Context dependent non canonical WNT signaling mediates activation of fibroblasts by transforming growth factor-β.

Abstract

Actions of transforming growth factor-β are largely context dependent. For instance, TGF-β is growth inhibitory to epithelial cells and many tumor cell-lines while it stimulates the growth of mesenchymal cells. TGF-β also activates fibroblast cells to a myofibroblastic phenotype. In order to understand how the responsiveness of fibroblasts to TGF-β would change in the context of transformation, we have compared the differential gene regulation by TGF-β in immortal fibroblasts (hFhTERT), transformed fibroblasts (hFhTERT-LTgRAS) and a human fibrosarcoma cell-line (HT1080). The analysis revealed regulation of 6735, 4163, and 3478 probe-sets by TGF-β in hFhTERT, hFhTERT-LTgRAS and HT1080 cells respectively. Intriguingly, 5291 probe-sets were found to be either regulated in hFhTERT or hFhTERT-LTgRAS cells while 2274 probe-sets were regulated either in hFhTERT or HT1080 cells suggesting that the response of immortal hFhTERT cells to TGF-β is vastly different compared to the response of both the transformed cells hFhTERT-LTgRAS and HT1080 to TGF-β. Strikingly, WNT pathway showed enrichment in the hFhTERT cells in Gene Set Enrichment Analysis. Functional studies showed induction of WNT4 by TGF-β in hFhTERT cells and TGF-β conferred action of these cells was mediated by WNT4. While TGF-β activated both canonical and non-canonical WNT pathways in hFhTERT cells, Erk1/2 and p38 Mitogen Activated Protein Kinase pathways were activated in hFhTERT-LTgRAS and HT1080 cells. This suggests that transformation of immortal hFhTERT cells by SV40 large T antigen and activated RAS caused a switch in their response to TGF-β which matched with the response of HT1080 cells to TGF-β. These data suggest context dependent activation of non-canonical signaling by TGF-β.