Analysis of somatic recombination in lymphoid cells to unravel DNA end joining regulation in cancer
Worldwide Cancer Research
Institut Pasteur
DNA double-strand breaks (DSBs) are toxic cellular lesions that must be efficiently repaired to maintain genome stability and prevent cancer. The two main DSB repair pathways are homologous recombination (HR) and nonhomologous end joining (NHEJ), with pathway choice partly determined by functional antagonism between the HR-promoting factor BRCA1 and NHEJ-promoting proteins, notably 53BP1/RIF1/MAD2L2. We recently identified two novel genes that encode for previously uncharacterized proteins termed shieldin (SHLD)1 and SHLD2 that form the shieldin complex, which we determined as being the downstream effector of 53BP1/RIF1/MAD2L2 in promoting NHEJ and antagonizing BRCA1-mediated HR. Importantly, loss of SHLD1 or SHLD2 renders poly(ADP-ribose) polymerase (PARP) inhibitors ineffective in BRCA1-deficient cancer cells. In addition, we have established that the shieldin complex plays major and distinct roles during antigen receptor gene diversification in lymphocytes, specifically RAG1/2-induced V(D)J recombination and AID-induced class switch recombination (CSR).     In this research program, we propose to utilize programmed DNA recombination processes in lymphocytes to unravel the functions of the 53BP1-MAD2L2-shieldin axis in DSB repair. Specifically, we will analyze at the molecular level the impact of the loss of 53BP1, MAD2L2, and the shieldin complex on recombination intermediates and products. We will also test genetic and functional interactions between NHEJ and the 53BP1-MAD2L2-shieldin axis during V(D)J recombination and CSR. In addition, we will identify the local protein complexes associated with MAD2L2 and SHLD1 upon induction of programmed DSBs. Finally, we will use dedicated genetically modified mouse models to reveal the roles of SHLD1 and SHLD2 in lymphopoiesis.  Ultimately, through these studies, we aim to discover novel modes of regulation of DSB response and repair that could contribute to the development of novel DNA repair based cancer therapies.
2.1 Biological and endogenous factors