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

Id2 regulates the proliferation of squamous cell carcinoma in vitro via the NF-κB/Cyclin D1 pathway

Squamous cell carcinoma (SCC) is a significant cause of cancer morbidity and mortality worldwide, with an incidence of up to 166 cases per 100 000 population. It arises in the skin, upper aerodigestive tract, lung, and cervix and affects more than 200 000 Americans each year. We report here that a microarray experiment comparing 41 SCC and 13 normal tissue specimens showed that Id2, a gene that controls the cell cycle, was significantly up-regulated in SCC. Enforced expression of Id2 in vitro stimulated the proliferation of SCC cells and up-regulated the transcription of nuclear factor kappa B (NF-κB) and cyclin D1. Enhancement of the NF-κB activity with p65 significantly increased the cell proliferation and the transcription of cyclin D1, whereas inhibition of the NF-κB activity with I kappa B alpha mutant (IκBα M) and pyrroline dithiocarbamate (PDTC) abrogated cell proliferation and transcription of cyclin D1. Furthermore, a mutated NF-κB binding site in the cyclin D1 promoter fully abrogated the Id2-induced transcription of cyclin D1. Taken together, these data indicate that Id2 induces SCC tumor growth and proliferation through the NF-κB/cyclin D1 pathway.

It takes two to tango: IκBs, the multifunctional partners of NF-κB

The inhibitory IκB proteins have been discovered as fundamental regulators of the inducible transcription factor nuclear factor-κB (NF-κB). As a generally excepted model, stimulus-dependent destruction of inhibitory IκBs and processing of precursor molecules, both promoted by components of the signal integrating IκB kinase complex, are the key events for the release of various NF-κB/Rel dimers and subsequent transcriptional activation. Intense research of more than 20 years provides evidence that the extending family of IκBs act not simply as reversible inhibitors of NF-κB activation but rather as a complex regulatory module, which assures feedback regulation of the NF-κB system and either can inhibit or promote transcriptional activity in a stimulus-dependent manner. Thus, IκB and NF-κB/Rel family proteins establish a complex interrelationship that allows modulated NF-κB-dependent transcription, tailored to the physiological environment.

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

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

NF-κB, the first quarter-century: remarkable progress and outstanding questions

The ability to sense and adjust to the environment is crucial to life. For multicellular organisms, the ability to respond to external changes is essential not only for survival but also for normal development and physiology. Although signaling events can directly modify cellular function, typically signaling acts to alter transcriptional responses to generate both transient and sustained changes. Rapid, but transient, changes in gene expression are mediated by inducible transcription factors such as NF-κB. For the past 25 years, NF-κB has served as a paradigm for inducible transcription factors and has provided numerous insights into how signaling events influence gene expression and physiology. Since its discovery as a regulator of expression of the κ light chain gene in B cells, research on NF-κB continues to yield new insights into fundamental cellular processes. Advances in understanding the mechanisms that regulate NF-κB have been accompanied by progress in elucidating the biological significance of this transcription factor in various physiological processes. NF-κB likely plays the most prominent role in the development and function of the immune system and, not surprisingly, when dysregulated, contributes to the pathophysiology of inflammatory disease. As our appreciation of the fundamental role of inflammation in disease pathogenesis has increased, so too has the importance of NF-κB as a key regulatory molecule gained progressively greater significance. However, despite the tremendous progress that has been made in understanding the regulation of NF-κB, there is much that remains to be understood. In this review, we highlight both the progress that has been made and the fundamental questions that remain unanswered after 25 years of study.

Role of Bcl-3 in solid tumors

Bcl-3 is an established oncogene in hematologic malignancies, such as B-cell chronic lymphocytic leukemias. Nevertheless, recent research has shown that it also participates in progression of diverse solid tumors. The present review summarizes the current knowledge of Bcl3 role in solid tumors progression, including some new insights in its possible molecular mechanisms of action.

Role of T cell-nuclear factor κB in transplantation

Nuclear factor (NF) κB is a pleiotropic transcription factor that is ubiquitously expressed. After transplantation of solid organs, NF-κB in the graft is activated within a few hours as a consequence of ischemia/reperfusion and then again after a few days in intragraft infiltrating cells during the process of acute allograft rejection. In the present article, we review the components of the NF-κB pathway, their mechanisms of activation, and their role in T cell and antigen-presenting cell activation and differentiation and in solid organ allograft rejection. Targeted inhibition of NF-κB in selected cell types may promote graft survival with fewer adverse effects compared with global immunosuppressive therapies.

Inhibition of Bcl3 gene expression mediates the anti-proliferative action of estrogen in pituitary lactotrophs in primary culture

In addition to their well-known stimulatory action, estrogens have an anti-proliferative effect. The present study was undertaken to investigate the mechanism by which 17β-estradiol (E2) inhibits insulin-like growth factor-1 (IGF-1)-induced proliferation in vitro in the rat pituitary lactotroph, a typical estrogen-responsive cell. E2 treatment of pituitary cells did not change levels of IGF-1-induced phosphorylation of proliferation-related protein kinases such as Erk1/2 and Akt. We performed global gene expression profiling by DNA microarray analysis and identified 177 genes regulated by E2 in the presence of IGF-1. These results were verified by quantitative real time PCR. The estrogen-regulated genes included several NFκB family related genes. As pharmacological inhibition of the NFκB pathway blocked IGF-1-induced lactotroph proliferation, we chose to investigate whether one NFκB pathway gene, Bcl3, was involved in the anti-proliferative action of E2. RNA interference-mediated knockdown of Bcl3 expression attenuated IGF-1-induced lactotroph proliferation. Even minimal induced overexpression of Bcl3 blocked the anti-proliferative action of E2. In contrast, Nfkb2, another E2-downregulated protein, required maximal overexpression to block the anti-proliferative action of E2. These results suggest that inhibition of Bcl3 expression is involved in the anti-proliferative action of estrogens in pituitary lactotrophs in culture.

NF-κB cellular and molecular regulatory mechanisms and pathways: therapeutic pattern or pseudoregulation?

As fascinating a molecule as it can potentially get, nuclear factor-κB (NF-κB), a regulatory transcription factor, is as intriguing. NF-κB is a dimeric complex that controls the transcription of essential genes. NF-κB is involved in a variety of responses that play a pivotal role in regulating the immune response to inflammation, infection, and nociception. Aberrant regulation of NF-κB has been linked to certain conditions such as cancer, inflammatory and autoimmune diseases, septic shock, viral infection, and improper immune responses. Cellular and molecular regulatory mechanisms and pathways involving the regulation of this transcription factor are being unraveled. Therapeutic approaches have emerged underlying the regulatory impact of oligonucleotides/decoys and other non-decoy inhibitors on NF-κB modulation. In this synopsis, we emphasize the role of decoy therapy in understanding the crucial influence of this transcription factor, and further weigh not only the efficacy of this therapeutic approach but also its necessity and contraindications.

Alterations in the expression of genes related to NF-κB signaling in liver and kidney of CuZnSOD-deficient mice

NF-κB signaling pathway plays a central role in regulation of the cellular response to stress. Among numerous factors that modulate NF-κB dependent transcription, reactive oxygen species attracted special attention. In the present work, we compared the expression of 84 genes related to NF-κB signaling between cytosolic superoxide dismutase (CuZnSOD)-deficient and wild-type mice. In kidney, we found seven genes which expression was significantly affected by CuZnSOD deficiency. Among them, four were up-regulated, Egr1, Fos, Il1b, Tnfrsf10b, and three down-regulated, Card10, Ikbkb, Tgfbr2. In the case of liver, six genes were up-regulated, Fos, Il1b, Il1r1, Jun, Tlr7, Tnfrsf10b, and five down-regulated, Casp8, Ikbke, Irak1, Nfkb1, Raf1. The results demonstrate that CuZnSOD deficiency has a significant impact on the expression of NF-κB related genes in both kidney and liver. The differences in gene expression reported in our work may contribute to understanding of the molecular mechanisms underlying phenotypic abnormalities in CuZnSOD-deficient mice, e.g., increase in the incidence of liver cancer.

NF-κB and STAT3 - key players in liver inflammation and cancer

Hepatocellular carcinoma (HCC), the major form of primary liver cancer, is one of the most deadly human cancers. The pathogenesis of HCC is frequently linked with continuous hepatocyte death, inflammatory cell infiltration and compensatory liver regeneration. Understanding the molecular signaling pathways driving or mediating these processes during liver tumorigenesis is important for the identification of novel therapeutic targets for this dreadful disease. The classical IKKβ-dependent NF-κB signaling pathway has been shown to promote hepatocyte survival in both developing and adult livers. In addition, it also plays a crucial role in liver inflammatory responses by controlling the expression of an array of growth factors and cytokines. One of these cytokines is IL-6, which is best known for its role in the liver acute phase response. IL-6 exerts many of its functions via activation of STAT3, a transcription factor found to be important for HCC development. This review will focus on recent studies on the roles of NF-κB and STAT3 in liver cancer. Interactions between the two pathways and their potential as therapeutic targets will also be discussed.

Deubiquitinases in the regulation of NF-κB signaling

Nuclear factor-kappa B (NF-κB) is a critical regulator of multiple biological functions including innate and adaptive immunity and cell survival. Activation of NF-κB is tightly regulated to preclude chronic signaling that may lead to persistent inflammation and cancer. Ubiquitination of key signaling molecules by E3 ubiquitin ligases has emerged as an important regulatory mechanism for NF-κB signaling. Deubiquitinases (DUBs) counteract E3 ligases and therefore play a prominent role in the downregulation of NF-κB signaling and homeostasis. Understanding the mechanisms of NF-κB downregulation by specific DUBs such as A20 and CYLD may provide therapeutic opportunities for the treatment of chronic inflammatory diseases and cancer.

Roles of Bcl-3 in the pathogenesis of murine type 1 diabetes

OBJECTIVE

It has long been recognized that autoimmunity is often associated with immunodeficiency. The mechanism underlying this paradox is not well understood. Bcl-3 (B-cell lymphoma 3) is an atypical member of the IκB (inhibitor of the nuclear factor-κB) family that is required for lymphoid organogenesis and germinal center responses. Mice deficient in Bcl-3 are immunodeficient because of the microarchitectural defects of their lymphoid organs. The goal of this study is to define the potential roles of Bcl-3 in type 1 diabetes.

RESEARCH DESIGN AND METHODS

Bcl-3-deficient NOD mice were generated by backcrossing Bcl-3-deficient C57BL/6 mice to NOD mice. Spontaneous and induced type 1 diabetes were studied in these mice by both pathologic and immunologic means. The effect of Bcl-3 on inflammatory gene transcription was evaluated in a promoter reporter assay.

RESULTS

We found that Bcl-3-deficient NOD and C57BL/6 mice were, paradoxically, more susceptible to autoimmune diabetes than wild-type mice. The increase in diabetes susceptibility was caused by Bcl-3 deficiency in hematopoietic cells but not nonhematopoietic cells. Bcl-3 deficiency did not significantly affect anti-islet Th1 or Th2 autoimmune responses, but markedly increased inflammatory chemokine and T helper 17 (Th17)-type cytokine expression. Upon transfection, Bcl-3 significantly inhibited the promoter activities of inflammatory chemokine and cytokine genes.

CONCLUSIONS

These results indicate that in addition to mediating lymphoid organogenesis, Bcl-3 prevents autoimmune diabetes by inhibiting inflammatory chemokine and cytokine gene transcription. Thus, a single Bcl3 gene mutation leads to both autoimmunity and immunodeficiency.

The NF-kappaB family of transcription factors and its regulation

Nuclear factor-kappaB (NF-kappaB) consists of a family of transcription factors that play critical roles in inflammation, immunity, cell proliferation, differentiation, and survival. Inducible NF-kappaB activation depends on phosphorylation-induced proteosomal degradation of the inhibitor of NF-kappaB proteins (IkappaBs), which retain inactive NF-kappaB dimers in the cytosol in unstimulated cells. The majority of the diverse signaling pathways that lead to NF-kappaB activation converge on the IkappaB kinase (IKK) complex, which is responsible for IkappaB phosphorylation and is essential for signal transduction to NF-kappaB. Additional regulation of NF-kappaB activity is achieved through various post-translational modifications of the core components of the NF-kappaB signaling pathways. In addition to cytosolic modifications of IKK and IkappaB proteins, as well as other pathway-specific mediators, the transcription factors are themselves extensively modified. Tremendous progress has been made over the last two decades in unraveling the elaborate regulatory networks that control the NF-kappaB response. This has made the NF-kappaB pathway a paradigm for understanding general principles of signal transduction and gene regulation.

NF-kappaB as a critical link between inflammation and cancer

NF-kappaB transcription factors have been suspected to be involved in cancer development since their discovery because of their kinship with the v-Rel oncogene product. Subsequent work led to identification of oncogenic mutations that result in NF-kappaB activation in lymphoid malignancies, but most of these mutations affect upstream components of NF-kappaB signaling pathways, rather than NF-kappaB family members themselves. NF-kappaB activation has also been observed in many solid tumors, but so far no oncogenic mutations responsible for NF-kappaB activation in carcinomas have been identified. In such cancers, NF-kappaB activation is a result of underlying inflammation or the consequence of formation of an inflammatory microenvironment during malignant progression. Most importantly, through its ability to up-regulate the expression of tumor promoting cytokines, such as IL-6 or TNF-alpha, and survival genes, such as Bcl-X(L), NF-kappaB provides a critical link between inflammation and cancer.

MicroRNAs modulate the noncanonical transcription factor NF-kappaB pathway by regulating expression of the kinase IKKalpha during macrophage differentiation

MicroRNAs are key regulators of many biological processes, including cell differentiation. Here we show that during human monocyte-macrophage differentiation, expression of the microRNAs miR-223, miR-15a and miR-16 decreased considerably, which led to higher expression of the serine-threonine kinase IKKalpha in macrophages. In macrophages, higher IKKalpha expression in conjunction with stabilization of the kinase NIK induced larger amounts of p52. Because of low expression of the transcription factor RelB in untreated macrophages, high p52 expression repressed basal transcription of both canonical and noncanonical NF-kappaB target genes. However, proinflammatory stimuli in macrophages resulted in greater induction of noncanonical NF-kappaB target genes. Thus, a decrease in certain microRNAs probably prevents macrophage hyperactivation yet primes the macrophage for certain responses to proinflammatory stimuli.

Depletion of the oncoprotein Bcl-3 induces centrosome amplification and aneuploidy in cancer cells

Bcl-3 is an atypical member of the inhibitor of NF-kappa B family of proteins since it can function as a coactivator of transcription. Although this oncogene was described in leukemia, it is overexpressed in a number of solid tumors as well. The oncogenic potential of Bcl-3 has been associated with its capacity to increase proliferation by means of activating the cyclin D1 promoter and to its antiapoptotic role mediated by the inhibiton of p53 activity. In the course of dissecting these properties, we found that depleting Bcl-3 protein using shRNAs induce a decrease of proliferation and clonogenic survival associated with the induction of multinucleation and increased ploidy. These effects were associated with a DNA damage response, a delay in G2/M checkpoint and the induction of centrosome amplification

BCL-3 degradation involves its polyubiquitination through a FBW7-independent pathway and its binding to the proteasome subunit PSMB1

The oncogenic protein BCL-3 activates or represses gene transcription through binding with the NF-kappaB proteins p50 and p52 and is degraded through a phospho- and GSK3-dependent pathway. However, the mechanisms underlying its degradation remain poorly understood. Yeast two-hybrid analysis led to the identification of the proteasome subunit PSMB1 as a BCL-3-associated protein. The binding of BCL-3 to PSMB1 is required for its degradation through the proteasome. Indeed, PSMB1-depleted cells are defective in degrading polyubiquitinated BCL-3. The N-terminal part of BCL-3 includes lysines 13 and 26 required for the Lys(48)-linked polyubiquitination of BCL-3. Moreover, the E3 ligase FBW7, known to polyubiquitinate a variety of substrates phosphorylated by GSK3, is dispensable for BCL-3 degradation. Thus, our data defined a unique motif of BCL-3 that is needed for its recruitment to the proteasome and identified PSMB1 as a key protein required for the proteasome-mediated degradation of a nuclear and oncogenic IkappaB protein.

IkappaBeta, a nuclear IkappaB protein, positively regulates the NF-kappaB-mediated expression of proinflammatory cytokines

NF-kappaB is a key mediator for inducible transcription of various proinflammatory genes in innate immune responses, and its activity is strictly regulated by several IkappaB proteins. Although signaling pathways leading from pattern recognition receptors to NF-kappaB's activation in the cytoplasm have been studied extensively, the detail regulatory mechanisms of NF-kappaB-mediated transcriptional activity in the nucleus still remain unclear. Here we describe a unique member of the nuclear IkappaB protein family, IkappaBeta. In a gene expression analysis of dendritic cells, we found a unique gene encoding an uncharacterized protein with ankyrin repeats. As it was structurally related to the IkappaB family, the protein was named "IkappaBeta" and further characterized in the innate immune response. IkappaBeta was widely expressed in various tissues and predominantly located in the nucleus. Moreover, biochemical analysis showed that IkappaBeta associated with the p50 subunit of NF-kappaB. Knockdown of IkappaBeta by siRNA suppressed the transcription of a subset of NF-kappaB-mediated proinflammatory cytokines in LPS-stimulated and poly (I:C)-transfected macrophages. These results indicate that IkappaBeta regulates the NF-kappaB-mediated transcription of a wide variety of proinflammatory genes, playing a crucial role in the regulation of innate immune responses.

The repressing function of the oncoprotein BCL-3 requires CtBP, while its polyubiquitination and degradation involve the E3 ligase TBLR1

The nuclear and oncogenic BCL-3 protein activates or represses gene transcription when bound to NF-kappaB proteins p50 and p52, yet the molecules that specifically interact with BCL-3 and drive BCL-3-mediated effects on gene expression remain largely uncharacterized. Moreover, GSK3-mediated phosphorylation of BCL-3 triggers its degradation through the proteasome, but the proteins involved in this degradative pathway are poorly characterized. Biochemical purification of interacting partners of BCL-3 led to the identification of CtBP as a molecule required for the ability of BCL-3 to repress gene transcription. CtBP is also required for the oncogenic potential of BCL-3 and for its ability to inhibit UV-mediated cell apoptosis in keratinocytes. We also defined the E3 ligase TBLR1 as a protein involved in BCL-3 degradation through a GSK3-independent pathway. Thus, our data demonstrate that the LSD1/CtBP complex is required for the repressing abilities of an oncogenic I kappaB protein, and they establish a functional link between the E3 ligase TBLR1 and NF-kappaB.

NF-kB and Bcl-3 activation are prognostic in metastatic colorectal cancer

PURPOSE

NF-kappaB is an antiapoptotic transcription factor that has been shown to be a mediator of treatment resistance. Bcl-3 is a regulator of NF-kappaB that may play a role in oncogenesis. The goal of this study was to correlate the activation status of NF-kappaB and Bcl-3 with clinical outcome in a group of patients with metastatic colorectal cancer (CRC).

METHODS

A retrospective study of 23 patients who underwent surgical resection of CRC at the University of North Carolina (UNC). Activation of NF-kappaB was defined by nuclear expression of select components of NF-kappaB (p50, p52, p65) and Bcl-3. Tissue microarrays were created from cores of normal mucosa, primary tumor, lymph node metastases and liver metastases in triplicate from disparate areas of the blocks, and an intensity score was generated by multiplying intensity (0-3+) by percent of positive tumor cells. Generalized estimating equations were used to note differences in intensity scores among normal mucosa and nonnormal tissues. Cox regression models were fit to see if scores were significantly associated with overall survival.

RESULTS

p65 NE was significantly higher in primary tumor and liver metastases than normal mucosa (both p < 0.01). p50 nuclear expression was significantly higher for all tumor sites than for normal mucosa (primary tumor and lymph node metastases p < 0.0001, liver metastases p < 0.01). Bcl-3 nuclear expression did not differ significantly between normal mucosa and tumor; however, nuclear expression in primary tumor for each of these components was strongly associated with survival: the increase in hazard for each 50-point increase in nuclear expression was 91% for Bcl-3, 66% for p65, and 52% for p50 (all p < 0.05).

CONCLUSIONS

Activation of canonical NF-kappaB subunits p50 and p65 as measured by nuclear expression is strongly associated with survival suggesting NF-kappaB as a prognostic factor in this disease. Primary tumor nuclear expression appears to be as good as, or better than, metastatic sites at predicting prognosis. Bcl-3 nuclear expression is also negatively associated with survival and deserves further study in CRC.

Expression of NF-kappaB and IkappaB proteins in skeletal muscle of gastric cancer patients

The mechanisms eliciting cancer cachexia are not well understood. Wasting of skeletal muscle is problematic because it is responsible for the clinical deterioration in cancer patients and for the ability to tolerate cancer treatment. Studies done on animals suggest that nuclear factor of kappa B (NF-kappaB) signalling is important in the progression of muscle wasting due to several types of tumours. However, there are no published studies in humans on the role of NF-kappaB in cancer cachexia. In this project, we studied the rectus abdominis muscle in patients with gastric tumours (n=14) and in age-matched control subjects (n=10) for markers of NF-kappaB activation. Nuclear levels of p65, p50 and Bcl-3 were the same in both groups of subjects. However, phospho-p65 was elevated by 25% in the muscles of cancer patients. In addition, expression of the inhibitor of kappa B alpha (IkappaBalpha) was decreased by 25% in cancer patients. Decreased expression of IkappaBalpha reflects its degradation by one of the IkappaBalpha kinases and is a marker of NF-kappaB activation. Interestingly, there was no correlation between the stage of cancer and the extent of IkappaBalpha decrease, nor was there a correlation between the degree of cachexia and decreased IkappaBalpha levels. This suggests that the activation of NF-kappaB is an early and sustained event in gastric cancer. The work implicates the NF-kappaB signalling in the initiation and progression of cancer cachexia in humans and demonstrates the need for additional study of this pathway; it also recommends NF-kappaB signalling as a therapeutic target for the amelioration of cachexia as has been suggested from studies done on rodents.

Glutathione S-transferase M1 inhibits dexamethasone-induced apoptosis in association with the suppression of Bim through dual mechanisms in a lymphoblastic leukemia cell line

Glutathione S-transferase mu (GSTM1) is mainly known as a detoxification enzyme but it has also been shown to be a negative regulator of apoptosis-related signaling cascades. Recently GSTM1 has been reported to be a significant risk factor for hematological relapse in childhood acute lymphoblastic leukemia, although the underlying mechanism remains largely unknown. Glucocorticoids play a crucial role in the treatment of childhood acute lymphoblastic leukemia, therefore we hypothesized that GSTM1 plays important roles in glucocorticoid-induced apoptotic pathways. To clarify the relationship between GSTM1 and drug resistance, GSTM1 was transfected into a T-acute lymphoblastic leukemia cell line, CCRF-CEM (CEM), and we established the GSTM1-expressing cell lines CEM/M1-4 and CEM/M1-9. Transduction of GSTM1 into CEM selectively decreased cellular sensitivity to dexamethasone in a manner that was independent of glutathione conjugation, but was due to apoptosis inhibition. Dexamethasone-induced p38-MAPK and Bim activation were concomitantly suppressed. Interestingly, nuclear factor kappa b (NF-kappaB) p50 activity was upregulated in GSTM1-expressing CEM. Inhibition of NF-kappaB by the pharmacological agent BAY11-7082 greatly enhanced the sensitivity of the GSTM1-expressing CEM to dexamethasone and was accompanied by an increase in Bim expression. Thus, we propose that GSTM1, a novel regulator of dexamethasone-induced apoptosis, causes dexamethasone resistance by suppression of Bim through dual mechanisms of both downregulation of p38-MAPK and upregulation of NF-kappaB p50.

Estrogen regulates transcription factors STAT-1 and NF-kappaB to promote inducible nitric oxide synthase and inflammatory responses

Estrogen regulation of inflammatory responses has broad physiological and pathological consequences. However, the molecular mechanism of estrogen regulation of inflammation is still poorly understood. In this study, we report that activation of both STAT-1 and NF-kappaB signaling is essential for Con A-induced inducible NO synthase (iNOS) and NO in murine splenocytes. Estrogen enhances STAT-1 DNA-binding activity without increasing the expression of phosphorylated and total STAT-1 protein. We have recently reported that estrogen blocks the nuclear expression of NF-kappaB p65 and modifies nuclear NF-kappaBp50. Here, we demonstrated that both nuclear STAT-1 and NF-kappaB are modified by serine protease-mediated proteolysis, which resulted in altered STAT-1 and NF-kappaB activity/signaling in splenocytes from estrogen-treated mice. Inhibition of serine protease activity with 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride (AEBSF) restores the nuclear expression of full-length STAT-1 and NF-kappaB proteins, and resulted in decreased STAT-1 DNA-binding activity and formation of NF-kappaB p65/p50 binding complexes in nuclei of splenocytes from estrogen-treated mice. Consequently, there is significantly decreased iNOS and IFN-gamma production in AEBSF-treated splenocytes from estrogen-treated mice, which suggests a positive regulatory role of truncated STAT-1 and/or NF-kappaB. Interestingly, there is increased production of MCP-1 in STAT-1 or NF-kappaB small interfering RNA-transfected cells, as well as in AEBSF-treated splenocytes from estrogen-treated mice. These data suggest a differential role of truncated STAT-1 and NF-kappaB in regulation of various inflammatory molecules in splenocytes from estrogen-treated mice. Together, our data reveal a novel molecular mechanism of estrogen-mediated promotion of inflammatory responses, which involves posttranslational modification of STAT-1 and NF-kappaB proteins.

Crosstalk in inflammation: the interplay of glucocorticoid receptor-based mechanisms and kinases and phosphatases

Glucocorticoids (GCs) are steroidal ligands for the GC receptor (GR), which can function as a ligand-activated transcription factor. These steroidal ligands and derivatives thereof are the first line of treatment in a vast array of inflammatory diseases. However, due to the general surge of side effects associated with long-term use of GCs and the potential problem of GC resistance in some patients, the scientific world continues to search for a better understanding of the GC-mediated antiinflammatory mechanisms. The reversible phosphomodification of various mediators in the inflammatory process plays a key role in modulating and fine-tuning the sensitivity, longevity, and intensity of the inflammatory response. As such, the antiinflammatory GCs can modulate the activity and/or expression of various kinases and phosphatases, thus affecting the signaling efficacy toward the propagation of proinflammatory gene expression and proinflammatory gene mRNA stability. Conversely, phosphorylation of GR can affect GR ligand- and DNA-binding affinity, mobility, and cofactor recruitment, culminating in altered transactivation and transrepression capabilities of GR, and consequently leading to a modified antiinflammatory potential. Recently, new roles for kinases and phosphatases have been described in GR-based antiinflammatory mechanisms. Moreover, kinase inhibitors have become increasingly important as antiinflammatory tools, not only for research but also for therapeutic purposes. In light of these developments, we aim to illuminate the integrated interplay between GR signaling and its correlating kinases and phosphatases in the context of the clinically important combat of inflammation, giving attention to implications on GC-mediated side effects and therapy resistance.

Gadd45 proteins as critical signal transducers linking NF-kappaB to MAPK cascades

The growth arrest and DNA damage-inducible 45 (Gadd45) proteins are a group of critical signal transducers that are involved in regulations of many cellular functions. Accumulated data indicate that all three Gadd45 proteins (i.e., Gadd45alpha, Gadd45beta, and Gadd45gamma) play essential roles in connecting an upstream sensor module, the transcription Nuclear Factor-kappaB (NF-kappaB), to a transcriptional regulating module, mitogen-activated protein kinase (MAPK). This NF-kappaB-Gadd45(s)-MAPK pathway responds to various kinds of extracellular stimuli and regulates such cell activities as growth arrest, differentiation, cell survival, and apoptosis. Defects in this pathway can also be related to oncogenesis. In the first part of this review, the functions of Gadd45 proteins, and briefly NF-kappaB and MAPK, are summarized. In the second part, the mechanisms by which Gadd45 proteins are regulated by NF-kappaB, and how they affect MAPK activation, are reviewed.

Impaired TNFalpha-induced A20 expression in E1A/Ras-transformed cells

Background:

Tumour necrosis factor (TNF) is capable of activating the cell death pathway, and has been implicated in killing transformed cells. However, TNF also activates survival signals, including NF-κB activation and the subsequent expression of anti-apoptotic genes, leading to protection against TNF toxicity.

Methods:

In this study, we show that, although untransformed mouse embryonic fibroblasts (MEFs) were resistant to TNF killing, E1A/Ras-transformed MEFs were susceptible to extensive apoptosis induced by TNF. The key factors for determining TNF sensitivity were explored by comparing wild-type and E1A/Ras-transformed MEFs.

Results:

TNF signalling to NF-κB and to its target genes such as IκBα seemed to be mostly intact in E1A/Ras-transformed cells. Instead, the induction of A20 was completely abolished in E1A/Ras-transformed MEFs, although A20 is known to be NF-κB dependent. Reintroduction of A20 into E1A/Ras-transformed MEFs rescued these cells from TNF-induced death and reduced the formation of the FADD/caspase-8 complex. This impaired A20 induction in E1A/Ras MEFs was not because of the stabilisation of p53 or a defective TNF-induced p38 and Jun N-terminal kinase (JNK) signalling. Consistently, we found a reduced A20 promoter activity but normal NF-κB activity in TNF-treated E1A/Ras MEFs. However, Bcl-3 seemed to have a role in the transactivation of the A20 promoter in E1A/Ras cells.

Conclusions:

Our results suggest that specific inhibition of certain survival factors, such as A20, may determine the sensitivity to TNF-induced apoptosis in transformed cells such as E1A/Ras MEFs.

Bcl-3 acts as an innate immune modulator by controlling antimicrobial responses in keratinocytes

Innate immune responses involve the production of antimicrobial peptides (AMPs), chemokines, and cytokines. We report here the identification of B-cell leukemia (Bcl)-3 as a modulator of innate immune signaling in keratinocytes. In this study, it is shown that Bcl-3 is inducible by the Th2 cytokines IL-4 and IL-13 and is overexpressed in lesional skin of atopic dermatitis (AD) patients. Bcl-3 was shown to be important to cutaneous innate immune responses as silencing of Bcl-3 by small-interfering RNA (siRNA) reversed the downregulatory effect of IL-4 on the HBD3 expression. Bcl-3 silencing enhanced vitamin D3 (1,25D3)-induced gene expression of cathelicidin AMP in keratinocytes, suggesting a negative regulatory function on cathelicidin transcription. Furthermore, 1,25D3 suppressed Bcl-3 expression in vitro and in vivo. This study identified Bcl-3 as an important modulator of cutaneous innate immune responses and its possible therapeutic role in AD.

A novel role for IkappaBzeta in the regulation of IFNgamma production

IkappaBzeta is a novel member of the IkappaB family of NFkappaB regulators, which modulates NFkappaB activity in the nucleus, rather than controlling its nuclear translocation. IkappaBzeta is specifically induced by IL-1beta and several TLR ligands and positively regulates NFkappaB-mediated transcription of genes such as IL-6 and NGAL as an NFkappaB binding co-factor. We recently reported that the IL-1 family cytokines, IL-1beta and IL-18, strongly synergize with TNFalpha for IFNgamma production in KG-1 cells, whereas the same cytokines alone have minimal effects on IFNgamma production. Given the striking similarities between the IL-1R and IL-18R signaling pathways we hypothesized that a common signaling event or gene product downstream of these receptors is responsible for the observed synergy. We investigated IkappaBzeta protein expression in KG-1 cells upon stimulation with IL-1beta, IL-18 and TNFalpha. Our results demonstrated that IL-18, as well as IL-1beta, induced moderate IkappaBzeta expression in KG-1 cells. However, TNFalpha synergized with IL-1beta and IL-18, whereas by itself it had a minimal effect on IkappaBzeta expression. NFkappaB inhibition resulted in decreased IL-1beta/IL-18/TNFalpha-stimulated IFNgamma release. Moreover, silencing of IkappaBzeta expression led to a specific decrease in IFNgamma production. Overall, our data suggests that IkappaBzeta positively regulates NFkappaB-mediated IFNgamma production in KG-1 cells.

Bcl3 interacts cooperatively with peroxisome proliferator-activated receptor gamma (PPARgamma) coactivator 1alpha to coactivate nuclear receptors estrogen-related receptor alpha and PPARalpha

Estrogen-related receptors (ERRs) play critical roles in regulation of cellular energy metabolism in response to inducible coactivators such as peroxisome proliferator-activated receptor gamma (PPARgamma) coactivator 1alpha (PGC-1alpha). A yeast two-hybrid screen led to the identification of the cytokine-stimulated transcriptional regulator, Bcl3, as an ERRalpha coactivator. Bcl3 was shown to synergize with PGC-1alpha to coactivate ERRalpha. Chromatin immunoprecipitation studies demonstrated that ERRalpha, PGC-1alpha, and Bcl3 form a complex on an ERRalpha-responsive element within the pyruvate dehydrogenase kinase 4 gene promoter in cardiac myocytes. Mapping studies demonstrated that Bc13 interacts with PGC-1alpha and ERRalpha, allowing for interaction with both proteins. Transcriptional profiling demonstrated that Bcl3 activates genes involved in diverse pathways including a subset involved in cellular energy metabolism known to be regulated by PGC-1alpha, ERRalpha, and a second nuclear receptor, PPARalpha. Consistent with the gene expression profiling results, Bcl3 was shown to synergistically coactivate PPARalpha with PGC-1alpha in a manner similar to ERRalpha. We propose that the cooperativity between Bcl3 and PGC-1alpha may serve as a point of convergence on nuclear receptor targets to direct programs orchestrating inflammatory and energy metabolism responses in heart and other tissues.

Bcl-3-regulated transcription from major immediate-early promoter of human cytomegalovirus in monocyte-derived macrophages

Monocytes/macrophages are key cells in the pathogenesis of human CMV (HCMV) infection, but the in vitro rate of viral production in primary human monocyte-derived macrophages (MDM) is considerably lower than in fibroblasts. Considering that the NF-kappaB signaling pathway is potentially involved in the replication strategy of HCMV through efficient transactivation of the major immediate-early promoter (MIEP), efficient viral replication, and late gene expression, we investigated the composition of the NF-kappaB complex in HCMV-infected MDMs and fibroblasts. Preliminary studies showed that HCMV could grow in primary MDM culture but that the viral titer in culture supernatants was lower than that observed in the supernatants of more permissive MRC5 fibroblasts. EMSA and microwell colorimetric NF-kappaB assay demonstrated that HCMV infection of MDMs increased p52 binding activity without activating the canonical p50/p65 complex. Moreover, Bcl-3 was up-regulated and was demonstrated to associate with p52, indicating p52/Bcl-3 complexes as the major component of the NF-kappaB complex in MDMs. Luciferase assays in promonocytic U937 cells transfected with an MIEP-luciferase reporter construct demonstrated MIEP activation in response to p52 and Bcl-3 overexpression. Chromatin immunoprecipitation assay demonstrated that p52 and Bcl-3 bind the MIEP in acutely HCMV-infected MDMs. In contrast, HCMV infection of MRC5 fibroblasts resulted in activation of p50/p65 heterodimers. Thus, activation of p52/Bcl-3 complexes in MDMs and p50/p65 heterodimers in fibroblasts in response to HCMV infection might explain the low-level growth of the virus in MDMs vs efficient growth in fibroblasts.

Regulation and function of NF-kappaB transcription factors in the immune system

The mammalian Rel/NF-kappaB family of transcription factors, including RelA, c-Rel, RelB, NF-kappaB1 (p50 and its precursor p105), and NF-kappaB2 (p52 and its precursor p100), plays a central role in the immune system by regulating several processes ranging from the development and survival of lymphocytes and lymphoid organs to the control of immune responses and malignant transformation. The five members of the NF-kappaB family are normally kept inactive in the cytoplasm by interaction with inhibitors called IkappaBs or the unprocessed forms of NF-kappaB1 and NF-kappaB2. A wide variety of signals emanating from antigen receptors, pattern-recognition receptors, receptors for the members of TNF and IL-1 cytokine families, and others induce differential activation of NF-kappaB heterodimers. Although work over the past two decades has shed significant light on the regulation of NF-kappaB transcription factors and their functions, much progress has been made in the past two years revealing new insights into the regulation and functions of NF-kappaB. This recent progress is covered in this review.

Bcl-3, a multifaceted modulator of NF-kappaB-mediated gene transcription

The transcription factor, NF-kappaB (nuclear factor-kappaB) and associated regulatory factors make up a multi-component signaling pathway that regulates a wide range of biological processes, including cell survival, proliferation, differentiation, stress response, and death, as well as immunity and inflammation. Aberrant NF-kappaB pathway activity is known to be associated with a host of diseases, including immune deficiencies, inflammatory disorders, and cancer. Recent advances in our understanding of the inner workings of the NF-kappaB pathway have led to the development of new therapeutic strategies for the treatment of these diseases. In this review, we focus on the regulation of the NF-kappaB pathway by Bcl-3 (B cell leukemia-3), a nuclear member of the IkappaB (inhibitor of NF-kappaB) family. Both the regulation and the function of Bcl-3 will be discussed.

Matrix Metalloproteinase-9 gene induction by a truncated oncogenic NF-kappaB2 protein involves the recruitment of MLL1 and MLL2 H3K4 histone methyltransferase complexes

Constitutive nuclear factor (NF)-kappaB activation in haematological malignancies is caused in several cases by loss of function mutations within the coding sequence of NF-kappaB inhibitory molecules such as IkappaBalpha or p100. Hut-78, a truncated form of p100, constitutively generates p52 and contributes to the development of T-cell lymphomas but the molecular mechanism underlying this oncogenic potential remains unclear. We show here that MMP9 gene expression is induced through the alternative NF-kappaB-activating pathway in fibroblasts and also on Hut-78 or p52 overexpression in fibroblasts as well as in lymphoma cells. p52 is critical for Hut-78-mediated MMP9 gene induction as a Hut-78 mutant as well as other truncated NF-kappaB2 proteins that are not processed into p52 failed to induce the expression of this metalloproteinase. Conversely, MMP9 gene expression is impaired in p52-depleted HUT-78 cells. Interestingly, MLL1 and MLL2 H3K4 methyltransferase complexes are tethered by p52 on the MMP9 but not on the IkappaBalpha promoter, and the H3K4 trimethyltransferase activity recruited on the MMP9 promoter is impaired in p52-depleted HUT-78 cells. Moreover, MLL1 and MLL2 are associated with Hut-78 in a native chromatin-enriched extract. Thus, we identified a molecular mechanism by which the recruitment of a H3K4 histone methyltransferase complex on the promoter of a NF-kappaB-dependent gene induces its expression and potentially the invasive potential of lymphoma cells harbouring constitutive activity of the alternative NF-kappaB-activating pathway.

Transgenic Bcl-3 slows T cell proliferation

Immunological adjuvants, such as bacterial LPS, increase the mRNA levels of the IkB-related NF-κB transcriptional transactivator, Bcl-3, in activated T cells. Adjuvants also increase the life expectancy of activated T cells, as does over-expression of Bcl-3, suggesting that Bcl-3 is part of the pathway whereby adjuvants affect T cell lifespans. However, previous reports, confirmed here, show that adjuvants also increase the life expectancies of Bcl-3-deficient T cells, making Bcl-3’s role and effects in adjuvant-induced survival uncertain. To investigate the functions of Bcl-3 further, here we confirm the adjuvant-induced expression of Bcl-3 mRNA and show Bcl-3 induction at the protein level. Bcl-3 was expressed in mice via a transgene driven by the human CD2 promoter. Like other protective events, over-expression of Bcl-3 slows T cell activation very early in T cell responses to antigen, both in vitro and in vivo. This property was intrinsic to the T cells over-expressing the Bcl-3 and did not require Bcl-3 expression by other cells such as antigen-presenting cells.

High expression of BCL3 in human myeloma cells is associated with increased proliferation and inferior prognosis

BACKGROUND

BCL3 is a putative oncogene encoding for a protein belonging to the inhibitory kappaB-family. We experienced that this putative oncogene was a common target gene for growth-promoting cytokines in myeloma cell lines.

METHODS

Gene expression of BCL3 was studied in 351 newly diagnosed myeloma patients, 12 patients with smouldering myeloma, 44 patients with monoclonal gammopathy of undetermined significance and 22 healthy individuals. Smaller material of samples was included for mRNA detection by RT-PCR, protein detection by Western blot and immunohistochemistry, and for cytogenetic studies. A total of eight different myeloma cell lines were studied.

RESULTS

Bcl-3 was induced in myeloma cell lines by interleukin (IL)-6, IL-21, IL-15, tumor necrosis factor-alpha and IGF-1, and its upregulation was associated with increased proliferation of the cells. In a population of 351 patients, expression levels of BCL3 above 75th percentile were associated with shorter 5-yr survival. When this patient population was divided into subgroups based on molecular classification, BCL3 was significantly increased in a poor risk subgroup characterized by overexpression of cell cycle and proliferation related genes. Intracellular localization of Bcl-3 was dependent on type of stimulus given to the cell.

CONCLUSION

BCL3 is a common target gene for several growth-promoting cytokines in myeloma cells and high expression of BCL3 at the time of diagnosis is associated with poor prognosis of patients with multiple myeloma (MM). These data may indicate a potential oncogenic role for Bcl-3 in MM.

The proto-oncogene Bcl3, induced by Tax, represses Tax-mediated transcription via p300 displacement from the human T-cell leukemia virus type 1 promoter

The etiology of human T-cell leukemia virus type 1 (HTLV-1)-induced adult T-cell leukemia is linked to the expression of the viral oncoprotein Tax. Although the mechanism of retroviral transformation is unknown, Tax interferes with fundamental cellular processes, including proliferation and apoptosis, and these events may directly link Tax to early steps in malignant progression. In this study, we examined the interplay between Tax and the potent proto-oncogene B-cell chronic leukemia protein 3 (Bcl3). Bcl3 is a critical regulator of cell survival and proliferation and is overexpressed in HTLV-1-infected cells. We found that Tax induced Bcl3 expression through stimulation of the NF-kappaB pathway. An intronic NF-kappaB binding site within the Bcl3 gene served as the primary target of Tax-induced NF-kappaB activation. We next considered the consequence of Bcl3 overexpression on Tax function. Interestingly, we found that Bcl3 formed a stable complex with Tax and that this complex potently inhibited Tax-dependent HTLV-1 transcription. Importantly, Bcl3 associated with the HTLV-1 promoter in a Tax-dependent manner and inhibited the binding of the critical cellular coactivator p300. The conserved ankyrin repeat domain of Bcl3 mediated both Tax binding and inhibition of p300 recruitment to the HTLV-1 promoter. Together, these data suggest that Tax-induced Bcl3 overexpression benefits the virus in two important ways. First, Bcl3 may promote cell division and thus clonal proliferation of the virus. Second, Bcl3 may attenuate virion production, facilitating immune evasion. One consequence of this regulatory loop may be Bcl3-induced malignant transformation of the host cell.

New regulators of NF-kappaB in inflammation

Research on the biological function of nuclear factor-kappaB (NF-kappaB), a key mediator of inducible transcription in the immune system, has traditionally focused on its role in the initiation of innate and adaptive immune responses. These studies have largely concentrated on the mechanisms of signalling that lead to NF-kappaB activation and on the positive role of NF-kappaB in both physiological immunity and pathological inflammation. More recently, there has been growing interest in the mechanisms that directly regulate the NF-kappaB transcriptional programmes. As a result, several new NF-kappaB regulatory components have been identified and some of the known components have been assigned new roles. In this Review, we discuss these new insights into the regulation of NF-kappaB.

NF-kappaB and epithelial to mesenchymal transition of cancer

During progression of an in situ to an invasive cancer, epithelial cells lose expression of proteins that promote cell-cell contact, and acquire mesenchymal markers, which promote cell migration and invasion. These events bear extensive similarities to the process of epithelial to mesenchymal transition (EMT), which has been recognized for several decades as critical feature of embryogenesis. The NF-kappaB family of transcription factors plays pivotal roles in both promoting and maintaining an invasive phenotype. After briefly describing the NF-kappaB family and its role in cancer, in this review we will first describe studies elucidating the functions of NF-kappaB in transcription of master regulator genes that repress an epithelial phenotype. In the second half, we discuss the roles of NF-kappaB in control of mesenchymal genes critical for promoting and maintaining an invasive phenotype. Overall, NF-kappaB is identified as a key target in prevention and in the treatment of invasive carcinomas.

Hepatocellular carcinoma and the ubiquitin-proteasome system

Hepatocellular carcinoma is one of the largest causes of cancer-related deaths worldwide for which there are very limited treatment options that are currently effective. The ubiquitin-proteasome system has rapidly become acknowledged as both critical for normal cellular function and a frequent target of de-regulation leading to disease. This review appraises the evidence linking the ubiquitin-proteasome system with this devastatingly intractable cancer and asks whether it may prove to be fertile ground for the development of novel therapeutic interventions against hepatocellular carcinoma.

Role of nuclear IkappaB proteins in the regulation of host immune responses

A variety of microbial components activate a transcription factor called nuclear factor-kappaB (NF-kappaB) that plays an essential role in the optimal activation of host immune systems. The transcriptional activity of NF-kappaB is tightly regulated at multiple steps in immune signaling pathways, because excessive activation is detrimental to the host. One mechanism to prevent NF-kappaB activation is mediated by cytoplasmic IkappaB family proteins. Although cytoplasmic IkappaBs interact with NF-kappaB subunits in the cytoplasm of unstimulated cells, IkappaBs are rapidly degraded on stimulation, allowing free NF-kappaB to translocate into the nucleus and activate the transcription of genes encoding various immune mediators. After the translocation of NF-kappaB from the cytoplasm to the nucleus, nuclear proteins that are structurally similar to cytoplasmic IkappaBs take part in the regulation of NF-kappaB transcriptional activity, as activators or inhibitors, by associating with NF-kappaB subunits. Therefore, the regulatory IkappaB-like nuclear molecules are described as "nuclear IkappaB proteins." In this review, the in vivo function of the nuclear IkappaB proteins, Bcl-3, IkappaBzeta, and IkappaBNS in the context of host immune responses and diseases will be discussed.

Heat shock factor 1 inhibits nuclear factor-kappaB nuclear binding activity during endotoxin tolerance and heat shock

RATIONALE

Sepsis, endotoxin tolerance, and heat shock (HS) all display down-regulation of innate immunity. We hypothesize that HS factor 1 (HSF-1) induces competitive inhibition of nuclear factor-kappaB (NF-kappaB)-induced signal transduction in both endotoxin tolerance and HS.

OBJECTIVES

We compared endotoxin tolerance and HS in RAW 264.7 cells. We transfected cells with an HS protein 70 (HSP70) plasmid to test whether HSP70 is the mediator of HS-induced NF-kappaB inhibition. We studied the effects of endotoxin stimulation and HS, both separately and together, on "wild-type" cells, cells transfected with the HSP70 plasmid, and cells transfected with vehicle.

FINDINGS

Heat shock protein 70 plasmid-transfected cells had increased HSP70 expression and demonstrated decreased nitric oxide (NO) release and inducible NO synthase messenger RNA expression in response to endotoxin compared with wild-type and empty plasmid-transfected cells. Heat shock completely abolished subsequent NO and inducible NO synthase messenger RNA expression in wild-type cells. Heat shock factor 1 reached maximum expression 60 to 90 minutes after HS. Heat shock protein 70-transfected cells still displayed endotoxin-induced NF-kappaB nuclear binding, whereas endotoxin tolerance, HS, and exposure to HSF-1, but not exposure to an unrelated promoter, inhibited NF-kappaB nuclear binding.

CONCLUSIONS

Endotoxin tolerance and HS appear to share a common immune suppressive effect, possibly through HSF-1-mediated competitive inhibition of NF-kappaB nuclear binding.

NF-kappaB p52, RelB and c-Rel are transported into the nucleus via a subset of importin alpha molecules

In resting cells NF-kappaB transcription factors are retained in the cytoplasm as latent inactive complexes, until they are activated and rapidly transported into the nucleus. We show that all NF-kappaB proteins are imported into the nucleus via a subset of importin alpha isoforms. Our data indicate that the NF-kappaB components of the classical and alternative pathways have somewhat different specifities to importin alpha molecules. Based on the results from binding experiments of in vitro-translated and Sendai virus infection-induced or TNF-alpha-stimulated endogenous NF-kappaB proteins, it can be predicted that the specifity of NF-kappaB proteins to importin alpha molecules is different and changes upon the composition of the imported dimer. p52 protein binds directly to importin alpha3, alpha4, alpha5 and alpha6 and c-Rel binds to importin alpha5, alpha6 and alpha7 via a previously described monopartite nuclear localization signals (NLSs). Here we show that RelB, instead, has a bipartite arginine/lysine-rich NLS that mediates the binding of RelB to importin alpha5 and alpha6 and subsequent nuclear translocation of the protein. Moreover, we show that the nuclear import of p52/RelB heterodimers is mediated exclusively by the NLS of RelB. In addition, we found that the NLS of p52 mediates the nuclear import of p52/p65 heterodimers.

Shared principles in NF-kappaB signaling

The transcription factor NF-kappaB has served as a standard for inducible transcription factors for more than 20 years. The numerous stimuli that activate NF-kappaB, and the large number of genes regulated by NF-kappaB, ensure that this transcription factor is still the subject of intense research. Here, we attempt to synthesize some of the basic principles that have emerged from studies of NF-kappaB, and we aim to generate a more unified view of NF-kappaB regulation.

Constitutive production of NF-kappaB2 p52 is not tumorigenic but predisposes mice to inflammatory autoimmune disease by repressing Bim expression

Normal development of the immune system requires regulated processing of NF-kappaB2 p100 to p52, which activates NF-kappaB2 signaling. Constitutive production of p52 has been suggested as a major mechanism underlying lymphomagenesis induced by NF-kappaB2 mutations, which occur recurrently in a variety of human lymphoid malignancies. To test the hypothesis, we generated transgenic mice with targeted expression of p52 in lymphocytes. In contrast to their counterparts expressing the tumor-derived NF-kappaB2 mutant p80HT, which develop predominantly B cell tumors, p52 transgenic mice are not prone to lymphomagenesis. However, they are predisposed to inflammatory autoimmune disease characterized by multiorgan infiltration of activated lymphocytes, high levels of autoantibodies in the serum, and immune complex glomerulonephritis. p52, but not p80HT, represses Bim expression, leading to defects in apoptotic processes critical for elimination of autoreactive lymphocytes and control of immune response. These findings reveal distinct signaling pathways for actions of NF-kappaB2 mutants and p52 and suggest a causal role for sustained NF-kappaB2 activation in the pathogenesis of autoimmunity.