Head and neck squamous cell carcinomas (HNSCC) represent 6% of all cancers. Despite of considerable advances in surgery, radiotherapy and chemotherapy, the overall 5-year survival rate for patients is less than 40% in advanced stage. The understanding of the new molecular pathways of HNSCC carcinogenesis would be helpful in improving diagnosis and therapy of the disease. MicroRNA(miRNA) are endogenous short non-coding RNA molecules, which regulate gene expression by repressing translation or cleaving RNA transcripts in a sequence-specific manner. miRNA over-expression could result in down-regulation of tumor suppressor genes, whereas their under-expression could lead to oncogenes activation. Expression levels of 665 human mature miRNAs were screened using the stem-loop real-time quantitative PCR method. We identified several down-regulated miRNAs based on miRNA expression signatures in HNSCC. A comparison of miRNA signatures from HSCC and our previous reports (Ichimi et al., Int J Cancer 2009, 125:342-352; Kano et al., AACR 2009, #552; Kikkawa et al., AACR 2009, #587) identified miR-133a that is down-regulated in common, suggesting that miR-133a is candidate tumor suppressor. Gain-of-function analysis revealed that miR-133a transfectant inhibits cell proliferation and cell invasion in cancer cells. For target genes silenced by miR-133a in cancer cells, we performed genome-wide screening (oligo microarray analysis and public database searche). Among the genome-wide analysis, several candidate genes were identified, such as, fascin homolog 1 (FSCN1) and glutathione S-transferase P1 (GSTP1). We focused on FSCN1, an actin-bundling protein, which induces parallel actin bundles in cell protrusions and increases cell motility in several human cancers. The miR-133a which has conserved sequence in the 3′UTR of FSCN1, inhibited of FSCN1 expression. The signal from a luciferase reporter assay was significantly decreased at miR-133a site, suggesting miR-133a directly regulate FSCN1. An FSCN1 loss-of-function assay found significant cell growth and invasion inhibition in HNSCC cells implying an FSCN1 is associated with HSCC carcinogenesis. Tumor suppressive miRNAs and target oncogenes may provide new insights into the mechanisms in cancer. Our findings have therapeutic implications and may be exploited for future HSCC treatments.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2088.