Screening and identification of mitochondrial miRNAs related to chemotherapy resistance in tongue squamous cell carcinoma

To investigate the differential expression of mitochondrial microRNAs (mitomiRs) in tongue squamous cell carcinoma (TSCC) and to screen out mitomiRs related to chemotherapy resistance.

Mitochondrial, cytoplasmic, and total cellular RNAs were extracted from the squamous cell carcinoma cell line CAL-27 and the cisplatin-resistant cell line CAL-27-re. High-throughput miRNA microarrays were used to screen for differentially expressed mitomiRs between the drug-resistant and parental cells. The upregulated mitomiRs in the CAL-27 and CAL-27-re cells and in samples from chemoresistant and chemosensitive tongue squamous cell carcinoma patients were verified by qRT-PCR.

The microarray detected 263 miRNAs in 6 components of the mitochondrial, cytoplasmic and total cellular RNAs from the CAL-27 and CAL-27-re cells, including 57 mitomiRs and 134 cytoplasmic microRNAs (cytomiRs). Compared with the total miRNAs, 35 mitomiRs were upregulated in the CAL-27-re cells, and 31 mitomiRs were upregulated in the CAL-27 cells (≥ 1.5-fold). Further comparative analysis of mitomiRs that were differentially expressed between the parental and drug-resistant cells identified 11 upregulated mitomiRs (miR-2392, miR-4462, miR-1290, miR-4449, miR-1268a, miR-1246, and miR-371a-5p, miR-3934-5p, miR-4271, miR-513p, and miR-664b-3p) and 5 downregulated mitomiRs (miR-188-5p, miR-1973, miR -3653, miR-4499, and miR-5787); the expression levels of the other 41 mitomiRs were almost identical in both cell lines. The qRT-PCR results were consistent with the miRNA microarray results. The 11 upregulated mitomiRs that were validated between the CAL-27 and CAL-27-re cells included miR-1268a, miR-2392, miR-4462, and miR-1290. Additionally, 5 mitomiRs, including miR-4449, were upregulated in the clinical chemotherapy-resistant tongue squamous cell carcinoma samples.

Differentially expressed mitomiRs were found between cisplatin-resistant and cisplatin-sensitive tongue squamous cell carcinoma cells. mitomiRs with high expression levels (miR-2392, miR-4462, miR-1290, miR-4449 and miR-1268a) may play important roles in the drug resistance of tongue squamous cell carcinoma.