TGF-β₁-mediated alterations of renal proximal tubular epithelial cell phenotype

Abstract

The aim of this study was to characterize the mechanism of transforming growth factor (TGF)-β1-mediated alteration of renal proximal tubular cell phenotype. TGF-β1 altered cell phenotype, with cells appearing elongated and spindle shaped. This was associated with loss of cell-cell contact and rearrangement of the actin cytoskeleton, increased formation of stress fibers, and focal adhesions. Addition of the tyrosine phosphatase inhibitor sodium orthovanadate also led to rapid but transient loss of cell-cell contact, but it did not lead to a change of phenotype comparable to that seen following addition of TGF-β1. There was, however, no change in the formation of focal adhesions and no associated reorganization of the Factin cytoskeleton. Disruption of the actin cytoskeleton with cytochalasin D prevented phenotypic alterations following addition of TGF-β1. Transient transfection with Smad2/4 or Smad3/4 expression vectors did not alter cell phenotype. Previously, we demonstrated β-catenin translocation to proximal tubule cell nuclei and its association with Smad proteins following addition of TGF-β1, suggesting the possibility that TGF-β1 may modulate Wnt signaling. The Wnt-responsive Xtwn-reporter construct was, however, silent in response to TGF-β1. Similarly, a second Wnt/LEF-1-regulated element, Toplflash, which does not contain Smad binding sites, was insensitive to TGF-β1 signaling. In contrast, phenotypic changes in response to TGF-β1 were abrogated by inhibitors of the RhoA downstream target ROCK, which also prevented loss of cell-cell contact and adherens junction disassembly.

TGFβ modulates cell-to-cell communication in early epithelial-to-mesenchymal transition

“…TGF-β1 decreases connexin-43 production Following in vitro activation of latent TGF-β1 by repeated freeze-thaw cycles in 7 day conditioned medium [34], a subsequent 48 h exposure of cells to the activated medium significantly decreased connexin-43 levels to 72±2.1% (mean±SEM) of that with conditioned 5 mmol/l control medium (n03; p<0.05) (Fig. 5a).…”

“…f Neutralisation of E-cadherin ligation using an immunoneutralising antibody (20 μg/ml) also restricted intercellular communication and prevented dye transfer. Scale bar 50 μm any suggested cellular migration associated with EMT [34,35]. The cadherin-catenin complex is crucial in epithelial cell-to-cell adhesion and facilitates cell communication via GJs.…”

The Murine Gastrin Promoter Is Synergistically Activated by Transforming Growth Factor-β/Smad and Wnt Signaling Pathways

“…In our study, we demonstrated the existence in gastric adenocarcinoma AGS cells of a complex composed of Smad proteins, TCF4, and ␤-catenin. Several published studies have recently reported on interactions between Wnt and TGF-␤ signaling (21,22,25,47,48). The TCF/LEF members have emerged as the integral players in coordinating Wnt and TGF-␤ signaling pathways.…”

Alterations of Wnt/β-catenin signaling pathway in hepatocellular carcinomas associated with hepatitis C virus

“…In the absence of TGF-β, both E-cadherin and β-catenin undergo degradation, with the resulting loss of intercellular junctions. At the same time, cytoplasmic accessibility of β-catenin becomes augmented and its transport to the cell nucleus becomes possible [58].…”