title: High LET radiation enhances apoptosis in mutated p53 cancer cells through Caspase-9 activation.
abstract: Although mutations in the p53 gene can lead to resistance to radiotherapy, chemotherapy and thermotherapy, high linear energy transfer (LET) radiation induces apoptosis regardless of p53 gene status in cancer cells. The aim of this study was to clarify the mechanisms involved in high LET radiation-induced apoptosis. Human gingival cancer cells (Ca9-22 cells) containing a mutated p53 (mp53) gene were irradiated with X-rays, C-ion (13-100 KeV/microm), or Fe-ion beams (200 KeV/microm). Cellular sensitivities were determined using colony forming assays. Apoptosis was detected and quantified with Hoechst 33342 staining. The activity of Caspase-3 was analyzed with Western blotting and flow cytometry. Cells irradiated with high LET radiation showed a high sensitivity with a high frequency of apoptosis induction. The relative biological effectiveness (RBE) values for the surviving fraction and apoptosis induction increased in a LET-dependent manner. Both RBE curves reached a peak at 100 KeV/microm, and then decreased at values over 100 KeV/microm. When cells were irradiated with high LET radiation, Caspase-3 was cleaved and activated, leading to poly (ADP-ribose) polymerase (PARP) cleavage. In addition, Caspase-9 inhibitor suppressed Caspase-3 activation and apoptosis induction resulting from high LET radiation to a greater extent than Caspase-8 inhibitor. These results suggest that high LET radiation enhances apoptosis by activation of Caspase-3 through Caspase-9, even in the presence of mp53.
authors.affiliation: Department of Oral and Maxillofacial Surgery, School of Medicine, Nara Medical University, 840 Shijo-cho, Kashihara, Nara 634-8521, Japan.
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Yamakawa
authors.forename: Akihisa
authors.initials: A
authors.lastname: Takahashi
authors.forename: Eiichiro
authors.initials: E
authors.lastname: Mori
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Imai
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Furusawa
authors.forename: Ken
authors.initials: K
authors.lastname: Ohnishi
authors.forename: Tadaaki
authors.initials: T
authors.lastname: Kirita
authors.forename: Takeo
authors.initials: T
authors.lastname: Ohnishi
mesh_terms: D017209:Apoptosis / Q000528:radiation effects*; D053148:Caspase 3 / Q000502:physiology; D053453:Caspase 9 / Q000502:physiology*; D045744:Cell Line, Tumor; D004307:Dose-Response Relationship, Radiation; D004789:Enzyme Activation; D016158:Genes, p53 / Q000502:physiology*; D020450:Heavy Ions; D006801:Humans; D018499:Linear Energy Transfer; D009154:Mutation; D009369:Neoplasms / Q000201:enzymology / Q000473:pathology / Q000532:radiotherapy*; D014965:X-Rays
chemical_list: D053148:Caspase 3; D053453:Caspase 9