title: Radiation-induced autophagy contributes to cell death and induces apoptosis partly in malignant glioma cells.
abstract: OBJECTIVE
  Radiation-induced autophagy has been shown to play two different roles, in malignant glioma (MG) cells, cytocidal or cytoprotective. However, neither the role of radiation-induced autophagy for cell death nor the existence of autophagy-induced apoptosis, a well-known cell-death pathway after irradiation, has been verified yet.
  
  
  METHODS
  We observed both temporal and dose-dependent response patterns of autophagy and apoptosis to radiation in MG cell lines. Additionally, we investigated the role of autophagy in apoptosis through knockdown of autophagy-related proteins.
  
  
  RESULTS
  Autophagic activity measured by staining of acidic vesicle organelles and Western blotting of LC-3 protein increased in proportion to radiation dose from day 1 to 5 after irradiation. Apoptosis measured by annexin-V staining and Western blotting of cleaved poly(ADP-ribose) polymerase demonstrated relatively late appearance 3 days after irradiation that increased for up to 7 days. Blocking of pan-caspase (Z-VAD-FMK) did not affect apoptosis after irradiation, but silencing of Atg5 effectively reduced radiation-induced autophagy, which decreased apoptosis significantly. Inhibition of autophagy in Atg5 knockdown cells was shown to be beneficial for cell survival. Stable transfection of GFP-LC3 cells was observed after irradiation. Annexin-V was localized in cells bearing GFP-LC3 punctuated spots, indicating autophagy in immunofluorescence. Some of these punctuated GFP-LC3 bearing cells formed conglomerated spots and died in final phase.
  
  
  CONCLUSIONS
  These findings suggest that autophagy appears earlier than apoptosis after irradiation and that a portion of the apoptotic population that appears later is autophagy-dependent. Thus, autophagy is a pathway to cell death after irradiation of MG cells.
authors.affiliation: Specific Organs Cancer Branch, National Cancer Center, Goyang, Korea.
authors.forename: Guk Heui
authors.initials: GH
authors.lastname: Jo
authors.affiliation: Department of Neurosurgery, University of Texas, MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Oliver
authors.initials: O
authors.lastname: Bögler
authors.affiliation: Department of Microbiology, Ajou University School of Medicine, Suwon, Korea.
authors.forename: Yong-Joon
authors.initials: YJ
authors.lastname: Chwae
authors.affiliation: Specific Organs Cancer Branch, National Cancer Center, Goyang, Korea.
authors.forename: Heon
authors.initials: H
authors.lastname: Yoo
authors.affiliation: Specific Organs Cancer Branch, National Cancer Center, Goyang, Korea.
authors.forename: Seung Hoon
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Specific Organs Cancer Branch, National Cancer Center, Goyang, Korea.
authors.forename: Jong Bae
authors.initials: JB
authors.lastname: Park
authors.affiliation: Specific Organs Cancer Branch, National Cancer Center, Goyang, Korea.
authors.forename: Youn-Jae
authors.initials: YJ
authors.lastname: Kim
authors.affiliation: Cancer Cell and Molecular Biology Branch, National Cancer Center, Goyang, Korea.
authors.forename: Jong Heon
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Neuro-oncology Clinic, National Cancer Center, Goyang, Korea.
authors.forename: Ho-Shin
authors.initials: HS
authors.lastname: Gwak
keywords: Apoptosis; Autophagy; Cell death; Glioma; Radiation