Myocardin regulates fibronectin expression and secretion from human pleural mesothelial cells

Am J Physiol Lung Cell Mol Physiol. 2024 Feb 13. doi: 10.1152/ajplung.00271.2023. Online ahead of print.ABSTRACTDuring the progression of pleural fibrosis, pleural mesothelial cells (PMCs) undergo a phenotype switching process known as mesothelial-mesenchymal transition (MesoMT). During MesoMT, transformed PMCs become myofibroblasts which produce increased extracellular matrix (ECM) proteins, including collagen and fibronectin (FN1) that is critical to develop fibrosis. Here, we studied the mechanism that regulates FN1 expression in myofibroblasts derived from HPMCs. We found that myocardin (Myocd), a transcriptional coactivator of serum response factor (SRF) and a master regulator of smooth muscle and cardiac muscle differentiation, strongly controls HPMC FN1 gene expression. Myocd gene silencing markedly inhibited FN1 expression. FN1 promoter analysis revealed that deletion of the Smad3 binding element diminished FN1 promoter activity, while deletion of the putative SRF binding element increased FN1 promoter activity. Smad3 gene silencing decreased FN1 expression, while SRF gene silencing increased FN1 expression. Moreover, SRF competes with Smad3 for binding to Myocd. These results indicate that Myocd activates FN1 expression through Smad3, while SRF inhibits FN1 expression in HPMCs. In HPMCs, TGF-β induced Smad3 nuclear localization, and the proximity ligation signal between Myocd and Smad3 was markedly increased after TGF-β stimulation at nucleus, suggesting that TGF-Î...
Source: American Journal of Physiology. Lung Cellular and Molecular Physiology - Category: Cytology Authors: Source Type: research