Integrity of cell-cell contacts is a critical regulator of TGF-beta 1-induced epithelial-to-myofibroblast transition: role for beta-catenin.
Injury of the tubular epithelium and TGF-beta1-induced conversion of epithelial cells to alpha-smooth muscle actin (SMA)-expressing myofibroblasts are key features of kidney fibrosis. Since injury damages intercellular junctions and promotes fibrosis, we hypothesized that cell contacts are critical regulators of TGF-beta 1-triggered epithelial-to-mesenchymal transition (EMT). Here we show that TGF-beta 1 was unable to induce EMT in intact confluent monolayers, but three different models of injury-induced loss of epithelial integrity (subconfluence, wounding, and contact disassembly by Ca(2+)-removal) restored its EMT-inducing effect. This manifested in loss of E-cadherin, increased fibronectin production and SMA expression. TGF-beta 1 or contact disassembly alone only modestly stimulated the SMA promoter in confluent layers, but together exhibited strong synergy. Since beta-catenin is a component of intact adherens junctions, but when liberated from destabilized contacts may act as a transcriptional co-activator, we investigated its role in TGF-beta 1-provoked EMT. Contact disassembly alone induced degradation of E-cadherin and beta-catenin, but TGF-beta1 selectively rescued beta-catenin and stimulated the beta-catenin-driven reporter TopFLASH. Moreover, chelation of free beta-catenin with the N-cadherin cytoplasmic tail suppressed the TGF-beta1 plus contact disassembly-induced SMA promoter activation and protein expression. These results suggest a beta-catenin-dependent two-hit mechanism in which both an initial epithelial injury and TGF-beta 1 are required for EMT.
Masszi
András
A
Department of Surgery, University Health Network and University of Toronto, Ontario, Canada.
Fan
Lingzhi
L
Rosivall
László
L
McCulloch
Christopher A
CA
Rotstein
Ori D
OD
Mucsi
István
I
Kapus
András
A
D000199:Actins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D015820:Cadherins / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002448:Cell Adhesion; D002450:Cell Communication; D003598:Cytoskeletal Proteins / Q000502:physiology*; D004847:Epithelial Cells / Q000166:cytology* / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology* / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D018374:LLC-PK1 Cells; D009130:Muscle, Smooth / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000166:cytology* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D013552:Swine; D015534:Trans-Activators / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1; D051176:beta Catenin
D000199:Actins; D015820:Cadherins; D003598:Cytoskeletal Proteins; D005353:Fibronectins; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D051176:beta Catenin; D002118:Calcium