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

Abstract

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.

Effects of endoplasmic reticulum stress on the autophagy, apoptosis, and chemotherapy resistance of human breast cancer cells by regulating the PI3K/AKT/mTOR signaling pathway

“…23 Based on the fact that tunicamycin exhibited similar effects as BEZ235 on inhibition of the PI3K/AKT/mTOR signaling pathway and stimulation of apoptosis, it was supposed that both chemicals might share similar mechanisms. With respect to autophagy, a recent study showed that tunicamycin enhanced conversion from LC3I to LC3II (autophagosome-associated form) and increased the Beclin1 levels, 24 which had also been described in this study. Further studies had illustrated that ERS increased autophagy, apoptosis, and chemotherapy resistance of MCF-7 cells via inhibition of the PI3K/AKT/mTOR signaling pathway.…”

Inhibition of apolipoprotein B synthesis stimulates endoplasmic reticulum autophagy that prevents steatosis

“…strated by the (a) disappearance of ER stress by 6 weeks when ER autophagy was active; (b) marked reductions in ER levels of TG and DG by 6 weeks compared with levels at 3 weeks; and (c) persistence of ER stress and the appearance of several markers of apoptosis, including cleaved caspase 12, which has been shown to be specifically induced by ER stress (42), when initiation of autophagy was blocked by ATG7 ASO treatment. The increased FA oxidation we observed when autophagy was blocked and which, like autophagy, prevented steatosis in the apoB ASO-and ATG7 ASOtreated mice, very likely resulted from lipids released directly from "sick" ER; we will attempt to better characterize this observation in future studies.…”

Resveratrol inhibits oral squamous cell carcinoma cells proliferation while promoting apoptosis through inhibition of CBX7 protein

“…The PARP and caspase have been confirmed to regulate the mechanism of apoptosis. 22,23 The caspase-3 is regarded as the most essential of the executioner caspases, activated caspase-3 can cleave various structural and regulatory proteins, which ultimately lead to the alterations in morphology and biochemistry of apoptotic cells. 24 Caspase-9 is the upstream caspase which is involved in the apoptotic process.…”