Cloning of a mitogen-inducible gene encoding a kappa B DNA-binding protein with homology to the rel oncogene and to cell-cycle motifs

Transcriptional Regulation during Aberrant Activation of NF-κB Signalling in Cancer

The NF-κB signalling pathway is a major signalling cascade involved in the regulation of inflammation and innate immunity. It is also increasingly recognised as a crucial player in many steps of cancer initiation and progression. The five members of the NF-κB family of transcription factors are activated through two major signalling pathways, the canonical and non-canonical pathways. The canonical NF-κB pathway is prevalently activated in various human malignancies as well as inflammation-related disease conditions. Meanwhile, the significance of non-canonical NF-κB pathway in disease pathogenesis is also increasingly recognized in recent studies. In this review, we discuss the double-edged role of the NF-κB pathway in inflammation and cancer, which depends on the severity and extent of the inflammatory response. We also discuss the intrinsic factors, including selected driver mutations, and extrinsic factors, such as tumour microenvironment and epigenetic modifiers, driving aberrant activation of NF-κB in multiple cancer types. We further provide insights into the importance of the interaction of NF-κB pathway components with various macromolecules to its role in transcriptional regulation in cancer. Finally, we provide a perspective on the potential role of aberrant NF-κB activation in altering the chromatin landscape to support oncogenic development.

Origin of the Functional Distinctiveness of NF-κB/p52

The transcription regulators of the NF-κB family have emerged as a critical factor affecting the function of various adult tissues. The NF-κB family transcription factors are homo- and heterodimers made up of five monomers (p50, p52, RelA, cRel and RelB). The family is distinguished by sequence homology in their DNA binding and dimerization domains, which enables them to bind similar DNA response elements and participate in similar biological programs through transcriptional activation and repression of hundreds of genes. Even though the family members are closely related in terms of sequence and function, they all display distinct activities. In this review, we discuss the sequence characteristics, protein and DNA interactions, and pathogenic involvement of one member of family, NF-κB/p52, relative to that of other members. We pinpoint the small sequence variations within the conserved region that are mostly responsible for its distinct functional properties.

The multifaceted NF-kB: are there still prospects of its inhibition for clinical intervention in pediatric central nervous system tumors?

Despite advances in the understanding of the molecular mechanisms underlying the basic biology and pathogenesis of pediatric central nervous system (CNS) malignancies, patients still have an extremely unfavorable prognosis. Over the years, a plethora of natural and synthetic compounds has emerged for the pharmacologic intervention of the NF-kB pathway, one of the most frequently dysregulated signaling cascades in human cancer with key roles in cell growth, survival, and therapy resistance. Here, we provide a review about the state-of-the-art concerning the dysregulation of this hub transcription factor in the most prevalent pediatric CNS tumors: glioma, medulloblastoma, and ependymoma. Moreover, we compile the available literature on the anti-proliferative effects of varied NF-kB inhibitors acting alone or in combination with other therapies in vitro, in vivo, and clinical trials. As the wealth of basic research data continues to accumulate, recognizing NF-kB as a therapeutic target may provide important insights to treat these diseases, hopefully contributing to increase cure rates and lower side effects related to therapy.

NF-κB and Its Regulators During Pregnancy

The transcriptional factor NF-κB is a nuclear factor involved in both physiological and pathological processes. This factor can control the transcription of more than 400 genes, including cytokines, chemokines, and their modulators, immune and non-immune receptors, proteins involved in antigen presentation and cell adhesion, acute phase and stress response proteins, regulators of apoptosis, growth factors, other transcription factors and their regulators, as well as different enzymes; all these molecules control several biological processes. NF-κB is a tightly regulated molecule that has also been related to apoptosis, cell proliferation, inflammation, and the control of innate and adaptive immune responses during onset of labor, in which it has a crucial role; thus, early activation of this factor may have an adverse effect, by inducing premature termination of pregnancy, with bad outcomes for the mother and the fetus, including product loss. Reviews compiling the different activities of NF-κB have been reported. However, an update regarding NF-κB regulation during pregnancy is lacking. In this work, we aimed to describe the state of the art around NF-κB activity, its regulatory role in pregnancy, and the effect of its dysregulation due to invasion by pathogens like Trichomonas vaginalis and Toxoplasma gondii as examples.

NF-κB/Rel Transcription Factors in Pancreatic Cancer: Focusing on RelA, c-Rel, and RelB

Regulation of Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)/Rel transcription factors (TFs) is extremely cell-type-specific owing to their ability to act disparately in the context of cellular homeostasis driven by cellular fate and the microenvironment. This is also valid for tumor cells in which every single component shows heterogenic effects. Whereas many studies highlighted a per se oncogenic function for NF-κB/Rel TFs across cancers, recent advances in the field revealed their additional tumor-suppressive nature. Specifically, pancreatic ductal adenocarcinoma (PDAC), as one of the deadliest malignant diseases, shows aberrant canonical-noncanonical NF-κB signaling activity. Although decades of work suggest a prominent oncogenic activity of NF-κB signaling in PDAC, emerging evidence points to the opposite including anti-tumor effects. Considering the dual nature of NF-κB signaling and how it is closely linked to many other cancer related signaling pathways, it is essential to dissect the roles of individual Rel TFs in pancreatic carcinogenesis and tumor persistency and progression. Here, we discuss recent knowledge highlighting the role of Rel TFs RelA, RelB, and c-Rel in PDAC development and maintenance. Next to providing rationales for therapeutically harnessing Rel TF function in PDAC, we compile strategies currently in (pre-)clinical evaluation.

Alternative NF-κB signaling promotes colorectal tumorigenesis through transcriptionally upregulating Bcl-3

Multiple studies have shown that chronic inflammation is closely related to the occurrence and development of colorectal cancer (CRC). Classical NF-κB signaling, the key factor in controlling inflammation, has been found to be of great importance to CRC development. However, the role of alternative NF-κB signaling in CRC is still elusive. Here, we found aberrant constitutive activation of alternative NF-κB signaling both in CRC tissue and CRC cells. Knockdown of RelB downregulates c-Myc and upregulates p27^Kip1 protein level, which inhibits CRC cell proliferation and retards CRC xenograft growth. Conversely, overexpression of RelB increases proliferation of CRC cells. In addition, we revealed a significant correlation between Bcl-3 and RelB in CRC tissues. The expression of RelB was consistent with the expression of Bcl-3 and the phosphorylation of Bcl-3 downstream proteins p-Akt (S473) and p-GSK3β (S9). Bcl-3 overexpression can restore the phenotype changes caused by RelB knockdown. Importantly, we demonstrated that alternative NF-κB transcriptional factor (p52:RelB) can directly bind to the promoter region of Bcl-3 gene and upregulate its transcription. Moreover, the expression of RelB, NF-κB2 p52, and Bcl-3 was associated with poor survival of CRC patients. Taken together, these results represent that alternative NF-κB signaling may function as an oncogenic driver in CRC, and also provide new ideas and research directions for the pathogenesis, prevention, and treatment of other inflammatory-related diseases.

The atypical IκB protein IκB(NS) is important for Toll-like receptor-induced interleukin-10 production in B cells

Although a major function of B cells is to mediate humoral immunity by producing antigen-specific antibodies, a specific subset of B cells is important for immune suppression, which is mainly mediated by the secretion of the anti-inflammatory cytokine interleukin-10 (IL-10). However, the mechanism by which IL-10 is induced in B cells has not been fully elucidated. Here, we report that IκBNS , an inducible nuclear IκB protein, is important for Toll-like receptor (TLR)-mediated IL-10 production in B cells. Studies using IκB(NS) knockout mice revealed that the number of IL-10-producing B cells is reduced in IκB(NS)(-/-) spleens and that the TLR-mediated induction of cytoplasmic IL-10-positive cells and IL-10 secretion in B cells are impaired in the absence of IκB(NS). The impairment of IL-10 production by a lack of IκB(NS) was not observed in TLR-triggered macrophages or T-cell-receptor-stimulated CD4(+) CD25(+) T cells. In addition, IκB(NS)-deficient B cells showed reduced expression of Prdm1 and Irf4 and failed to generate IL-10(+) CD138(+) plasmablasts. These results suggest that IκB(NS) is selectively required for IL-10 production in B cells responding to TLR signals, so defining an additional role for IκB(NS) in the control of the B-cell-mediated immune responses.

Group A Streptococcus induces less p65 nuclear translocation and non-classical nuclear factor kappa B activation in macrophages, which possibly leads to a weaker inflammatory response

OBJECTIVES

The aim of this study was to explore the pathogenic mechanism of group A Streptococcus (GAS) and to investigate how GAS evades phagocytosis by immune cells.

METHODS

The classical inflammatory signaling pathway of macrophages infected with GAS was investigated by protein microarray, real-time PCR, Western blot, immunoprecipitation, and flow cytometry.

RESULTS

GAS induced a lower level of inflammatory mediators in macrophages than either the Gram-positive Staphylococcus aureus or the Gram-negative Escherichia coli. Therefore, the conventional inflammatory signal pathway was investigated. It was found that GAS and S. aureus induced both toll-like receptor (TLR)2 and TLR4 expression, while Gram-negative E. coli only activated TLR4 in RAW264.7 cells. Although MyD88, the main adaptor protein, was activated by the three pathogens, there was no difference in MyD88 expression in macrophages. Nuclear factor kappa B (NF-κB) is the classical transcription factor of inflammatory signals, and the results of the present study showed that GAS, similar to E. coli, induced a weaker p65 nuclear translocation compared to S. aureus. Interestingly, GAS activated NF-κB by inducing p65-p52 heterodimer, but not the classical heterodimer of NF-κB (p65-p50), while E. coli activated NF-κB by inducing both p65-p50 and p65-p52 heterodimers.

CONCLUSIONS

Compared to S. aureus and E. coli infection, GAS induced a weaker nuclear translocation and distinct combination of NF-κB subunits in macrophages, which probably leads to a weak inflammatory response.

Maternal control of the Drosophila dorsal-ventral body axis

The pathway that generates the dorsal-ventral (DV) axis of the Drosophila embryo has been the subject of intense investigation over the previous three decades. The initial asymmetric signal originates during oogenesis by the movement of the oocyte nucleus to an anterior corner of the oocyte, which establishes DV polarity within the follicle through signaling between Gurken, the Drosophila Transforming Growth Factor (TGF)-α homologue secreted from the oocyte, and the Drosophila Epidermal Growth Factor Receptor (EGFR) that is expressed by the follicular epithelium cells that envelop the oocyte. Follicle cells that are not exposed to Gurken follow a ventral fate and express Pipe, a sulfotransferase that enzymatically modifies components of the inner vitelline membrane layer of the eggshell, thereby transferring DV spatial information from the follicle to the egg. These ventrally sulfated eggshell proteins comprise a localized cue that directs the ventrally restricted formation of the active Spätzle ligand within the perivitelline space between the eggshell and the embryonic membrane. Spätzle activates Toll, a transmembrane receptor in the embryonic membrane. Transmission of the Toll signal into the embryo leads to the formation of a ventral-to-dorsal gradient of the transcription factor Dorsal within the nuclei of the syncytial blastoderm stage embryo. Dorsal controls the spatially specific expression of a large constellation of zygotic target genes, the Dorsal gene regulatory network, along the embryonic DV circumference. This article reviews classic studies and integrates them with the details of more recent work that has advanced our understanding of the complex pathway that establishes Drosophila embryo DV polarity. For further resources related to this article, please visit the WIREs website.

CONFLICT OF INTEREST

The authors have declared no conflicts of interest for this article.

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.

NF-κB and the link between inflammation and cancer

The nuclear factor-κB (NF-κB) transcription factor family has been considered the central mediator of the inflammatory process and a key participant in innate and adaptive immune responses. Coincident with the molecular cloning of NF-κB/RelA and identification of its kinship to the v-Rel oncogene, it was anticipated that NF-κB itself would be involved in cancer development. Oncogenic activating mutations in NF-κB genes are rare and have been identified only in some lymphoid malignancies, while most NF-κB activating mutations in lymphoid malignancies occur in upstream signaling components that feed into NF-κB. NF-κB activation is also prevalent in carcinomas, in which NF-κB activation is mainly driven by inflammatory cytokines within the tumor microenvironment. Importantly, however, in all malignancies, NF-κB acts in a cell type-specific manner: activating survival genes within cancer cells and inflammation-promoting genes in components of the tumor microenvironment. Yet, the complex biological functions of NF-κB have made its therapeutic targeting a challenge.

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.

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.

Adapted Boolean network models for extracellular matrix formation

BACKGROUND

Due to the rapid data accumulation on pathogenesis and progression of chronic inflammation, there is an increasing demand for approaches to analyse the underlying regulatory networks. For example, rheumatoid arthritis (RA) is a chronic inflammatory disease, characterised by joint destruction and perpetuated by activated synovial fibroblasts (SFB). These abnormally express and/or secrete pro-inflammatory cytokines, collagens causing joint fibrosis, or tissue-degrading enzymes resulting in destruction of the extra-cellular matrix (ECM).We applied three methods to analyse ECM regulation: data discretisation to filter out noise and to reduce complexity, Boolean network construction to implement logic relationships, and formal concept analysis (FCA) for the formation of minimal, but complete rule sets from the data.

RESULTS

First, we extracted literature information to develop an interaction network containing 18 genes representing ECM formation and destruction. Subsequently, we constructed an asynchronous Boolean network with biologically plausible time intervals for mRNA and protein production, secretion, and inactivation. Experimental gene expression data was obtained from SFB stimulated by TGFbeta1 or by TNFalpha and discretised thereafter. The Boolean functions of the initial network were improved iteratively by the comparison of the simulation runs to the experimental data and by exploitation of expert knowledge. This resulted in adapted networks for both cytokine stimulation conditions. The simulations were further analysed by the attribute exploration algorithm of FCA, integrating the observed time series in a fine-tuned and automated manner. The resulting temporal rules yielded new contributions to controversially discussed aspects of fibroblast biology (e.g., considerable expression of TNF and MMP9 by fibroblasts stimulation) and corroborated previously known facts (e.g., co-expression of collagens and MMPs after TNFalpha stimulation), but also revealed some discrepancies to literature knowledge (e.g., MMP1 expression in the absence of FOS).

CONCLUSION

The newly developed method successfully and iteratively integrated expert knowledge at different steps, resulting in a promising solution for the in-depth understanding of regulatory pathways in disease dynamics. The knowledge base containing all the temporal rules may be queried to predict the functional consequences of observed or hypothetical gene expression disturbances. Furthermore, new hypotheses about gene relations were derived which await further experimental validation.

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.

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.

Neuroadaptations in human chronic alcoholics: dysregulation of the NF-kappaB system

Background

Alcohol dependence and associated cognitive impairments apparently result from neuroadaptations to chronic alcohol consumption involving changes in expression of multiple genes. Here we investigated whether transcription factors of Nuclear Factor-kappaB (NF-κB) family, controlling neuronal plasticity and neurodegeneration, are involved in these adaptations in human chronic alcoholics.

Methods and Findings

Analysis of DNA-binding of NF-κB (p65/p50 heterodimer) and the p50 homodimer as well as NF-κB proteins and mRNAs was performed in postmortem human brain samples from 15 chronic alcoholics and 15 control subjects. The prefrontal cortex involved in alcohol dependence and cognition was analyzed and the motor cortex was studied for comparison. The p50 homodimer was identified as dominant κB binding factor in analyzed tissues. NF-κB and p50 homodimer DNA-binding was downregulated, levels of p65 (RELA) mRNA were attenuated, and the stoichiometry of p65/p50 proteins and respective mRNAs was altered in the prefrontal cortex of alcoholics. Comparison of a number of p50 homodimer/NF-κB target DNA sites, κB elements in 479 genes, down- or upregulated in alcoholics demonstrated that genes with κB elements were generally upregulated in alcoholics. No significant differences between alcoholics and controls were observed in the motor cortex.

Conclusions

We suggest that cycles of alcohol intoxication/withdrawal, which may initially activate NF-κB, when repeated over years downregulate RELA expression and NF-κB and p50 homodimer DNA-binding. Downregulation of the dominant p50 homodimer, a potent inhibitor of gene transcription apparently resulted in derepression of κB regulated genes. Alterations in expression of p50 homodimer/NF-κB regulated genes may contribute to neuroplastic adaptation underlying alcoholism.

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

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

Overexpression of Phospholipid-hydroperoxide Glutathione Peroxidase in Human Dermal Fibroblasts Abrogates UVA Irradiation-induced Expression of Interstitial Collagenase/Matrix Metalloproteinase-1 by Suppression of Phosphatidylcholine Hydroperoxide-mediated NFκB Activation and Interleukin-6 Release

Phospholipid-hydroperoxide glutathione peroxidase (PHGPx) exhibits high specific activity in reducing phosphatidylcholine hydroperoxides (PCOOHs) and thus may play a central role in protecting the skin against UV irradiation-triggered detrimental long term effects like cancer formation and premature skin aging. Here we addressed the role of PHGPx in the protection against UV irradiation-induced expression of matrix metalloproteinase-1 (MMP-1). For this purpose, we created human dermal fibroblast cell lines overexpressing human PHGPx. Overexpression led to a significant increase in PHGPx activity. In contrast to a maximal 4.5-fold induction of specific MMP-1 mRNA levels in vector-transfected cells at 24 h after UVA irradiation, no MMP-1 induction occurred at any studied time point after UVA treatment of PHGPx-overexpressing fibroblasts. As interleukin-6 (IL-6) was earlier shown to mediate the UVA induction of MMP-1, we studied whether PHGPx overexpression might interfere with the NFkappaB-mediated IL-6 induction and downstream signaling. Using transient transfections of IL-6 promoter constructs containing NFkappaB binding sites, we observed a high induction of the reporter gene luciferase in vector-transfected control cells and a significantly lower induction in PHGPx-overexpressing fibroblasts following UVA irradiation. Consistently both UVA irradiation and treatment of fibroblasts with PCOOHs led to phosphorylation and nuclear translocation of the p65 subunit, whereas cells overexpressing PHGPx exhibited impaired NFkappaB activation, p65 phosphorylation, and nuclear translocation. In line with this, the PHGPx-overexpressing fibroblasts showed a reduced constitutive and UVA irradiation-induced IL-6 release. After incubating PHGPx-overexpressing cells with PCOOHs a reduced induction of IL-6 was observed. This together with the suppression of UVA irradiation-induced IL-6 release in the presence of Trolox, a chain breaker of PCOOH-initiated lipid peroxidation, indicates that UVA irradiation-induced PCOOHs and subsequent lipid peroxides initiate the NFkappaB-mediated induction of IL-6, which mediates the induction of MMP-1. Our finding is particularly relevant in light of the already available small molecule mimetics of PHGPx.

Control of T cell viability

The factors affecting T cell viability vary depending on the type and status of the T cell involved. Naive T cells die via a Bcl-2/Bim dependent route. Their deaths are prevented in animals by IL-7 and contact with MHC. Activated T cells die in many different ways. Among these is a pathway involving signals that come from outside the T cell and affect it via surface receptors such as Fas. Activated T cells also die through a pathway driven by signals generated within the T cell itself, a cell autonomous route. This pathway involves members of the Bcl-2 family, in particular Bcl-2, Bcl-xl, Bim, and probably Bak. The viability of CD8+ and CD4+ memory T cells is controlled in different ways. CD8+ memory T cells are maintained by IL-15 and IL-7. The control of CD4+ memory T cells is more mysterious, with roles reported for IL-7 and/or contact via the TCR.

Proteins controlling the nuclear uptake of NF-kappa B, Rel and dorsal

The two DNA-binding subunits of the transcription factor NF-kappa B, the products of the rel oncogene family and the product of the developmental control gene dorsal of Drosophila are homologous within a 300 amino acid region. This sequence represents a novel DNA-binding and dimerization domain. The access of the NF-kappa B/Rel/dorsal (NRD) transcription factor family to the cell nucleus is regulated. There is now evidence that functionally and structurally related accessory proteins of NF-kappa B, Rel and dorsal control the nuclear entry as well as DNA-binding activity of the transcription factors. This review summarizes current knowledge about the nuclear-uptake regulatory proteins (NURPs) I kappa B-alpha, I kappa B-beta/pp40 and cactus.

Induced stabilization of IkappaBalpha can facilitate its re-synthesis and prevent sequential degradation

The transcription factor NF-kappaB is responsible for regulating genes that can profoundly impact cell proliferation, apoptosis, inflammation, and immune responses. The NF-kappaB inhibitor IkappaBalpha is rapidly degraded and then re-synthesized after an NF-kappaB stimulus. We have found that the re-synthesis of IkappaBalpha in a human colon-derived cell line (HT-29) includes the post-translational stabilization of newly synthesized IkappaBalpha. The TNF-alpha-induced stabilization of newly synthesized IkappaBalpha involves the C-terminal PEST region of the protein: N-terminal deletion mutants (lacking the IkappaB kinase phosphorylation sites) were readily stabilized by TNF-alpha, whereas deletion of the C-terminus resulted in a constitutively stable protein. The role of the C-terminus in stabilization was further supported by the finding that fusion of the IkappaBalpha C-terminus to GFP generated a protein that could also be stabilized by TNF-alpha. The p38 mitogen-activated protein (MAP) kinase inhibitor SB203580 prevented stabilization of IkappaBalpha and delayed the re-emergence of IkappaBalpha following TNF-alpha-induced degradation. The IkappaBalpha stabilization pathway could prevent sequential rounds of IkappaBalpha degradation without preventing IkappaBalpha phosphorylation. Analysis of two other cell lines (SW480 and THP-1) revealed similarities and cell-specific differences in the regulation of IkappaBalpha stabilization. We propose that cytokine stabilization of newly synthesized IkappaBalpha in some cell types is a critical homeostatic mechanism that limits inflammatory gene expression.

Effect of subtoxic concentrations of metal ions on NFkappaB activation in THP-1 human monocytes

THP-1 human monocytes and human peripheral blood monocytes have altered inflammatory cytokine secretion profiles after exposure to a variety of metal ions known to be released from biomaterials. Transcriptional regulation of these cytokines often involves activation of the transcription factor NFkappaB. The present study was designed to determine whether metal ion treatment of monocytes results in changes in levels of activated NFkappaB. THP-1 cells were grown in suspension in the presence of sublethal concentrations of ions of Ag(+), Co(2+), Cu(2+), Hg(2+), Ni(2+), and Pd(2+). After 24 h of exposure to metal ions, the cells were harvested, counted, and the nuclear proteins extracted. Electrophoretic mobility shift assays were performed using a (32)P-ATP end-labeled oligonucleotide consensus sequence for the NFkappaB transcription factor. DNA/protein complexes were quantified by phosphorimage analysis and compared by ANOVA (Tukey, alpha = 0.05). Exposure of THP-1 cells to 100 microM of Pd(2+) caused a significant increase in activated NFkappaB (p < 0.05) whereas treatment with 5 microM of Ag(+) resulted in significantly decreased levels of nuclear NFkappaB (p < 0.05). No other metal ions tested caused a significant change in basal levels of nuclear NFkappaB (Co(2+), Hg(2+), Ni(2+), and Cu(2+)). However, exposure to 50 microM of Cu(2+) resulted in a reproducible, though not significant, increase in nuclear NFkappaB levels. These results indicate that inflammatory responses to some metal ions may be influenced by NFkappaB-mediated transcriptional regulation.

Metal ions alter lipopolysaccharide-induced NFκB binding in monocytes

Metals are components of a variety of biomaterials used in orthopedic and dental appliances; however, their biocompatibility with the surrounding tissues is not completely understood. Monocytes are important immune cells that respond to inflammatory stimuli by rapidly producing a variety of inflammatory proteins. Regulation of this response often involves activation of the transcription factor NF kappa B. The current study was designed to determine whether monocyte activation of NF kappa B in response to bacterial lipopolysaccharide (LPS) is affected by pretreatment with metal ions. Concentrations of metal ions that affected cell number after 24 h of exposure were first determined. Then THP-1 human monocytes were cultured for 2 h in media containing metal ions at concentrations below levels that altered cell growth. Parallel cultures were treated with 10 microg/mL Escherichia coli LPS, and all samples were cultured an additional 2 h. Nuclear proteins were extracted and normalized amounts were incubated with [(32)P]-end-labeled NF kappa B consensus oligonucleotide. NF kappa B-DNA complexes were identified and quantified by electrophoretic mobility shift analysis. The extent of NF kappa B-DNA complex formation after metal ion pretreatment with or without LPS induction was compared to no treatment or LPS-only treated controls. Finally, LPS-induced IL1 beta secretion was measured from palladium-treated and control cells. Concentrations were identified for each metal ion (Ag(+), Co(2+), Cu(2+), Hg(2+), Ni(2+), and Pd(2+)) that did not reduce cell number after 24 h of exposure (ranging from 5 microM for Ag(+) and Hg(2+) to 200 microM for Ni(2+)). Exposures of 2 h at these concentrations did not alter cell morphology, staining with trypan blue, or cell number. LPS exposure had no effect on cell number with or without metal ions after 2 h. When metal treatment alone was assessed, none of the metal ions had a significant effect on NF kappa B-DNA binding. However, pretreatment with Co(2+), Ni(2+), Ag(1+), Hg(2+), and Pd(2+) significantly decreased NF kappa B-DNA binding by 40-70% versus LPS alone. Only Cu(2+) had no effect on LPS-induced NF kappa B-DNA complex formation. Pd(2+) lowered, but did not abolish, IL1 beta secretion at concentrations comparable to those that altered NF kappa B-DNA binding. These results suggest that many commonly used metals alter monocyte function at concentrations that are not overtly toxic, and that protein levels controlled in part by NF kappa B also may be altered.

Attenuated transcriptional responses to oxidative stress in the aged rat brain

The aged nervous system displays impaired cognitive functions, and these impairments are exacerbated in several neurodegenerative diseases. A role for oxidative stress has been suggested for several of these age-associated dysfunctions. In addition, recovery from more acute traumatic insults that also generate oxidative stress is impaired in the aged. Here we examine the response of aged rat hippocampi to normobaric hyperoxia treatments and demonstrate an attenuation in the DNA binding activity of the AP-1 and nuclear factor-kappa B transcription factors, which are important components of stress response signal transduction pathways and can determine shifts in cellular commitments to necrosis, apoptosis, or functional recovery in the central nervous system.

Identification of cytokine-induced nuclear factor-kappaB target genes in ovarian and breast cancer cells

NF-kappaB is a pleiotropic transcription factor controlling the expression of many genes and viruses. NF-kappaB plays a role in immune response, cellular adhesion or acute phase response. It also inhibits apoptosis and favors cancer cell survival. We studied the expression of genes controlled by NF-kappaB in ovarian and breast adenocarcinoma cancer cells. We stably transfected OVCAR-3 and MCF7 A/Z cells with an expression vector coding for the mutated inhibitor IkappaBalpha, which sequesters NF-kappaB in the cytoplasm. We stimulated control and IkappaBalpha expressing cells with IL-1beta or TNF-alpha and extracted the RNA, which was reverse-transcribed and hybridized to DNA microarrays. Several of the genes identified were not known as NF-kappaB target genes. Among them, we confirmed the differential expression of ephrin-A1 and caveolin-1 by quantitative real-time polymerase chain reaction. Our results showed an NF-kappaB-dependent induction of ephrin-A1 and caveolin-1 mRNAs after stimulation with TNF-alpha and IL-1beta, confirming that NF-kappaB controls target genes implied in tumor angiogenesis and cell transformation.

Regulation of antibacterial and antifungal innate immunity in fruitflies and humans

Insects have been very successful in adapting to their environment, and the ability of the insect immune system to detect and elicit the appropriate response against various invading pathogens has helped in this success. Unlike the vertebrate immune system, which consists of both innate and adaptive components, insect immunity probably consists entirely of an innate immune response, as no evidence of an adaptive response has been found. The innate immune response is described as either a reaction against "lack of self," or the interaction between host germline-encoded receptors and molecules unique to a particular class of invading organisms. Once the invading organism is recognized, the host immune response can be activated via signaling pathways that lead to the appropriate reaction. This review endeavors to put forth how through genetic, molecular, and biochemical studies of the fruit fly Drosophila melanogaster, as well as other insects, it is now understood that aspects of the insect and vertebrate innate immune system are very similar.

Cytokine-induced stabilization of newly synthesized I(kappa)B-alpha

NF-kappaB activation is triggered by the degradation of inhibitory proteins, such as I(kappa)B-alpha. I(kappa)B-alpha levels are only transiently lowered since one gene activated by NF-kappaB is I(kappa)B-alpha. We found that I(kappa)B-alpha was replenished rapidly in a human colon cell line (HT-29), even in the presence of degradation-inducing phosphorylation (at serine-32). This finding lead us to hypothesize that posttranscriptional mechanisms were also in place to facilitate I(kappa)B-alpha replenishment. Expression of I(kappa)B-alpha from the constitutive, non-NF-kappaB regulated cytomegalovirus promoter in HT-29 cells showed that TNF-alpha or IL-1beta treatment increased I(kappa)B-alpha levels in the absence of transcriptional activation. The TNF-alpha-induced increase in transgenic I(kappa)B-alpha appeared to result from the stabilization of newly synthesized I(kappa)B-alpha, since this increase was effectively preempted by a proteasome inhibitor (MG132) or by I(kappa)B-alpha stabilization through the deletion C-terminal destabilizing elements (without additive or synergistic effects). Analysis of a hepatoma cell line (Hepa 1-4C7) indicated that the I(kappa)B-alpha stabilization may be constitutive in these cells. NF-kappaB stimuli therefore appear to trigger negative feedback pathways in some cells that terminate a NF-kappaB response by increasing the stability of newly synthesized I(kappa)B-alpha.

Transcriptional regulation of the BCL-X gene by NF-kappaB is an element of hypoxic responses in the rat brain

Signal transduction pathways that mediate neuronal commitment to apoptosis involve the nuclear factor kappa B (NF-kappaB) transcription factor. The bcl-x gene is a member of the bcl-2 family of genes that regulate apoptosis, and gives rise to two proteins, Bcl-XL and Bcl-XS, via alternative mRNA splicing. BCl-XL protein, like Bcl-2, is a dominant inhibitor of apoptotic cell death, whereas Bcl-XS promotes apoptosis. While there is high expression of Bcl-XL in the developing and adult brain, few transcriptional control elements have been identified in the bcl-x promoter. There are two functional nuclear factor-kappa B (NF-kappaB) DNA binding sites clustered upstream of the brain-specific transcription start site in the upstream promoter region of murine bcl-x. Recombinant NF-kappaB proteins bind to these sites. Also NF-kappaB overexpression, coupled with bcl-x promoter/reporter assays using a series of murine bcl-x promoter and deletion mutants, has identified the downstream 1.1kb of the bcl-x promoter as necessary for basal promoter activity and induction by NF-kappaB in support of the hypothesis that NF-kappaB can act to enhance BCl-XL expression via highly selective interactions with the bcl-x promoter, where NF-kappaB binding and promoter activation are dependent on specific DNA binding site sequences and NF-kappaB protein dimer composition. Hypoxia induces apoptosis in the hippocampus where the NF-kappaB dimers c-Rel/p50 and p50/pS0 bind to the bcl-x promoter NF-kappaB site.

Cell cycle regulation of NF-kappa b-binding activity in cells from human glioblastomas

Glioblastoma multiforme is a highly malignant and anaplastic tumor of the central nervous system representing more than 50% of all malignant gliomas. The cell origin of this highly undifferentiated tumor remains obscure, although it is postulated that glioblastomas are developed from astrocytes. The rapid growth of the glioma and the state of its undifferentiation are attributed to the deregulation of several signal transduction pathways and cell cycle events. Recent studies showed diverse functions for the NF-kappa B/Rel family of inducible transcription factors including differentiation, apoptosis, oncogenesis, and cell cycle regulation. We sought to examine the level of NF-kappa B activity throughout the glioma's cell cycle. Results from band-shift studies indicated a biphasic NF-kappa B DNA-binding activity in the nuclei of cycling glioblastoma cells. We showed that NF-kappa B-binding activity maximizes in nuclear extracts at specific cell cycle stages including G0/G1, mid-late G1, and S phase. Results from Northern blotting studies revealed that the differential expression of the NF-kappa B subunits, p50 and p65, may not be responsible for cell cycle stage-specific association of NF-kappa B subunits with DNA. However, results from Western blotting analysis utilizing nuclear extracts from glioma cells throughout the cell cycle demonstrated that the nuclear accumulation of p50 and p65 perfectly correlates with their DNA-binding activity. These observations suggest that the nuclear translocation of the p50/p65 subunit of NF-kappa B in glioma cells is cell cycle stage-dependent and that is distinct from the differential mRNA expression of these genes during glioma cell cycling. The possible role of NF-kappa B in glioma cell formation and regulation of cellular genes by NF-kappa B in these tumor cells is discussed.

Shared pathways of IkappaB kinase-induced SCF(betaTrCP)-mediated ubiquitination and degradation for the NF-kappaB precursor p105 and IkappaBalpha

p105 (NFKB1) acts in a dual way as a cytoplasmic IkappaB molecule and as the source of the NF-kappaB p50 subunit upon processing. p105 can form various heterodimers with other NF-kappaB subunits, including its own processing product, p50, and these complexes are signal responsive. Signaling through the IkappaB kinase (IKK) complex invokes p105 degradation and p50 homodimer formation, involving p105 phosphorylation at a C-terminal destruction box. We show here that IKKbeta phosphorylation of p105 is direct and does not require kinases downstream of IKK. p105 contains an IKK docking site located in a death domain, which is separate from the substrate site. The substrate residues were identified as serines 923 and 927, the latter of which was previously assumed to be a threonine. S927 is part of a conserved DSGPsi motif and is functionally most critical. The region containing both serines is homologous to the N-terminal destruction box of IkappaBalpha, -beta, and -epsilon. Upon phosphorylation by IKK, p105 attracts the SCF E3 ubiquitin ligase substrate recognition molecules betaTrCP1 and betaTrCP2, resulting in polyubiquitination and complete degradation by the proteasome. However, processing of p105 is independent of IKK signaling. In line with this and as a physiologically relevant model, lipopolysaccharide (LPS) induced degradation of endogenous p105 and p50 homodimer formation, but not processing in pre-B cells. In mutant pre-B cells lacking IKKgamma, processing was unaffected, but LPS-induced p105 degradation was abolished. Thus, a functional endogenous IKK complex is required for signal-induced p105 degradation but not for processing.

HTLV-I Tax related dysfunction of cell cycle regulators and oncogenesis of adult T cell leukemia

HTLV-I is causually related to the oncogenesis of adult T cell leukemia (ATL). However, the precise mechanism of HTLV-I oncogenesis is unclear. HTLV-I Tax protein functions as an activator of various cellular genes, including IL-2, IL-2 receptor-alpha, and c-fos through the activation of nuclear transfer factors such as NF-kappaB and SRF, and also potently activates trascription of viral genes through CREB/ATF sites in the viral LTR. However, Tax activation of HTLV-I infected T cells through the above pathways induces polyclonal proliferation of the cells in vitro; Tax however may function only transiently in the immediate post-infection period following infection in vivo. The long latent period of 60 years from infection to onset of disease suggests other mechanisms for ATL oncogenesis. Recent studies suggest that the malignant transformation of ATL is a multi-hit phenomena, suggesting that discrete genetic events are responsible for ATL oncogenesis. These genetic events could be responsible for the different stages of ATL: smoldering, chronic, lymphoma, and acute type, p16 and p53 genes are important negative regulators of the cell cycle and are often found to be mutated in neoplasms. Recent studies including ours demonstrated a high frequency of alteration of these two genes in primary ATL cells. Furthermore, alteration of the two genes is associated with acute but not chronic type ATL. In addition, p16 gene alteration is linked to the growth rate of ATL cells, suggesting that the alteration of these cell cycle regulatory genes may be related to progression from smoldering or chronic to acute or lymphoma type ATL. Tax may be involved in mutagenesis of these genes through suppression of DNA-beta polymerase gene expression during the process from latent period to acute/lymphoma type. Once transformation occurs, activation of the pathway between Tax and the three nuclear transfer factors, NF-kappaB, SRF, and CREB/ATF, contributes to establish the aggressive manifestations of acute/lymphoma type ATL cells.

Selenium: a key element that controls NF-kappa B activation and I kappa B alpha half life

Treatment of mammalian cells with hydrogen peroxide induces the nuclear translocation of the transcription factor NF-kappa B and its binding to kappa B DNA sequences present in the promoter region of numerous genes. The role of selenium in NF-kappa B activation was analyzed in human T47D cells overexpressing the seleno-dependent detoxifiant enzyme glutathione peroxidase. Following exposure to H(2)O(2), these cells showed a seleno-dependent decreased accumulation of intracellular ROS and NF-kappa B activation. This phenomenon was correlated with an inhibition of the nuclear translocation of NF-kappa B (p50 subunit) and with an absence of I kappa B alpha degradation. We also report that the half-life of I kappa B alpha in untreated cells was increased two-fold by the overexpression of active glutathione peroxidase. These results suggest that selenium is a key element that through its modulation of glutathione peroxidase activity can inhibit NF-kappa B activation and can up-regulate I kappa B alpha normal half life.

One path to cell death in the nervous system

Both acute and chronic insults to the nervous system can result in changes in homeostasis that result in cell death or recovery processes that alter function. The signaling mechanisms for this broad spectrum of events that impair neurological function span the gamut from abrupt injury to the slow onset of neurodegenerative diseases in extreme aging. A common element in all of these events is the triggering of signal cascades that determine cellular commitment to apoptosis as a ameliorative alternative to inflammatory necrosis. Key in these cascades is the activation of the caspase and Bcl-family of proteins by the NF-kappaB transcription factor. Here we consider aspects of specificity of activation as a result of the differential expression of NF-kappaB proteins and their regulation of selective genes as a result of binding to select DNA consensus sequences out of the 64 different combinations that constitute the NF-kappaB DNA binding consensus sequence.

Adenovirus-mediated gene transduction of IkappaB or IkappaB plus Bax gene drastically enhances tumor necrosis factor (TNF)-induced apoptosis in human gliomas

Tumor necrosis factor-alpha (TNF), which was initially supposed to be a promising cancer therapeutic reagent, does not kill most types of cancer cells partly due to the activation of an anti-apoptotic gene, NF-kappaB. NF-kappaB forms an inactive complex with the inhibitor kappa B alpha (IkappaBalpha), which is rapidly phosphorylated and degraded in response to various extracellular signals. To disrupt this protective mechanism, we introduced an inhibitor kappa B alpha (IkappaBdN) gene, a deletion mutant gene lacking the nucleotides for the N-terminal 36 amino acids of IkappaBalpha, into human glioma cells (U251, T-98G, and U-373MG) via an adenoviral (Adv) vector in addition to treatment of the glioma cells with recombinant TNF. Immunohistochemical analysis revealed that NF-kappaB was translocated to nuclei by TNF treatment in U251 and T-98G cells, but not in U-373MG cells. Neither transduction of IkappaBdN nor treatment with TNF protein alone induced apoptosis in U251 and T-98G cells, whereas both cell lines underwent drastic TNF-induced apoptosis after transduction of IkappaBdN. On the other hand, U-373MG cells were refractory to TNF-induced apoptosis even when they were transduced with the IkappaBdN gene. U-373MG cells underwent drastically increased apoptosis when co-transduced with the IkappaBdN and Bax gene in the presence of TNF. Adv-mediated transfer of IkappaBdN or IkappaBdN plus Bax may be a promising therapeutic approach to treat gliomas through TNF-mediated apoptosis.

NF-kappaB involvement in the activation of primary adult T-cell leukemia cells and its clinical implications

The HTLV-I provirus-encoded Tax protein induces NF-kappaB in Tax-transfected Jurkat T cells or HTLVL-I- infected T cells in vitro. Tax induction of NF-kappaB is presumed to be involved in proliferation and activation of primary leukemia cells in vivo. Recent studies have demonstrated that NF-kappaB activities in human T cells are mediated by at least four c-Rel-related DNA binding proteins - p50, p55, p75 and p85. We examined the significance of NF-kappaB induction in primary adult T cell leukemia cells and the induction kinetics of each of the four NF-kappaB species. Marked NF-kappaB activity was detected using an electrophoretic mobility shift assay (EMSA) in the primary cells of patients with acute disease, but little activity was noted in the cells of chronic patients. NF-kappaB activity was enhanced in a time-dependent manner in acute type cells cultured with mitogen-free medium; there was no induction of activity in chronic type cells. UV crosslinking demonstrated all four species of NFkappaB complex - high levels of p50 and lower levels of p55 and p75, in acute type cells; chronic type cells showed only the p50. As a control, normal resting T cells similarly showed only p50; control cells showed little change in activity when cultured without mitogenic stimulation, analogous to chronic type ATL. Northern blotting revealed enhancement of c-rel (encoding p85) and KBFI (encoding p50 and p55) expression in acute type cells during culture, while there was no significant enhancement of mRNAs in chronic type ATL cells or unstimulated normal T cells. Northern blotting also revealed that Tax is upregulated at the mRNA level in acute- but not chronic-type cells during culture. Expression of c-rel and KBF1 mRNAs in acute type cells appeared to be related to Tax mRNA expression. These results suggest that Tax is capable of inducing nuclear expression of all four NF-kappaB species in primary ATL cells of acute type patients, with marked effects on p55, p75, and p85. Tax induction of NF-kappaB species is regulated, at least in part, at a pretranslational level involving increases in c-rel and KBF1 mRNA.

Interleukin-9 Regulates NF-κB Activity Through BCL3 Gene Induction

BCL3 encodes a protein with close homology to IκB proteins and interacts with p50 NF-κB homodimers. However, the regulation and transcriptional activity of BCL3 remain ill-defined. We observed here that interleukin-9 (IL-9) and IL-4, but not IL-2 or IL-3, transcriptionally upregulated BCL3 expression in T cells and mast cells. BCL3 induction by IL-9 was detected as soon as 4 hours after stimulation and appeared to be dependent on the Jak/STAT pathway. IL-9 stimulation was associated with an increase in p50 homodimers DNA binding activity, which was mimicked by stableBCL3 expression. This contrasts with tumor necrosis factor (TNF)-dependent NF-κB activation, which occurs earlier, involves p65/p50 dimers, and is dependent on IκB degradation. Moreover, IL-9 stimulation or BCL3 transient transfection similarly inhibited NF-κB–mediated transcription in response to TNF. Taken together, our observations show a new regulatory pathway for the NF-κB transcription factors through STAT-dependent upregulation ofBCL3 gene expression.

Interleukin-9 Regulates NF-κB Activity Through BCL3 Gene Induction

BCL3 encodes a protein with close homology to IκB proteins and interacts with p50 NF-κB homodimers. However, the regulation and transcriptional activity of BCL3 remain ill-defined. We observed here that interleukin-9 (IL-9) and IL-4, but not IL-2 or IL-3, transcriptionally upregulated BCL3 expression in T cells and mast cells. BCL3 induction by IL-9 was detected as soon as 4 hours after stimulation and appeared to be dependent on the Jak/STAT pathway. IL-9 stimulation was associated with an increase in p50 homodimers DNA binding activity, which was mimicked by stableBCL3 expression. This contrasts with tumor necrosis factor (TNF)-dependent NF-κB activation, which occurs earlier, involves p65/p50 dimers, and is dependent on IκB degradation. Moreover, IL-9 stimulation or BCL3 transient transfection similarly inhibited NF-κB–mediated transcription in response to TNF. Taken together, our observations show a new regulatory pathway for the NF-κB transcription factors through STAT-dependent upregulation ofBCL3 gene expression.

Regulation of NF-kappaB activity by I kappaB-related proteins in adenocarcinoma cells

Constitutive NF-kappaB activity varies widely among cancer cell lines. In this report, we studied the expression and the role of different I kappaB inhibitors in adenocarcinoma cell lines. High constitutive NF-kappaB activity and low I kappaB-alpha expression was found in a number of these cell lines. Moreover, some of these cells showed a high p100 expression, responsible for the cytoplasmic sequestration of most of p65 complexes. Treatment of these cells with TNF-alpha or other NF-kappaB activating agents induced only weakly nuclear NF-kappaB activity without significant p100 processing and led to a very weak transcription of NF-kappaB-dependent reporter gene. Induction of NF-kappaB activity can be restored by expression of the Tax protein or by treatment with antisense p100 oligonucleotides. In MCF7 A/Z cells stably transfected with a p100 expression vector, p65 complexes were sequestered in the cytoplasm by p100. These cells showed a reduced nuclear NF-kappaB induction and NF-kappaB-dependent gene transcription following TNF-alpha stimulation. As a consequence of a competition between I kappaB-alpha and p100, cells expressing high levels of p100 respond poorly to NF-kappaB activating stimuli as TNF-alpha.

Characterization of Chlamydomonas reinhardtii zygote-specific cDNAs that encode novel proteins containing ankyrin repeats and WW domains

Genes that are expressed only in the young zygote are considered to be of great importance in the development of an isogamous green alga, Chlamydomonas reinhardtii. Clones representing the Zys3 gene were isolated from a cDNA library prepared using zygotes at 10 min after fertilization. Sequencing of Zys3 cDNA clones resulted in the isolation of two related molecular species. One of them encoded a protein that contained two kinds of protein-to-protein interaction motifs known as ankyrin repeats and WW domains. The other clone lacked the ankyrin repeats but was otherwise identical. These mRNA species began to accumulate simultaneously in cells beginning 10 min after fertilization, and reached maximum levels at about 4 h, after which time levels decreased markedly. Genomic DNA gel-blot analysis indicated that Zys3 was a single-copy gene. The Zys3 proteins exhibited parallel expression to the Zys3 mRNAs at first, appearing 2 h after mating, and reached maximum levels at more than 6 h, but persisted to at least 1 d. Immunocytochemical analysis revealed their localization in the endoplasmic reticulum, which suggests a role in the morphological changes of the endoplasmic reticulum or in the synthesis and transport of proteins to the Golgi apparatus or related vesicles.

Reduced phosphorylation of p50 is responsible for diminished NF-kappaB binding to the major histocompatibility complex class I enhancer in adenovirus type 12-transformed cells

Reduced cell surface levels of major histocompatibility complex class I antigens enable adenovirus type 12 (Ad12)-transformed cells to escape immunosurveillance by cytotoxic T lymphocytes (CTL), contributing to their tumorigenic potential. In contrast, nontumorigenic Ad5-transformed cells harbor significant cell surface levels of class I antigens and are susceptible to CTL lysis. Ad12 E1A mediates down-regulation of class I transcription by increasing COUP-TF repressor binding and decreasing NF-kappaB activator binding to the class I enhancer. The mechanism underlying the decreased binding of nuclear NF-kappaB in Ad12-transformed cells was investigated. Electrophoretic mobility shift assay analysis of hybrid NF-kappaB dimers reconstituted from denatured and renatured p50 and p65 subunits from Ad12- and Ad5-transformed cell nuclear extracts demonstrated that p50, and not p65, is responsible for the decreased ability of NF-kappaB to bind to DNA in Ad12-transformed cells. Hypophosphorylation of p50 was found to correlate with restricted binding of NF-kappaB to DNA in Ad12-transformed cells. The importance of phosphorylation of p50 for NF-kappaB binding was further demonstrated by showing that an NF-kappaB dimer composed of p65 and alkaline phosphatase-treated p50 from Ad5-transformed cell nuclear extracts could not bind to DNA. These results suggest that phosphorylation of p50 is a key step in the nuclear regulation of NF-kappaB in adenovirus-transformed cells.

Expression of IkappaBalpha in the nucleus of human peripheral blood T lymphocytes

According to current models the inhibitory capacity of I(kappa)B(alpha) would be mediated through the retention of Rel/NF-kappaB proteins in the cytosol. However, I(kappa)B(alpha) has also been detected in the nucleus of cell lines and when overexpressed by transient transfection. To gain better insight into the potential role of nuclear I(kappa)B(alpha) in a physiological context we have analysed its presence in the nucleus of human peripheral blood T lymphocytes (PBL). We demonstrate the nuclear localization of I(kappa)B(alpha) in PBL by different techniques: Western blot, indirect immunofluorescence and electron microscopy. Low levels of nuclear I(kappa)B(alpha) were detected in resting cells whereas a superinduction was obtained after PMA activation. The nuclear pool of I(kappa)B(alpha) showed a higher stability than cytosolic I(kappa)B(alpha) and was partially independent of the resynthesis of the protein. Unexpectedly, the presence of nuclear I(kappa)B(alpha) did not inhibit NF-kappaB binding to DNA and this phenomenon was not due to the presence of IkappaBbeta at the nuclear level. Immunoprecipitation experiments failed to demonstrate an association between nuclear I(kappa)B(alpha) and NF-kappaB proteins. Our results demonstrate that in resting and PMA-activated human PBL, I(kappa)B(alpha) is present in the nucleus in an apparently inactive form unable to disrupt NF-kappaB binding from DNA.

Involvement of regulatory and catalytic subunits of phosphoinositide 3-kinase in NF-kappaB activation

Hypoxia, reoxygenation, and the tyrosine phosphatase inhibitor pervanadate activate the transcription factor NF-kappaB, involving phosphorylation of its inhibitor IkappaB-alpha on tyrosine 42. This modification does not lead to degradation of IkappaB by the proteasome/ubiquitin pathway, as is seen on stimulation of cells with proinflammatory cytokines. It is currently unknown how tyrosine-phosphorylated IkappaB is removed from NF-kappaB. Here we show that p85alpha, the regulatory subunit of PI3-kinase, specifically associates through its Src homology 2 domains with tyrosine-phosphorylated IkappaB-alpha in vitro and in vivo after stimulation of T cells with pervanadate. This association could provide a mechanism by which newly tyrosine-phosphorylated IkappaB is sequestered from NF-kappaB. Another mechanism by which PI3-kinase contributed to NF-kappaB activation in response to pervanadate appeared to involve its catalytic p110 subunit. This was evident from the inhibition of pervanadate-induced NF-kappaB activation and reporter gene induction by treatment of cells with nanomolar amounts of the PI3-kinase inhibitor wortmannin. The compound had virtually no effect on tumor necrosis factor- and interleukin-1-induced NF-kappaB activities. Wortmannin did not inhibit tyrosine phosphorylation of IkappaB-alpha or alter the stability of the PI3-kinase complex but inhibited Akt kinase activation in response to pervanadate. Our data suggest that both the regulatory and the catalytic subunit of PI3-kinase play a role in NF-kappaB activation by the tyrosine phosphorylation-dependent pathway.