407055

MIR99A

MIRN99A;microRNA 99a;MIR99A;microRNA 99a

hsa-mir-99a

21q21.1

ncRNA

In our in-depth analysis carried out by the Illumina Solexa massive parallel signature sequencing, microRNA-99a (miR-99a) was found to be the sixth abundant microRNA in the miRNome of normal human liver but was markedly down-regulated in hepatocellular carcinoma (HCC). Compelling evidence has suggested the important roles of microRNAs in HCC development. However, the biological function of miR-99a deregulation in HCC remains unknown. In this study, we found that miR-99a was remarkably decreased in HCC tissues and cell lines. Importantly, lower miR-99a expression in HCC tissues significantly correlated with shorter survival of HCC patients, and miR-99a was identified to be an independent predictor for the prognosis of HCC patients. Furthermore, restoration of miR-99a dramatically suppressed HCC cell growth in vitro by inducing the G(1) phase cell cycle arrest. Intratumoral injection of cholesterol-conjugated miR-99a mimics significantly inhibited tumor growth and reduced the alpha-fetoprotein level in HCC-bearing nude mice. Insulin-like growth factor 1 receptor (IGF-1R) and mammalian target of rapamycin (mTOR) were further characterized as the direct targets of miR-99a. Furthermore, protein levels of IGF-1R and mTOR were found to be inversely correlated with miR-99a expression in HCC tissues. miR-99a mimics inhibited IGF-1R and mTOR pathways and subsequently suppressed expression of cell cycle-related proteins, including cyclin D1 in HCC cells. Conclusively, miR-99a expression was frequently down-regulated in HCC tissues and correlates with the prognosis of HCC patients, thus proposing miR-99a as a prospective prognosis predictor of HCC. miR-99a suppresses HCC growth by inducing cell cycle arrest, suggesting miR-99a as potential tumor suppressor for HCC therapeutics.

BACKGROUND: The purpose of this study was to investigate the clinical significance of microRNA-99a expression in lung adenocarcinoma. METHODS: qRT-PCR assay was performed to detect miR-99a expression in lung adenocarcinoma cells or tissues. The correlations of miR-99a expression with clinicopathological factors and prognosis of lung adenocarcinoma patients were analyzed. The effects of miR-99a expression on growth and apoptosis of lung adenocarcinoma cell line and its potential target gene were determined by MTT, flow cytometry, luciferase reporter, and Western blot assays. RESULTS: The relative miR-99a expression in lung adenocarcinoma cells was significantly lower than that in normal lung bronchial epithelium cell line. Also, miR-99a expression in lung adenocarcinoma tissues was significantly lower than that in corresponding nontumor tissues. Low miR-99a expression was found to be closely correlated with advanced clinical stage and lymph node metastasis. Kaplan-Meier survival and Cox regression analyses showed that the status of miR-99a expression was an independent prognosis factor for lung adenocarcinoma patients. Functional analyses showed that upregulation of miR-99a could inhibit growth and induce apoptosis in lung adenocarcinoma cells by targeting mTOR. CONCLUSION: Low MiR-99a expression was a poor prognostic factor for patients with lung adenocarcinoma, and miR-99a functions as a tumor suppressor by targeting mTOR.

BACKGROUND: microRNAs (miRNAs), small noncoding RNA molecules can function as oncogenes or tumor suppressors in tumorigenesis. Oral squamous cell carcinoma (OSCC) is one of the most prevalent cancers worldwide with a 5-year survival rate of approximately 50%. METHODS: The expression of microRNA-99a (miR-99a) in OSCC tissues and cell lines was investigated using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis. The functions of miR-99a in migration/invasion and lung colonization were determined by transwell and tail vein injection assays, respectively. Specific targets of miR-99a were determined by software prediction, correlation with target protein expression, and luciferase reporter assay. The signaling pathways involved in regulation of miR-99a were investigated using the kinase inhibitors. RESULTS: We observed reduced levels of miR-99a, identified as one of the most downregulated miRNA in OSCC and all tested OSCC cell lines compared to normal oral keratinocytes. Ectopic miR-99a expression in OSCC cells markedly reduced migration and invasion in vitro as well as lung colonization in vivo. When evaluating the specific targets of miR-99a, we found that ectopic miR-99a expression downregulates insulin-like growth factor 1 receptor (IGF1R) protein and that the expression of miR-99a correlates negatively with IGF1R protein in OSCC cells. Insertion of the 3UTR of IGF1R mRNA into the 3UTR of a reporter gene markedly reduced luciferase activity in OSCC cells expressing miR-99a, suggesting that miR-99a reduces luciferase activity by targeting the 3UTR of IGF1R mRNA. When evaluating the mechanisms of miR-99a downregulation, we observed the upregulation of miR-99a expression in serum-starved conditions and its suppression in response to insulin-like growth factor (IGF1) stimulation. Inhibitors of phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) kinase inhibited IGF1-induced suppression of miR-99a, suggesting the negative regulation of miR-99a expression by IGF1R signaling. CONCLUSION: Overall, results indicate that miR-99a functions as a tumor metastasis suppressor in OSCC cells and mutually regulates IGF1R expression in a reciprocal regulation.