Radiosensitive T–B– severe combined immunodeficiency (RS-SCID) is caused by defects in the nonhomologous end-joining (NHEJ) DNA repair pathway, which results in failure of functional V(D)J recombination. Here we have identified the first human RS-SCID patient to our knowledge with a DNA-PKcs missense mutation (L3062R). The causative mutation did not affect the kinase activity or DNA end-binding capacity of DNA-PKcs itself; rather, the presence of long P-nucleotide stretches in the immunoglobulin coding joints indicated that it caused insufficient Artemis activation, something that is dependent on Artemis interaction with autophosphorylated DNA-PKcs. Moreover, overall end-joining activity was hampered, suggesting that Artemis-independent DNA-PKcs functions were also inhibited. This study demonstrates that the presence of DNA-PKcs kinase activity is not sufficient to rule out a defect in this gene during diagnosis and treatment of RS-SCID patients. Further, the data suggest that residual DNA-PKcs activity is indispensable in humans.
Mirjam van der Burg, Hanna IJspeert, Nicole S. Verkaik, Tuba Turul, Wouter W. Wiegant, Keiko Morotomi-Yano, Pierre-Olivier Mari, Ilhan Tezcan, David J. Chen, Malgorzata Z. Zdzienicka, Jacques J.M. van Dongen, Dik C. van Gent