Switch recombination in a transfected plasmid occurs preferentially in a B cell line that undergoes switch recombination of its chromosomal Ig heavy chain genes
Bradley, Sean P.
Waite, Debra J.
Rogers, Paul R.
Kenter, Amy L.
UMass Chan AffiliationsDepartment of Molecular Genetics and Microbiology
Document TypeJournal Article
Gene Rearrangement, B-Lymphocyte, Heavy Chain
Immunoglobulin Class Switching
Immunoglobulin Heavy Chains
Immunoglobulin Switch Region
Mice, Inbred BALB C
Molecular Sequence Data
Polymerase Chain Reaction
Tumor Cells, Cultured
Medicine and Health Sciences
MetadataShow full item record
AbstractAb class switching is induced upon B cell activation in vivo by immunization or infection or in vitro by treatment with mitogens, e. g. LPS, and results in the expression of different heavy chain constant region (CH) genes without a change in the Ab variable region. This DNA recombination event allows Abs to alter their biological activity while maintaining their antigenic specificity. Little is known about the molecular mechanism of switch recombination. To attempt to develop an assay for enzymes, DNA binding proteins, and DNA sequences that mediate switch recombination, we have constructed a plasmid DNA substrate that will undergo switch recombination upon stable transfection into the surface IgM+ B cell line (I.29 mu), a cell line capable of undergoing switch recombination of its endogenous genes. We demonstrate that recombination occurs between the two switch regions of the plasmid, as assayed by PCRs across the integrated plasmid switch regions, followed by Southern blot hybridization. Nucleotide sequence analysis of the PCR products confirmed the occurrence of S mu-S alpha recombination in the plasmid. Recombination of the plasmid in I.29 mu cells does not require treatment with inducers of switch recombination, suggesting that recombinase activity is constitutive in I.29 mu cells. Recombination does not require high levels of transcription across the switch regions of the plasmid. Fewer recombination events are detected in four different B and T cell lines that do not undergo switch recombination of their endogenous genes.
SourceJ Immunol. 1999 Aug 15;163(4):2028-40.
Permanent Link to this Itemhttp://hdl.handle.net/20.500.14038/50669
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Induction of immunoglobulin isotype switching in cultured I.29 B lymphoma cells. Characterization of the accompanying rearrangements of heavy chain genesStavnezer, Janet; Sirlin, S.; Abbott, J. (1985-03-01)The murine B cell lymphoma I.29 contains cells expressing surface IgM or IgA with identical heavy chain variable regions (9, 25, and D. Klein and J. Stavnezer, unpublished data). Purified IgM+ cells from the lymphoma have been adapted to culture and induced to switch to IgA, IgE, or IgG2 by treatment with lipopolysaccharide (LPS) or by treatment with a monoclonal anti-I.29 antiidiotype plus LPS. Clones of IgM+ cells have been obtained and induced to switch. Under optimal conditions, 30% of the cells in the culture expressed IgA 8 d after the inducers were added, and by 15 d 90% of the cells were IgA+. In actively switching cultures, up to 50% of the cells whose cytoplasm stained positively with anti-IgA stained simultaneously with anti-IgM, which indicates that the appearance of IgA+ cells in the cultures was due to isotype switching and not to clonal outgrowth. Examination by Southern blotting experiments of the Ig heavy chain genes in I.29 cells before and after switching revealed that isotype switching was accompanied by DNA recombinations that occurred within or immediately 5' to the tandemly repeated switch sequences. Within 3 d after the addition of inducers of switching, the nonexpressed chromosome underwent a variety of deletions or expansions within the S mu region, and a portion of the S alpha regions had undergone a 0.9-kb deletion. In cultures that contained at least 12% IgA+ cells, rearranged, expressed alpha genes, produced by recombination between the S mu region within the expressed mu gene and the S alpha region, were detected.
Overexpression of BSAP/Pax-5 inhibits switching to IgA and enhances switching to IgE in the I.29 mu B cell lineQiu, G.; Stavnezer, Janet (1998-09-15)B cell-specific activator protein (BSAP)/Pax-5 is a paired domain DNA-binding protein expressed in the developing nervous system, testis, and in all B lineage cells, except terminally differentiated plasma cells. BSAP regulates transcription of several genes expressed in B cells and also the activity of the 3' IgH enhancer. As it has binding sites within or 5' to the switch regions of nearly all Ig heavy chain C region genes and also is known to increase transcription of the germline epsilon RNA, BSAP has been hypothesized to be involved in regulation of Ab class switch recombination. To directly examine the effects of BSAP on isotype switching, we use a tetracycline-regulated expression system to overexpress BSAP in the surface IgM+ I.29 mu B cell line, a mouse cell line that can be induced to undergo class switch recombination. We find that overexpression of BSAP inhibits switching to IgA in I.29 mu cells stimulated with LPS + TGF-beta 1 + nicotinamide, but enhances switching to IgE in cells stimulated with LPS + IL-4 + nicotinamide. Parallel to its effects on switching, overexpression of BSAP inhibits germline alpha RNA expression and the transcriptional activity of the germline alpha promoter, while enhancing activity of the germline epsilon promoter. Proliferation of I.29 mu cells is not affected in this system. The possible mechanisms and significance of the effect of BSAP on isotype switching are discussed.
Rearrangements and deletions of immunoglobulin heavy chain genes in the double-producing B cell lymphoma I.29Stavnezer, Janet; Marcu, K. B.; Sirlin, S.; Alhadeff, B.; Hammerling, U. (1982-08-01)The B cell lymphoma I.29 consists of a mixture of cells expressing membrane-bound immunoglobulin M (IgM) (lambda) and IgA (lambda) of identical idiotypes. Whereas most of the cells express either IgM or IgA alone, 1 to 5% of the cells in this tumor express IgM and IgA simultaneously within the cytoplasm and on the cell membrane (R. Sitia et al., J. Immunol. 127:1388-1394, 1981; R. Sitia, unpublished data). When IgM+ cells are purified from the lymphoma and passaged in mice or cultured, a portion of the cells convert to IgA+. These properties suggest that some cells of the I.29 lymphoma may undergo immunoglobulin heavy chain switching, although it is also possible that the mixed population was derived by a prior switching event in a clone of cells. We performed Southern blotting experiments on genomic DNAs isolated from populations of I.29 cells containing variable proportions of IgM+ and IgA+ cells and on a number of cell lines derived from the lymphoma. The results were consistent with the deletion model for heavy chain switching, as the IgM+ cells contained rearranged mu genes and alpha genes in the germ line configuration on both the expressed and nonexpressed heavy chain chromosomes, whereas the IgA+ cells had deleted both mu genes and contained one rearranged and one germ line alpha gene. In addition, segments of DNA located within the intervening sequence 5' to the mu gene, near the site of switch recombination, were deleted from both the expressed and the nonexpressed chromosomes. Although mu genes were deleted from both chromosomes in the IgA+ cells, the sites of DNA recombination differed on the two chromosomes. On the expressed chromosome, Smu sequences were recombined with S alpha sequences, whereas on the nonexpressed chromosome, Smu sequences were recombined with S gamma 3 sequences.