Inhibition of autophagy promotes caspase-mediated apoptosis by tunicamycin in HepG2 cells

Tunicamycin (TM) causes accumulation of unfolded protein in endoplasmic reticulum (ER) lumen and introduces from elsewhere ER stress. This study was to assess the apoptosis and autophagy effect induced by TM on HepG2 cells and the role of autophagy in the system. The viability of HepG2 cells was significantly inhibited by TM in a dose-dependent manner detected by MTT assay. Then, the apoptotic morphology change, increasing apoptotic cell rate suggested that apoptosis was induced by TM in a time-and dose-dependent manner. To further determine the involvement of caspase-dependent pathway in TM-induced apoptosis, we discover that the activity of caspase-3/7, 8, 9 and cleavage of PARP markedly increased after TM treatment and the apoptosis was effectively attenuated by using caspase-9 and pan caspase inhibitor. Moreover, provided the rising stained acidic vacuoles and an increased level of LC3II and activation of Beclin1, we concluded that autophagy could be triggered by TM in a time-and dose-dependent manner. In addition, the inhibition of autophagy efficiently promoted TM-induced cell death identified by MTT assay. Meanwhile, the apoptotic cell rate and caspase-3 activation increased significantly after autophagy blockage. In conclusion, we found that TM initiated apoptosis and autophagy both in a time-and dose-dependent manner in HepG2 cells; and inhibition of autophagy may promote TM-induced cell death through enhancing apoptosis.