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ADP-ribosylation is a unique posttranslational modification catalyzed by poly(ADP-ribose) polymerases (PARPs) using NAD+ as ADP-ribose donor. PARPs play an indispensable role in DNA damage repair and small molecule PARP inhibitors have emerged as potent anticancer drugs. However, to date, PARP inhibitor treatment has been restricted to patients with BRCA1/2 mutation-associated breast and ovarian cancer. One of the major challenges to extend the therapeutic potential of PARP inhibitors to other cancer types is the absence of predictive biomarkers. Here, we show that ovarian cancer cells with higher level of NADP+, an NAD+ derivative, are more sensitive to PARP inhibitors. We demonstrate that NADP+ acts as a negative regulator and suppresses ADP-ribosylation both in vitro and in vivo. NADP+ impairs ADP-ribosylation-dependent DNA damage repair and sensitizes tumor cell to chemically synthesized PARP inhibitors. Taken together, our study identifies NADP+ as an endogenous PARP inhibitor that may have implications in cancer treatment.

Optimal DNA damage response is associated with ADP‐ribosylation of histones. However, the underlying molecular mechanism of DNA damage‐induced histone ADP‐ribosylation remains elusive. Herein, using unbiased mass spectrometry, we identify that glutamate residue 141 (E141) of variant histone H2AX is ADP‐ribosylated following oxidative DNA damage. In‐depth studies performed with wild‐type H2AX and the ADP‐ribosylation‐deficient E141A mutant suggest that H2AX ADP‐ribosylation plays a critical role in base excision repair (BER). Mechanistically, ADP‐ribosylation on E141 mediates the recruitment of Neil3 glycosylase to the sites of DNA damage for BER. Moreover, loss of this ADP‐ribosylation enhances serine‐139 phosphorylation of H2AX (γH2AX) upon oxidative DNA damage and erroneously causes the accumulation of DNA double‐strand break (DSB) response factors. Taken together, these results reveal that H2AX ADP‐ribosylation not only facilitates BER repair, but also suppresses the γH2AX‐mediated DSB response. Synopsis: The role of histone ADP‐ribosylation after DNA damage has remained elusive. Here, ADP‐ribosylation of histone variant H2AX on a specific residue upon oxidative damage is found to not only promote base excision repair (BER), but to also suppress γH2AX‐associated DNA double‐strand break (DSB) responses. Glutamate residue 141 (E141) of histone H2AX is ADP‐ribosylated following oxidative DNA damage.ADP‐ribosylation on E141 mediates recruitment of the BER glycosylase Neil3 to the sites of oxidative damage.H2AX E141A mutation abolishes ADP‐ribosylation and enhances serine‐139 phosphorylation to create γH2AX upon oxidative damage.Oxidative damage‐induced γH2AX formation in H2AX‐E141A mutants causes erroneous accumulation of DSB response factors. [ABSTRACT FROM AUTHOR]

53BP1 performs essential functions in DNA double-strand break (DSB) repair and it was recently reported that Tudor interacting repair regulator (TIRR) negatively regulates 53BP1 during DSB repair. Here, we present the crystal structure of the 53BP1 tandem Tudor domain (TTD) in complex with TIRR. Our results show that three loops from TIRR interact with 53BP1 TTD and mask the methylated lysine-binding pocket in TTD. Thus, TIRR competes with histone H4K20 methylation for 53BP1 binding. We map key interaction residues in 53BP1 TTD and TIRR, whose mutation abolishes complex formation. Moreover, TIRR suppresses the relocation of 53BP1 to DNA lesions and 53BP1-dependent DNA damage repair. Finally, despite the high-sequence homology between TIRR and NUDT16, NUDT16 does not directly interact with 53BP1 due to the absence of key residues required for binding. Taken together, our study provides insights into the molecular mechanism underlying TIRR-mediated suppression of 53BP1-dependent DNA damage repair. [ABSTRACT FROM AUTHOR]

ADP-ribosylation is a unique posttranslational modification catalyzed by poly(ADP-ribose) polymerases (PARPs) using NAD+ as ADP-ribose donor. PARPs play an indispensable role in DNA damage repair and small molecule PARP inhibitors have emerged as potent anticancer drugs. However, to date, PARP inhibitor treatment has been restricted to patients with BRCA1/2 mutation-associated breast and ovarian cancer. One of the major challenges to extend the therapeutic potential of PARP inhibitors to other cancer types is the absence of predictive biomarkers. Here, we show that ovarian cancer cells with higher level of NADP+, an NAD+ derivative, are more sensitive to PARP inhibitors. We demonstrate that NADP+ acts as a negative regulator and suppresses ADP-ribosylation both in vitro and in vivo. NADP+ impairs ADP-ribosylation-dependent DNA damage repair and sensitizes tumor cell to chemically synthesized PARP inhibitors. Taken together, our study identifies NADP+ as an endogenous PARP inhibitor that may have implications in cancer treatment. Cancer cells respond differently to inhibitors of Poly (ADP-ribose) polymerase. Here the authors reveal that ovarian cancer cells with higher cellular NADP+ levels are more sensitive to clinically relevant PARP1 inhibitors and show that NADP+ act as an endogenous inhibitor of PARP enzymes. [ABSTRACT FROM AUTHOR]

ADP-ribosylation is a unique posttranslational modification catalyzed by poly(ADP-ribose) polymerases (PARPs) using NAD + as ADP-ribose donor. PARPs play an indispensable role in DNA damage repair and small molecule PARP inhibitors have emerged as potent anticancer drugs. However, to date, PARP inhibitor treatment has been restricted to patients with BRCA1/2 mutation-associated breast and ovarian cancer. One of the major challenges to extend the therapeutic potential of PARP inhibitors to other cancer types is the absence of predictive biomarkers. Here, we show that ovarian cancer cells with higher level of NADP + , an NAD + derivative, are more sensitive to PARP inhibitors. We demonstrate that NADP + acts as a negative regulator and suppresses ADP-ribosylation both in vitro and in vivo. NADP + impairs ADP-ribosylation-dependent DNA damage repair and sensitizes tumor cell to chemically synthesized PARP inhibitors. Taken together, our study identifies NADP + as an endogenous PARP inhibitor that may have implications in cancer treatment.