CCL2-CCL5/CCR4 contributed to radiation-induced epithelial-mesenchymal transition of HPAEpiC cells via the ERK signaling pathways.

Radiation-induced lung toxicity, including radiation pneumonitis and pulmonary fibrosis, often occurs in patients receiving radiation therapy. Epithelial-mesenchymal transition (EMT) of alveolar epithelial cells (AECs) plays critical roles in radiation-induced lung toxicity. In the present study, RNA sequencing was applied to examine the whole transcriptomes of human pulmonary AEC cells (HPAEpiC) with or without radiation treatment. We found that cytokine, chemokine and cell adhesion signaling pathways were enriched in radiation-treated cells. CCL2 (C-C Motif Chemokine Ligand 2), CCL5 and CCR4 (C-C Motif Chemokine Receptor 4) were among the top enriched genes in chemokine signaling pathway. The upregulation of CCL2, CCL5 and CCR4 in response to irradiation was confirmed at both mRNA and protein levels by real-time PCR, western blotting and enzyme-linked immunosorbent assay analyses. Ophiopogonin B, a bioactive ingredient of Radix Ophiopogon japonicas, was found to attenuate radiation-induced EMT in HPAEpiC cells as demonstrated by the alteration in cell morphology, and the expression of E-cadherin and Vimentin. Ophiopogonin B could also reduce radiation-induced expression of CCL2, CCL5, CCR4 and phosphorylated ERK (p-ERK). Moreover, CCR4 knockdown, U0126 (a MEK/ERK inhibitor) or ophiopogonin B also partially blocked the EMT promoting effects of CCL2 and CCL5. Our data suggested CCL2, CCL5 and CCR4 may be potential therapeutic targets for radiation-induced lung toxicity. Ophiopogonin B, which could down-regulate CCL2, CCL5 and CCR4, may be a useful radioprotective agent.