Macrophage migration inhibitory factor has a permissive role in concanavalin A-induced cell death of human hepatoma cells through autophagy

Concanavalin A (ConA) is a lectin and T-cell mitogen that can activate immune responses. In recent times, ConA-induced cell death of hepatoma cells through autophagy has been reported and its therapeutic effect was confirmed in a murine in situ hepatoma model. However, the molecular mechanism of ConA-induced autophagy is still unclear. As macrophage migration inhibitory factor (MIF), which is a proinflammatory cytokine, can trigger autophagy in human hepatoma cells, the possible involvement of MIF in ConA-induced autophagy was investigated in this study. We demonstrated that cell death is followed by an increment in MIF expression and secretion in the ConA-stimulated human hepatoma cell lines, HuH-7 and Hep G2. In addition, ConA-induced autophagy and cell death of hepatoma cells were blocked in the presence of an MIF inhibitor. Knockdown of endogenous MIF by small hairpin RNA confirmed that MIF is required for both ConA-induced autophagy and death of hepatoma cells. Furthermore, signal pathway studies demonstrated that ConA induces signal transducer and activator of transcription 3 (STAT3) phosphorylation to trigger MIF upregulation, which in turn promotes Bcl-2/adenovirus E1B 19 kDa-interacting protein 3 (BNIP3)-dependent autophagy. By using a murine in situ hepatoma model, we further demonstrated that MIF contributes to anti-hepatoma activity of ConA by regulating STAT3-MIF-BNIP3-dependent autophagy. In summary, our findings uncover a novel role of MIF in lectin-mediated anti-hepatoma activities by regulating autophagy.