miR-221/222 enhances radiation resistance of glioblastoma by Akt pathway

Objective To study the pathway of miR-221/222 in enhancing radiation resistance of glioblastoma. Methods After 2 Gy of X-ray irradiation, the expressions of miR-221/222 in U251, U87 and LN229 glioblastma cells were detected with real-time PCR. Clonogenic assay was used to measure the radiosensitivity of glioblastoma after knocking down miR-221/222. ChIP assay was used to identify the combination situation of c-jun and miR-221/222. Luciferase assay was applied to check whether PTEN was a target of miR-221/222. Western blot was used to detect the expression of relevant proteins in the glioblastoma cells after knocking down miR-221/222. The effect of miR-221/222 and irradiation on growth of glioblastoma in nude mice was also observed. Results The expression of miR-221/222 was increased by irradiation(t=5.48~29.21, P<0.05) and the radiosensitivity of anti-miR-221/222-transfected cells was also increased(F=1 202.22, 1 789.12, 1 012.32, P<0.05). MiR-221/222 was transcriptionally regulated by c-jun with a target of PTEN(t=13.16, P<0.05). When miR-221/222 was knocked-down, the expression of pAkt and DNA-PKcs were down-regulated while PTEN and GSK-3β were up-regulated, and the expression of Akt were not changed. Moreover, the growth of xenograft tumor was significantly inhibited by the combination treatment of anti-miR-221/222 and irradiation(F=56.36, P<0.05). Conclusions The expression of miR-221/222 in glioblastoma cells can be increased by irradiation, and the activation of Akt pathway downstream miR-221/222 could enhance the radiation resistance of glioblastoma. Key words: Glioblastoma; Radiation resistance; MiR-221/222; DNA damage; Akt