Transforming growth factor-beta targets Formin-like 2 for Angiopoietin-like 4 secretion during the epithelial mesenchymal transition
Epithelial to Mesenchymal transition (EMT) is a highly dynamic process that plays a crucial role in tumor progression and metastasis. While remodelling of the actin cytoskeleton is a hallmark of EMT, the responsible actin regulating factors are less well understood. Formins are involved in numerous...
|PDF Full Text
No Tags, Be the first to tag this record!
|Epithelial to Mesenchymal transition (EMT) is a highly dynamic process that plays a crucial role in tumor progression and metastasis. While remodelling of the actin cytoskeleton is a hallmark of EMT, the responsible actin regulating factors are less well understood. Formins are involved in numerous cellular mechanisms, ranging from cytokinesis to cell adhesion and motility. The Rho-GTPase effectors of the formin family compromise the largest group of actin nucleators and are emerging as relevant pharmacological targets. A critical role of Formin-like 2 (FMNL2) in the assembly of junctional actin at newly forming cell-cell contacts in a 3D matrix has been described. This activity originates downstream of Rac1 and is in line with a physical association of FMNL2 and components of the cadherin-catenin complex. FMNL2 was further recently implicated in β1-integrin trafficking as a direct PKC target required for cancer cell invasion. Here we found that transforming growth factor-beta (TGFβ)-driven EMT leads to an upregulation of PKC resulting in the phosphorylation and activation of FMNL2 in epithelial cells. Proteomic screening for TGFβ-mediated phospho-FMNL2 binding partners identified the tumor promotor ANGPTL4 as a specific binding partner. ANGPTL4 has important roles in cancer development and progression including promoting invasion and metastasis. We found that FMNL2 and ANGPTL4 directly interact under TGF-induced EMT. Our data show that FMNL2 is a critical regulator of ANGPTL4 secretion. Secretion of ANGPTL4 is diminished upon loss of FMNL2 and its phosphorylation. We further observed that ANGPTL4 is sequestered in the Golgi apparatus colocalizing with markers of the trans-Golgi network. Live imaging of vesicle secretion from the Golgi confirmed the transient co-localization of ANGPTL4 and FMNL2. Moreover, ANGPTL4 and FMNL2 modulate cell-cell contact integrity and ANGPTL4 silenced cells fail to disassemble their underlying cell-cell contacts to execute EMT. This effect was further enhanced upon FMNL2 knockout using FMNL2 CRISPR/Cas9 cell line. However, re-introduction of ANGPTL4 restored the mesenchymal phenotype and prompted the dissolution of cell-cell adhesions. Finally, we found that cellular invasion promoted by TGFβ depends on FMNL2 and is reduced upon ANGPTL4 silencing. Taken together, our data point towards a crucial role of FMNL2 for EMT via ANGPTL4 secretion.