Abstract 2988: A PP6-phosphatase complex is required for homology-directed repair of DNA double-strand breaks

Abstract

Abstract DNA double-strand breaks (DSBs) are among the most lethal lesions associated with genome stability which, when destabilized, predisposes organs to cancers. DSBs are primarily fixed either with little fidelity by non-homologous end joining (NHEJ) repair or with high fidelity by homology-directed repair (HDR). The phosphorylated form of H2AX on serine 139 (g-H2AX) is a marker of DSBs. It is dephosphorylated by PP2A-like protein phosphatases (PP2A, PP4, and PP6). Here, we identify three novel PP6 subunits. Several PP6c (the catalytic subunit of PP6)-containing heterotrimeric complexes show phosphatase activities against g-H2AX in the in vitro phosphatase assays using bacterially-produced proteins, providing direct evidence that the PP6 holoenzyme is a PP6c-containing heterotrimeric complex. Furthermore, depletion of PP6c, PP6R2, or MyPT1 leads to defective HDR, and expression of phosphatase-inactive PP6c fails to rescue this defect. Chromatin immunoprecipitation assays demonstrated that PP6c is recruited to the region adjacent to the DSB sites. Expression of PP6R2, but not PP6c or MyPT1, is associated with improved overall survival in patients with breast cancer at five years (n=100, p=0.038). Taken together, our results suggest that the PP6-PP6R2-MyPT1 complex is required for HDR and PP6R2 is a potential therapeutic target. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2988.