Caspase independence of radio-induced cell death.
Colon carcinoma cells subjected to gamma-irradiation (4 Gy) manifest signs of apoptosis (caspase activation, chromatin condensation, phosphatidylserine (PS) exposure on the cell surface, sub-diploid DNA content), correlating with their radiosensitivity, which is increased in cells lacking the 14-3-3sigma protein as compared to wild-type controls. Inhibition of caspases by addition of Z-Val-Ala-DL-Asp (OMe)-fluoromethylketone, by stable transfection with the Baculovirus gene coding for p35, or by Bax knockout reduced all signs of apoptosis, yet failed to suppress radio-induced micro- and multinucleation. Moreover, pharmacological caspase inhibition, p35 expression or Bax knockout had no effect on the clonogenic survival that was reduced by gamma-irradiation and caspase inhibition failed to abolish the increased radiosensitivity of 14-3-3sigma-deficient cells. Micro- and multinucleation was detectable among non-apoptotic cells lacking PS exposure, as well as among cells undergoing apoptosis. Moreover, a fraction of micro- or multinucleated cells manifested caspase activation, and videomicroscopic analyses revealed that such cells could succumb to caspase-dependent apoptosis. Altogether, these results suggest that genomic instability induced by gamma-irradiation can trigger apoptosis, although apoptosis is dispensable for radio-induced clonogenic death.
Zhang
P
P
UPRES-EA2710, Institut Gustave Roussy, Villejuif, France.
Castedo
M
M
Tao
Y
Y
Violot
D
D
Métivier
D
D
Deutsch
E
E
Kroemer
G
G
Bourhis
Jean
J
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects*; D061945:Caspase Inhibitors; D020169:Caspases / Q000502:physiology*; D004789:Enzyme Activation; D005720:Gamma Rays; D045325:HCT116 Cells; D006801:Humans; D010718:Phosphatidylserines / Q000494:pharmacology; D011836:Radiation Tolerance
D000590:Amino Acid Chloromethyl Ketones; D061945:Caspase Inhibitors; D010718:Phosphatidylserines; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D020169:Caspases