Analyses of TCRB rearrangements substantiate a profound deficit in recombination signal sequence joining in SCID foals: implications for the role of DNA-dependent protein kinase in V(D)J recombination.
We reported previously that the genetic SCID disease observed in Arabian foals is explained by a defect in V(D)J recombination that profoundly affects both coding and signal end joining. As in C.B-17 SCID mice, the molecular defect in SCID foals is in the catalytic subunit of the DNA-dependent protein kinase (DNA-PKCS); however, in SCID mice, signal end resolution remains relatively intact. Moreover, recent reports indicate that mice that completely lack DNA-PKCS also generate signal joints at levels that are indistinguishable from those observed in C.B-17 SCID mice, eliminating the possibility that a partially active version of DNA-PKCS facilitates signal end resolution in SCID mice. We have analyzed TCRB rearrangements and find that signal joints are reduced by approximately 4 logs in equine SCID thymocytes as compared with normal horse thymocytes. A potential explanation for the differences between SCID mice and foals is that the mutant DNA-PKCS allele in SCID foals inhibits signal end resolution. We tested this hypothesis using DNA-PKCS expression vectors; in sum, we find no evidence of a dominant-negative effect by the mutant protein. These and other recent data are consistent with an emerging consensus: that in normal cells, DNA-PKCS participates in both coding and signal end resolution, but in the absence of DNA-PKCS an undefined end joining pathway (which is variably expressed in different species and cell types) can facilitate imperfect signal and coding end joining.
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Harold C. Simmons Arthritis Research Center, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75235, USA.
Rijkers
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Pastink
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Meek
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D000483:Alleles; D000818:Animals; D020134:Catalytic Domain / Q000235:genetics; D002460:Cell Line; D003062:Codon / Q000032:analysis / Q000235:genetics / Q000276:immunology; D004254:DNA Nucleotidyltransferases / Q000037:antagonists & inhibitors / Q000235:genetics; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D015333:Gene Rearrangement, beta-Chain T-Cell Antigen Receptor; D006736:Horses; D019426:Integrases; D007438:Introns / Q000235:genetics / Q000276:immunology; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000235:genetics*; D045522:Recombinases; D011995:Recombination, Genetic / Q000276:immunology*; D016511:Severe Combined Immunodeficiency / Q000201:enzymology / Q000235:genetics* / Q000276:immunology; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D013601:T-Lymphocytes / Q000201:enzymology / Q000276:immunology / Q000473:pathology
D003062:Codon; D004268:DNA-Binding Proteins; D016693:Receptors, Antigen, T-Cell, alpha-beta; D045522:Recombinases; D051747:DNA-Activated Protein Kinase; D017346:Protein Serine-Threonine Kinases; D004254:DNA Nucleotidyltransferases; D019426:Integrases; C115006:integron integrase IntI1