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Backgrounds & objectives: Colorectal cancer (CRC) is the third leading cause of cancer death worldwide. Micro RNAs are a group of non-coding small RNAs that inhibit the translation of target mRNA. MiR-146a-5p, as a tumor suppressor, has abnormal expression in many cancers. In this basic research, our goal was to restore the expression level of miR-146a-5p to normal level and to investigate its effect on the expression of the MMP9 gene in HT-29 cells.
Methods: this study evaluates the effect of transfection of miR-146a-5p in HT-29 cell line. At first, the HT-29 cell line from colorectal cancer was cultured in RPMI-1640 culture media and then  were transfected with miR-146a-5p using Jet-PEI reagent. qRT-PCR technique was employed to evaluate the expression level of miR-146a-5p and MMP9 genes. The statistical analysis was performed using GraphPad Prism 6 software.
Results: According to the obtained data, the onset of the invasion and metastasis, in particular, at the final stage of colorectal cancer may be related to a reduction in the expression of miR-146a-5p. The results of the qrRT-PCR test showed that by increasing the expression level of miR-146a-5p in HT-29 cells, the expression level of MMP9 gene decreased in the miR-146a-5p transfected group compared to the control group.
Conclusions: According to this study, activation of metastatic pathways was due to the down regulation of miR146a-5p. Accordingly, miR-146a-5p can inhibits migration of these cells through down-regulating the expression of metastasis-related genes. Hence, miR-146a-5p can be a new diagnostic biomarker and new therapeutic target for CRC.