Down-regulation of NAMPT expression by miR-154 reduces the viability of breast cancer cells and increases their susceptibility to doxorubicin

Abstract Background Nicotinamide phosphoribosyltransferase (NAMPT) acts as an important enzyme in the salvage pathway of nicotinamide adenine dinucleotide (NAD) biosynthesis. Deregulation of NAD could be associated with progression of many cancers including breast cancer. Here, we evaluated the effect of NAMPT inhibition via miR-154 on survival of breast cancer cells. Methods Breast cancer cell lines including MCF-7 and MDA-MB-231 were transfected with miR-154-5p mimic, inhibitor and their negative controls. Using real-time PCR and western blotting techniques the expression levels of NAMPT and miR-154 were determined and compared with the untreated cells. NAD levels were measured by an enzymatic method. Subsequently, colorimetric methods and flow cytometry were performed to evaluate cell viability and apoptosis. Bioinformatics analyses were performed to investigate whether NAMPT 3′-UTR is a direct target of miR-154 and the findings were confirmed by luciferase reporter assay. Results According to the obtained results, NAMPT 3′-UTR was identified as a direct target of miR-154 and the levels of this miRNA was inversely associated with NAMPT expression both at mRNA and protein levels in breast cancer cell lines. Functionally, miR-154 inhibited the NAD salvage pathway leading to a remarkable decrease in cell survival and induction of apoptosis. Co-treatment of breast cancer cells with doxorubicin and miR-154 mimic significantly reduced cell viability compared to treatment with doxorubicin alone in both cell lines. Conclusions Hence, it was concluded that the inhibition of NAD production by miR-154 might be introduced as a promising therapeutic strategy for the treatment of breast cancer either alone or in combination with other conventional chemotherapeutic agents.