MicroRNA-409-5p is upregulated in breast cancer and its downregulation inhibits cancer development through downstream target of RSU1.

We investigated the expression and function of miR-409-5p in human breast cancer. Quantitative real-time polymerase chain reaction was conducted to evaluate endogenous miR-409-5p expression in breast cancer tumors and breast cancer cell lines. Lentiviral transduction was performed to stably downregulate miR-409-5p in breast cancer cell lines MDA-MB-231 and MCF-7 and cells. The effects of miR-409-5p downregulation on breast cancer proliferation, migration, and xenograft development were then evaluated. Downstream target gene of miR-409-5p, Ras suppressor protein 1, was examined by dual-luciferase activity assay, quantitative real-time polymerase chain reaction, and western blot in lentiviral-transduced breast cancer cells. Ras suppressor protein 1 was also inhibited in miR-409-5p-downregulated breast cancer cells to examine its functional effect on breast cancer proliferation and migration. MiR-409-5p was aberrantly upregulated in both breast cancer tumors and cell lines. Lentiviral transduction successfully downregulated endogenous miR-409-5p expression as well as suppressed proliferation, migration, and xenograft development in MDA-MB-231 and MCF-7 cells. Ras suppressor protein 1 was confirmed to be directly targeted by miR-409-5p in breast cancer cells. Small interfering RNA-mediated Ras suppressor protein 1 inhibition reversely promoted cancer proliferation and migration in miR-409-5p-downregualted breast cancer cells. MiR-409-5p is downregulated in breast cancer and its inhibition has anti-cancer effect on breast cancer development both in vitro and in vivo. The regulatory effect of miR-409-5p inhibition is likely through the inverse upregulation of Ras suppressor protein 1 in breast cancer.