An immunoglobulin promoter displays cell-type specificity independently of the enhancer

Genes activated in the presence of an immunoglobulin enhancer or promoter are negatively regulated by a T-lymphoma cell line

The tissue-specific expression of immunoglobulin genes can be partially explained by a requirement for activating factors found only in B lymphocytes and their derivatives. However, loss of immunoglobulin expression upon fusion of an immunoglobulin-producing myeloma cell with a T lymphoma cell (BW5147) or fibroblast (L cell) suggests that negatively acting factors also play a role in the tissue specificity of immunoglobulin genes. Expression of a cloned immunoglobulin heavy-chain gene introduced into myeloma cells was suppressed after fusion of the myeloma transformants with BW5147. The presence of either the immunoglobulin heavy-chain enhancer or promoter conferred suppression, under similar conditions, upon a heterologous gene that is normally expressed in both B and T lymphocytes. These immunoglobulin heavy-chain gene control regions, or gene modifications induced by them, are subject to negative control by T-lymphocyte-derived factors.

Identification and purification of a human immunoglobulin-enhancer-binding protein (NF-kappa B) that activates transcription from a human immunodeficiency virus type 1 promoter in vitro

The enhancer-binding factor NF-kappa B, which is found only in cells that transcribe immunoglobulin light chain genes, has been purified from nuclear extracts of Namalwa cells (human Burkitt lymphoma cells) by sequence-specific DNA affinity chromatography. The purified NF-kappa B has been identified as a 51-kDa polypeptide by UV-crosslinking analysis. "Footprint" and methylation-interference analyses have shown that purified NF-kappa B has a binding activity specific for the kappa light chain enhancer sequence. The purified factor activated in vitro transcription of the human immunodeficiency virus type I promoter by binding to an upstream NF-kappa B-binding site.

A conserved heptamer upstream of the IgH promoter region octamer can be the site of a coordinate protein-DNA interaction

Immunoglobulin genes contain a conserved eight base sequence element 5' to the site of transcription initiation. This octamer can serve as a site for the binding of nuclear proteins which are presumably involved in the cell type specific expression of this family of genes. In studying the binding of nuclear proteins to this conserved sequence element, we have detected a protein interaction that involves, in addition to the octamer, nucleotides which are immediately upstream. We have characterized this additional contact as a sequence specific interaction with a heptameric sequence element (CTCATGA) that is conserved among Ig heavy chain promoters. Protein binding to the heptamer is unique in that it is dependent upon the proximity and orientation of, as well as protein interaction with, the conserved octamer.

Purification of a nuclear trans-acting factor involved in the regulated transcription of a human immunoglobulin heavy chain gene

The expression of the rearranged human immunoglobulin gamma 1 heavy chain gene (HIG1) was shown to be induced through its enhancer by the positive regulatory trans-acting factor(s) that was contained only in cells of B lineage. The trans-acting factors were purified from mouse myeloma NS1 cells, and HIG1-inducing activity was found mainly in fractions of molecular weight 53-127 kd and in a fraction eluted from a heparin-Sepharose column with 0.5 M KCI. This semipurified fraction contained proteins binding to the conserved octamer sequence, ATGCAAAT, in the promoter region, as well as to sequences in the enhancer region. The 0.5 M KCI eluates from a heparin-Sepharose column were applied to a DNA affinity column of synthetic oligonucleotides of the octamer sequence and the sequence TATTTTAGGAAGCAAA in the HpaII-BgIII region of the HIG1 gene enhancer. The protein eluted from the enhancer sequence-specific DNA affinity column showed a strong inducing activity for the HIG1 gene, and the molecular weight of a predominant protein was 96 kd.

Genes activated in the presence of an immunoglobulin enhancer or promoter are negatively regulated by a T-lymphoma cell line

The tissue-specific expression of immunoglobulin genes can be partially explained by a requirement for activating factors found only in B lymphocytes and their derivatives. However, loss of immunoglobulin expression upon fusion of an immunoglobulin-producing myeloma cell with a T lymphoma cell (BW5147) or fibroblast (L cell) suggests that negatively acting factors also play a role in the tissue specificity of immunoglobulin genes. Expression of a cloned immunoglobulin heavy-chain gene introduced into myeloma cells was suppressed after fusion of the myeloma transformants with BW5147. The presence of either the immunoglobulin heavy-chain enhancer or promoter conferred suppression, under similar conditions, upon a heterologous gene that is normally expressed in both B and T lymphocytes. These immunoglobulin heavy-chain gene control regions, or gene modifications induced by them, are subject to negative control by T-lymphocyte-derived factors.

Identification of murine nuclear proteins that bind to the conserved octamer sequence of the immunoglobulin promoter region

Sequence-specific DNA-affinity chromatography was used to purify a nuclear protein from the B-cell leukemia cell line BCL1 that specifically binds to the octamer sequence ATTTGCAT, previously shown to be important in the regulation of immunoglobulin genes. This protein has a molecular mass of approximately 70 kDa and is responsible for the protein-DNA interaction specific to lymphoid cells. Other proteins of molecular mass 80-90 kDa and 50-55 kDa that specifically bind to the octamer sequence were also identified. These results demonstrate that the octamer is recognized by several biochemically distinct nuclear proteins, perhaps to differentially regulate the expression of immunoglobulin genes.

Multiple positive and negative 5' regulatory elements control the cell-type-specific expression of the embryonic skeletal myosin heavy-chain gene

To identify the DNA sequences that regulate the expression of the sarcomeric myosin heavy-chain (MHC) genes in muscle cells, a series of deletion constructs of the rat embryonic MHC gene was assayed for transient expression after introduction into myogenic and nonmyogenic cells. The sequences in 1.4 kilobases of 5'-flanking DNA were found to be sufficient to direct expression of the MHC gene constructs in a tissue-specific manner (i.e., in differentiated muscle cells but not in undifferentiated muscle and nonmuscle cells). Three main distinct regulatory domains have been identified: (i) the upstream sequences from positions -1413 to -174, which determine the level of expression of the MHC gene and are constituted of three positive regulatory elements and two negative ones; (ii) a muscle-specific regulatory element from positions -173 to -142, which restricts the expression of the MHC gene to muscle cells; and (iii) the promoter region, downstream from position -102, which directs transcription initiation. Introduction of the simian virus 40 enhancer into constructs where subportions of or all of the upstream sequences are deleted (up to position -173) strongly increases the level of expression of such truncated constructs but without changing their muscle specificity. These upstream sequences, which can be substituted for by the simian virus 40 enhancer, function in an orientation-, position-, and promoter-dependent fashion. The muscle-specific element is also promoter specific but does not support efficient expression of the MHC gene. The MHC promoter in itself is not muscle specific. These results underline the importance of the concerted action of multiple regulatory elements that are likely to represent targets for DNA-binding-regulatory proteins.

Tissue-specific activity of the pro-opiomelanocortin gene promoter

The pro-opiomelanocortin (POMC) gene is specifically expressed in corticotroph cells of the anterior pituitary. To define the POMC promoter sequences responsible for tissue-specific expression, we assessed POMC promoter activity by gene transfer into POMC-expressing pituitary tumor cells (AtT-20) and fibroblast L cells. The rat POMC promoter was only efficiently utilized and correctly transcribed in AtT-20 cells. 5'-End deletion analysis revealed two promoter regions required for activity in AtT-20 cells. When tested by fusion to a heterologous promoter, DNA fragments corresponding to both regions exhibited tissue-specific activity, suggesting the presence of at least two tissue-specific DNA sequence elements within the promoter. In summary, POMC promoter sequences from -480 to -34 base pairs appear sufficient to mimic the specificity of anterior pituitary expression.

Transfection of an immunoglobulin kappa gene into mature human B lymphocytes

We show in this report that the transcription induced by interleukin-2 or pokeweed mitogens of the kappa MOPC 41 immunoglobulin light-chain gene transfected into primary human or murine B lymphocytes initiates from a previously unobserved start site about 26 base pairs upstream of the start site used in myeloma cell lines.

Tissue preferential expression of the hepatitis B virus (HBV) surface antigen gene in two lines of HBV transgenic mice

Two transgenic mice were produced by microinjection of the entire hepatitis B virus (HBV) genome as a 3.2-kilobase EcoRI DNA fragment into one-cell embryos. Each animal contained a single, unique locus of HBV sequence. One founder animal, G7, contained a partially deleted HBV genome lacking both putative HBV surface antigen (HBsAg) promoters. The other animal, G26, contained greater-than-genome-length HBV sequences organized as a partial head-to-tail dimer. Both transgenic animals transmitted the HBV sequences in a Mendelian fashion, and all subsequent transgenic animals had detectable HBsAg in the serum. Expression of HBV sequences in tissues from G7- and G26-derived mice showed preferential expression of the 2.1-kilobase HBsAg RNA transcript in liver and kidney tissues by Northern (RNA) blot analysis. These data are consistent with the notion that HBV DNA contains cis-acting regulatory sequences which are responsible for the predominant expression of HBsAg transcripts in the liver and kidney of transgenic mice.

Transfection of an immunoglobulin kappa gene into mature human B lymphocytes

We show in this report that the transcription induced by interleukin-2 or pokeweed mitogens of the kappa MOPC 41 immunoglobulin light-chain gene transfected into primary human or murine B lymphocytes initiates from a previously unobserved start site about 26 base pairs upstream of the start site used in myeloma cell lines.

Alterations in binding characteristics of the human immunodeficiency virus enhancer factor

Five regions of the human immunodeficiency virus (HIV) long terminal repeat (LTR) serve as binding sites for cellular proteins as demonstrated by DNase I footprinting. These include the negative regulatory, enhancer, SP1, TATA, and untranslated regions. The HIV enhancer region contains two direct repeats of a sequence, GGGACTTTCC, which is also found in the enhancer sequences of simian virus 40, cytomegalovirus, and the immunoglobulin kappa gene. To further characterize binding to the enhancer sequences in the HIV LTR, DNase I footprinting was performed using extracts prepared from several different cell lines. Extracts prepared from lymphoid cells gave altered binding over the enhancer region as compared with extracts prepared from either monocytes or HeLa cells. This altered binding in extracts prepared from lymphoid cells resulted in protection of both direct repeats in the HIV LTR in contrast to complete protection of only one direct repeat with HeLa cell extracts. When HeLa cells were treated with phorbol esters in either the presence or absence of the protein synthesis inhibitor cycloheximide, the binding characteristics over the enhancer element became similar to those seen in extracts prepared from lymphoid cells. These results suggest that phorbol esters may induce posttranslational modifications of cellular transcription factors that alter their DNA-binding characteristics.

Purification of an octamer sequence (ATGCAAAT)-binding protein from human B cells

The highly conserved octamer sequence ATGCAAAT or its inverse complement found in all human and murine immunoglobulin gene promoters has been demonstrated to be necessary in the lymphoid-specific transcription by deletion analysis. Trans-acting factors that interact with the octamer motif are thought to be involved in this tissue-specific expression. Using a gel mobility shift assay, we have identified both lymphoid-specific and ubiquitous nuclear factors that interact with a human gamma 1 heavy chain gene promoter region containing the octamer motif, consistent with the results obtained with murine heavy or light chain promoter regions. We have purified an octamer binding protein from human B cells by sequence-specific DNA affinity chromatography. Renaturation of gel-purified protein allowed the identification of a polypeptide with a molecular weight of 74 kilodaltons (kD) that is capable of recognizing and binding to the octamer motif. This 74 kD protein seems to be also present in T-cells and non-lymphoid cells. The possible function of the factor is discussed.

Identification and purification of a human lymphoid-specific octamer-binding protein (OTF-2) that activates transcription of an immunoglobulin promoter in vitro

The octamer sequence 5'-ATGCAAAT, in either orientation, serves as an upstream element in a variety of promoters and also occurs as a modular enhancer element. It is of particular interest in immunoglobulin genes since it is found in the upstream regions of all heavy and light chain promoters and in the heavy chain enhancer, both of which are known to be necessary for cell-specific expression. We report here the chromatographic separation of ubiquitous and B cell-specific octamer-binding proteins. The B cell factor was purified to homogeneity using affinity chromatography and consists of three peptides of 62, 61, and 58.5 +/- 1.5 kd. Each of the polypeptides was renatured after SDS-PAGE and shown to bind to the octamer sequence. The specific DNA binding activity of the pure B cell-specific factor was indistinguishable from that of the affinity-purified ubiquitous factor. This B cell-specific octamer-binding factor, in pure form, activated transcription from a kappa light chain promoter in vitro, thus demonstrating that it is indeed a B cell-specific transcription factor for this gene. In addition to the ubiquitous and B cell-specific octamer-binding factors, we identified several additional proteins, one of which is B cell-specific, that interact with the kappa promoter.

Multiple positive and negative 5' regulatory elements control the cell-type-specific expression of the embryonic skeletal myosin heavy-chain gene

To identify the DNA sequences that regulate the expression of the sarcomeric myosin heavy-chain (MHC) genes in muscle cells, a series of deletion constructs of the rat embryonic MHC gene was assayed for transient expression after introduction into myogenic and nonmyogenic cells. The sequences in 1.4 kilobases of 5'-flanking DNA were found to be sufficient to direct expression of the MHC gene constructs in a tissue-specific manner (i.e., in differentiated muscle cells but not in undifferentiated muscle and nonmuscle cells). Three main distinct regulatory domains have been identified: (i) the upstream sequences from positions -1413 to -174, which determine the level of expression of the MHC gene and are constituted of three positive regulatory elements and two negative ones; (ii) a muscle-specific regulatory element from positions -173 to -142, which restricts the expression of the MHC gene to muscle cells; and (iii) the promoter region, downstream from position -102, which directs transcription initiation. Introduction of the simian virus 40 enhancer into constructs where subportions of or all of the upstream sequences are deleted (up to position -173) strongly increases the level of expression of such truncated constructs but without changing their muscle specificity. These upstream sequences, which can be substituted for by the simian virus 40 enhancer, function in an orientation-, position-, and promoter-dependent fashion. The muscle-specific element is also promoter specific but does not support efficient expression of the MHC gene. The MHC promoter in itself is not muscle specific. These results underline the importance of the concerted action of multiple regulatory elements that are likely to represent targets for DNA-binding-regulatory proteins.

Regulation of immunoglobulin transcription rates and mRNA processing in proliferating normal B lymphocytes by activators of protein kinase C

Immunoglobulin gene expression in normal splenic B lymphocytes stimulated with lipopolysaccharide was selectively down-regulated by anti-IgM antibodies and a protein-kinase C-activating phorbol ester, phorbol 12,13-dibutyrate. This control was concomitant with a decreased rate of transcription of the IgM gene while "polymerase pausing" was induced in the IgD gene. The suppression was resistant to treatment with cycloheximide, indicating that it was not caused by a labile repressor protein. The down-regulation of immunoglobulin gene expression affected only the secretory form of immunoglobulin, while the mRNA levels for the membrane-bound form of immunoglobulin remained unaltered. We conclude that the mechanisms controlling immunoglobulin gene expression in untransformed B lymphocytes differ from those operating in tumors derived from the same cell lineage.

Tissue-specific activity of the pro-opiomelanocortin gene promoter

The pro-opiomelanocortin (POMC) gene is specifically expressed in corticotroph cells of the anterior pituitary. To define the POMC promoter sequences responsible for tissue-specific expression, we assessed POMC promoter activity by gene transfer into POMC-expressing pituitary tumor cells (AtT-20) and fibroblast L cells. The rat POMC promoter was only efficiently utilized and correctly transcribed in AtT-20 cells. 5'-End deletion analysis revealed two promoter regions required for activity in AtT-20 cells. When tested by fusion to a heterologous promoter, DNA fragments corresponding to both regions exhibited tissue-specific activity, suggesting the presence of at least two tissue-specific DNA sequence elements within the promoter. In summary, POMC promoter sequences from -480 to -34 base pairs appear sufficient to mimic the specificity of anterior pituitary expression.

A cell type specific factor recognizes the rat thyroglobulin promoter

We have fused a 900 base pair long DNA segment containing the transcriptional start site of the rat thyroglobulin (Tg) gene to the bacterial gene for chloramphenicol acetyltransferase (cat). The fusion gene has been introduced into three different cell lines derived from the rat thyroid gland and into a rat liver cell line. Expression of the fusion gene was detected only in the one thyroid cell line that is able to express the endogenous Tg gene. The minimum DNA sequence required for the cell type specific expression was determined by deletion analysis; it extends 170 nucleotides upstream of the transcription initiation site. The Tg promoter contains a readily detectable binding sites for a factor present in salt extracts of thyroid cell nuclei. This binding site is not recognized by the nuclear extracts of any other cell type that we have tested, suggesting that it may help mediate the cell type specific expression of the Tg gene.

The HLA-DQ beta gene upstream region contains an immunoglobulin-like octamer motif that binds cell-type specific nuclear factors

A method is described for scanning relatively large fragments of DNA for sequences which bind nuclear factors. This method was used to identify an octamer (ATTTGTAT) in the DQ beta gene upstream region which differs from the immunoglobulin gene octamer (ATTTGCAT) by only 1 bp. The DQ beta gene octamer binds two proteins, one (B2) appears to be B cell specific while the other (B1) is not. These factors are either similar or identical to factors which bind to the octamer motif in immunoglobulin genes. All other class II MHC genes for which sequence information is available contain an octamer motif in their upstream region. Thus, the possibility that these sequences regulate B cell specific expression of class II MHC genes requires careful evaluation.

An octamer oligonucleotide upstream of a TATA motif is sufficient for lymphoid-specific promoter activity

The octamer sequence ATGCAAAT or its inverse complement ATTTGCAT is well-conserved in all immunoglobulin gene promoters and has been implicated in promoter function by deletion analysis. Although immunoglobulin promoters are tissue-specific, the octamer is also a functional element in non-tissue-specific upstream regions--like those controlling U1 and U2 small nuclear RNA and histone H2B genes--where it is associated with additional canonical elements. Specific interactions occur between the octamer motif and both lymphoid-specific and ubiquitous proteins. By using a synthetic octamer oligonucleotide inserted upstream of the beta-globin TATA box we show here that the octamer element by itself is sufficient for directing lymphocyte-specific RNA synthesis when within 70 base pairs of the start site of transcription. We also demonstrate that mutations in any position of the conserved motif interfere with this function.

Regulation of immunoglobulin gene transcription by labile repressor factor(s)

The cloned human gamma 1 heavy chain gene (HIG1) was scarcely expressed in the stable transformants of a mouse fibroblast line, L cell or a T cell line, EL4, and no gamma 1 heavy chain was produced in these cells. Upon treatment with cycloheximide or other kinds of protein synthesis inhibitors, the transcription of HIG1 gene was induced in L cell transformants as well as in T cell transformants. Transcription rate of bacterial gpt gene, which was derived from the plasmid vector used for transfection of HIG1 gene and located just upstream of HIG1 in the transformants, was also greatly enhanced after cycloheximide treatment. But the expression of several endogenous genes in the L cells tested was not affected by the cycloheximide treatment. Nuclear transcription assay indicated that the appearance of HIG1 gene transcripts after treatment with cycloheximide was mainly due to the induction of the transcription. Deletion of an enhancer element from HIG1 gene lowered the inducing activity of cycloheximide in the L cell transformants, but a low level of HIG1 gene expression was still observed. These results suggested that trans-acting factors similar to those present in B lymphoid cells are also functioning in non-B lymphoid cells but their activity is inhibited by short-lived repressor protein(s). Such repressor protein(s) appear to act on regulatory element(s) of the immunoglobulin heavy chain gene including enhancer region as well as 5' flanking region.

In vitro transcription of immunoglobulin genes in a B-cell extract: effects of enhancer and promoter sequences

Transfection experiments have led to the identification of three DNA sequences that are responsible for the tissue-specific expression of immunoglobulin genes. As a first step toward characterizing these regulatory phenomena at the biochemical level, we report the development of an in vitro transcription system from cells of the B lymphoid lineage. In these extracts, transcription of the MOPC41 kappa promoter is correctly initiated and dependent on the presence of an upstream sequence element located between -44 and -79 base pairs from the cap site. Second, although standard in vitro transcriptions are not affected by the presence or absence of enhancer sequences, we observed that the addition of polyethylene glycol led to a B-cell extract-specific suppression of transcription from a template that carries an immunoglobulin enhancer.

Interaction between two different regulatory elements activates the murine alpha A-crystallin gene promoter in explanted lens epithelia

Previous experiments have indicated that 5' flanking DNA sequences (nucleotides-366 to +46) are capable of regulating the lens-specific transcription of the murine alpha A-crystallin gene. Here we have analyzed these 5' regulatory sequences by transfecting explanted embryonic chicken lens epithelia with different alpha A-crystallin-CAT (chloramphenicol acetyltransferase) hybrid genes (alpha A-crystallin promoter sequences fused to the bacterial CAT gene in the pSVO-CAT expression vector). The results indicated the presence of a proximal (-88 to +46) and a distal (-111 to -88) domain which must interact for promoter function. Deletion experiments showed that the sequence between -88 and -60 was essential for function of the proximal domain in the explanted epithelia. A synthetic oligonucleotide containing the sequence between -111 and -84 activated the proximal domain when placed in either orientation 57 base pairs upstream from position -88 of the alpha A-crystallin-CAT hybrid gene.

The cis-acting regulatory elements of immunoglobulin heavy chain gene involved in enhanced immunoglobulin production after lipopolysaccharide (LPS) stimulation

In the present study, the transient expression of the human immunoglobulin heavy chain gene (HIG1) was analyzed in a mouse pre-B-cell line, 70Z/3, after LPS stimulation. HIG1 gene and its recombinant plasmids were transfected by the calcium phosphate method into 70Z/3 cells and the cells were stimulated with lipopolysaccharide (LPS) 48 hr after DNA transfection. The amounts of human heavy chain gene products greatly increased in 70Z/3 cells after LPS stimulation, but the increment was diminished by deletion of the heavy chain gene enhancer element (MluI-HpaI fragment) in the J-C intron from the HIG1 gene. The gene, delta 3, which contained the 5' promoter region and the rearranged VDJ region of HIG1 but lacked the enhancer element, was weakly transcribed in 70Z/3 cells after LPS stimulation. Insertion of the enhancer element into the delta 3 gene greatly enhanced the transcription of the VDJ gene. The highest enhancement of the VH gene transcription rate was obtained when the 3' half of the enhancer element was ligated to the delta 3 gene. The present data suggest that the 3' half of the enhancer element of the heavy chain gene may play an important role in the enhanced production of immunoglobulin which is induced with LPS stimulation.

Protein-nucleotide contacts in the immunoglobulin heavy-chain promoter region

Immunoglobulin heavy-chain variable-region genes contain the octanucleotide ATGCAAAT upstream from the site of transcription initiation. The complement of this sequence, in the reverse orientation, is found at an identical location in light-chain variable-region genes. This sequence element is thought to be involved in the lymphoid-specific expression of immunoglobulin genes. Analysis of nuclear extracts from both lymphoid and nonlymphoid cells in a gel migration inhibition assay, using an immunoglobulin promoter region fragment containing the octamer, reveals multiple migration-retarded species that represent specific DNA-protein complexes. The number and relative level of these complexes vary with cell type; some complexes are detected with all extracts, whereas one complex is lymphoid-specific and may represent an interaction involved in the lymphoid-restricted expression of immunoglobulin genes. Mitogenic stimulation of a B-lymphoid line can increase the level of the protein responsible for this lymphoid-specific complex. Analysis of the complexes detected in the gel migration inhibition assay by DNase I protection ("footprinting") has revealed that all of these DNA-protein complexes involve contact of the protein with the nucleotides of the octamer. One complex, present in both lymphoid and nonlymphoid cells, displays an additional DNA-protein contact adjacent to the octamer. Our results also indicate that the interaction of proteins with the octameric sequence can cause a local alteration in the structure of the DNA helix.

Dual tissue-specific expression of apo-AII is directed by an upstream enhancer

Apolipoprotein-AII (apo-AII) is one of a family of evolutionarily related proteins which play a crucial role in lipid transport and metabolism. The serum levels of human apo-AII have been shown to be inversely correlated to the incidence of coronary heart disease and its expression to be limited to the liver and intestine. Here we demonstrate that this dual tissue-specificity involves DNA sequences located in a 259 bp region centred 782 bp upstream from the transcription initiation site. These sequences function in an orientation-independent manner and are absolutely required for transcription from the apo-AII promoter. The regulatory region contains sequences which are homologous to the apo-AI, beta-globin and immunoglobulin gene promoters and to the immunoglobulin heavy-chain enhancer.

In vitro transcription of immunoglobulin genes in a B-cell extract: effects of enhancer and promoter sequences

Transfection experiments have led to the identification of three DNA sequences that are responsible for the tissue-specific expression of immunoglobulin genes. As a first step toward characterizing these regulatory phenomena at the biochemical level, we report the development of an in vitro transcription system from cells of the B lymphoid lineage. In these extracts, transcription of the MOPC41 kappa promoter is correctly initiated and dependent on the presence of an upstream sequence element located between -44 and -79 base pairs from the cap site. Second, although standard in vitro transcriptions are not affected by the presence or absence of enhancer sequences, we observed that the addition of polyethylene glycol led to a B-cell extract-specific suppression of transcription from a template that carries an immunoglobulin enhancer.

Cell type-specificity elements of the immunoglobulin heavy chain gene enhancer

A strong transcriptional enhancer was created by oligomerization of a short segment from the immunoglobulin heavy chain (IgH) enhancer. This segment was analyzed in parallel for biological activity in vivo and factor binding in vitro. In transfection experiments the oligomerized segment stimulates transcription in a cell type-specific manner similar to the entire IgH enhancer. Transfections of mutants identified two sequence motifs whose integrity is required for efficient and cell type-specific activity of this enhancer. The first is a sequence suggested previously to be bound by a factor in vivo, and the second is a highly conserved decanucleotide which also occurs in Ig variable gene promoters. The ability of these two sequence motifs to bind proteins in vitro was tested by band shift assays. Under our in vitro conditions we could not detect proteins binding to the in vivo footprint region. However, we found protein factors binding to the decanucleotide. A ubiquitous form of this factor is present in every cell line analyzed. Additional variants are detected exclusively in cells where the IgH enhancer and the segment thereof are active. Elimination of the decanucleotide motif is not only a strong down mutation in vivo but also abolishes binding of all factor variants in vitro. Thus our data suggest that the two enhancer motifs analyzed are involved in positive rather than negative control of transcription.

Interaction between two different regulatory elements activates the murine alpha A-crystallin gene promoter in explanted lens epithelia

Previous experiments have indicated that 5' flanking DNA sequences (nucleotides-366 to +46) are capable of regulating the lens-specific transcription of the murine alpha A-crystallin gene. Here we have analyzed these 5' regulatory sequences by transfecting explanted embryonic chicken lens epithelia with different alpha A-crystallin-CAT (chloramphenicol acetyltransferase) hybrid genes (alpha A-crystallin promoter sequences fused to the bacterial CAT gene in the pSVO-CAT expression vector). The results indicated the presence of a proximal (-88 to +46) and a distal (-111 to -88) domain which must interact for promoter function. Deletion experiments showed that the sequence between -88 and -60 was essential for function of the proximal domain in the explanted epithelia. A synthetic oligonucleotide containing the sequence between -111 and -84 activated the proximal domain when placed in either orientation 57 base pairs upstream from position -88 of the alpha A-crystallin-CAT hybrid gene.

Nuclear factors binding to the human immunoglobulin heavy-chain gene enhancer

The human immunoglobulin heavy chain (IgH) gene contains at least two tissue-specific regulatory regions, which are similar to the mouse IgH gene. One is the J-C enhancer and another is located in the 5' promoter region. Using an electrophoretic mobility shift assay and DNase I footprint, we have examined the interaction of factors in B cell nuclear extracts with the two regulatory regions of the human IgH gene. We have identified a nuclear factor in mouse B cell nuclear extracts which bound to specific sequence in the human IgH enhancer. This factor is apparently not present in mouse fibroblast nuclear extracts. We also found factor(s) which bound to the highly conserved octanucleotide sequence within the human IgH enhancer and 5' promoter regions.

Accessibility of the promoter sequence in the J-chain gene is regulated by chromatin changes during B-cell differentiation

The gene for the immunoglobulin M (IgM)-polymerizing protein, the J chain, is activated when the mature B cell is triggered to secrete pentamer IgM. Activation of the gene was found to be associated with chromatin changes in a 240-base-pair region at the 5' end of the gene. Analyses of lymphoid lines showed that the 5' region was resistant to nuclease digestion at the immature B-cell stage; it became slightly more accessible in mature B cells and cells at an early stage in the IgM response and then displayed an open, hypersensitive structure in IgM-secreting cells. In addition, analyses of normal, mitogen-stimulated lymphocytes showed that the open hypersensitive structure was coinducible with J-chain gene expression. These results suggest that the 5' chromatin changes precede transcription, making control sequences within the site accessible to regulatory factors.

Structural differences in a single gene encoding the V kappa Ser group of light chains explain the existence of two mouse light-chain genetic markers

Two phenotypic markers of mouse immunoglobulin kappa light chains, the IB-peptide marker and the Ef1a isoelectric focusing marker, are expressed by the C58/J, AKR/J, RF/J, and PL/J strains (called expressor strains) but not by BALB/c and most inbred strains. Expression is linked to the kappa light-chain locus and the Lyt-2/Lyt-3 genes on chromosome 6. Light chains bearing these markers belong to a group of variable region kappa chain (V kappa) regions called V kappa Ser, which has a serine amino terminus and a framework 1 region not observed to date among BALB/c light chains. Southern hybridization of genomic DNA with a V kappa Ser-specific cDNA probe has demonstrated a single strongly hybridizing DNA fragment in all strains of mice tested. Characteristic restriction enzyme polymorphisms define the V kappa Ser alleles of expressor (Igk-VSera) and nonexpressor (Igk-VSerb) strains. In the present study, the unrearranged V kappa Ser gene and its flanking regions from an expressor (C.C58) and nonexpressor (BALB/c) strain have been cloned and their nucleotide sequences determined. The C.C58 V kappa Ser gene isolated (the Igk-VSera allele) was shown to code for the two phenotypic markers described. While the nucleotide sequence of the BALB/c coding region (the Igk-VSerb allele) shows 97% identity with the C.C58 gene, single nucleotide substitutions lead to structural changes in the encoded protein which render it IB-negative and Ef1a-negative. These differences alone can explain the failure of strains containing the BALB/c allele to express these kappa-chain phenotypic markers. Also, the BALB/c gene contains a single substitution in a conserved octamer sequence approximately equal to 100 nucleotides upstream of the coding region, which could affect its expression. Finally, the C.C58 allele contains a BAM5/R repetitive DNA element approximately equal to 1200 nucleotides upstream of the coding regions that is not present in BALB/c. This element gives rise to the EcoRI and BamHI restriction enzyme polymorphisms, which distinguish the Igk-VSera and Igk-VSerb alleles.

The 5'-flanking sequences of the human growth hormone gene contain a cell-specific control element

The 5'-flanking sequences of the human growth hormone (hGH) gene contain a cell-specific control element. Hybrid genes containing truncated 5'-flanking DNA fragments from the hGH gene fused to the chloramphenicol acetyl transferase (cat) gene were examined using transient transfection of rat anterior pituitary (GC) and nonpituitary cell lines (HeLa, Rat 2, and KB); preferential expression of these gene hybrids was only observed in GC cells. Deletions through the 5'-flanking sequences of the hGH gene revealed that the region containing nucleotides -230 to -180 is required for efficient cat gene expression in GC cells. This region of DNA is highly homologous to a region of the rGH gene that contains a tissue-specific control element. A hybrid gene containing the tissue-specific control element, but lacking the proximal promoter elements, of the hGH gene upstream from the promoter of the thymidine kinase gene (TKp) from herpes simplex virus ligated to the cat gene produced more CAT activity than the TKp.cat gene in GC cells but not in HeLa cells. These data suggest that the tissue-specific control element located in the 5'-region of the hGH gene can act in the presence of a heterologous promoter and is specific for expression in pituitary cells.

Upstream regulatory sequences of immunoglobulin genes are recognized by nuclear proteins which also bind to other gene regions

The decanucleotide sequence (dc) TNATTTGCAT is an upstream regulatory sequence of immunoglobulin genes and occurs also upstream of certain other eukaryotic and prokaryotic genes (compiled in the accompanying paper). We now investigated the binding of proteins from nuclear extracts of a number of cell types and organisms to the dc sequence using a sensitive gel electrophoretic DNA binding assay. Binding studies with specifically designed oligonucleotides led to the following conclusions: the central T of the dc sequence can be altered with only a slight decrease of protein binding activity: the sequences in the neighborhood of dc have a positive or negative effect on the efficiency of protein binding; C-rich sequences which occur in many K chain promoters have a protein binding activity independent of dc; the dc binding protein(s) of human lymphoid cells elute from a Sephadex column in the 30.000-60.000 molecular weight range; dc binding proteins were found in nuclear extracts of lymphoid as well as non-lymphoid human and murine cell lines, of Xenopus oocytes, and of yeast cells. The finding of dc binding proteins in a wide variety of different organisms and the occurrence of dc-related sequences in the regulatory regions of several gene families point to a general role in the transcriptional regulation of the respective genes.

Sequences closely related to an immunoglobulin gene promoter/enhancer element occur also upstream of other eukaryotic and of prokaryotic genes

Decanucleotide sequences closely related to the TNATTTGCAT element which occurs upstream of the immunoglobulin genes and in the immunoglobulin gene enhancer were found also upstream of other eukaryotic and of prokaryotic genes. The possibility of evolutionary and functional relationships between the various transcriptional systems is discussed.

A model system for peptide hormone action in differentiation: interleukin 2 induces a B lymphoma to transcribe the J chain gene

Physiological levels of a purified T cell hormone, interleukin 2 (IL-2), were found to stimulate a cloned murine B cell line (BCL1) to secrete pentamer IgM antibody. The peptide hormone acts at the cell surface via specific IL-2 receptors and induces changes in the 5' chromatin of the J chain gene that correlate with its transcription and with the production of the J chain protein required for pentamer IgM assembly. There was no effect of IL-2 on cell proliferation nor on mu heavy chain gene transcription. These results define a specific function for IL-2 in B cell differentiation. In addition, the IL-2/BCL1 system provides a model for examining the mechanism by which signals generated by hormone-receptor interaction are transmitted to the nucleus and regulate gene expression.

Accessibility of the promoter sequence in the J-chain gene is regulated by chromatin changes during B-cell differentiation

The gene for the immunoglobulin M (IgM)-polymerizing protein, the J chain, is activated when the mature B cell is triggered to secrete pentamer IgM. Activation of the gene was found to be associated with chromatin changes in a 240-base-pair region at the 5' end of the gene. Analyses of lymphoid lines showed that the 5' region was resistant to nuclease digestion at the immature B-cell stage; it became slightly more accessible in mature B cells and cells at an early stage in the IgM response and then displayed an open, hypersensitive structure in IgM-secreting cells. In addition, analyses of normal, mitogen-stimulated lymphocytes showed that the open hypersensitive structure was coinducible with J-chain gene expression. These results suggest that the 5' chromatin changes precede transcription, making control sequences within the site accessible to regulatory factors.

Cell-type-specific transcription of an immunoglobulin kappa light chain gene in vitro

We have established a cell-free system, derived from a human B-cell lymphoma, in which immunoglobulin kappa light chain gene promoters are both accurately transcribed and regulated in a cell-type-specific manner. Thus, accurate transcription from the T1 kappa light chain gene promoter was much more efficient in B-cell extracts than in HeLa cell extracts, whereas control promoters (adenovirus major late and histone H2B) were transcribed equally well in either extract. More important, the increased kappa light chain gene transcription in B-cell extracts was dependent upon upstream sequences (containing the conserved decanucleotide element) previously shown to be necessary for B-cell-specific transcription in vivo; in contrast, removal of these sequences had no effect on the low level of kappa transcription in HeLa extracts. The maximal level of upstream sequence-mediated transcription was dependent upon template topology. These studies show that there is at least one B-cell-specific factor that stimulates transcription from purified DNA templates, and they further suggest that the in vivo action of the factor(s) on other components of the transcription machinery is direct rather than indirect (e.g., via the maintenance of an open chromatin structure). The cell-free system described here should facilitate both purification and functional studies of the B-cell-specific factor(s).

Functional analysis of the murine IgH enhancer: evidence for negative control of cell-type specificity

We have carried out a mutational analysis of the mouse IgH enhancer. Consistent with previous reports, deletions extending from either the 5' side or the 3' side of the enhancer fail to reveal distinct boundaries which define enhancer function in lymphoid cells. Interestingly, internal point mutations and deletions within the "enhancer core" regions fail to identify any necessary functional role for these conserved elements. When tested in CV1 cells, which do not normally respond to the IgH enhancer, certain deletions exhibit significant enhancer activity. We take these findings to indicate that the functional domains of the IgH enhancer are complex and that cell type specificity is defined in part by negative factors present in non-lymphoid cells.

A lymphoid-specific protein binding to the octamer motif of immunoglobulin genes

Immunoglobulin gene promoters are active only in lymphoid cells and this tissue-specific activity requires an octamer sequence, ATTTGCAT. Paradoxically, this same octamer motif seems to be a transcriptional control element in promoters which are active in all tissues. Using an electrophoretic mobility shift assay to identify DNA binding proteins, we have now detected two species of nuclear proteins which bind specifically to this octamer. One previously characterized form (NF-A1) was found in all cell lines tested while the other form (NF-A2) was restricted to lymphoid cell lines. NF-A2 was found in cell lines representing all stages of B-cell differentiation and in half of the T-lymphoma cell lines tested. The identification of a lymphoid-specific octamer binding protein may account for the lymphoid-specific activity of immunoglobulin promoters.

Interaction of cell-type-specific nuclear proteins with immunoglobulin VH promoter region sequences

All human and murine immunoglobulin heavy chain variable region (VH) genes contain the sequence ATGCAAAT approximately 70 nucleotides 5' from the site of transcription initiation. This octanucleotide, in reverse orientation, is also found in all light chain variable region (VL) genes, and in the immunoglobulin heavy chain transcriptional enhancer. Transfection studies have established that this octamer is involved in the lymphoid-specific transcription of immunoglobulin genes. Octamer-containing fragments have been reported to bind a factor present in nuclear extracts of human cell lines; however, identical binding activity was detected in both B lymphoid and non-lymphoid cells. Here we establish that nuclear extracts from distinct cell types differ in their ability to interact with octamer-containing fragments. We have also detected a DNA-protein interaction that may be involved in the cell-type specificity of immunoglobulin expression, and we have determined that a sequence upstream of the octamer participates in an interaction with a nuclear protein(s).

Multiple nuclear factors interact with the immunoglobulin enhancer sequences

To characterize proteins that bind to the immunoglobulin (Ig) heavy chain and the kappa light chain enhancers, an electrophoretic mobility shift assay with end-labeled DNA fragments was used. Three binding proteins have been found. One is NF-A, a factor found in all tested cell types that binds to the octamer sequence found upstream of all Ig variable region gene segments and to the same octamer in the heavy chain enhancer. The second, also ubiquitous, protein binds to a sequence in both the heavy chain and the kappa enhancers that was previously shown to be protected from methylation in vivo. Other closely related sites do not compete for this binding, implying a restriction enzyme-like binding specificity. The third protein binds to a sequence in the kappa enhancer (and to an identical sequence in the SV40 enhancer) and is restricted in its occurrence to B cells.

B-lymphocyte targeting of gene expression in transgenic mice with the immunoglobulin heavy-chain enhancer

A hybrid gene containing rabbit beta-globin structural sequences (-9 to +1650), and a chicken conalbumin gene promoter (+62 to -102) in the place of the beta-globin promoter (upstream from -9), was inactive in 5 different transgenic mouse line. Adding the mouse immunoglobulin heavy-chain (IgH) enhancer to this construction specifically stimulated expression in B-cells. These results show that IgH enhancer is specifically active in B-cells. Expression of the hybrid gene was low compared to the endogenous immunoglobulin heavy and light-chain genes. Substituting the mouse immunoglobulin kappa light-chain gene (Ig kappa) promoter (+4 to -800) for the heterologous conalbumin promoter was not sufficient to restore gene expression to level of the endogenous genes. In addition to the reproducible B cell expression, we also found inheritable unexpected expression in certain tissues, which varied from line to line.

Organization and evolution of variable region genes of the human immunoglobulin heavy chain

We have isolated 23 different cosmid clones of the heavy-chain variable region genes (VH) of human immunoglobulin. These clones encompass about 1000 X 10(3) base-pairs of DNA containing 61 VH genes. Characterization of the 23 clones by Southern blot hybridization showed that VH genes belonging to different families were physically linked in many regions. Cluster 71, which was analyzed in detail, comprised seven VH segments arranged in the same orientation with different intervals. This clone contained internal homology regions, each carrying two VH segments of different families. Comparison of the nucleotide sequences of VH segments within each family showed that profiles of accumulation of mutations in framework (FR) and complementarity-determining (CDR) regions were different. CDR had more mutations at amino-acid-substituting positions than at silent positions, whereas FR had the reverse distribution of mutations. Five out of seven VH segments of this cluster were pseudogenes containing various mutations. VH pseudogenes were classified into two distinct groups; one with a few replacement mutations (conserved pseudogenes), and the other with rather extensive mutations (diverged pseudogenes). The possibility that conserved pseudogenes serve as a reservoir of VH segments is discussed.

Synergism between immunoglobulin enhancers and promoters

Enhancers are DNA sequences that stimulate transcription from eukaryotic promoters. This stimulatory effect can be exerted over large distances and from a position either 5' or 3' of a promoter. Enhancers have been found in the genomes of many viruses, and in some cellular genes such as those encoding immunoglobulin heavy chain and kappa light chain. An important feature of both viral and cellular enhancers is the ability of each enhancer to stimulate transcription from many promoters other than the one with which it is found associated. However, the question of whether cellular enhancers stimulate their 'own' promoter more efficiently than other promoters has apparently not been investigated. We show here that the kappa light-chain enhancer stimulates a kappa promoter about 20-fold more than it stimulates either the simian virus 40 (SV40) early promoter or a metallothionein (MT) promoter, two promoters that are very sensitive to other enhancers. Similarly, the heavy-chain enhancer stimulates a heavy-chain promoter much more than it stimulates the SV40 and MT promoters. This synergism between immunoglobulin enhancers and promoters might be due to the action of a protein that binds specifically to each of the regulatory elements.

Tandem kappa immunoglobulin promoters are equally active in the presence of the kappa enhancer: implications for models of enhancer function

Transcription of immunoglobulin kappa genes is regulated by enhancer and promoter elements, both of which function in a tissue-specific fashion. We have studied the interaction of these elements by transfecting plasmacytoma cells with genes that have tandem kappa promoters located next to a single kappa enhancer and assaying these genes for transient or stable transcription. We find that the promoters located proximal and distal to the enhancer function identically whether they are separated by 440 bp or by 2.7 kb or whether they are located 1.7 or 7.7 kb away from the enhancer. Our results indicate that the immunoglobulin kappa enhancer does not operate as a bidirectional entry site for RNA polymerase or for other factors associated with the transcription complex. Rather, they suggest that the enhancer exerts its influence uniformly over large distances and independently of the presence of intervening promoters.