RhoA/ROCK Signaling Regulates TGFβ-Induced Epithelial-Mesenchymal Transition of Lens Epithelial Cells through MRTF-A

Transforming growth factor (TGF)-beta-induced epithelial-mesenchymal transition (EMT) leads to the formation of ocular fibrotic pathologies, such as anterior subcapsular cataract and posterior capsule opacification. Remodeling of the actin cytoskeleton, mediated by the Rho family of GTPases, plays a key role in EMT. However, how actin dynamics affect downstream markers of EMT has not been fully determined. Our previous work suggests that myocardin-related transcription factor A (MRTF-A), an actin-binding protein, might be an important mediator of TGF beta-induced EMT in lens epithelial cells. The aim of the current study was to determine the requirement of RhoA/ROCK signaling in mediating TGF beta-induced nuclear accumulation of MRTF-A and ultimate expression of alpha-smooth muscle actin (alpha SMA), a marker of a contractile myofibroblast phenotype. Using rat lens epithelial explants, we demonstrate that ROCK inhibition using Y-27632 prevents TGF beta-induced nuclear accumulation of MRTF-A, E-cadherin/beta-catenin complex disassembly, and alpha SMA expression. Using a novel inhibitor specifically targeting MRTF-A signaling, CCG-203971, we further demonstrate the requirement of MRTF-A nuclear localization and activity in the induction of alpha SMA expression. Overall, our findings suggest that TGF beta-induced cytoskeletal reorganization through RhoA/ROCK/MRTF-A signaling is critical to EMT of lens epithelial cells.