MicroRNA Let-7f Inhibits Tumor Invasion and Metastasis by Targeting MYH9 in Human Gastric Cancer

BACKGROUND: MicroRNAs (miRNAs) are important regulators that play key roles in tumorigenesis and tumor progression. A previous report has shown that let-7 family members can act as tumor suppressors in many cancers. Through miRNA array, we found that let-7f was downregulated in the highly metastatic potential gastric cancer cell lines GC9811-P and SGC7901-M, when compared with their parental cell lines, GC9811 and SGC7901-NM; however, the mechanism was not clear. In this study, we investigate whether let-7f acts as a tumor suppressor to inhibit invasion and metastasis in gastric cancers. METHODOLOGY/PRINCIPAL: Real-time PCR showed decreased levels of let-7f expression in metastatic gastric cancer tissues and cell lines that are potentially highly metastatic. Cell invasion and migration were significantly impaired in GC9811-P and SGC7901-M cell lines after transfection with let-7f-mimics. Nude mice with xenograft models of gastric cancer confirmed that let-7f could inhibit gastric cancer metastasis in vivo after transfection by the lentivirus pGCsil-GFP- let-7f. Luciferase reporter assays demonstrated that let-7f directly binds to the 3'UTR of MYH9, which codes for myosin IIA, and real-time PCR and Western blotting further indicated that let-7f downregulated the expression of myosin IIA at the mRNA and protein levels. CONCLUSIONS/SIGNIFICANCE: Our study demonstrated that overexpression of let-7f in gastric cancer could inhibit invasion and migration of gastric cancer cells through directly targeting the tumor metastasis-associated gene MYH9. These data suggest that let-7f may be a novel therapeutic candidate for gastric cancer, given its ability to reduce cell invasion and metastasis

Nuclear expression of Twist promotes lymphatic metastasis in esophageal squamous cell carcinoma

China Postdoctoral Science Foundation [20090461447]; National Natural Science Foundation of China [81172288]Twist-1 protein (also called Twist) has been suggested to be involved in tumor epithelial-mesenchymal transition (EMT) related progression, however, the mechanism by which Twist promotes lymph node metastasis is not fully understood. In the present study, we found that nuclear Twist expression is clearly correlated with lymph node (LN) metastasis as determined by immunohistochemistry (IHC). A highly invasive EC109 cell subline, EC109-P, was established by repeated in vitro transwell isolations for the cell model. Immunofluorescence (IF) assay demonstrated that nuclear Twist expression was markedly higher in the highly invasive EC109-P cell line when compared with EC109 and EC9706 cells. Based on our cell model, the function and mechanism by which Twist regulates LN metastasis in ESCC was investigated. The results showed that the overexpression of Twist could significantly increase the invasion and VEGF-C expression of EC9706 cells, whereas the knockdown of Twist expression results in the opposite effects. This finding was further strengthened by the results of the analysis of co-expression of Twist and VEGF-C by IHC in ESCC clinical samples. In summary, our study indicates that nuclear Twist plays an important role in ESCC lymphatic metastasis by increasing the expression of VEGF-C. The combination of Twist and VEGF-C detection could be a reliable prediction of LN metastasis in ESCC