Background and objectives: MicroRNAs (miRNAs) are small non-coding double-stranded RNA with size of approximately 22 nucleotides, and those inhibit protein translation by binding the 3 f-untranslated region of target mRNAs. MiRNAs can act as tumor suppressors or oncogenes in human malignancies. In this study, we have attempted to identify the novel tumor suppressive miRNAs (TS-miRs) in human oral cancer cells.

Methods: To identify TS-miRs in human oral cancer cells, function-based screening using human miRNA overexpression library were carried out. We transfected human oral squamous cell carcinoma (OSCC) cells (GFP-SAS) and salivary gland cancer (SGC) cells (GFP-ACCM) with approximately 1000 synthetic miRNAs mimicking human mature miRNAs. After transfection for 3 days, the growth of these cells was evaluated by WST-8 assay. Furthermore, target genes of TS-miRs were explored with the use of microarray and Ingenuity Pathway Analysis (IPA). We also investigated the expression levels of TS-miRs in OSCC and SGC tissues by real-time quantitative RT-PCR (qRT-PCR).

Results: In comprehensive functional analysis using human synthetic mature miRNAs, miRNA-1289 (miR-1289) markedly inhibited the growth of both types of cells. The growth rate of GFP-SAS and GFP-ACCM cells transfected with miR-1289 reduced by 86.4% and 50.7%, respectively. In microarray and IPA, the expression of 13 cancer-related genes including cyclin E1 was commonly down-regulated in human oral cancer cells by transfection with miR-1289. Furthermore, qRT-PCR revealed decreased expression of miR-1289 in 32 of 45 OSCC and 3 of 5 SGC tissues compared to normal oral mucosa and salivary gland tissues, respectively.

Conclusions: These results suggest that miR-1289 functions as a novel TS-miR in human oral cancer cells, and may be a useful therapeutic tool for the patients with oral cancer.

Key words: microRNA; oral cancer; tumor suppressor