Epidermal growth factor promotes transforming growth factor-β1-induced epithelial-mesenchymal transition in HK-2 cells through a synergistic effect on Snail

Epithelial-mesenchymal transition (EMT) is a central mechanism for wound healing, tissue repair, organ fibrosis and carcinoma progression in adults. Evidence shows that both epidermal growth factor (EGF) and transforming growth factor-beta 1 (TGF-beta 1) are upregulated during renal interstitial fibrosis, and that co-stimulation of EGF and TGF-beta 1 could induce renal tubular epithelial cells to undergo EMT more effectively than EGF or TGF-beta 1 alone. This study was intended to explore the molecular mechanism underlying this effect. HK-2 cells underwent apparent EMT with increased cell motility after co-stimulation of EGF and TGF-beta 1 as compared with TGF-beta 1 or EGF alone. Co-stimulation of EGF and TGF-beta 1 resulted in rapid and robust ERK1/2 activation and induced persistent high expression of Snail protein. Treatment with the MEK inhibitor U0126 followed by co-stimulation with EGF and TGF-beta 1 prevented the upregulation of Snail protein, EMT and motility, without impairing Snail mRNA. TGF-beta 1 induced Snail at the transcriptional level, which was not influenced by EGF. Inhibition of Snail expression by siRNA interference also prevented EMT caused by co-stimulation of EGF and TGF-beta 1. These data suggest that EGF promotes TGF-beta 1-induced EMT through a synergistic effect on Snail at the post-transcriptional level in HK-2 cells.