Endoplasmic reticulum stress promotes epithelial‑mesenchymal transition via the PERK signaling pathway in paraquat‑induced pulmonary fibrosis.

Pulmonary fibrosis is the primary reason for mortality in patients with paraquat (PQ) poisoning. Our previous study demonstrated that epithelial‑mesenchymal transition (EMT) had a role in PQ‑induced pulmonary fibrosis. However, the role of endoplasmic reticulum (ER) stress in PQ‑induced EMT remains clear. The present study aimed to determine the role of ER stress in EMT in PQ‑induced pulmonary fibrosis. A549 and RLE‑6TN cells were incubated with LY294002 (a PI3K inhibitor) or transfected with protein kinase RNA‑like ER kinase (PERK) small interfering RNA (si) for 24 h prior to being exposed to PQ. Next, the expression levels of ER stress‑related proteins, PI3K/AKT/GSK‑3β signaling pathway‑related proteins and EMT‑related markers were analyzed by performing western blotting, reverse transcription‑quantitative PCR and immunofluorescence assays. The results of the present study revealed that the protein expression levels of PERK, phosphorylated (p)‑PERK, p‑eukaryotic initiation factor 2 (eIF2)α were significantly upregulated in the PQ group, whereas p‑PI3K, p‑AKT and p‑GSK‑3β were significantly upregulated in the sicontrol + PQ group compared with the sicontrol group. , following transfection with siPERK or treatment with the PI3K inhibitor, the protein expression levels of E‑cadherin (an epithelial marker) were upregulated, whereas the protein expression levels of α‑SMA (a mesenchymal marker) were downregulated. Immunofluorescence analysis revealed that the levels of E‑cadherin were markedly upregulated, whereas the levels of α‑SMA were notably downregulated following transfection with siPERK compared with the sicontrol group. The results of wound healing assay demonstrated that cell migration in the siPERK + PQ group was markedly decreased compared with the sicontrol + PQ group. These indicated that PQ‑induced EMT was suppressed after silencing PERK. The expression levels of p‑GSK‑3β, p‑AKT and p‑PI3K were also markedly downregulated in the siPERK + PQ group compared with the sicontrol + PQ group. In conclusion, the findings of the present study suggested that ER stress may promote EMT through the PERK signaling pathway in PQ‑induced pulmonary fibrosis. Thus, ER stress may represent a potential therapeutic target for PQ‑induced pulmonary fibrosis.