MiR-29c Induces Cell Cycle Arrest In Esophageal Squamous Cell Carcinoma By Modulating Cyclin E Expression

Esophageal cancer is the eighth most common cancer and the sixth most common cause of cancer deaths worldwide. The incidence of esophageal squamous cell carcinoma (ESCC) is more frequent in China. Despite the advances in therapy; ESCC is still one of the most lethal malignancies in China, with an overall 5-year survival rate of 20-30% after curative surgery. The development of ESCC is a multistep, progressive process, and a number of canonical genetic alterations in the tumor cells have been identified. However, how specific molecules regulate the initiation and progression of esophageal squamous cell carcinoma and are utilized for a clinical target therapy remains to be elucidated.miRNAs are 19-22 nt in length, highly conserved noncoding RNA that control gene expression post-transcriptionally. miRNAs play important roles in cell proliferation, differentiation, and apoptosis. Recent cumulative evidences suggested that miRNAs play important roles in the tumor growth and development. Our previously microarray analysis demonstrated that miR-29c expression was down-regulated in esophageal squamous cell carcinoma. The aim of this study was to evaluate the miR-29c expression patterns and the role of miR-29c in esophageal squamous cell carcinoma.Increasing evidence has suggested that dysregulation of certain miRNAs may contribute to tumorigenesis. Downregulation of miR-29c was observed in various types of cancers. However, the biological function of miR-29c in esophageal squamous cell carcinoma (ESCC) is still unknown. In our study, we showed that the expression of miR-29c was significantly decreased in ESCC tissues and five ESCC cell lines. Moreover, miR-29c could suppress in vitro and in vivo proliferation of ESCC cells. Cyclin E, which was critical for G1/S transition and was overexpression in most of esophageal squamous cell carcinoma, was identified as a target of miR-29c by luciferase assay. The cyclin E protein expression was detected in ESCC cell lines by western blotting. Interestingly, inverse correlations between miR-29c and cyclin E protein level were found in five ESCC cell lines. Introduction of miR-29c could reduce the expression of cyclin E protein but not the cyclin E mRNA, and the expression of cyclin E was decreased along with the increased miR-29c level. In addition, we observed that increased expression of miR-29c could induce cell cycle G0/G1 arrest and suppress the phosphorylation of Rb in ESCC cell lines. These results suggest that miR-29c may regulate G1/S transition through the cyclin E/Cdk2-pRb signaling pathway. We detect the expression of other G1 related protein such as cyclin Dl, cyclin D2, CDK2, and CDK6. The results confirmed that overexpression of miR-29c can not affect the expression of these proteins in ESCC cell lines. Furthermore, miR-29c induces cell cycle arrest in esophageal squamous cell carcinoma by modulating expression of cyclin E mainly.Taken together, our study demonstrates that the miR-29c can regulate cyclin E and function as a tumor suppressor in ESCC. Recent evidences show the level of cyclin E protein has been found to increase in ESCC tissue and cell lines. miR-29c inhibits the translation of cyclin E mRNA by targeting its 3'UTR, which add a new explain of deregulation of cyclin E expression in ESCC. Therefore, miR-29c may serve as a useful therapeutic agent for miRNA-based ESCC therapy.