MiR-145 mediates the antiproliferative and gene regulatory effects of vitamin D3 by directly targeting E2F3 in gastric cancer cells miR-145 mediates the antiproliferative and gene regulatory effects of vitamin D3 by directly targeting E2F3 in gastric cancer cells

Background: MicroRNAs are regulators that can play an essential role in tumorigenesis. Although miR-302 families have been suggested to be tumor repressors in human cancer, the mechanism by which they suppress tumor development remains to be defined. In this study, we discover that miR302b suppresses tumor proliferation may due to directly targeting EGFR in human hepatocellular carcinoma (HCC). Methods: QRT-PCR was used to assess miR-302b and EGFR expression in 27 pairs of clinical hepatocellular carcinoma tissues and their corresponding adjacent nontumorous liver tissues. MTT, colony formation, immunofluorescence staining, and cell cycle assays were used to examine the tumor suppressor role of miR302b in cell proliferation. Luciferase assays were performed to assess the EGFR was a novel target of miR-302b. Western blot assay was used to validate the protein expression level. Results: We demonstrated that miR-302b was frequently down-regulated, whereas EGFR was up-regulated in 27 pairs of clinical HCC and non-tumorous counterparts. The dual-luciferase reporter assays revealed that EGFR was a novel target of miR-302b. Re-expression of miR-302b resulted in the inhibition of proliferation in hepatocellular carcinoma SMMC-7721 cells. The silencing of EGFR by miR-302b or siEGFR led to down-regulation of proliferation-related proteins, such as AKT2, CCND1, and CDK2. Conclusion: miR-302b suppresses HCC growth may due to targeting the EGFR/AKT2/CCND1 pathway.

Results from recent studies suggest that aberrant microRNA expression is common in numerous cancers. Although miR-338-3p has been implicated in hepatocellular carcinoma, its role in gastric cancer is unknown. To this end, we report that miR-338-3p is downregulated in both gastric cancer tissue and cell lines. Forced expression of miR-338-3p inhibited cell proliferation and clonogenicity and induced a G₁–S arrest as well as apoptosis in gastric cancer cells. Furthermore, P-Rex2a (PREX2) was identified as a direct target of miR-338-3p, and silencing P-Rex2a resulted in the same biologic effects of miR-338-3p expression in gastric cancer cells. Furthermore, both enforced expression of miR-338-3p or silencing of P-Rex2a resulted in activation of PTEN, leading to a decline in AKT phosphorylation. Also, miR-338-3p markedly inhibited the in vivo tumorigenicity in a nude mouse xenograft model system. These results demonstrate that miR-338-3p affects gastric cancer progression through PTEN—AKT signaling by targeting P-Rex2a in gastric cancer cells, which posits miR-338-3p as a novel strategy for gastric cancer treatment. Implications: miR-338-3p acts as a novel tumor suppressor that blocks the growth of gastric cancer cells through PTEN—PI3K signaling by targeting P-Rex2a. Mol Cancer Res; 12(3); 313–21. ©2013 AACR.

The cross-talk between RNA binding proteins (RBPs) and microRNAs (miRNAs) in the regulation of gene expression is a complex process. Here, we describe a new mode of regulation of TRIM25 expression mediated by an antagonistic interplay between IGF2BP3 and miR-3614-3p. The expression level of TRIM25, IGF2BP3, pri-miR-3614 and miR-3614-3p in breast cancer (BC) tissues, non-tumor tissues and BC cell lines were detected by qRT-PCR, Western blot and Immunohistochemistry (IHC). Binding of miR-3614-3p and IGF2BP3 to TRIM25 RNA was verified using luciferase activation assays, RNA immunoprecipitation (RIP) and biotin pull-down assays. In vitro and in vivo loss- and gain-of-function studies were performed to reveal the effects and related mechanism of IGF2BP3-miR-3614-3p-TRIM25 axis in in breast cancer cells proliferation. We found that an intragenic miRNA-3614-3p inhibits the expression of its host gene TRIM25 by binding to its 3'- untranslated region (UTR). Interestingly, IGF2BP3 can competitively occupy this binding site and inhibit miRNA-3614 maturation, thereby protecting TRIM25 mRNA from miR-3614-mediated degradation. The overexpression of miR-3614-3p dramatically inhibited breast cancer cell growth through the downregulation of TRIM25. Furthermore, the silencing of IGF2BP3 reduced TRIM25 expression, suppressed cell proliferation, and exhibited a synergistic effect with miR-3614-3p overexpression. Collectively, these results demonstrate that control of TRIM25 RNA by an interplay between IGF2BP3 and miR-3614-3p represents a mechanism for breast cancer cell proliferation. FUND: The scientific research and sharing platform construction project of Shaanxi Province, Opening Project of Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, China Postdoctoral Science Foundation and The National Natural Science Foundation of China.