microRNA-320 a inhibits tumor invasion by targeting neuropilin 1 and is associated with liver metastasis in colorectal cancer

MicroRNAs (miRNAs) have been implicated in regulating diverse cellular pathways. Although there is emerging evidence that various miRNAs function as oncogenes or tumor suppressors in colorectal cancer (CRC), the role of miRNAs in mediating liver metastasis remains unexplored. The expression profile of miRNAs in liver metastasis and primary CRC tissues was analyzed by miRNA microarrays and verified by real-time polymerase chain reaction (PCR). In 62 CRC patients, the expression levels of miR-320a were determined by real-time PCR, and the effects on migration and invasion of miR-320a were determined using a transwell assay. miR-320a target genes were confirmed by luciferase assay, real-time PCR and Western blot analysis. A set of miRNAs was found to be dysregulated in the liver metastasis tissues compared to matched primary CRC tissues, and the expression levels of miR-320a were significantly decreased in the liver metastasis tissues examined. miR-320a was correlated with tumor progression in CRC. miR-320a was downregulated in liver metastatic colon cancer cells and inhibited liver metastatic colon cancer cell migration and invasion. miR-320a directly binds to the 3'UTR of neuropilin 1 (NRP-1), a protein that functions as a co-receptor of vascular epithelial growth factor. miR-320a downregulated the expression of NRP-1 at both the mRNA and protein levels. These data demonstrated that miR-320a may be useful for identifying CRC patients that are at an elevated risk for developing liver metastasis. Our findings suggest that miR-320a may be a novel therapeutic candidate for the treatment of colorectal cancer. Introduction Colorectal cancer (CRC) is the second most common cause of cancer-related death worldwide (1). Approximately 50% of patients diagnosed with CRC die as a result of complications from distant metastases, which occur mainly in the liver. The occurrence of liver metastasis ranges from 20% in stage II to 70% in stage IV CRC patients, according to the UICC stage guidelines. Of all patients who die of advanced colorectal cancer (ACRC), 60-70% display liver metastasis (2). Metastasis to the liver is the major cause of death in CRC patients (3). The formation of liver metastases is a multistep process involving the escape of tumor cells from a primary CRC, intravasation into the systemic circulation, survival during transit in the vasculature, extravasation into the parenchyma of liver tissues, and ultimately the outgrowth of macroscopic liver metastasis formation through proliferation and angiogenesis (4-6). Although research has identified multiple genes responsible for liver metastasis (7), the epigenetic alterations that drive metastasis to the liver are largely unknown. MicroRNAs (miRNAs) are a family of small, highly conserved non-coding RNAs that post-transcriptionally regulate gene expression through sequence-specific interactions with the 3'untranslated regions (UTRs) of cognate mRNA targets. miRNAs silence genes by promoting both translational inhibition and mRNA degradation (8). More than 1000 human miRNAs have currently been identified, and each individual miRNA may control hundreds of target genes. Approximately 30% of human genes are believed to be putative miRNA targets (9). More than 50% of miRNA-encoding loci are located within chromosomal regions that are altered during tumorigenesis (10). Some miRNAs can function either as oncogenes or tumor suppressors (11,12). Expression profiling analyses have revealed characteristic miRNA signatures in certain types of human cancers (13,14). MiRNAs contribute to the pathogenesis of CRC by regulating the expression of oncogenes and tumor suppressors and also by directly functioning as oncogenes or tumor suppressors (15,16). The role of miRNAs in the development of metastasis has been demonstrated in several cancer types, including breast cancer, hepatocellular carcinomas, head and neck cancer and brain tumors (17). Most studies involving CRC have analyzed the association between miRNAs and microRNA-320a inhibits tumor invasion by targeting neuropilin 1 and is associated with liver metastasis in colorectal cancer YUJUN ZHANG1, XIANGJUN HE1, YULAN LIU1,2, YINGJIANG YE3, HUI ZHANG3, PEIYING HE1, QI ZHANG1, LINGYI DONG3, YUJING LIU1 and JIANQIANG DONG1 1Institute of Clinical Molecular Biology, and Departments of 2Gastroenterology and 3General Surgery, Peking University, People's Hospital, Beijing 100044, P.R. China Received September 13, 2011; Accepted October 26, 2011 DOI: 10.3892/or.2011. 1561 Correspondence to: Dr Yujun Zhang or Dr Yulan Liu, Institute of Clinical Molecular Biology, Peking University, Beijing 100044, P.R.