The role of the kappa enhancer and its binding factor NF-kappa B in the developmental regulation of kappa gene transcription

Unfolding the symbiosis of AID, chromatin remodelers, and epigenetics-The ACE phenomenon of antibody diversity

Activation-induced cytidine deaminase (AID) is responsible for the initiation of somatic hypermutation (SHM) and class-switch recombination (CSR), which result in antibody affinity maturation and isotype switching, thus producing pathogen-specific antibodies. Chromatin dynamics and accessibility play a significant role in determining AID expression and its targeting. Chromatin remodelers contribute to the accessibility of the chromatin structure, thereby influencing the targeting of AID to Ig genes. Epigenetic modifications, including DNA methylation, histone modifications, and miRNA expression, profoundly impact the regulation of AID and chromatin remodelers targeting Ig genes. Additionally, epigenetic modifications lead to chromatin rearrangement and thereby can change AID expression levels and its preferential targeting to Ig genes. This interplay is symbolized as the ACE phenomenon encapsulates three interconnected aspects: AID, Chromatin remodelers, and Epigenetic modifications. This review emphasizes the importance of understanding the intricate relationship between these aspects to unlock the therapeutic potential of these molecular processes and molecules.

Protective effects of alpha-lipoic acid on anxiety-like behavior, memory and prevention of hippocampal oxidative stress in methamphetamine-treated rats

RATIONALE

Alpha-lipoic acid is an essential cofactor for aerobic metabolism and acts as a potent antioxidant in the body. It has been shown that acute exposure to methamphetamine induces oxidative stress, which is responsible for severe cognitive deficits in animals. The hippocampus plays a crucial role in the processing of memory and anxiety-like behavior.

OBJECTIVES

In this study, preventive effect of the alpha-lipoic acid on memory impairment in methamphetamine-induced neurotoxicity was investigated.

METHODS

Wistar male rats (200-220 g) were allocated to five groups (seven rats in each group): (1) saline + saline, (2) saline + vehicle (sunflower oil as alpha-lipoic acid solvent), (3) methamphetamine + vehicle, (4) methamphetamine + alpha-lipoic acid 10 mg/kg, and (5) methamphetamine + alpha-lipoic acid 40 mg/kg. Rats received intraperitoneal methamphetamine repeatedly (2 × 20 mg/kg, 2 h interval). Alpha-lipoic acid was injected 30 min, 24 h, and 48 h after the last injection of methamphetamine. The passive avoidance test and open field were used for evaluation of memory retrieval and anxiety, respectively. After behavioral test, rats were anesthetized, their brains were extracted, and after preparing hippocampal homogenates, malondialdehyde (MDA) level, catalase, and superoxide dismutase (SOD) activities were evaluated.

RESULTS

Statistical analysis showed that injection of saline or sunflower oil had no significant effect on anxiety, memory, or oxidative stress markers. Methamphetamine induced memory impairment, increased anxiety-like behavior and MDA level, but it reduced catalase and SOD activity. Treatment with alpha-lipoic acid decreased MDA, increased catalase and SOD activity, and also prevented memory impairment and anxiety-like behavior. Our results showed that alpha-lipoic acid protected the hippocampus from oxidative stress by elevating SOD and CAT activities and reduced memory impairment following acute methamphetamine injection. These findings suggest that alpha-lipoic acid may have a protective effect against the adverse effects of methamphetamine exposure on the hippocampus. Therefore, the current data indicated that ALA can reduce oxidative stress predominantly by its antioxidant property.

The enhancer activity of long interspersed nuclear element derived microRNA 625 induced by NF-κB

Transposable elements (TEs) are DNA sequences that cut or introduced into the genome, and they represent a massive portion of the human genome. TEs generate a considerable number of microRNAs (miRNAs) are derived from TEs (MDTEs). Numerous miRNAs are related to cancer, and hsa-miRNA-625 is a well-known oncomiR derived from long interspersed nuclear elements (LINEs). The relative expression of hsa-miRNA-625-5p differs in humans, chimpanzees, crab-eating monkeys, and mice, and four primers were designed against the 3'UTR of GATAD2B to analyze the different quantities of canonical binding sites and the location of miRNA binding sites. Luciferase assay was performed to score for the interaction between hsa-miRNA-625 and the 3'UTR of GATAD2B, while blocking NF-κB. In summary, the different numbers of canonical binding sites and the locations of miRNA binding sites affect gene expression, and NF-κB induces the enhancer activity of hsa-miRNA-625-5p by sharing the binding sites.

The Impact of Gut Microbiota Disorders on the Blood-Brain Barrier

The gut microbiota is symbiotic with the human host and has been extensively studied in recent years resulting in increasing awareness of the effects of the gut microbiota on human health. In this review, we summarize the current evidence for the effects of gut microbes on the integrity of the cerebral blood-brain barrier (BBB), focusing on the pathogenic impact of gut microbiota disorders. Based on our description and summarization of the effects of the gut microbiota and its metabolites on the nervous, endocrine, and immune systems and related signaling pathways and the resulting destruction of the BBB, we suggest that regulating and supplementing the intestinal microbiota as well as targeting immune cells and inflammatory mediators are required to protect the BBB.

NF-κB signaling and crosstalk during carcinogenesis

Transcription factors (TFs) are proteins that control the transcription of genetic information from DNA to mRNA by binding to specific DNA sequences either on their own or with other proteins as a complex. TFs thus support or suppress the recruitment of the corresponding RNA polymerase. In general, TFs are classified by structure or function. The TF, Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), is expressed in all cell types and tissues. NF-κB signaling and crosstalk are involved in several steps of carcinogenesis including in sequences involving pathogenic stimulus, chronic inflammation, fibrosis, establishment of its remodeling to the precancerous niche (PCN) and transition of a normal cell to a cancer cell. Triggered by various inflammatory cytokines, NF-κB is activated along with other TFs with subsequent stimulation of cell proliferation and inhibition of apoptosis. The involvement of NF-κB in carcinogenesis provides an opportunity to develop anti-NF-κB therapies. The complexity of these interactions requires that we elucidate those aspects of NF-κB interactions that play a role in carcinogenesis, the sequence of events leading to cancer.

Novel role of NF-κB-p65 in antioxidant homeostasis in human kidney-2 cells

Nuclear factor-κB (NF-κB) plays a role in inflammation. However, we recently reported an association between NF-κB and antioxidant enzymes in renal proximal tubules of exercise-trained rats, suggesting its role in antioxidant homeostasis (George L, Lokhandwala MF, Asghar M. Am J Physiol Renal Physiol 297: F1174-F1180, 2009). A direct role of NF-κB in antioxidant homeostasis in renal cells has not been elucidated and warrants investigation. Therefore, we examined whether NF-κB has a direct role in antioxidant homeostasis and redox balance in human kidney-2 cells overexpressing NF-κB-p65 and compared them with the cells overexpressing Nrf-2, a well-known transcription factor involved in antioxidant homeostasis. The ability of NF-κB-p65 to increase antioxidant enzymes, to reduce reactive oxygen species (ROS), and to rescue ROS-induced renal dopamine D1 receptor dysfunction, was studied. The transcription activity of NF-κB-p65 and Nrf-2, measured as luciferase reporter activity, increased in cells overexpressing these nuclear factors. The levels of mRNA and activity of glutathione peroxidase as well as the protein levels of superoxide dismutase-1 and glutamylcystein transferase were increased in cells overexpressing NF-κB-p65 and Nrf-2. Furthermore, the levels of ROS decreased and D1 receptor agonist SKF38393-mediated [(35)S]GTPγS binding (index of D1 receptor function) increased in the presence of hydrogen peroxide in cells overexpressing NF-κB-p65 and Nrf-2. These results suggest a direct role of NF-κB-p65 in antioxidant homeostasis, contributing to redox balance in renal cells.

Local immune regulatory effects of Bangdeyun on the endometrium of mice with embryo implantation dysfunction during the implantation time

This study examined the effects of Bangdeyun on the expressions of nuclear factor-kappaB (NF-kappaB), interferon-gamma (IFN-gamma) and interleukin-10 (IL-10) in the endometrium of mice with embryo implantation dysfunction (EID) during the implantation time (namely on pregnancy day 5, 6, 7 and 8) and explored the local immune regulatory effects of Bangdeyun. The gestational mice were randomly divided into normal group, model group and Bangdeyun-treated group. EID models of mice were established by using indomethacin. The endometrial expression of NF-kappaB was detected by immunohistochemistry and Western blotting. IFN-gamma and IL-10 were measured by enzyme-linked immunosorbent assay (ELISA). The results showed that in the normal group, NF-kappaB and IFN-gamma were weakly expressed and IL-10 was strongly expressed in the endometrium during the whole implantation period. In the model group, the expressions of NF-kappaB and IFN-gamma were increased on pregnancy day 5, 6 and 7, and IL-10 expression decreased during the whole implantation time when compared with those in the normal group (P<0.01 for all). In the Bangdeyun-treated group, little amount of NF-kappaB and IFN-gamma was expressed and IL-10 expression was strong, much the way they were expressed in the normal group (P>0.05). The expressions of NF-kappaB and IFN-gamma were much lower in the Bangdeyun-treated group than those in the model group on pregnancy day 5, 6 and 7 (P<0.01 for all), while the expression of IL-10 was much higher than in the model group during the whole implantation time (P<0.01). It was suggested Bangderun may favor a shift from Th1- to Th2-type immune response, therefore inhibiting the maternal immune rejection, inducing the immune tolerance and improving the fetal implantation.

Long-range interactions between three transcriptional enhancers, active Vkappa gene promoters, and a 3' boundary sequence spanning 46 kilobases

The mouse immunoglobulin kappa (Igkappa) gene contains an intronic enhancer and two enhancers downstream of its transcription unit. Using chromosome conformation capture technology, we demonstrate that rearranged and actively transcribed Igkappa alleles in MPC-11 plasmacytoma cells exhibit mutual interactions over 22 kb between these three enhancers and Vkappa gene promoters. In addition, the 5' region of the active transcription unit exhibits a continuum of interactions with downstream chromatin segments. We also observe interactions between Ei and E3' with 3' boundary sequences 24 kb downstream of Ed, adjacent to a neighboring housekeeping gene. Very similar interactions between the enhancers are also exhibited by normal B cells isolated from mouse splenic tissue but not by germ line transcriptionally inactive alleles of T cells or P815 mastocytoma cells, which exhibit a seemingly linear chromatin organization. These results fit a looping mechanism for enhancer function like in the beta-globin locus and suggest a dynamic modulation of the spatial organization of the active Igkappa locus. Chromatin immunoprecipitation experiments reveal that the interacting Igkappa gene cis-acting sequences are associated with AP-4, E47, and p65NF-kappaB, potential protein candidates that may be responsible for initiating and/or maintaining the formation of these higher-order complexes. However, S107 plasmacytoma cells that lack NF-kappaB still exhibit mutual interactions between the Igkappa gene enhancers.

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.

I-kappa B kinase beta is critical for B cell proliferation and antibody response

The NF-kappaB proteins are critical in the regulation of the immune and inflammatory response. Stimulation of the NF-kappaB pathway leads to increases in I-kappaB kinase beta (IKKbeta) kinase activity to result in the enhanced phosphorylation and degradation of I-kappaB and the translocation of the NF-kappaB proteins from the cytoplasm to the nucleus. In this study, a dominant-negative IKKbeta mutant expressed from the IgH promoter was used to generate transgenic mice to address the role of IKKbeta on B cell function. Although these transgenic mice were defective in activating the NF-kappaB pathway in B cells, they exhibited no defects in B lymphocyte development or basal Ig levels. However, they exhibited defects in the cell cycle progression and proliferation of B cells in response to treatment with LPS, anti-CD40, and anti-IgM. Furthermore, selective defects in the production of specific Ig subclasses in response to both T-dependent and T-independent Ags were noted. These results suggest that IKKbeta is critical for the proliferation of B cells and the control of some aspects of the humoral response.

Lentivirus replication and regulation

Lentiviruses are associated with chronic diseases of the hematological and neurological systems in animals and man. In particular, human immunodeficiency virus type 1 (HIV-1) is the etiological agent of the global AIDS epidemic. The genomes of lentiviruses are complex, encoding a number of regulatory and accessory proteins not found in other retroviruses. This complexity is reflected in their replication cycle, which reveals intricate regulatory pathways and unique mechanisms for viral persistence. In this review, we highlight some of these unique features for HIV-1, with particular focus on the transcriptional and posttranscriptional control of gene expression. Although our understanding of the biology of HIV-1 is far from complete, the knowledge gained thus far has already led to novel strategies for both virus intervention and exploiting the lentiviruses for therapeutic applications.

Urine free light chains in SLE: clonal markers of B-cell activity and potential link to in vivo secreted Ig

As a marker of in vivo B-cell activity, urine levels of free light chain (FLC) were measured twice weekly by radioimmunoassay (RIA) and correlated with disease activity over periods of 5-10 months in seven patients with systemic lupus erythematosus (SLE). In addition, RIA-measured urine albumin was used to track glomerular injury, and alpha1-microglobulin (alpha1-M) levels, 28- to 32-kDa protein, provided control measurements on excretion of low-molecular-weight proteins. As controls, urine FLC levels were obtained from healthy normals and in subjects with acute pharyngitis, sickle-cell anemia, and acute sepsis or pneumonia. The control results showed that with acute sepsis/pneumonia had marked increases in urine FLC, while pharyngitis and sickle-cell controls had normal FLC levels. In SLE, active patients receiving intravenous cyclophosphamide and high-dose steroids exhibited highly increased urine FLC that fluctuated widely during therapy and fell to normal range levels with disease remission. During active SLE, urine albumin often was increased, while alpha1-M levels remained in normal range. In contrast to the increased FLC of active disease, inactive patients on low-dose maintenance therapy had predominantly normal FLC levels throughout the collection period. These results support our hypothesis that longitudinal levels of urine FLC can be used to track disease-related B-cell activity in SLE. Furthermore, we suggest that the urine FLC of active SLE would share LC idiotype with the clonal associated in vivo secreted Ig, and thus permit the identification of these antibodies that are targeted to the culprit immunogen(s) responsible for the pathogenesis of SLE.

Activation of c-myc promoter P1 by immunoglobulin kappa gene enhancers in Burkitt lymphoma: functional characterization of the intron enhancer motifs kappaB, E box 1 and E box 2, and of the 3' enhancer motif PU

Deregulated expression of the proto-oncogene c- myc in Burkitt lymphoma (BL) cells carrying a t(2;8) translocation is mediated by a synergistic interaction of the translocated immunoglobulin (Ig) kappa gene intron (kappaEi) and 3' (kappaE3') enhancers and characterized by a strong activation of the promoter P1. We have investigated the functional role of distinct kappa enhancer sequence motifs in P1 activation on both mini-chromosomes and reporter gene constructs. Stable and transient transfections of BL cells revealed critical roles of the kappaEi and kappaE3' elements kappaB and PU, respectively. Joint mutation of kappaB and PU completely abolished P1 activity, implying that an interaction of kappaB- and PU-binding factors is essential for the enhancer synergism. Mutation of the E box 1 and E box 2 motifs markedly decreased P1 activity in transient but not in stable transfection experiments. Co-expression of the NF-kappaB subunit p65(RelA) and Sp1, an essential factor for P1 transcription, in Drosophila melanogaster SL2 cells synergistically enhanced promoter activity. Our results support a model which proposes cross-talk between promoter and enhancer binding factors as the basic mechanism for kappa enhancer-mediated c- myc activation in BL cells.

Prf, a novel Ets family protein that binds to the PU.1 binding motif, is specifically expressed in restricted stages of B cell development

During the development of lymphocytes, expression of the Ig genes is strictly regulated in a tissue-specific manner and in a time-ordered fashion. We have previously shown that the PU.1 binding motif in the Igkappa 3' enhancer (kappaE3') and a novel Ets family protein other than PU.1 may be possibly involved in the control of V(kappa)-J(kappa) joining. In the attempt to isolate the novel Ets family protein, we have screened cDNA libraries with the yeast one-hybrid method and identified a new PU.1-related factor, Prf. This novel Ets family protein is shown to interact with the PU.1 binding sequences in various promoters and enhancers, including kappaE3'. It was found that expression of the prf gene is predominant in the B-lineage cells, with the exception of immature B cells. Since Prf does not exhibit functions of transcriptional activity, this novel protein may act as an antagonist against other Ets family proteins, e.g. PU.1 and Spi-B. Possible roles of Prf with respect to the B cell differentiation are discussed.

Overexpression of RelA causes G1 arrest and apoptosis in a pro-B cell line

NF-kappaB/Rel family proteins form a network of post-translationally regulated transcription factors that respond to a variety of extracellular stimuli and mediate distinct cellular responses. These responses include cytokine gene expression, regulated cell cycle activation, and both the protection from and induction of the cell death program. To examine the function of individual Rel family proteins in B cell development and resolve their role in the signaling of apoptosis, we used a tetracycline-regulated gene expression system to overexpress either c-Rel or RelA in the transformed pro-B cell line 220-8. Elevated levels of RelA, but not c-Rel, induced a G1 cell cycle arrest followed by apoptosis. Both the DNA binding and transactivation domains of RelA were required for this effect. When RelA was overexpressed in the immature B cell line WEHI 231 or the mature B cell line M12, neither cell cycle arrest nor apoptosis was evident. The differential effects of elevated RelA levels in these cell lines suggests that susceptibility to NF-kappaB-induced apoptosis may reflect a relevant selection event during B cell development.

Tetracycline repressor, tetR, rather than the tetR-mammalian cell transcription factor fusion derivatives, regulates inducible gene expression in mammalian cells

This article describes the first (to our knowledge) tetracycline-inducible regulatory system that demonstrates that the tetracycline repressor (tetR) alone, rather than tetR-mammalian cell transcription factor fusion derivatives, can function as a potent trans-modulator to regulate gene expression in mammalian cells. With proper positioning of tetracycline operators downstream of the TATA element and of human epidermal growth factor (hEGF) as a reporter, we show that gene expression from the tetracycline operator-bearing hCMV major immediate-early enhancer-promoter (pcmvtetO) can be regulated by tetR over three orders of magnitude in response to tetracycline when (1) the reporter was cotransfected with tetR-expressing plasmid in transient expression assays, and (2) the reporter unit was stably integrated into the chromosome of a tetR-expressing cell line. This level of tetR-mediated inducible gene regulation is significantly higher than that of other repression-based mammalian cell transcription switch systems. In an in vivo porcine wound model, close to 60-fold tetR-mediated regulatory effects were detected and it was reversed when tetracycline was administered. Collectively, this study provides a direct implementation of this tetracycline-inducible regulatory switch for controlling gene expression in vitro, in vivo, and in gene therapy.

Somatic mutations in the Ig variable region genes and expression of novel Cmu-germline transcripts in a B-lymphoma cell line ("Farage") not producing Ig polypeptide chains

Non-Hodgkin's B-lymphomas (B-NHL) are a very heterogeneous group of B-cell neoplasias originating from the germinal centers of lymphatic follicles. Thus, they represent a suitable experimental model to study the molecular basis of certain key events which take place in the lymphatic follicles, including somatic hypermutation and heavy chain isotypic switch. An unusual B-NHL cell line ("Farage") not producing Ig polypeptide chains was previously shown to rearrange its IgH and Igkappa genes and transcribe seemingly normal size mu and kappa mRNAs. In an attempt to characterize the phenotype of Farage cells better and to elucidate the molecular basis of the failure of Farage cells to synthesize Ig chains, we sequenced its VH and Vkappa rearranged gene segments by PCR and RT-PCR. It was found that both V genes are somatically, heavily mutated compared to their germline counterparts. In addition, this rearranged VDJ gene of the heavy chain is not transcribed. Instead, the Farage cells express a low level of a new family of germline transcripts starting with a VH like sequence, continuing with a small segment of the 3'VH germline flanking region, and ending within the Cmu region. These transcripts lack D and J segments and do not contain the open reading frame of the full-length Cmu protein. Thus, Farage cells fail to produce mu heavy chains due to silencing of the expression of the conventional VDJCmu transcript and expression of unusual Cmu-germline transcripts. In contrast to the IgH genes, the rearranged VJ gene of Farage is transcribed and gives rise to a full-size kappa-mRNA. This transcript, however, is not translated to a full-length kappa-chain, as it contains a stop codon in its coding region. All the above show that Farage cells are unable to produce Ig polypeptide chains, due to somatic mutations altering the kappa-chain gene, and mutations and/or regulatory events that shutoff the transcription of the IgH gene. The heavily mutated Vkappa and Vkappa genes found, support the conclusion that the Farage cell line originated either from germinal center cells or from the mantle zone of the lymphoid follicle.

Transcription factor Pip can enhance DNA binding by E47, leading to transcriptional synergy involving multiple protein domains

The transcription factors E2A (E12/E47) and Pip are both required for normal B-cell development. Each protein binds to regulatory sequences within various immunoglobulin enhancer elements. Activity of E2A proteins can be regulated by interactions with other proteins which influence their DNA binding or activation potential. Similarly, Pip function can be influenced by interaction with the protein PU.1, which can recruit Pip to bind to DNA. We show here that a previously unidentified Pip binding site resides adjacent to the E2A binding site within the immunoglobulin kappa 3' enhancer. Both of these binding sites are crucial for high-level enhancer activity. We found that E47 and Pip can functionally interact to generate a very potent 100-fold transcriptional synergy. Through a series of mutagenesis experiments, we identified the Pip sequences necessary for transcriptional activation and for synergy with E47. Two synergy domains (residues 140 to 207 and 300 to 420) in addition to the Pip DNA binding domain (residues 1 to 134) are required for maximal synergy with E47. We also identified a Pip domain (residues 207 to 300) that appears to mask Pip transactivation potential. Part of the synergy mechanism between E47 and Pip appears to involve the ability of Pip to increase DNA binding by E47, perhaps by inducing a conformational change in the E47 protein. E47 may also induce a conformational change in Pip which unmasks sequences important for transcriptional activity. Based upon our results, we propose a model for E47-Pip transcriptional synergy.

The mutant plasmacytoma cell line S107 allows the identification of distinct pathways leading to NF-kappaB activation

Studies on the mechanisms of inducible and constitutive activity of NF-kappaB transcription factors have been hampered by the lack of appropriate mutant cell lines. We have analyzed the defect in the murine S107 plasmacytoma cell line, which was previously found to lack both constitutive and inducible NF-kappaB activity. Our analysis shows that these cells bear a specific defect that interferes with NF-kappaB induction by many diverse stimuli, such as lipopolysaccharide, phorbol 12-myristate 13-acetate, UV light, x-rays, and H2O2. This does not however represent a general signal transduction defect, because AP-1 transcription factors are readily induced by the same stimuli. Phosphatase inhibitors such as okadaic acid as well as calyculin A can efficiently induce NF-kappaB in S107 cells via a pathway apparently insensitive to the radical scavenger pyrrolidine dithiocarbamate. Furthermore, MEKK1 a protein kinase supposedly induced by some of the above stimuli, is also capable of activating NF-kappaB. Interestingly, both the potent physiological inducer of NF-kappaB TNFalpha as well as endoplasmic reticulum overload can induce NF-kappaB via a PDTC sensitive pathway. In all cases, DNA-binding NF-kappaB complexes are comprised predominantly of p50-RelA heterodimers, and NF-kappaB activation results in the induction of transiently transfected or resident reporter genes. In summary, these results suggest that the pathways for many NF-kappaB-inducing stimuli converge at a specific junction, and this pivotal step is mutated in the S107 cell line. Yet there are alternative routes bypassing this critical step that also lead to NF-kappaB induction. These routes utilized by tumor necrosis factor alpha and endoplasmic reticulum overload are still intact in this cell line.

Evidence of stage-specific element for germ-line transcription of the TCR alpha gene located upstream of J alpha49 locus

T cell receptor (TCR) genes are rearranged and expressed in an ordered manner during T cell development. The basic mechanism regulating this stepwise DNA alteration is poorly understood. To address this issue, we explored the presence of a stage-specific element for germ-line transcription of the TCR alpha gene which is closely associated with gene rearrangement. First, germ-line transcription of the TCR alpha gene including the first segment of the J alpha locus, J alpha49, was delayed compared to that of the TCR beta gene in both normal and TCR-transgenic (Tg) mice. Furthermore, expression of this transcript could be induced by CD3epsilon-mediated signals in recombination-activating gene (RAG)-2-deficient mice. In TCR-Tg mice, the endogenous J alpha49 germ-line transcript could not yet be observed at the CD25+ double-negative (DN) stage when the TCR alpha transgene was expressed. Of immature T cell hybridomas derived from either scid thymocytes (CD25+ DN) or immature CD8-single positive (ISP) thymocytes, only the latter hybridoma expressed the J alpha49 germ-line transcript. These data indicate that the J alpha49 germ-line transcription occurs only at a specific developmental stage. Second, to determine which elements may be regulating stage specificity, we performed transient transfection analysis with a reporter gene and demonstrated that the upstream region of the J alpha49 locus possesses promoter activity in correlation with germ-line transcription in ISP-derived but not in SCID-derived hybridomas. These results indicate that the expression of TCR alpha germ-line transcripts is regulated in a stage-specific manner by a cis-element located within the J alpha locus.

Pentoxifylline Inhibits Ig κ Gene Transcription and Rearrangements in Pre-B Cells

Pentoxifylline (PF) has been used in a wide variety of clinical situations; however, the molecular consequences of this drug are not well characterized. In this paper we assayed the effects of PF in two models of pre-B differentiation. In 70Z pre-B cells, transcriptional induction of rearranged Ig κ-chain gene in response to LPS was suppressed by PF, without affecting the induction of Rel family proteins. In contrast, κ induction by IFN-γ was not suppressed by PF, indicating that the drug inhibited certain activation pathways. We also found that LPS-induced activation of germline κ transcription and Vκ to Jκ recombination were inhibited by PF in the pre-B cell line 38B9. These observations suggest that PF may adversely affect B lymphopoiesis during chronic administration.

Primary B cells essentially lack constitutive NF-kappa B activity

Based primarily on the analysis of B cell lines, mature B cells are considered distinct from non-B cells and immature B cells by having constitutive nuclear NF-kappaB activity. By their comparison to splenic non-B cells or activated B cells we show here that primary resting B cells lack cell-autonomous NF-kappaB activity. This finding indicates that the role of the transcription factor in B cells is similar to that in other cells, namely a common mediator of activation and stress signals. Whereas the absence of constitutive NF-kappaB activity in mature B cells does not argue against a role of NF-kappaB in B cell development, it does not support the notion of the essential function of the factor in maintaining the unique transcriptional activities in B cells.

A Two-Step Mechanism for Recruitment of Pip by PU.1

Transcription of the Ig κ light chain gene is controlled in part by the 3′ κ enhancer. Two of the proteins that bind to the 3′ enhancer, PU.1 and Pip, show tissue-restricted expression and may be responsible for the tissue specificity of 3′ enhancer activity. PU.1 alone can bind to DNA; however, Pip cannot bind to its 3′ enhancer site in electrophoretic mobility shift assays, unless recruited by PU.1. Previously, we showed that the PU.1 PEST domain (rich in the amino acids proline, glutamate, serine, and threonine; sequences 118–160) is necessary for Pip recruitment to DNA. Here we used detailed mutagenic analyzes of PU.1 to more precisely identify sequences required for Pip recruitment by electrophoretic mobility shift assay. We found that mutation of three segments within the PU.1 PEST domain (118–125, 133–139, and 141–147) modulated the efficiency of Pip recruitment, while mutation of sequences between residues 88–118 and 154–168 had no effect. Interestingly, we found that the PU.1 ETS domain (residues 170 to 255) is both necessary and sufficient for Pip interaction in solution and that other ETS domain proteins can physically interact with Pip as well. Our results suggest that Pip recruitment to DNA by PU.1 occurs via a two-step mechanism. First, a physical interaction that is not sufficient to recruit Pip occurs via the PU.1 ETS domain. Second, a conformational change in the PU.1 PEST domain, apparently mediated by serine phosphorylation, induces a conformational change in Pip enabling it to bind to DNA. We also show that the PU.1 PEST domain does not target PU.1 for rapid turnover.

RelB is a key player for both kappa B-dependent transcription and demethylation in B cells

NF-kappa B was originally identified as a B cell-specific nuclear factor binding to the intronic kappa-light-chain enhancer element. It is found constitutively in the nucleus of mature B and plasma cells. In other cell types including pre-B cells, NF-kappa B is sequestered in the cytoplasm but can be induced by a variety of stimuli. In contrast to essentially all other mature B cells and plasma cell lines, the S107 plasmacytoma cell line lacks both constitutive and inducible kappa B-binding activity. A molecular characterization of the defect in these S107 cells suggests that the primary defect lies in the signal transduction pathway leading to NF-kappa B induction. Ectopic expression of RelB after stable transfection of these cells restores constitutive nuclear kappa B-binding activity. Moreover, kappa B-dependent transcription is also restored. Finally we demonstrate, that in contrast to parental S107 cells, the stable RelB transfectants have also regained the ability to specifically demethylate a transfected immunoglobulin kappa-locus. These data suggest that RelB is critically involved in both B cell-specific transcription and demethylation directed by the intronic kappa-enhancer element.

Sequence elements downstream of the human immunodeficiency virus type 1 long terminal repeat are required for efficient viral gene transcription

We investigated the role of a 54-nucleotide region (+200 to +253) located downstream of the HIV-1 long terminal repeat (LTR) on virus gene expression and found, using RT-PCR and p24 CA analysis, that deletion of this region inhibited synthesis of both viral RNA and protein. CAT assays showed that these results were attributable to decreased transcription efficiency of the HIV-1 LTR and not to the stability of the RNA transcripts produced. Further deletional analysis and transfection studies showed that the most important sequences with regard to proviral DNA expression were located between nucleotide positions +218 and +237. Furthermore, substitutional mutational analysis showed that a CTCTCTC sequence at positions +227 to +233, homologous to the pyrimidine-rich initiator (Inr) region found in several promoters, was required for efficient production of both viral RNA and protein. Deletion of the sequence +200 to +217, homologous to the interferon-stimulated response element (ISRE), resulted in impaired LTR promoter activity and decreased synthesis of viral RNA and protein. However, when the latter region was replaced by homologous ISRE sequences from an interferon-stimulated gene (ISG-54), an even more severe effect on HIV gene expression and replication was observed, suggesting that ISRE-like sequences in HIV act differently from homologous sequences in interferon-responsive cellular genes.

Regulation of IkappaB beta in WEHI 231 mature B cells

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

Failure of lymphopoiesis after adoptive transfer of NF-kappaB-deficient fetal liver cells

Mice deficient in the p65 subunit of NF-kappaB die during fetal development. Introduction of p50/p65-deficient fetal liver cells into lethally irradiated hosts resulted in a severe deficit of fetal liver-derived lymphocytes and their immediate precursors but an overabundance of fetal liver-derived granulocytes. Surprisingly, simultaneous transplantation of wild-type bone marrow cells rescued the production of p50/p65-deficient lymphocytes. Expression of immunoglobulin K light chains on these rescued NF-kappaB-deficient B lymphocytes was normal. These results suggest that while p50 and p65 do not regulate the maturation of pre-B cells, NF-kappaB mediates the development or survival of an early lymphocyte precursor through regulation of an extracellular factor.

In vivo occupancy of the kappa light chain enhancers in primary pro- and pre-B cells: a model for kappa locus activation

The immunoglobulin kappa light chain locus has two enhancer elements: the intronic enhancer, which lies between the Jkappa cluster and the Ckappa exon, and the 3'kappa enhancer, which is located downstream of Ckappa. To address the contribution of these elements to the developmentally regulated activation of germline kappa locus transcription and rearrangement, we purified primary pro- and pre-B cells and determined by in vivo footprinting the sites within each enhancer that were occupied. We found that the kappa intronic enhancer NF-kappaB site is occupied in both pro- and pre-B cells, while CRE, BSAP, and PU.1/pip sites within the 3'kappa enhancer undergo changes in occupancy as cells progress from the pro-B to the pre-B cell stage. These findings suggest that regulation of the kappa locus in primary pre-B cells may be mediated by factors that bind the 3'kappa enhancer.

Identification of a novel NF-kappaB p50-related protein in B lymphocytes

In most cell types other than mature B lymphocytes and macrophages, the transcription factor NF-kappaB remains in an inactive form in the cytosol by being bound to the inhibitory proteins IkappaBalpha and IkappaBbeta. To investigate the regulation of constitutively active NF-kappaB in B lymphocytes, we have examined the composition of Rel protein complexes in different mouse B-cell lines. As reported previously, the constitutively active complex in mature B cells was predominantly p50:c-Rel. However, the kappaB binding complex in the plasmacytomas that were examined lacked c-Rel and instead contained only a p50-related protein. This p50-related protein (p55) cross-reacts with three different p50 antisera, exists in both the cytosol and the nucleus, and is the protein that binds to kappaB sites in plasma cells. Transfection of reporter constructs into plasma cells indicates that the p55 complex is also transcriptionally active. The p55 protein can be detected in splenocytes from mice lacking the p105/p50 gene, and therefore it appears to be the product of a distinct gene. The implications of the existence of a NF-kappaB p50-related protein in plasma cells that is capable of binding to kappaB sites and activating transcription are discussed.

Human TAFII 105 is a cell type-specific TFIID subunit related to hTAFII130

We previously characterized Drosophila and human TAF subunits that make up the core TFIID complex found in all cells. Here, we report that differentiated B cells contain a novel substoichiometric TAF of 105 kDa not found associated with TFIID isolated from other cell types. The cDNA encoding hTAFII105 reveals a highly conserved C-terminal domain shared by hTAFII130 and oTAFII110, while the N-terminal coactivator domain has diverged significantly. All cells tested express TAFII105 mRNA, but only B cells contain significant levels of protein associated with TFIID. Transient overexpression of hTAFII105 selectively squelches the transcription of some genes in B cells. These properties suggest that TAFII105 is a cell type-specific subunit of TFIID that may be responsible for mediating transcription by a subset of activators in B cells.

A role for nuclear NF-kappaB in B-cell-specific demethylation of the Igkappa locus

The immunoglobulin kappa gene is specifically demethylated during B-cell maturation in a process which utilizes discrete cis-acting modules such as the intronic kappa enhancer element and the matrix attachment region (MAR). While any MAR sequence is sufficient for this reaction, mutation analysis indicates that tissue specificity is mediated by kappaB binding sequences within the kappa intronic enhancer. The plasmacytoma cell line S107 lacks kappaB binding activity and fails to demethylate the kappa locus. However, B-cell specific demethylation is restored by the introduction of an active kappaB binding protein gene relB. This represents the first demonstration of a trans-acting factor involved in cell-type-specific demethylation, and suggests that the same protein-DNA recognition system used for transcription may also contribute to the earlier developmental events that bring about activation of the kappa locus.

Identification and functional characterization of a highly conserved sequence in the intron of the kappa light chain gene

A highly conserved 225 bp sequence was identified within the J-C intron of the murine kappa light-chain immunoglobulin gene and its nuclear protein-binding and regulatory function were examined. The binding of nuclear proteins to this fragment was found to reflect the differentiation state of the cell used to prepare the nuclear extracts and three different complexes are seen with this fragment: CI, CII and CIII. CIII is present in all cell types. CI is present in fibroblasts, T cells and early B cells, but not mature B cells. Moreover, nuclear extracts prepared from the early pre-B cell line, 70Z/3, that was treated with agents which activate kappa gene transcription have a reduced ability to form CI. Therefore, the presence of CI correlates with the absence of kappa gene transcription. CII is present in all stages of B cell development, however its composition changes with B cell maturation. Contained within the 225 bp element is the ets family-binding motif GGAA and the B-cell-and-macrophage-specific family member, PU.1 binds this sequence and participates in CII formation. The 225 bp fragment showed modest augmentation of expression in CAT reporter constructs containing the heavy chain enhancer (HCE) and a light chain promoter in the plasmacytoma, S194, and uninduced 70Z/3 cells and mediated a small but reproducible response to IFN-gamma in 70Z/3 cells. Thus, the 225 bp sequence contained within the J-C intron may function as a regulatory element for kappa light chain gene expression.

A developmentally modulated chromatin structure at the mouse immunoglobulin kappa 3' enhancer

Transcription of the mouse immunoglobulin kappa gene is controlled by two enhancers: the intronic enhancer (Ei) that occurs between the joining (J kappa) and constant (C kappa) exons and the 3' enhancer (E3') located 8.5 kb downstream of the gene. To understand the role of E3' in the activation of the mouse immunoglobulin kappa gene, we studied its chromatin structure in cultured B-cell lines arrested at various stages of differentiation. We found that 120 bp of the enhancer's transcriptional core becomes DNase I hypersensitive early in B-cell development. Genomic footprinting of pro-B and pre-B cells localized this chromatin alteration to B-cell-specific protections at the region including the direct repeat (DR) and the sequence downstream of the DR (DS), the PU.1-NFEM-5 site, and the core's E-box motif, identifying bound transcription factors prior to kappa gene rearrangement. Early footprints were, however, not detected at downstream sites proposed to play a negative role in transcription. The early chromatin structure persisted through the mature B-cell stage but underwent a dramatic shift in plasma cells, correlating with the loss of guanosine protection within the DR-DS junction and the appearance of novel footprints at a GC-rich motif upstream and the NF-E1 (YY1/delta)-binding site downstream. Gel shift analysis demonstrated that the DR-DS junction is bound by a factor with properties similar to those of BSAP (B-cell-specific activator protein). These results reveal developmental-stage-specific changes in the composition of nuclear factors bound to E3', clarify the role of factors that bind constitutively in vitro, and point to the differentiation of mature B cells to plasma cells as an important transitional point in the function of this enhancer. The observed changes in nuclear factor composition were accompanied by the rearrangement of positioned nucleosomes that flank the core region, suggesting a role for both nuclear factors and chromatin structure in modulating kappa E3' function during B-cell development. The functional implications of the observed chromatin alterations are discussed in the context of recent studies on kappa E3' and the factors that bind to it.

Expression of the alpha(1,3)fucosyltransferase Fuc-TVII in lymphoid aggregate high endothelial venules correlates with expression of L-selectin ligands

Lymphocyte homing to lymph nodes and Peyer's patches is mediated, in part, by adhesive interactions between L-selectin expressed by lymphocytes and L-selectin ligands displayed at the surface of the cuboidal endothelial cells lining the post-capillary venules within lymphoid aggregates. Candidate terminal oligosaccharide structures thought to be essential for effective L-selectin ligand activity include a sulfated derivative of the sialyl Lewis x tetrasaccharide. Cell type-specific synthesis of this oligosaccharide is presumed to require one or more alpha(1,3)fucosyltransferases, operating upon common 3'-sialylated and/or sulfated N-acetyllactosamine-type precursors. The identity of the alpha(1,3)fucosyltransferase(s) expressed in cells that bear L-selectin ligands has not been defined. We report here the molecular cloning and characterization of a murine alpha(1,3)fucosyltransferase locus whose expression pattern correlates with expression of high affinity ligands for L-selectin. In situ hybridization and immunohistochemical analyses demonstrate that this cDNA and its cognate alpha(1,3)fucosyltransferase are expressed in endothelial cells lining the high endothelial venules of peripheral lymph nodes, mesenteric lymph nodes, and Peyer's patches. These expression patterns correlate precisely with the expression pattern of L-selectin ligands identified with a chimeric L-selectin/IgM immunohistochemical probe and by the high endothelial venule-reactive monoclonal antibody MECA-79. Transcripts corresponding to this cDNA are also detected in isolated bone marrow cells, a source rich in the surface-localized ligands for E- and P-selectins. Sequence and functional analyses indicate that this murine enzyme corresponds to the human Fuc-TVII locus. These observations suggest that Fuc-TVII participates in the generation of alpha(1,3)fucosylated ligands for L-selectin and provide further evidence for a role for this enzyme in E- and P-selectin ligand expression in leukocytes.

Accessibility control of antigen-receptor variable-region gene assembly: role of cis-acting elements

Antigen receptor variable region genes are assembled from germline variable (V), diversity (D), and joining (J) gene segments. This process requires expression of V(D)J recombinase activity, and "accessibility" of variable gene segments to this recombinase. The exact mechanism by which variable gene segments become accessible during development is not known. However, several studies have shown that cis-acting elements that regulate transcription may also function to regulate accessibility. Here we review the evidence that transcriptional promoters, enhancers, and silencers are involved in regulation of accessibility. The manner in which these elements may combine to regulate accessibility is addressed. In addition, current and potential strategies for identifying and analyzing cis-acting elements that mediate locus accessibility are discussed.

Molecular cloning, expression, chromosomal assignment, and tissue-specific expression of a murine alpha-(1,3)-fucosyltransferase locus corresponding to the human ELAM-1 ligand fucosyl transferase

Terminal Fuc alpha 1-3GlcNAc moieties are displayed by mammalian cell surface glycoconjugates in a tissue-specific manner. These oligosaccharides participate in selectin-dependent leukocyte adhesion and have been implicated in adhesive events during murine embryogenesis. Other functions for these molecules remain to be defined, as do the tissue-specific expression patterns of the corresponding alpha-(1-3)-fucosyltransferase (alpha 1-3FT) genes. This report characterizes a murine alpha 1-3FT that shares 77% amino acid sequence identity with human ELAM ligand fucosyltransferase (ELFT, also termed Fuc-TIV). The corresponding gene maps to mouse chromosome 9 in a region of homology with the Fuc-TIV locus on human chromosome 11q. In vitro, the murine alpha 1-3FT can efficiently fucosylate the trisaccharide Gal alpha 1-3Gal beta 1-4GlcNAc (apparent Km of 0.71 mM) to form an unusual tetrasaccharide (Gal alpha 1-3Gal beta 1-4[Fuc alpha 1-3]GlcNAc) described in periimplantation mouse tissues. The enzyme can also form the Lewis x determinant from Gal beta 1-4GlcNAc (Km = 2.05 mM), and the sialyl Lewis x determinant from NeuNAc alpha 2-3Gal beta 1-4GlcNAc (Km = 1.78mM). However, it does not yield sialyl Lewis x determinants when expressed in a mammalian cell line that maintains sialyl Lewis x precursors. Transcripts from this gene accumulate to low levels in hematopoietic organs, but are unexpectedly abundant in epithelia that line the stomach, small intestine, colon, and epididymus. Epithelial cell-specific expression of this gene suggests function(s) in addition to, and distinct from, its proposed role in selectin ligand synthesis.

Interleukin-4 inhibits kappa light chain expression and NF kappa B activation but not I kappa B alpha degradation in 70Z/3 murine pre-B cells

The murine pre-B cell line 70Z/3 responds to lipopolysaccharide by up-regulating the surface expression of kappa (kappa) light chain through activation of the transcription factor NF kappa B. Interleukin-4 (IL-4), a T cell cytokine, is a known inhibitor of some LPS-mediated events. We investigated whether IL-4 could inhibit the up-regulation of kappa light chain and activation of NF kappa B by LPS in 70Z/3. IL-4 partially inhibited both the LPS-induced expression of kappa light chain and also the activation of NF kappa B as judged by an NF kappa B reporter gene assay. Additionally, electrophoretic mobility shift assays confirmed this effect on LPS-induced NF kappa B DNA binding activity in the nucleus. Surprisingly, proteolytic degradation of I kappa B alpha (MAD3), a prerequisite for NF kappa B activation, was unaffected by IL-4, implying that this cytokine inhibits some subsequent undefined event in the activation of NF kappa B. IL-4 was also found partially to inhibit NF kappa B activity induced by tumor necrosis factor-alpha (TNF-alpha) and interleukin-1-beta (IL-1 beta). These results indicate that there may be a common mechanism for the well-documented anti-inflammatory effects of IL-4 and that this mechanism involves the transcription factor NF kappa B.

Activating transcription factor 1 and cyclic AMP response element modulator can modulate the activity of the immunoglobulin kappa 3' enhancer

Previously we determined that the immunoglobulin kappa 3' enhancer (kappa E3') contains at least two functional DNA sequences (PU.1/NF-EM5 and E2A) within its 132-base pair active core. We have determined that the activities of these two sequences are insufficient to account for the entire activity of the 132-base pair core. Using site-directed linker scan mutagenesis across the core fragment we identified several additional functional sequences. We used one of these functional sequences to screen a lambda gt11 cDNA expression library resulting in the isolation of cDNA clones encoding the transcription factors ATF-1 (activating transcription factor) and CREM (cyclic AMP response element modulator). Because ATF-1 and CREM are known to bind to cAMP response elements (CRE), this functional sequence was named the kappa E3'-CRE. We show that dibutyryl cAMP can increase kappa E3' enhancer activity, and in transient expression assays ATF-1 caused a 4-5-fold increase in the activity of the core enhancer while CREM-alpha expression resulted in repression of enhancer activity. RNA analyses showed increased levels of ATF-1 mRNA during B cell development and some changes in CREM transcript processing. By joining various fragments of the kappa E3' enhancer to the kappa E3'-CRE, we observed that the kappa E3'-CRE can synergistically increase transcription in association with the PU.1/NF-EM5 binding sites, suggesting a functional interaction between the proteins that bind to these DNA sequences. Consistent with this possibility, we found that ATF-1 and CREM can physically interact with PU.1. The isolation of activator and repressor proteins that bind to the kappa E3'-CRE may relate to previous conflicting results concerning the role of the cAMP signal transduction pathway in kappa gene transcription.

A well-differentiated B-cell line is permissive for somatic mutation of a transfected immunoglobulin heavy-chain gene

pSV2neo plasmids containing an IgM heavy-chain gene with nonsense mutations in either the variable (V) or the constant (C) region were transfected into four differentiated mouse plasma cell lines: S107 and the NSO fusion partner (myeloma cell lines) and 2C3 and 36.65 (hybridoma cell lines). The frequencies of reversion of the nonsense mutations in multiple independent transfectants were determined with the spot ELISA and rates of reversion were calculated by fluctuation analysis. Mutations in both V and C regions were confirmed by sequence analyses. In the S107 cell line, spontaneous point mutations occurred in the V region at a rate of approximately 5 x 10(-5)/bp per cell generation, > 400-fold higher than the rate of V-region mutation in the NSO cell line and considerably higher than the rates in 2C3 and 36.65 hybridoma cell lines. These studies suggest that S107 is a relatively permissive cell line in which V-region mutations can occur constitutively, even though it represents a late stage of B-cell differentiation. Further, the results show that the construct used contains sufficient information in its flanking and coding sequences to allow a relatively high rate of V-region mutation, at least in the S107 cell line.

Diphosphoryl lipid A from Rhodobacter sphaeroides transiently activates NF-kappa B but inhibits lipopolysaccharide induction of kappa light chain and Oct-2 in the B-cell lymphoma line 70Z/3

Lipopolysaccharide (LPS) is implicated in much of the pathophysiology associated with gram-negative septic shock. One approach to this serious clinical problem is to develop new drugs that antagonize the action of toxic LPS. A model system to study LPS action and test for potential antagonists is readily provided by LPS regulation of the kappa gene in the murine B-cell line 70Z/3. Rhodobacter sphaeroides diphosphoryl lipid A (RsDPLA) effectively blocked toxic LPS induction of kappa light-chain immunoglobulin expression in 70Z/3 cells. Induction of kappa expression by LPS is dependent on the activation of at least two transcription factors, Oct-2 and NF-kappa B. RsDPLA completely repressed the long-term activation of NF-kappa B observed after 24 h of Salmonella typhosa LPS treatment and antagonized activation of oct-2 mRNA expression. However, RsDPLA was not an inert competitor of LPS. RsDPLA alone strongly activated NF-kappa B binding activity by 30 min but not beyond 9 h of treatment. It also induced a small increase in oct-2 mRNA levels. RsDPLA is not simply a weak agonist; we found no graded increase in kappa expression with increasing RsDPLA concentrations up to 50 micrograms/ml. The NF-kappa B complexes activated by RsDPLA and S. typhosa LPS were both composed of the p50-p65 heterodimer. These results suggest that the physiological LPS receptor(s) on B cells transmits qualitatively different signals depending on the nature of the binding ligand and that the fatty acyl groups of LPS play an important role in activating signal transduction.

HIV type 1 protease activation of NF-kappa B within T lymphoid cells

NF-kappa B is a nuclear protein of the rel oncogene family capable of enhancing transcription of several cellular genes, including IL-2 and the IL-2 receptor, and viral genes transcribed from the HIV-1 LTR. It has been reported that HIV-1 protease may cleave the NF-kappa B precursor to its active form in vitro. In this study the effects of HIV protease on NF-kappa B precursor activation were examined in Jurkat T cells by introducing a protease expression vector into the cells. Increased NF-kappa B activity was observed and this increased activity was blocked by a specific inhibitor of the viral protease. Viral transcription, as measured using LTR-CAT assays, was only slightly enhanced in the HIV-protease expressing cells, while secretion of IL-2 and expression of the IL-2 receptor were not affected. The limited activation of NF-kappa B by HIV protease appears unlikely to have a significant effect on virus expression or T cell function.

Targeted disruption of the p50 subunit of NF-kappa B leads to multifocal defects in immune responses

NF-kappa B, a heterodimeric transcription factor composed of p50 and p65 subunits, can be activated in many cell types and is thought to regulate a wide variety of genes involved in immune function and development. Mice lacking the p50 subunit of NF-kappa B show no developmental abnormalities, but exhibit multifocal defects in immune responses involving B lymphocytes and nonspecific responses to infection. B cells do not proliferate in response to bacterial lipopolysaccharide and are defective in basal and specific antibody production. Mice lacking p50 are unable effectively to clear L. monocytogenes and are more susceptible to infection with S. pneumoniae, but are more resistant to infection with murine encephalomyocarditis virus. These data support the role of NF-kappa B as a vital transcription factor for both specific and nonspecific immune responses, but do not indicate a developmental role for the factor.