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

Abstract

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.One of the critical events in the differentiation of a B lymphocyte to an immunoglobulin M (IgM)-secreting cell is the synthesis of the IgM-polymerizing component, the J chain (13). Analyses of J-chain-specific RNA in both mitogen-stimulated B cells and transformed B lymphoma lines have shown that synthesis of the J protein is initiated at the level of transcription (14, 18). The J-chain gene remains silent during the early antigen-independent stages of differentiation, but becomes activated when the mature B cell is driven to secretion by contact with antigen and T cellderived lymphokines (24). Moreover, structural analyses of the J-chain gene have suggested that transcription is activated by changes in chromatin structure. The coding information is organized in a simple transcription unit that requires neither gene rearrangement nor differential RNA processing to produce a functional protein product (19).Two types of chromatin changes have been identified in actively transcribed genes on the basis of their susceptibility to digestion by nucleases. One is a general opening-up of the nucleoprotein complex that is manifested by a severalfold increase in nuclease sensitivity. This change in overall structure is thought to reflect a commitment by the cell to the expression of the gene. The second type is an extensive disruption of local areas within the opened-up gene that produces another 10-fold increase in nuclease sensitivity. These changes in local chromatin structure have been implicated in the regulation of transcription (8,11,29,35,40). Hypersensitive sites usually map to the control regions of expressed genes, as in 5'-flanking or enhancer sequences, and many have been shown by transfection to contain sequences critical to transcription (12,28). Moreover, recent evidence indicates that hypersensitive sites demarcate the binding of regulatory molecules. Thus, the immunoglobulin heavy and light chain enhancers, both of which are associated with tissue-specific DNase I-hypersensitive sites (23, 26), have been shown to interact with binding factors by a variety of criteria (5,22,30 (kDa) heat shock gene has been identified as the target for a specifi...

A promoter element that exerts positive and negative control of the interleukin 2-responsive J-chain gene.

“…For these experiments, a reference plasmid was constructed from pCAT3M by inserting 1.24 kb of 5' J-chain sequence in the polylinker upstream of the CAT gene and 1.0 kb ofu heavy-chain enhancer sequence (19) at a BamHI site downstream. The J-chain insert spanned base pairs -1150 to +88 and included the region (-170 to +88) that becomes DNase I hypersensitive upon transcription (14). The translational start site encoded within the J-chain insert was altered by site-specific mutagenesis to ensure correct initiation of CAT translation.…”

“…A single nuclease hypersensitive site is coinduced with J-chain gene expression either in normal B lymphocytes stimulated with mitogen or in BCL1 cells stimulated with recombinant IL-2 (14). This finding suggested that the lymphokine signal alters the 5' structure of the J-chain gene to allow access of the transcriptional machinery.…”

Mechanism of Interleukin-2 Signaling: Mediation of Different Outcomes by a Single Receptor and Transduction Pathway

“…A few clues to the mechanisms involved have been obtained in the case of J chain gene activation. Transcription of the gene has been shown to correlate with the development of a 5' hypersensitive site and a change in protein binding to that region (9,36). In contrast, essentially nothing is known ofthe events that regulate proliferation.…”

B Cell-specific Activator Protein Prevents Two Activator Factors from Binding to the Immunoglobulin J ChainPromoter until the Antigen-driven Stages of B Cell Development

“…For efficient J chain transcription to occur, activation signals from both the B cell receptor and the interleukin-2 (IL-2) 1 or IL-5 receptors are needed. Correlating with IL-2/IL-5 induced gene transcription is the appearance of a DNase I-hypersensitive site (bp Ϫ170 to ϩ88) on the J chain promoter of activated B cells (2,3). The full activity of the J chain promoter is contained within this hypersensitive region, as has been shown using 5Ј deletion mutants in a CAT reporter system (4).…”