The transcription factor BSAP (NF-HB) is essential for immunoglobulin germ-line epsilon transcription.
Treatment of murine splenic B lymphocytes and certain B-lineage cell lines with mitogen (LPS) and the lymphokine IL-4 has been shown to induce expression of germ-line epsilon transcripts (l epsilon transcripts) and class switching to the C epsilon gene. Three protein complexes, one of which (complex 3) is constitutively expressed, have been shown to bind to a 179-base pair LPS/IL-4-responsive l epsilon promoter (Rothman, P., S. C. Li, B. Gorham, L. Glimcher, F. W. Alt, and M. Boothby. 1991. Mol. Cell. Biol. 11:5551). Complex 3 is indispensable for this inducible promoter activity. In this report, we have used electrophoretic mobility shift assays (EMSA) to demonstrate that the early B cell-specific transcription factor (BSAP) is involved in the formation of complex 3. In addition, BSAP is implicated functionally in l epsilon transcription because a BSAP binding site either from a sea urchin histone promoter (H2A-2.2) or from 5' of murine immunoglobulin S gamma 2a can substitute for the epsilon-associated site (epsilon(foot), as assayed by transient transfection assays of the l epsilon:CAT reporter constructs into the M12.4.1 B cell line. Like the sea urchin histone BSAP site, the complex 3 binding site (epsilon(foot)) functions as an upstream promoter element when assayed in the OVEC vector. These results indicate that BSAP is an essential protein required for LPS/IL-4 induction of the l epsilon promoter. In addition, experiments showing that a BSAP binding site from 5' of S gamma 2a also functions as an upstream promoter element in OVEC suggest a potential role for BSAP in regulation of the IgG2a isotype.
Liao
F
F
Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461.
Birshtein
B K
BK
Busslinger
M
M
Rothman
P
P
D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology; D001483:Base Sequence; D001665:Binding Sites; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000502:physiology*; D006657:Histones / Q000235:genetics; D007139:Immunoglobulin epsilon-Chains / Q000235:genetics*; D015847:Interleukin-4 / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000502:physiology*; D051757:PAX5 Transcription Factor; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; D006657:Histones; D007139:Immunoglobulin epsilon-Chains; D008070:Lipopolysaccharides; D009687:Nuclear Proteins; D051757:PAX5 Transcription Factor; C497282:Pax5 protein, mouse; D014157:Transcription Factors; D015847:Interleukin-4