PolyADP-ribosylation is a post-translational modification of proteins, and poly(ADP-ribose) (PAR) polymerase (PARP) family proteins synthesize PAR using NAD as a substrate. Poly(ADP-ribose) glycohydrolase (PARG) functions as the main enzyme for the degradation of PAR. In this study, we investigated the effects of Parg deficiency on tumorigenesis and therapeutic efficacy of DNA damaging agents, using mouse ES cell-derived tumor models. To examine the effects of Parg deficiency on tumorigenesis, Parg^+/+ and Parg^−/− ES cells were subcutaneously injected into nude mice. The results showed that Parg deficiency delays early onset of tumorigenesis from ES cells. All the tumors were phenotypically similar to teratocarcinoma and microscopic findings indicated that differentiation spectrum was similar between the Parg genotypes. The augmented anti-tumor therapeutic effects of X-irradiation were observed under Parg deficiency. These results suggest that Parg deficiency suppresses early stages of tumorigenesis and that Parg inhibition, in combination with DNA damaging agents, may efficiently control tumor growth in particular types of germ cell tumors.

Poly(ADP-ribose) (PAR) formation is catalyzed by poly(ADP-ribose) polymerase (PARP) family proteins in nuclei as well as in cytosols. The anti-PAR antibodies that specifically detect PAR are useful for the quantitative measurement of PAR in cells, in tissue, and in the body. In clinical trials of PARP inhibitors, a pharmacodynamic (PD) assay for the measurement of PARP activity inhibition in peripheral blood mononuclear cells (PBMCs) with dot-blot assay or an ELISA assay using anti-PAR antibodies have been used. In these assays, ex vivo PARP activity and its inhibition assay have been used. For a PD assay to assess the efficacy of the treatment, the measurement of PARP activity inhibition in tumor tissues/cells has been recommended. A dot or slot blot assay may also be suitable for the measurement of such crude tissue samples. Here, we investigate the optimum conditions for a dot/slot blot assay of an ex vivo PARP activity assay by utilizing physical and chemical crosslinking methods. Using 10H monoclonal antibody to PAR, we show that use of a nylon membrane and UV crosslink at 254 nm can stably enhance the detection level of PAR. However, the limitation of this assay is that the size of PAR detectable using the 10H antibody must be around 20 ADP-ribose residues, since the antibody cannot bind PAR of lower size.