title: The ubiquitously expressed DNA-binding protein late SV40 factor binds Ig switch regions and represses class switching to IgA.
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.
authors.affiliation: Division of Molecular Genetics, Dana--Farber Cancer Institute and Harvard Medical School, and Department of Biology, Boston University, Boston, MA 02215, USA.
authors.forename: Elise E
authors.initials: EE
authors.lastname: Drouin
authors.forename: Carol E
authors.initials: CE
authors.lastname: Schrader
authors.forename: Janet
authors.initials: J
authors.lastname: Stavnezer
authors.forename: Ulla
authors.initials: U
authors.lastname: Hansen
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D001666:Binding Sites, Antibody / Q000235:genetics; D002460:Cell Line; D002843:Chromatin / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D020868:Gene Silencing; D018698:Glutamic Acid / Q000235:genetics; D005973:Glutamine / Q000235:genetics; D006801:Humans; D007070:Immunoglobulin A / Q000096:biosynthesis* / Q000235:genetics; D017578:Immunoglobulin Class Switching / Q000235:genetics; D007134:Immunoglobulin Switch Region / Q000235:genetics; D007137:Immunoglobulin alpha-Chains / Q000235:genetics / Q000378:metabolism; D007148:Immunoglobulin mu-Chains / Q000378:metabolism; D007930:Leucine / Q000235:genetics; D016393:Lymphoma, B-Cell / Q000235:genetics / Q000276:immunology; D008239:Lysine / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D016601:RNA-Binding Proteins; D012097:Repressor Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D013154:Spleen / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D014158:Transcription, Genetic / Q000276:immunology; D014407:Tumor Cells, Cultured
chemical_list: D002843:Chromatin; D004268:DNA-Binding Proteins; D007070:Immunoglobulin A; D007137:Immunoglobulin alpha-Chains; D007148:Immunoglobulin mu-Chains; D016601:RNA-Binding Proteins; D012097:Repressor Proteins; C501906:TFCP2 protein, human; C501905:Tfcp2 protein, mouse; D014157:Transcription Factors; D005973:Glutamine; D018698:Glutamic Acid; D007930:Leucine; D008239:Lysine