LiLi Tu

MicroRNA-1/206 Targets c-Met and Inhibits Rhabdomyosarcoma Development

MicroRNAs (miRNAs) are endogenous short (∼22) nucleotide RNAs that regulate gene function by modification of target mRNAs. miRNA-1 (miR-1) and miRNA-206 (miR-206) are highly expressed in skeletal muscle. Due to the tissue-specific nature of miR-1/206 for skeletal muscles, we investigated the role of miR-1/206 in the development of rhabdomyosarcoma. Initially, we demonstrated that miR-1/206 expression was suppressed in rhabdomyosarcomas and found at very low levels in a rhabdomyosarcoma RD cell line. Transient transfection of miR-1/206 into cultured RD cells led to a significant decrease in cell growth and migration. Using bioinformatics, we identified two putative miR-1/206 binding sites within the 3′-untranslated region of the human c-Met mRNA. miR-1/206 was then shown to have activity on mRNA expression by targeting the c-Met 3′-untranslated region. The expression of c-Met protein was shown to be down-regulated by subsequent Western blot analysis. Conversely, up-regulation of c-Met was confirmed in tissue samples of human rhabdomyosarcoma, with its level inversely correlated with miR-1/206 expression. In vivo, miR-1/206-expressing tumor cells showed growth delay in comparison with negative control. Our results demonstrated that miR-1/206 suppressed c-Met expression in rhabdomyosarcoma and could function as a potent tumor suppressor in c-Met-overexpressing tumors. Inhibition of miR-1/206 function could contribute to aberrant cell proliferation and migration, leading to rhabdomyosarcoma development.

Deletion of G protein-coupled receptor 48 leads to ocular anterior segment dysgenesis (ASD) through down-regulation of Pitx2

The development of the anterior segment of the mammalian eye is critical for normal ocular function, whereas abnormal development can cause glaucoma, a leading cause of blindness in the world. We report that orphan G protein-coupled receptor 48 (Gpr48/LGR4) plays an important role in the development of the anterior segment structure. Disruption of Gpr48 causes a wide spectrum of anterior segment dysgenesis (ASD), including microphthalmia, iris hypoplasia, irdiocorneal angle malformation, cornea dysgenesis, and cataract. Detailed analyses reveal that defective iris myogenesis and ocular extracellular matrix homeostasis are detected at early postnatal stages of eye development, whereas ganglion cell loss, inner nuclear layer thinness, and early onset of glaucoma were detected in 6-month-old Gpr48−/− mice. To determine the molecular mechanism of ASD caused by the deletion of Gpr48, we performed gene expression analyses and revealed dramatic down-regulation of Pitx2 in homozygous knockout mice. In vitro studies with the constitutively active Gpr48 mutant receptor demonstrate that Pitx2 is a direct target of the Gpr48-mediated cAMP-CREB signaling pathway in regulating anterior segment development, suggesting a role of Gpr48 as a potential therapeutic target of ASD.

Involvement of PI3K/Akt Signaling Pathway in Hepatocyte Growth Factor-Induced Migration of Uveal Melanoma Cells

PURPOSE Uveal melanoma is the most common primary intraocular malignancy in adult humans. Unlike cutaneous melanoma, uveal melanoma disseminates preferentially to the liver through the hematogenous system. To date, the mechanism underlying this metastatic homing is largely unknown. This study investigated the effect of hepatocyte growth factor (HGF)-triggered signaling pathways to identify the role of HGF and its downstream effectors in inducing the migration of uveal melanoma cells. METHODS Migration of uveal melanoma cells was measured by in vitro wound healing and transwell migration assays. The expression and translocation of c-Met were detected using indirect immunofluorescence. The activation of extracellular signal-regulated kinase (ERK)1/2 and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathways was analyzed using specific antibodies against phospho-ERK1/2 and phospho-Akt. The impact of HGF treatment on the expression of cell adhesion molecules was measured using Western blotting. RESULTS HGF was found to enhance cell migration, and that HGF-induced migration depends on PI3K/Akt pathway. The activation of PI3K/Akt pathway induced by the HGF/c-Met axis is involved in the downregulation of cell adhesion molecules E-cadherin and beta-catenin, contributing to the attenuation of cell-cell adhesion and promoting the enhanced motility and migration of uveal melanoma cells. On HGF stimulation, receptor c-Met is translocated to the nucleus in a ligand-dependent manner, suggesting that c-Met may modulate the expression of genes involved in melanoma cell migration. CONCLUSIONS Data from this study directly linked the central PI3K/Akt pathway to uveal melanoma migration and pointed to new avenues for therapeutic intervention in hepatic metastasis.

Role of microRNA-182 in posterior uveal melanoma: regulation of tumor development through MITF, BCL2 and cyclin D2.

MicroRNAs (miRNAs) are endogenous small non-coding RNAs that play central roles in diverse pathological processes. In this study, we investigated the effect of microRNA-182 (miR-182) on the development of posterior uveal melanomas. Initially, we demonstrated that miR-182 expression was dependent on p53 induction in uveal melanoma cells. Interestingly, transient transfection of miR-182 into cultured uveal melanoma cells led to a significant decrease in cell growth, migration, and invasiveness. Cells transfected with miR-182 demonstrated cell cycle G1 arrest and increased apoptotic activity. Using bioinformatics, we identified three potential targets of miR-182, namely MITF, BCL2 and cyclin D2. miR-182 was shown to have activity on mRNA expression by targeting the 3′ untranslated region of MITF, BCL2 and cyclin D2. Subsequent Western blot analysis confirmed the downregulation of MITF, BCL2 and cyclin D2 protein expression. The expression of oncogene c-Met and its downstream Akt and ERK1/2 pathways was also downregulated by miR-182. Concordant with the findings that miR-182 was decreased in uveal melanoma tissue samples, overexpression of miR-182 also suppressed the in vivo growth of uveal melanoma cells. Our results demonstrated that miR-182, a p53 dependent miRNA, suppressed the expression of MITF, BCL2, cyclin D2 and functioned as a potent tumor suppressor in uveal melanoma cells.

GPR48 Regulates Epithelial Cell Proliferation and Migration by Activating EGFR during Eyelid Development

PURPOSE Eyelid development is a dynamic process involving cell proliferation, differentiation, and migration regulated by a number of growth factors and cytokines. Mice deficient in the orphan G protein-coupled receptor 48 (GPR48) showed an eye open at birth (EOB) phenotype. In this study, the authors attempted to clarify the role of GPR48 in eyelid development and the molecular mechanisms leading to the EOB phenotype. METHODS Phenotypic analysis of the eyelids of Gpr48(-/-) mice was carried out using histology and scanning electron microscopy. GPR48 expression pattern was determined using X-gal staining. In vitro scratch assay was used to determine cell motility defects in Gpr48(-)(/)(-) keratinocytes. The molecular mechanism underlying GPR48-mediated eyelid closure was explored using Western blot and immunostaining analyses. Expression levels of EGFR and its phosphorylated counterpart were examined in Gpr48(-/-) and wild-type keratinocytes and in eyelids. RESULTS GPR48 is highly expressed in the epithelium and apical mesenchymal cells of eyelids during embryonic development. Detailed analysis revealed that Gpr48(-/-) mice exhibited delayed leading-edge extension, reduced filopodia formation, and decreased rounded periderm cell formation around eyelid margins. Keratinocytes lacking GPR48 are defective in cell proliferation and migration with reduced F-actin staining. In addition, the phosphorylation of EGFR was dramatically decreased in cultured keratinocytes and developing eyelids in the absence of GPR48. CONCLUSIONS Inactivation of GPR48 induces the EOB phenotype by reducing epithelial cell proliferation and migration, indicating that GPR48 plays an essential role in eyelid development. Furthermore, GPR48 contributes to eyelid development through the regulation of the EGFR signaling pathway.

Inhibitory Effect of MicroRNA-34a on Retinal Pigment Epithelial Cell Proliferation and Migration

PURPOSE Retinal pigment epithelial (RPE) cells play important roles in ophthalmologic diseases such as proliferative vitreoretinopathy, AMD, and diabetic retinopathy. MicroRNA-34a (miR-34a) has been reported to be important in the regulation of cell proliferation, migration, differentiation, and apoptosis. In this study, we explored the effects of miR-34a on RPE cells. METHODS The expression level of miR-34a in subconfluent and postconfluent ARPE-19 cells was investigated with quantitative real-time PCR. MicroRNA mimic and small interfering RNA (siRNA) were transiently transfected into RPE cells. Transfected RPE cells were analyzed with WST-1 proliferation assay, and their migration was analyzed with transwell assay and in vitro scratch study. The expression or activation of target proteins was detected by Western blotting. RESULTS MicroRNA-34a was significantly downregulated in subconfluent ARPE-19 cells compared with postconfluent cells. Introduction of miR-34a inhibited the proliferation and migratory ability of RPE cells without obvious cell apoptosis. In miR-34a transfected cells, many important proliferation and/or migration related molecules such as c-Met, CDK2, CDK4, CDK6, E2F1, and phosphorylated-Cdc2 (p-Cdc2) were downregulated. Small interfering RNA designed to target c-Met also inhibited the proliferation and migration of RPE cells and downregulated CDK2, CDK6, E2F1, and p-Cdc2. CONCLUSIONS MicroRNA-34a is downregulated in subconfluent RPE cells. MicroRNA-34a can inhibit the proliferation and migration of RPE cells through downregulation of its targets c-Met and other cell cycle-related molecules. Our results indicated that miR-34a is involved in the regulation of RPE cells.

MicroRNA-206: Effective Inhibition of Gastric Cancer Progression through the c-Met Pathway.

MicroRNAs are endogenous short chain nucleotide RNAs that regulate gene function by direct binding of target mRNAs. In this study, we investigated the effects of microRNA-206 (miR-206) on the development of gastric cancer. miR-206 was first confirmed to be downregulated in gastric cancer specimens. Conversely, upregulation of c-Met was confirmed in tissue samples of human gastric cancer, with its level inversely correlated with miR-206 expression. Introduction of miR-206 inhibited cellular proliferation by inducing G1 cell cycle arrest, as well as migration and invasion. Moreover, important proliferation and/or migration related molecules such as c-Met, CDK4, p-Rb, p-Akt and p-ERK were confirmed to be downregulated by Western blot analysis. Targeting of c-Met also directly affected AGS cell proliferation, migration and invasion. In vivo, miR-206 expressing tumor cells also displayed growth delay in comparison to unaffected tumor cells. Our results demonstrated that miR-206 suppressed c-Met expression in gastric cancer and could function as a potent tumor suppressor in c-Met overexpressing tumors. Inhibition of miR-206 function could contribute to aberrant cell proliferation and migration, leading to gastric cancer development.

GPR48-Induced keratinocyte proliferation occurs through HB-EGF mediated EGFR transactivation.

GPR48 can mediate keratinocyte proliferation and migration. Our investigations showed that AG1478, an inhibitor of EGFR tyrosine kinase, could block GPR48‐mediated cellular processes. AG1478 treatment of Gpr48 +/+ cells also decreased phosphorylation of EGFR, ERK and STAT3. Subsequent screening using conditioned media immunodepleted of EGFR ligands identified HB‐EGF as the ligand responsible for phosphorylation of EGFR, ERK and STAT3. HB‐EGF was reduced in Gpr48 −/− cell culture medium, but its addition restored the phosphorylation of EGFR, ERK, STAT3, as well as cell proliferation. Confirmation that GPR48 mediates EGFR signaling pathway through HB‐EGF was subsequently performed using an inhibitor of HB‐EGF.

MicroRNA Expression Profile and the Role of miR-204 in Corneal Wound Healing.

PURPOSE MicroRNAs (miRNAs) are endogenous short chain (∼ 22-nucleotide) noncoding RNAs that inhibit protein translation through binding to target mRNAs. Recent studies have implied that miRNAs play a regulatory role in corneal development. Here we profile their involvement in corneal epithelial renewal, develop an miRNA-target network that affects wound healing outcome, and investigate the function of miR-204 in this response. METHODS NanoString nCounter technology and bioinformatics analyzed miRNA expression levels and their targets during mouse corneal epithelial wound healing. Real-time RT-PCR was performed to detect miR-204 expression in mouse corneal epithelium. Human corneal epithelial cells (HCECs) were transfected with miR-204 using transfection reagent. MTS (3-[4,5-dimethylthiazol-2-yl]-5-[3-carboxymethoxyphenyl]-2-[4-sulfophenyl]-2H-tetrazolium, inner salt) and a scratch wound-healing assay evaluated the effects of miR-204 expression on HCEC proliferation and migration, respectively. Cell cycle analysis was performed by flow cytometry. Expression of sirtuin 1 (SIRT1) was determined by Western blot analysis. RESULTS Fifteen miRNAs were dramatically downregulated, whereas 14 other miRNAs were markedly upregulated during corneal wound healing. Expression of miR-204 fell the most during this process. Transfection of miR-204 into HCECs led to a significant decline in cell proliferation and induced cell cycle G1-arrest. Furthermore, in these cells, miR-204 also inhibited migration. Sirtuin 1 was confirmed as a target of miR-204. CONCLUSIONS During mouse corneal epithelial wound healing, a complex miRNA-gene network was resolved that is modulated by changes in miR-204 expression. Downregulation of this miRNA appears to be an essential response to injury since its decline promotes human corneal epithelial cell proliferation and migration. Therefore, miR-204 could be a biomarker of this process.

LGR4 Is a Direct Target of MicroRNA-34a and Modulates the Proliferation and Migration of Retinal Pigment Epithelial ARPE-19 Cells

The pathology of proliferative vitreoretinopathy and proliferative diabetic retinopathy is linked to proliferation, migration, and adhesion of the retinal pigment epithelium. MicroRNA-34a (miR-34a) expression modulates changes in proliferation and migration of retinal pigment epithelial cell line ARPE-19. In this study, we determined that miR-34a interacts with LGR4, identified by bioinformatics using TargetScan Human 5.0, to affect these changes. Double luciferase gene reporter assay confirmed miR-34a involvement in mediating control. miR-34a mimic transfection decreased LGR4 expression. Western blot analysis documented corresponding protein expression inhibition. MTS, Ki67 immunostaining, scratch and transwell testing, along with attachment assay showed that miR-34a upregulation inhibited ARPE-19 cell proliferation, migration and attachment partly through downregulation of LGR4 protein expression. Western blot analysis revealed that both miR-34a upregulation and LGR4 downregulation induced declines in E2F1, p-CDC2, CDK2, CDK4 and CDK6 protein expression. Taken together, miR-34a gene expression upregulation inhibits ARPE-19 cell proliferation, migration and adhesion partly by suppressing LGR4 expression. These results substantiate earlier indications that both miR-34a and LGR4 are potential drug targets to prevent fibrosis in a clinical setting.