Murine pre-B Cell Line Research Articles

Transgenic human lambda 5 rescues the murine lambda 5 nullizygous phenotype.

The human lambda 5 (hu lambda 5) gene is the structural homologue of the murine lambda 5 (m lambda 5) gene and is transcriptionally active in pro-B and pre-B lymphocytes. The lambda 5 and VpreB polypeptides together with the Ig mu H chain and the signal-transducing subunits, Ig alpha and Ig beta, comprise the pre-B cell receptor. To further investigate the pro-B/pre-B-specific transcription regulation of hu lambda 5 in an in vivo model, we generated mouse lines that contain a 28-kb genomic fragment encompassing the entire hu lambda 5 gene. High levels of expression of the transgenic hu lambda 5 gene were detected in bone marrow pro-B and pre-B cells at the mRNA and protein levels, suggesting that the 28-kb transgene fragment contains all the transcriptional elements necessary for the stage-specific B progenitor expression of hu lambda 5. Flow cytometric and immunoprecipitation analyses of bone marrow cells and Abelson murine leukemia virus-transformed pre-B cell lines revealed the hu lambda 5 polypeptide on the cell surface and in association with mouse Ig mu and mouse VpreB. Finally, we found that the hu lambda 5 transgene is able to rescue the pre-B lymphocyte block when bred onto the m lambda 5-/- background. Therefore, we conclude that the hu lambda 5 polypeptide can biochemically and functionally substitute for m lambda 5 in vivo in pre-B lymphocyte differentiation and proliferation. These studies on the mouse and human pre-B cell receptor provide a model system to investigate some of the molecular requirements necessary for B cell development.

Development of a continuous IL-7-dependent murine pre-B cell line PB-1 suitable for the biological characterisation and assay of human IL-7

Human interleukin-7 (IL-7) is a cytokine that appears to be critical for early T- and B-cell development and although IL-7 is currently under investigation as a therapeutic agent in a variety of hematolymphopoietic disorders, there have been few instances of the detection or investigation of this cytokine using a biological assay. This has been due, in the main, to the lack of a widely available, stable, easy to maintain and use, IL-7 responsive cell line. We have developed a pre-B-cell line, PB-1, from murine bone marrow, that is dependent on IL-7 for growth and has been maintained continually for up to 1 year without loss of responsiveness. The cells survive freezing and reviving, having been stored for periods of up to 4 years. The IL-7 bioassay is reproducible and sensitive, able to reliably detect 50 pg/ml IL-7. The assay is completely unresponsive to any other stimulatory cytokines tested and is not affected by a wide variety of inhibitory cytokines, with the exception of high levels of interferon alpha. The assay can be made completely specific for human IL-7 by including specific neutralizing antibodies for IL-7 and has been shown to be suitable for the estimation of IL-7 in both plasma and serum samples.

Amino-terminally Modified RANTES Analogues Demonstrate Differential Effects on RANTES Receptors

Modification of the amino terminus of regulated on activated normal T-cell expressed (RANTES) has been shown to have a significant effect on biological activity and produces proteins with antagonist properties. Two amino-terminally modified RANTES proteins, Met-RANTES and aminooxypentane-RANTES (AOP-RANTES), exhibit differential inhibitory properties on both monocyte and eosinophil chemotaxis. We have investigated their binding properties as well as their ability to activate the RANTES receptors CCR1, CCR3, and CCR5 in cell lines overexpressing these receptors. We show that Met-RANTES has weak activity in eliciting a calcium response in Chinese hamster ovary cells expressing CCR1, CCR3, and CCR5, whereas AOP-RANTES has full agonist activity on CCR5 but is less effective on CCR3 and CCR1. Their ability to induce chemotaxis of the murine pre-B lymphoma cell line, L1.2, transfected with the same receptors, consolidates these results. Monocytes have detectable mRNA for CCR1, CCR2, CCR3, CCR4, and CCR5, and they respond to the ligands for these receptors in chemotaxis but not always in calcium mobilization. AOP-RANTES does not induce calcium mobilization in circulating monocytes but is able to do so as these cells acquire the macrophage phenotype, which coincides with a concomitant up-regulation of CCR5. We have also tested the ability of both modified proteins to induce chemotaxis of freshly isolated monocytes and eosinophils. Cells from most donors do not respond, but occasionally cells from a particular donor do respond, particularly to AOP-RANTES. We therefore hypothesize that the occasional activity of AOP-RANTES to induce leukocyte chemotaxis is due to donor to donor variation of receptor expression.

Regulation of actin cytoskeleton in lymphocytes: PKC-delta disrupts IL-3-induced membrane ruffles downstream of Rac1.

In the murine pre-B lymphoid cell line Baf3, the presence of IL-3 is required for the formation of membrane ruffles that intensely stain for actin and are responsible for the elongated cell phenotype. Withdrawal of IL-3 dissolves ruffled protrusions and converts the cell phenotype to round. Flow cytometric analysis of the cell shape showed that an inactive analog of Rac1 but not inactive RhoA or inactive cdc42 rounds the cells in the presence of IL-3. Constitutively activated Rac1 restores the elongated cell phenotype to IL-3-starved cells. We conclude that the activity of Rac1 is necessary and sufficient for the IL-3-induced assembly of membrane ruffles. Similar to the IL-3 withdrawal, phorbol 12-myristate 13-acetate (PMA) dissolves actin-formed membrane ruffles and rounds the cells in the presence of IL-3. Flow cytometric analysis of the cell shape demonstrated that in the presence of IL-3 the PMA-induced cell rounding cannot be abolished by constitutively active Rac1 but can be imitated by inactive Rac1. These data indicate that PMA disrupts the IL-3 pathway downstream of Rac1. Cells rounded by PMA return to the elongated phenotype concomitantly with PKC depletion. PMA-induced cell rounding can be reversed by the PKC-specific inhibitor GF109203X. Experiments with overexpression in Baf3 of individual PKC isoforms and a dominant negative PKC-delta indicate that activation of PKC-delta but not other PKC isoforms is responsible for disruption of membrane ruffles.

The α-Chemokine, Stromal Cell-derived Factor-1α, Binds to the Transmembrane G-protein-coupled CXCR-4 Receptor and Activates Multiple Signal Transduction Pathways

The alpha-chemokine stromal cell-derived factor (SDF)-1alpha binds to the seven transmembrane G-protein-coupled CXCR-4 receptor and acts to modulate cell migration and proliferation. The signaling pathways that mediate the effects of SDF-1alpha are not well characterized. We studied events following SDF-1alpha binding to CXCR-4 in a model murine pre-B cell line transfected with human CXCR-4. There was enhanced tyrosine phosphorylation and association of components of focal adhesion complexes such as the related adhesion focal tyrosine kinase, paxillin, and Crk. We also observed activation of phosphatidylinositol 3-kinase. Wortmannin, a selective inhibitor of phosphatidylinositol 3-kinase, partially inhibited the SDF-1alpha-induced migration and tyrosine phosphorylation of paxillin. SDF-1alpha treatment selectively activated p44/42 mitogen-activated protein kinase (Erk 1 and Erk 2) and its upstream kinase mitogen-activated protein kinase kinase but not p38 mitogen-activated protein kinase, c-Jun amino-terminal kinase or mitogen activated protein kinase kinase. We also observed that SDF-1alpha treatment increased NF-kappaB activity in nuclear extracts from the CXCR-4 transfectants. Taken together, these studies revealed that SDF-1alpha activates distinct signaling pathways that may mediate cell growth, migration, and transcriptional activation.

Possible stage-specific function of NF-κB 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-κB is essential to induce the expression of the Igκ 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-κB binding activity was induced at early times by LPS treatment, but its DNA binding activity disappeared after 84 h of LPS treatment. Accumulation of IκBα protein in the nucleus correlated with the disappearance of NF-κB activity at 72, 84 and 96 h, and treatment of nuclear extracts of 72–96 h LPS-treated cells with Na-deoxycholate restored NF-κB binding activity. The data indicate that NF-κB, while important to initiate the process of Igκ gene transcription in 70Z/3 pre-B cells, is no longer required for its maintenance in differentiated 70Z/3 cells.

Induction of apoptosis by valinomycin: mitochondrial permeability transition causes intracellular acidification.

In order to determine whether disruption of mitochondrial function could trigger apoptosis in murine haematopoietic cells, we used the potassium ionophore valinomycin. Valinomycin induces apoptosis in the murine pre-B cell line BAF3, which cannot be inhibited by interleukin-3 addition or Bcl-2 over-expression. Valinomycin triggers rapid loss of mitochondrial membrane potential. This precedes cytoplasmic acidification, which leads to cysteine-active-site protease activation, DNA fragmentation and cell death. Bongkrekic acid, an inhibitor of the mitochondrial permeability transition, prevents acidification and subsequent induction of apoptosis by valinomycin.

Macrophage-derived Chemokine Is a Functional Ligand for the CC Chemokine Receptor 4

Macrophage-derived chemokine (MDC) is a recently identified member of the CC chemokine family. MDC is not closely related to other chemokines, sharing most similarity with thymus- and activation-regulated chemokine (TARC), which contains 37% identical amino acids. Both chemokines are highly expressed in the thymus, with little expression seen in other tissues. In addition, the genes for MDC and TARC are encoded by human chromosome 16. To explore this relationship in greater detail, we have more precisely localized the MDC gene to chromosome 16q13, the same position reported for the TARC gene. We have also examined the interaction of MDC with CC chemokine receptor 4 (CCR4), recently shown to be a receptor for TARC. Using a fusion protein of MDC with secreted alkaline phosphatase, we observed high affinity binding of MDC-secreted alkaline phosphatase to CCR4-transfected L1.2 cells (Kd = 0.18 nM). MDC and TARC competed for binding to CCR4, while no binding competition was observed for six other chemokines (MCP-1, MCP-3, MCP-4, RANTES (regulated on activation normal T cell expressed and secreted), macrophage inflammatory protein-1 alpha, macrophage inflammatory protein-1 beta). MDC was tested for calcium mobilization in L1.2 cells tranfected with seven different CC chemokine receptors. MDC induced a calcium flux in CCR4-transfected cells, but other receptors did not respond to MDC. TARC, which also induced calcium mobilization in CCR4 transfectants, was unable to desensitize the response to MDC. In contrast, MDC fully desensitized a subsequent response to TARC. Both MDC and TARC functioned as chemoattractants for CCR4 transfectants, confirming that MDC is also a functional ligand for CCR4. Since MDC and TARC are both expressed in the thymus, one role for these chemokines may be to attract CCR4-bearing thymocytes in the process of T cell education and differentiation.

Dissociation of Chemotaxis from Agonist-induced Receptor Internalization in a Lymphocyte Cell Line Transfected with CCR2B

To investigate the role of the carboxyl-terminal region (52 amino acids) of the monocyte chemoattractant protein 1 receptor (CCR2B) in chemotaxis, we created a series of mutants and expressed them in a murine pre-B lymphocyte cell line. Truncation of the cytoplasmic carboxyl tail to 20 amino acids had little or no effect on chemotaxis or signal transduction, but further truncation resulted in marked functional defects. Upon incubation with monocyte chemoattractant protein 1, CCR2B underwent rapid and extensive internalization, and this was impaired progressively as the carboxyl tail was truncated from 52 to 8 amino acids. Mutation of all of the serine and threonine residues in the carboxyl tail to alanine also resulted in markedly impaired receptor internalization but did not affect signaling or chemotaxis. We conclude that the membrane-proximal portion of the cytoplasmic carboxyl tail of CCR2B is critically involved in chemotaxis and signal transduction, but neither phosphorylation of carboxyl serines or threonines nor internalization of the receptor is required for robust chemotaxis.

Identification of a Stat-6-responsive element in the promoter of the human interleukin-4 gene.

Interleukin (IL)-4 is an immunomodulatory cytokine produced by a number of cell types including T cells, basophils, and mast cells. This pleiotropic cytokine has a number of immunoregulatory functions; however, the molecular mechanisms controlling the transcription of this gene are not yet completely understood. Several studies have implicated a possible autoregulatory mechanism for its own expression. Here, we have identified a Stat-6-responsive element (Stat-6RE) in the promoter of the human IL-4 gene. Utilizing electrophoretic mobility shift analysis, we have demonstrated the presence of two specific IL-4-responsive DNA-protein complexes in nuclear extracts of both human Th1 and Th2 clones. Phytohemagglutinin-blasted peripheral blood T cells also generated an inducible complex in response to stimulation with IL-4 and the IL-4-like cytokine IL-13. Transient transfection of the murine pre-B cell line BA/F3 stably transfected with the full-length human IL-4 receptor alpha chain demonstrated the ability of multicopy Stat-6RE to initiate transcription from a heterologous promoter upon IL-4 or IL-13 stimulation. These results indicate a possible autocrine mechanism for the regulation of IL-4 gene transcription through the Stat-6RE as well as a possible mechanism for IL-13 regulation of the human IL-4 promoter.

The T Cell-directed CC Chemokine TARC Is a Highly Specific Biological Ligand for CC Chemokine Receptor 4

Thymus and activation-regulated chemokine (TARC) is a recently identified CC chemokine that is expressed constitutively in thymus and transiently in stimulated peripheral blood mononuclear cells. TARC functions as a selective chemoattractant for T cells that express a class of receptors binding TARC with high affinity and specificity. To identify the receptor for TARC, we produced TARC as a fusion protein with secreted alkaline phosphatase (SEAP) and used it for specific binding. By stably transfecting five orphan receptors and five known CC chemokine receptors (CCR1 to -5) into K562 cells, we found that TARC-SEAP bound selectively to cells expressing CCR4. TARC-SEAP also bound to K562 cells stably expressing CCR4 with a high affinity (Kd = 0.5 nM). Only TARC and not five other CC chemokines (MCP-1 (monocyte chemoattractant protein-1), RANTES (regulated upon activation, normal T cells expressed and secreted), MIP-1alpha (macrophage inflammatory protein-1alpha), MIP-1beta, and LARC (liver and activation-regulated chemokine)) competed with TARC-SEAP for binding to CCR4. TARC but not RANTES or MIP-1alpha induced migration and calcium mobilization in 293/EBNA-1 cells stably expressing CCR4. K562 cells stably expressing CCR4 also responded to TARC in a calcium mobilization assay. Northern blot analysis revealed that CCR4 mRNA was expressed strongly in human T cell lines and peripheral blood T cells but not in B cells, natural killer cells, monocytes, or granulocytes. Taken together, TARC is a specific functional ligand for CCR4, and CCR4 is the specific receptor for TARC selectively expressed on T cells.

Characterization of a mutant cell line that does not activate NF-kappaB in response to multiple stimuli.

Numerous genes required during the immune or inflammation response as well as the adhesion process are regulated by nuclear factor kappaB (NF-kappaB). Associated with its inhibitor, I kappaB, NF-kappaB resides as an inactive form in the cytoplasm. Upon stimulation by various agents, I kappaB is proteolyzed and NF-kappaB translocates to the nucleus, where it activates its target genes. The transduction pathways that lead to I kappaB inactivation remain poorly understood. In this study, we have characterized a cellular mutant, the 70/Z3-derived 1.3E2 murine pre-B cell line, that does not activate NF-kappaB in response to several stimuli. We demonstrate that upon stimulation by lipopolysaccharide, Taxol, phorbol myristate acetate, interleukin-1, or double-stranded RNA, I kappaB alpha is not degraded, as a result of an absence of induced phosphorylation on serines 32 and 36. Neither a mutation in I kappaB alpha nor a mutation in p50 or relA, the two major subunits of NF-kappaB in this cell line, accounts for this phosphorylation defect. As well as culminating in the inducible phosphorylation of I kappaB alpha on serines 32 and 36, all the stimuli that are inactive on 1.3E2 cells exhibit a sensitivity to the antioxidant pyrrolidine dithiocarbamate (PDTC). In contrast, stimuli such as hyperosmotic shock or phosphatase inhibitors, which use PDTC-insensitive pathways, induce I kappaB alpha degradation in 1.3E2. Analysis of the redox status of 1.3E2 does not reveal any difference from wild-type 70Z/3. We also report that the human T-cell leukemia virus type 1 (HTLV-1)-derived Tax trans-activator induces NF-kappaB activity in 1.3E2, suggesting that this viral protein does not operate via the defective pathway. Finally, we show that two other I kappaB molecules, I kappaB beta and the recently identified I kappaB epsilon, are not degraded in the 1.3E2 cell line following stimulation. Our results demonstrate that 1.3E2 is a cellular transduction mutant exhibiting a defect in a step that is required by several different stimuli to activate NF-kappaB. In addition, this analysis suggests a common step in the signaling pathways that trigger I kappaB alpha, I kappaB beta, and I kappaB epsilon degradation.

Characterization of adenosine deaminase binding to human CD26 on T cells and its biologic role in immune response.

CD26, a T cell activation Ag, also known as dipeptidyl peptidase IV, is directly associated with adenosine deaminase (ADA) on the surface of T cells and T cell lines. In the present study, we examined both the binding of ADA and CD26 and the functional consequences of this interaction. We found that ADA was associated with CD26 on T cell lines lacking either ADA or dipeptidyl peptidase IV enzymatic activity, indicating that the association between dipeptidyl peptidase IV and ADA did not require enzymatic activity. Moreover, using immunoelectron microscopy, we demonstrated that CD26 and ADA co-localized on the cell surface, but not inside cells, suggesting that CD26 did not transport ADA to the surface. In keeping with this observation, we showed that human CD26-transfected murine pre-B cell lines lacking human ADA acquired ADA from an extracellular source. More importantly, adenosine in the absence of cell surface ADA inhibited T cell proliferation and IL-2 production induced by various stimuli. On the other hand, cells expressing ADA and CD26 on the surface were much more resistant to the inhibitory effect of adenosine. These data suggest that ADA on the cell surface is involved in an important immunoregulatory mechanism by which released ADA binds to cell surface CD26, and this complex is capable of reducing the local concentration of adenosine.

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.

Deoxyspergualin inhibits kappa light chain expression in 70Z/3 pre-B cells by blocking lipopolysaccharide-induced NF-kappa B activation.

Deoxyspergualin (DSG) is a potent immunosuppressive agent that is currently undergoing clinical trials for treatment of transplant rejection, preventive of human anti-mouse Ab response, and blocking autoimmune disease progression. The mechanism of action of DSG appears to be novel, with in vivo activity attributable to the suppression of both humoral and cell-mediated immunity. In this study we investigated the effect of DSG on the induction of lg expression in the 70Z/3 murine pre-B cell line. Treatment of 70Z/3 cells with DSG for 24, 48, or 72 h before LPS or IFN-gamma induction resulted in a time-dependent inhibition of surface lgM expression, with greater than 80% inhibition observed after 72 h of pretreatment. Inhibition of surface expression was specific for lgM, as neither MHC class I nor CD45 (B220) surface expression was affected by DSG pretreatment. Cyclosporin A was ineffective at suppressing surface igM induction. DSG pretreatment results in a 10-fold reduction in LPS- or IFN-gamma-induced kappa L chain protein and mRNA expression. No change was observed in either mu or beta-actin mRNA levels. Analysis of nuclear and cytoplasmic NF-kappa B expression using electrophoretic mobility shift analysis and Western analysis, revealed that DSG blocked LPS-induced NF-kappa B nuclear translocation, but had no effect on cytoplasmic NF-kappa B levels. We conclude that DSG may act to suppress humoral immune responses by blocking the transcriptional activation of kappa L chain expression during certain stages of B cell development.

Differentiation of a Murine Pre-B Cell Line by an Adiuvant Muramyl Peptide via NF-κB Activation

Muramyl dipeptide (MDP) induces NF-κB 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-l. In the present study we investigated whether NF-κB 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 κB-binding activity in 70Z/3 cells. The LPS or IL-l induced NF-κB 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-κB 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-l or IFN γ was not obtained in this variant. The ability of various treatments to activate the κ gene enhancer was quantitatively evaluated in cells transfected with a κ-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-l. 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 κ light chain expression did not increase the basal response in the transfected 70Z/3 cells, indicating that NF-zB activation was not related to the adjuvant potency of MDP but correlated with the κ induction.

The critical region in the cytoplasmic domain of human IL-4 receptor for induction of IgE synthesis

To examine the region critical for differentiation in the human IL-4 receptor (hIL-4R), we transfected the Abelson murine leukemia virus (A-MuLV)-transformed murine pre-B cell line A20 with plasmid DNA encoding the hIL-4R. Transfectants expressed high affinity hIL-4Rs on the cell surface. Treatment with LPS and hIL-4 induced germline Cε transcripts in hIL-4R expressing A20 cells. Several hIL-4R mutant plasmids were then transfected into A20 cells and the transfectants were examined for hIL-4R expression and the ability to induce germline Cε transcripts upon stimulation with LPS and hIL-4. Although all A20 transfectants tested expressed the high-affinity hIL-4R, A20 transfectants expressing the mutant hIL-4R, which contains only 8 amino acids in the cytoplasmic domain, did not respond to LPS and hIL-4 with germline Cε transcripts. In addition, A20 transfectants expressing an internally deleted hIL-4R, in which the deleted region has been identified as the critical region for growth signal transduction in the previous study, failed to induce germline Cε transcripts with LPS and hIL-4. These results indicate that the critical region for the differentiation signal in the hIL-4R is identical to that for the growth signal, suggesting that IL-4 may share, at least partly, a common signal pathway for both growth and differentiation.

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-γ (IFNγ) by κ 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 IFNγ, 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 κ gene expression in 70Z/3 cells nor increase the MDP effect. The stimulating effect displayed by MDP could be related to NF-κB activation.

ERP, a new member of the ets transcription factor/oncoprotein family: cloning, characterization, and differential expression during B-lymphocyte development.

The ets gene family encodes a group of proteins which function as transcription factors under physiological conditions and, if aberrantly expressed, can cause cellular transformation. We have recently identified two regulatory elements in the murine immunoglobulin heavy-chain (IgH) enhancer, pi and microB, which exhibit striking similarity to binding sites for ets-related proteins. To identify ets-related transcriptional regulators expressed in pre-B lymphocytes that may interact with either the pi or the microB site, we have used a PCR approach with degenerate oligonucleotides encoding conserved sequences in all members of the ets family. We have cloned the gene for a new ets-related transcription factor, ERP (ets-related protein), from the murine pre-B cell line BASC 6C2 and from mouse lung tissue. The ERP protein contains a region of high homology with the ETS DNA-binding domain common to all members of the ets transcription factor/oncoprotein family. Three additional smaller regions show homology to the ELK-1 and SAP-1 genes, a subgroup of the ets gene family that interacts with the serum response factor. Full-length ERP expresses only negligible DNA-binding activity by itself. Removal of the carboxy terminus enables ERP to interact with a variety of ets-binding sites including the E74 site, the IgH enhancer pi site, and the lck promoter ets site, suggesting a carboxy-terminal negative regulatory domain. At least three ERP-related transcripts are expressed in a variety of tissues. However, within the B-cell lineage, ERP is highly expressed primarily at early stages of B-lymphocyte development, and expression declines drastically upon B-cell maturation, correlating with the enhancer activity of the IgH pi site. These data suggest that ERP might play a role in B-cell development and in IgH gene regulation.

ERP, a New Member of the ets Transcription Factor/Oncoprotein Family: Cloning, Characterization, and Differential Expression during B-Lymphocyte Development

The ets gene family encodes a group of proteins which function as transcription factors under physiological conditions and, if aberrantly expressed, can cause cellular transformation. We have recently identified two regulatory elements in the murine immunoglobulin heavy-chain (IgH) enhancer, pi and microB, which exhibit striking similarity to binding sites for ets-related proteins. To identify ets-related transcriptional regulators expressed in pre-B lymphocytes that may interact with either the pi or the microB site, we have used a PCR approach with degenerate oligonucleotides encoding conserved sequences in all members of the ets family. We have cloned the gene for a new ets-related transcription factor, ERP (ets-related protein), from the murine pre-B cell line BASC 6C2 and from mouse lung tissue. The ERP protein contains a region of high homology with the ETS DNA-binding domain common to all members of the ets transcription factor/oncoprotein family. Three additional smaller regions show homology to the ELK-1 and SAP-1 genes, a subgroup of the ets gene family that interacts with the serum response factor. Full-length ERP expresses only negligible DNA-binding activity by itself. Removal of the carboxy terminus enables ERP to interact with a variety of ets-binding sites including the E74 site, the IgH enhancer pi site, and the lck promoter ets site, suggesting a carboxy-terminal negative regulatory domain. At least three ERP-related transcripts are expressed in a variety of tissues. However, within the B-cell lineage, ERP is highly expressed primarily at early stages of B-lymphocyte development, and expression declines drastically upon B-cell maturation, correlating with the enhancer activity of the IgH pi site. These data suggest that ERP might play a role in B-cell development and in IgH gene regulation.