title: Parg deficiency confers radio-sensitization through enhanced cell death in mouse ES cells exposed to various forms of ionizing radiation.
abstract: Poly(ADP-ribose) glycohydrolase (Parg) is the main enzyme involved in poly(ADP-ribose) degradation. Here, the effects of Parg deficiency on sensitivity to low and high linear-energy-transfer (LET) radiation were investigated in mouse embryonic stem (ES) cells. Mouse Parg(-/-) and poly(ADP-ribose) polymerase-1 deficient (Parp-1(-/-)) ES cells were used and responses to low and high LET radiation were assessed by clonogenic survival and biochemical and biological analysis methods. Parg(-/-) cells were more sensitive to γ-irradiation than Parp-1(-/-) cells. Transient accumulation of poly(ADP-ribose) was enhanced in Parg(-/-) cells. Augmented levels of phosphorylated H2AX (γ-H2AX) from early phase were observed in Parg(-/-) ES cells. The induction level of p53 phophorylation at ser18 was similar in wild-type and Parp-1(-/-) cells and apoptotic cell death process was mainly observed in the both genotypes. These results suggested that the enhanced sensitivity of Parg(-/-) ES cells to γ-irradiation involved defective repair of DNA double strand breaks. The effects of Parg and Parp-1 deficiency on the ES cell response to carbon-ion irradiation (LET13 and 70 keV/μm) and Fe-ion irradiation (200 keV/μm) were also examined. Parg(-/-) cells were more sensitive to LET 70 keV/μm carbon-ion irradiation than Parp-1(-/-) cells. Enhanced apoptotic cell death also accompanied augmented levels of γ-H2AX in a biphasic manner peaked at 1 and 24h. The induction level of p53 phophorylation at ser18 was not different between wild-type and Parg(-/-) cells. The augmented level of poly(ADP-ribose) accumulation was noted after carbon-ion irradiation compared to γ-irradiation even in the wild-type cells. An enhanced poly(ADP-ribose) accumulation was further observed in Parg(-/-) cells. Both Parg(-/-) cells and Parp-1(-/-) cells did not show sensitization to Fe-ion irradiation. Parg deficiency sensitizes mouse ES cells to a wide therapeutic range of LET radiation through the effects on DNA double strand break repair responses and enhanced cell death.
authors.affiliation: Division of Genome Stability Research, National Cancer Center Research Institute, 5-1-1 Tsukiji, Tokyo 104-0045, Japan.
authors.forename: Hidenori
authors.initials: H
authors.lastname: Shirai
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Fujimori
authors.forename: Akemi
authors.initials: A
authors.lastname: Gunji
authors.forename: Daisuke
authors.initials: D
authors.lastname: Maeda
authors.forename: Takahisa
authors.initials: T
authors.lastname: Hirai
authors.forename: Anna R
authors.initials: AR
authors.lastname: Poetsch
authors.forename: Hiromi
authors.initials: H
authors.lastname: Harada
authors.forename: Tomoko
authors.initials: T
authors.lastname: Yoshida
authors.forename: Keisuke
authors.initials: K
authors.lastname: Sasai
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Okayasu
authors.forename: Mitsuko
authors.initials: M
authors.lastname: Masutani
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000528:radiation effects*; D002244:Carbon; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D053595:Embryonic Stem Cells / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects*; D005434:Flow Cytometry; D005720:Gamma Rays; D006026:Glycoside Hydrolases / Q000172:deficiency* / Q000235:genetics; D020450:Heavy Ions; D006657:Histones / Q000378:metabolism; D015151:Immunoblotting; D051379:Mice; D018345:Mice, Knockout; D010766:Phosphorylation / Q000528:radiation effects; D011064:Poly Adenosine Diphosphate Ribose / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000172:deficiency* / Q000235:genetics; D011839:Radiation, Ionizing; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D002244:Carbon; D006026:Glycoside Hydrolases; D006657:Histones; D011064:Poly Adenosine Diphosphate Ribose; D011065:Poly(ADP-ribose) Polymerases; D016159:Tumor Suppressor Protein p53; C022407:poly ADP-ribose glycohydrolase; C475961:gamma-H2AX protein, mouse