Cell contact-dependent regulation of epithelial-myofibroblast transition via the rho-rho kinase-phospho-myosin pathway

Mol Biol Cell. 2007 Mar;18(3):1083-97. doi: 10.1091/mbc.e06-07-0602. Epub 2007 Jan 10.

Abstract

Epithelial-mesenchymal-myofibroblast transition (EMT), a key feature in organ fibrosis, is regulated by the state of intercellular contacts. Our recent studies have shown that an initial injury of cell-cell junctions is a prerequisite for transforming growth factor-beta1 (TGF-beta1)-induced transdifferentiation of kidney tubular cells into alpha-smooth muscle actin (SMA)-expressing myofibroblasts. Here we analyzed the underlying contact-dependent mechanisms. Ca(2+) removal-induced disruption of intercellular junctions provoked Rho/Rho kinase (ROK)-mediated myosin light chain (MLC) phosphorylation and Rho/ROK-dependent SMA promoter activation. Importantly, myosin-based contractility itself played a causal role, because the myosin ATPase inhibitor blebbistatin or a nonphosphorylatable, dominant negative MLC (DN-MLC) abolished the contact disruption-triggered SMA promoter activation, eliminated the synergy between contact injury and TGF-beta1, and suppressed SMA expression. To explore the responsible mechanisms, we investigated the localization of the main SMA-inducing transcription factors, serum response factor (SRF), and its coactivator myocardin-related transcription factor (MRTF). Contact injury enhanced nuclear accumulation of SRF and MRTF. These processes were inhibited by DN-Rho or DN-MLC. TGF-beta1 strongly facilitated nuclear accumulation of MRTF in cells with reduced contacts but not in intact epithelia. DN-myocardin abrogated the Ca(2+)-removal- +/- TGF-beta1-induced promoter activation. These studies define a new mechanism whereby cell contacts regulate epithelial-myofibroblast transition via Rho-ROK-phospho-MLC-dependent nuclear accumulation of MRTF.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / genetics
  • Animals
  • CHO Cells
  • Calcium / metabolism
  • Cell Communication*
  • Cell Nucleus / metabolism
  • Cricetinae
  • Cricetulus
  • Cytoplasm / metabolism
  • Epithelial Cells / cytology*
  • Fibroblasts / cytology*
  • Humans
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Kidney Tubules / cytology
  • Muscle, Smooth / metabolism
  • Myosins / metabolism*
  • Phosphoproteins / metabolism*
  • Phosphorylation
  • Promoter Regions, Genetic / genetics
  • Protein Isoforms / metabolism
  • Protein Transport
  • Protein-Serine-Threonine Kinases / metabolism*
  • Serum Response Factor / metabolism
  • Trans-Activators / metabolism
  • rho GTP-Binding Proteins / metabolism*
  • rho-Associated Kinases

Substances

  • Actins
  • Intracellular Signaling Peptides and Proteins
  • Mrtfa protein, mouse
  • Phosphoproteins
  • Protein Isoforms
  • Serum Response Factor
  • Trans-Activators
  • Protein-Serine-Threonine Kinases
  • rho-Associated Kinases
  • Myosins
  • rho GTP-Binding Proteins
  • Calcium