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A promoter element that exerts positive and negative control of the interleukin 2-responsive J-chain gene
R D Lansford1, H J McFadden, S T Siu
1Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Insights
Interleukin 2 (IL-2) signaling in B lymphocytes activates J-chain gene expression. A specific regulatory region (JB) within the J-chain gene is identified as the key target for this IL-2-mediated immune response.
Area of Science:
- Immunology
- Molecular Biology
- Gene Regulation
Background:
- B lymphocytes are crucial for adaptive immunity, producing antibodies.
- Interleukin 2 (IL-2) is a key cytokine in immune responses.
- The J chain is essential for immunoglobulin (antibody) polymerization.
Purpose of the Study:
- To elucidate the signaling mechanism by which IL-2 induces J-chain gene expression in B cells.
- To identify regulatory sequences and nuclear factors controlling the J-chain gene.
- To pinpoint the specific target of IL-2 signaling within the J-chain gene's regulatory region.
Main Methods:
- Analysis of the J-chain gene's 5' flanking region for regulatory elements.
- Deletion and mutation analyses of identified regulatory sequences.
- Electrophoretic mobility shift assays (EMSAs) to detect nuclear factor binding.
- Correlation of regulatory element activity with J-chain gene transcription in B cells.
Main Results:
- A major control region (-75 to -45) in the J-chain gene was identified.
- This region contains two adjacent elements: JA (T-rich, positive regulation) and JB (A+G-rich, bifunctional regulation).
- The JB element functions as a repressor in J-chain-silent cells and an activator in J-chain-expressing cells.
- A B-cell-specific nuclear factor, NF-JB, binds to JB in an IL-2-responsive manner, mediating activation.
Conclusions:
- The bifunctional JB regulatory element is the primary target of IL-2 signaling in B lymphocytes.
- IL-2 signaling modulates the activity of the JB element, likely through the B-cell-specific transcription factor NF-JB.
- This mechanism explains how IL-2 induces J-chain gene expression during primary immune responses.
Abstract:
In a primary immune response a signal from interleukin 2 (IL-2) induces B lymphocytes to express the gene for the IgM joining component, the J chain. The signaling mechanism was pursued in this study by examining the J-chain gene 5' flanking region for regulatory sequences and interacting nuclear factors. The analyses identified a major control region located between -75 and -45 that encodes two adjacent elements: a T-rich sequence (JA) containing a single positive regulatory motif and an A+G-rich sequence (JB) containing overlapping positive and negative regulatory motifs. Dissection of the two elements indicated that the bifunctional JB sequence is the likely target of the IL-2 signal. The evidence was based on findings that (i) JB activity correlated with J-chain gene transcription--i.e., JB acts as a repressor in J-chain-silent B cells and as an activator in J-chain-expressing cells, and (ii) JB activator function is mediated by a B-cell-specific nuclear protein, NF-JB, that exhibits an IL-2-responsive binding pattern.