Abstract 2493: Identification of the mutant p53-PARP-MCM chromatin axis as a triple negative breast cancer replication stress target

Approximately 15% of all breast cancer is triple-negative and of these about 80% are found to have mutations in the gene for the tumor suppressor p53 (TP53). Many TP53 mutations encode gain-of-function oncogenic mutant p53 (GOF mtp53) protein. We used inducible knockdown of endogenous GOF mtp53 in MDA-MB-468 cells in conjunction with stable isotope labeling with amino acids in cell culture (SILAC) and subcellular fractionation. We sequenced over 70,000 total peptides for chromatin and cytoplasmic reciprocal data sets and were able to identify 3,010 unique cytoplasmic fraction proteins and 3,403 unique chromatin fraction proteins. We found that the heterohexomeric minichromosome maintenance (MCM) complex (MCM 2-7) along with PARP are high mtp53-chromatin associated pathways. When we depleted R273H mtp53 we found a large reduction of the amount of MCM complex and PARP proteins on the chromatin. Furthermore a direct mtp53-MCM2 interaction was detected. Overexpressed mtp53, but not wild type p53, showed a protein-protein interaction with MCM2 and MCM4. We treated cells with the PARP inhibitor talazoparib and the alkylating agent temozolomide and detected synergistic activation of apoptosis only in the presence of functional MCM2-7 and mtp53. The mtp53-PARP-MCM axis has potential use as a therapeutic and diagnostic target. Citation Format: Wei-Gang Qiu, Alla Polotskaia, Gu Xiao, Lia Di, Yuhan Zhao, Wenwei Hu, John Philip, Ronald Hendrickson, Jill Bargonetti. Identification of the mutant p53-PARP-MCM chromatin axis as a triple negative breast cancer replication stress target [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2493. doi:10.1158/1538-7445.AM2017-2493