DNA repair dysfunction in cancer induced by altered BRCA2 localization

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PROJECT SUMMARY/ABSTRACT BRCA2, as part of the DNA repair pathway, is a key regulator in homology-directed repair (HDR) and fork protection mechanism, which ensures genome instability. For full activity, BRCA2 must be transported into the nucleus to repair DNA double-strand breaks (DSBs). In normal cells, loss of nuclear BRCA2 can lead to genome instability and cancer but, in tumor cells, BRCA2 cytosolic mislocalization can lead to sensitivity to targeted therapies. I identified a paradoxical relationship between BRCA2 nuclear import and treatment. Pathogenic missense mutations in the DNA binding domain of BRCA2 direct the protein to the cytosol which increase sensitivity to PARP inhibitors (PARPi) and platinum drugs. Therefore, although BRCA2 mislocalization might be a cause of cancer, keeping it out of the nucleus allows for much better treatment outcomes. This has opened an avenue of research that I am perfectly aligned to study. In this K22 proposal I will address the nuclear transport of BRCA2, how cancer-driver mutations lead to cytosolic mislocalization and how BRCA2 localization can be used as a diagnostic tool. To test this, I will define the molecular mechanism(s) regulating nuclear/cytoplasmic shuttling of BRCA2 pathogenic missense variants (Aim 1), determine the impact of BRCA2 cellular localization on HDR, fork protection and cytosolic processes (Aim 2) and exploit BRCA2 localization as a cancer diagnostic tool (Aim 3). My priority will be to focus on missense variants identified during my postdoctoral career to decipher the underlying molecular mechanism of nuclear/cytosolic BRCA2 trafficking. At the successful completion of this K22 proposal, I will reveal novel pathways and factors that ensure proper localization of BRCA2 and how pathogenic BRCA2 missense variants have altered localization and functionality. This knowledge will give us a better understanding of the pathogenicity of BRCA2 missense variants and how we can modulate the functionality of BRCA2. My career goal is to obtain an independent position at a leading institution where I will dissect the functionality of missense variants in DNA repair proteins and how their cellular localization is important for genome stability as a tool to predict cancer risk and to treat cancer patients. My successful transition will be supported by advancing my expertise in cell biology, biochemistry, mass spectrometry and human cellular models. I will use these acquired skills to define why and how certain pathogenic BRCA2 missense variants are mislocalized to the cytosol. Importantly, the protected time that this award provides me will allow me to elucidate the factors and pathways by which BRCA2 is transported from the cytosol to the nucleus, how this might be altered in BRCA2 missense variants and how this could be used for targeted therapies. Furthermore, the success of this project will be greatly enhanced by the outstanding advisors and collaborators that advise me through the K22 period. The receipt of this award will allow me to expand my research plan and establish myself as a principal investigator in the field of cancer biology.