Abstract: Objective To explore the regulatory effect of microRNA-155 （miR-155） on the proliferation， apoptosis and expression of breast cancer resistance protein. Methods The real-time quantitative PCR （qRT-PCR） was employed to measure the miR-155 level in MCF-7 cells and human normal breast epithelium cells. The MCF-7 cells were randomly assigned into four groups according to the experiment protocol： control group， blank group， inhibition group （transfection with miR-155 inhibitor） and over-expression group （transfection with miR-155 mimics）. The qRT-PCR was used to detect the transfection effect at 24， 48， 72 and 96 h after transfection. Methyl thiazolyl tetrazolium （MTT） assay was used to assess the proliferation ability at 24， 48， 72 and 96 h after transfection. The apoptosis rate was evaluated at 24 and 48 h after transfection by PI／Annexin V double staining with flow cytometry. Western blotting was used to measure the expression levels of breast cancer resistance protein （BRCP）， P-glycoprotein （P-gp） and multidrug resistance associated protein 1 （MRP1） protein.
ResultsThere was higher level of miR-155 in MCF-7 cells versus human normal breast epithelium cells （P＜0.05）. Transfection with miR-155 inhibitor or mimics could reduce or increase the level of miR155 in time dependent manner in MCF-7 cells （P＜0.05）； In comparison with control group， the rates of proliferation and expression levels of BRCP， P-gp and MRP1 decreased in inhibition group but increased in overexpression group （P＜0.05）. The apoptosis rate increased in inhibition group but decreased in overexpression group（P＜0.05）. Conclusion There is higher level of miR-155 in MCF-7 cells. Down-regulation of miR-155 presents an inhibitory effect on the proliferation and expression of drug resistance related protein along with the induction of apoptosis.