The ubiquitously expressed DNA-binding protein late SV40 factor binds Ig switch regions and represses class switching to IgA
Drouin, Elise E. ; Schrader, Carol E. ; Stavnezer, Janet ; Hansen, Ulla
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UMass Chan Affiliations
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Keywords
Animals
Base Sequence
*Binding Sites, Antibody
Cell Line
Chromatin
DNA-Binding Proteins
Gene Silencing
Glutamic Acid
Glutamine
Humans
Immunoglobulin A
*Immunoglobulin Class Switching
*Immunoglobulin Switch Region
Immunoglobulin alpha-Chains
Immunoglobulin mu-Chains
Leucine
Lymphoma, B-Cell
Lysine
Mice
Mice, Inbred C57BL
Molecular Sequence Data
RNA-Binding Proteins
Repressor Proteins
Spleen
Transcription Factors
Transcription, Genetic
Tumor Cells, Cultured
Life Sciences
Medicine and Health Sciences
Women's Studies
Subject Area
Embargo Expiration Date
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Abstract
Ig heavy chain class switch recombination (CSR) determines the expression of Ig isotypes. The molecular mechanism of CSR and the factors regulating this process have remained elusive. Recombination occurs primarily within switch (S) regions, located upstream of each heavy chain gene (except Cdelta). These repetitive sequences contain consensus DNA-binding sites for the DNA-binding protein late SV40 factor (LSF) (CP2/leader-binding protein-1c). In this study, we demonstrate by EMSA that purified rLSF, as well as LSF within B cell extracts, directly binds both Smu and Salpha sequences. To determine whether LSF is involved in regulating CSR, two different LSF dominant negative variants were stably expressed in the mouse B cell line I.29 mu, which can be induced to switch from IgM to IgA. Overexpression of these dominant negative LSF proteins results in decreased levels of endogenous LSF DNA-binding activity and an increase in cells undergoing CSR. Thus, LSF represses class switching to IgA. In agreement, LSF DNA-binding activity was found to decrease in whole cell extracts from splenic B cells induced to undergo class switching. To elucidate the mechanism of CSR regulation by LSF, the interactions of LSF with proteins involved in chromatin modification were tested in vitro. LSF interacts with both histone deacetylases and the corepressor Sin3A. We propose that LSF represses CSR by histone deacetylation of chromatin within S regions, thereby limiting accessibility to the switch recombination machinery.
Source
J Immunol. 2002 Mar 15;168(6):2847-56.