Here, we confirmed that miR-138 is also frequently down-regulated in TSCC

Here, we confirmed that miR-138 is also frequently down-regulated in TSCC. of these 194 down-regulated transcripts are potential direct targets for miR-138. These targets include: chloride channel, nucleo-tide-sensitive, 1A (CLNS1A), G protein alpha inhibiting activity polypeptide 2 (GNAI2), solute carrier family 20, member 1 (SLC20A1), eukaryotic translation initiation factor 4E binding protein 1 (EIF4EBP1), and Rho-related GTP-binding protein C (RhoC). GNAI2 is a known proto-oncogene that is involved in the initiation and progression of several different types of tumors. Direct targeting of miR-138 to two candidate binding sequences located SB-505124 HCl in the 3-untranslated region of GNAI2 mRNA was confirmed using luciferase reporter gene assays. Knockdown of miR-138 in TSCC cells enhanced the expression of GNAI2 at both mRNA and protein levels. In contrast, ectopic trans-fection of miR-138 reduced the expression of GNAI2, which, in SB-505124 HCl consequence, led to reduced proliferation, cell cycle arrest and apoptosis. In summary, we identified a number of high-confident miR-138 target genes, including proto-oncogene GNAI2, which may play an important role in TSCC initiation and progression. == Introduction == Oral squamous cell carcinoma (OSCC) is a complex disease that arises in various sub-sites. Tumors from these different sub-sites have distinct clinical presentations and outcomes, and are associated with different genetic characteristics (Timar et al. 2005). In this study, we focused on oral tongue SCC (TSCC), one of the most common types of OSCCs. TSCC is significantly more aggressive than other forms of OSCCs, with a propensity for rapid local invasion and metastatic spread (Franceschi et al. 1993). The incidence of TSCC is actually increasing in young and middle age populations (Annertz et al. 2002;Mackenzie SB-505124 HCl et al. 2000;Schantz and Yu 2002). While attempts have been made to identify genomic alterations that contribute to initiation and progression of TSCC, most efforts are focused on protein coding genes. Our knowledge of genomic aberrations associated with non-coding genes (e.g., microRNA) and their contributions to the onset and propagation of TSCC is relatively limited. MicroRNAs are not directly involved in protein coding, but are able to control the expression of their target genes at post-transcriptional levels. Several microRNAs have been functionally classified as proto-oncogenes or tumor suppressors and are aberrantly expressed in different cancer types including leukemia (Calin et al. 2002;Calin SB-505124 HCl et al. 2004), lymphoma (Metzler et al. 2004), breast cancer (Bhaumik et al. 2008;Kondo et al. 2008), colorectal cancer (Michael et al. 2003), lung cancer (Takamizawa et al. 2004;Yanaihara et al. 2006), liver cancer (Murakami et al. 2006;Wang et al. 2008), and OSCC (Hebert et al. 2007;Kozaki et al. 2008;Tran et al. 2007;Wong et al. 2008b). Deregulation (e.g., overexpression or RHOJ loss of expression) of these cancerous microRNAs can figure prominently in tumor initiation and progression (Calin and Croce 2006;Esquela-Kerscher and Slack 2006) by facilitating an inappropriate cellular program that promotes uncontrolled proliferation, favors survival, inhibits differentiation and/or promotes invasive behavior. The deregulation of miR-138 has been frequently observed in a number of cancer types, including OSCC (Kozaki et al. 2008;Wong et al. 2008b), thyroid cancer (Mitomo et al. 2008), and lung cancer (Seike et al. 2009). Two miR-138 precursor genes, termed pre-miR-138-1 and pre-miR-138-2, were recently identified in the mouse genome (Obernosterer et al. 2006), and their human homologs were mapped to chromosome 3p21.33 and 16q13, respectively. Interestingly, loss of heterozygosity (LOH) at both chromosome loci has been frequently detected in OSCC (Hogg et al. 2002;Piccinin et al. 1998;Wang et al. 1999). Our recent study demonstrated that reduced miR-138 level is associated with enhanced cell growth and invasion SB-505124 HCl in OSCC (Liu et al. 2009b). However, the molecular mechanism(s) underlying the effect of miR-138 on the initiation and progression of TSCC is poorly understood. This study seeks to identify the potential miR-138 targets and investigate the molecular mechanism(s) that underlie the potential tumor suppressor effect of miR-138 in TSCC..