RESUMEN
<p><b>OBJECTIVE</b>To study the radiobiological characteristic of human nasopharyngeal carcinoma cell lines CNE1 and CNE2 and the changes in expression MRN (Mre11-Rad50-Nbs1) complex in the cell lines exposed to irradiation.</p><p><b>METHODS</b>CNE1 and CNE2 were irradiated by a linear accelerator. Radiobiological characteristics were detected by colony assay and MTT assay. MRN complex expression were examined by Western blot.</p><p><b>RESULTS</b>Surviving fraction at 2 Gy (SF2), quasi-threshold Dose (Dq), and mean lethal dose (Do) of CNE1 were 0.56, 1.449 Gy and 1.480 Gy; SF2, Dq, and Do of CNE2 were 0.44, 0.776 Gy and 1.685 Gy, respectively. Survival fraction of CNE1 at the day 6 after 4 Gy irradiation was 0.59 and that of CNE2 was 0.79 when compared with control, with the up-regulated expressions of Rad50 in CNE1 and Mre11, Rad50 and Nbs1 in CNE2 (P < 0.05).</p><p><b>CONCLUSIONS</b>CNE1 and CNE2 were sensitive to radiation, but there were radioresistance cells in CNE2. The expressions of some components of MRN complex were up-regulated to repair DNA lesions induced by radiation.</p>