Identification of a second inducible DNA-protein interaction in the kappa immunoglobulin enhancer

LMP1-augmented kappa intron enhancer activity contributes to upregulation expression of Ig kappa light chain via NF-kappaB and AP-1 pathways in nasopharyngeal carcinoma cells

BACKGROUND

Expression of kappa gene is under the control of distinct cis-regulatory elements, including the kappa intron enhancer (iE kappa) and the kappa 3' enhancer (3'E kappa). The active enhancers and expression of immunoglobulin is generally considered to be restricted to B lymphocytes. However, accumulating evidence indicated that epithelial cancer cells, including nasopharyngeal carcinoma (NPC) cell lines, express immunoglobulins. The mechanisms underlying the expression of Igs in nonlymphoid cells remain unknown. On the basis of our previous finding that expression of kappa light chain in NPC cells can be upregulated by EBV-encoded latent membrane protein 1(LMP1) through the activation of NF-kappaB and AP-1 signaling pathways, we thus use NPC cells as model to further explore the molecular mechanisms of nonlymphoid cells expressing Ig kappa.

RESULTS

In this study, luciferase reporter plasmid containing human wild-type iE kappa, and its derivative plasmids containing mutant binding sites for transcription factor NF-kappaB or AP-1 were constructed. Luciferase reporter assays demonstrate iE kappa is active in Ig kappa-expressing NPC cells and LMP1 expression can upregulate the activity of iE kappa in NPC cells. Mutation of the NF-kappaB or AP-1 site within and downstream the iE kappa, inhibition of the NF-kappaB and AP-1 pathways by their respective chemical inhibitor Bay11-7082 and SP600125 as well as stable or transient expression of dominant-negative mutant of I kappaB alpha (DNMI kappaB alpha) or of c-Jun (TAM67) indicate that both sites are functional and LMP1-enhanced iE kappa activity is partly regulated by these two sites. Gel shift assays show that LMP1 promotes NF-kappaB subunits p52 and p65 as well as AP-1 family members c-Jun and c-Fos binding to the kappa NF-kappaB and the kappa AP-1 motifs in vitro, respectively. Both chemical inhibitors and dominant negative mutants targeting for NF-kappaB and AP-1 pathways can attenuate the LMP1-enhanced bindings. Co-IP assays using nuclear extracts from HNE2-LMP1 cells reveal that p52 and p65, c-Jun and c-Fos proteins interact with each other at endogenous levels. ChIP assays further demonstrate p52 and p65 binding to the kappaB motif as well as c-Jun and c-Fos binding to the AP-1 motif of Ig kappa gene in vivo.

CONCLUSION

These results suggest that human iE kappa is active in Ig kappa-expressing NPC cells and LMP1-stimulated NF-kappaB and AP-1 activation results in an augmenting activation of the iE kappa. LMP1 promotes the interactions of heterodimeric NF-kappaB (p52/p65) and heterodimeric AP-1 (c-Jun/c-Fos) transcription factors with the human iE kappa enhancer region are important for the upregulation of kappa light chain in LMP1-positive nasopharyngeal carcinoma cells.

Transcription factor network downstream of protease activated receptors (PARs) modulating mouse bladder inflammation

BACKGROUND

All four PARs are present in the urinary bladder, and their expression is altered during inflammation. In order to search for therapeutic targets other than the receptors themselves, we set forth to determine TFs downstream of PAR activation in the C57BL/6 urinary bladders.

METHODS

For this purpose, we used a protein/DNA combo array containing 345 different TF consensus sequences. Next, the TF selected was validated by EMSA and IHC. As mast cells seem to play a fundamental role in bladder inflammation, we determined whether c-kit receptor deficient (Kit w/Kit w-v) mice have an abrogated response to PAR stimulation. Finally, TFEB antibody was used for CHIP/Q-PCR assay and revealed up-regulation of genes known to be downstream of TFEB.

RESULTS

TFEB, a member of the MiTF family of basic helix-loop-helix leucine zipper, was the only TF commonly up-regulated by all PAR-APs. IHC results confirm a correlation between inflammation and TFEB expression in C57BL/6 mice. In contrast, Kit w/Kit w-v mice did not exhibit inflammation in response to PAR activation. EMSA results confirmed the increased TFEB binding activity in C57BL/6 but not in Kit w/Kit w-v mice.

CONCLUSION

This is the first report describing the increased expression of TFEB in bladder inflammation in response to PAR activation. As TFEB belongs to a family of TFs essential for mast cell survival, our findings suggest that this molecule may influence the participation of mast cells in PAR-mediated inflammation and that targeting TFEB/MiTF activity may be a novel approach for the treatment of bladder inflammatory disorders.

In vitro evaluation of cancer-specific NF-kappaB-CEA enhancer-promoter system for 5-fluorouracil prodrug gene therapy in colon cancer cell lines

Nuclear factor-kappa B (NF-κB) is a transcription factor with high transcriptional activity in cancer cells. In this study, we developed a novel enhancer–promoter system, κB4-CEA205, in which the basal carcinoembryonic antigen (CEA) promoter sequence (CEA205) was placed downstream of the four tandem-linked NF-κB DNA-binding sites (κB4). In combination with a κB4 enhancer, the transcriptional activity of the CEA promoter was significantly enhanced (three- to eight-fold) in cancer cell lines but not in normal cells. In cancer cell lines, the transcriptional activity of κB4-CEA205 was comparable with that of the SV40 promoter. We also constructed vectors in which the thymidine phosphorylase (TP) cDNA was under the control of CEA205, κB4, κB4-CEA205 and CMV promoters, respectively. TP protein and enzyme activity were detected at comparable levels in κB4-CEA205- and CMV-driven TP cDNA-transfected cancer cell lines (H630 and RKO). The κB4-TP and CEA205-TP-transfected cell lines, respectively, only demonstrated negligible and low levels of TP protein and enzyme activity. Both CMV- and κB4-CEA205-driven TP cDNA transiently transfected cells were 8- to 10-fold sensitised to 5-fluorouracil (5-FU) prodrug, 5′-deoxy-5-fluorouradine (5′-DFUR), in contrast to only 1.5- to 2-fold sensitised by the κB4- and CEA205-driven TP cDNA-transfected cells. The bystander killing effect of CMV- and κB4-CEA205-driven TP cDNA-transfected cells was comparable. This is the first report that indicates that the NF-κB DNA-binding site could be used as a novel cancer-specific enhancer to improve cancer-specific promoter activity in gene-directed enzyme prodrug therapy.

Comparison of mouse and rabbit Ei kappa enhancers indicates that different elements within the enhancer may mediate activation of transcription and recombination

The intronic Ig kappa-light chain enhancer (Eikappa) has been implicated in regulation of transcription and Vkappa-Jkappa recombination at the kappa locus. To identify sequences within the Eikappa enhancer which are involved in control of recombination, we have made use of the finding that the Eikappa element from the rabbit b9 kappa locus is capable of inducing rearrangement, but not transcription of kappa genes in mouse lymphoid cells. We have therefore compared the binding of murine nuclear proteins to the mouse and rabbit Eikappa elements. DNase I footprinting and gel mobility shift assays indicate that only the kappaB, kappaE1, and kappaE2 sites of the rabbit enhancer are able to interact with murine trans-acting factors. Moreover, although the rabbit kappaB site binds murine NF-kappaB p50/p50 and p50/p65 complexes with high affinity, this site is not capable of mediating transcriptional activation of transient transfection reporter constructs in mouse B lineage cells. These results therefore suggest that, in contrast to the maintenance of kappa enhancer transcription which requires all of the Eikappa sites, only the kappaB, kappaE1, and kappaE2 sites may be necessary for the recombinational activity of the enhancer. Furthermore, NF-kappaB-mediated effects on transcription and recombination appear to involve separate downstream activation pathways.

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.

Developmental regulation of the kappa locus involves both positive and negative sequence elements in the 3' enhancer that affect synergy with the intron enhancer

Expression of the mouse immunoglobulin kappa locus is regulated by the intron and 3' enhancers. Previously, we have reported that these enhancers can synergize at mature B cell stages. Here we present our recent studies on the identification and characterization of the 3' enhancer sequences that play important roles in this synergy. By performing mutational analyses with novel reporter constructs, we find that the 5' region of the cAMP response element (CRE), the PU. 1/PIP, and the E2A motifs of the 3' enhancer are critical for the synergy. These motifs are known to contribute to the enhancer activity. However, we also show that mutating other functionally important sequences has no significant effect on the synergy. Those sequences include the 3' region of the CRE motif, the BSAP motif, and the region 3' of the E2A motif. We have further demonstrated that either the 5'-CRE, the PU.1/PIP, or the E2A motif alone is sufficient to synergize with the intron enhancer. Moreover, the PU.1 motif appears to act as a negative element at pre-B cell stages but as a positive element at mature B cell stages. We have also identified a novel negative regulatory sequence within the 3' enhancer that contributes to the regulation of synergy, as well as developmental stage and tissue specificity of expression. While the levels of many of the 3' enhancer binding factors change very little in cell lines representing different B cell stages, the intron enhancer binding factors significantly increase at more mature B cell stages.

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.

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.

Octamer independent activation of transcription from the kappa immunoglobulin germline promoter

Previous analyses of immunoglobulin V region promoters has led to the discovery of a common octamer motif which is functionally important in the tissue-specific and developmentally regulated transcriptional activation of immunoglobulin genes. The germline promoters (Ko) located upstream of the J region gene segments of the kappa locus also contain an octamer motif (containing a single base pair mutation and referred to as the variant octamer) which has been shown previously to bind Oct-1 and Oct-2 transcription factors in vitro. To further elucidate the role of this variant octamer motif in the regulation of germline transcription from the unrearranged kappa locus, we have quantitated the relative binding affinity of Oct-1 and Oct-2 for the variant octamer motif and determined the functional role of this octamer motif in transcriptional activation. We find that, although the variant octamer motif binds Oct-1 and Oct-2 in vitro with 5-fold lower affinity than the consensus octamer motif, mutation of the variant octamer motif to either a consensus octamer or non-octamer motif has no effect on transcriptional activation from the germline promoter. We also find significant differences in activation of germline and V region promoters by kappa enhancers. Our results suggest that the germline promoters and V region promoters differ in their dependence on octamer for activation and respond differently to enhancer activation. These findings have important implications in regulation of germline transcription as well as concomitant activation of the V-J recombination of the kappa light chain locus.

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

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

An AP1 binding site upstream of the kappa immunoglobulin intron enhancer binds inducible factors and contributes to expression

Expression of the kappa immunoglobulin light chain gene requires developmental- and tissue-specific regulation by trans-acting factors which interact with two distinct enhancer elements. A new protein-DNA interaction has been identified upstream of the intron enhancer, within the matrix-associated region of the J-C intron. The binding activity is greatly inducible in pre-B cells by bacterial lipopolysaccharide and interleukin-1 but specific complexes are found at all stages of B cell development tested. The footprinted binding site is homologous to the consensus AP1 motif. The protein components of this complex are specifically competed by an AP1 consensus motif and were shown by supershift to include c-Jun and c-Fos, suggesting that this binding site is an AP1 motif and that the Jun and Fos families of transcription factors play a role in the regulation of the kappa light chain gene. Mutation of the AP1 motif in the context of the intron enhancer was shown to decrease enhancer-mediated activation of the promoter in both pre-B cells induced with LPS and constitutive expression in mature B cells.

Selective synergy of immunoglobulin enhancer elements in B-cell development: a characteristic of kappa light chain enhancers, but not heavy chain enhancers

We have examined the interactions of the enhancers of the kappa immunoglobulin light chain gene as well as the interactions of the intron, mu, and 3' alpha enhancers of the heavy chain locus in mouse. We have observed that each of the kappa enhancers is very weak in comparison with the heavy chain intron enhancer. The mouse heavy chain 3' alpha enhancer is relatively weak as well. However, two kappa enhancers together synergistically activate transcription of a luciferase reporter gene to a level that is roughly equivalent to the heavy chain mu enhancer. Additionally, dimerization of either kappa enhancer results in synergistic increases in transcription. This property of synergism appears to be confined to the enhancers of the kappa locus, as addition of the 3' alpha E to mu E containing constructs increases transcription only modestly, and neither heavy chain enhancer synergizes when dimerized. We have gone on to characterize some of the minimal requirements for synergism between the kappa enhancers and find that the KB and E2 sites are required, but not the E3 site. The implications of these results for the coordinate regulation of the heavy and light chain transcription are discussed.

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.

Kappa immunoglobulin promoters and enhancers display developmentally controlled interactions

We have investigated the interaction of the kappa immunoglobulin light chain intron and 3' enhancers with two different kappa promoters at distinct stages of B-cell development. We find that transiently transfected reporter gene constructs driven by either the kappa V-region promoter, or the kappa germline promoter, are controlled by the known enhancers of the locus in a developmentally regulated fashion. We have, however, observed differences in promoter activation by each enhancer. Moreover, constructs controlled by a combination of both enhancers are synergistically activated at the B-cell and plasma cell stages as compared with constructs containing either enhancer alone. This synergy is not observed early in development, at the pre-B cell stage. The pattern of enhancer and promoter interactions is discussed in the context of the known developmental regulation of the locus.

Molecular dissection of the mouse interleukin-4 promoter

Understanding the molecular mechanisms regulating the expression of interleukin 4 (IL-4) may shed light on the differentiation of lymphokine-producing phenotypes of CD4+ T cells. We have identified two DNA segments that are necessary for full phorbol 12-myristate 13-acetate (PMA)-induced activity of the IL-4 promoter region in the thymoma cell line EL4. Through deletion and mutation analyses, one of these segments (-57 through -47) was shown to be indispensable for promoter function. We designated this sequence consensus sequence 1 (CS1), as it shares homology with a sequence (ATTTTCCNNTG) that appears five times in the proximal 302-base-pair (bp) region 5' of the gene. We examined CS1 in further detail, as well as a second consensus sequence, CS2, located at nucleotides -75 through -65; both are within a minimal 83-bp construct that expresses full promoter activity. CS1- and CS2-spanning oligonucleotides bound apparently distinct PMA-inducible, sequence-specific factors in mobility-shift assays. Multimer constructs linking CS1- or CS2-spanning oligonucleotides to a heterologous promotor revealed that the CS1 construct had the greater enhancer activity in EL4 cells. Mutating the CS1 sequence within the context of the 302-bp promoter abolished all activity of the promoter, while mutating the CS2 sequence alone had little effect. Furthermore, a CS1 multimer could drive a heterologous promoter in an IL-4-producing [helper T-cell type 2 (TH2-type)] T-cell clone but not in a non-IL-4-producing (TH1-type) clone, suggesting a mechanism by which IL-4 production could be differentially regulated in TH subsets.

Negative regulation of immunoglobulin kappa light-chain gene transcription by a short sequence homologous to the murine B1 repetitive element

B-cell-specific expression of the immunoglobulin kappa light-chain (Ig kappa) gene is in part accomplished by negative regulatory influences. Here we describe a new negatively acting element (termed kappa NE) immediately upstream of the NF-kappa B-binding site in the Ig kappa intronic enhancer. The 27-bp kappa NE sequence is conserved in the corresponding positions in the rabbit and human Ig kappa genes, and the human kappa NE homolog was shown to have a similar negative regulatory activity. Data base searches using the mouse kappa NE sequence revealed a striking homology to murine B1 repetitive sequences. A sequence homologous to kappa NE and B1 was also noted in a previously identified silencer element in the murine T-cell receptor alpha locus. The homologous T-cell receptor alpha locus sequence, but notably not a corresponding 27-bp B1 consensus sequence, showed a negative regulatory potential similar to that of kappa NE. The negative effect of kappa NE by itself was not cell type specific but became so when paired with its 5'-flanking sequence in the Ig kappa enhancer. A short (30-bp) fragment upstream of kappa NE (termed kappa BS) was found to be necessary and sufficient for abolishing the negative effect of kappa NE in B cells. Point mutations in a T-rich motif within the kappa BS sequence allowed the transcriptional repression by kappa NE to be evident in B cells as well as other cells. As suggested by this cell-independent negative activity, proteins binding to the mouse and human kappa NE sequences were identified in all cell types tested.

Negative regulation of immunoglobulin kappa light-chain gene transcription by a short sequence homologous to the murine B1 repetitive element

B-cell-specific expression of the immunoglobulin kappa light-chain (Ig kappa) gene is in part accomplished by negative regulatory influences. Here we describe a new negatively acting element (termed kappa NE) immediately upstream of the NF-kappa B-binding site in the Ig kappa intronic enhancer. The 27-bp kappa NE sequence is conserved in the corresponding positions in the rabbit and human Ig kappa genes, and the human kappa NE homolog was shown to have a similar negative regulatory activity. Data base searches using the mouse kappa NE sequence revealed a striking homology to murine B1 repetitive sequences. A sequence homologous to kappa NE and B1 was also noted in a previously identified silencer element in the murine T-cell receptor alpha locus. The homologous T-cell receptor alpha locus sequence, but notably not a corresponding 27-bp B1 consensus sequence, showed a negative regulatory potential similar to that of kappa NE. The negative effect of kappa NE by itself was not cell type specific but became so when paired with its 5'-flanking sequence in the Ig kappa enhancer. A short (30-bp) fragment upstream of kappa NE (termed kappa BS) was found to be necessary and sufficient for abolishing the negative effect of kappa NE in B cells. Point mutations in a T-rich motif within the kappa BS sequence allowed the transcriptional repression by kappa NE to be evident in B cells as well as other cells. As suggested by this cell-independent negative activity, proteins binding to the mouse and human kappa NE sequences were identified in all cell types tested.

The second century of the antibody. Molecular perspectives in regulation, pathophysiology, and therapeutic applications

The modern age of immunology began in 1890 with the discovery of antibodies as a major component of protective immunity. The 2nd century of the antibody begins with a focus on the molecular physiology and pathophysiology of immunoglobulin production. Numerous human variable-region antibody genes have been identified through advances in molecular cloning and anti-variable-region monoclonal antibodies. Some of these variable-region genes are now known to be involved in specific stages of B-lymphocyte differentiation and immune development. This connection has yielded new insights into the pathogenesis of immune dyscrasias and lymphoid neoplasia; common variable immunodeficiency and cryoglobulinemia are highlighted here. The molecular regulation of immunoglobulin expression suggests new targets for pathogenesis and clinical intervention. Finally, genetically engineered antibodies offer novel opportunities for diagnostic and therapeutic applications.

Two conserved essential motifs of the murine immunoglobulin lambda enhancers bind B-cell-specific factors

Two highly homologous enhancers associated with the two murine immunoglobulin lambda constant-region clusters were recently identified. In order to better understand the molecular basis for the developmental stage- and cell-type-restricted expression of lambda genes, we have undertaken an analysis of the putative regulatory domains of these enhancers. By using a combination of DNase I footprinting, electrophoretic mobility shift assay, and site-specific mutations, four candidate protein binding sites have been identified at analogous positions in both enhancers. A mutation of any of these sites decreases enhancer activity. Two of the sites, lambda A and lambda B, are essential for enhancer function, and both of these sites appear to bind both B-cell-specific and general factors. Nevertheless, isolated lambda A and lambda B sites show no evidence of inherent transactivating potential, alone or together, even when present in up to three copies. We suggest that the generation of transactivating signals from these enhancers may require the complex interaction of multiple B-cell-specific and nonspecific DNA-binding factors.

Two conserved essential motifs of the murine immunoglobulin lambda enhancers bind B-cell-specific factors

Two highly homologous enhancers associated with the two murine immunoglobulin lambda constant-region clusters were recently identified. In order to better understand the molecular basis for the developmental stage- and cell-type-restricted expression of lambda genes, we have undertaken an analysis of the putative regulatory domains of these enhancers. By using a combination of DNase I footprinting, electrophoretic mobility shift assay, and site-specific mutations, four candidate protein binding sites have been identified at analogous positions in both enhancers. A mutation of any of these sites decreases enhancer activity. Two of the sites, lambda A and lambda B, are essential for enhancer function, and both of these sites appear to bind both B-cell-specific and general factors. Nevertheless, isolated lambda A and lambda B sites show no evidence of inherent transactivating potential, alone or together, even when present in up to three copies. We suggest that the generation of transactivating signals from these enhancers may require the complex interaction of multiple B-cell-specific and nonspecific DNA-binding factors.

Regulation of immunoglobulin gene transcription

Analysis of the immunoglobulin gene suggests that their expression is controlled through the combinatorial action of tissue- and stage-specific factors (OTF-2, TF-microB, NF-kappa B), as well as more widely expressed E motif-binding factors such as E47/E12. Two basic issues cloud understanding of how these factors are involved in immunoglobulin gene regulation. First, cloning of these factors shows them to be members of families of proteins, all with similar DNA-binding specificities. OTF-2 is a member of the POU domain family, NF-kappa B is a related protein, and the microE5/kappa E2-binding factors are members of the bHLH family. Second, these binding sites and associated factors are involved in the regulation of many genes, not only the immunoglobulin genes, and in fact not only lymphoid-specific genes. These facts complicate understanding which member of a family is in fact responsible for interaction with, and activation of, a particular binding element in an enhancer/promoter. Recently, more detailed analysis of the interactions between such proteins and their related binding sites suggest that a certain level of specificity may in fact be encoded by the DNA element such that one family member of a protein is preferentially bound, or alternatively that the protein-DNA interactions that occur give subtle alterations in protein conformation that unmask an activation or protein-protein interactive domain. An additional level of regulation is imparted by combinatorial mechanisms such as adjacent DNA-binding elements and factors that may alter activity, as well as "cofactors" that, by forming a complex with the bound factor, affect its activation of a gene in a particular cell type. A third level of specificity may be obtained by factors such as NF-kappa B and the bHLH family due to their ability to create heterogeneous complexes, creating unique complexes in a tissue- or stage-specific manner. The multiple functions transcription factors such as NF-kappa B and OTF-2 play in the transcriptional regulation of multiple genes seems complex in contrast to a one factor, one gene regulation model. However, this type of organization may limit the number of factors lymphocytes would require if each lymphoid-specific gene were activated by a unique factor. Thus what appears to be complexity at the molecular level may reflect an economical organization at the cellular level. Investigation of the key factors controlling these genes suggests an ordered cascade of transcription factors becomes available in the cell during B cell differentiation.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

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.

Enhancer mediated suppression of epsilon heavy-chain gene expression in a murine IgE-producing hybridoma

In vitro co-culture of IgE-secreting hybridoma cells (B53) with spleen cells harvested from mice with established B53 tumours results in a specific, T cell-dependent suppression of epsilon-chain expression in the B53 cells. The role of immunoglobulin enhancers in the suppression of IgE synthesis in B53 cells was examined by transfecting B53 cells with CAT expression vectors containing the immunoglobulin heavy- or kappa light-chain intron enhancers or a Rous sarcoma virus (RSV) LTR. When epsilon-chain expression of transfected cells was suppressed in vitro. CAT expression was also suppressed in cells transfected with vectors containing the immunoglobulin heavy-chain gene enhancer, but not in cells transfected with vectors containing the kappa enhancer or RSV LTR. Thus, the T cell-dependent suppression of IgE synthesis in B53 cells correlates with a specific inactivation of the immunoglobulin heavy chain enhancer, strongly suggesting that T cell-mediated suppression of Ig synthesis can normally occur through specific repression of Ig enhancer function. This represents a new regulatory pathway involved in the control of IgE synthesis and is the first indication that the enhancer mediated expression of Ig genes in B cells can be modulated through T cell-dependent processes.

Silencing of the expression of the immunoglobulin kappa gene in non-B cells

Although the activating factor NF-kappa B can be present in the nucleus of many cell types, transcription and rearrangement of the immunoglobulin kappa chain gene is restricted to cells of the B lineage. Part of this specificity is determined by sequences within the major intron of the kappa gene that specifically silence gene expression in non-B cells (T cells and HeLa cells). These sequences are found in a 232-bp fragment located 5' of the NF-kappa B binding sequence of the enhancer. When this fragment is added back upstream of an active NF-kappa B site, it specifically decreases the expression of a linked gene by more than 10-fold in activated T cells but it has no effect on expression in B cells. The kappa silencer region acts in an orientation- and distance-independent manner and appears to be composed of multiple negative elements. The kappa silencer may act to restrict transcription and rearrangement of the C kappa locus to cells of the B lineage.

Silencing of the expression of the immunoglobulin kappa gene in non-B cells

Although the activating factor NF-kappa B can be present in the nucleus of many cell types, transcription and rearrangement of the immunoglobulin kappa chain gene is restricted to cells of the B lineage. Part of this specificity is determined by sequences within the major intron of the kappa gene that specifically silence gene expression in non-B cells (T cells and HeLa cells). These sequences are found in a 232-bp fragment located 5' of the NF-kappa B binding sequence of the enhancer. When this fragment is added back upstream of an active NF-kappa B site, it specifically decreases the expression of a linked gene by more than 10-fold in activated T cells but it has no effect on expression in B cells. The kappa silencer region acts in an orientation- and distance-independent manner and appears to be composed of multiple negative elements. The kappa silencer may act to restrict transcription and rearrangement of the C kappa locus to cells of the B lineage.

The importance of the 3'-enhancer region in immunoglobulin kappa gene expression

The first enhancers to be identified in the immunoglobulin gene loci are located in the J-C intron. However, deletion of the immunoglobulin kappa intron-enhancer has little effect on the transcription of kappa transgenes. Here we ask whether the second kappa enhancer which we recently identified at the 3'-end of the locus plays a role in kappa gene expression. We show that its omission leads to 20-40 fold lower expression of kappa transgenes and to poor allelic exclusion. Transfection experiments show that activity of the 3'-enhancer, like that of the kappa-intron enhancer, can be induced in a pre-B cell line by incubation with bacterial lipopolysaccharide. Whereas induction of the kappa-intron enhancer is due to induction of NF-kappa B activity, deletion mapping of the 3'-enhancer localises its activity to a 50 nucleotide region that lacks an NF-kappa B site; indeed the 3'-enhancer allows kappa expression in a cell line which lacks NF-kappa B. Thus, both the 3'- and intron-enhancers can be induced at the same stage of differentiation but by distinct pathways. Furthermore, unlike the intron-enhancer, the 3'-enhancer plays a critical role in the transcription of rearranged immunoglobulin kappa genes.

Identification of an octamer-binding site in the human kappa light-chain enhancer

Octamer motifs contribute to the function and tissue specificity of immunoglobulin heavy- and light-chain gene promoters and the heavy-chain enhancer. A variant octamer-binding site within a conserved region of the human kappa light-chain gene enhancer which contributes to the function of this enhancer has been identified.

Identification of an octamer-binding site in the human kappa light-chain enhancer

Octamer motifs contribute to the function and tissue specificity of immunoglobulin heavy- and light-chain gene promoters and the heavy-chain enhancer. A variant octamer-binding site within a conserved region of the human kappa light-chain gene enhancer which contributes to the function of this enhancer has been identified.