MicroRNAs are small functional RNAs that modulate various biological processes in cells by interfering with gene translation. We have previously demonstrated that certain miRNAs play a crucial role in the innate immune responses of human oral epithelial cells to Porphyromonas gingivalis. While addressing the mechanisms of P. gingivalis induced apoptosis in these cells, we discovered that certain miRNAs are upregulated upon stimulation with live bacteria. These upregulated miRNAs include hsa-miR-584, hsa-miR-572, hsa-miR-210, hsa-miR-492, hsa-miR-623 and hsa-miR-663. Further analysis revealed an unexpected role for hsa-miR-663 (miR-663). To further evaluate miR-663 function, we overexpressed miR-663 in epithelial cells which resulted in cellular apoptosis. The bioinformatics analysis of the miR-663 target prediction, revealed a strong binding affinity to a 3' UTR region of Apoptosis Antagonizing Transcription Factor (AATF) mRNA. To demonstrate the binding of miR-663 to AATF mRNA, the putative miR-663 target site within the 3'-UTR region of AATF was cloned in luciferase vector and transfected to HEK293T cells. Luminescence data showed the downregulation of luciferase activity in cells that had the full length target region of the putative binding site, confirming that AATF is one of the targets for miR-663. This prompted us to further evaluate its role in a cancer cell line (MCF-7) to determine miR-663s' apoptotic function. The overexpression of miR-663 led to a significant increase in apoptosis of MCF-7 cells. Taken together, miR-663 may function as an 'apoptomiR' by inhibiting the anti-apoptotic gene AATF to induce apoptosis. These findings could have therapeutic implications for epithelial cell targeting in cancer therapy.
Keywords: ApoptomiRs; Cell death; MicroRNAs; Porphyromonas gingivalis; Primary oral epithelial cells.