Mutations in the DNA-binding Domain of the Transcription Factor Bright Act as Dominant Negative Proteins and Interfere with Immunoglobulin Transactivation
Oklahoma City University, Oklahoma City, Oklahoma, United States Journal of Biological Chemistry
(Impact Factor: 4.57).
01/2005; 279(50):52465-72. DOI: 10.1074/jbc.M403028200
Bright, for B cell regulator of immunoglobulin heavy chain transcription, binds A+T-rich sequences in the intronic enhancer regions of the murine heavy chain locus and 5'-flanking sequences of some variable heavy chain promoters. Most resting B cells do not express Bright; however, it is induced after stimulation with antigen or polyclonal mitogens. Bright activation results in up-regulation of mu transcription; however, it is not clear whether Bright function is critical for normal B cell development. To begin to address Bright function during B cell development, seven mutated forms of Bright were produced. Five of the seven mutants revealed little or no DNA binding activity. Furthermore, because Bright binds DNA as a dimer, two of the mutants formed complexes with wild type Bright and acted in a dominant negative fashion. Dominant negative Bright prevented the up-regulation of mu transcription in transfected Chinese hamster ovary cells transfected with wild type Bright. These data identify regions within Bright that are required for the DNA binding activity of Bright and for its function as a transcription factor.
Available from: Michelle Ratliff
- "Dimerization of Bright was required for binding to the IgH locus in mobility shift assays (8). Earlier antibody supershift assays were the first to suggest that the Bright complex might also contain additional proteins, potentially including topoisomerase II (40). "
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ABSTRACT: ARID3a/Bright is a DNA-binding protein that was originally discovered for its ability to increase immunoglobulin transcription in antigen-activated B cells. It interacts with DNA as a dimer through its ARID, or A/T-rich interacting domain. In association with other proteins, ARID3a increased transcription of the immunoglobulin heavy chain and led to improved chromatin accessibility of the heavy chain enhancer. Constitutive expression of ARID3a in B lineage cells resulted in autoantibody production, suggesting its regulation is important. Abnormal ARID3a expression has also been associated with increased proliferative capacity and malignancy. Roles for ARID3a in addition to interactions with the immunoglobulin locus were suggested by transgenic and knockout mouse models. Over-expression of ARID3a resulted in skewing of mature B cell subsets and altered gene expression patterns of follicular B cells, whereas loss of function resulted in loss of B1 lineage B cells and defects in hematopoiesis. More recent studies showed that loss of ARID3a in adult somatic cells promoted developmental plasticity, alterations in gene expression patterns, and lineage fate decisions. Together, these data suggest new regulatory roles for ARID3a. The genes influenced by ARID3a are likely to play pivotal roles in lineage decisions, highlighting the importance of this understudied transcription factor.
Available from: bum-kyu Lee
- "(C) Recombinant BRIGHT binds to the proximal enhancer (PE) and to (D) the Bb region of Oct4; (E) to the R1 region of Sox2; and (F) to the proximal promoter (PP) region of Nanog. aBRIGHT, anti-BRIGHT polyclonal antibody; preimmune, sera collected prior to immunization; IVT BRIGHT, recombinant BRIGHT protein; IgV H , an established BRIGHT DNA binding motif from an immunoglobulin variable region promoter (Nixon et al., 2004). Black arrows denote specific complexes; empty arrows denotes free probe. "
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ABSTRACT: We show here that singular loss of the Bright/Arid3A transcription factor leads to reprograming of mouse embryonic fibroblasts (MEFs) and enhancement of standard four-factor (4F) reprogramming. Bright-deficient MEFs bypass senescence and, under standard embryonic stem cell (ESC) culture conditions, spontaneously form clones that in vitro express pluripotency markers, differentiate to all germ lineages, and in vivo form teratomas and chimeric mice. We demonstrate that BRIGHT binds directly to the promoter/enhancer regions of Oct4, Sox2, and Nanog to contribute to their repression in both MEFs and ESCs. Thus, elimination of the BRIGHT barrier may provide an approach for somatic cell reprogramming.
Available from: Carol F Webb
- "Predicted Bright-binding sites are present upstream of over half of the variable region genes and within the intronic Eμ enhancer necessary for expression of all Igs (Herrscher et al., 1995;Johnston et al., 2006). Bright Ig enhancing function requires a multiprotein complex containing Bright dimers (Nixon et al., 2004a) and both Bruton's tyrosine kinase (Btk) and its substrate, TFII-I (Rajaiya et al., 2006;Rajaiya et al., 2005). More recent data suggest that Bright may also affect genes outside of the Ig locus. "
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ABSTRACT: Previous data suggested that constitutive expression of the transcription factor Bright (B cell regulator of immunoglobulin heavy chain transcription), normally tightly regulated during B cell differentiation, was associated with autoantibody production. Here we show that constitutive Bright expression results in skewing of mature B lineage subpopulations toward marginal zone cells at the expense of the follicular subpopulation. C57Bl/6 transgenic mice constitutively expressing Bright in B lineage cells generated autoantibodies that were not the result of global increases in immunoglobulin or of breaches in key tolerance checkpoints typically defective in other autoimmune mouse models. Rather, autoimmunity correlated with increased numbers of marginal zone B cells and alterations in the phenotype and gene expression profiles of lymphocytes within the follicular B cell compartment. These data suggest a novel role for Bright in the normal development of mature B cell subsets and in autoantibody production.
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