Decreased E12 and/or E47 Transcription Factor Activity in the Bone Marrow As Well As in the Spleen of Aged Mice1 (original) (raw)
Experimental Gerontology, 2004
We have investigated the effects of aging on the E2A-encoded transcription factor E47, a key regulator of B cell functions, in B cell precursors and in splenic B cells. Here, we show that old mice can be classified as severely depleted, moderately depleted or not depleted mice, according to the percentage of pre-B cells in their bone marrow. IL-7-expanded populations of pro-B/early pre-B cells from bone marrow of both severely depleted and moderately depleted old mice exhibit a reduced E47 DNA-binding and expression compared to young mice, and this defect in severely depleted old mice is more dramatic than that in moderately depleted old mice. However, mRNA levels were comparable, suggesting that E47 in the bone marrow is not transcriptionally regulated. In the spleen, activated B cells from both severely depleted and moderately depleted old mice show a lower E47 DNA-binding and expression than young mice. However, in contrast to precursor B cells, E47 DNA-binding and expression are similarly and only moderately reduced in both severely depleted and in moderately depleted mice. The mRNA levels were found to be decreased in stimulated splenic B cells from old as compared to young mice, suggesting that E47 mRNA in the spleen may be both transcriptionally and/or post-transcriptionally regulated.
The Journal of Immunology, 2003
The E2A-encoded transcription factors E12 and E47 are key regulators of B cell functions. They bind to the E-box site, found in regulatory regions of B cell-specific genes; promote cell survival of early pre-B cells; help to initiate Ig rearrangements; and are also involved in class switch in mature B cells in the periphery. We have investigated the expression and function of E47 and E12 in IL-7-expanded pro-B/pre-B cell precursors and in unstimulated or LPS-activated splenic B cells from young and old BALB/c mice. Results show that B cell precursors from the bone marrow of old mice exhibit a reduced expression of E2A proteins and a reduced ability to bind DNA, as compared with young mice. In the spleen, E2A protein expression and DNA binding are present in unstimulated B cells from young mice and, to a significantly lesser extent, from old mice. These are both strongly induced by activation in splenic B cells from young mice but only moderately induced in old mice, indicating that aging affects the expression and activity of E2A-encoded genes and also that DNA binding correlates with the amount of protein expression. The levels of E2A DNA binding in the spleen correlate with those in the bone marrow for individual mice. In splenic mature B cells, only E47/E47 complexes bind DNA; whereas in bone marrow B cell precursors, E47/E12 complexes participate in DNA binding. Only nuclear extracts of splenic mature B cells, but both nuclear and cytoplasmic extracts of bone marrow B cell precursors, exhibit DNA binding.
Journal of Experimental Medicine, 1998
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, IL7R ␣ , 5, and Rag-1, and the ability to induce 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.
El2 and E47 are two helix-loop-helix transcription factors that arise by alternative splicing of the E2A gene. Both have been implicated in the regulation of immunoglobulin gene expression. We have now generated E2A (-I-) mice by gene targeting. ESA-null mutant mice fail to generate mature B cells. The arrest of B cell development occurs at an early stage, since no immunoglobulin DJ rearrangements can be detected in homozygous mutant mice. While immunoglobulin germline I, RAG-I, mb-f, CD19, and 15 transcripts are dramatically reduced in fetal livers of E2A (-I-) mice, 829 and pa transcripts are present, but at lower levels. In addition, we show that Pax-5 transcripts are significantly reduced in fetal livers of E2A (-I-) mice. These data suggest a crucial role for E2A products as central regulators in early B cell differentiation.
E2A and E2-2 are subunits of B-cell-specific E2-box DNA-binding proteins
Molecular and cellular biology, 1993
A class of helix-loop-helix (HLH) proteins, including E2A (E12 and E47), E2-2, and HEB, that bind in vitro to DNA sequences present in the immunoglobulin (Ig) enhancers has recently been identified. E12, E47, E2-2, and HEB are each present in B cells. The presence of many different HLH proteins raises the question of which of the HLH proteins actually binds the Ig enhancer elements in B cells. Using monoclonal antibodies specific for both E2A and E2-2, we show that both E2-2 and E2A polypeptides are present in B-cell-specific Ig enhancer-binding complexes. E2-box-binding complexes in pre-B cells contain both E2-2 and E2A HLH subunits, whereas in mature B cells only E2A gene products are present. We show that the difference in E2-box-binding complexes in pre-B and mature B cells may be caused by differential expression of E2A and E2-2.
Journal of Experimental Medicine, 1998
In mature B lymphocytes, the zinc finger transcription factor early growth response 1 (Egr-1) is one of the many immediate-early genes induced upon B cell antigen receptor engagement. However, its role during earlier stages of lymphopoiesis has remained unclear. By examining bone marrow B cell subsets, we found Egr-1 transcripts in pro/pre-B and immature B lymphocytes, and Egr-1 protein in pro/pre-B-I cells cultivated on stroma cells in the presence of interleukin (IL)-7. In recombinase-activating gene (RAG)-2-deficient mice overexpressing an Egr-1 transgene in the B lymphocyte lineage, pro/pre-B-I cells could differentiate past a developmental block at the B220 low BP-1 Ϫ stage to the stage of B220 low BP-1 ϩ pre-B-I cells, but not further to the B220 low BP-1 ϩ CD25 ϩ stage of pre-B-II cells. Therefore, during early B lymphopoiesis progression from the B220 low BP-1 Ϫ IL-2R Ϫ pro/pre-B-I stage to the B220 low BP-1 ϩ IL-2R ϩ pre-B-II stage seems to occur in at least two distinct steps, and the first step to the stage of B220 low BP-1 ϩ pre-B-I cells can be promoted by the overexpression of Egr-1 alone. Wild-type mice expressing an Egr-1 transgene had increased proportions of mature immunoglobulin (Ig)M ϩ B220 high and decreased proportions of immature IgM ϩ B220 low bone marrow B cells. Since transgenic and control precursor B cells show comparable proliferation patterns, overexpression of Egr-1 seems also to promote entry into the mature B cell stage. Analysis of changes in the expression pattern of potential Egr-1 target genes revealed that Egr-1 enhances the expression of the aminopeptidase BP-1/6C3 in pre-B and immature B cells and upregulates expression of the orphan nuclear receptor nur77 in IgM ϩ B cells.
Immunological Reviews, 2005
Both mouse and human exhibit deficiencies in humoral immunity during 'old age'. While alterations in phenotype and function have been well documented, the molecular mechanisms that result in immune senescence remain undefined. B lymphopoiesis is suppressed in senescent mice, which may result from deficits at the pre-B-cell stage or earlier (e.g. pro-B cells). This deficit contrasts with the maintenance of the normal number of total peripheral B lymphocytes in senescent mice. However, mature peripheral B cells in aged mice can exhibit reduced efficiencies of both immunoglobulin isotype switching and somatic hypermutation. The basic helix-loop-helix transcription factor E2A is crucial at several stages of B-lymphocyte differentiation, including the development of pro-B and pre-B cells within the bone marrow and in isotype switch and somatic hypermutation among peripheral B cells. Therefore, we have focused on the regulation of E2A expression and function during both B lymphopoiesis and isotype class switching in senescent mice. These studies show that E2A expression is normally under complex control at both post-transcriptional and post-translational levels. Alterations in E2A expression at both the B-cell precursor and mature B-cell developmental stages are hypothesized to contribute to defects in humoral immunity during senescence.
The Journal of Immunology, 2006
The role of specific transcription factors in the initiation and regulation of Ig gene rearrangements has been studied extensively in mouse models, but data on normal human precursor B cell differentiation are limited. We purified five human precursor B cell subsets, and assessed and quantified their IGH, IGK, and IGL gene rearrangement patterns and gene expression profiles. Pro-B cells already massively initiate D H -J H rearrangements, which are completed with V H -DJ H rearrangements in pre-B-I cells. Large cycling pre-B-II cells are selected for in-frame IGH gene rearrangements. The first IGK/IGL gene rearrangements were initiated in pre-B-I cells, but their frequency increased enormously in small pre-B-II cells, and in-frame selection was found in immature B cells. Transcripts of the RAG1 and RAG2 genes and earlier defined transcription factors, such as E2A, early B cell factor, E2-2, PAX5, and IRF4, were specifically up-regulated at stages undergoing Ig gene rearrangements. Based on the combined Ig gene rearrangement status and gene expression profiles of consecutive precursor B cell subsets, we identified 16 candidate genes involved in initiation and/or regulation of Ig gene rearrangements. These analyses provide new insights into early human precursor B cell differentiation steps and represent an excellent template for studies on oncogenic transformation in precursor B acute lymphoblastic leukemia and B cell differentiation blocks in primary Ab deficiencies. The Journal of Immunology, 2005, 175: 5912-5922. P recursor B cells develop from hemopoietic stem cells and differentiate through a number of stages in the bone marrow (BM) 3 before they migrate to the periphery as naive mature B lymphocytes. The ultimate purpose of B cell differentiation is to produce the broad repertoire of B cell Ag receptors, which are composed of two identical Ig heavy chains and two identical Ig light chains (reviewed in Ref. 1). Early in differentiation, V(D)J recombination is initiated in the Ig H chain (IGH) locus with D H to J H rearrangements in pro-B cells. The lymphocyte-specific RAG1 and RAG2 proteins introduce a singlestranded nick between the recombination signal sequence (RSS) and the flanking D or J gene segment, which results in the generation of a dsDNA break (2, 3). The DNA-bending high mobility group proteins HMGB1 and HMGB2 stimulate the RAG proteins in DNA binding and the generation of the dsDNA breaks (4), which are subsequently repaired via nonhomologous end joining (NHEJ) (5). In the next stage (pre-B-I), a V H segment is rearranged to the DJ H element, and if an in-frame VDJ H exon is formed, a pre-BCR is expressed, which is composed of IgH chains and surrogate light chains (VpreB and 14.1). The expression of this receptor initiates several cycles of proliferation (large cycling pre-B-II cell stage). After this proliferation phase, Ig L chain rearrangements are initiated in the small pre-B-II cells. If a functional Ig L chain (Ig or Ig) is expressed that is able to assemble with the Ig H chain, the cell becomes a surface membrane Ig ϩ (SmIg ϩ ) immature B cell. If this cell is nonautoreactive, it migrates to the periphery as a naive mature B cell.