TGF-beta1-induced EMT Can Occur Independently of Its Proapoptotic Effects and is Aided by EGF Receptor Activation

Apoptosis and epithelial-mesenchymal transdifferentiation (EMT) occur in stressed tubular epithelial cells and contribute to renal fibrosis. Transforming growth factor (TGF)-beta(1) promotes these responses and we examined whether the processes were interdependent in vitro. Direct (caspase inhibition) and indirect [epidermal growth factor (EGF) receptor stimulation] strategies were used to block apoptosis during TGF-beta(1) stimulation, and the subsequent effect on EMT was assessed. HK-2 cells were exposed to TGF-beta(1) with or without preincubation with ZVAD-FMK (pan-caspase inhibitor) or concomitant treatment with EGF plus or minus preincubation with LY-294002 (PI3-kinase inhibitor). Cells were then assessed for apoptosis and proliferation by flow cytometry, crystal violet assay, and Western blotting. Markers of EMT were assessed by microscopy, immunofluorescence, real-time RT-PCR, Western blotting, PAI-1 reporter assay, and collagen gel contraction assay. TGF-beta(1) caused apoptosis and priming for staurosporine-induced apoptosis. This was blocked by ZVAD-FMK. However, ZVAD-FMK did not prevent EMT following TGF-beta(1) treatment. EGF inhibited apoptosis and facilitated TGF-beta(1) induction of EMT by increasing proliferation and accentuating E-cadherin loss. Additionally, EGF significantly enhanced TGF-beta(1)-induced collagen I gel contraction. EGF increased Akt phosphorylation during EMT, and the prosurvival effect of this was confirmed using LY-294002, which reduced EGF-induced Akt phosphorylation and reversed its antiapoptotic and proproliferatory effects. TGF-beta(1) induces EMT independently of its proapoptotic effects. TGF-beta(1) and EGF together lead to EMT. EGF increases proliferation and resistance to apoptosis during EMT in a PI3-K Akt-dependent manner. In vivo, EGF receptor activation may assist in the selective survival of a transdifferentiated, profibrotic cell type.