Aberrantly expressed miRNAs are linked to the regulation of oncogenes and/or tumor suppression genes within the cell signal transduction pathway network, thereby contributing to carcinogenesis. miRNA function can be antagonized, thus representing a novel anti-tumor approach for integrated cancer therapy. In this study, we designed adenovirally-expressed shRNAs that functionally co-repressed the expression of miR-221 and miR-222, which are related to glioblastoma, to overcome the low efficiency of gene therapy. In addition, we generated novel shRNAs whose 3' ends were mutated in the region complementary to the target miRNA's 5' seed region to reduce the stability of binding with the miRNA. Various inhibition levels of miRNA were achieved: classic shRNAs yielded the greatest reduction in miRNA levels, followed by mutated shRNAs and the blank control, as determined by qRT-PCR. These results were confirmed by the protein expression of p27kip1, the validated target of miR-221/222, the effect on cell cycle arrest in G1 phase, and the impact on cell apoptosis. These results suggested that we could produce shRNAs encoded by adenovirus that co-repressed multiple tumor-related miRNAs simultaneously, and that the level of repression and the effect on the function of a specific miRNA could be achieved in a semi-quantitative manner.

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