PubMed · 7964034
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K Tominaga, H Wakasa. 1994-06-10. [Basic structure of lymph nodes].. https://pubmed.ncbi.nlm.nih.gov/7964034/
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Primary mediastinal B-cell lymphoma is a locally highly aggressive but poorly disseminating tumor composed of medium sized or large cells most probably of thymic medullary origin. It has a mature B-cell phenotype, typically lacks immunoglobulin expression and has variable defects in expression of HLA-molecules. We present here a cell line, MedB-1, derived from such a tumor. As is frequently found in mediastinal B-cell lymphomas in situ, MedB-1 is CD10(-), CD19(+), CD21(-), CD22(+), CD23(+), CD25(-), CD37(+), CD38(-), CD39(+), CD40(+), CD54(+), CD95(+). Like the parental tumor, MedB-1 lacks HLA-A,B,C alpha-chains and beta(2)microglobulin and expresses HLA-D molecules at decreased levels. Both parental tumor and MedB-1 cells are clonally related as shown by immunoglobulin heavy chain gene rearrangement analysis. Unlike the parental tumor tissue, the MedB-1 cell line cytoplasmically expresses IgG/kappa in a very small subset of cells under standard culture conditions. MedB-1 does not contain any Epstein-Barr virus DNA. In a tissue adhesion assay MedB-1 cells showed an extensive binding to the medullary region of normal thymus. Altogether, MedB-1 is a suitable tool for functional and molecular analysis of this distinct lymphoma entity.
Interferon regulatory factor (IRF) genes encode DNA-binding proteins that are involved in the innate immune response to infection. Two of these proteins, IRF-3 and IRF-7, serve as direct transducers of virus-mediated signaling and play critical roles in the induction of type I interferon genes. We have now shown that another factor, IRF-5, participates in the induction of interferon A (IFNA) and IFNB genes and can replace the requirement for IRF-7 in the induction of IFNA genes. We demonstrate that, despite the functional similarity, IRF-5 possesses unique characteristics and does not have a redundant role. Thus, 1) activation of IRF-5 by phosphorylation is virus-specific, and its in vivo association with the IFNA promoter can be detected only in cells infected with NDV, not Sendai virus, while both viruses activate IRF-3 and IRF-7, and 2) NDV infection of IRF-5-overexpressing cells preferentially induced the IFNA8 subtype, while IFNA1 was primarily induced in IRF-7 expressing cells. These data indicate that multiple signaling pathways induced by infection may be differentially recognized by members of the IRF family and modulate transcription of individual IFNA genes in a virus and cell type-specific manner.
Bright (B cell regulator of IgH transcription) is a B cell-specific, matrix associating region-binding protein that transactivates gene expression from the IgH intronic enhancer (E mu). We show here that Bright has multiple contextual requirements to function as a transcriptional activator. Bright cannot transactivate via out of context, concatenated binding sites. Transactivation is maximal on integrated substrates. Two of the three previously identified binding sites in E mu are required for full Bright transactivation. The Bright DNA binding domain defined a new family, which includes SWI1, a component of the SWI.SNF complex shown to have high mobility group-like DNA binding characteristics. Similar to one group of high mobility group box proteins, Bright distorts E mu binding site-containing DNA on binding, supporting the concept that it mediates E mu remodeling. Transfection studies further implicate Bright in facilitating spatially separated promoter-enhancer interactions in both transient and stable assays. Finally, we show that overexpression of Bright leads to enhanced DNase I sensitivity of the endogenous E mu matrix associating regions. These data further suggest that Bright may contribute to increased gene expression by remodeling the immunoglobulin locus during B cell development.