Single nucleotide polymorphisms in genes encoding microRNAs (miRNA-SNPs) may affect the maturation steps of miRNAs or target mRNA recognition, leading to changes in the expression of target mRNAs to cause gain- or loss-of-function changes. Several miRNA-SNPs are known to be associated with the risk of diseases such as cancer. The purpose of this study was to comprehensively determine the miRNA-SNPs in Japanese individuals to evaluate the differences in allele frequencies between ethnicities by comparing data from the global population in the 1000 Genomes Project and differences between healthy subjects and cancer patients. We performed next-generation sequencing targeting genes encoding 1809 pre-miRNAs. As a result, 403 miRNA-SNPs (146 miRNA-SNPs per subject on average) were identified in 28 healthy Japanese subjects. We observed significant differences in the allele frequencies between ethnicities in 33 of the 403 miRNA-SNPs. The numbers of miRNA-SNPs per subject in 44 non-small cell lung cancer (NSCLC), 33 colorectal cancer (CRC), and 15 soft tissue sarcoma (STS) patients were almost equal to those in healthy subjects. Significant differences in allele frequencies were observed for 14, 11, and 9 miRNA-SNPs in NSCLC, CRC, and STS patients compared with the frequencies in healthy subjects, suggesting that these SNPs can be biomarkers of risk for each type of cancer assessed. In summary, we comprehensively characterized miRNA-SNPs in Japanese individuals and found differences in allele frequencies of several miRNA-SNPs between ethnicities and between healthy subjects and cancer patients. Studies investigating a larger number of subjects should be performed to confirm the potential of miRNA-SNPs as biomarkers of cancer risk.

Secreted microRNAs (miRNAs) reside in a complex regulatory network with extracellular matrix (ECM) macromolecules, which affect cell-cell communication, therefore miRNA expression highlights its significance in several aspects of human diseases, including cancer. miRNA-mediated regulation of breast cancer has received considerable attention due to evidence that shows miRNAs to mediate estrogen receptor (ER) status, metastasis, chemoresistance and epithelial-to-mesenchymal transition (EMT). miR-200b is a pluripotent miRNA, which is inversely regulated by ERα and ERβ in mammary cancer. It has been identified as tumor suppressor and EMT inhibitor serving as a critical biomarker, as its expression in breast tumor determines the disease-free survival, thus highlighting its roles in breast cancer invasion and metastasis. The main goal of this study was to investigate the role of miR-200b in modulating the behavior of breast cancer cells with different ER status. We demonstrate that estrogen signaling through ERs reduces miR-200b expression levels in ERα-positive breast cancer cells. Moreover, miR-200b upregulation reduces the aggressive phenotype of ERβ-positive breast cancer cells by inhibiting cell invasiveness and motility, followed by ECM reorganization as well as cytoskeletal and morphological changes concluded from deep inspection of cell topography. Future investigation towards the mechanistic perspective of miR-200b effects in the behavior of aggressive mammary cancer cells appears rewarding in order to expand our understanding of miR-200b as a novel mediator beyond breast cancer diagnosis and pharmaceutical targeting.

Several proteins and RNAs expressed by mammalian viruses have been reported to interfere with RNA interference (RNAi) activity. We investigated the ability of the HIV-1-encoded RNA elements Trans-Activation Response (TAR) and Rev-Response Element (RRE) to alter RNAi. MicroRNA let7-based assays showed that RRE is a potent suppressor of RNAi activity, while TAR displayed moderate RNAi suppression. We demonstrate that RRE binds to TAR-RNA Binding Protein (TRBP), an essential component of the RNA Induced Silencing Complex (RISC). The binding of TAR and RRE to TRBP displaces small interfering (si)RNAs from binding to TRBP. Several stem-deleted RRE mutants lost their ability to suppress RNAi activity, which correlated with a reduced ability to compete with siRNA-TRBP binding. A lentiviral vector expressing TAR and RRE restricted RNAi, but RNAi was restored when Rev or GagPol were coexpressed. Adenoviruses are restricted by RNAi and encode their own suppressors of RNAi, the Virus-Associated (VA) RNA elements. RRE enhanced the replication of wild-type and VA-deficient adenovirus. Our work describes RRE as a novel suppressor of RNAi that acts by competing with siRNAs rather than by disrupting the RISC. This function is masked in lentiviral vectors co-expressed with viral proteins and thus will not affect their use in gene therapy. The potent RNAi suppressive effects of RRE identified in this study could be used to enhance the expression of RNAi restricted viruses used in oncolysis such as adenoviruses.