miR-200c inhibits breast cancer proliferation by targeting KRAS

The microRNA, miR-200c, is involved in the tumorigenesis and progression of a variety of cancers. The purpose of this study was to investigate the expression, mechanism and prognostic roles of miR-200c in breast cancer. We found that miR-200c was downregulated in both breast cancer tissue and cell lines using quantitative real-time PCR (qRT-PCR). In situ hybridization (ISH) and microarrays showed that low miR-200c expression was associated with poor patient overall survival (OS) and disease free survival (DFS). We used luciferase reporter plasmids to find that miR-200c inhibited the AKT and ERK pathways by directly targeting KRAS. Repression of KRAS by miR-200c suppressed the proliferation and survival of breast cancer cells in vitro and in vivo. miR-200c also had an anti-tumor effect by negatively regulating KRAS in a xenograft mouse model. Our findings provide clues regarding the role of miR-200c as a tumor suppressor in breast cancer through the inhibition of KRAS translation both in vitro and in vivo. miR-200c could be a potential therapeutic target in breast cancer.     

miR‐20a inhibits hypoxia‐induced autophagy by targeting ATG5/FIP200 in colorectal cancer

Autophagy is a highly conserved lysosome‐mediated protective cellular process in which cytosolic components, including damaged organelles and long‐lived proteins, are cleared. Many studies have shown that autophagy was upregulated in hypoxic regions. However, the precise molecular mechanism of hypoxia‐induced autophagy in colorectal cancer (CRC) is still elusive. In this study, we found that miR‐20a was significantly downregulated under hypoxia in colon cancer cells, and overexpression of miR‐20a alleviated hypoxia‐induced autophagy. Moreover, miR‐20a inhibits the hypoxia‐induced autophagic flux by targeting multiple key regulators of autophagy, including ATG5 and FIP200. Furthermore, by dual‐luciferase assay we demonstrated that miR‐20a directly targeted the 3′‐untranslated region of ATG5 and FIP200, regulating their messenger RNA and protein levels. In addition, reintroduction of exogenous ATG5 or FIP200 partially reversed miR‐20a‐mediated autophagy inhibition under hypoxia. A negative correlation between miR‐20a and its target genes is observed in the hypoxic region of colon cancer tissues. Taken together, our findings suggest that hypoxia‐mediated autophagy was regulated by miR‐20a/ATG5/FI200 signaling pathway in CRC. miR‐20a‐mediated autophagy defect that might play an important role in hypoxia‐induced autophagy during colorectal tumorigenesis.     

Retracted: Glabridin attenuates the migratory and invasive capacity of breast cancer cells by activating microRNA‐200c

Current treatments for breast cancer, a common malignancy in human females, are less than satisfactory because of high rates of metastasis. Glabridin (GLA), which acts through the FAK/ROS signaling pathway, has been used as an antioxidant and anti‐metastatic agent. However, little is known regarding the effect of microRNA (miRNA) on GLA's anti‐metastatic activity. The miRNA‐200 family, which is frequently expressed at low levels in triple negative breast cancers, inhibits metastasis by blocking the epithelial–mesenchymal transition. Here, we found that GLA attenuated the migratory and invasive capacity of breast cancer cells by activating miR‐200c. GLA induced the mesenchymal–epithelial transition in vitro and in vivo, as determined by increased expression of the epithelial marker, E‐cadherin, and decreased expression of the mesenchymal marker, vimentin. Overexpression of miR‐200c enhanced the expression of E‐cadherin and decreased the expression of vimentin. Furthermore, in MDA‐MB‐231 and BT‐549 breast cancer cells exposed to GLA, knockdown of miR‐200c blocked the GLA‐induced mesenchymal–epithelial transition and alleviated the GLA‐induced inhibition of migration and invasion. Thus, elevation of miR‐200c by GLA has considerable therapeutic potential for anti‐metastatic therapy for breast cancer patients.     

Inhibition of Cathepsin D (CTSD) enhances radiosensitivity of glioblastoma cells by attenuating autophagy

Postoperative radiotherapy combined with chemotherapy is a commonly used treatment for glioblastoma (GBM) but radiotherapy often fails to achieve the expected results mainly due to tumor radioresistance. In this study, we established a radioresistant subline from human glioma cell line U251 and found that Cathepsin D (CTSD), a gene closely related to the clinical malignancy and prognosis in glioma, had higher expression level in radioresistant clones than that in parental cells, and knocking down CTSD by small interfering RNA (siRNA) or its inhibitor Pepstatin-A increased the radiosensitivity. The level of autophagy was enhanced in the radioresistant GBM cells compared with its parent cells, and silencing autophagy by light chain 3 (LC3) siRNA significantly sensitized GBM cells to ionizing radiation (IR). Moreover, the protein expression level of CTSD was positively correlated with the autophagy marker LC3 II/I and negatively correlated with P62 after IR in radioresistant cells. As expected, through the combination of Western blot and immunofluorescence assays, inhibition of CTSD increased the formation of autophagosomes, while decreased the formation of autolysosomes, which indicating an attenuated autophagy level, leading to radiosensitization ultimately. Our results revealed for the first time that CTSD regulated the radiosensitivity of glioblastoma by affecting the fusion of autophagosomes and lysosomes. In significance, CTSD might be a potential molecular biomarker and a new therapeutic target in glioblastoma.     

The tumor suppressor microRNA‐29c is downregulated and restored by celecoxib in human gastric cancer cells

MicroRNAs (miRNAs) are small noncoding RNAs that function as endogenous silencers of target genes and play critical roles during carcinogenesis. The selective cyclooxygenase‐2 (COX‐2) inhibitor celecoxib has been highlighted as a potential drug for treatment of gastrointestinal tumors. The aim of this study was to investigate the role of miRNAs in gastric carcinogenesis and the feasibility of a new therapeutic approach for gastric cancer. miRNA expression profiles were examined in 53 gastric tumors including gastric adenomas (atypical epithelia), early gastric cancers and advanced gastric cancers and in gastric cancer cells treated with celecoxib. miRNA microarray analysis revealed that miR‐29c was significantly downregulated in gastric cancer tissues relative to nontumor gastric mucosae. miR‐29c was significantly activated by celecoxib in gastric cancer cells. Downregulation of miR‐29c was associated with progression of gastric cancer and was more prominent in advanced gastric cancers than in gastric adenomas and early gastric cancer. In addition, expression of the oncogene Mcl‐1, a target of miR‐29c, was significantly increased in gastric cancer tissues relative to nontumor gastric mucosae. Activation of miR‐29c by celecoxib induced suppression of Mcl‐1 and apoptosis in gastric cancer cells. These results suggest that downregulation of the tumor suppressor miR‐29c plays critical roles in the progression of gastric cancer. Selective COX‐2 inhibitors may have clinical promise for the treatment of gastric cancer via restoration of miR‐29c.     

Tumor‐suppressive microRNA‐218 inhibits cancer cell migration and invasion via targeting of LASP1 in prostate cancer

Our recent studies of the microRNA (miRNA) expression signature in prostate cancer (PCa) indicated that miRNA‐218 (miR‐218) was significantly downregulated in clinical specimens, suggesting that miR‐218 might act as a tumor‐suppressive miRNA in PCa. The aim of the present study was to investigate the functional significance of miR‐218 in PCa and to identify novel miR‐218‐regulated cancer pathways and target genes involved in PCa oncogenesis and metastasis. Restoration of miR‐218 in PCa cell lines (PC3 and DU145) revealed that this miRNA significantly inhibited cancer cell migration and invasion. Gene expression data and in silico analysis demonstrated that LIM and SH3 protein 1 (LASP1) is a potential target of miR‐218 regulation. LASP1 is a cytoskeletal scaffold protein that plays critical roles in cytoskeletal organization and cell migration. Luciferase reporter assays showed that miR‐218 directly regulated expression of LASP1. Moreover, downregulating the LASP1 gene significantly inhibited cell migration and invasion in cancer cells, and the expression of LASP1 was upregulated in cancer tissues. We conclude that loss of tumor‐suppressive miR‐218 enhanced cancer cell migration and invasion in PCa through direct regulation of LASP1. Our data on pathways regulated by tumor‐suppressive miR‐218 provide new insight into the potential mechanisms of PCa oncogenesis and metastasis.