Radiation-induced apoptosis in human non-small-cell lung cancer cell lines is secondary to cell-cycle progression beyond the G2-phase checkpoint.
OBJECTIVE
To characterize the relationship between cell-cycle progression and radiation-induced apoptosis in NSCLC cell lines with different p53 status.


METHODS
Cell lines with functional (H460, A549) and non-functional p53 (H661 and H520) were irradiated with 20 Gy. Multiparameter flow-cytometry was used to follow the progression of synchronized cells through the cell cycle after irradiation.


RESULTS
Delayed apoptosis was observed after cell-cycle progression beyond the G2 block, either in the late G2/M-phase of the same cell cycle being irradiated (H661, H520) or in the G1-phase of the subsequent cell cycle (H460, A549). The apoptotic fraction in H661 and H520 was 60-80% at 144h after irradiation, higher than in A549 and H460 (5 and 35%, respectively). As an alternative to apoptosis in cells cycling beyond the G2 restriction point, hyperploid cells were generated by all cell lines. Inhibition of cell-cycle progression through the G2/M-phase efficiently reduced the induction of late apoptosis. After irradiation in S-phase, 50-60% of cells with functional p53 remained arrested at the G2 restriction point until 144 h post-irradiation, while only 20% of the H661 or H520 did so.


CONCLUSIONS
These data characterize radiation-induced apoptosis in NSCLC cell lines as a removal pathway of clonogenically inactivated cells secondary to cell-cycle progression beyond G2/M, and is unlikely to be a critical factor for cellular radiation sensitivity.
Stuschke
M
M
Department of Radiotherapy, Humboldt-University, Charité, Berlin, Germany. martin.stuschke@uni-essen.de
Sak
A
A
Wurm
R
R
Sinn
B
B
Wolf
G
G
Stüben
G
G
Budach
V
V
D017209:Apoptosis / Q000528:radiation effects*; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics / Q000473:pathology* / Q000532:radiotherapy*; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D002869:Chromosome Aberrations / Q000528:radiation effects; D004249:DNA Damage; D016195:G2 Phase / Q000528:radiation effects; D015870:Gene Expression / Q000528:radiation effects; D016158:Genes, p53 / Q000528:radiation effects; D019833:Genistein / Q000494:pharmacology; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D009154:Mutation; D011836:Radiation Tolerance; D014407:Tumor Cells, Cultured; D014410:Tumor Stem Cell Assay
D019833:Genistein