Objectives MicroRNA deregulation is a critical event in head and neck squamous cell carcinoma (HNSCC). Several microRNA profiling studies aimed at deciphering the microRNA signatures of HNSCC have been reported, but there tends to be poor agreement among studies. The objective of this study was to survey the published microRNA profiling studies on HNSCC, and to assess the commonly deregulated microRNAs in an independent sample set. Materials and Methods Meta-analysis of 13 published microRNA profiling studies was performed to define microRNA signatures in HNSCC. Selected microRNAs (including members of miR-99 family) were evaluated in an independent set of HNSCC cases. The potential contributions of miR-99 family to the tumorigenesis of HNSCC were assessed by in vitro assays. Results We identified 67 commonly deregulated microRNAs. The up-regulation of miR-21, miR-155, miR-130b, miR-223 and miR-31, and the down-regulation of miR-100, miR-99a and miR-375 were further validated in an independent set of HNSCC cases with quantitative RT-PCR. Among these validated microRNAs, miR-100 and miR-99a belong to the miR-99 family. Our in vitro study demonstrated that restoration of miR-100 to the HNSCC cell lines suppressed cell proliferation and migration, and enhanced apoptosis. Furthermore, ectopic transfection of miR-99 family members down-regulated the expression of insulin-like growth factor 1 receptor (IGF1R) and mechanistic target of rapamycin (mTOR) genes. Conclusion In summary, we described a panel of frequently deregulated microRNAs in HNSCC, including members of miR-99 family. The deregulation of miR-99 family contributes to the tumorigenesis of HNSCC, in part by targeting IGF1R and mTOR signaling pathways.

miR-7 (microRNA-7) has been characterized as a tumour suppressor in several human cancers. It targets a number of proto-oncogenes that contribute to cell proliferation and survival. However, the mechanism(s) by which miR-7 suppresses tumorigenesis in TSCC (tongue squamous cell carcinoma) is unknown. The present bioinformatics analysis revealed that IGF1R (insulin-like growth factor 1 receptor) mRNA is a potential target for miR-7. Ectopic transfection of miR-7 led to a significant reduction in IGF1R at both the mRNA and protein levels in TSCC cells. Knockdown of miR-7 in TSCC cells enhanced IGF1R expression. Direct targeting of miR-7 to three candidate binding sequences located in the 3′-untranslated region of IGF1R mRNA was confirmed using luciferase-reporter-gene assays. The miR-7-mediated down-regulation of IGF1R expression attenuated the IGF1 (insulin-like growth factor 1)-induced activation of Akt (protein kinase B) in TSCC cell lines, which in turn resulted in a reduction in cell proliferation and cell-cycle arrest, and an enhanced apoptotic rate. Taken together, the present results demonstrated that miR-7 regulates the IGF1R/Akt signalling pathway by post-transcriptional regulation of IGF1R. Our results indicate that miR-7 plays an important role in TSCC and may serve as a novel therapeutic target for TSCC patients.

Down-regulation of miR-138 (microRNA-138) has been frequently observed in various cancers, including HNSCC (head and neck squamous cell carcinoma). Our previous studies suggest that down-regulation of miR-138 is associated with mesenchymal-like cell morphology and enhanced cell migration and invasion. In the present study, we demonstrated that these miR-138-induced changes were accompanied by marked reduction in E-cad (E-cadherin) expression and enhanced Vim (vimentin) expression, characteristics of EMT (epithelial–mesenchymal transition). On the basis of a combined experimental and bioinformatics analysis, we identified a number of miR-138 target genes that are associated with EMT, including VIM, ZEB2 (zinc finger E-box-binding homeobox 2) and EZH2 (enhancer of zeste homologue 2). Direct targeting of miR-138 to specific sequences located in the mRNAs of the VIM, ZEB2 and EZH2 genes was confirmed using luciferase reporter gene assays. Our functional analyses (knock-in and knock-down) demonstrated that miR-138 regulates the EMT via three distinct pathways: (i) direct targeting of VIM mRNA and controlling the expression of VIM at a post-transcriptional level, (ii) targeting the transcriptional repressors (ZEB2) which in turn regulating the transcription activity of the E-cad gene, and (iii) targeting the epigenetic regulator EZH2 which in turn modulates its gene silencing effects on the downstream genes including E-cad. These results, together with our previously observed miR-138 effects on cell migration and invasion through targeting RhoC (Rho-related GTP-binding protein C) and ROCK2 (Rho-associated, coiled-coil-containing protein kinase 2) concurrently, suggest that miR-138 is a multi-functional molecular regulator and plays major roles in EMT and in HNSCC progression.

MicroRNAs are post-transcriptional regulators that control mRNA stability and the translation efficiency of their target genes. Mature microRNAs are approximately 22-nucleotide in length. They mediate post-transcriptional gene regulation by binding to the imperfect complementary sequences (a.k.a. microRNA regulatory elements, MRE) in the target mRNAs. It is estimated that more than one-third of the protein-coding genes in the human genome are regulated by microRNAs. The experimental methods to examine the interaction between the microRNA and its targeting site(s) in the mRNA are important for understanding microRNA functions. The luciferase reporter gene assay has recently been adapted to test the effect of microRNAs. In this chapter, we use a previously identified miR-138 targeting site in the 3′-untranslated region (3′-UTR) of the RhoC mRNA as an example to describe a quick method for testing the interaction of microRNA and mRNA.