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BackgroundMicroRNAs (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/PrincipalReal-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/SignificanceOur 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.

Chronic inflammatory diseases, such as rheumatoid arthritis and periodontitis, are the most common causes of bone tissue destruction. Recently, human periodontal ligament tissue-derived mesenchymal stem cells (PDLSCs), a population of multipotent stem cells, have been used to reconstruct tissues destroyed by chronic inflammation. However, the impact of the local inflammatory microenvironment on tissue-specific stem cells and the mechanisms controlling the effects of the local inflammatory environment remain poorly understood. In this study, we found that the multidifferentiation potential of mesenchymal stem cells (MSCs) isolated from periodontitis-affected periodontal ligament tissue (P-PDLSCs) was significantly lower than that of MSCs isolated from healthy human periodontal ligament tissue (H-PDLSCs). Inflammation in the microenvironment resulted in an inhibition of miR-17 levels, and a perturbation in the expression of miR-17 partly reversed the differentiation potential of PDLSCs in this microenvironment. Furthermore, inflammation in the microenvironment promoted the expression of Smad ubiquitin regulatory factor one (Smurf1), an important negative regulator of MSC osteogenic differentiation. Western blotting and 3′ untranslated regions (3′-UTR) reporter assays confirmed that Smurf1 is a direct target of miR-17 in PDLSCs. Our data demonstrate that excessive inflammatory cytokine levels, miR-17, and Smurf1 were all involved in a coherent feed-forward loop. In this circuit, inflammatory cytokines led to direct activation of Smurf1 and downregulation of miR-17, thereby increasing degradation of Smurf1-mediated osteoblast-specific factors. The elucidation of the molecular mechanisms governing MSC osteogenic differentiation in a chronic inflammatory microenvironment could provide us with a better knowledge of chronic inflammatory disorder and improve stem cell-mediated inflammatory bone disease therapy.

Cancer stem cells (CSCs), or tumor initiating cells, are a subpopulation of cancer cells with self-renewal and differentiation properties. However, there has been no direct observation of the properties of gastric CSCs in vitro. Here we describe a vincristine (VCR)-preconditioning approach to obtain cancer stem-like cells (CSLCs) from the gastric cancer cell line SGC7901. The CSLCs displayed mesenchymal characteristics, including the up-regulated mesenchymal markers Snail, Twist, and vimentin, and the down-regulated epithelial marker E-cadherin. Using a Matrigel-based differentiation assay, CSLCs formed 2D tube-like and 3D complex lumen-like structures, which resembled differentiated gastric crypts. The characteristic of cellular differentiation was also found by transmission electron microscopy and up-regulation of gastrointestinal genes CDX2 and SOX2. We further showed that CSLCs could self-renew through significant asymmetric division compared with parent cells by tracing PKH-26, BrdU, and EDU label-retaining cells. In addition, these CSLCs also increased expression of CD44, CD90, and CXCR4 at the mRNA level, which was identified as novel targets. Furthermore, drug sensitivity assays and xenograft experiments demonstrated that the cells developed multi-drug resistance (MDR) and significant tumorigenicity in vivo. In summary, gastric CSCs were identified from VCR-preconditioned SGC7901 cell line, characterized by high tumorigenicity and the capacity for self-renewal and differentiation.

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Mesenchymal stem cells (MSCs) have been shown to integrate into the tumor stroma; however, the precise mechanisms of this process are still elusive. In this study, the EMT phenotype and the enhanced metastatic ability of tumor cells were observed using transwell and trans-endothelial migration assays, respectively, as well as by using electron and laser confocal microscopy. Critical genes were screened and validated using gene arrays and clinical samples, and the changes at the protein level were examined both in vitro and in vivo. Cancer cells acquired an "activated" carcinoma-associated fibroblasts (CAFs) phenotype after being in close contact with MSCs and enhancing tumor metastasis and growth in vivo. Paracrine signals also induced EMT and promoted transwell and trans-endothelial migration, the changes were dependent on β-catenin, MMP-16, snail and twist. Notably, the higher expression levels of β-catenin and MMP-16 were correlated with tumor invasion and distant organ and lymph node metastases in intestinal type gastric cancer. MSCs within the tumor niche significantly facilitated tumor growth and metastasis by paracrine cues and close physical connection. This occurred partly through snail, twist and its downstream targets, specifically β-catenin/MMP-16.

Liver injuries are repaired by fibrosis and regeneration. The core stage is the repair response and fibrosis formation as a scar. The cause of overly-responsive scar formation and diminished regeneration, especially in liver fibrosis and cirrhosis, is still unknown. The epithelial to mesenchymal transition (EMT), a previously discovered mechanism, plays an important role in liver fibrosis and tumor metastasis. Recently, EMT has been found to be associated with liver and bile duct cell fibrosis. Analyzing the established models and chronic disease processes, we propose that EMT liver cells may also lose their regenerative capability due to phenotype changes and that the remaining liver cells may quickly lose their regenerative capability in liver fibrosis or cirrhosis. Recognizing these phenotype changes or transition cells may play an important role in targeting therapy to reverse fibrosis not only by disrupting the transition that is necessary to produce the extracellular matrix but also by restoring the regenerative capacity of EMT-like cells.

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