Effect of radiation on the radiosensitivity of a human malignant glioma cell line

Objective To observe the differences of the radio-biological characteristics between the human malignant glioma cell line SHG-44 and its progeny cells SHG-4410 Gy and to probe the underlying mechanism.Methods The SHG-4410 Gy cells were the progeny of SHG cells that had been irradiated with 10 Gy X-rays and then passaged for 15 generations.The radiosensitivity of SHG-44 and SHG-4410 Gy wre measured by clonogenic assay and the multi-target single-hit model was used to fit the survival curve.The cell cycle redistribution and apoptosis were analyzed by flow cytometry assay.Quantitative Real Time-PCR (qRT-PCR) was used to determine the relative levels of cyclin B1 mRNA and miR-21.Stat3 protein levels were detected by Western blot.Results The values of D0,Dq and SF2 of SHG-4410 Gy cells were significantly higher than those of SHG-44 cells.Flow cytometric analysis showed that there was less G2/M phase arrest in SHG-4410 Gy (F =22.21,P ＜ 0.05).Radiation-induced early apoptotic population was increased from (17.60 ± 0.26) ％ to (28.00 ± 0.36) ％ for SHG-44 cells,but increased from only (4.20 ± 0.30)％ to (5.17 ± 0.65)％ for SHG-4410 Gy.miR-21 in SHG-4410 Gy cells were increased by 1.44 fold of SHG-44 cells,which was associated with the increase of Stat3 protein expression.Conclusions Radioresistance is observed in the progeny of human malignant glioma cell line SHG-44 which had been irradiated with 10 Gy X-rays.The underlying mechanisms may be relative to the upregulation of cyclin B1 that acts as a key downstream gene in the signaling pathway of G2/M phase transition.In addition,the upregulation of miR-21 may be involved in the apoptosis of SHG-4410 Gy cells. Key words: Glioma; Radioresistance; cyclin B1; miR-21; Stat3