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Molecular Cancer

, 13:6

First Online: 10 January 2014Received: 24 July 2013Accepted: 06 January 2014DOI: 10.1186-1476-4598-13-6

Cite this article as: Yen, YC., Shiah, SG., Chu, HC. et al. Mol Cancer 2014 13: 6. doi:10.1186-1476-4598-13-6


BackgroundMicroRNAs 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%.

MethodsThe 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.

ResultsWe 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 3′UTR of IGF1R mRNA into the 3′UTR of a reporter gene markedly reduced luciferase activity in OSCC cells expressing miR-99a, suggesting that miR-99a reduces luciferase activity by targeting the 3′UTR 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.

ConclusionOverall, results indicate that miR-99a functions as a tumor metastasis suppressor in OSCC cells and mutually regulates IGF1R expression in a reciprocal regulation.

KeywordsMicroRNA-99a Tumor metastasis suppressor Insulin-like growth factor 1 receptor Reciprocal regulation Oral squamous cell carcinoma AbbreviationsOSCCOral squamous cell carcinoma



IGF1RInsulin-like growth factor 1 receptor

mTORmammalian target of rapamycin

IGF1Insulin–like growth factor 1

MAPKMitogen-activated protein kinase

PI3KPhosphatidylinositol 3-kinase

AKT-PKBProtein kinase B


qRT-PCRquantitative reverse transcription-polymerase chain reaction

3′UTR3′ untranslated region.

Electronic supplementary materialThe online version of this article doi:10.1186-1476-4598-13-6 contains supplementary material, which is available to authorized users.

Yi-Chen Yen, Shine-Gwo Shiah contributed equally to this work.

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Autor: Yi-Chen Yen - Shine-Gwo Shiah - Hsiao-Chien Chu - Yuan-Ming Hsu - Jenn-Ren Hsiao - Jang-Yang Chang - Wen-Chun Hung - Chun-T


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