The levels of expression of O6-methylguanine-DNA
methyltransferase (MGMT) are relevant in predicting the response to the alkylating
chemotherapy in patients affected by
glioblastoma. MGMT promoter methylation and the published MGMT regulating
microRNAs (
miRNAs) do not completely explain the expression pattern of MGMT in clinical
glioblastoma specimens. Here we used a genome-wide microarray-based approach to identify MGMT regulating
miRNAs. Our screen unveiled three novel MGMT regulating
miRNAs, miR-127-3p, miR-409-3p, and miR-124-3p, in addition to the previously identified miR-181d-5p. Transfection of these three novel
miRNAs into the T98G
glioblastoma cell line suppressed MGMT
mRNA and
protein expression. However, their MGMT- suppressive effects are 30-50% relative that seen with miR-181d-5p transfection. In silico analyses of The
Cancer Genome Atlas (TCGA) and Chinese
Glioma Genome Atlas (CGGA) revealed that miR-181d-5p is the only
miRNA that consistently exhibited inverse correlation with MGMT
mRNA expression. However, statistical models incorporating both miR-181d-5p and miR-409-3p expression better predict MGMT expression relative to models involving either
miRNA alone. Our results confirmed miR-181d-5p as the key MGMT-regulating
miRNA. Other MGMT regulating
miRNAs, including the miR-409-3p identified in this report, modify the effect of miR-181d-5p on MGMT expression. MGMT expression is, thus, regulated by cooperative interaction between key MGMT-regulating
miRNAs.