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Hung-Chi J. Chen, Yingting Zhu, Szu-Yu Chen, Scheffer C. Tseng; p120-Catenin Controls Contact Inhibition in Postconfluent ARPE-19 Cells via Rho-ROCK Signaling. Invest. Ophthalmol. Vis. Sci. 2011;52(14):869.
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Mitosis of in vivo and in vitro retinal pigment epithelial cells (RPE) is dictated by contact inhibition. Our earlier work has shown that p120 catenin (p120) in the adherent junction controls contact inhibition of post-confluent human corneal endothelial cells. Because p120 is known to inhibit the RhoA activity, we thus wonder if p120 plays a similar role in cultured RPE via the RhoA-ROCK signaling.
ARPE-19 cells cultured to 7 days after post-confluence were treated with 100 nM siRNA to p120, β-catenin, N-cadherin and ZO-1 for 48 h. Before termination, cells were further treated with 5 ug/ml Rho inhibitor CT-04 for 8 h, 20 ug/ml ROCK inhibitor Y27632 for 5 h and 10 µM BrdU for 4 h. Immunostaining was performed to monitor cytolocalization of p120, β-catenin, N-cadherin, ZO-1 and BrdU labeling. Western blotting was used to measure total RhoA and active RhoA-GTP precipitated by rhotekin bead.
Immunostaining revealed that BrdU labeling was significantly enhanced by siRNA to p120, but not to β-catenin, N-cadherin or ZO-1. Surprisingly, p120, but not β-catenin, N-cadherin and ZO-1, was translocalized to the nucleus and colocalized with BrdU labeling. Further analysis indicated that p120 siRNA knockdown induced 8-fold increase of Rho-GTP activity without changing the level of total Rho protein. Such cell proliferation and nuclear translocation of p120 were completely blocked by CT-04 or Y27632.
In post-confluent ARPE-19 cells, p120 plays a dominant role in mediating contact inhibition by down-regulating RhoA-ROCK signaling. Downregulation by p120 siRNA is a novel technique to induce proliferation by activating the Rho-ROCK singling in contact-inhibited ARPE-19 cells. Further investigation of how nuclear translocation of p120 is controlled by RhoA-ROCK signaling may unravel the controlling mechanism of contact inhibition.
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