Overexpression of BSAP/Pax-5 inhibits switching to IgA and enhances switching to IgE in the I.29 mu B cell line
Department of Molecular Genetics and Microbiology
Adjuvants, Immunologic; Animals; B-Cell-Specific Activator Protein; B-Lymphocytes; Base Sequence; Binding Sites; DNA-Binding Proteins; Gene Expression Regulation; Immunoglobulin A; Immunoglobulin Class Switching; Immunoglobulin E; Immunoglobulin alpha-Chains; Immunoglobulin epsilon-Chains; Immunoglobulin mu-Chains; Immunosuppressive Agents; Lymphoma, B-Cell; Mice; Molecular Sequence Data; Nuclear Proteins; Promoter Regions (Genetics); Tetracycline; *Transcription Factors; Transfection; Tumor Cells, Cultured
Life Sciences | Medicine and Health Sciences | Women's Studies
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.
Rights and Permissions
Citation: J Immunol. 1998 Sep 15;161(6):2906-18.