GRP78 silencing enhances hyperoxia-induced alveolar epithelial cell apoptosis via CHOP pathway

Abstract

Hyperoxia is one of the primary causes of bronchopulmonary dysplasia, which may occur in premature infants following supplemental oxygen therapy. Glucose regulated protein 78 (GRP78), which is a molecular chaperone located in the lumen of the endoplasmic reticulum (ER), has been reported to regulate hyperoxia‑associated ER stress. The role of GRP78 in lung epithelial cells during hyperoxia remains to be elucidated. In the present study, the A549 cultured human lung epithelial cell line was exposed to hyperoxic conditions, and then transfected with short interfering (si)RNA targeted to GRP78. siRNA or pEGFP‑N1 plasmid were used to knockdown or overexpress specific genes, reverse transcription-quantitative polymerase chain reaction and western blot analysis were used to detect RNA and protein levels of gene expression, and flow cytometry was used to detect apoptosis. The expression levels of ER stress‑associated genes were determined, and a significant increase in C/EBP homologous protein (CHOP) expression and apoptosis of A549 cells was observed, following GRP78 knockdown. The overexpression of CHOP downregulated B‑cell lymphoma (Bcl)‑2 expression levels, upregulated BCL2 associated X (Bax), and increased apoptosis of A549 cells under conditions of hyperoxia. CHOP knockdown demonstrated the opposite effect on Bcl‑2 and Bax expression levels. These results suggested that GRP78 silencing promoted lung epithelial cell apoptosis during hyperoxia, via regulation of the CHOP pathway.

Synergistic activity of sorafenib and betulinic acid against clonogenic activity of non‐small cell lung cancer cells

“…CHOP is a transcription factor involved in the ER stress response. The overexpression of CHOP induces apoptosis through downregulation of Bcl‐2 and upregulation of the pro‐apoptotic proteins like Bim, Bax and Puma . In our investigation, CHOP was rapidly induced by combination of sorafenib and betulinic acid.…”

“…The overexpression of CHOP induces apoptosis through downregulation of Bcl-2 and upregulation of the pro-apoptotic proteins like Bim, Bax and Puma. (45,46) In our investigation, CHOP was rapidly induced by combination of sorafenib and betulinic acid. We found that combined treatment with sorafenib and betulinic acid induced both caspase 9 and caspase 8 in A549 cells, suggesting that both mitochondrial-dependent and mitochondrial-independent factors were responsible for the apoptotic potential.…”

TNF‐α enhances apoptosis by promoting chop expression in nucleus pulposus cells: role of the MAPK and NF‐κB pathways

“…CHOP is the first identified protein that mediates ER stress‐induced apoptosis, and the role of this molecule in apoptosis has been extensively studied . It is widely accepted that Bcl‐2 is a pro‐survival protein and Bax is a pro‐apoptotic protein . Moreover, researchers demonstrated that CHOP sensitizes cells to ER stress by down‐regulating Bcl‐2 and up‐regulating Bax .…”

“…29 It is widely accepted that Bcl-2 is a pro-survival protein and Bax is a pro-apoptotic protein. 29,30 Moreover, researchers demonstrated that CHOP sensitizes cells to ER stress by down-regulating Bcl-2 and up-regulating Bax. 29,30 In this study, CHOP siRNA significantly blocked TNF-induced Bax expression and TNF-inhibited Bcl-2 expression.…”

“…29,30 Moreover, researchers demonstrated that CHOP sensitizes cells to ER stress by down-regulating Bcl-2 and up-regulating Bax. 29,30 In this study, CHOP siRNA significantly blocked TNF-induced Bax expression and TNF-inhibited Bcl-2 expression. We confirmed that CHOP induced apoptosis by promoting the pro-apoptotic protein Bax and suppressing the anti-apoptosis protein Bcl-2 in NP cells.…”