RESUMO
MicroRNAs (mirs) are small noncoding RNA molecules (~22 nucleotides) that regulate posttranscriptional gene expression. Currently, there has not been a comprehensive study of their role in primary head and neck squamous cell carcinoma (HNSCC). To determine the role of mirs in HNSCC, we screened for altered microRNA expression in HNSCC primary tissue and cell lines. We then further tested the functional impact of alterations of specific mirs. An initial screening of 4 primary HNSCC, 4 normal mucosal controls and 4 HNSCC cell lines was analyzed for mature microRNA expression by microarray. Significance was determined using significance analysis of microarrays (SAM). Nine microRNAs were found by SAM to be upregulated or downregulated in tumor tissue including mir-21, let-7, 18, 29c, 142-3p, 155, 146b (overexpressed) and 494 (underexpressed). Mir-21 was validated by qRT-PCR. Functional validation by growth assays was performed, further validating mir-21. Transfection of mir-21 into JHU-011 and JHU-012 cell lines showed a 39% increase in cell growth at 72 hr relative to controls (p < 0.05). Transfection of the inhibitor into JHU-O12 cell lines showed a 92% decrease in cell growth relative to controls at 72 hr (p < 0.05). In addition, flow cytometry analysis of JHU-012 cells 48 hr after mir-21 inhibitor transfection showed a statistically significant increase in cytochrome c release and increased apoptosis. These differentially expressed microRNAs may be of interest as potential novel oncogenes and tumor suppressor genes in HNSCC. Mir-21 is a putative oncogenic microRNA in head and neck cancer.