Loss of PPP2R2A Inhibits Homologous Recombination DNA Repair and Predicts Tumor Sensitivity to PARP Inhibition

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. Cancer Res; 72(24); 6414-24. Ó2012 AACR.

Regulation of polo-like kinase 1 by DNA damage and PP2A/B55α

“…After all, it has been well established that dysregulation of Plk1 contributes to cancer progression and resistance, and the DNA damage checkpoint pathway constitutes an important anti-cancer barrier. A recent finding also showed that B55a negatively regulates ATM, 47 which is not in apparent agreement with the role of B55a as a tumor suppressor. However, it is plausible that B55a may play a rather complex role in the DDR by targeting multiple DDR factors.…”

LB100, a small molecule inhibitor of PP2A with potent chemo- and radio-sensitizing potential

“…140,141 Recently, PP2A was demonstrated to regulate HRR pathway activity via increased ATM signaling and act as a potential predictor of response to PARP inhibition. 142 Wei et al showed in vitro that LB100 treatment in pancreatic cells inhibited HRR in concurrently radiated cells and also has decreased Rad51 foci and increased gamma-H2AX foci, indicative of increased double strand DNA damage with decreased HRR repair. As such, inhibition of PP2A with LB100 may not only drive cancer cells through the mitotic cycle, but also decease HRR repair of radiation-induced DNA double stranded breaks.…”

p16INK4a Impairs Homologous Recombination–Mediated DNA Repair in Human Papillomavirus–Positive Head and Neck Tumors

“…The soluble nuclear fraction and insoluble chromatin fraction were extracted as previously described (17,18). The chromatin fraction was sonicated before gel electrophoresis and immunoblotting.…”

“…Immunofluorescence was performed as previously described (18). Briefly, the cells were plated on mClear 96-well plates (Greiner Bio-One) and fixed with 4% paraformaldehyde.…”