NF-kappaB) plays a central role in the pathogenesis of classical Hodgkin lymphoma (cHL). In anaplastic large-cell lymphomas (ALCLs), which share molecular lesions with cHL, the NF-kappaB system has not been equivalently investigated. Here we describe constitutive NF-kappaB p50 homodimer [(p50)2] activity in ALCL cells in the absence of constitutive activation of the IkappaB kinase (IKK) complex. Furthermore, (p50)2 contributes to the NF-kappaB activity in Hodgkin/Reed-Sternberg (HRS) cells. Bcl-3, which is an inducer of nuclear (p50)2 and is associated with (p50)2 in ALCL and HRS cell lines, is abundantly expressed in ALCL and HRS cells. Notably, a selective overexpression of Bcl-3 target genes is found in ALCL cells. By immunohistochemical screening of 288 lymphoma cases, a strong Bcl-3 expression in cHL and in peripheral T-cell non-Hodgkin lymphoma (T-NHL) including ALCL was found. In 3 of 6 HRS cell lines and 25% of primary ALCL, a copy number increase of the BCL3 gene locus was identified. Together, these data suggest that elevated Bcl-3 expression has an important function in cHL and peripheral T-NHL, in particular ALCL.

Opposing Roles for RelB and Bcl-3 in Regulation of T-Box Expressed in T Cells, GATA-3, and Th Effector Differentiation

CD4+ T cells with a block in the NF-kappaB signaling pathway exhibit decreases in Th1 responses and diminished nuclear levels of multiple transactivating NF-kappaB/Rel/IkappaB proteins. To determine the lineage-intrinsic contributions of these transactivators to Th differentiation, T cells from mice deficient in specific subunits were cultured in exogenous cytokines promoting either Th1 or Th2 differentiation. RelB-deficient cells exhibited dramatic defects in Th1 differentiation and IFN-gamma production, whereas no consistent defect in either Th1 or Th2 responses was observed with c-Rel-deficient cells. In sharp contrast, Bcl-3-null T cells displayed no defect in IFN-gamma production, but their Th2 differentiation and IL-4, IL-5, and IL-13 production were significantly impaired. The absence of RelB led to a dramatic decrease in the expression of T-box expressed in T cells and Stat4. In contrast, Bcl-3-deficient cells exhibited decreased GATA-3, consistent with evidence that Bcl-3 can transactivate a gata3 promoter. These data indicate that Bcl-3 and RelB exert distinct and opposing effects on the expression of subset-determining transcription factors, suggesting that the characteristics of Th cell responses may be regulated by titrating the stoichiometry of transactivating NF-kappaB/Rel/IkappaB complexes in the nuclei of developing helper effector cells.

Stimulation of CD30 in anaplastic large cell lymphoma leads to production of nuclear factor-kappaB p52, which is associated with hyperphosphorylated Bcl-3

Anaplastic large cell lymphoma (ALCL) and Hodgkin lymphoma (HL) express CD30 at high levels, but stimulation of this molecule has been reported to induce contradictory effects. To elucidate the molecular mechanism of CD30-mediated apoptosis of ALCL, we compared the gene expression profiles of t(2;5)(p23;q35)-positive ALCL with those of HL altered by CD30 agonistic stimulation. The results showed that BCL3, the high-level expression of which in ALCL was previously reported, was further upregulated in response to CD30 stimulation, along with several pro-apoptotic genes. Bcl-3 protein was present as an intermediate phospho-form in the resting-state ALCL, becoming hyperphosphorylated (Bcl-3P) upon stimulation. We next found that the stimulation promoted de novo synthesis of the nuclear factor (NF)-kappaB2/p100 precursor as well as processing to p52, and a series of immunoprecipitation and western blotting analyses consistently showed association of Bcl-3P with p52 in CD30-stimulated ALCL. An electrophoretic mobility shift assay revealed the induction of kappaB binding activity of the p52 homodimer, and nuclear colocalization of Bcl-3 and p52 was demonstrated in anaplastic lymphoma kinase-positive ALCL tumor tissues by immunohistochemistry. As Bcl-3 can act as an anti-repressor or transactivator or both, we propose that the (p52)2/Bcl-3P ternary complex, which is specifically induced in CD30-stimulated ALCL, can modulate expression of apoptosis-related genes regulated by NF-kappaB, thereby accounting for CD30-mediated apoptosis of ALCL.

Lipopolysaccharide induces 5-lipoxygenase-activating protein gene expression in THP-1 cells via a NF-κB and C/EBP-mediated mechanism

We examined induced expression of the 5-lipoxygenase-activating protein (FLAP), which is critical for leukotriene synthesis in mononuclear phagocytes. Prolonged exposure to the bacterial component, lipopolysaccharide (LPS), increased FLAP gene transcription, mRNA expression, and protein expression in the human monocyte-like THP-1 cell line. Activation and inhibition of the NF-κB pathway modulated LPS induction of FLAP gene expression. An NF-κB-mediated mechanism of action was supported by overexpression of dominant-negative IκBα and p50/p65 proteins. EMSA/supershift and DNase I footprint analyses revealed that p50 binds to an NF-κB site located in the proximal FLAP promoter, while chromatin immunoprecipitation assays demonstrated that LPS induced binding of p50 but not of p65. Moreover, EMSA/supershift analyses demonstrated that LPS induced time-dependent binding of THP-1 nuclear extracts (containing p50) to this promoter region. Mutation of the NF-κB site decreased basal promoter activity and abolished the p50- and p65-associated induction. EMSA/supershift analyses also demonstrated that LPS induced binding of THP-1 nuclear extracts [containing CCAAT/enhancer binding protein (C/EBP)-α, -δ, and -ε] to a C/EBP site located adjacent to the NF-κB site in the FLAP promoter. We conclude that LPS enhances FLAP gene expression via both NF-κB- and C/EBP-mediated transcriptional mechanisms in mononuclear phagocytes.

Linkage analysis between BCL3 and nearby genes on 19q13.2 and non-syndromic cleft lip with or without cleft palate in multigenerational Japanese families

OBJECTIVE

To investigate the linkage between candidate genes on chromosome 19 and cleft lip with or without cleft palate in Japanese using a parametric method.

MATERIALS AND METHODS

After informed consent was obtained, blood samples were drawn from 90 individuals in 14 families, 30 of whom were affected, and genomic DNAs were extracted. PCR-amplified products using four microsatellite markers, D19S178, BCL3, APOC2[007/008] and APOC2[AC1/AC2] located in 19q13.2, were separated by 8% polyacrylamide gel electrophoresis. Linkage analysis was carried out using the MLINK and LINKMAP programs, and logarithm of odds (LOD) scores were calculated for each family.

RESULTS

Before undertaking linkage analysis, we analyzed 74 healthy Japanese subjects and found racial differences in that the observed number of alleles and their heterozygosity were lower in Japanese than in Caucasians, and that both populations tended to show a different allele distribution. In 14 families, two-point maximum LOD score (Zmax) for BCL3 was 0.341 and multi-point Zmax was less than -2 excluding linkage. But in 9 families with left and bilateral CL/P, two-point Zmax for APOC2[AC1/AC2] was 1.701 and multi-point Zmax at APOC2 locus was 1.909.

CONCLUSION

The LOD score was relatively high but provided no evidence of linkage for CL/P to BCL3 and nearby genes in Japanese subjects.

Abnormalities in the NF-kappaB family and related proteins in endometrial carcinoma

The NF-kappaB family of transcription factors regulates a wide variety of cellular processes including cell growth, differentiation, and apoptosis. A tissue microarray was constructed from paraffin wax-embedded blocks from 95 endometrial carcinomas (EC), previously studied for microsatellite instability, as well as for alterations in PTEN, k-RAS and beta-catenin. Immunohistochemical evaluation included members of the NF-kappaB (p50, p65, p52, c-Rel, Rel-B) and the IkappaB (IkappaBalpha, IkappaBbeta, IkappaBepsilon, Bcl-3) families, as well as putative targets of NF-kappaB such as Flip, Bcl-xL, Cyclin D1, and oestrogen and progesterone receptors. Results were correlated with the clinical and pathological data. Nuclear immunostaining for members of the NF-kappaB family was frequent in EC (p50, 20%; p65, 16.5-21.9%; p52, 9.3%; c-Rel, 48.9%; Rel-B, 15.7%); and it correlated with negativity for members of the IkappaB family in some cases. There was a statistically significant association between immunoreaction for p50 and p65 (p = 0.006), suggesting activation of the so-called 'classic form' of NF-kappaB, similar to that described in breast cancer. Bcl-3 nuclear immunostaining was detected in 60.7% of cases. The vast majority of p52-positive tumours showed Bcl-3 nuclear immunoreaction (p = 0.038). Immunostaining for putative targets of NF-kappaB was as follows: Bcl-xL, 76.2% (p = 0.001); Flip 43.0%; Cyclin D1, 64.79%. p65 immunostaining correlated with increased immunoreaction for steroid hormone receptors. No correlation was found between NF-kappaB nuclear pattern and the presence of microsatellite instability, or alterations in PTEN, k-RAS, or beta-catenin. These results suggest that the NF-kappaB and IkappaB families of genes may be important in endometrial carcinogenesis, by controlling apoptosis and cell proliferation.

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.

NF-kappa B regulates expression of the MHC class I-related chain A gene in activated T lymphocytes

MHC class I-related chain A gene (MICA) is a stress-regulated, HLA-related molecule which exhibits a restricted pattern of expression. MICA protein is up-regulated on different tumor cells, and is recognized by the lectin-like NKG2D molecule expressed by cytotoxic gammadelta T lymphocytes, CD8+ alphabeta T lymphocytes, and NK cells. Although MICA is not expressed on resting lymphocytes, we demonstrated that it is induced on activated T cells. Because NF-kappaB is actively involved in T cell activation, and is constitutively activated in many tumors, here we investigated whether NF-kappaB may modulate MICA expression. Treatment with the NF-kappaB inhibitor sulfasalazine (Sz) resulted in a dose-dependent inhibition of MICA expression in anti-CD3- and anti-CD28/PMA-activated T lymphocytes, as assessed by Western blot and RT-PCR analysis. Moreover, Sz also down-regulated MICA expression on epithelial tumor HeLa cells. MICA expression was accompanied by a Sz-sensitive IkappaBalpha degradation. EMSA with nuclear extracts from anti-CD3- and anti-CD28/PMA-stimulated T lymphocytes demonstrated the binding of a potential NF-kappaB family transcription factor to a MICA gene intron 1-derived oligonucleotide that contains a putative kappaB binding site. Supershift assays demonstrated the presence of p65(RelA)/p50 heterodimers and p50/p50 homodimers in the NF-kappaB complexes bound to the kappaB-MICA oligonucleotide. Transient transfection of HeLa cells with p65(RelA) up-regulated MICA expression, as assessed by Western blot and flow cytometry analysis. Hence, we conclude that NF-kappaB regulates MICA expression on activated T lymphocytes and HeLa tumor cells, by binding to a specific sequence in the long intron 1 of the MICA gene. This constitutes the first description of a transcription factor that regulates MICA gene expression.

Synergistic activation of the CMV promoter by NF-kappaB P50 and PKG

Several DNA binding NF-kappaB subunits are substrates for cGMP-dependent kinase (PKG) and their transactivation from cognate sites is induced by phosphorylation. This includes p50, which does not have a transcriptional activation domain and therefore needs to bind to other proteins to mediate gene expression. Here, we describe the synergistic transactivation by p50 and PKG from the CMV promoter. This is caused not only by phosphorylation of p50, leading to increased DNA binding, but also by PKG-dependent activation of CRE sites in the promoter. One of the CRE sites is located directly adjacent to a NF-kappaB site and is essential for p50-mediated induction of transcription. According to the binding of CREB to p50 in pull-down assays and according to the inhibition of p50-dependent transactivation by dominant-negative CREB, this reflects the formation of a transcription factor complex containing CREB and p50. The nuclear translocation of NF-kappaB is insufficient to distinguish among the multitude of promoters that harbor cognate recognition sites. The phosphorylation of multiple transcription factors by an upstream kinase, such as PKG, can lead to the formation of transcription factor complexes and differential transactivation from a subset of NF-kappaB sites. These interactions may be relevant for the activation of viral gene expression.

GSK3-mediated BCL-3 phosphorylation modulates its degradation and its oncogenicity

The oncoprotein BCL-3 is a nuclear transcription factor that activates NF-kappaB target genes through formation of heterocomplexes with p50 or p52. BCL-3 is phosphorylated in vivo, but specific BCL-3 kinases have not been identified so far. In this report, we show that BCL-3 is a substrate for the protein kinase GSK3 and that GSK3-mediated BCL-3 phosphorylation, which is inhibited by Akt activation, targets its degradation through the proteasome pathway. This phosphorylation modulates its association with HDAC1, -3, and -6 and attenuates its oncogenicity by selectively controlling the expression of a subset of newly identified target genes such as SLPI and Cxcl1. Our results therefore suggest that constitutive BCL-3 phosphorylation by GSK3 regulates BCL-3 turnover and transcriptional activity.