Purpose: Recent studies have reported that miR-181b contributes to chemoresistance in several cancer types and functions as a tumor suppressor in glioma. This study aimed to explore whether miR-181b could enhance the chemotherapeutic effect of temozolomide in glioma cells and sought to identify the candidate target genes which mediated the effect.
Methods: Using 48 frozen samples from patients with glioma who had received in vitro chemosensitivity assay, we measured MGMT promoter methylation status by methylation-specific PCR and miR-181b expression by qRT-PCR. Then, miR-181b expression level was correlated with temozolomide IC₅₀ and MGMT promoter methylation status. To investigate the mechanism of miR-181b-induced chemosensitivity, assays were performed using stable miR-181b-expressing transfectants of glioma cell lines created by a lentiviral system.
Results: Glioma cells rich in miR-181b were more sensitive to temozolomide. miR-181b expression was not correlated with MGMT promoter methylation status. miR-181b combined with temozolomide enhanced glioma cell sensitivity and apoptosis. The effects were through posttranscriptional repression of MEK1. We demonstrated that miR-181b bound directly to the 3' untranslated regions of MEK1, thus reducing both the mRNA and protein levels of MEK1. Additionally, knockdown of MEK1 using small interfering RNA resulted in effects similar to ectopic miR-181b expression, whereas enforced expression of MEK1 lacking the 3' untranslated regions abrogated the effects. Finally, inverse correlation between miR-181b and MEK1 was established in glioma specimens.
Conclusion: miR-181b independently predicted chemoresponse to temozolomide and enhanced temozolomide sensitivity via MEK1 downregulation. A combination of miR-181b and temozolomide may be an effective therapeutic strategy for gliomas.