Abstract
Reversible phosphorylation plays a critical role in DNA repair. Here, we report the results of a loss-of-function screen that identifies the PP2A heterotrimeric serine/threonine phosphatases PPP2R2A, PPP2R2D, PPP2R5A, and PPP2R3C in double-strand break (DSB) repair. In particular, we found that PPP2R2A-containing complexes directly dephosphorylated ATM at S367, S1893, and S1981 to regulate its retention at DSB sites. Increased ATM phosphorylation triggered by PPP2R2A attenuation dramatically upregulated the activity of the downstream effector kinase CHK2, resulting in G(1) to S-phase cell-cycle arrest and downregulation of BRCA1 and RAD51. In tumor cells, blocking PPP2R2A thereby impaired the high-fidelity homologous recombination repair pathway and sensitized cells to small-molecule inhibitors of PARP. We found that PPP2R2A was commonly downregulated in non-small cell lung carcinomas, suggesting that PPP2R2A status may serve as a marker to predict therapeutic efficacy to PARP inhibition. In summary, our results deepen understanding of the role of PP2A family phosphatases in DNA repair and suggest PPP2R2A as a marker for PARP inhibitor responses in clinic.
Highlights
Genome stability is essential for the prevention of undue cellular death and cancer development
Previous studies showed that phosphatase 2A (PP2A) negatively regulates phosphoinositide 3-kinase–like kinase (PIKK)-induced signaling, more recent reports have shown that PP2A inhibition impairs DNA repair [7, 8]
To systematically identify PP2A complexes that mediate double-strand breaks (DSB) repair, we conducted a loss-of-function screen using short hairpin RNA (shRNA) library that targets each of the known PP2A B regulatory subunits [16]. Quantitative real-time reverse transcription PCR (qRT-PCR) analysis confirmed the knockdown (KD) in each of the shRNA-expressing cell lines (Fig. 1C; Supplementary Fig. S3B)
Summary
Genome stability is essential for the prevention of undue cellular death and cancer development. Cells have evolved multiple DNA repair pathways [1]. One of the most powerful activators of the DNA repair response is double-strand breaks (DSB). Initiation of DSB repair is controlled by the phosphoinositide 3-kinase–like kinase (PIKK) family. A wave of phosphorylation events radiating from PIKKs is amplified to convey the signals to a large number of substrates. This cascade has been studied in a great detail, the biologic relevance of many of these phosphorylation events and the mechanisms that control their downregulation remain unknown [2]. Phosphorylation of a number of PIKKs, including ataxia telangiectasia mutated (ATM), ATR, and CHK2, oscillates
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