High expression of circadian gene mPer2 diminishes radiosensitivity of tumor cells.

OBJECTIVE

The aim of this study was to study mPeriod2 gene expression influencing the radiosensitivity of mouse tumor cells exposed to 60Co-gamma-rays.

MATERIALS AND METHODS

Lewis lung carcinoma (LLC) and EMT6 cells were induced by phorbol myristate acetate or transfected with pcDNA3.1-mPer2 and irradiated with 60Co-gamma-rays, then analyzed with several methods, such as flow cytometry, single-cell gel electrophoresis assay (SCGE), reverse-transcriptase polymerase chain reaction (RT-PCR), immunohistochemistry, cell-clone-forming analysis, and so forth.

RESULTS

In SCGE analysis, the mPer2 high-expression groups exposed to gamma-rays presented lighter DNA damage, compared with controls (p < 0.05). Clone-forming efficiency and cell-survival curve showed that cells transfected with pcDNA3.1-mPer2 formed more clones than control groups and had augmented mean lethal dose (D(0)), near field dose (Dq), decreasing extrapolation number (N), and a higher survival and clone-forming rate. RT-PCR analysis revealed a decreased expression of bax and p53, an increased expression of c-myc, bcl-2, and Rad51, and increased proportionality of bcl-2/bax, whereas p21 didn't change obviously in irradiated mPer2-transfected LLC cells.

CONCLUSIONS

This research suggests that the circadian system is involved in the protection and restoration of tumor cells against environmental detriments, such as 60Co-gamma-ray radiographic inspection. The gene, mPer2, might be considered as an inhibitor in tumor radiotherapy.