Epidermal growth factor and transforming growth factor-β1 enhance HK-2 cell migration through a synergistic increase of matrix metalloproteinase and sustained activation of ERK signaling pathway

Epidermal growth factor (EGF) and transforming growth factor-β1 (TGF-β1), upregulated in renal diseases, have a combinational effect on epithelial-mesenchymal transformation (EMT) of renal proximal tubular cells. The aim of this study was to examine the mechanism regarding the combinational effect of EGF and TGF-β1 on cell migration following EMT. The results demonstrated that EGF (10 ng/ml) and TGF-β1 (3 ng/ml) synergistically increased cell migration, accompanied by an increase in matrix metalloproteinase-9 (MMP-9) gene expression, production and activity. Inhibition of MMP-9 production and activity by an MMP-2/MMP-9-specific inhibitor blocked the synergistic effect of EGF and TGF-β1 on cell migration. The kinetic profile of extracellular signal-regulated kinase (ERK) signals demonstrated that ERK1/2 activation was rapidly and strongly induced by EGF but delayed and less marked by TGF-β1 stimulation. In contrast, co-administration of EGF and TGF-β1 caused an early pronounced and persistent ERK1/2 activation. Inhibition of the ERK1/2 activity by PD98059 abrogated the synergistic effect of EGF and TGF-β1 on cell migration, MMP-9 production and activity, indicating that EGF and TGF-β1 converged at the ERK signaling pathway to mediate cell migration. This study demonstrates that EGF and TGF-β1 synergistically stimulate proximal tubular cell migration through the increased MMP-9 function and enhanced ERK1/2 activation.