[Significance of apoptotic processes in radiotherapy. I]

Radiation induced chromosome aberrations and clonogenic survival in human lymphoblastoid cell lines with different p53 status

PURPOSE

To better understand the relation of radiation induced chromosome aberrations and clonogenic survival in cells with different p53 status.

MATERIALS AND METHODS

The human lymphoblasts TK6 and WTK1 were derived from the same donor, but differ in radiosensitivity, p53 status and kinetics of apoptosis. TK6 cells have wild type p53 (p53wt), whereas WTK1 cells have a mutated, non-functional p53 (p53mut). Additionally, a HPV16 E6 transfected TK6 cell line (TK6E6), which is also negative for p53 function (p53neg), was studied. The cells were irradiated, incubated with colcemid, hypotonically lysed and fixed. After staining with Giemsa, asymmetric chromosomal exchange type aberrations were counted in 50 mitoses each per dose point (0 to 4 Gy). Clonogenic survival was determined using the microtiter plate assay. All experiments were performed in triplicate.

RESULTS

WTK1 (p53mut) show a higher spontaneous frequency of chromosome aberrations than TK6 (p53wt). No significant differences were noted in radiation induced aberration frequency. TK6E6 (p53neg) show comparable aberration frequencies like TK6. However, the dose required to reduce survival to 10% (D10) was about 2 Gy for TK6 and TK6E6, whereas the D10 for WTK1 was approximately 3 Gy.

CONCLUSION

The p53 status influences the radiosensitivity in this lymphoblast cell system showing a high rate of radiation induced apoptosis. Cells with p53mut (WTK1), survive with a damaged genome, because they do not undergo apoptosis to loose their clonogenicity. There was no difference between the p53wt (TK6) and p53neg cells (TK6E6) suggesting a suppression of radiation induced apoptosis by p53mut.