RESUMEN
Plasma cells are cellular factories devoted entirely to the manufacture and export of a single product: soluble immunoglobulin (Ig). As the final mediators of a humoral response, plasma cells play a critical role in adaptive immunity. Although intense effort has been devoted to studying the regulation and requirements for early B cell development, little information has been available on plasma cells. However, more recent work-including studies on genetically altered mice and data from microarray analyses-has begun to identify the regulatory cascades that initiate and maintain the plasma cell phenotype. This review will summarize our current understanding of the molecules that regulate commitment to a plasma cell fate and those that mediate plasma cell function.
Asunto(s)
Linfocitos B/inmunología , Células Plasmáticas/inmunología , Animales , Antígenos de Diferenciación de Linfocitos B/metabolismo , Diferenciación Celular , Linaje de la Célula , Inmunoglobulinas/biosíntesis , Memoria Inmunológica , Ratones , Modelos Inmunológicos , Receptores de Quimiocina/metabolismo , Bazo/inmunología , Factores de Transcripción/fisiologíaRESUMEN
Representational difference analysis (RDA) cloning has identified transcriptional intermediary factor 1 beta (TIF1beta) as a gene inducibly expressed early during myeloid differentiation of the promyelocytic cell lines HL-60 and U937. To assess the role of TIF1beta, U937 cell lines were made that expressed antisense-hammerhead ribozymes targeted specifically against TIF1beta mRNA. These cells failed to differentiate into macrophages, as determined by several criteria: a nonadherent morphology, a failure to arrest cell cycle, lowered levels of macrophage-specific cell surface markers, resistance to Legionella pneumophila infection, a loss of the ability to phagocytose and chemotax, and decreased expression of chemokine mRNAs. One way TIF1beta acts in macrophage differentiation is to augment C/EBPbeta transcriptional activity. Furthermore, we show by EMSA supershifts and coimmunoprecipitation that C/EBPbeta and TIF1beta physically interact. Although TIF1beta is necessary for macrophage differentiation of U937 cells, it is not sufficient, based on the inability of ectopically expressed TIF1beta to induce or augment phorbol ester-induced macrophage differentiation. We conclude that TIF1beta plays an important role in the terminal differentiation program of macrophages, which involves the coactivation of C/EBPbeta and induction of C/EBPbeta-responsive myeloid genes.
Asunto(s)
Proteína beta Potenciadora de Unión a CCAAT/metabolismo , Proteínas de Unión al ADN/metabolismo , Proteínas de Unión al ADN/fisiología , Proteínas Represoras/metabolismo , Proteínas Represoras/fisiología , Sitios de Unión , Northern Blotting , Western Blotting , Ciclo Celular/efectos de los fármacos , Diferenciación Celular , Línea Celular , Núcleo Celular/metabolismo , Separación Celular , Quimiocina CCL5/metabolismo , Relación Dosis-Respuesta a Droga , Citometría de Flujo , Células HL-60 , Humanos , Legionella pneumophila/metabolismo , Macrófagos/citología , Macrófagos/metabolismo , Fagocitosis , Plásmidos/metabolismo , Pruebas de Precipitina , Unión Proteica , ARN Catalítico/metabolismo , ARN Mensajero/metabolismo , Retroviridae/genética , Ribonucleasas/metabolismo , Transcripción Genética , Transducción Genética , Transfección , Proteína 28 que Contiene Motivos Tripartito , Células U937RESUMEN
Blimp-1 is a transcriptional repressor that is both required and sufficient to trigger terminal differentiation of B lymphocytes and monocyte/macrophages. Here we report the organization of the mouse Blimp-1 gene, an analysis of Blimp-1 homologs in different species, the characterization of Blimp-1 mRNA isoforms and initial studies on the transcription of Blimp-1. The murine Blimp-1 gene covers approximately 23 kb and contains eight exons. There are Blimp-1 homologs in species evolutionarily distant from mouse (Caenorhabditis elegans and Drosophila melanogaster) but no homolog was found in the unicellular yeast Saccharomyces cerevisiae. The three major Blimp-1 mRNA isoforms result from the use of different polyadenylation sites and do not encode different proteins. Run-on transcription analyses were used to show that the developmentally regulated expression of Blimp-1 mRNA in B cells is determined by transcription initiation. Multiple Blimp-1 transcription initiates sites were mapped near an initiator element and a region conferring basal promoter activity has been identified.
Asunto(s)
Empalme Alternativo/genética , Regiones Promotoras Genéticas/genética , Proteínas Represoras , Factores de Transcripción/genética , Secuencia de Aminoácidos , Animales , Linfocitos B/citología , Linfocitos B/metabolismo , Secuencia de Bases , Diferenciación Celular , Línea Celular , Clonación Molecular , ARN Polimerasas Dirigidas por ADN/metabolismo , Evolución Molecular , Exones/genética , Regulación del Desarrollo de la Expresión Génica , Genes Reporteros/genética , Humanos , Ratones , Datos de Secuencia Molecular , Ensayos de Protección de Nucleasas , Poli A/genética , Factor 1 de Unión al Dominio 1 de Regulación Positiva , Isoformas de Proteínas/genética , ARN Mensajero/análisis , ARN Mensajero/genética , TATA Box/genética , Factores de Transcripción/química , Transcripción Genética/genética , TransfecciónRESUMEN
The importance of CCAAT/enhancer binding proteins (C/EBPs) and binding sites for HIV-1 replication in primary macrophages, T cell lines and primary CD4(+) T cells was examined. When lines overexpressing the C/EBP dominant-negative protein LIP were infected with HIV-1, replication occurred in Jurkat T cells but not in U937 promonocytes, demonstrating a requirement for C/EBP activators by HIV-1 only in promonocytes. Primary macrophages did not support the replication of HIV-1 harboring mutant C/EBP binding sites in the long terminal repeat but Jurkat, H9 and primary CD4(+) T cells supported replication of wild-type and mutant HIV-1 equally well. Thus the requirement for C/EBP sites is also confined to monocyte/macrophages. The requirement for C/EBP proteins and sites identifies the first uniquely macrophage-specific regulatory mechanism for HIV-1 replication.
Asunto(s)
Linfocitos T CD4-Positivos/virología , Proteínas de Unión al ADN/fisiología , VIH-1/fisiología , Macrófagos/virología , Proteínas Nucleares/fisiología , Replicación Viral , Sitios de Unión/inmunología , Proteínas Potenciadoras de Unión a CCAAT , Antígenos CD4 , Linfocitos T CD4-Positivos/inmunología , Humanos , Células Jurkat , Macrófagos/inmunología , Especificidad de ÓrganosRESUMEN
Previous work has shown that C/EBP sites and C/EBP transcriptional activators are necessary for HIV-1 LTR activity in monocytes/macrophages. We have investigated the role that C/EBP proteins play in induction and replication of HIV-1. Ectopic expression of the dominant negative C/EBP protein LIP inhibited HIV-1 mRNA and virus production in activated U1 cells, demonstrating that C/EBP proteins are required for provirus induction. U1 lines overexpressing C/EBP activator NF-IL-6 produced more viral mRNA and virus particles following cellular activation than control lines, demonstrating that C/EBP proteins are limiting for virus transcription. HIV-1 harboring mutations within two C/EBP sites were crippled in their ability to replicate in U937 promonocytic cells, indicating that these sites are required for replication. These data identify C/EBP proteins as regulators of HIV-1 expression in monocytes/macrophages.
Asunto(s)
Proteínas de Unión al ADN/biosíntesis , VIH-1/fisiología , Monocitos/virología , Proteínas Nucleares/biosíntesis , Provirus/crecimiento & desarrollo , Factores de Transcripción/biosíntesis , Activación Viral/inmunología , Replicación Viral/inmunología , Antivirales/farmacología , Secuencia de Bases , Proteína delta de Unión al Potenciador CCAAT , Proteínas Potenciadoras de Unión a CCAAT , Proteínas de Unión al ADN/genética , Humanos , Linfoma de Células B Grandes Difuso/genética , Linfoma de Células B Grandes Difuso/virología , Datos de Secuencia Molecular , Proteínas Nucleares/genética , Factores de Transcripción/farmacología , Transcripción Genética/inmunología , Células Tumorales Cultivadas , Virión/efectos de los fármacosRESUMEN
Three binding sites for C/EBP proteins are found in the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) (V. M. Tesmer, A. Rajadhyaksha, J. Babin, and M. Bina, Proc. Natl. Acad. Sci. USA 90:7298-7302, 1993). We have determined the functional role of C/EBP proteins and C/EBP sites in regulating transcription from the HIV-1 LTR in monocytes/macrophages. Inhibition of endogenous C/EBP proteins, using either an excess of C/EBP binding sites or a trans-dominant negative inhibitor, demonstrated that C/EBP proteins are required for basal and activated levels of HIV-1 LTR transcription in the promonocytic cell line U937. Northern (RNA) blots and binding assays showed that NF-IL6 is the only known C/EBP family member which is increased when U937 cells are activated. Mutational analyses of the HIV-1 LTR showed that one C/EBP site is required for normal LTR transcription both before and after cellular activation and that the two 3' C/EBP sites are functionally equivalent. However, transcription from crippled HIV-1 LTRs lacking C/EBP sites can still be induced following activation of U937 cells. Several models are suggested for how elevated NF-IL6 may participate in an autostimulatory loop involving HIV infection, macrophage activation, cytokine expression, and HIV replication.
Asunto(s)
Proteínas de Unión al ADN/metabolismo , Regulación Viral de la Expresión Génica , Duplicado del Terminal Largo de VIH , VIH-1/metabolismo , Proteínas Nucleares/metabolismo , Secuencia de Bases , Sitios de Unión , Proteínas Potenciadoras de Unión a CCAAT , Diferenciación Celular , Línea Celular , Cloranfenicol O-Acetiltransferasa/biosíntesis , Cartilla de ADN , Expresión Génica , VIH-1/genética , Humanos , Lipopolisacáridos/farmacología , Luciferasas/biosíntesis , Macrófagos/metabolismo , Macrófagos/virología , Datos de Secuencia Molecular , Monocitos/metabolismo , Monocitos/virología , Reacción en Cadena de la Polimerasa , Proteínas Recombinantes/biosíntesis , Mapeo Restrictivo , Factores de Transcripción/metabolismo , Transcripción Genética , TransfecciónRESUMEN
c-Abl, a nonreceptor tyrosine kinase, appears to play a role in cell cycle progression, cell proliferation and differentiation. Mice homozygous for a mutation in c-abl (ablml), show pleiotropic abnormalities, including neonatal death, developmental defects, susceptibility to infection and dehydration (Schwartzberg et al., 1991). However, the exact substrates of c-Abl and the signal transduction pathways it might initiate are not known. We have examined how c-Abl affects c-myc expression by studying ablml mice. Quantitative riboprobe analyses demonstrated that in the heart, liver, thymus, brain, testes, intestines and lung, there were no differences in the steady-state level of c-myc RNA between the ablml mice and littermate controls. However, in adrenal glands, kidneys and splenic B cells, c-myc RNA levels were decreased approximately 50% compared to littermate controls. Induction of c-myc mRNA following activation of splenic B cells with LPS is also defective in ablml splenocytes. Finally, we show that c-Abl can directly transactivate c-myc transcription. These results suggest that c-Abl is involved in the normal transcription regulation of c-myc in selected tissues and that decreased c-myc RNA could be one cause of abnormalities in the ablml mice.
Asunto(s)
Genes myc , Proteínas Proto-Oncogénicas c-abl/fisiología , Glándulas Suprarrenales/metabolismo , Animales , Ciclo Celular , Regulación de la Expresión Génica , Genes abl , Riñón/metabolismo , Activación de Linfocitos , Ratones , Ratones Mutantes , Regiones Promotoras Genéticas , ARN Mensajero/metabolismo , Transducción de Señal , Bazo/metabolismo , Distribución TisularRESUMEN
In this article, we consider basic principles of eukaryotic gene transcriptional regulation which have emerged from studies on immunoglobulin heavy chain and kappa chain genes. Four areas are considered: (1) regulation by distant enhancer elements, (2) multiple regulators in a given element including particular families of regulators which were discovered by studying Ig genes, (3) achieving tissue specificity of transcription by multiple mechanisms and (4) the importance of chromatin structure for transcriptional regulation.
Asunto(s)
Regulación de la Expresión Génica , Genes de Inmunoglobulinas , Transcripción Genética , Animales , HumanosRESUMEN
The importance of C/EBP proteins in B cell biology is suggested by the occurrence of functionally important C/EBP binding sites in Ig gene enhancers and promoters, and the knowledge that family member NF-IL-6 is induced in other systems in response to regulators of B cell differentiation. We have studied the expression pattern and activity of C/EBP family transcriptional regulators in B cells at different developmental stages by using B cell lines and normal splenic B cells. Two family members, Ig/EBP and NF-IL-6, seem to be the major regulators of C/EBP site-dependent transcriptional activity in B cells. Negative regulator Ig/EBP is predominantly present in early B cells; activator NF-IL-6 increases in more mature B cells and is induced by LPS activation of splenic B cells. LIP, an N-terminally truncated form of NF-IL-6, was found in most B cell lines tested; LIP can act as a weak transcriptional activator in B cell lines. Partly as a result of the differential amounts of C/EBP family proteins, C/EBP sites do not function as activator sites in early B cells but are activator sites in terminally differentiated B cells.
Asunto(s)
Linfocitos B/inmunología , Proteínas de Unión al ADN/biosíntesis , Proteínas Nucleares/biosíntesis , Factores de Transcripción/biosíntesis , Animales , Western Blotting , Proteínas Potenciadoras de Unión a CCAAT , Diferenciación Celular/fisiología , Línea Celular , Regulación hacia Abajo/inmunología , Femenino , Cadenas Pesadas de Inmunoglobulina/biosíntesis , Lipopolisacáridos/inmunología , Ratones , Ratones Endogámicos , ARN Mensajero/biosíntesis , Bazo/citología , Transfección/genética , Regulación hacia Arriba/inmunologíaRESUMEN
Three high-affinity binding sites for the GATA family of transcriptional regulators have been identified within the T-cell receptor beta-chain (TCR beta) transcriptional enhancer, and their functional significance has been determined in an effort to understand the T-cell specificity of the enhancer more fully. One site, TE4, is important for activity of the enhancer in T cells. Neither site TE1 nor site TE2 can functionally replace a mutated TE4 site in T cells; however, the same protein, probably GATA-3, binds all three sites, as judged by electrophoretic mobility shift, oligonucleotide competition, and proteolytic clipping assays. These data suggest that additional proteins are critical for the ability of GATA-3 to activate the TCR beta enhancer. In fibroblasts, the GATA sequence at site TE1 appears to bind a negative regulator. Since this is not true in B cells, B cells and fibroblasts appear to have different mechanisms for negative regulation of the TCR beta enhancer.
Asunto(s)
Proteínas de Unión al ADN/metabolismo , Elementos de Facilitación Genéticos , Expresión Génica , Receptores de Antígenos de Linfocitos T alfa-beta/biosíntesis , Receptores de Antígenos de Linfocitos T alfa-beta/genética , Linfocitos T/metabolismo , Transactivadores/metabolismo , Factores de Transcripción/metabolismo , Animales , Secuencia de Bases , Sitios de Unión , Línea Celular , Núcleo Celular/metabolismo , Cloranfenicol O-Acetiltransferasa/biosíntesis , Cloranfenicol O-Acetiltransferasa/metabolismo , Cartilla de ADN , Factor de Transcripción GATA3 , Ratones , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Oligodesoxirribonucleótidos , Reacción en Cadena de la Polimerasa , Linfocitos T/inmunología , Transcripción Genética , TransfecciónRESUMEN
A combination of site-directed mutagenesis and exon exchange has been used to further define the structure on IgG recognized by monoclonal IgM rheumatoid factors (RFs) from patients with Waldenstrom macroglobulinemia. Most of these RFs bound IgG1, -2, and -4 but not IgG3. For these RFs, His-435 is a critical residue for binding and replacing it with arginine, the residue present in IgG3, destroys or reduces RF binding. However, additional polymorphic sequences in both the heavy-chain constant-region domains (CH) 2 and 3 are important for RF binding. Among the important residues in CH2 are amino acids 252-254 and 309-311, which are conserved among IgG isotypes and comprise two loops of amino acids on the surface of the domain. Therefore, at least three regions, two from CH2 and one from CH3, contribute significantly to the epitope recognized by the RFs. Although this epitope contains many of the same residues as the staphylococcal protein A binding site on IgG, the binding specificities of staphylococcal protein A and monoclonal RFs are not identical. Sera from patients with rheumatoid arthritis contain antibodies directed not only at this epitope but also at other sites on IgG.
Asunto(s)
Epítopos , Inmunoglobulina G/inmunología , Inmunoglobulina M/metabolismo , Factor Reumatoide/metabolismo , Secuencia de Aminoácidos , Anticuerpos Antiidiotipos/metabolismo , Anticuerpos Antiidiotipos/ultraestructura , Anticuerpos Monoclonales/metabolismo , Anticuerpos Monoclonales/ultraestructura , Reacciones Antígeno-Anticuerpo , Sitios de Unión de Anticuerpos , Gráficos por Computador , Análisis Mutacional de ADN , Humanos , Inmunoglobulina G/genética , Inmunoglobulina G/ultraestructura , Cadenas Pesadas de Inmunoglobulina/química , Cadenas Pesadas de Inmunoglobulina/inmunología , Modelos Moleculares , Datos de Secuencia Molecular , Unión Proteica , Conformación Proteica , Factor Reumatoide/ultraestructura , Relación Estructura-ActividadRESUMEN
To localize regions on IgG bound by rheumatoid factors (RF), we studied IgM RF binding to chimeric IgG antibodies consisting of murine V regions fused to human constant regions. Using a modified RF ELISA, we showed that polyclonal RF from rheumatoid arthritis patients bound IgG1, 2, and 4 strongly; IgG3 was also bound, although less well. The majority of 18 monoclonal RF from patients with Waldenstrom's macroglobulinemia bound IgG1, 2, and 4 only. In contrast to RF from RA, 14 of 18 monoclonal RF did not react with IgG3. Only 3 of 18 monoclonal RF bound IgG3 well. By shuffling C region domains between IgG3 and IgG4, we showed that sequence variation in the CH3 domain is responsible for the differential binding of monoclonal RF to IgG3 and IgG4. Hybrid IgG3/IgG4 antibodies containing the CH3 domain of IgG4 were bound by monoclonal RF, whereas those containing the CH3 domain of IgG3 were not. To evaluate the contribution of the N-linked carbohydrate moiety at Asn-297 to RF binding sites on IgG, we measured RF binding to aglycosylated IgG antibodies produced by mutating Asn-297 to another amino acid. Glycosylated and aglycosylated IgG1, 2, and 4 were bound identically by monoclonal and polyclonal RF. Aglycosylated IgG3, however, was bound better than glycosylated IgG3 by polyclonal RF and by IgG3-reactive monoclonal RF.
Asunto(s)
Inmunoglobulina G/metabolismo , Inmunoglobulina M/metabolismo , Factor Reumatoide/metabolismo , Animales , Anticuerpos Monoclonales/metabolismo , Especificidad de Anticuerpos , Artritis Reumatoide/inmunología , Compuestos de Dansilo/metabolismo , Ensayo de Inmunoadsorción Enzimática , Epítopos/química , Glicosilación , Haptenos/metabolismo , Humanos , Cadenas Pesadas de Inmunoglobulina/metabolismo , Isotipos de Inmunoglobulinas/metabolismo , Ratones , Mutagénesis Sitio-Dirigida , Proteínas Recombinantes de Fusión/metabolismo , Macroglobulinemia de Waldenström/inmunologíaRESUMEN
Genomic footprinting studies in vivo and experiments using synthetic metal regulatory elements (MREs) in vitro suggest protein binding to the MREs of the mouse and rat metallothionein I (MT-I) genes. Using gel-retardation assays of promoter fragments, we observe a cadmium-dependent binding factor for the rat MT-I promoter in rat hepatoma cells. This factor is present in extracts from both uninduced and cadmium-induced cells, but requires the presence of cadmium to bind to the promoter. The formation of a cadmium-dependent complex is competed by an oligonucleotide containing two MREs. This competition is lost when when one of the MREs is mutated, indicating a requirement for at least two MREs for binding of this factor. The cadmium-dependent factor dissociates more rapidly from the MT-I promoter than does a factor that binds to a consensus Sp1 site present on the same DNA fragment. UV crosslinking analysis using nuclear extracts from cadmium induced cells, in the presence of an oligonucleotide probe containing both 5-bromodeoxyuridine and 32P-deoxycytidine, identifies a 39 kDalton protein associated with the metal inducible complex.
Asunto(s)
Cadmio/farmacología , Núcleo Celular/metabolismo , Metalotioneína/genética , Proteínas Nucleares/metabolismo , Regiones Promotoras Genéticas , Factores de Transcripción/metabolismo , Animales , Secuencia de Bases , Sitios de Unión , Línea Celular , Neoplasias Hepáticas Experimentales , Datos de Secuencia Molecular , Sondas de Oligonucleótidos , Regiones Promotoras Genéticas/efectos de los fármacos , Ratas , Mapeo Restrictivo , Transcripción Genética , Rayos UltravioletaRESUMEN
A potential new therapeutic approach to control gene expression is the use of double-stranded (ds) oligodeoxyribonucleotides (oligos) to compete for the binding of nuclear factors to specific promoter and enhancer elements. As a model, we have tested the effect of oligo length, sequence and number of nuclear factor binding sites on in vitro transcription of adenovirus (Ad)E1b. Short ds oligos containing an SP1-binding sequence (sp1) inhibited transcription of E1b by more than 90%. Oligos containing multiple sp1 sequences were more effective inhibitors than would be expected for a comparable number of unlinked sp1 sites. A ds oligo with phosphorothioate (PS) linkages inhibited transcription at one-tenth the concentration needed for its normal homologue. An oligo with sp1 and a consensus TATA site was no more effective than one with sp1 alone. The stability of the PS-linked oligos will allow testing of this approach in vivo if they are adequately incorporated into whole cells.
Asunto(s)
Elementos de Facilitación Genéticos , Oligodesoxirribonucleótidos/farmacología , Regiones Promotoras Genéticas , Transcripción Genética/efectos de los fármacos , Composición de Base , Secuencia de Bases , Sitios de Unión , Unión Competitiva , Expresión Génica/efectos de los fármacos , Datos de Secuencia Molecular , ARN/genética , ARN sin Sentido , ARN Mensajero/antagonistas & inhibidores , Mapeo RestrictivoRESUMEN
Recently, many of the proteins involved in transcriptional regulation of immunoglobulin genes have been identified, purified and their cDNAs cloned. This detailed molecular information has revealed fascinating similarities among different classes of DNA-binding proteins and has dramatically expanded the number of potential mechanisms for achieving precise tissue- and developmental stage-specific immunoglobulin transcription.
Asunto(s)
Genes de Inmunoglobulinas , Factores de Transcripción/genética , Transcripción Genética , Linfocitos B/metabolismo , Regulación de la Expresión Génica , Regiones Promotoras GenéticasRESUMEN
We have begun to purify and characterize several proteins which bind to the mouse immunoglobulin heavy-chain enhancer to understand the molecular interactions important for enhancer activity. Three proteins which bind to different sites on the immunoglobulin heavy-chain enhancer have been chromatographically separated and partially purified. One protein binds a site which has not been reported previously and does not bind to other reported protein-binding sites on the immunoglobulin heavy-chain enhancer. Binding-site boundaries for the three partially purified proteins have been precisely mapped by methylation interference, DNase I footprinting, and orthophenanthroline/copper chemical nuclease footprinting. We have also characterized these three proteins with respect to dissociation rate constants.
Asunto(s)
Proteínas de Unión al ADN/metabolismo , Elementos de Facilitación Genéticos , Cadenas Pesadas de Inmunoglobulina/genética , Animales , Secuencia de Bases , Sitios de Unión , Núcleo Celular/análisis , Cromatografía Líquida de Alta Presión , Cobre , ADN/metabolismo , Proteínas de Unión al ADN/aislamiento & purificación , Desoxirribonucleasa I , Electroforesis en Gel de Poliacrilamida , Indicadores y Reactivos , Metilación , Ratones , Datos de Secuencia Molecular , Fenantrolinas , Plasmacitoma/análisis , Unión ProteicaRESUMEN
Seven protein-binding sites on the immunoglobulin heavy-chain (IgH) enhancer element have been identified by exonuclease III protection and gel retardation assays. It appears that the seven sites bind a minimum of four separate proteins. Three of these proteins also bind to other enhancers or promoters, but one protein seems to recognize exclusively IgH enhancer sequences. A complex of four binding sites, recognized by different proteins, is located within one 80-base-pair region of IgH enhancer DNA. Close juxtaposition of enhancer proteins may allow protein-protein interactions or be part of a mechanism for modulating enhancer protein activity. All IgH enhancer-binding proteins identified in this study were found in extracts from nonlymphoid as well as lymphoid cells. These data provide the first direct evidence that multiple proteins bind to enhancer elements and that while some of these proteins recognize common elements of many enhancers, others have more limited specificities.
Asunto(s)
Proteínas de Unión al ADN/metabolismo , Elementos de Facilitación Genéticos , Genes Reguladores , Cadenas Pesadas de Inmunoglobulina/genética , Proteínas de Neoplasias/metabolismo , Animales , Secuencia de Bases , Sitios de Unión , Línea Celular , Enzimas de Restricción del ADN , Ratones , Plasmacitoma/inmunología , Unión ProteicaRESUMEN
We examined the chromatin structure of the rat metallothionein I gene, both in uninduced cells and in cells induced by heavy metals or dexamethasone, using hypersensitivity to DNase I as an assay. The metallothionein I gene of the H4IIE rat hepatoma cell line, expressed at basal level, has a single DNase I-hypersensitive site. This site maps between putative hormone and basal level control sequences. Induction of the gene by cadmium or zinc resulted in the appearance of a new hypersensitive site near the start site of transcription, in a region near the metal-regulatory elements. In contrast, induction of the metallothionein I gene by dexamethasone did not alter the basal pattern of hypersensitivity. Thus, different mechanisms of induction of metallothionein transcription lead to distinct alterations in the chromatin containing the 5' sequences regulating the expression of this gene.
Asunto(s)
Cromatina/ultraestructura , Genes , Metalotioneína/genética , Animales , Células Cultivadas , Desoxirribonucleasa I/metabolismo , Dexametasona/farmacología , Regulación de la Expresión Génica , Neoplasias Hepáticas Experimentales/genética , Metales/farmacología , Peso Molecular , RatasRESUMEN
Analysis of immunoglobulin gene rearrangements in 16 B-cell lineages clonally propagated from two mononucleosis patients supported the notion that mononucleosis is a polyclonal B-lymphoproliferative disorder. Three of seven cell clones from a patient with a fatal B lymphoma revealed the same pattern of immunoglobulin gene rearrangement, indicating that this patient's disease was oligoclonal. The three similar clones were propagated from two sites (blood and spleen), indicating that they represent a metastatic cell lineage which arose during the patient's fatal B lymphoproliferation.