Title: Phosphorylation dependent structural function of DNA-PKcs in DNA repair and hematopoiesis
Description: Genomic stability is essential for maintaining cellular function and preventing oncogenic transformation. DNA double strand breaks (DSBs) are the most severe form of DNA damage. Classical non-homologous end joining (cNHEJ) is one of two major DSB repair pathways in mammalian cells. During lymphocyte development, NHEJ is required for the repair of programmed double strand breaks (DSBs) occurring during V(D)J recombination and Class Switch Recombination (CSR). Defects in cNHEJ cause severe combined immunodeficiency (SCID) in patients and animal models. Misrepair of physiological DSBs generated during normal lymphocyte development results in clonal translocations, which is characteristic of human lymphoid malignancy: it is the most common cancer type in children and the third leading cancer type in adults. Lymphoid malignancies are characterized by clonal translocations involving the antigen receptor loci, which often arise from the misrepair of programmed double strand breaks (DSBs). Furthermore, cNHEJ also plays a critical role in aging and therapeutic responses to genotoxic cancer therapy.

My thesis study focuses on the function and regulation of DNA-dependent protein kinase catalytic subunit (DNA-PKcs). DNA-PKcs is a vertebrate specific NHEJ factor and one of most abundant proteins in human cells. Together with the DNA binding Ku70 and Ku80 heterodimer, DNA-PKcs forms the DNA dependent protein kinase (DNA-PK) holoenzyme. In addition to its important role in cNHEJ, DNA-PK also orchestrates the mammalian DNA damage response (DDR) together with the related ATM and ATR kinases by phosphorylating hundreds of partially overlapping substrates. My thesis goes deeper than the kinase and signaling function of DNA-PKcs during cNHEJ. We investigated the structural function of DNA-PKcs in cNHEJ (chapter 2) and A-EJ (chapter 3), using a mouse model with point mutations that lead to the expression of kinase dead (KD) DNA-PKcs. Second, we explored potential roles of DNA-PKcs outside of cNHEJ and A-EJ with a mouse model of DNA-PKcs lacking specific phosphorylation sites (chapter 4). Altogether, our results identified an unexpected structural function of DNA-PKcs in cNHEJ and the DNA damage response and expanded the purview of the function of DNA-PKcs into new areas, including hematopoiesis, alternative end-joining and potentially nucleoli stress.