The role of mir-21 in breast cancer

Breast cancer as an heterogeneous disease needs to have an individual treatment program. Development of this disease is very complicated and result in comprehensive change in the physiology and hormonal status of women body. Micro RNAs (miRNAs) are short single strand RNA molecules which have about 22 nucleotides length. miRNAs act as gene expression regulator through post translational, suppressing or destroying processes on mRNA molecules. The miRNAs function often turn off target genes. It seems that miRNAs could participate in cancer development as some of them were identified in primary tumors. MiRNAs have potential to use as biological markers. A miRNA can target up to 200 mRNAs and regulates a large number of cellular function such as development, differentiation, and growth. The association between cancer and miRNA was discovered in the year of 2002. miRNAs act in multiple types of cancers. For example, abnormally expression of miRNAs in the breast cancer tissue are so more than that in the normal tissue. The expression of mir-21 increases in the breast cancer. This miRNA involved in the progression and malignancy of the cancer by controlling expression of the tumor suppressors such as PTEN. In addition, there are six miRNAs (mir- 10a, mir-26, mir-30c, mir-126a, mir-210, mir-519a) which play roles in tamoxifen resistance through estrogen receptor (ER). The expression of mir-100 in MCF-7 cell lines (breast cancer) arrests cell cycle and apoptosis. On the other hand, it was determined that miRNAs could be involved in circulation. That finding is so important because differentiation and activation of various tumors might be related to immune cells as well as specific miRNAs. Some evidences confirmed this statement; increase of mir- 10 expression in cancer cells result in decrease of MICB and trepan to kill the tumor by natural killer cells, increase of mir-155 expression in cancer cells decreases SOCS1 and trepan to enable the SATAT3 signaling pathway, and increase of mir-424 expression in cancer cell decreases PDL1 and CD80 trepan to active T cells. using of miRNAs in the treatment of breast cancer is possible through altering and manipulating of miRNA expression (over expression or silencing of miRNAs) to improve existing therapies.