Role of miR-223/paired box 6 signaling in temozolomide chemoresistance in glioblastoma multiforme cells

Glioblastoma (GBM) is the predominant and most fatal type of brain tumor in adults. The prognosis of GBM remains poor despite advances in surgery, chemotherapy and radiotherapy. It is common that patients with GBM exhibit innate or acquired resistance to temozolomide (TMZ), a standard chemotherapeutic agent for GBM, and a previous report demonstrated that miRNA233 (miR223) promotes the growth and invasion of GBM cells by targeting tumor suppressor paired box 6 (PAX6). The present study explored the effect of TMZ on miR223/PAX6 signaling in addition to the effect of miR223/PAX6 signaling on TMZ chemoresistance in human GBM cells. Luciferase reporter assays confirmed that miR223 directly targets PAX6 through binding to its 3'untranslated region. TMZ reduced the expression level of miR223 in a concentrationdependent manner in U251 and U118 GBM cells, which led to increased expression of PAX6. miR223 and/or PAX6 were overexpressed and knocked down in U251 and U118 cells, and the half maximal inhibitory concentration (IC50) of TMZ and cell proliferation under TMZ treatment were used as measures of TMZ chemoresistance. The results demonstrated that overexpression of miR-223 in GBM cells markedly decreased TMZ-induced inhibition of cell proliferation and increased TMZ IC50, which could be abolished by overexpression of PAX6. On the other hand, knocking down miR223 in GBM cells with antagomir significantly enhanced the inhibitory effect of TMZ on GBM cell proliferation and decreased the TMZ IC50, which could be abolished by knockdown of PAX6. In conclusion, the present study demonstrated that TMZ inhibits GBM cell proliferation by inhibiting the expression of miR223, which leads to increased expression of tumor suppressor PAX6. Overexpression of miR223 increases TMZ chemoresistance, while inhibition of miR223 with antagomir markedly decreases TMZ chemoresistance in GBM cells. The present study provided novel insight into the molecular mechanisms underlying the pharmacological effects, in addition to the chemoresistance, of TMZ for GBM.