Human embryonic kidney 293聽T (293T) cells were infected with pLL3.7-miR-223 plasmid to generate the pLL3.7-miR-223 and -empty virus (EV) lentivirus (miR-223 and EV). A dual luciferase assay in which the reporter contained wild-type 3鈥?untranslated region (UTR) of ATM was performed. U87MG聽cells were infected with miR-223 or EV to establish the overexpressed stable cell lines (U87-223 or U87-EV, respectively). Cells were irradiated in聽vitro, and dose enhancement ratios at 2聽Gy (DER2) were calculated. Hind legs of BALB/c athymic mice were injected with U87-223 or U87-EV cells; after 2聽weeks, half of the tumors were irradiated. Tumor volumes were tracked for a total of 5聽weeks.
The dual luciferase reporter assay showed a significant reduction in luciferase activity of 293T cells cotransfected with miR-223 and the ATM 3鈥睻TR compared to that in EV control. Overexpression of miR-223 in U87MG聽cells showed that ATM expression was significantly downregulated in the U87-223聽cells compared to that in U87-EV (ATM/尾-actin mRNA 1.0 vs 1.5, P<.05). U87-223聽cells were hypersensitive to radiation compared to U87-EV cells in聽vitro (DER2聽=聽1.32, P<.01). Mice injected with miR-223-expressing tumors had almost the same tumors after 3聽weeks (1.5聽cm3 vs 1.7聽cm3). However, irradiation significantly decreased tumor size in miR-223-expressing tumors compared to those in controls (0.033聽cm3 vs 0.829聽cm3).
miR-223 overexpression downregulates ATM expression and sensitizes U87聽cells to radiation in聽vitro and in聽vivo. MicroRNA-223 may be a novel cancer-targeting therapy, although its cancer- and patient-specific roles are currently undefined.