This study reports for the first time the microRNA expression profile of human breast cancer MCF-7 cells and the effect of green tea. Although hundreds of miRNAs have been identified in humans, only a small proportion (25.6%) of miRNAs are expressed in MCF-7 cells. Low concentration treatment with Polyphenon-60 significantly alters the miRNA expression profile in MCF-7 cells. Twenty three miRNAs have been identified with differential expression after a 48 h treatment with 10 μg/ml Polyphenon-60 (green tea extract). These miRNAs include miR-21 and miR-27 that were found to be down-regulated following treatment with green tea. These two miRNAs have previously been identified as being overexpressed in MCF-7 breast cancer cells, with miR-21 specifically implicated in down-regulating the tumor suppressor gene, tropomyosin-1. This data supports the hypothesis that Polyphenon-60-induced modification of the breast cancer miRNA expression profile contributes to the efficacy of green tea treatment. The resulting decrease in carcinogenesis is further supported by the altered miRNA regulation of potential oncogenes and tumor-suppressor genes.
"Elevated levels of elF4E were found in a broad spectrum of solid tumors (breast, head and neck, colon and bladder carcinomas as well as in non- Hodgkin's lymphomas) . miR-21 was reported to be positively associated with poor breast cancer free survival in early stage patients , and to promote breast cancer cell invasion in multiple cell lines in vitro through regulation of tissue inhibitors of metalloproteinase3 (TIMP3) expression . TIMPs inhibit the activity of MMP and contain a consensus miR-21 binding sites . "
"It is well established that miRNAs regulate EMT through the regulation of E-cadherin and other molecules, such as the transcription factor ZEB353637383940. Additionally, recent studies have suggested that natural agents, including the polyphenols curcumin, (-)-epigallocatechin-3-gallate, and resveratrol, can alter miRNA expression profiles, leading to the reversal of EMT and enhancing the efficacy of conventional cancer therapeutics41424344454647484950. As such, we hypothesized that the plant polyphenol silibinin may also function as a previously unrecognized regulator of miRNAs that might lead to the reversal of the EMT phenotype. "
[Show abstract][Hide abstract] ABSTRACT: The flavolignan silibinin was studied for its ability to restore drug sensitivity to EGFR-mutant NSCLC xenografts with epithelial-to-mesenchymal transition (EMT)-driven resistance to erlotinib. As a single agent, silibinin significantly decreased the tumor volumes of erlotinib-refractory NSCLC xenografts by approximately 50%. Furthermore, the complete abrogation of tumor growth was observed with the co-treatment of erlotinib and silibinin. Silibinin fully reversed the EMT-related high miR-21/low miR-200c microRNA signature and repressed the mesenchymal markers SNAIL, ZEB, and N-cadherin observed in erlotinib-refractory tumors. Silibinin was sufficient to fully activate a reciprocal mesenchymal-to-epithelial transition (MET) in erlotinib-refractory cells and prevent the highly migratogenic phenotype of erlotinib-resistant NSCLC cells. Given that the various mechanisms of resistance to erlotinib result from EMT, regardless of the EGFR mutation status, a water-soluble, silibinin-rich milk thistle extract might be a suitable candidate therapy for upcoming clinical trials aimed at preventing or reversing NSCLC progression following erlotinib treatment.
"Adherent cells can be transfected with higher efficiency and therefore MCF7 cells were used to construct the target cell library. Expression profiling of MCF7 has shown that these cells only express 25% of the profiled miRNAs (19) and accordingly the established library of approximately 40 000 independent MCF7 clones expressing 5626 different cDNAs could be used to identify targets for many more miRNAs. "
[Show abstract][Hide abstract] ABSTRACT: MicroRNAs (miRNA) are a class of small RNA molecules that regulate numerous critical cellular processes and bind to partially complementary sequences resulting in down-regulation of their target genes. Due to the incomplete homology of the miRNA to its target site identification of miRNA target genes is difficult and currently based on computational algorithms predicting large numbers of potential targets for a given miRNA. To enable the identification of biologically relevant miRNA targets, we describe a novel functional assay based on a 3'-UTR-enriched library and a positive/negative selection strategy. As proof of principle we have used mir-130a and its validated target MAFB to test this strategy. Identification of MAFB and five additional targets and their subsequent confirmation as mir-130a targets by western blot analysis and knockdown experiments validates this strategy for the functional identification of miRNA targets.
Nucleic Acids Research 02/2012; 40(10):e75. DOI:10.1093/nar/gks145 · 9.11 Impact Factor
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