Abstract A022: Poly (ADP-Ribose) glycohydrolase (PARG) removes repressive Poly-ADP Ribose marks from DNA polymerase theta (polq) to stimulate DNA double-strand breaks repair in myeloid malignancies
Authors: Vekariya Umeshkumar , Minakhin Leonid , Tyagi Mrityunjay , Kent Tatiana , Chandramouly Gurushankar , Sullivan-Reed Katherine , Atkins Jessica , Nieborowska-Skorska Margaret , Kukuyan Anna-Mariya , Pomerantz Richard , Skorski Tomasz 
Published: January 2024

Abstract
Poly (ADP-ribose) polymerase 1 (PARP1) dependent poly-(ADP)-ribosylation (PARylation) of proteins is one of the major post-translational modification events involved in the DNA damage response (DDR). PARylation is tightly controlled by the glycohydrolase activity of poly (ADP-ribose) glycohydrolase (PARG). Thus, interplay between PARP1 and PARG is thought to regulate the PARylation status of relevant DDR proteins and multiple studies demonstrated that both PARP1 and PARG contribute to DDR. Here, we investigated whether the interplay of PARP1 and PARG is important for the regulation of TMEJ and the specific activities of Polq in myeloid malignancies harboring OTKs. We found that upon DNA damage OTKs exerted temporal effect on Polq, PARP1 and PARG detection in chromatin fractions. While both Polq and PARG displayed continuous time-dependent accumulation during 120 min. after irradiation, PARP1 levels sharply increased at 20 min. and dissipated at 120 min. post-irradiation confocal microscopy detected spatiotemporal changes of Polq - PARP1 – PARG colocalization and PARylation of Polq. Polq - PARP1 interaction and PARylation of Polq was detected early followed by dissipation of that interaction and enhanced colocalization of Polq and PARG and dePARylation of Polq. At the time when Polq was PARylated by PARP1, it was not detected at DSBs marked by gH2AX whereas PARG-mediated dePARylation of Polq was associated with its colocalization with DSBs. We find that PARP1 binds to and directly PEGylates Polq in vitro and in cells. Biochemical assays revealed that PARP1 recruits Polq to the vicinity of DNA damage via PARylation-dependent formation of biomolecular condensates containing Polq. However, PARylated Polq is unable to perform TMEJ due to its inability to bind directly to DNA. Hence, PARG is needed to reactivate Polq DNA binding and its TMEJ activity by removing repressive PAR marks on Polq. In support of this, cellular studies show that PARP1-PARG – regulated spatiotemporal recruitment of Polq to DSBs is essential for TMEJ activity. In conclusion, using intracellular and biochemical approaches we show here that both PARP1 and PARG are required for TMEJ despite their counteracting enzymatic activities. We also pinpointed a unique dynamic spatiotemporal interplay between Polq, PARP1 and PARG to regulate TMEJ activity in OTK-positive myeloid malignant cells. Our studies support a two-step mechanism of a PARP1-PARG regulatory axis of Polq and TMEJ. In the first step, the rate of PARP1-Polq spatiotemporal recruitment to DNA damage foci supports a rapid step whereby PARP1 PARylates Polq and facilitates its recruitment to the vicinity of DNA damage in an inactive state. The rate of PARG spatiotemporal recruitment supports a second step whereby subsequent recruitment of PARG corresponds to dissipation of PARP1 and PAR at DNA damage sites, PARG-mediated removal of PAR repressive marks on Polq, and activation of TMEJ.
Citation Format: Umeshkumar Vekariya, Leonid Minakhin, Mrityunjay Tyagi, Tatiana Kent, Gurushankar Chandramouly, Katherine Sullivan-Reed, Jessica Atkins, Margaret Nieborowska-Skorska, Anna-Mariya Kukuyan, Richard Pomerantz, Tomasz Skorski. Poly (ADP-Ribose) glycohydrolase (PARG) removes repressive Poly-ADP Ribose marks from DNA polymerase theta (polq) to stimulate DNA double-strand breaks repair in myeloid malignancies [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: DNA Damage Repair: From Basic Science to Future Clinical Application; 2024 Jan 9-11; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2024;84(1 Suppl):Abstract nr A022.