Shikonin differentially regulates glucose metabolism via PKM2 and HIF1α to overcome apoptosis in a refractory HCC cell line

In tumor cells, shikonin treatment has been reported to inhibit glycolysis by suppressing the activity of pyruvate kinase M2 (PKM2) and to induce apoptosis by increasing reactive oxygen species (ROS) production. However, hepatocellular carcinoma (HCC) shows variable sensitivity to shikonin treatment, and the mechanism for these differences remains unclear. We evaluated the effects of shikonin on metabolic and oxidative pathways in sensitive and refractory HCC cell lines to identify mechanisms of differential sensitivity.Cell viability and apoptosis were evaluated by MTT assay, PI/Annexin V and JC-1 staining. Mitochondrial function was further evaluated by measurements of ROS and mitochondrial mass. Oxygen consumption rates, NAD+/NADH, ATP and lactate were measured as indicators of energy metabolism and glycolysis. Protein expression associated with glycolysis and apoptosis was evaluated by western blotting, RT-qPCR and immunofluorescence staining.The sensitivity to shikonin treatment was significantly higher for HepG2 cells than for HCCLM3 cells, with less dramatic effects in HCCLM3 cells on apoptosis, ROS, and oxidative phosphorylation. Shikonin up-regulated mitochondrial biogenesis to increase mitochondrial oxidative phosphorylation in HepG2 cells, but displayed the opposite trend in HCCLM3 cells. Mechanistically, shikonin promoted nuclear expression of PKM2 and HIF1α in HCCLM3 cells, with upregulation of glycolysis-related gene transcription and glycolysis.These results suggest that PKM2 rewires glucose metabolism, which explains the differential sensitivity to shikonin-induced apoptosis in HCC cells. Our findings elucidate mechanisms for differential responses to shikonin, provide potential biomarkers, and indicate a theoretical basis for targeting glycolytic enzymes in refractory HCC.