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

Adenovirus E1B-55K interferes with cellular IκB kinase complex subunit proteins

Human adenovirus (HAdV) infections can cause high mortality rates in immunocompromised patients due to the activation of unhampered cytokine storms that are mainly induced by activation of pro-inflammatory cytokines. NF-κB is a transcription factor that is involved in numerous biological processes such as regulation of cell death and proliferation, as well as the activation of innate immune responses including the expression of pro-inflammatory cytokines, chemokines, and other immune response genes. The IKK complex plays a crucial role in the NF-κB pathway by phosphorylating and activating IκB proteins, which leads to the degradation of IκB and the subsequent release and nuclear translocation of NF-κB dimers to initiate gene transcription. The host NF-κB pathway, particularly the formation of the IKK complex, is a common target for viruses to regulate host immune responses or to utilize or inhibit its function for efficient viral replication. So far, investigations of the immune response to adenovirus infection mainly focused on transduction of adenoviral vectors or high-titer infections. Therefore, the molecular mechanism of HAdV- and HAdV gene product-mediated modulation of the NF-κB response in lytic infection is not well understood. Here, we show that HAdV-C5 infection counteracts cellular IκB kinase complex formation. Intriguingly, the IKK complex protein IKKα is targeted to the nucleus and localizes juxtaposed to viral replication centers. Furthermore, IKKα interacts with the early viral E1B-55K protein and facilitates viral replication. Together, our data provide evidence for a novel HAdV-C5 mechanism to escape host immune responses by utilizing NF-κB pathway-independent nuclear functions of IKKα to support efficient viral progeny production.

Targeting the MHC Class II antigen presentation pathway in cancer immunotherapy

The success of immunotherapy relies on the participation of all arms of the immune system and the role of CD4+ T lymphocytes in preventing tumor growth is now well established. Understanding how tumors evade immune responses holds the key to the development of cancer immunotherapies. In this review, we discuss how MHC Class II expression varies in cancer cells and how this influences antitumor immune responses. We also discuss the means that are currently available for harnessing the MHC Class II antigen presentation pathway for the development of efficient vaccines to activate the immune system against cancer.

Expression of FK506-binding protein 51 (FKBP51) in Mycosis fungoides

BACKGROUND

Mycosis fungoides (MF) is the major subtype of cutaneous T-cell lymphomas (CTCL). It usually has a prolonged indolent clinical course with a minority of cases acquiring a more aggressive biological profile and resistance to conventional therapies, partially attributed to the persistent activation of nuclear factor-kappa B (NF-κB) pathway. In the last decade, several papers suggested an important role for the FK506-binding protein 51 (FKBP51), an immunophilin initially cloned in lymphocytes, in the control of NF-κB pathway in different types of human malignancies.

OBJECTIVES

We aimed to investigate the possible value of FKBP51 expression as a new reliable marker of outcome in patients with MF.

METHODS

We assessed by immunohistochemistry (IHC) FKBP51 expression in 44 patients with MF, representative of different stages of the disease. Immunohistochemical results were subsequently confirmed at mRNA level with quantitative PCR (qPCR) in a subset of enrolled patients. In addition, IHC and qPCR served to study the expression of some NF-κB-target genes, including the tumour necrosis factor receptor-associated factor 2 (TRAF2).

RESULTS

Our results show that FKBP51 was expressed in all evaluated cases, with the highest level of expression characterizing MFs with the worst prognosis. Moreover, a significant correlation subsisted between FKBP51 and TRAF2 IHC expression scores.

CONCLUSIONS

We hypothesize a role for FKBP51 as a prognostic marker for MF and suggest an involvement of this immunophilin in deregulated NF-κB pathway of this CTCL.

NFκBiz protein downregulation in acute kidney injury: Modulation of inflammation and survival in tubular cells

Acute kidney injury is characterized by decreased renal function, tubular cell death and interstitial inflammation. The transcription factor NF-κB is a key regulator of genes involved in cell survival and the inflammatory response. In order to better understand the regulation and role of NF-κB in acute kidney injury we explored the expression of NF-κB-related genes in experimental acute kidney injury induced by a folic acid overdose. NFκBiz, a member of the IκB family of NF-κB regulators encoding NFκBiz, was among the top up-regulated NF-κB-related genes at the mRNA level in experimental acute kidney injury. However, the NFκBiz protein was constitutively expressed by normal tubular cells but was down-regulated in experimental acute kidney injury. Kidney NFκBiz mRNA upregulation and protein downregulation was also observed in acute kidney injury induced by cisplatin or unilateral kidney injury resulting from ureteral obstruction. Thus, we studied the consequences of NFκBiz protein downregulation by specific siRNA in cultured tubular epithelial cells. NFκBiz mRNA and protein were up-regulated by inflammatory cytokines (IL-1β or TWEAK/TNFα/IFNγ) and by LPS in cultured tubular cells. However, TWEAK only induced a very mild and short lived NFκBiz upregulation. NFκBiz targeting increased chemokine production and dampened Klotho downregulation induced by TWEAK, without modulating cell proliferation. NFκBiz targeting also rendered cells more resistant to apoptosis induced by serum deprivation or inflammatory cytokines. In conclusion, NFκBiz differentially regulates NF-κB-mediated responses of tubular cells to inflammatory cytokines in a gene-specific manner, and may be of potential therapeutic interest to limit inflammation in kidney disease.

The rLrp of Mycobacterium tuberculosis inhibits proinflammatory cytokine production and downregulates APC function in mouse macrophages via a TLR2-mediated PI3K/Akt pathway activation-dependent mechanism

We demonstrate that Mycobacterium tuberculosis recombinant leucine-responsive regulatory protein (rLrp) inhibits lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNF-α), interleukin-6, and interleukin-12 production and blocks the nuclear translocation of subunits of the nuclear-receptor transcription factor NF-κB (Nuclear factor-kappa B). Moreover, rLrp attenuated LPS-induced DNA binding and NF-κB transcriptional activity, which was accompanied by the degradation of inhibitory IκBα and a consequent decrease in the nuclear translocation of the NF-κB p65 subunit. RLrp interfered with the LPS-induced clustering of TNF receptor-associated factor 6 and with interleukin-1 receptor-associated kinase 1 binding to TAK1. Furthermore, rLrp did not attenuate proinflammatory cytokines or the expression of CD86 and major histocompatibility complex class-II induced by interferon-gamma in the macrophages of Toll-like receptor 2 deletion (TLR2^-/-) mice and in protein kinase b (Akt)-depleted mouse cells, indicating that the inhibitory effects of rLrp were dependent on TLR2-mediated activation of the phosphatidylinositol 3-OH kinase (PI3K)/Akt pathway. RLrp could also activate the PI3K/Akt pathway by stimulating the rapid phosphorylation of PI3K, Akt, and glycogen synthase kinase 3 beta in macrophages. In addition, 19 amino acid residues in the N-terminus of rLrp were determined to be important and required for the inhibitory effects mediated by TLR2. The inhibitory function of these 19 amino acids of rLrp raises the possibility that mimetic inhibitory peptides could be used to restrict innate immune responses in situations in which prolonged TLR signaling has deleterious effects. Our study offers new insight into the inhibitory mechanisms by which the TLR2-mediated PI3K/Akt pathway ensures the transient expression of potent inflammatory mediators.

Reactive oxygen species: friend or foe?

It is a need to define the line between pathological and physiological functions of reactive oxygen species (ROS) in order to understand their beneficial role over their injurious consequences.

Microarray characterization of gene expression changes in blood during acute ethanol exposure

Background

As part of the civil aviation safety program to define the adverse effects of ethanol on flying performance, we performed a DNA microarray analysis of human whole blood samples from a five-time point study of subjects administered ethanol orally, followed by breathalyzer analysis, to monitor blood alcohol concentration (BAC) to discover significant gene expression changes in response to the ethanol exposure.

Methods

Subjects were administered either orange juice or orange juice with ethanol. Blood samples were taken based on BAC and total RNA was isolated from PaxGene™ blood tubes. The amplified cDNA was used in microarray and quantitative real-time polymerase chain reaction (RT-qPCR) analyses to evaluate differential gene expression. Microarray data was analyzed in a pipeline fashion to summarize and normalize and the results evaluated for relative expression across time points with multiple methods. Candidate genes showing distinctive expression patterns in response to ethanol were clustered by pattern and further analyzed for related function, pathway membership and common transcription factor binding within and across clusters. RT-qPCR was used with representative genes to confirm relative transcript levels across time to those detected in microarrays.

Results

Microarray analysis of samples representing 0%, 0.04%, 0.08%, return to 0.04%, and 0.02% wt/vol BAC showed that changes in gene expression could be detected across the time course. The expression changes were verified by qRT-PCR.

The candidate genes of interest (GOI) identified from the microarray analysis and clustered by expression pattern across the five BAC points showed seven coordinately expressed groups. Analysis showed function-based networks, shared transcription factor binding sites and signaling pathways for members of the clusters. These include hematological functions, innate immunity and inflammation functions, metabolic functions expected of ethanol metabolism, and pancreatic and hepatic function. Five of the seven clusters showed links to the p38 MAPK pathway.

Conclusions

The results of this study provide a first look at changing gene expression patterns in human blood during an acute rise in blood ethanol concentration and its depletion because of metabolism and excretion, and demonstrate that it is possible to detect changes in gene expression using total RNA isolated from whole blood. The analysis approach for this study serves as a workflow to investigate the biology linked to expression changes across a time course and from these changes, to identify target genes that could serve as biomarkers linked to pilot performance.

Mitochondria and reactive oxygen species: physiology and pathophysiology

The air that we breathe contains nearly 21% oxygen, most of which is utilized by mitochondria during respiration. While we cannot live without it, it was perceived as a bane to aerobic organisms due to the generation of reactive oxygen and nitrogen metabolites by mitochondria and other cellular compartments. However, this dogma was challenged when these species were demonstrated to modulate cellular responses through altering signaling pathways. In fact, since this discovery of a dichotomous role of reactive species in immune function and signal transduction, research in this field grew at an exponential pace and the pursuit for mechanisms involved began. Due to a significant number of review articles present on the reactive species mediated cell death, we have focused on emerging novel pathways such as autophagy, signaling and maintenance of the mitochondrial network. Despite its role in several processes, increased reactive species generation has been associated with the origin and pathogenesis of a plethora of diseases. While it is tempting to speculate that anti-oxidant therapy would protect against these disorders, growing evidence suggests that this may not be true. This further supports our belief that these reactive species play a fundamental role in maintenance of cellular and tissue homeostasis.

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

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

Inhibition of the promotion of hepatocarcinogenesis by 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153) by the deletion of the p50 subunit of NF-kappa B in mice

Polychlorinated biphenyls (PCBs) are persistent and ubiquitous environmental chemicals that bioaccumulate and have hepatic tumor promoting activity in rodents. The present study examined the effect of deleting the p50 subunit of NF-kappaB on the hepatic tumor promoting activity of 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153) in mice. Both wild-type and p50-/- male mice were injected i.p. with diethylnitrosamine (DEN, 90 mg/kg) and then subsequently injected biweekly with 20 i.p. injections of PCB-153 (300 micromol/kg/injection). p50 deletion decreased the tumor incidence in both PCB- and vehicle-treated mice, whereas PCB-153 slightly (P=0.09) increased the tumor incidence in wild-type and p50-/- mice. PCB-153 increased the total tumor volume in both wild-type and p50-/- mice, but the total tumor volume was not affected by p50 deletion in either PCB- or vehicle-treated mice. The volume of tumors that were positive for glutamine synthetase (GS), which is indicative of mutations in the beta-catenin gene, was increased in both wild-type and p50-/- mice administered PCB-153 compared to vehicle controls, and inhibited in p50-/- mice compared to wild-type mice (in both PCB- and vehicle-treated mice). The volume of tumors that were negative for GS was increased in p50-/- mice compared to wild-type mice but was not affected by PCB-153. PCB-153 increased cell proliferation in normal hepatocytes in wild-type but not p50-/- mice; this increase was inhibited in p50-/- mice. In hepatic tumors, the rate of cell proliferation was much higher than in normal hepatocytes, but was not affected by PCB treatment or p50 deletion. The rate of apoptosis, as measured by the TUNEL assay, was not affected by PCB-153 or p50 deletion in normal hepatocytes. In hepatic tumors, the rate of apoptosis was lower than in normal hepatocytes; PCB-153 slightly (P=0.10) increased apoptosis in p50-/- but not wild-type mice; p50 deletion had no effect. Taken together, these data indicate that the absence of the NF-kappaB p50 subunit inhibits the promoting activity of PCB-153 and alters the proliferative and apoptotic changes in mouse liver in the response to PCBs.

The nuclear I kappaB protein I kappaB zeta specifically binds NF-kappaB p50 homodimers and forms a ternary complex on kappaB DNA

Although they share sequence homology to classical cytoplasmic I kappaB inhibitors of transcription factor NF-kappaB, the proteins I kappaB zeta, Bcl-3, and I kappa BNS function in the nucleus as factors that influence NF-kappaB-dependent gene expression profiles. Through the use of purified recombinant proteins and by comparison with the classical I kappaB protein I kappaB alpha, we have discovered mechanistic details of the interaction between I kappaB zeta and functional NF-kappaB dimers. Whereas I kappaB alpha and other classical I kappaB proteins bind tightly to NF-kappaB dimers that possess the p65 subunit, I kappaB zeta binds preferentially to NF-kappaB p50 homodimers. This altered specificity is particularly interesting in light of the fact that both NF-kappaB subunits exhibit high sequence and structural homology, while the I kappaB alpha and I kappaB zeta proteins are also conserved in primary amino acid sequence. We further show that I kappaB zeta is capable of forming a stable ternary complex with the NF-kappaB p50 homodimer and kappaB DNA. Again, this is a stark contrast from I kappaB alpha, which inhibits NF-kappaB p65 homodimer binding to NF-kappaB target DNA sequences. Removal of the DNA sequences flanking the NF-kappaB binding site does not directly affect the interaction of p50 and I kappaB zeta. Rather, we have discovered that the carboxy-terminal glycine-rich region of the NF-kappaB p50 homodimer is involved in mediating high-affinity binding of I kappaB zeta and NF-kappaB p50. We conclude that the NF-kappaB p50 homodimer functions as a legitimate activator of gene expression through formation of a ternary complex between itself, I kappaB zeta, and DNA. The requirement for formation of this complex could explain why the nuclear I kappaB protein I kappaB zeta is absolutely required for expression of the pluripotent pro-inflammatory cytokine interleukin-6 in peritoneal macrophages.

Negative transcriptional regulation of human colonic smooth muscle Cav1.2 channels by p50 and p65 subunits of nuclear factor-kappaB

BACKGROUND & AIMS

The expression of Cav1.2 channels in colonic circular smooth muscle cells and the contractility of these cells are suppressed in inflammation. Our aim was to investigate whether the activation of p50 and p65 nuclear factor-kappaB subunits mediates these effects.

METHODS

Primary cultures of human colonic circular smooth muscle cells and muscle strips were used.

RESULTS

The messenger RNA and protein expression of the pore-forming alpha1C subunit of Cav1.2 channels decreased time dependently in response to tumor necrosis factor alpha. This effect was blocked by prior transient transfection of the cells with antisense oligonucleotides to p50 or p65. The overexpression of p50 and p65 inhibited the constitutive expression of alpha1C. Three putative kappaB binding motifs were identified on the 5' flanking region of exon 1b of the human L-type calcium channel alpha1C gene. Progressive 5' deletions of the promoter and point mutations of the kappaB binding motifs indicated that the two 5' binding sites, but not the third 3' binding site, were essential for the suppression of alpha1C. Transient transfection of human colonic circular muscle strips with antisense oligonucleotides to p50 and p65 decreased expression of the 2 nuclear factor-kappaB units and reversed the suppression of alpha1C, as well as that of the contractile response to acetylcholine, by 24 hours of treatment with tumor necrosis factor alpha.

CONCLUSIONS

The activation of p50 and p65 by tumor necrosis factor alpha suppresses the expression of the alpha1C subunit of Cav1.2 channels in human colonic circular smooth muscle cells and their contractile response to acetylcholine. Nuclear factor-kappaB must bind concurrently to the two 5' kappaB motifs on the promoter of alpha1C to produce this effect.

Mycobacterium tuberculosis LprG (Rv1411c): a novel TLR-2 ligand that inhibits human macrophage class II MHC antigen processing

MHC class II (MHC-II)-restricted CD4(+) T cells are essential for control of Mycobacterium tuberculosis infection. This report describes the identification and purification of LprG (Rv1411c) as an inhibitor of primary human macrophage MHC-II Ag processing. LprG is a 24-kDa lipoprotein found in the M. tuberculosis cell wall. Prolonged exposure (>16 h) of human macrophages to LprG resulted in marked inhibition of MHC-II Ag processing. Inhibition of MHC-II Ag processing was dependent on TLR-2. Short-term exposure (<6 h) to LprG stimulated TLR-2-dependent TNF-alpha production. Thus, LprG can exploit TLR-2 signaling to inhibit MHC-II Ag processing in human macrophages. Inhibition of MHC-II Ag processing by mycobacterial lipoproteins may allow M. tuberculosis, within infected macrophages, to avoid recognition by CD4(+) T cells.

Dissecting MHC class II export, B cell maturation, and DM stability defects in invariant chain mutant mice

Invariant (Ii) chain loss causes defective class II export, B cell maturation, and reduced DM stability. In this study, we compare Ii chain and class II mutant mouse phenotypes to dissect these disturbances. The present results demonstrate that ER retention of alphabeta complexes, and not beta-chain aggregates, disrupts B cell development. In contrast, we fail to detect class II aggregates in Ii chain mutant thymi. Ii chain loss in NOD mice leads to defective class II export and formation of alphabeta aggregates, but in this background, downstream signals are misregulated and mature B cells develop normally. Finally, Ii chain mutant strains all display reduced levels of DM, but mice expressing either p31 or p41 alone, and class II single chain mutants, are indistinguishable from wild type. We conclude that Ii chain contributions as a DM chaperone are independent of its role during class II export. This Ii chain/DM partnership favors class II peptide loading via conventional pathway(s).

Nuclear factor-kappaB modulation as a therapeutic approach in hematologic malignancies

Nuclear factor-kappaB (NF-kappaB) is a collective term that refers to a small class of dimeric transcription factors for a number of genes, including growth factors, angiogenesis modulators, cell-adhesion molecules, and antiapoptotic factors. Although most NF-kappaB proteins promote transcription, some act as inactivating or repressive complexes. The most common p50-RelA (p65) dimer known "specifically" as NF-kappaB, is relatively abundant, controls the expression of numerous genes, and exists as an inactive cytoplasmic complex bound to inhibitory proteins of the NF-kappaB inhibitor (IkappaB) family. The inactive NF-kappaB-IkappaB complex is activated by a variety of stimuli, including proinflammatory cytokines, mitogens, growth factors, and stress-inducing agents. The release of NF-kappaB facilitates its translocation to the nucleus, where it promotes cell survival by initiating the transcription of genes encoding stress-response enzymes, cell-adhesion molecules, proinflammatory cytokines, and antiapoptotic proteins. Constitutive activation of NF-kappaB in the nucleus is observed in some hematologic disorders. With the recent approval of bortezomib for patients with advanced multiple myeloma, NF-kappaB modulation is likely to be a therapeutic endeavor of increasing interest in coming years.

NF-kappaB binds to a polymorphic repressor element in the MMP-3 promoter

A 5T/6T polymorphic site in the matrix metalloproteinase-3 (MMP-3) promoter has been identified as a repressor element involved in inhibiting induction of MMP-3 transcription by interleukin 1; and the 6T allele has been associated with decreased expression of MMP-3 as compared to the 5T allele. Zinc-binding protein-89 (ZBP-89) was cloned from a yeast one-hybrid assay via its ability to interact with this site, but when the protein was over-expressed, it resulted in activation of the MMP-3 promoter rather than repression. Here we show that in nuclear extracts isolated from human gingival fibroblasts stimulated with IL-1, this site is bound by p50 and p65 components of NF-kappaB in addition to ZBP-89, and that recombinant p50 binds preferentially to the 6T binding site. These results are consistent with a role for NF-kappaB in limiting the cytokine induced expression of MMP-3.

Nuclear factor-kappaB activates transcription of the androgen receptor gene in Sertoli cells isolated from testes of adult rats

The androgen receptor (AR) in Sertoli cells mediates the actions of testosterone on spermatogenesis. However, the transcription factors responsible for AR gene regulation in Sertoli cells remain unknown. In this study, we determined that nuclear factor-kappaB (NF-kappaB) regulates transcription of AR in primary cultures of Sertoli cells isolated from testes of adult rats. Electrophoretic mobility shift and antibody supershift assays with nuclear extracts prepared from Sertoli cells identified two binding sites, termed kappaB1 at -491/-482 bp and kappaB2 at -574/-565 bp, upstream of the transcription start site of the AR gene that bind the NF-kappaB subunits, p50 and p65. DNAse I footprint analyses showed that binding of the p50 NF-kappaB subunit protected the same regions on the rat AR promoter. Analyses of AR promoter-luciferase reporter gene activity after transfection of primary cultures of Sertoli cells demonstrated that mutation of the kappaB2 site or combined mutation of the kappaB1 and kappaB2 sites reduced activity by 40%. Preferential binding of the transcriptionally active p65/p50 heterodimer to the kappaB2 site rather than to the kappaB1 site supported these observations. Overexpression of the NF-kappaB p65 and p50 subunits in Sertoli cells increased activity from the wild-type AR promoter and the promoter with mutation of the kappaB1 site, but not the kappaB2 site. Activity was further stimulated by CBP (CREB binding protein), a coactivator of p65 transcriptional activity. Taken together, our data show that NF-kappaB is an activator of AR gene transcription in Sertoli cells and may be an important determinant of androgen activity during spermatogenesis.

Induction of macrophage-inflammatory protein-3alpha gene expression by TNF-dependent NF-kappaB activation

Macrophage-inflammatory protein-3alpha (MIP-3alpha), also designated as liver and activation-regulated chemokine (LARC), Exodus, or CCL20, is a recently identified CC chemokine that is expected to play a crucial role in the initiation of immune responses. In this study, we describe that MIP-3alpha expression is under the direct control of NF-kappaB, a key transcription factor of immune and inflammatory responses. Overexpression of the p65/RelA subunit of NF-kappaB significantly increased the MIP-3alpha mRNA level. MIP-3alpha transcription was stimulated by TNF, and this stimulation was inhibited by an NF-kappaB inhibitor, I-kappaBalpha superrepressor. Analysis of the human MIP-3alpha promoter demonstrated a functional NF-kappaB site responsible for its expression. We also show that MIP-3alpha expression is induced in LPS-treated mouse livers that were primed with Propionibacterium acnes, which developed massive liver injury with infiltration of inflammatory cells. This induction was fully dependent on the TNF signaling cascade, because it was not observed in the livers of TNFR1-deficient mice. Furthermore, pretreatment with gliotoxin, an inhibitor of NF-kappaB activity, abrogated the P. acnes/LPS-induced MIP-3alpha expression of wild-type mice. These results clearly demonstrate that MIP-3alpha gene expression is dependent on NF-kappaB activity in vitro, and indicate that the TNFR1-mediated TNF signaling cascade that leads to NF-kappaB activation plays an essential role in MIP-3alpha expression in the murine liver injury model.

Promoter-specific functions of CIITA and the MHC class II enhanceosome in transcriptional activation

Transcription of the major histocompatibility complex class II family of genes is regulated by conserved promoter elements and two gene-specific trans-activators, RFX and CIITA. RFX binds DNA and nucleates the assembly of an enhanceosome, which recruits CIITA through protein--protein interactions. Transcriptional activation is a complex, multi-step process involving chromatin modification and recruitment of the transcription apparatus. To examine the roles of the enhanceosome and CIITA in these processes, we analysed the level of promoter-associated hyperacetylated histones H3 and H4, TBP, TFIIB and RNA poly merase II in cells lacking RFX or CIITA. We compared four genes co-regulated by RFX and CIITA (HLA-DRA, HLA-DPB, HLA-DMB and Ii) and found that the enhanceosome and CIITA make variable, promoter-dependent contributions to histone acetylation and transcription apparatus recruitment. CIITA is generally implicated at multiple levels of the activation process, while the enhanceosome contributes in a CIITA-independent manner only at certain promoters. Our results support the general notion that the impact of a particular activator on transcription in vivo may vary depending on the promoter and the chromatin context.

Reciprocal antagonism between estrogen receptor and NF-kappaB activity in vivo

The functional interaction, or "cross-talk," between estrogen receptor (ER) and the proinflammatory transcription factor nuclear factor (NF)-kappaB demonstrated in vitro has been suggested to play a role in estrogen prevention of cardiovascular disease. Here, we demonstrate that this reciprocal cross-talk occurs in vivo. Ovariectomized C57BL/6 mice fed an atherogenic diet had increased hepatic levels of active NF-kappaB and numerous inflammatory genes, including MHC invariant chain (Ii), vascular cell adhesion molecule-1, tumor necrosis factor-alpha, and RANTES. Treatment with 17alpha-ethinylestradiol (EE) strongly blocked induction of these genes but had no effect on their basal expression levels. ER was required for this activity, because the antagonist ICI 182,780 completely blocked the inhibitory activity of EE. Gene activation by EE was not required for inhibition of inflammatory gene expression, because both the phytoestrogen genistein and low doses of EE were effective in blocking inflammatory gene induction without inducing marker genes such as intestinal trefoil factor (ITF) or myo-inositol-1-phosphate synthase (IPS). The in vivo transcriptional interference was reciprocal, with EE induction of ITF and IPS greatly reduced in animals fed the atherogenic diet versus chow-fed controls. This interference was specific to the liver, because diet had no effect on uterine weight increases produced by EE. Transfection experiments confirmed that the extent of inhibition of ER-mediated transcription by inflammatory stimuli correlated with the extent of NF-kappaB activation. These results suggest that the cross-talk between ER and NF-kappaB does occur in vivo and may indeed contribute significantly to the cardioprotective effects of estrogen.

Adenosine, oxidative stress and cytoprotection

Adenosine, a metabolite of ATP, serves a number of important physiological roles in the body. These actions contribute to sedation, bradycardia, vasorelaxation, inhibition of lipolysis and regulation of the immune system and are mediated, in part, through activation of three distinct adenosine receptor (AR) subtypes. To date, four receptor types have been cloned: A1, A2A, A2B and A3. It is becoming increasing clear that adenosine contributes significantly to cytoprotection, a function mediated principally by the A1AR and A3AR. In this review, we survey the literature on the role of adenosine and the mechanisms underlying cytoprotection and ischemic preconditioning, a process characterized by cytoprotection derived from repeated brief ischemic challenges. An important recent observation is that the expression of several AR subtypes could be regulated by oxidative stress to provide a greater cytoprotective role. Thus, like other proteins known to be regulated during ischemia, the A1AR and A3AR can be considered as being inducible receptors.

Tumor necrosis factor-alpha inhibits aquaporin 5 expression in mouse lung epithelial cells

Aquaporin 5 (AQP5), the major water channel expressed in alveolar, tracheal, and upper bronchial epithelium, is significantly down-regulated during pulmonary inflammation and edema. The mechanisms that underlie this decrease in AQP5 levels are therefore of considerable interest. Here we show that AQP5 expression in cultured lung epithelial cells is decreased 2-fold at the mRNA level and 10-fold at the protein level by the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha). Treatment of murine lung epithelial cells (MLE-12) with TNF-alpha results in a concentration- and time-dependent decrease in AQP5 mRNA and protein expression. Activation of the p55 TNF-alpha receptor (TNFR1) with an agonist antibody is sufficient to cause decreased AQP5 expression, demonstrating that the TNF-alpha effect is mediated through TNFR1. Inhibition of nuclear factor kappaB (NF-kappaB) translocation to the nucleus blocks the effect of TNF-alpha on AQP5 expression, indicating that activation of NF-kappaB is required, whereas inhibition of extracellular signal-regulated or p38 mitogen-activated protein kinases showed no effect. These data show that TNF-alpha decreases AQP5 mRNA and protein expression and that the molecular pathway for this effect involves TNFR1 and activated NF-kappaB. The ability of inflammatory cytokines to decrease aquaporin expression may help explain the connection between inflammation and edema.

Characterization of rabbit SP-B promoter region responsive to downregulation by tumor necrosis factor-alpha

Surfactant protein B (SP-B) is essential for the maintenance of biophysical properties and physiological function of pulmonary surfactant. Tumor necrosis factor-alpha (TNF-alpha), an important mediator of lung inflammation, inhibits surfactant phospholipid and surfactant protein synthesis in the lung. In the present study, we investigated the TNF-alpha inhibition of rabbit SP-B promoter activity in a human lung adenocarcinoma cell line (NCI-H441). Deletion experiments indicated that the TNF-alpha response elements are located within -236 bp of SP-B 5'-flanking DNA. The TNF-alpha response region contained binding sites for nuclear factor-kappa B (NF-kappa B), Sp1/Sp3, thyroid transcription factor (TTF)-1, and hepatocyte nuclear factor (HNF)-3 transcription factors. Inhibitors of NF-kappa B activation such as dexamethasone and N-tosyl-L-phenylalanine chloromethyl ketone and mutation of the NF-kappa B element did not reverse TNF-alpha inhibition of SP-B promoter, indicating that TNF-alpha inhibition of SP-B promoter activity occurs independently of NF-kappa B activation. TNF-alpha treatment decreased the binding activities of TTF-1 and HNF-3 elements without altering the nuclear levels of TTF-1 and HNF-3 alpha proteins. Pretreatment of cells with okadaic acid reversed TNF-alpha inhibition of SP-B promoter activity. Taken together these data indicated that in NCI-H441 cells 1) TNF-alpha inhibition of SP-B promoter activity may be caused by decreased binding activities of TTF-1 and HNF-3 elements, 2) the decreased binding activities of TTF-1 and HNF-3 alpha are not due to decreased nuclear levels of the proteins, and 3) okadaic acid-sensitive phosphatases may be involved in mediating TNF-alpha inhibition of SP-B promoter activity.

Role of the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and its natural ligand 15-deoxy-Delta12, 14-prostaglandin J2 in the regulation of microglial functions

The peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a member of a large group of nuclear receptors controlling the proliferation of peroxisomes that is involved in the downregulation of macrophage functions. Here, we report that PPAR-gamma was constitutively expressed in rat primary microglial cultures and that such expression was downregulated during microglial activation by endotoxin (LPS). The presence of the PPAR-gamma natural ligand 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) counteracted the repression of PPAR-gamma expression caused by LPS. In microglial cultures stimulated by LPS, interferon-gamma (IFN-gamma) or by their combination, 15d-PGJ2 reduced the production of nitric oxide (NO) and the expression of inducible NO synthase (iNOS). The inhibitory effect was dose-dependent and did not involve an elevation of cyclic AMP, a second messenger known to inhibit NOS expression in microglia. In addition, 15d-PGJ2 down-regulated other microglial functions, such as tumour necrosis factor-alpha (TNF-alpha) synthesis and major histocompatibility complex class II (MHC class II) expression. The effects of 15d-PGJ2 occurred, at least in part, through the repression of two important transcription factors, the signal transducer and activator of transcription 1 and the nuclear factor kappaB, known to mediate IFN-gamma and LPS cell signalling. Our observations suggest that 15d-PGJ2, the synthesis of which is likely to occur within the brain, could play an important role in preventing brain damage associated with excessive microglial activation.

Lipopolysaccharide-induced MCP-1 gene expression in rat tubular epithelial cells is nuclear factor-kappaB dependent

BACKGROUND

Endotoxin is an important factor in the development of acute renal failure related to infection and in acceleration of chronic nephritis. Lipopolysaccharide (LPS; the major component of endotoxin) is one of the most potent triggers for renal cells to produce monocyte chemoattractant protein-1 (MCP-1), a key cytokine involved in immune cell recruitment into the renal interstitium in acute and chronic renal diseases. Knowledge about the transcriptional regulation of MCP-1 in renal tubular epithelial cells in response to LPS is incomplete.

METHODS

Transcriptional regulation of MCP-1 was investigated in rat proximal tubule cells (PTCs) in primary culture and was exposed to LPS using electromobility shift assay and supershift analysis for nuclear factor-kappaB (NF-kappaB) and Western blot for the NF-kappaB inhibitory protein IkappaB. To prove the role for NF-kappaB, activator protein (AP-1), and sequence-specific transcription factor (Sp1), mutation and deletion analysis was performed using a 3.5 kb fragment of rat MCP-1 5'-flanking region inserted into a luciferase reporter construct transfected into tubular epithelial cell line (NRK-52E).

RESULTS

LPS increased NF-kappaB in a dose- and time-dependent manner, which paralleled that of MCP-1 mRNA expression. IkappaBalpha decreased within 30 minutes of LPS treatment, but returned to basal levels by two hours. IkappaBbeta levels were depressed within one hour and remained low throughout the culture period after LPS stimulation. The activity of the transfected 5'-flanking region of the MCP-1 gene increased nearly threefold after LPS stimulation. Mutation or deletion of NF-kappaB binding sites, located in the enhancer region of the 5'-flanking region, resulted in a total loss of LPS-induced increase in luciferase activity. Mutation of putative AP-1 and Sp1 sites, located in the proximal promoter region of MCP-1, reduced basal luciferase activity in unstimulated cells, but had no effect on LPS-stimulated luciferase activity.

CONCLUSIONS

These studies prove that NF-kappaB is critical for LPS-induced MCP-1 transcription, and AP-1 and Sp1 are essential for basal expression of MCP-1 in rat tubule cells. The species-specific nature of transcriptional regulation of MCP-1 has important implications for the delineation of treatment to prevent endotoxin-mediated renal injury.

A mechanism of suppression of TGF-beta/SMAD signaling by NF-kappa B/RelA

A number of pathogenic and proinflammatory stimuli, and the transforming growth factor-beta (TGF-beta) exert opposing activities in cellular and immune responses. Here we show that the RelA subunit of nuclear factor kappaB (NF-kappaB/RelA) is necessary for the inhibition of TGF-beta-induced phosphorylation, nuclear translocation, and DNA binding of SMAD signaling complexes by tumor necrosis factor-alpha (TNF-alpha). The antagonism is mediated through up-regulation of Smad7 synthesis and induction of stable associations between ligand-activated TGF-beta receptors and inhibitory Smad7. Down-regulation of endogenous Smad7 by expression of antisense mRNA releases TGF-beta/SMAD-induced transcriptional responses from suppression by cytokine-activated NF-kappaB/RelA. Following stimulation with bacterial lipopolysaccharide (LPS), or the proinflammatory cytokines TNF-alpha and interleukin-1beta (IL-1beta, NF-kappaB/RelA induces Smad7 synthesis through activation of Smad7 gene transcription. These results suggest a mechanism of suppression of TGF-beta/SMAD signaling by opposing stimuli mediated through the activation of inhibitory Smad7 by NF-kappaB/RelA.

A role of p75 in NGF-mediated down-regulation of the A(2A) adenosine receptors in PC12 cells

Nerve growth factor (NGF) induces differentiation of the rat pheochromocytoma clone (PC12) by activating the high affinity receptor, p140(trkA), linked to mitogen-activated protein kinase. While the physiological role of the low affinity NGF receptor (p75) has not been clearly defined, this receptor promotes activation of nuclear factor (NF) kappaB in Schwann cells. PC12 cells express the A(2A) adenosine receptor (AR), whose expression is significantly decreased by NGF treatment. In this study, we determined whether TrkA or p75 is involved in NGF-mediated regulation of A(2A)AR expression. NGF treatment decreased A(2A)AR in a time-dependent manner, with maximal effects observed by 1 day, and continued down-regulation of the receptor for up to 3 days in the presence of NGF. The decrease in A(2A)AR was associated with a more delayed decrease in the steady-state levels of the A(2A)AR mRNA. Down-regulation of the A(2A)AR at 1 day was mimicked by activators of NFkappaB, such as H(2)O(2), and ceramide, and was attenuated by the inhibitor pyrrolidine dithiocarbamate or following transient transfection of PC12 cells with a dominant negative IkappaBalpha mutant. Moreover, NGF stimulated nuclear accumulation of p65 subunits of NFkappaB (but not p50 subunits) in PC12 cells, as determined by electrophoretic mobility shift assays and by Western blotting. In contrast, inhibition of TrkA by AG879 or of TrkA-dependent mitogen-activated protein kinase mitogen-activated protein kinase kinase with PD98059 blocked PC12 cell differentiation without affecting A(2A)AR down-regulation, suggesting dissociation between these two phenomena. Taken together, these data provide strong support for the involvement of the p75/NFkappaB pathway in NGF-mediated down-regulation of A(2A)AR in PC12 cells.

Salicylates inhibit NF-kappaB activation and enhance TNF-alpha-induced apoptosis in human pancreatic cancer cells

INTRODUCTION

Tumor necrosis factor (TNF-alpha)-induced apoptosis is limited by its coactivation of nuclear factor kappa B (NF-kappaB)-dependent anti-apoptotic genes. Sodium salicylate (NaSal) inhibits NF-kappaB activation by limiting phosphorylation and degradation of its bound inhibitor protein, IkappaB-alpha. We examined whether NaSal enhances TNF-alpha-induced apoptosis in cultured human pancreatic cancer cell lines.

METHODS

Two cultured human pancreatic cancer cell lines were studied. PANC-1 and BxPC-3 cells were serum-starved for 12 h, pretreated or not for 1 h with NaSal (5-20 mM), and then stimulated with recombinant human TNF-alpha (400 units/ml). Western blots of cytoplasmic lysates were performed to demonstrate IkappaB-alpha phosphorylation and degradation. Western blots of nuclear extracts were performed to assess nuclear translocation of NF-kappaB. In separate cultures, apoptosis was measured 4.5 h after TNF-alpha stimulation by both ELISA detection of interhistone DNA fragments and flow cytometry with propidium iodide staining.

RESULTS

TNF-alpha induced IkappaB-alpha phosphorylation and degradation, which was inhibited by NaSal in both cell lines. TNF-alpha-induced apoptosis (DNA fragmentation) increased significantly when BxPC-3 cells were pretreated with NaSal. Flow cytometry confirmed this, demonstrating increases in apoptotic cell fractions: 8.5% (untreated), 9.3% (TNF-alpha alone), 14.9% (15 mM NaSal), and 22.9% (NaSal and TNF-alpha). In contrast, no increases in apoptosis were measured in the PANC-1 cell line among the various treatment groups.

CONCLUSIONS

NaSal enhances TNF-alpha-induced apoptosis while inhibiting IkappaB-alpha phosphorylation and degradation in BxPC-3 human pancreatic cancer cells.

Activation of nuclear factor-kappaB in macrophages by mycoplasmal lipopeptides

Mycoplasmas are potent macrophage stimulators. The active principle are lipopeptides or lipoproteins with a characteristic N-terminal S-[dihydroxypropyl]-cysteinyl group bearing two ester-bound fatty acids and lacking the amide-bound one common to other bacterial lipoproteins. Using synthetic analogues of mycoplasmal lipopeptides, we investigated activation of the transcription factor NF-kappaB in the C3H/HeJ mouse-derived DMBM-3 cell line. The lipopeptides activated NF-kappaB at below nanomolar concentrations. Activation in the murine system occurred distinctly earlier than TNF-alpha liberation, excluding autocrine stimulation by TNF-alpha. As determined from a supershift experiment, the active NF-kappaB complex consisted of the heterodimer p50/p65(RelA). The relevance of these findings for the inflammatory response to mycoplasmas and for mycoplasma-mediated effects on HIV-infected macrophages is discussed.

Role of NF-kappaB in immune and inflammatory responses in the gut

NF-kappaB is a pleiotropic transcription factor with key functions in the intestinal immune system. NF-kappaB family members control transcriptional activity of various promoters of proinflammatory cytokines, cell surface receptors, transcription factors, and adhesion molecules that are involved in intestinal inflammation. The perpetuated activation of NF-kappaB in patients with active inflammatory bowel disease suggests that regulation of NF-kappaB activity is a very attractive target for therapeutic intervention. Such strategies include antioxidants, proteasome inhibitors, inhibition of NF-kappaB by adenoviral I kappaB alpha expression vectors, and antisense DNA targeting of NF-kappaB. These approaches will hopefully permit the design of new treatment strategies for chronic intestinal inflammation.

Transcriptional regulation during B cell development

Information is increasingly available concerning the molecular events that occur during primary and antigen-dependent stages of B cell development. In this review the roles of transcription factors and coactivators are discussed with respect to changes in expression patterns of various genes during B cell development. Transcriptional regulation is also discussed in the context of developmentally regulated immunoglobulin gene V(D)J recombination, somatic hypermutation, and isotype switch recombination.

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

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

Discrimination between RelA and RelB transcriptional regulation by a dominant negative mutant of IkappaBalpha

RelA and RelB belong to the nuclear factor-kappaB (NF-kappaB-Rel) transcription factor family. Both proteins are structurally and functionally related, but their intracellular and tissue distributions are different. In resting cells, RelB is found mostly in the nucleus, whereas RelA is sequestered in the cytosol by protein inhibitors, among which IkappaBalpha is the dominant form in lymphocytes. Upon cellular activation IkappaBalpha is proteolyzed, allowing RelA dimers to enter the nucleus and activate target genes. To study the selectivity of gene regulation by RelA and RelB, we generated T cell lines stably expressing a dominant negative mutant of IkappaBalpha. We show that selective inhibition of RelA-NF-kappaB decreased induction of NFKB1, interleukin-2, and interleukin-2Ralpha genes but not c-myc. Transcription driven by the IkappaBalpha promoter was blocked by the transgenic IkappaBalpha; however, wild type IkappaBalpha was expressed in the transgenic cell clones but with much slower kinetics than that in control cells. Wild type IkappaBalpha expression was concomitant with RelB up-regulation, suggesting that RelB could be involved in transcription of IkappaBalpha through binding to an alternative site. These results indicate that RelB and RelA have both distinct and overlapping effects on gene expression.

Multiple regulatory elements control transcription of the peripheral myelin protein zero gene

The gene encoding protein zero (P0), the most abundant protein of peripheral nervous system myelin, is expressed uniquely in Schwann cells. Previous studies have demonstrated that much of the cell type specificity of this expression is due to transcriptional control elements in the 1.1-kilobase pair 5'-regulatory region of the gene. We have now analyzed this region and have identified a set of functional elements in the 500 base pairs proximal to the transcription start site. DNA sequence conservation within the 5' regions of the human, mouse, and rat P0 genes correlates closely with the results of promoter deletion analysis of the 1.1-kilobase pair region assayed in Schwann cell cultures and reveals a potent proximal region from position -350 to +45. Sites of protein/DNA interaction within the proximal 500 base pairs of the promoter were identified by footprinting assays. Functional transcriptional elements were identified within the protected regions in the proximal promoter by mutation and transient transfection analysis in P0-expressing cell lines. The core (or basal) P0 promoter is identified as two regulatory elements, a G/C-rich element that binds nuclear factor Sp1 and a CAAT box that binds NF-Y. These core elements are essential for the transcription observed from the transfected promoter in cultured Schwann cells.

A kappaB-related binding site is an integral part of the mts1 gene composite enhancer element located in the first intron of the gene

The transcription of the mts1 gene correlates with the metastatic potential of mouse adenocarcinomas. Here we describe strong enhancer whose location coincides with the DNase I hypersensitivity area in the first intron of the mts1 gene. The investigation of the transcriptional activity of a series of plasmids bearing deletions in the first intron sequences revealed that the observed enhancer has a composite structure. The enhancer activity is partially formed by the kappaB-related element: GGGGTTTTTCCAC. This sequence element was able to form several sequence-specific complexes with nuclear proteins extracted from both Mts1-expressing CSML100 and Mts1-non-expressing CSML0 adenocarcinoma cells. Two of these complexes were identified as NF-kappaB/Rel-specific p50.p50 homo- and p50.p65 heterodimers. The third complex was formed by the 200-kDa protein. Even though the synthetic kappaB-responsible promoter was active in mouse adenocarcinoma cells, a mutation preventing NF-kappaB binding had no effect on the mts1 natural enhancer activity. On the contrary, the mutation in the kappaB-related element, which abolished the binding of the 200-kDa protein, led to the functional inactivation of this site in the mts1 first intron. The mts1 kappaB-like element activated transcription from its own mts1 gene promoter, as well as from the heterologous promoter in both CSML0 and CSML100 cells. However, in vivo occupancy of this site was observed only in Mts1-expressing CSML100 cells, suggesting the involvement of the described element in positive control of mts1 transcription.

Differential nuclear localization of p50, p52, and RelB proteins in human accessory cells of the immune response in situ

The Rel/NF-kappa B proteins, p50, p52, p65, c-Rel, and RelB, constitute a family of transcription factors involved in the positive regulation of a variety of genes during the immune response. Recently, it has been shown that RelB knockout mice have no dendritic cells (DC). An overexpression of p50 has been described in follicular dendritic cells (FDC). A constitutive NF-kappa B activity has been reported in mature macrophages. This led to the hypothesis that some of the Rel/NF-kappa B proteins were key nuclear factors in functions of accessory cells of the immune response. Therefore, we investigated in situ the nuclear localization of Rel/NF-kappa B proteins in accessory cells of the immune system by immunohistochemistry and double labeling by immunofluorescence from five normal human tonsils and five lymph nodes with follicular hyperplasia. Nuclear p65 and c-Rel proteins were found in all cell types including lymphocytes. In germinal centers GC, p50, p52, and RelB were found in the nuclei of FDC only and were not detected in the nuclei of CD68+ cells. In T cell areas, p50, p52, and RelB were found in the nuclei of HLA-DR+ cells with an antigen-presenting cell (APC) morphology. p52 and RelB were detected in the nuclei in both CD1a+ and CD68+ cells from the T cell area, whereas p50 was found only in CD68- and CD1a- cells. Cells with nuclear p50 were negative for the CD38, CD20 and CD2 markers. These results show that, physiologically, high levels of nuclear of p50, p52 and RelB are restricted to accessory cells of the immune system, which include FDC in GC, and DC and macrophages in the T cell zone, that specialized scavenger macrophages from GC do not have detectable levels of p52 and RelB, whereas macrophages from the T cell area, known to present the antigen to T cells, do have both nuclear p52 and RelB, and that in the T cell zone, p52 and RelB are located in nuclei of both CD1a+, CD68+ or both, cells APC, whereas p50 is restricted to CD1a- and CD68- APC. The different patterns of p50, p52 and RelB protein nuclear localization may provide insight into their different roles during the immune response in vivo.

The NF-kappa B and I kappa B proteins: new discoveries and insights

The transcription factor NF-kappa B has attracted widespread attention among researchers in many fields based on the following: its unusual and rapid regulation, the wide range of genes that it controls, its central role in immunological processes, the complexity of its subunits, and its apparent involvement in several diseases. A primary level of control for NF-kappa B is through interactions with an inhibitor protein called I kappa B. Recent evidence confirms the existence of multiple forms of I kappa B that appear to regulate NF-kappa B by distinct mechanisms. NF-kappa B can be activated by exposure of cells to LPS or inflammatory cytokines such as TNF or IL-1, viral infection or expression of certain viral gene products, UV irradiation, B or T cell activation, and by other physiological and nonphysiological stimuli. Activation of NF-kappa B to move into the nucleus is controlled by the targeted phosphorylation and subsequent degradation of I kappa B. Exciting new research has elaborated several important and unexpected findings that explain mechanisms involved in the activation of NF-kappa B. In the nucleus, NF-kappa B dimers bind to target DNA elements and activate transcription of genes encoding proteins involved with immune or inflammation responses and with cell growth control. Recent data provide evidence that NF-kappa B is constitutively active in several cell types, potentially playing unexpected roles in regulation of gene expression. In addition to advances in describing the mechanisms of NF-kappa B activation, excitement in NF-kappa B research has been generated by the first report of a crystal structure for one form of NF-kappa B, the first gene knockout studies for different forms of NF-kB and of I kappa B, and the implications for therapies of diseases thought to involve the inappropriate activation of NF-kappa B.

Major histocompatibility complex class II-associated invariant chain gene expression is up-regulated by cooperative interactions of Sp1 and NF-Y

Expression of the major histocompatibility complex (MHC) class II-associated invariant chain (Ii) is required for efficient and complete presentation of antigens by MHC class II molecules and a normal immune response. The Ii gene is generally co-regulated with the MHC class II molecules at the level of transcription and a shared SXY promoter element has been described. This report defines the proximal promoter region of Ii which may regulate Ii transcription distinct from MHC class II. In vivo genomic footprinting identified an occupied, imperfect CCAAT box and an adjacent GC box in the proximal region. These sites are bound in Ii-ositive cell lines and upon interferon-gamma induction of Ii transcription. In contrast, both sites are unoccupied in Ii-egative cell lines and in inducible cell lines prior to interferon-gamma treatment. Together these two sites synergize to stimulate transcription. Independently, the transcription factor NF-Y binds poorly to the imperfect CCAAT box with a rapid off rate, while Sp1 binds to the GC box. Stabilization of NF-Y binding occurs upon Sp1 binding to DNA. In addition, the half-life of Sp1 binding also increased in the presence of NF-Y binding. These findings suggest a mechanism for the complete functional synergy of the GC and CCAAT elements observed in Ii transcription. Furthermore, this report defines a CCAAT box of imperfect sequence which binds NF-Y and activates transcription only when stabilized by an adjacent factor, Sp1.

Multi-step activation of NF-kappa B/Rel transcription factors

Transcription factors belonging to the NF-kappa B/Rel family are specialized in the transduction of primarily pathogenic signals from the cytoplasm to the cell nucleus. To date, the family comprises five distinct DNA-binding subunits and five regulatory proteins with inhibitory function, called I kappa B proteins. The interaction of dimers of the DNA-binding subunits with the I kappa B proteins leads to the cytoplasmatic retention of the complex and inhibition of its DNA binding. Following stimulation of cells, the I kappa B proteins become phosphorylated and are subsequently degraded, presumably, by the proteasome. The released NF-kappa B/Rel transcription factors can then enter the nucleus, bind to decameric DNA cognate sequences and stimulate transcription of numerous immunologically important target genes. In this article, we discuss several distinct levels at which the NF-kappa B/Rel transcription factors can be regulated.

Regulation of androgen action by receptor gene inhibition

Regulated functions of hormonal agents play a critical role in health and disease. Target cell responsiveness to a hormonal signal is a product of both cellular concentrations of the hormone ligand and the corresponding receptor protein. The major thrust of the drug design for treatment of endocrine-related problems, so far, has been directed to ligand derivatives. In certain cases, receptor regulation through antigene technology has much to offer with improvements in both target cell and hormonal specificity. Three different antigene approaches are currently being explored. The first approach is to inhibit the expression of the receptor gene by disrupting the DNA protein interaction at critical cis-elements by short triple helix-forming oligonucleotides. The second approach is to sequester and inactivate the receptor mRNA by the antisense mRNA produced in the target tissue directed by a heterologous tissue-specific promoter. The third approach is the tissue-specific expression of a catalytic ribozyme that binds to the specific receptor mRNA and selectively degrades it before its translation into the protein. In this study, we have characterized the promoter of the rat androgen receptor, and by progressive deletion from its 5' end have identified two critical cis-regulatory elements, one at the -960 to -940 region and the other at the -554 to -574 positions. The former is an activator while the latter is an inhibitor domain. The inhibitory domain is the binding site for the nuclear factor kappa B (NF-kappa B) and more specifically, the p50/p50 homodimer of this transcription factor family. We have also provided correlative data to show that under normal physiological conditions, the NF-kappa B functions as an antiandrogen during the age-dependent desensitization of the liver. In addition to the naturally functioning antiandrogenic influence of NF-kappa B, we have designed an artificial antiandrogenic agent, a triplex-forming oligonucleotide (TFO) directed to the -960/-940 activator domain of the rat androgen receptor gene promoter. This oligonucleotide at a TFO-to-promoter ratio of 500 is able to cause about 60% inhibition of rAR promoter function in transfected COS-1 cells. These results clearly demonstrate the feasibility of the antigene approach for effective inhibition of steroid hormone action.

Nuclear factor kappa B functions as a negative regulator for the rat androgen receptor gene and NF-kappa B activity increases during the age-dependent desensitization of the liver

Transcriptional regulation of the steroid hormone receptor genes plays a central role in temporal changes of target cell sensitivity during development, maturation, and aging. Sequence-specific DNA-protein interactions mediate these regulatory functions. Progressive 5' deletion of the rat androgen receptor (rAR) gene immediately beyond the -572 base pair (bp) region causes a marked increase in its promoter activity. DNase I footprinting with nuclear proteins revealed a protected area encompassing -574- to -554-bp positions that begins with a perfectly palindromic nuclear factor kappa B (NF-kappa B) motif. Electrophoretic mobility shift analyses (EMSA) showed that the decameric rAR NF-kappa B site at positions -574 to -565 cross-competes with the authentic kappa immunoglobulin light chain enhancer for specific protein binding. Supershift with specific antibodies to NF-kappa B subunits confirmed that the two retarded bands observed in the EMSA with the labeled rAR probe are due to p50/p65 and p50/p50 dimers of the NF-kappa B/Rel proteins. Fragments of rAR promoter with either deletion or point mutation of the NF-kappa B site are found to be about 2- to 3-fold more effective as compared to the wild type control in driving a heterologous reporter gene in cellulo. Thus, unlike most other known cases, NF-kappa B acts as a negative regulator for the rAR gene. The physiological relevance of this repressor function is evident from a 10-fold increase in the p50/p50 form of the NF-kappa B activity in the liver of aged rats exhibiting hepatic androgen desensitization. The newly identified repressor element is a rare example of a naturally occurring perfect palindromic binding motif for the NF-kappa B/Rel family of transcription factors. This repressor factor and the positively acting age-dependent factor, ADF, described earlier (Supakar, P. C., Song, C. S., Jung, M. H., Slomczynska, M. A., Kim, J.-M., Vellanoweth, R. L., Chatterjee, B. & Roy, A. K. (1993) J. Biol. Chem. 268, 26400-26408) function to coordinate the tissue-specific down-regulation of the rAR gene during aging.

Molecular analysis of G1B and G3A IFN gamma mutants reveals that defects in CIITA or RFX result in defective class II MHC and Ii gene induction

Class II major histocompatibility complex (MHC) genes and the invariant (Ii) gene are inducible by interferon-gamma (IFN gamma) but not by interferon-alpha and interferon-beta. The promoter regions of these genes contain three regulatory elements that mediate constitutive and IFN gamma-induced expressions; however, none of the DNA-binding proteins that interact with these elements are regulated by IFN gamma. Recently, a gene coding for a transactivator (CIITA) of class II MHC genes that complements a HLA-DR-negative immunodeficiency has been isolated. Using one IFN gamma mutant cell line (G3A) that is selectively defective in HLA-DR and Ii induction, four lines of evidence are presented to show that CIITA mediates the IFN gamma induction of HLA-DR and Ii genes. Analysis of another mutant line, G1B, indicates that the lack of DRA and Ii gene induction by IFN gamma is correlated with the lack of RFX DNA binding activity, thus providing the link between RFX and an IFN gamma response.