82 | Chapter 4 Abstract The recombination activating gene (RAG) 1 and RAG2 protein complex introduces DNA breaks at Tcr and Ig gene segments that are required for V(D)J recombination in developing lymphocytes. Proper regulation of RAG1/2 expression safeguards the ordered assembly of antigen (Ag) receptors and the development of lymphocytes, while minimizing the risk of collateral damage. The ataxia telangiectasia mutated (ATM) kinase is involved in the repair of RAG1/2-mediated DNA breaks and prevents their propagation. The simultaneous occurrence of RAG1/2-dependent and –independent DNA breaks in developing lymphocytes exposed to genotoxic stress increases the risk of aberrant recombinations. Here we assessed the effect of genotoxic stress on RAG1/2 expression in pre-B cells and show that activation of the DNA damage response resulted in the rapid ATM-dependent down-regulation of RAG1/2 mRNA and protein expression. We show that DNA damage led to the loss of FOXO1-binding to the enhancer region of the RAG1/2 locus (Erag) and provoked FOXO1 cleavage. We also show that DNA damage caused by RAG1/2 activity in pre-B cells was able to down-modulate RAG1/2 expression and activity, confirming the existence of a negative feedback regulatory mechanism. Our data suggest that pre-B cells are endowed with a protective mechanism that reduces the risk of aberrant recombinations and chromosomal translocations when exposed to DNA damage, involving the ATM-dependent regulation of FOXO1-binding to the Erag enhancer region.
RkJQdWJsaXNoZXIy MTk4NDMw