Induction of kappa transcription by interferon-gamma without activation of NF-kappa B

Revisiting the regulatory roles of the TGF-β family of cytokines

TGF-β family members are multipotent cytokines that are involved in many cellular processes, including cell differentiation, organ development, wound healing and immune regulation. TGF-β has pleiotropic effects on adaptive immunity, especially in the regulation of CD4(+) T cell and B cell responses. Furthermore, identification of CD4(+) T cell subsets that produce TGF-β3 revealed unexpected roles of TGF-β3 in the control of adaptive immunity. In contrast to TGF-β1, which induces extensive fibrosis, TGF-β3 induces non-scarring wound healing and counteracts tissue fibrosis. Recent progress in the understanding of the activation mechanism of TGF-β may enable us to develop novel biologic therapies based on advanced protein engineering.

Therapeutic potential of regulatory cytokines that target B cells

Autoreactive B cells play a crucial role in the pathogenesis of autoimmune diseases by producing auto-antibodies and presenting antigens. Regulatory cytokines that simultaneously suppress multiple pathways have the potential to control autoreactive B cells. The generally inhibitory cytokine IL-10 may have a stimulatory effect on human B-cell survival and antibody production. TGF-β family cytokines can decrease or increase antibody production and can suppress B-cell proliferation and differentiation. In contrast to TGF-β1, which induces extensive fibrosis, TGF-β3 and bone morphogenetic protein 6 (BMP-6)/BMP-7 induce non-scarring wound healing and counteract tissue fibrosis. Therefore, TGF-β3 and BMP-6/BMP-7 may be clinically applicable as therapeutic cytokines that target B cells. Recent progress in protein engineering may enable us to generate novel biologic therapies based on TGF-β family cytokines.

Role of IL-17, transforming growth factor-beta, and IL-6 in the development of arthritis and production of anti-outer surface protein A borreliacidal antibodies in Borrelia-vaccinated and -challenged mice

We showed recently that the adaptive immune events leading to the development of arthritis in Borrelia burgdorferi isolate 297-vaccinated and Borrelia bissettii-challenged mice involve IL-17. Here, we show in Borrelia-vaccinated and -challenged mice that two cytokines known to induce the production of IL-17, IL-6 and transforming growth factor (TGF)-beta, are also involved in the development of arthritis. Vaccinated and challenged mice administered either anti-TGF-beta or anti-IL-6 antibodies developed histopathologic changes of the hind paws similar to or greater than untreated control mice. By contrast, simultaneous blockage of these cytokines reduced the severity of arthritis in Borrelia-vaccinated and -challenged mice. Moreover, administration of anti-IL-17 antibodies to these dual-antibody-treated mice completely prevented the development of histopathologic changes of the ankle joints, significantly reduced edema of the hind paws, and prevented the production of anti-outer surface protein A borreliacidal antibodies. These findings demonstrate a role for the combined effects of IL-17, IL-6, and TGF-beta in the adaptive immune events leading to the development of Borrelia-induced arthritis.

Transforming growth factor-beta regulation of immune responses

Transforming growth factor-beta (TGF-beta) is a potent regulatory cytokine with diverse effects on hemopoietic cells. The pivotal function of TGF-beta in the immune system is to maintain tolerance via the regulation of lymphocyte proliferation, differentiation, and survival. In addition, TGF-beta controls the initiation and resolution of inflammatory responses through the regulation of chemotaxis, activation, and survival of lymphocytes, natural killer cells, dendritic cells, macrophages, mast cells, and granulocytes. The regulatory activity of TGF-beta is modulated by the cell differentiation state and by the presence of inflammatory cytokines and costimulatory molecules. Collectively, TGF-beta inhibits the development of immunopathology to self or nonharmful antigens without compromising immune responses to pathogens. This review highlights the findings that have advanced our understanding of TGF-beta in the immune system and in disease.

The IkappaB kinase complex and NF-kappaB act as master regulators of lipopolysaccharide-induced gene expression and control subordinate activation of AP-1

Toll-like receptors (TLRs) recognize conserved products of microbial pathogens to initiate the innate immune response. TLR4 signaling is triggered upon binding of lipopolysaccharides (LPS) from gram-negative bacteria. Using comparative gene expression profiling, we demonstrate a master regulatory role of IkappaB kinase (IKK)/NF-kappaB signaling for immediate-early gene induction after LPS engagement in precursor B cells. IKK/NF-kappaB signaling controls a large panel of gene products associated with signaling and transcriptional activation and repression. Intriguingly, the induction of AP-1 activity by LPS in precursor B cells and primary dendritic cells fully depends on the IKK/NF-kappaB pathway, which promotes expression of several AP-1 family members, including JunB, JunD, and B-ATF. In pre-B cells, AP-1 augments induction of a subset of primary NF-kappaB targets, as shown for chemokine receptor 7 (CCR7) and immunoglobulin kappa light chain. Thus, our data illustrate that NF-kappaB orchestrates immediate-early effects of LPS signaling and controls secondary AP-1 activation to mount an appropriate biological response.

Genes expressed during the IFN gamma-induced maturation of pre-B cells

Interferon-gamma (IFN gamma) exerts diverse responses in B cell development ranging from growth arrest and apoptosis to proliferation and differentiation. IFN gamma stimulates murine 70Z/3 pre-B cells to express surface immunoglobulin (Ig) and this system serves as a useful model for the pre-B to immature B cell transition in B cell development. To analyze this developmental transition, we used a PCR-based subtractive hybridization in combination with miniarray screening to identify differentially-expressed genes in IFN gamma-stimulated compared with unstimulated 70Z/3 pre-B cells. The majority (44%) of the differentially-expressed genes obtained were known IFN gamma-inducible. These included multiple isolates from each of three multi-gene families, including two guanylate-binding protein (47 and 67kDa GBP) families of GTPases and the hematopoietic IFN gamma-inducible nuclear protein family (HIN-200). These multiple isolates of genes comprised the majority of the total isolated and sequenced clones. Other known IFN gamma-induced genes in this group included Ig kappa light chain and Ly-6, as well as genes with functions in antigen processing, cellular regulation, and cytoskeletal organization. Another 36% of the genes identified were previously known, but not known to be IFN gamma-inducible (e.g. pre-B cell enhancing factor, PBEF). The remaining 20% of the IFN gamma-induced isolates did not match entries in Genbank, and thus, may represent novel genes involved in IFN gamma responses and/or in the pre-B to immature B cell transition. Overall, the majority of the individual genes isolated were either not known to be IFN gamma responsive or were not previously known.

Soluble CD14 enriched in colostrum and milk induces B cell growth and differentiation

Induction of resting B cell growth and differentiation requires a complex series of temporally coordinated signals that are initiated on contact with activated helper T cells. These signals complement one another, each rendering the B cell susceptible to factors supporting progressive activation. Here, we demonstrate that soluble CD14 (sCD14) bypasses the physiological sequelae of events that limit B cell activation. B cell growth and differentiation in vitro is induced by both native and recombinant forms of sCD14 at nanomolar concentrations. sCD14-mediated cellular activation does not require membrane CD14 expression, depends on a region of CD14 that is not involved in lipopolysaccharide binding, and requires functional Toll-like receptor 4. Consistent with biological activity of sCD14 in vitro, its administration to neonatal mice enhances Ig secretion. The results presented establish sCD14 as a naturally occurring soluble B cell mitogen of mammalian origin.

Transcriptional Regulation of the Igκ Gene by Promoter-Proximal Pausing of RNA Polymerase II

Transcriptional regulation can occur at the level of initiation and RNA elongation. We report that the rearranged, nontranscribed Igκ gene in the pre-B cell line 70Z/3 harbors a paused RNA polymerase II (pol II) at a position between 45 and 89 bp downstream of the transcription initiation site. LPS, an inducer of NF-κB, activated Igκ gene transcription by increasing the processivity of pol II. TGF-β inhibited the LPS-induced transcription of the Igκ gene, but not initiation and pausing of pol II. A rearranged copy of the Igκ gene was introduced into 70Z/3 cells using an episomal vector system. The episomal Igκ was regulated by LPS and TGF-β like the endogenous gene and established a paused pol II, whereas a construct with a deletion of the intron enhancer and the C region did not establish a paused pol II. Two distinct functions can therefore be assigned to the deleted DNA elements: loading of pol II to its pause site and induction of processive transcription upon LPS stimulation. It had been proposed that somatic hypermutation of Ig genes is connected to transcription. The pause site of pol II described in this work resides upstream of the previously defined 5′ boundary of mutator activity at Igκ genes. The possible role of pausing of pol II for somatic hypermutation is discussed.

Regulation of c-myc and immunoglobulin kappa gene transcription by promoter-proximal pausing of RNA polymerase II

In normal cells, the proto-oncogene c-myc is regulated by promoter-proximal pausing of RNA polymerase II (pol II). In Burkitt lymphoma cells, c-myc is chromosomally translocated to one of the three immunoglobulin (Ig) gene loci and its transcription is driven constitutively by Ig enhancers. Promoter-proximal pausing of pol II is abolished on the translocated c-myc allele. This raised the question whether induction of Ig gene transcription also involves activation of promoter-proximal paused pol II. Here we have studied the transcriptional activation of a functionally rearranged Ig kappa gene in the mouse pre B cell line 70Z/3. We show that pol II pauses approximately 50 bp downstream of the transcriptional start site of the uninduced Ig kappa gene.

Possible stage-specific function of NF-kappaB during pre-B cell differentiation

Lipopolysaccharide (LPS)-induced differentiation of the murine pre-B cell line 70Z/3 is a model for pre-B to B cell differentiation and has been used to show that the transcription factor NF-kappaB is essential to induce the expression of the Ig kappa gene. We have investigated the mechanism involved in late stages of the process when all cells have reached a more mature B phenotype, i.e. beyond 48 up to 96 h of LPS treatment. NF-kappaB binding activity was induced at early times by LPS treatment, but its DNA binding activity disappeared after 84 h of LPS treatment. Accumulation of IkappaB alpha protein in the nucleus correlated with the disappearance of NF-kappaB activity at 72, 84 and 96 h, and treatment of nuclear extracts of 72-96 h LPS-treated cells with Na-deoxycholate restored NF-kappaB binding activity. The data indicate that NF-kappaB, while important to initiate the process of Ig kappa gene transcription in 70Z/3 pre-B cells, is no longer required for its maintenance in differentiated 70Z/3 cells.

Induction of early B cell factor (EBF) and multiple B lineage genes by the basic helix-loop-helix transcription factor E12

The transcription factors encoded by the E2A and early B cell factor (EBF) genes are required for the proper development of B lymphocytes. However, the absence of B lineage cells in E2A- and EBF-deficient mice has made it difficult to determine the function or relationship between these proteins. We report the identification of a novel model system in which the role of E2A and EBF in the regulation of multiple B lineage traits can be studied. We found that the conversion of 70Z/3 pre-B lymphocytes to cells with a macrophage-like phenotype is associated with the loss of E2A and EBF. Moreover, we show that ectopic expression of the E2A protein E12 in this macrophage line results in the induction of many B lineage genes, including EBF, IL7Ralpha, lambda5, and Rag-1, and the ability to induce kappa light chain in response to mitogen. Activation of EBF may be one of the critical functions of E12 in regulating the B lineage phenotype since expression of EBF alone leads to the activation of a subset of E12-inducible traits. Our data demonstrate that, in the context of this macrophage line, E12 induces expression of EBF and together these transcription factors coordinately regulate numerous B lineage-associated genes.

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.

Coordinate transcription and V(D)J recombination of the kappa immunoglobulin light-chain locus: NF-kappaB-dependent and -independent pathways of activation

To further elucidate the potential role of mitogens and cytokines in regulation of the kappa immunoglobulin light-chain locus, we have characterized the activation of transcription factor binding, kappa germ line transcription, DNase I hypersensitivity, and Vkappa-to-Jkappa recombination upon induction of model pre-B-cell lines. We find that both lipopolysaccharide (LPS) and gamma interferon (IFN-gamma) are capable of activating germ line transcription, DNase I hypersensitivity, and recombination of the kappa locus. We also find that transforming growth factor beta is capable of completely inhibiting LPS activation of transcription and recombination but has no apparent effect on activation of transcription factor binding, including activation of NF-kappaB. To address the functional role of NF-kappaB in LPS and IFN-gamma induction of these events, we blocked the nuclear translocation of NF-kappaB by overexpression of a dominant negative mutant of IkappaB-alpha (IkappaB deltaN). Overexpression of the IkappaB deltaN protein results in an inhibition of LPS but not IFN-gamma activation of germ line transcription, DNase I hypersensitivity, and Vkappa-to-Jkappa recombination. Our results demonstrate that activation of NF-kappaB is necessary but not sufficient for LPS activation of transcription and recombination at kappa. These results also suggest that NF-kappaB is not required for IFN-gamma activation of transcription or recombination. These results are important in establishing that there are multiple independent pathways of activation of both transcription and recombination.

Induction of liver-associated transforming growth factor beta 1 (TGF-beta 1) mRNA expression by carbon tetrachloride leads to the inhibition of T helper 2 cell-associated lymphokines

Acute treatment of B6C3F1 mice with a hepatotoxic dose (500 mg/kg) of carbon tetrachloride (CCl4) produced a marked but transient increase in transforming growth factor beta 1 (TGF-beta 1) mRNA expression in the liver within 24 hr. We have previously shown that an identical dose of CCl4 also produces a marked increase in serum TGF-beta 1 concentrations which peak at 48 hr and produce a marked inhibition of the anti-sRBC IgM antibody forming cell (AFC) response. Similar increases in TGF-beta 1 transcripts scripts in the liver were also induced by an acute hepatotoxic dose (600 mg/kg) of acetaminophen. No increase in TGF-beta 1 mRNA expression was detected in the spleen following treatment with either agent. Direct addition of TGF-beta 1 (0.05-1.0 ng/ml) to naive splenocyte cultures produced a marked and dose-related inhibition of the anti-sRBC IgM AFC response. Under the same conditions, TGF-beta 1 induced a marked decrease in IL-4 and IL-5 mRNA expression in sRBC-sensitized splenocytes. Concomitantly, TGF-beta 1 induced a rapid increase in NF-kappa B/Rel trans-acting factor binding within the first 24 hr post-sRBC sensitization of splenocytes. Conversely, NF-kappa B/Rel binding activity was inhibited on Days 2 through 4 in sRBC-sensitized splenocytes in the presence of TGF-beta 1. The increase in NF-kappa B/Rel binding within 24 hr following sRBC sensitization is consistent with the positive influence TGF-beta 1 exerts on Th1 cytokines such as IL-2 and IFN-gamma. Conversely the decrease in NF-kappa B/Rel binding at the later time period during the AFC response (Days 2-4) coincides with the inhibitory effects TGF-beta 1 exerted on IgM production by B cells.

A promoter ISRE and dual 5' YY1 motifs control IFN-gamma induction of the IRG-47 G-protein gene

The IRG-47 gene is the prototype for a new family of genes encoding guanine nucleotide binding proteins (G-proteins) which are selectively induced in different cell lineages in response to activation signals. The IRG-47 gene is rapidly and transiently induced by interferon-gamma (IFN-gamma) in cells of the B lymphocyte lineage and in stromal cells and fibroblasts. Here we report features controlling the uninduced and IFN-gamma-induced expression of the IRG-47 gene. The minimal IFN-gamma-inducible IRG-47 gene promoter is 96 bp long and contains a TATA box and an ISRE motif with an internal IRF-1/IRF-2 motif. Mutation of the ISRE motif abolishes IFN-gamma induction by the minimal promoter. Constitutively expressed IRF-2 and IFN-gamma-induced IRF-1 factors specifically bind to the wild-type, but not the mutated ISRE motif. An upstream region containing two tandemly repeated YY1 motifs represses the expression of the IRG-47 promoter in uninduced cells and determines the magnitude of IRG-47 promoter activity in IFN-gamma-induced cells. The IRG-47 minimal promoter has the same functional features and organization as the IFN-gamma-inducible promoters of the unrelated murine GBP G-protein multigene family.

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.

The interferon-inducible protein kinase PKR modulates the transcriptional activation of immunoglobulin kappa gene

PKR is an interferon (IFN)-induced serine/threonine protein kinase that regulates protein synthesis through phosphorylation of eukaryotic translation initiation factor-2 (eIF-2). In addition to its demonstrated role in translational control, recent findings suggest that PKR plays an important role in regulation of gene transcription, as PKR phosphorylates I kappa B alpha upon double-stranded RNA treatment resulting in activation of NF-kappa B DNA binding in vitro (Kumar, A., Haque, J., Lacoste, J., Hiscott, J., and Williams, B.R.G. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 6288-6292). To further investigate the role of PKR in transcriptional signaling, we expressed the wild type human PKR and a catalytically inactive dominant negative PKR mutant in the murine pre-B lymphoma 70Z/3 cells. Here, we report that expression of wild type PKR had no effect on kappa-chain transcriptional activation induced by lipopolysaccharide or IFN-gamma. However, expression of the dominant negative PKR mutant inhibited kappa gene transcription independently of NF-kappa B activation. Phosphorylation of eIF-2 alpha was not increased by lipopolysaccharide or IFN-gamma, suggesting that PKR mediates kappa gene transcriptional activation without affecting protein synthesis. Our findings further support a transcriptional role for PKR and demonstrate that there are at least two distinct PKR-mediated signal transduction pathways to the transcriptional machinery depending on cell type and stimuli, NF-kappa B-dependent and NF-kappa B-independent.

Expression and function of the murine CD95/FasR/APO-1 receptor in relation to B cell ontogeny

Mice defective in Fas-mediated apoptosis (lpr phenotype) have an intrinsic B cell abnormality that predisposes them to autoantibody production. To investigate potential roles for the Fas receptor (FasR) in B cell tolerance, FasR expression and function were evaluated at different stages of B cell development. FasR expression was very low or absent on pro- and pre-B cells, but was detected in early B cell lines and was up-regulated following IFN-gamma-induced maturation of the pre-B cell line 70-Z. Whereas FasR expression was very low in resting mature sIgM+ B cells, expression was markedly increased following mitogen activation and was also elevated in two mature sIgG+ lymphoma lines. FasR expression correlated strongly with the ability of B cells to undergo Fas-mediated apoptosis. In addition, although Fas did not appear to play a direct role in apoptosis mediated by cross-linking of sIg with anti-IgM, anti-FasR and sublethal concentrations of anti-Ig were additive in the induction of apoptosis in the early B cell line WEHI 231. These findings suggest that the Fas pathway is not involved in the elimination of pro- and pre-B cells, but are compatible with an ancillary role for FasR in the elimination of early B cells and elimination of mature B cells following activation.

Differentiation of murine pre-B cell line by an adjuvant muramyl peptide via NF-kappa B activation

Muramyl dipeptide (MDP) induces NF-kappa B activation in the murine pre-B cell line 70Z/3, increases the expression of surface immunoglobulins, and potentiates the response to other inducers such as LPS or IL-1. In the present study we investigated whether NF-kappa B activation was related to the MDP-stimulated immunoglobulin expression. In a gel shift assay our results confirmed that MDP but not MDP(D,D), an adjuvant-inactive stereoisomer, could induce a kappa B-binding activity in 70Z/3 cells. The LPS or IL-1 induced NF-kappa B binding activity was increased in the presence of MDP but not of MDP(D,D). A mutant of the cell line called 1.3E2, defective in NF-kappa B activations by LPS, did not respond to MDP. The enhanced surface immunoglobulin expression induced in the wild type 70Z/3 cells by MDP alone or combined to LPS, IL-1 or IFN gamma was not obtained in this variant. The ability of various treatments to activate the kappa gene enhancer was quantitatively evaluated in cells transfected with a kappa-enhancer-luciferase expression plasmid. Treatment of transfected 70Z/3 cells with MDP resulted in a dose-dependent enhancement of luciferase activity, an additive effect to that induced by LPS or IL-1. Treatment of the defective variant transfected with the same construct did not result in luciferase expression after stimulation with the various agents. The transient transfection assays were used to compare the effectiveness of some MDP analogs. Two adjuvant-active compounds unable to enhance kappa light chain expression did not increase the basal response in the transfected 70Z/3 cells, indicating that NF-kappa B activation was not related to the adjuvant potency of MDP but correlated with the kappa induction.

Cytokine regulation of HIV-1 LTR transactivation in human hepatocellular carcinoma cell lines

Human hepatocellular carcinoma (HCC) cell lines, HEP-G2, J5, and SK-HEP-1, which differ in their differentiation status, were compared for their trans-activating activities after treatment with cytokines or 12-O-tetradecanoylphorbol-13-acetate (TPA). These cells were transfected with a long terminal repeat (LTR) which was derived from human immunodeficiency virus type 1 (HIV-1) and ligated to chloramphenicol acetyl transferase (CAT) gene. After treatment with interleukin-1 alpha (IL-1 alpha), interleukin-6 (IL-6), interferon-gamma (IFN-gamma), or TPA, they exhibited various degrees of enhancement of transactivation. The well differentiated HEP-G2 cells exhibited the highest degree of enhancement with these agents, while the poorly differentiated SK-HEP-1 cells showed no enhancement with cytokines and slight enhancement with TPA. The J5 cells, which were intermediate in their status of differentiation, showed a moderate degree of enhancement with cytokines and TPA. These results suggest that HCC cells at different stages of differentiation may produce different levels of cellular transacting factors activated by each of these agents. To map the cytokine response elements (CREs) in the HIV-1-LTR, HEP-G2 cells were transfected with nested series of 5' deletion mutants of HIV-1-LTR and treated with each of these cytokines. It was found that not only the degrees but also the patterns of enhancement varied depending upon the presence of positive or negative regulatory sequences in HIV-1-LTR, and that the NF-kappa B sequence played an important role, either by itself or in conjunction with the 5'-proximal response elements (REs) to interact with cellular trans-activating factors elicited by the cascade of transduction responses to cytokines. Despite the presence of promoters including kappa B and IFN-gamma RE as well as IL-6RE sequence in HIV-1-LTR-transfected cells, the poorly differentiated SK-HEP-1 cells showed no enhancement of transactivation by these cytokines, suggesting the lack of receptors or activity of some signal transduction factors which are present in well differentiated HEP-G2 and moderately differentiated J5 cells.

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.

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.

Differential regulation of surface immunoglobulin expression by various muramyl dipeptides in a murine pre-B cell line

The murine pre-B cell line 70Z/3 responds to lipopolysaccharide (LPS), interleukin-1 (IL-1) or interferon-gamma (IGN gamma) by kappa gene transcription and expression of surface IgM (sIg). We found that muramyl dipeptide (MDP), a synthetic immunoadjuvant analog of a bacterial membrane structure, produced a weak increase in the number of sIg-positive 70Z/3 cells as measured by immunofluorescence staining. This number was significantly increased after exposure to MDP. Moreover, when MDP was used in combination with LPS, IL-1 or IFN gamma, an enhancement of sIg expression was observed showing an early influence of MDP in the presence of a second stimulant. Unexpectedly, two adjuvant-active analogs of MDP did not share its capacity to stimulate differentiation of the cell line when used alone or associated with other agents, indicating that adjuvanticity of MDP was not the only requirement. Two other products of bacterial origin, a Staphylococcus aureus cell extract (SAC) and the Toxic Shock Syndrome Toxin TSST-1 could neither enhance the kappa gene expression in 70Z/3 cells nor increase the MDP effect. The stimulating effect displayed by MDP could by related to NF-kappa B activation.

Two different IFN-gamma nonresponsive variants derived from the B-cell lymphoma 70Z/3

The kappa immunoglobulin (Igk) light chain locus is transcriptionally silent in the mouse B-cell lymphoma 70Z/3. However, exposure to lipopolysaccharide (LPS) or interferon-gamma (IFN) causes a marked increase in Igk transcription. By immunoselection, we isolated two variants that are nonresponsive to IFN. One variant, AT7.2, has retained its response to LPS (IFN-LPS+), whereas the other, AT3.3, is also nonresponsive to LPS (IFN-LPS-). Stable transfection of an intact Igk gene does not rescue the phenotype of either variant. Both variants have intact Igk genes and neither is deficient in the binding or uptake of IFN. Nuclear extracts from LPS-treated wild-type 70Z/3 cells show strong increases in three transcription factors: OTF-2, NF-kappa B, and kBF-A. Remarkably, when the IFN-LPS- variant is treated with LPS, all three transcription factors are still observed in the nuclear extracts. Treatment of wild-type cells with either LPS or IFN also causes a decrease in nuclear complexes that bind to two other regions of the Igk intron enhancer, the octenh and the E kappa MHCIC regions. Both of these changes are also observed after LPS or IFN treatment of the IFN-LPS- variant. Thus, this variant transduces the IFN and LPS signals at least into the nuclear compartment, but still fails to activate Igk transcription. In contrast, the IFN-LPS+ variant decreases neither the octenh nor the E kappa MHCIC binding complexes in response to IFN. This variant may be defective in transducing the IFN signal to the nucleus. These variants will be useful in studying the activation of Igk transcription and the IFN signaling pathway in B cells.

C/EBP, NF-kappa B, and c-Ets family members and transcriptional regulation of the cell-specific and inducible macrophage inflammatory protein 1 alpha immediate-early gene

Macrophage inflammatory protein 1 alpha (MIP-1 alpha) cytokine gene expression is restricted to a limited number of cells of hemopoietic origin and is rapidly and transiently induced by serum and endotoxin in macrophages. A single nuclear DNase I-hypersensitive site, which maps to the proximal promoter of the MIP-1 alpha gene, was identified in macrophage cells but was absent in cells which do not express basal levels of MIP-1 alpha mRNA. The proximal promoter sequences (+36 to -220 bp) are sufficient to confer cell-specific and inducible transcription in transfection assays. In vitro DNA-binding studies revealed five major nuclear protein binding sites in the proximal promoter which bind C/EBP, NF-kappa B, and/or c-Ets family members. Cell-specific differences in DNA binding by members of the NF-kappa B and c-Ets families correlate with the cell-specificity of MIP-1 alpha gene expression and the chromosomal conformation of the promoter. Changes in promoter binding by members of the C/EBP and NF-kappa B families correlate with the transcriptional up-regulation observed in serum- or endotoxin-stimulated macrophages in functional studies.

C/EBP, NF-kappa B, and c-Ets family members and transcriptional regulation of the cell-specific and inducible macrophage inflammatory protein 1 alpha immediate-early gene

Macrophage inflammatory protein 1 alpha (MIP-1 alpha) cytokine gene expression is restricted to a limited number of cells of hemopoietic origin and is rapidly and transiently induced by serum and endotoxin in macrophages. A single nuclear DNase I-hypersensitive site, which maps to the proximal promoter of the MIP-1 alpha gene, was identified in macrophage cells but was absent in cells which do not express basal levels of MIP-1 alpha mRNA. The proximal promoter sequences (+36 to -220 bp) are sufficient to confer cell-specific and inducible transcription in transfection assays. In vitro DNA-binding studies revealed five major nuclear protein binding sites in the proximal promoter which bind C/EBP, NF-kappa B, and/or c-Ets family members. Cell-specific differences in DNA binding by members of the NF-kappa B and c-Ets families correlate with the cell-specificity of MIP-1 alpha gene expression and the chromosomal conformation of the promoter. Changes in promoter binding by members of the C/EBP and NF-kappa B families correlate with the transcriptional up-regulation observed in serum- or endotoxin-stimulated macrophages in functional studies.

Comparison of IL-1 alpha effectiveness in activating murine pre-B and T cell lines

Interleukin-1 (IL-1) is a potent agent that induces a wide range of biological effects. The action of IL-1 is mediated by surface IL-1 receptors (IL-1R). Two types of IL-1 receptors have been identified in lymphocytes. In this study we examined activity of IL-1 alpha in two murine lymphocyte lines that express different types of IL-1 receptors. The T lymphoid cell line EL-4 6.1 C10 expresses type I IL-1R that mediates IL-1 alpha-induced IL-2 gene expression and secretion of IL-2. The pre-B lymphoid cell line 70Z/3 was previously shown to express type II IL-1R and responds to IL-1 alpha by expressing immunoglobulin kappa light chain mRNA and increased levels of surface IgM. We found that IL-1 alpha was as potent in inducing IgM expression in 70Z/3 cells as it was in inducing IL-2 secretion in EL-4 6.1 C10 cells. Likewise, the IL-1 alpha concentration sufficient to trigger kappa light chain gene expression in 70Z/3 cells was similar to the concentration of IL-1 alpha sufficient to trigger IL-2 gene expression in EL-4 6.1 C10. In both cell lines, IL-1 alpha activated NF-kappa B-like DNA-binding activity but in EL-4 6.1 C10 cells the IL-1 alpha concentration sufficient to induce NF-kappa B response was 1000-fold lower than in 70Z/3 cells. Monoclonal antibody, mAb M15, to the type I IL-1R blocked IL-1-induced responses in EL-4 6.1 C10 cells. Surprisingly mAb M15 also blocked IL-1 action in 70Z/3 cells, even though these cells predominantly express type II IL-1R. 15% of the total IL-1 binding sites in 70Z/3 cells were recognized by mAb M15. Human IL-1 receptor antagonist (IL-1ra), which binds to the natural murine type I but not the type II IL-1R, blocked IL-1 alpha responses in EL-4 6.1 C10 and 70Z/3 cells. Although at low levels, Northern blot analysis confirmed that 70Z/3 cells express low levels of type I IL-1R mRNA. Taken together, these results suggest that type I IL-1R are expressed and transduce IL-1 signals in both 70Z/3 and El-4 6.1 C10 cells.

Interferon-gamma arrests proliferation and causes apoptosis in stromal cell/interleukin-7-dependent normal murine pre-B cell lines and clones in vitro, but does not induce differentiation to surface immunoglobulin-positive B cells

Normal pre-B cells from fetal liver or bone marrow of the mouse proliferate for long periods of time in tissue culture on stromal cells in the presence of interleukin-7 (IL-7). Their IgH loci are partly in germ-line, partly in DHJH-rearranged configuration, while their light chain loci are in germ-line configuration. They express the pre-B cell-specific genes VpreB and lambda 5. Proliferation of these pre-B cells is inhibited by interferon (IFN)-gamma, with half-maximal inhibition at concentrations between 0.1 and 1 unit/ml. Normal pre-B cells exposed to IFN-gamma die by apoptosis, as is evidenced by the disintegration of pre-B cell DNA into oligonucleosomal multimers of 180-200 bp. While the proliferation of pre-B cells from E mu-bcl-2 transgenic (tg) mice is inhibited by IFN-gamma, these cells do not die by apoptosis. IFN-gamma does not induce differentiation to more mature B lineage cells. In the absence of IL-7 normal pre-B cells differentiate to VHDHJH/VLJL-rearranged, surface immunoglobulin-positive B cells expressing the alpha chain of the IL-2 receptor. They also down-regulate the expression of VpreB and lambda 5, and lose the capacity to proliferate on stromal cells in the presence of IL-7. In contrast, both normal and E mu-bcl-2 tg pre-B cells exposed to IFN-gamma in the presence of stromal cells and IL-7 fail to differentiate, i.e. do not express surface immunoglobulin, retain expression of VpreB and lambda 5, do not express the alpha chain of the IL-2 receptor, and retain the capacity to proliferate on stromal cells in the presence of IL-7, once IFN-gamma is removed. The potential usefulness of a treatment of acute lymphocytic leukemia of the B cell lineage (pre B-ALL) with IFN-gamma is discussed.

Expression of diphtheria toxin A-chain in mature B-cells: a potential approach to therapy of B-lymphoid malignancy

Specifically targeted expression of a toxin gene potentially represents a novel approach to cancer therapy. With a view to the ablation of B-cell malignancies, we have constructed a plasmid, designated pTHA71, which expresses the A-chain of diphtheria toxin (DT-A) with high efficiency and specificity in transfected, mature B-lymphoid cells. The construction incorporated immunoglobulin (Ig) kappa light chain gene regulatory sequences, including a kappa promoter, small intron, partial constant region exon, and 3'-flanking sequence (but lacking a known enhancer). These sequences conferred substantially more efficient expression of DT-A in mature B-cells than was seen from constructs that included only Ig promoters and enhancers. When transfected into the 70Z/3 murine pre-B-cell line, pTHA71 was only expressed efficiently if the cells were induced to express their endogenous, rearranged Ig kappa gene by prior exposure to lipopolysaccharide. The insertion of the enhancer from the Ig kappa large intron into pTHA71, generating pTHA81, did not markedly influence the level of DT-A expression in 70Z/3 cells. The observed absence of expression in pre-B-cells suggests that DT-A constructs similar to pTHA71 might be used for the therapeutic ablation of malignant B-cells of mature stages, while sparing normal progenitor cells.

Transfection of CD14 into 70Z/3 cells dramatically enhances the sensitivity to complexes of lipopolysaccharide (LPS) and LPS binding protein

Bacterial endotoxin (lipopolysaccharide [LPS]) causes fatal shock in humans and experimental animals. The shock is mediated by cytokines released by direct LPS stimulation of cells of monocytic origin (monocyte/macrophage [MO]). Recent studies have supported the concept that the plasma protein, LPS binding protein (LBP), plays an important role in controlling MO responses to LPS. Specifically, evidence has been presented to suggest that CD14, a membrane protein present in MO, serves as a receptor for complexes of LPS and the plasma protein LPS binding protein (LBP). In this function CD14 mediates attachment of LPS-bearing particles opsonized with LBP and appears to play an important role in regulating cytokine production induced by complexes of LPS and LBP. The CD14-, murine pre-B cell line 70Z/3 responds to LPS by synthesis of kappa light chains and consequent expression of surface IgM. To better understand the role of CD14 in controlling cellular responses to LPS, we investigated the effect of transfection of CD14 into 70Z/3 cells on LPS responsiveness. We report here that transfection of human or rabbit CD14 cDNA into 70Z/3 cells results in membrane expression of a glycosyl-phosphatidylinositol-anchored CD14. When LPS is complexed with LBP, CD14-bearing 70Z/3 cells bind more LPS than do the parental or 70Z/3 cells transfected with vector only. Remarkably, the expression of CD14 lowers the amount of LPS required to stimulate surface IgM expression by up to 10,000-fold when LPS dose-response curves in the CD14-, parental and CD14-bearing, transfected 70Z/3 cells are compared. In contrast, the response of CD14-bearing 70Z/3 cells and the parental 70Z/3 cell line (CD14-) to interferon gamma is indistinguishable. LPS stimulation of the parental and CD14-bearing 70Z/3 cells results in activation of NF-kB. These data provide evidence to support the concept that the LPS receptor in cells that constitutively express CD14 may be a multiprotein complex containing CD14 and membrane protein(s) common to a diverse group of LPS-responsive cells.

Lipopolysaccharide-induced NF-kappa B activation in mouse 70Z/3 pre-B lymphocytes is inhibited by mevinolin and 5'-methylthioadenosine: roles of protein isoprenylation and carboxyl methylation reactions

We show that both the lipopolysaccharide (LPS)-induced activation of NF-kappa DNA binding and kappa gene expression are blocked by treating murine pre-B lymphocyte 70Z/3 cells with 5'-methylthioadenosine (MTA), an inhibitor of several S-adenosylmethionine-dependent methylation reactions. We further show that the LPS-induced incorporation of radioactivity from [methyl-3H]methionine into methyl ester-like linkages on a group of membrane polypeptides is also inhibited by MTA treatment, suggesting the involvement of protein methylation reactions in the LPS signal transduction pathway. We also find that NF-kappa B and kappa gene activation in LPS-treated 70Z/3 cells is blocked by mevinolin, an inhibitor that prevents protein isoprenylation. Interestingly, mevinolin-treated cells also exhibited a marked reduction in the methylation of membrane proteins. Neither MTA nor mevinolin significantly inhibited NF-kappa B activation by phorbol myristate acetate, suggesting that these agents act early in signal transduction. These results provide the first evidence that carboxyl methylated and/or isoprenylated proteins play an essential role in the LPS-signaling pathway.

Lipopolysaccharide-induced NF-kappa B activation in mouse 70Z/3 pre-B lymphocytes is inhibited by mevinolin and 5'-methylthioadenosine: roles of protein isoprenylation and carboxyl methylation reactions

We show that both the lipopolysaccharide (LPS)-induced activation of NF-kappa DNA binding and kappa gene expression are blocked by treating murine pre-B lymphocyte 70Z/3 cells with 5'-methylthioadenosine (MTA), an inhibitor of several S-adenosylmethionine-dependent methylation reactions. We further show that the LPS-induced incorporation of radioactivity from [methyl-3H]methionine into methyl ester-like linkages on a group of membrane polypeptides is also inhibited by MTA treatment, suggesting the involvement of protein methylation reactions in the LPS signal transduction pathway. We also find that NF-kappa B and kappa gene activation in LPS-treated 70Z/3 cells is blocked by mevinolin, an inhibitor that prevents protein isoprenylation. Interestingly, mevinolin-treated cells also exhibited a marked reduction in the methylation of membrane proteins. Neither MTA nor mevinolin significantly inhibited NF-kappa B activation by phorbol myristate acetate, suggesting that these agents act early in signal transduction. These results provide the first evidence that carboxyl methylated and/or isoprenylated proteins play an essential role in the LPS-signaling pathway.

Cross-linking of surface IgM activates NF-kappa B in B lymphocyte

In B lymphocytes, cross-linking of surface IgM activates changes in both the cell cycle and differentiation. In normal B cells and B cell tumors, many stimuli induce the activation of NF-kappa B and its translocation from the cytoplasm to the nucleus. In this study we sought to determine if cross-linking of surface IgM led to the activation of NF-kappa B. Our results show that activation of B cells by cross-linking anti-IgM antibodies activated NF-kappa B in the murine B lymphoid cell lines 70Z/3 and M12, and in the dense fraction of splenic cells. The activation of NF-kappa B required optimal doses of anti-IgM antibodies and took 5 to 10 min to reach maximal levels. Cross-linking of IgM has also been shown to activate protein kinases including protein kinase C (PKC). To test whether PKC activation was required for NF-kappa B translocation, we treated 70Z/3 cells for 18 h with phorbol 12-myristate 13-acetate, a procedure which depletes these cells of functional PKC. This treatment did not abrogate the nuclear translocation of NF-kappa B following anti-IgM cross-linking. These results indicate that the nuclear translocation of NF-kappa B is rapidly induced by surface IgM cross-linking and that this activation appears to use a pathway which does not require PKC.

The plasmacytoma J558L lacks constitutively active NF-kappa B and is deficient in early response gene activation

In mature B cells the nuclear factor NF-kappa B which binds within the kappa enhancer is constitutively present in the nucleus. However, the lambda light chain producing myeloma J558L has been found to lack constitutively functional NF-kappa B. Deoxycholate released functional NF-kappa B from cytoplasmic extracts and functional NF-kappa B was present in J558L following cycloheximide but not phorbol ester treatment. J558L was also unable to respond to phorbol ester stimulation with synthesis of mRNA from the early response gene TIS11. J558L differs from S107, another myeloma which was found to be deficient in the synthesis of NF-kappa B but not in the activation of TIS11. Somatic cell hybrids were used to further define the defect in J558L; hybrids were made with the myelomas S107 and S194 and the pre-B cell line 70Z/3. In general, complementation of the defect in J558L was observed; however there was not a direct correlation between the levels of TIS11 mRNA and NF-kappa B expression in the somatic cell hybrids, suggesting that the pathways of activation of these genes, while possibly sharing common elements, are not identical. The defect in J558L was surprising given that it has frequently been used for the expression of transfected light chain genes.

Regulation and a possible stage-specific function of Oct-2 during pre-B-cell differentiation

The Oct-2 gene appears to encode a developmental regulator of immunoglobulin gene transcription. We demonstrate that the Oct-2 gene is expressed at low levels in a variety of transformed pre-B-cell lines and is induced specifically in these cells by lipopolysaccharide signalling. This work extends an earlier observation in the pre-B-cell line 70Z/3 and therefore suggests that the inducible expression of the Oct-2 gene, like that of the kappa gene, is a characteristic feature of the pre-B stage of B-cell development. In 70Z/3 cells, the lymphokine interleukin-1 also induces the expression of the Oct-2 and kappa loci. Interestingly, expression of the Oct-2 gene is rapidly induced at the transcriptional level and may not require de novo protein synthesis. Since the changes in the activity of the Oct-2 locus completely correlate with the changes of the activity of the kappa locus, the two genes may be transcriptionally regulated by a common trans-acting factor. In 70Z/3 cells, transforming growth factor beta, an inhibitor of kappa-gene induction, blocks the upregulation of Oct-2 but not the activation of NF-kappa B. These results suggest that the combinatorial action of increased levels of Oct-2 and activated NF-kappa B may be necessary for the proper stage-specific expression of the kappa locus.

Novel protein-DNA interactions associated with increased immunoglobulin transcription in response to antigen plus interleukin-5

Although much has been learned about basal levels of immunoglobulin (Ig) transcription, the regulatory effects of cytokines and antigen (Ag) upon Ig expression in lymphocytes have not been fully characterized. We previously reported that Ag plus interleukin-5 (IL-5) caused increased steady-state Ig mRNA levels in Ag-specific cell lines. In this study, we have identified a region between -250 and -125 bp 5' of the Ig transcription start site that is necessary for the induction of increased mu mRNA levels by Ag plus IL-5. Mobility shift and UV cross-linking studies indicated that IL-5 plus Ag induced increased protein binding to this region. Furthermore, this sequence was found to be closely related to another A + T-rich sequence at -525 bp 5' of the transcription start site. Both sequences exhibited similar B-cell-specific and inducible protein binding. Our data suggest that treatment with IL-5 plus Ag induces several DNA-binding proteins, some of which may participate in increasing Ig transcription above basal levels by binding to sequences 5' of the octamer motif.

Novel protein-DNA interactions associated with increased immunoglobulin transcription in response to antigen plus interleukin-5

Although much has been learned about basal levels of immunoglobulin (Ig) transcription, the regulatory effects of cytokines and antigen (Ag) upon Ig expression in lymphocytes have not been fully characterized. We previously reported that Ag plus interleukin-5 (IL-5) caused increased steady-state Ig mRNA levels in Ag-specific cell lines. In this study, we have identified a region between -250 and -125 bp 5' of the Ig transcription start site that is necessary for the induction of increased mu mRNA levels by Ag plus IL-5. Mobility shift and UV cross-linking studies indicated that IL-5 plus Ag induced increased protein binding to this region. Furthermore, this sequence was found to be closely related to another A + T-rich sequence at -525 bp 5' of the transcription start site. Both sequences exhibited similar B-cell-specific and inducible protein binding. Our data suggest that treatment with IL-5 plus Ag induces several DNA-binding proteins, some of which may participate in increasing Ig transcription above basal levels by binding to sequences 5' of the octamer motif.

Regulation and a possible stage-specific function of Oct-2 during pre-B-cell differentiation

The Oct-2 gene appears to encode a developmental regulator of immunoglobulin gene transcription. We demonstrate that the Oct-2 gene is expressed at low levels in a variety of transformed pre-B-cell lines and is induced specifically in these cells by lipopolysaccharide signalling. This work extends an earlier observation in the pre-B-cell line 70Z/3 and therefore suggests that the inducible expression of the Oct-2 gene, like that of the kappa gene, is a characteristic feature of the pre-B stage of B-cell development. In 70Z/3 cells, the lymphokine interleukin-1 also induces the expression of the Oct-2 and kappa loci. Interestingly, expression of the Oct-2 gene is rapidly induced at the transcriptional level and may not require de novo protein synthesis. Since the changes in the activity of the Oct-2 locus completely correlate with the changes of the activity of the kappa locus, the two genes may be transcriptionally regulated by a common trans-acting factor. In 70Z/3 cells, transforming growth factor beta, an inhibitor of kappa-gene induction, blocks the upregulation of Oct-2 but not the activation of NF-kappa B. These results suggest that the combinatorial action of increased levels of Oct-2 and activated NF-kappa B may be necessary for the proper stage-specific expression of the kappa locus.

Evidence that interleukin-1 and phorbol esters activate NF-kappa B by different pathways: role of protein kinase C

Nuclear factor kappa B (NF-kappa B) is a ubiquitous transcription factor that affects expression of many genes, including immunoglobulin kappa (kappa), the interleukin-2 receptor alpha chain, and two genes in HIV-1. NF-kappa B can be activated by a number of stimuli, including pharmacological stimulation of protein kinase C by phorbol 12-myristate 13-acetate (PMA) and treatment in vitro with either protein kinase C or protein kinase A. This has lead to the proposal that these kinases are key enzymes in the physiological activation of NF-kappa B as well. We have used a murine B cell line, 70Z/3, and T cell line, EL-4 6.1 C10, to study the activation of NF-kappa B by two physiological activators, interleukin-1 alpha (IL-1) and lipopolysaccharide (LPS). There are four reasons to propose that these agents activate pathways that do not include protein kinase C as a major component in these cell lines. First, the protein kinase C inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) strongly inhibited PMA-induced activation of NF-kappa B in 70Z/3 cells but had no effect on NF-kappa B activated by IL-1 or LPS. Second, depletion of protein kinase C by prolonged growth of 70Z/3 in PMA abrogated the capacity of the cells to activate NF-kappa B in response to further PMA treatment. However, these same cells activated NF-kappa B normally after either IL-1 or LPS treatment. Third, IL-1 effectively activated NF-kappa B in EL-4 6.1 C10 cells, but PMA did not. Fourth, interferon-gamma is a potent activator of protein kinase C in 70Z/3 cells, but is completely inactive in the mobilization of NF-kappa B. These results suggest that the physiological inducers IL-1 and LPS activate NF-kappa B by pathways independent of protein kinase C in both 70Z/3 and EL-4 6.1 C10 cells.

Functional characterization of the developmentally controlled immunoglobulin kappa 3' enhancer: regulation by Id, a repressor of helix-loop-helix transcription factors

We have functionally characterized an enhancer element (kappa E3') which lies 8.5 kb downstream of the immunoglobulin kappa gene. The activity of this enhancer is developmentally controlled. It is inactive at the pre-B-cell stage but active at the B-cell and plasma cell stages. This enhancer is also functional in S107 plasmacytoma cells, which lack NF-kappa B and therefore intron enhancer activity. The activity of the kappa E3' enhancer therefore provides an explanation for the transcriptional activity of endogenous kappa genes in S107 cells in the absence of intron enhancer function. We have identified a 132-bp segment of the kappa E3' enhancer that retains 75% of the activity of the entire enhancer observed in plasmacytoma cells. Within this 132-bp core, there are at least two functional elements, one of which binds to a B-cell-specific nuclear factor. This element contains a potential binding site for the B-cell- and macrophage-specific transcription factor PU.1. The kappa intron and kappa E3' enhancers were also found to be regulatable by Id, an inhibitor of helix-loop-helix transcription factors. The site of action of Id on the kappa E3' enhancer was mapped to a 25-bp region which contains a potential binding site for a helix-loop-helix transcription factor. A possible model for the developmental control of kappa gene transcription is discussed.

Functional characterization of the developmentally controlled immunoglobulin kappa 3' enhancer: regulation by Id, a repressor of helix-loop-helix transcription factors

We have functionally characterized an enhancer element (kappa E3') which lies 8.5 kb downstream of the immunoglobulin kappa gene. The activity of this enhancer is developmentally controlled. It is inactive at the pre-B-cell stage but active at the B-cell and plasma cell stages. This enhancer is also functional in S107 plasmacytoma cells, which lack NF-kappa B and therefore intron enhancer activity. The activity of the kappa E3' enhancer therefore provides an explanation for the transcriptional activity of endogenous kappa genes in S107 cells in the absence of intron enhancer function. We have identified a 132-bp segment of the kappa E3' enhancer that retains 75% of the activity of the entire enhancer observed in plasmacytoma cells. Within this 132-bp core, there are at least two functional elements, one of which binds to a B-cell-specific nuclear factor. This element contains a potential binding site for the B-cell- and macrophage-specific transcription factor PU.1. The kappa intron and kappa E3' enhancers were also found to be regulatable by Id, an inhibitor of helix-loop-helix transcription factors. The site of action of Id on the kappa E3' enhancer was mapped to a 25-bp region which contains a potential binding site for a helix-loop-helix transcription factor. A possible model for the developmental control of kappa gene transcription is discussed.

Modulation of IFN-mediated Ly-6E antigen induction by cAMP in a T cell lymphoma: opposite effects on the responses to IFN-gamma and IFN-alpha/beta

This study was initiated to examine the role of cyclic nucleotides in the regulation of the expression of the Ly-6E cell surface Ag by IFN. As a model system, we used the YAC T cell lymphoma where this Ag is constitutively absent but is highly inducible by both IFN-gamma and IFN-alpha/beta. Treatment with cAMP or cGMP analogs did not cause Ly-6E expression in the absence of IFN. However, treatment with cAMP analogs, but not with cGMP analogs, markedly altered Ly-6E expression triggered by IFN, both at the mRNA and at the cell surface protein levels. Interestingly, these effects depended on whether Ly-6E induction was mediated by IFN-gamma or IFN-alpha/beta. Thus, the response to IFN-gamma was enhanced up to tenfold, whereas the response to IFN-alpha/beta was suppressed by 90-95%. Similar differential modulations of Ly-6E induction were also exerted by forskolin and cholera toxin, which are known to elevate intracellular cAMP concentration through distinct mechanisms. A YAC cell variant (C10) was isolated, where cAMP analogs or cAMP inducers could not modify Ly-6E induction. Although resistant to the biological effect of cAMP, the C10 mutant exhibited normal IFN-mediated Ly-6E responses. Moreover, in this mutant, Ly-6E induction was still affected by the PKC activator PMA, as in wild-type YAC cells. Altogether, our data demonstrate that cAMP (and cGMP) is not directly involved as second messenger in Ly-6E induction mediated by IFNs. However, a rise of cAMP modulates in an opposite fashion the Ly-6E-inducing actions of IFN-gamma and IFN-alpha/beta, which suggests that the two types of IFN utilize separate biochemical pathways to regulate Ly-6E expression.

In situ detection of stage-specific genes and enhancers in B cell differentiation via gene-search retroviruses

We demonstrate that infection of an LPS-responsive pre-B cell line with transcriptionally-defective retroviruses containing a reporter gene (lacZ) can result in viral integrations where expression of lacZ is differentiation stage-dependent. Because expression of lacZ is dependent upon flanking cellular sequences these retroviral integrations represent in situ gene fusions with cellular enhancers (Enhsr1) and genes (Gensr1) which are either induced or repressed during LPS-stimulated differentiation. One of the well-documented effects of LPS upon pre-B cells is the induction of kappa light chain transcription via NF-kappa B. The identification of LPS-stimulated gene repression during B cell differentiation indicates that LPS has multiple effects upon gene expression during the pre-B to B cell transition. The identification of cellular enhancers and genes which are downregulated during the transition from the pre-B to the B cell stage indicates that other transcription factors, in addition to NF-kappa B, are required for this step in differentiation. Finally, we present some initial experiments which indicate the gene-search retroviruses can introduce expression of lacZ into normal hematopoietic cells in vitro and in vivo.

Diphosphoryl lipid A derived from lipopolysaccharide (LPS) of Rhodopseudomonas sphaeroides inhibits activation of 70Z/3 cells by LPS

Diphosphoryl lipid A derived from nontoxic lipopolysaccharide (LPS) of Rhodopseudomonas sphaeroides ATCC 17023 did not stimulate the murine pre-B cell line 70Z/3 to synthesize surface immunoglobulin or kappa mRNA. However, it effectively blocked Escherichia coli LPS-induced activation of 70Z/3 cells in a concentration-dependent manner. This inhibition was specific only to cells activated by LPS, since it did not inhibit activation of 70Z/3 cells by gamma interferon. Maximal inhibitory effect occurred when the antagonist was added within 2 h before adding the LPS. These results strongly suggested that R. sphaeroides diphosphoryl lipid A is competing with E. coli LPS for physiological lipid A receptors on the 70Z/3 cells.

Up-regulation and down-regulation of cell surface and mRNA expression of CD5 antigen by various humoral factors on murine 70Z/3 pre-B cell leukemia cell line: IL-4 down-regulates CD5 antigen expression

CD5, a pan-T cell antigen, is expressed on a minor subset of normal B lymphocytes and on cells of most B lineage tumors or transformed B cells in both man and animal models. In the present study, the effects of various humoral factors on CD5 expression by cells of a subcloned 70Z/3 murine pre-B leukemia cell line were investigated. Among the humoral factors studied, only LPS up-regulated CD5 expression on 70Z/3 cells (three- to fourfold) in a dose-dependent manner. However, this up-regulatory effect of LPS was not observed when cells were cultured in serum-free medium. NZB-serum factor (NZB-SF), a cytokine we have identified and shown to enhance the maturation and proliferation of immature B cells, synergistically enhanced CD5 expression in the presence of suboptimal doses of LPS. IL-4 down-regulated CD5 expression by 70Z/3 cells induced by LPS or LPS plus NZB-SF in a dose-dependent manner. IL-4 also suppressed spontaneous CD5 expression by 70Z/3 cells. No other cytokine tested showed an inhibitory effect. LPS, IFN-gamma, NZB-SF, and IL-1 enhanced sIg expression on 70Z/3 cells and their action on sIg expression was not inhibited by IL-4. Thus, the down-regulatory action of IL-4 on CD5 expression appeared specific for this antigen. IFN-gamma, which inhibits IL-4 induced CD23 and DR expression on B cells, does not abolish the down-regulatory action of IL-4 on CD5 expression by 70Z/3 cells. Changes in mRNA levels on coding CD5 were also examined following the incubation of 70Z/3 cells (24 hr) in the presence of humoral factors which can influence CD5 Ag expression. The levels of mRNA for CD5 Ag were moderately increased in the presence of LPS and NZB-SF. IL-4 appeared to suppress the actions of NZB-SF and LPS at least in part by reducing the levels of mRNA encoding CD5.