MiR-23b-3p Regulates The Sensitivity Of Glioblastoma Cells To Temozolomide By Targeting Connexin 43

Glioblastoma(GBM)is well known for its highly aggressive and drug-resistant ability.It usually invades into functional areas of brain and is liable to metastasis.For these reasons,operation normally can not achieve commendable clinical benefit.Temozolomide(TMZ)is the Fist-line treatment of GBM.However,drug resistance confined the therapeutic effect of TMZ and lead to lower survival rate of patients.miR-23b-3p is widely distributed in various types of cells.And it was reported to participate in the regulation of drug-resisitance in different cancers,including gastric adenocarcinoma and breast cancer.Connexin 43(Cx43)plays a regulatory role in chemoresistance of GBM.But whether miR-23b-3p is involved in the drug-resistance of GBM and its target is related to Cx43 have not been reported.Thus,the exact mechanism of miR-23b-3p in regulating GBM drug resistance remains to be further studied.In this study,we first examined the expression of miR-23b-3p in different glioma cells and its sensitivity to TMZ.It was found that the expression of miR-23b-3p in drug-resistant U87MG cell line was significantly lower than that in U251 and A172 which were sensitive to TMZ.Overexpression of miR-23b-3p mimic in U87MG upregulated the drug sensitivity of this cell to TMZ and increased the level of apoptosis in drug-treated cells.Moreover,the use of miR-23b-3p-inhibitor in U251 and A172 downregulated the sensitivity of GBM to TMZ and reduced the apoptosis.The expression level of Cx43 protein was negatively correlated with the chemosensitivity of GBM to TMZ.Knockdown of Cx43 protein with shRNA can increase the sensitivity of GBM to TMZ and decrease apoptosis with drug treatment.And overexpression of Cx43 increased the resistance of GBM to TMZ.The TargetScan database predicted that the Cx43mRNA 3’UTR had a binding site for miR-23b-3p,suggesting that miR-23b-3p may target Cx43.Furthermore,we overexpressed miR-23b-3p mimic in glioma cells and found that Cx43 protein level was significantly inhibited.While using miR-23b-3p-inhibitor,Cx43 protein level was up-regulated.In addition,The Dual-luciferase reporter gene showed that miR-23b-3p bound to the 3’-UTR of Cx43.Finally,we knocked down Cx43 with shRNA in glioma cells and found that it can reverse the sensitization of miR-23b-3p to TMZ,suggesting that the effect of miR-23b-3p on glioma resistance was related to Cx43.In conclusion,we have demonstrated that miR-23b-3p binds to the 3’-UTR of Cx43 mRNA and then downregulates the expression of Cx43,which contributes to the increasing sensitivity of malignant glioma to TMZ.