Up-regulation of recombination activating gene expression by signal transduction through the surface Ig receptor.
Recent evidence has demonstrated that a signal transduced through the lymphocyte Ag receptor may regulate the expression of the recombination activating genes (RAG). Although several groups have shown that such a signal may be required to down-regulate RAG-1 and RAG-2 after a functional Ag receptor has been generated in early mature T or B cells, recently it has been suggested that under some circumstances, cross-linking the B cell Ag receptor may result in up-regulation of RAG expression. To study this possibility, we used a unique set of cell variants isolated from a human mature B cell line, which differ in their expression of both the surface Ig receptor (sIg) and RAG-1 and RAG-2 genes. Two forms of stimulation were employed to generate a signal; either a soluble F(ab')2 anti-mu fragment or the combination of PMA and ionomycin. Northern blot analysis demonstrated that RAG-1 mRNA levels were increased in sIg+ variants after cross-linking with anti-mu. Increases were also observed in all variants after stimulation with PMA and ionomycin. Further analysis of cross-linked sIg+ variants suggests that the observed up-regulation in RAG expression was a reversible event. Furthermore, we have determined that both increased transcription and transcript stabilization contributed to this inducible up-regulation. We thus describe a mature B cell line in which RAG expression is up-regulated after sIg cross-linking. This finding is discussed in the context of its potential role in situations where sIg+ B cells may undergo secondary rearrangements for the purpose of "editing" their sIg receptors.
Verkoczy
L K
LK
Department of Immunology, University of Toronto, Ontario, Canada.
Stiernhdm
B J
BJ
Berinstein
N L
NL
D015152:Blotting, Northern; D002118:Calcium / Q000378:metabolism; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D004268:DNA-Binding Proteins; D005455:Fluorescent Antibody Technique; D018398:Homeodomain Proteins; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D009687:Nuclear Proteins; D014176:Protein Biosynthesis; D012313:RNA / Q000096:biosynthesis; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology; D015854:Up-Regulation / Q000276:immunology
D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D007140:Immunoglobulin Fab Fragments; D009687:Nuclear Proteins; C499311:RAG2 protein, human; D011947:Receptors, Antigen, B-Cell; D011971:Receptors, Immunologic; C064655:V(D)J recombination activating protein 2; C064658:RAG-1 protein; D012313:RNA; D002118:Calcium