Inhibition of p38 mitogen-activated protein kinase potentiates the apoptotic effect of berberine/tumor necrosis factor-related apoptosis-inducing ligand combination therapy

It was previously reported that berberine (BBR) and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) exhibited a synergistic apoptotic effect on triple negative breast cancer (TNBC) cells. In addition, the BBR/TRAIL combination treatment sensitized TRAILresis-tant TNBC cells to TRAIL. The aim of the present study was to investigate a novel pathway for enhancing the apoptotic effect of BBR/TRAIL through mitogen-activated protein kinases (MAPKs). Selective inhibitors and small interfering RNAs were utilized to understand the role of p38 MAPK in this pathway. The results demonstrated that p38 MAPK was activated in response to the combination therapy in TRAIL-resistant TNBC cells. In addition, it was revealed that the inhibition of p38 enhanced apoptosis in epidermal growth factor receptor (EGFR) -overexpressing MDA-MB-468 TNBC cells and EGFR-mutant PC-9 non-small-cell lung carcinoma cells, which was associated with the downregulation of EGFR serine phosphorylation. Viability assays for these two cell lines also confirmed the significant reduction of cell viability following p38 inhibition in BBR/TRAIL-treated cells. In conclusion, the present study provided novel evidence for the role of p38 in suppressing BBR/TRAIL-mediated apoptosis and its association with EGFR, which may explain the mechanism of treatment resistance in certain types of cancer.