No abstract

MicroRNAs (miRNA) are a large family of small single-stranded RNA molecules found in all multicellular organisms. Early studies have been shown that miRNA are involved in cancer development and progression, and this role can be done by working as an oncogenes and tumor suppressor genes, so manipulation of this molecules can be a promising approach in cancer therapy, and experimental results represented that the modification in breast cancer phenotype is possible by miRNA expression alteration. miR-16, which is located in 13q14 chromosome, plays critical roles as a tumor suppressor by targeting several oncogenes which regulate cell cycle and apoptosis. Hence, in the present study, we investigated whether miR-16 could decline growth and survival of MCF-7 cell line as model of human breast cancer. MCF-7 cell line was infected with lentiviruses containing miR-16 precursor sequence. The effects of ectopic expression of miR-16 on breast cancer phenotype were examined by cell cycle analysis and apoptosis assays. miR-16 cytotoxicity effect was measured by the MTT assay. We showed that the miR-16 overexpression reduces Cyclin D1 and BCL2 at messenger RNA (mRNA) and protein levels in MCF-7 cell line. In addition, this is found that enforced expression of miR-16 decreases cell growth and proliferation and induces apoptosis in MCF-7 cells. In conclusion, our results revealed that upregulation of miR-16 would be a potential approach for breast cancer therapy.

MicroRNAs (miRNA) are small RNA molecules that negatively regulate gene expression through base pairing interactions between 3'-UTR of the target mRNAs and seed sequence of miRNA. Any changes in the recognition site could destroy binding sites or modify binding affinity, resulting in evasion from miRNA regulation. A putative binding site for miR-491-5p resides in 3'-UTR of MMP9, and a genetic variant (rs1056628 A → C) is present in this region. The role of MMP9 over expression well marked in various cancers. However, whether rs1056628 SNP in miR-491-5p binding site of MMP9 3'-UTR could abrogate its post-transcriptional regulation and affect cancer susceptibility remains largely unknown. To test this, the rs1056628 SNP was genotyped in 300 cases of lung, gastric and breast cancers and 200 age- and sex-matched healthy controls. The results showed that compared with the AA genotype, C was a risk genotype for all three cancers development and was also associated with gastric and breast cancers metastasis and invasion. Based on the base pairing analysis and secondary structure evaluation of MMP9 mRNA and miR-491-5p, we found that miR-491-5p had a higher binding affinity for A genotype than the C genotype. The Luciferase activity of MMP9 3'-UTR indicates differential regulation of two genetic variations of MMP9. Overexpression of miR-491-5p decreased MMP9 mRNA level in cell lines of gastric, breast and lung cancers and thus leads to decreasing of the invasion ability. Therefore, for the first time we imply that the C variant of MMP9 contributes to the likelihood of gastric, breast and lung cancers susceptibility via a novel mechanism of subtle gene regulation through miRNA binding capacity.