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S. C. Tseng, Y.-T. Zhu, S.-Y. Chen; Differential Role of p120/Kaiso and β-catenin/Wnt Signaling in Unlocking the Mitotic Block Mediated by Contact-inhibited Monolayers of Human Corneal Endothelial Cells Derived from Stripped Descemet Membrane. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1795.
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The mitotic block mediated by contact inhibition is universal and explains why human corneal endothelial cells (HCEC) have a limited proliferative capacity in vitro and in vivo. When cadherins are disrupted in the adherent junction, two signaling pathways can potentially be elicited by liberating β-catenin and p120 catenin (p120), respectively, to reach nucleus. The former acts as a transcriptional coactivator through binding with TCF/LEF transcription factor, while the latter releases the repressor activity of Kaiso. We speculate that these two signaling pathways play a different role in unlocking the mitotic block caused by contact inhibition.
In contact-inhibited HCEC monolayers, we have discovered that the aforementioned two pathways could be activated by 2 mg/ml EDTA for 1h followed by 20 ng/ml bFGF and by transfection with p120 siRNA, respectively. Before termination, monolayers were labeled with 10 µM BrdU for 24h. Immunostaining to p120, Kaiso, β-catenin, TCF/LEF, ZO-1, N-cadherin, Na+, K+, ATPase, S100A4, and BrdU were compared.
Phase contrast showed that hexagonal pattern of HCEC was disrupted by EDTA/bFGF leading to more spindle cells, but maintained by p120 siRNA transfection. Immunostaining confirmed that β-catenin, but not p120, was disrupted from the adherent junction and translocated to the nucleus with an increase of TCF/LEF nuclear staining in EDTA/bFGF-treated cultures. In contrast, p120, but not β-catenin, from the adherent junction, was disrupted by p120 siRNA, leading to nuclear translocation and release of Kaiso from nucleus. Although both treatments resulted in significantly higher BrdU labeling than respective controls, the normal HCEC phenotype was restored upon withdrawal of p120 siRNA, while the EDTA/bFGF treatment resulted in loss of intercellular distribution of N-cadherin and nuclear localization of S100A4.
These results indicate that activation of the p120/Kaiso pathway unlocks the mitotic block mediated by contact inhibition via the formation of adherent junction, but retaining the normal phenotype. Although proliferation is also promoted by activation of β-catenin/Wnt pathway, the resultant cellular change risks in the development of endothelial mesenchymal transformation. They shed new insight on not only how HCEC can be best engineered ex vivo, but also how new therapeutics may be developed to switch on and off cellular proliferation without disrupting the intercellular junction in vivo where mitosis is known to be inhibited because of contact inhibition.
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