Breast cancer is the most prevalent diagnosed cancer and the second cause of cancer death among women worldwide. There are different mechanisms that play crucial roles in the onset and progression of breast cancer including microRNAs. microRNAs are small noncoding RNAs that regulate gene expression by repressing translation post-transcriptionally. miR-31 is an integrin modulator implicated in different cellular processes such as apoptosis, cell cycle control, and DNA repair. According to the literature, RhoA is one of the genes regulated by miR-31. It has an important role in actin-myosin contraction and subsequently in cell motility and migration in metastasis cascade. Breast cancer cell lines, MCF-7 and MDA-MB-231, as well as normal breast cells, MCF-10A, were cultured. RNA extraction, cDNA synthesis, and SYBR Green I quantitative real-time PCR were used to investigate the expression of miR-31 and RhoA. In addition, 10 metastatic breast cancer clinical samples were analyzed to assess miR-31 and RhoA expression, and normal cells from the same patients were used as controls. Pearson’s correlation co-efficient was applied to find out any probable relation between miR-31 and RhoA expression. Gene expression analyses in MCF-7 cell line showed downregulation of miR-31 while RhoA was upregulated in the cell line (inverse correlation). miR-31 and RhoA were both upregulated in metastatic MDA-MB-231 cell line and downregulated in 90% of clinical samples. Pearson’s correlation co-efficient showed complete positive correlation between miR-31 and RhoA expression. The expression of miR-31 and RhoA is positively correlated, and it is declined in metastatic breast that cancer clinical samples save MDA-MB-231 cells. Unlike previous reports, we found that miR-31 is not the main silencer of RhoA expression. Therefore, more investigation on genes and miRNAs affecting metastasis process can elucidate new biomarkers and therapeutic targets for metastatic breast cancer.Highlights miR-31 is an important miRNA implicated in different cellular processes as well as cancer.The protein product of RhoA gene plays a role in actin-myosin contraction and cell motility in cancer metastasis.We approved bioinformatically and experimentally that RhoA is one of the genes regulated by miR-3
