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

Abstract

Transforming growth factor (TGF)-β-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 TGFβ-induced EMT in lens epithelial cells. The aim of the current study was to determine the requirement of RhoA/ROCK signaling in mediating TGFβ-induced nuclear accumulation of MRTF-A and ultimate expression of α-smooth muscle actin (αSMA), a marker of a contractile myofibroblast phenotype. Using rat lens epithelial explants, we demonstrate that ROCK inhibition using Y-27632 prevents TGFβ-induced nuclear accumulation of MRTF-A, Ecadherin/β-catenin complex disassembly, and αSMA 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 αSMA expression. Overall, our findings suggest that TGFβ-induced cytoskeletal reorganization through RhoA/ROCK/MRTF-A signaling is critical to EMT of lens epithelial cells.

The Role of the RhoA/ROCK Signaling Pathway in Mechanical Strain-Induced Scleral Myofibroblast Differentiation

“…17 We proved that RhoA activation promoted MRTF-A translocation to the nucleus under strain status and SRF expression. Moreover, we showed that RhoA silence or ROCK inhibition prevented strain-induced expression of MRTF-A and SRF, which corresponded with the absence of a-SMA, suggesting that mechanical signals through RhoA/ROCK-MRTF-A/SRF induce a-SMA expression.…”

“…[15][16][17] Of these, RhoA is known to have a key role in actin cytoskeleton reorganization, regulation of cell shape, adhesion, and migration and transformation of cellular phenotypes. 17,18 The Rho kinase (ROCK) family members, including ROCK1 and ROCK2, are important effectors of RhoA. Analysis of ROCK1 and ROCK2 distribution in a recent study revealed a dramatically higher expression of ROCK2 in the eye.…”

“…31,32 MRTF-A mediated gene expression has been shown to be mediated by the activation of RhoA/ROCK pathway. 17 With the growing evidence available in cellular and animal models, we hypothesized that RhoA/ROCK2 constitute an intrinsic mechanotransduction pathway that could transduce and convert mechanical stimulation to a signal that promoted scleral a-SMA expression in a mammalian myopia model. Moreover, strain-induced nuclear accumulation of MRTF-A is RhoA/ROCK-dependent and required for expression of a-SMA.…”

Transforming growth factor-beta and Forkhead box O transcription factors as cardiac fibroblast regulators

“…TGF-β rapidly activates Rho family guanosine triphophatases (GTPases) (29). TGF-β dependent activation of RhoA pathway induces the translocation of myocardin related transcription factor A (MRTF-A) to the nucleus to regulate a profibrotic response (30,31). TGF-β activates mitogen-activated protein kinases, including (extracellular signal-regulated kinases) ERKs, p38, and c-Jun N-terminal kinases (JNKs) through their upstream kinase activators such as transforming growth factor-β activated kinase-1 (TAK1) (29).…”

Melatonin Attenuates Endothelial-to-Mesenchymal Transition of Glomerular Endothelial Cells via Regulating miR-497/ROCK in Diabetic Nephropathy

“…ROCKs are ubiquitously expressed, though ROCK1 is not expressed in the brain and muscle [11]. They mediate a wide array of cellular processes in cytoskeleton organization and assembly, energy metabolism, cell proliferation, and epithelial-to-mesenchymal transition [12,13]. ROCKs are activated in the kidneys and in cultured cells of diabetic models [14,15].…”