Investigating Tumor Suppressors in the DNA Damage Response: Caretakers of the Genome and Biomarkers to Predict Therapeutic Response: A Dissertation

Abstract

Our genome is constantly challenged by sources that cause DNA damage. To repair DNA damage and maintain genomic stability eukaryotes have evolved a complex network of pathways termed the DNA damage response (DDR). The DDR consists of signal transduction pathways that sense DNA damage and mediate tightly coordinated reactions to halt the cell cycle and repair DNA with a collection of different enzymes. In this manner, the DDR protects the genome by preventing the accumulation of mutations and DNA aberrations that promote cellular transformation and cancer development. Loss of function mutations in DDR genes and genomic instability occur frequently in many tumor types and underlie numerous cancer-prone hereditary syndromes such as Fanconi Anemia (FA). My thesis research applies candidate-based and unbiased experimental approaches to investigate the role of several tumor suppressor genes (TSGs) in the DDR. My dissertation will first describe a novel function for the breast and ovarian cancer tumor suppressor and FA-associated gene FANCJ in the DDR to ultraviolet (UV) irradiation. In response to UV irradiation FANCJ supports checkpoint induction, the arrest of DNA synthesis, and suppresses UV induced point mutations. Suggesting that FANCJ could suppress UV induced cancers, in sequenced melanomas from multiple databases I found somatic mutations in FANCJ previously associated with breast/ovarian cancer and FA syndrome. The second part of my dissertation will describe an RNA interference screen to identify genes modulating cellular sensitivity to the chemotherapeutic drug cisplatin. The hereditary breast/ovarian cancer tumor suppressor BRCA2 is essential for DNA repair, thus BRCA2 mutant ovarian cancer cells are initially sensitive to cisplatin chemotherapy that induces DNA damage. However, drug resistance develops and remains a major problem in the clinic. My screen identified the chromatin remodeling factor CHD4 as a potent modulator of cisplatin sensitivity and predictor of response to chemotherapy in BRCA2 mutant cancers. Taken together, my investigations highlight the important contribution of the DDR and the role they play in tumorigenesis and predicting therapeutic response.