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D. C. Dean, Y. Liu; Targets of the Hippo Cell Contact Pathway, Yap and Taz, Regulate Zeb1 to Control RPE Proliferation and Differentiation. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1868.
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Disruption of cell-cell contacts initiates proliferation and epithelial-mesenchymal transition (EMT) in RPE cells. Onset of proliferation and EMT correlates with induction of the EMT transcription factor Zeb1. Mutation of the Zeb1 gene or shRNA knockdown prevents proliferation and EMT in RPE cells. Our purpose was to relate cell-cell contact, Zeb1 expression, and RPE proliferation and EMT.
RPE was isolated from Zeb1 heterozygous and null mutant mice, and Zeb1 expression was knocked down in RPE from wild type mice by lentiviral shRNA. Cell proliferation was assessed along with cell morphology, and expression of genes involved in proliferation, epithelial specification and pigment synthesis were analyzed by real time PCR. Immunostaining was used to follow protein expression and nuclear vs. cytoplasmic location. Chromatin immunoprecipitation was used to assess transcription factor binding to the Zeb1 promoter in vivo.
Binding of cadherins on the cell surface activate a cascade of protein kinases known as the Hippo signaling pathway. This pathway phosphorylates a family of two transcription factors know as Yap and Taz. This phosphorylation prevent entry of the factors into the nucleus. We show that one target of Yap and Taz activation is the Zeb1 gene. Zeb1 is required to prevent expression of the cell cycle inhibitory cyclin dependent kinase inhibitors p15INK4b and p21CDKN1A as well as Mitf, which is required to maintain RPE differentiation.
These studies provide the first molecular details of how cell-cell contacts in RPE are linked to cell proliferation and maintenance of differentiation.
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