Background and purpose: Multiple microRNAs (miRNAs) are abnormally expressed in breast cancer and play an important role in the regulation of breast cancer. miRNAs may be a new target for the treatment of breast cancer. This study aimed to investigate the expression of miR-199a-3p in breast cancer and the effect of miR-199a-3p on proliferation and apoptosis of breast cancer. Methods: Real-time PCR was used to test the expression of miR-199a-3p in breast cancer tissues

normal breast tissues

breast cancer cells and normal breast cells. Overexpression (or silencing the expression) of miR-199a-3p was conducted by transfecting MDA-MB-231 with miR-199a-3p mimics (or inhibitors). The proliferation of MDA-MB-231 was detected by MTT method. The apoptosis of MDA-MB-231 was investigated by Hoechst staining and caspase-3 activity assay kit. Results: Compared to corresponding non-tumor breast tissues (or normal breast cell HBL-100)

lower levels of miR-199a-3p were expressed in breast cancer tissues or breast cancer cells. Overexpression of miR-199a-3p induced by miR-199a-3p mimic inhibited the proliferation and promoted the apoptosis of MDA-MB-231

while silencing the expression of miR-199a-3p induced by miR-199a-3p inhibito increased the proliferation and suppressed the apoptosis of MDA-MB-231. Conclusion: The expression of miR-199a-3p is lower in breast cancer

which shows its tumor suppression effect by regulating the proliferation and apoptosis of breast cancer cells.