Activation of diverse pathways to apoptosis by (125)IdUrd and gamma-photon exposure.
OBJECTIVE
To delineate the mechanisms underlying induction of apoptosis in malignant cells irradiated by DNA-incorporated iodine-125 or gamma-photons.


METHODS
Human tumor cells (RKO, LS174T, TE671, and MCF7) were irradiated by DNA-incorporated 5-[125I]iodo-2'-deoxyuridine (125IdUrd) or by gamma-photons. Clonogenic survival was determined by the colony-forming assay. Caspase-3 induction was measured with a fluorogenic substrate assay, and DNA fragmentation was determined by ligation-mediated polymerase chain reaction. DNA arrays were used to assess the expression of the B-cell lymphoma/leukaemia-2 (Bcl-2) family and related genes in RKO cells and in caspase-3-gene-defective MCF7 cells.


RESULTS
After 125IdUrd or y-photon exposure, the highest induction of caspase-3 was observed in the radiation-sensitive cell lines (RKO and LS174T). DNA fragmentation was prominent in the radiosensitive cells and undetectable in TE671 (125IdUrd and gamma-photons) and MCF7 (125IdUrd only) cells. Exposure of RKO and MCF7 cells to 125I decay led to up-regulation of several pro-apoptotic and antiapoptotic Bcl-2 family genes whereas y-irradiation produced minimal activation.


CONCLUSIONS
Apoptosis generated by a DNA-incorporated Auger electron emitter is induced through the mitochondrial/caspase-3-mediated pathway and correlates with cellular radiosensitivity. Apoptosis caused by y-radiation can be signaled without activation of Bcl-2 family genes, and DNA fragmentation occurs with or without caspase-3 activation.
Urashima
Tetsuro
T
Harvard Medical School, 200 Longwood Avenue, Armenise Building, D2-137, Boston, MA, USA.
Wang
Ketai
K
Adelstein
S James
SJ
Kassis
Amin I
AI
D017209:Apoptosis / Q000528:radiation effects*; D045744:Cell Line, Tumor / Q000528:radiation effects; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D015972:Gene Expression Regulation, Neoplastic / Q000528:radiation effects*; D006801:Humans; D007065:Idoxuridine / Q000009:adverse effects*; D009369:Neoplasms / Q000235:genetics / Q000503:physiopathology*; D017785:Photons; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D011829:Radiation Dosage; D019275:Radiopharmaceuticals / Q000009:adverse effects; D015398:Signal Transduction / Q000528:radiation effects*
D019253:Proto-Oncogene Proteins c-bcl-2; D019275:Radiopharmaceuticals; D004247:DNA; D007065:Idoxuridine