Ataxia telangiectasia mutated (Atm) and DNA-PKcs kinases have overlapping activities during chromosomal signal joint formation

Abstract

Lymphocyte antigen receptor gene assembly occurs through the process of V(D)J recombination, which is initiated when the RAG endonuclease introduces DNA DSBs at two recombining gene segments to form broken DNA coding end pairs and signal end pairs. These paired DNA ends are joined by proteins of the nonhomologous end-joining (NHEJ) pathway of DSB repair to form a coding joint and signal joint, respectively. RAG DSBs are generated in G1-phase developing lymphocytes, where they activate the ataxia telangiectasia mutated (Atm) and DNA-PKcs kinases to orchestrate diverse cellular DNA damage responses including DSB repair. Paradoxically, although Atm and DNA-PKcs both function during coding joint formation, Atm appears to be dispensible for signal joint formation; and although some studies have revealed an activity for DNA-PKcs during signal joint formation, others have not. Here we show that Atm and DNA-PKcs have overlapping catalytic activities that are required for chromosomal signal joint formation and for preventing the aberrant resolution of signal ends as potentially oncogenic chromosomal translocations.

Functional redundancy between the XLF and DNA-PKcs DNA repair factors in V(D)J recombination and nonhomologous DNA end joining

“…ATM and its substrates also have been suggested to function in DSB synapsis (20,39). It is notable that combined deficiency for ATM and DNA-PKcs leads to decreased RS joining (16,23), but not nearly to the extent found in the absence of either ATM or DNA-PKcs and XLF (ref. 31 and Fig.…”

“…For example, all three proteins might contribute directly to synapsis, or, alternatively, DNAPKcs and ATM might contribute to synapsis, and XLF could recruit repair factors to enhance the kinetics with which C-NHEJ ligates ends before they separate. Many other possible direct or indirect functionally redundant roles could be imagined in the context of proposed overlapping activities of ATM and DNA-PKcs (8,16,23). Whatever their redundant functions with XLF, DNAPKcs and ATM have distinct roles, as neither can substitute for XLF in the absence of the other.…”

“…Combined deficiency for ATM and DNA-PKcs in mice leads to embryonic lethality (21,22). Moreover, ATM and DNA-PKcs have redundant functions in SE joining in pro-B cells (16,23). When both proteins are inactivated, or when ATM-deficient and DNA-PKcs-deficient pro-B cells are treated with DNAPKcs and ATM specific inhibitors, respectively, SE joining is greatly impaired (16,23).…”

“…Moreover, ATM and DNA-PKcs have redundant functions in SE joining in pro-B cells (16,23). When both proteins are inactivated, or when ATM-deficient and DNA-PKcs-deficient pro-B cells are treated with DNAPKcs and ATM specific inhibitors, respectively, SE joining is greatly impaired (16,23). ATM and DNA-PKcs also have redundant functions in CSR, as switching to IgG1 and IgG3 was Author contributions: V.O., V.K., X.L., C.G., B.S., S.Z., and F.W.A.…”

Programmed DNA breaks in lymphoid cells: repair mechanisms and consequences in human disease

“…It acts in concert with the MRN complex (comprising the exonuclease MRE11, RAD50 and NBS1, which is formed stably only when all three proteins are present) 10, 11. Whereas DNA‐PKcs contributes to signalling DSBs at signal ends, the kinase activity of ATM, which belongs within the same family of kinases as DNA‐PKcs, can partially compensate for its function at signal ends 12, 13…”