Formin-dependent TGF-β signaling for epithelial to mesenchymal transition

Abstract

The role of distinct actin filament architectures in epithelial plasticity remains incompletely understood. We therefore determined roles for formins and the Arp2/3 complex, which are actin nucleators generating unbranched and branched actin filaments, respectively, in the process of epithelial to mesenchymal transition (EMT). In clonal lung, mammary, and renal epithelial cells, the formin activity inhibitor SMIFH2 but not the Arp2/3 complex activity inhibitor CK666 blocked EMT induced by TGF-β. SMIFH2 prevented the proximal signal of increased Smad2 phosphorylation and hence also blocked downstream EMT markers, including actin filament remodeling, decreased expression of the adherens junction protein E-cadherin, and increased expression of the matrix protein fibronectin and the transcription factor Snail. The short hairpin RNA silencing of formins DIAPH1 and DIAPH3 but not other formins phenocopied SMIFH2 effects and inhibited Smad2 phosphorylation and changes in Snail and cadherin expression. Formin activity was not necessary for the cell surface expression or dimerization of TGF-β receptors, or for nuclear translocation of TAZ, a transcription cofactor in Hippo signaling also regulated by TGF-β. Our findings reveal a previously unrecognized role for formin-dependent actin architectures in proximal TGF-β signaling that is necessary for Smad2 phosphorylation but not for cross-talk to TAZ.

A polycomb-independent role of EZH2 in TGFβ1-damaged epithelium triggers a fibrotic cascade with mesenchymal cells

“…To understand how actin could impact the fibrotic transcriptional complex, we treated TGFβ1-induced pro-fibrotic EPCs with the Rho-kinase inhibitor Y27632 35 . Consistent with previous data 30 , TGFβ1 treatment increased actin polymerisation and non-muscle myosin II activity marked by the phosphorylation of its light chain (ph-MLC2, Fig. 4a,b).…”

“…To unravel the mechanisms of the ph-EZH2-mediated pro-fibrotic gene expression, we investigated the potential binding partners of EZH2 upon TGFβ1-induced damage in EPCs. It has been shown that remodelling of the actin cytoskeleton is a major pathway involved in TGFβ1 signalling 30 . Actin is constantly shuttled between the cytoplasm and the nucleus, where it has been shown to associate with the chromatin remodelling complex and POL2 to enhance transcriptional activity 31-33 .…”

mDia2 formin selectively interacts with catenins and not E-cadherin to regulate Adherens Junction formation

“…Our findings are consistent with recent publications that propose a role for formins in regulating the epithelial mesenchymal transition (EMT). Both formin inhibition with SMIFH2 and depletion of mDia1 and mDia2 prevented TGF-β-induced EMT in lung, mammary, and renal epithelial cells [68]. Others demonstrated the role of formins including FHOD1 and FMNL2 in the morphological changes associated with EMT [68-70].…”

“…Both formin inhibition with SMIFH2 and depletion of mDia1 and mDia2 prevented TGF-β-induced EMT in lung, mammary, and renal epithelial cells [68]. Others demonstrated the role of formins including FHOD1 and FMNL2 in the morphological changes associated with EMT [68-70]. In ovarian cancer, decreased E-cadherin expression is associated with peritoneal seeding of tumor cells and lower overall survival rate [43, 71].…”

Arp2/3 complex-mediated actin assembly drives microtubule-independent motility and phagocytosis in the evolutionarily divergent amoebaNaegleria

“…In addition to inhibiting formins, SMIFH2 was also recently shown to inhibit some myosins (Sellers et al, 2020), and therefore may be better described as an inhibitor of contractile networks. Regardless, targeting formins with SMIFH2 has been a reliable indicator for the involvement of formins in other systems (Fattouh et al, 2015;Rana et al, 2018;Velle and Campellone, 2018).…”