CHOP favors endoplasmic reticulum stress-induced apoptosis in hepatocellular carcinoma cells via inhibition of autophagy.

Yan Lei,Bingshuang Ren,Lianghu Huang,Jin Wang,Shuiliang Wang,Jun Lu,Shihuai Zhan,Yunfeng Fu,Jianming Tan,Jin Chen

doi:10.1371/journal.pone.0183680

Abstract

C/EBP-homologous protein (CHOP) is an important component of the endoplasmic reticulum (ER) stress response. We demonstrated the induction of ER stress in response to tunicamycin stimulation, as evidenced by increased expression of chaperone proteins Grp78, Grp94, and enhanced eukaryotic initiation factor 2 subunit 1 (eIF2α) phosphorylation in hepatocellular carcinoma cells. Tunicamycin-induced ER stress resulted in apoptosis and autophagy simultaneously. While inhibition of autophagy mediated by 3-methyladenine pretreatment or direct knockdown of LC3B promoted cell apoptosis, activation of autophagy with rapamycin decreased tunicamycin- induced apoptosis in HCC cells. Furthermore, CHOP was shown to be significantly upregulated upon treatment with tunicamycin in HCC cells. Specific knockdown of CHOP not only enhanced tunicamycin-induced autophagy, but also significantly attenuated ER stress-induced apoptosis in HCC cells. Accordingly, simultaneous inhibition of autophagy in HCC cells with CHOP-knockdown could partially resensitize ER stress-induced apoptosis. Taken together, our data indicate that CHOP may favor ER stress-induced apoptosis in HCC cells via inhibition of autophagy in vitro.

Highlights

Tumor hypoxia inhibits the formation of protein glycosylation and disulfide bonds, resulting in the accumulation of unfolded or misfolded proteins in endoplasmic reticulum (ER)
Our data here indicated that ER stress induced by TM could result in apoptosis in hepatocellular carcinoma (HCC) cells
C/EBP-homologous protein (CHOP) favors ER-induced apoptosis in HCC cells in the ER leads to a failure of protein degradation by proteasome, causing the upregulation of autophagy[29].In our current study, we further showed that autophagy was activated under TM-induced ER stress

Summary

Introduction

Tumor hypoxia inhibits the formation of protein glycosylation and disulfide bonds, resulting in the accumulation of unfolded or misfolded proteins in endoplasmic reticulum (ER) This condition is defined as ER stress, which reflects an imbalance between the cellular demand for ER function and ER protein folding ability [1,2]. The sensors of ER stress are PERK (PKR-like ER kinase; known as eukaryotic translation initiation factor 2 alpha kinase 3 or EIF2AK3), ATF6 (activating transcription factor 6), and IRE1 (inositol-requiring enzyme 1). These 3 proteins activate the unfolded protein response.

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Conclusion