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 miRNA-233 (miR-223) 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 miR-223/PAX6 signaling in addition to the effect of miR-223/PAX6 signaling on TMZ chemoresistance in human GBM cells. Luciferase reporter assays confirmed that miR-223 directly targets PAX6 through binding to its 3′-untranslated region. TMZ reduced the expression level of miR-223 in a concentration-dependent manner in U251 and U118 GBM cells, which led to increased expression of PAX6. miR-223 and/or PAX6 were overexpressed and knocked down in U251 and U118 cells, and the half maximal inhibitory concentration (IC(50)) 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 IC(50), which could be abolished by overexpression of PAX6. On the other hand, knocking down miR-223 in GBM cells with antagomir significantly enhanced the inhibitory effect of TMZ on GBM cell proliferation and decreased the TMZ IC(50), 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 miR-223, which leads to increased expression of tumor suppressor PAX6. Overexpression of miR-223 increases TMZ chemoresistance, while inhibition of miR-223 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.