Hereditary mutations in the BRCA1 gene predispose carriers to ovarian cancer. The BRCA1 protein is involved in repairing DNA damage induced by chemotherapies such as platinum and PARP inhibitors (PARPi) using a DNA repair process known as homologous recombination. BRCA1 mutations often render the protein product dysfunctional, consequently tumors cannot repair DNA damage caused by chemotherapy, and so these types of tumors are highly sensitive to DNA damaging agents. However, patients with BRCA1 mutant cancers often develop drug resistance and DNA damage can be repaired once more. In this study, we aim to improve the current understanding of BRCA1 mutant cancer biology.
We compiled a panel of cancer cell lines and compared accumulation of DNA damage response proteins at sites of DNA damage in BRCA1 mutant cancer cells and cancer cells with functional BRCA1. We discovered that BRCA1 mutant cell lines exhibit reduced accumulation of 53BP1 at sites of DNA damage. 53BP1 is a DNA damage response protein that counteracts BRCA1 activity and prevents repair by homologous recombination. Therefore, we suspect that the reduced 53BP1 accumulation allows BRCA1 mutant cancer cells to repair DNA damage and continue to grow. To determine the cause of reduced 53BP1 accumulation, we examined the proteins responsible for recruiting 53BP1 to DNA damage and found one of those proteins, RNF168, to be significantly reduced in the BRCA1 mutant cancer cell lines. Furthermore, we examined patient ovarian tumor samples and found that patients with BRCA1 mutations also exhibited a reduction in RNF168. We hypothesize that BRCA1 mutant cancers reduce RNF168 to prevent 53BP1 accumulation at sites of DNA damage, which allows for repair of DNA damage and cell growth.
Ultimately, we hope to translate this improved understanding of DNA repair in BRCA1 mutant cancers into new strategies for improving patient outcome. Our goal is to generate information that leads to better predictions of therapy responsiveness and novel therapeutic approaches for BRCA1 mutant ovarian cancers.
This grant was made possible by a generous donation by Phil and Judy Messing, in memory of Carol Messing.
Dr. John Krais is a postdoctoral researcher in the laboratory of Dr. Neil Johnson at Fox Chase Cancer Center. John received his BS degree in bioengineering from the University of Pittsburgh in 2011 and PhD in biomedical engineering from the University of Oklahoma in 2014. As a graduate student working with Dr. Roger Harrison, John explored novel methodologies for targeted delivery of cancer therapeutics and focused on the preclinical development of strategies for targeting tumor vasculature. At Fox Chase Cancer Center, John was a recipient of a T32 postdoctoral fellowship and focused on investigating the DNA damage response in BRCA1 mutant cancers. John found reduced expression of the DNA damage signaling protein RNF168 in BRCA1 null cell lines and PDX models. John’s current project examines the regulation of RNF168 and its effects on the DNA damage response and cell viability in BRCA1 mutant ovarian cancers. The overarching goal of this work is to enhance the current understanding of DNA repair mechanisms in BRCA1 mutant ovarian cancers and to develop improved strategies for the treatment of BRCA1 mutation-carrying patients.