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N.J. Philp, D. Wang; ERK Signaling is Activated by Cyclophilin A in Retinal Pigment Epithelial Cells . Invest. Ophthalmol. Vis. Sci. 2003;44(13):375.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To test the hypothesis that cyclophilin A (CyPA), via interaction with CD147, activates signaling cascades in RPE cells that could lead to changes observed in proliferative disease. CyPA is a ubiquitously expressed cytoplasmic protein that is secreted in response to oxidative stress or inflammatory stimuli. CD147, a member of the immunoglobulin superfamily that is highly expressed in RPE, was recently identified as the receptor for CyPA. Binding of CyPA to CD147 initiates a signaling cascade that leads to activation of extracellular signal-regulated protein kinase (ERK1/2). Since the ERK signaling pathway was shown to mediate RPE proliferation, we determined whether CyPA activates ERK in RPE cells. Methods: For these studies we used ARPE-19, a human RPE cell line. Western blot and immunohistochemical anaysis was used to demonstrate the expression of CD147 in ARPE-19 cells. To study of CyPA-CD147 signaling, purified human recombinant CyPA (hrCyPA) was added to ARPE-19 cultures that were serum starved for 24 hours. ERK activation was determined in control and treated cultures by Western blot analysis using antibodies that recognize either total or activated ERK. Immunohistochemical localization was used to monitor nuclear translocation of activated ERK. Results: CD147 was found to be abundantly expressed in the apical and basolateral membranes of ARPE-19 cells. The addition of hrCyPA to ARPE-19 cells stimulated ERK1/2 activation in a concentration and time dependent manner. The time course of ERK1/2 activation showed two peaks of activation at 10 minutes and 2 hours. Immunohistochemical analysis with anti-phosphorylated ERK1/2 antibody revealed that activated ERK1/2 was translocated to the cell nucleus after 15 minutes of stimulation with ERK1/2. Nuclear localization of activated ERK was also detected at 2 hours. Conclusions: In these studies we demonstrate that CyPA activates ERK1/2 signaling in ARPE-19 cells. Studies from other laboratories have shown that activation of the ERK signaling pathway plays a key role in RPE proliferation. We hypothesize that activation of the ERK1/2 pathway in RPE cells via a CyPA-CD147 complex may play an important role in the pathogenesis of retinal disease. Identification of CyPA-CD147 as activators of the ERK signaling cascade will aid in the development of therapeutic strategies for the treatment of proliferative retinal diseases.
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