Inhibition of apoptosis in breast cancer cells by si‑FoxO3a through the protein digestion and absorption signaling pathway

FoxO3a is closely associated with the occurrence and development of tumors. The present study aimed to evaluate the effect of FoxO3a on apoptosis in breast cancer, and to clarify the regulation of the protein digestion and absorption pathway in two breast cancer cell lines, through interfering with the expression of FoxO3a. MCF-7 and MDA-MB-231 were selected as the focal cells to study, and small interfering (si)RNA transfection technology was used to knockdown the expression of FoxO3a in both cell types. Clinical antitumor drugs were selected to treat cancer cells transfected with negative control sequences (si-NC) and sequences targeting FoxO3a (si-FoxO3a) in order to determine both the number of apoptotic cells and their morphology, and to assess migration levels using a wound healing assay. The cells were divided into si-NC and si-FoxO3a dosing groups for proteomics analyses, which were conducted using the differentially expressed proteins (DEPs) and the common signaling pathways were investigated. Finally, key proteins were validated using western blotting. First, the baseline expression levels of FoxO3a in two types of breast cancer cells were validated, confirming the presence of FoxO3a expression in both cell types. Next, FoxO3a was knocked down. Drug concentrations of tamoxifen (25 µmol/ml) and doxorubicin (30 µmol/ml) were selected for MCF-7 and MDA-MB-231 cells, respectively. si-FoxO3a reduced tumor cell death, and the apoptosis rate of cells treated with si-FoxO3a was notably decreased, indicated by Hoechst staining with reduced brightness. There was also a notable increase in scratch healing rate. After screening of DEPs by proteomics analysis, Gene Ontology enrichment analyses revealed common molecular functions of DEPs in both breast cancer cell lines at the cellular component and molecular function levels, predominantly extracellular space and L-glutamine transmembrane transporter activity. Kyoto Encyclopedia of Genes and Genomes functional enrichment analysis demonstrated that the main signaling pathway involved in apoptosis of both cell lines after FoxO3a knockdown was the protein digestion and absorption pathway. Protein-protein interaction mapping results showed a close relationship between DEPs. Focal DEPs were validated, and the findings were consistent with the proteomics results. Overall, the results demonstrated that si-FoxO3a inhibited the apoptosis of breast cancer cells through the protein digestion and absorption signaling pathway.