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AIMTo investigate the protective effect of prostaglandin E1 (PGE1) against endoplasmic reticulum (ER) stress-induced hepatocyte apoptosis, and to explore its underlying mechanisms.METHODSThapsigargin (TG) was used to induce ER stress in the human hepatic cell line L02 and hepatocarcinoma-derived cell line HepG2. To evaluate the effects of PGE1 on TG-induced apoptosis, PGE1 was used an hour prior to TG treatment. Activation of unfolded protein response signaling pathways were detected by western blotting and quantitative real-time RT-PCR. Apoptotic index and cell viability of L02 cells and HepG2 cells were determined with flow cytometry and MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay.RESULTSPretreatment with 1 μmol/L PGE1 protected against TG-induced apoptosis in both L02 cells and HepG2 cells. PGE1 enhanced the TG-induced expression of C/EBP homologous protein (CHOP), glucose-regulated protein (GRP) 78 and spliced X box-binding protein 1 at 6 h. However, it attenuated their expressions after 24 h. PGE1 alone induced protein and mRNA expressions of GRP78; PGE1 also induced protein expression of DNA damage-inducible gene 34 and inhibited the expressions of phospho-PKR-like ER kinase, phospho-eukaryotic initiation factor 2α and CHOP. Treatment with protein kinase A (PKA)-inhibitor H89 or KT5720 blocked PGE1-induced up-regulation of GRP78. Further, the cytoprotective effect of PGE1 on hepatocytes was not observed after blockade of GRP78 expression by H89 or small interfering RNA specifically targeted against human GRP78.CONCLUSIONOur study demonstrates that PGE1 protects against ER stress-induced hepatocyte apoptosis via PKA pathway-dependent induction of GRP78 expression.

Background: The aim of this study was to explore the effects of endoplasmic reticulum (ER) stress on hepatitis B virus (HBV) replication and the antiviral effect of entecavir (ETV).Methods: Thapsigargin (TG) and stearic acid (SA) were used to induce ER stress in HepG2.2.15 cells and HepAD38 cells that contained an integrated HBV genome, while ETV was used to inhibit HBV replication. The expression levels of glucose-regulated protein 78 (GRP78) and phosphorylated eukaryotic translation initiation factor 2 subunit alpha (p-eIF2α) were measured by western blotting. Intracellular HBV DNA was determined by qPCR; HBsAg by western blotting; HBV RNA by real-time RT-qPCR; HBsAg and HBeAg in supernatants by enzyme-linked immunosorbent assay (ELISA); and HBV DNA in supernatants by qPCR.Results: TG and SA induced ER stress in HepG2.2.15 cells and HepAD38 cells from 12 to 48 h post treatment. However, 4-phenylbutyric acid (PBA) partly alleviated the TG-induced ER stress. Moreover, TG inhibited HBsAg, HBeAg, and HBV DNA secretion from 12 to 48 h, while different concentrations of SA inhibited HBsAg and HBV DNA secretion at 48 h. TG promoted intracellular HBV DNA and HBsAg accumulation and the transcription of the HBV 3.5-kb mRNA and S mRNA. PBA treatment restored the secretion of HBsAg and HBV DNA. Finally, ER stress accelerated extracellular HBV DNA clearance but delayed intracellular HBV DNA clearance after ETV treatment.Conclusions: Hepatocyte ER stress promoted intracellular HBV DNA and HBsAg accumulation by inhibiting their secretion. Our study also suggested that hepatocyte ER stress delayed intracellular HBV DNA clearance after ETV treatment.