Abstract 2427 In Vitro Study of the Effect of PALB2 Phosphorylation on BRCA1-PALB2 Dimerization

BRCA1 and PALB2 are two proteins that heterodimerize to efficiently repair DNA damage through homologous recombination. Inability for these proteins to dimerize due to genetic variations can increase an individual's risk of developing breast and ovarian cancer. Currently, most BRCA1 and PALB2 missense variants in the dimerization domains are classified as variants of unknown significance (VUSs) due to insufficient data to predict pathogenicity. In vivo methods to predict pathogenicity of these variants are time consuming and costly. As a result, we aimed to create a high-throughput and cell-free assay to test the effect of VUSs on the BRCA1-PALB2 binding interaction. Importantly, we wanted to recreate any relevant cellular conditions to obtain the most accurate data, and currently, the effect of PALB2 phosphorylation on the BRCA1-PALB2 binding interaction in vitro is unknown. To determine if phosphorylation affects the binding interaction, we mimic the phosphorylation states of PALB2 using site-directed mutagenesis and test their effect on BRCA1 binding using isothermal titration calorimetry. We will present our results which indicate a surprising finding: PALB2 phosphorylation does not significantly alter the strength of the BRCA1-PALB2 binding interaction with minimized constructs in vitro. Thus, we hypothesize it is not critical to recreate the phosphorylation states of PALB2 when testing the effect of VUSs on the BRCA1-PALB2 binding interaction. We will also present hypotheses for mechanisms that allow for phosphorylation to alter dimerization in vivo, but not in vitro. We would like to thank Texas Christian University's Science and Engineering Research Center (SERC) and The National Institute of Health (NIH) for their support in funding this project.