Ha natural, which comprises a 15-22 nt

Ha – MiRNAs are short strands of 19 to 22 nucleotides has long been discovered in microbial, animal, plant and human genetics. The different between miRNAs with messenger RNA (mRNA) is not involved in protein biosynthesis, so it has been named non-protein coding RNA. These characteristics make them like a tool that has ability for inhibiting protein transfer. So far, many studies have shown that miRNA is involved in the development of cancer cells. Furthermore, miRNAs as therapeutic tools for cancer management in future. The objective of this review is to discuss the generation, mechanism and function of miRNAs. The treatment base on miRNA strategies is currently being evaluated for use in cancer and the current advantages as well as the challenges of miRNAs in clinical.miRNAs are short RNA fragments has been discovered for a long time, but until 1993 that isolation and qualitative analysis of the lin-4 and let-7 miRNAs of the Caenorhabditis elegans which worm living in the soil, etc. had been completed. The scientists had the proofs that illustrated the present of miRNA related to the increase of tumors and cells. The functionality of a miRNA is based on the catalytic process of miRNAs in the natural, which comprises a 15-22 nt single-stranded RNA that enters the cytoplasmic RNA-induced silencing complex (RISC) to pair with mRNAs carrying complementary sequences consequently, repress gene expression. (D Brown et al., 2011)
In the biological process, the miRNA gene was activated by the enzyme RNA Polymerase II, which converted and produced the original microRNA, called pri-miRNA. This is a long string of thousands of bases, and it carries the 5′-CAP, and the 3 ‘is the Poly A, AAAA. Pri-miRNAs contain at least one or more hairpin loops, each containing about 70 nucleotides. After being affected by the DROSHA in the nucleus, the RNA loop (Stem-Loop) called the pre-miRNA, which is absorbed into the cytoplasm, and then they are cut by DICER into miRNA with 22 nucleotides. If the miRNA is combined with the Antagomir artificial antisense RNA which is capable of binding more strongly to the mRNA, then the original RNA sequence will be generated, and the process will be reversed from the beginning. The combination of miRNA with RNA interference (RNAi) under the presence of RNA-induced silencing complex (RNA) will affect part of mRNA in the form of base-pairing to inhibit the continued reproduction or resolution of mRNAs that appeared in the cell. miRNA can act on nearly 200 RNA transcripts and many miRNAs can exert regulatory effects on a protein-coding gene.
Multivariate expression of the miRNA gene between normal and malignant cells is a complex phenomenon that requires simultaneous co-occurrence of several factors, including control of miRNA expression by oncogenes, Tumor suppression genes, epigenetic mechanisms and the preferred gene position of miRNAs in cancer-related regions (Maitri Y. Shah et al., 2016).  The experiments are built in order to identify miRNA abnormalities in human cancers by cutting transcriptional regulators. In addition, the miRNA hypermethylation characteristic of human metastasis was identified which show that somatic mutations in DICER1 and DROSHA impaired biogenesis of tumor suppressive miRNA, including let-7 family, in Wilms tumor (Rakheja et al., 2014). These are only initial steps towards understanding about the cause of the suppression of miRNA that control during metastasis, and new mechanisms will continue to be identified in future. (Maitri Y. Shah et al,. 2016)
The impediment on the RNAs that are not directly related to the process of protein are a new direction for medical research, promising a new drug that will effectively treat genetic diseases. The finding it will change the cancer treated method in humans. Next to miRNAs that promising agents in cancer therapy, however, this studies have not found the best fit therapies for cancer.  At the same time, it promotes the later research processes of scientists.