Reduced switching in SCID B cells is associated with altered somatic mutation of recombined S regions.
Deoxyribonucleic acid double-stranded breaks act as intermediates in Ig V(D)J recombination and probably perform a similar function in class switch recombination between IgH C genes. In SCID mice, V(D)J recombination is blocked because the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) protein is defective. We show in this study that switching to all isotypes examined was detectable when the SCID mutation was introduced into anti-hen egg lysozyme transgenic B cells capable of undergoing class switch recombination, but switching was significantly reduced in comparison with control B cells of the same specificity lacking the RAG1 gene. Thus, DNA-PKcs is involved in switching to all isotypes, but plays a lesser role in the switching process than it does in V(D)J-coding joint formation. The higher level of switching observed by us in SCID B cells compared with that observed by others in DNA-PKcs(null) cells raises the possibility that kinase-deficient DNA-PKcs can function in switching. Point mutation of G:C base pairs with cytidines on the sense strand was greatly reduced in recombined switch regions from SCID cells compared with control RAG1(-/-) B cells. The preferential loss of sense strand cytidine mutations from hybrid S regions in SCID cells suggests the possibility that nicks might form in S regions of activated B cells on the template strand independently of activation-induced cytidine deaminase and are converted to double-strand breaks when activation-induced cytidine deaminase deaminates the non-template strand.
Cook
Adam J L
AJ
Centenary Institute of Cancer Medicine and Cell Biology, Newtown, NSW, Australia.
Oganesian
Liana
L
Harumal
Pearly
P
Basten
Antony
A
Brink
Robert
R
Jolly
Christopher J
CJ
D000818:Animals; D016175:B-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*; D020134:Catalytic Domain / Q000235:genetics; D002470:Cell Survival / Q000235:genetics / Q000276:immunology; D002478:Cells, Cultured; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D015536:Down-Regulation / Q000235:genetics* / Q000276:immunology*; D018398:Homeodomain Proteins / Q000235:genetics; D017578:Immunoglobulin Class Switching / Q000235:genetics* / Q000502:physiology; D007074:Immunoglobulin G / Q000096:biosynthesis; D007143:Immunoglobulin Heavy Chains / Q000096:biosynthesis / Q000235:genetics; D007132:Immunoglobulin Isotypes / Q000096:biosynthesis / Q000235:genetics; D007075:Immunoglobulin M / Q000096:biosynthesis; D007134:Immunoglobulin Switch Region / Q000235:genetics*; D007135:Immunoglobulin Variable Region / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D016513:Mice, SCID; D008822:Mice, Transgenic; D009113:Muramidase / Q000276:immunology; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000235:genetics; D011995:Recombination, Genetic / Q000276:immunology*; D019076:Transgenes / Q000276:immunology
D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D007074:Immunoglobulin G; D007143:Immunoglobulin Heavy Chains; D007132:Immunoglobulin Isotypes; D007075:Immunoglobulin M; D007135:Immunoglobulin Variable Region; C064658:RAG-1 protein; D051747:DNA-Activated Protein Kinase; D017346:Protein Serine-Threonine Kinases; C421864:hen egg lysozyme; D009113:Muramidase