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S. A. Morales, D. Telander, J. Braun, L. K. Gordon; Epithelial Membrane Protein 2 (EMP2) Controls VEGF Expression in ARPE-19 Cells. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4102.
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Age-related macular degeneration (AMD) is the primary cause of blindness in people 50 and older in developed countries. VEGF production by retinal pigment epithelial cells has been shown to be a key molecule regulating aberrant angiogenesis in the retina. Epithelial membrane protein 2 (EMP2), a member of the tetraspan protein family, is highly expressed in the RPE and has been shown to regulated FAK activation. FAK signal transduction is implicated in VEGF production. The purpose of this study is to determine whether changes in EMP2 expression modulate VEGF expression levels in RPE.
An EMP2 blocking diabody was recombinantly constructed using a phage library. ARPE-19 cells were engineered to overexpress EMP2 (ARPE-19/EMP2). Both ARPE-19 and ARPE-19/EMP2 cells were evaluated for VEGF expression. In some experiments, the cells were pretreated with 20µg/ml of anti-EMP2 or control diabody for 2 hours. The small molecule inhibitor PP2 was used to inhibit FAK activation. VEGF levels were measured by Western Blot and ELISA.
VEGF expression in ARPE-19/EMP2 cells was about 150% of wild type ARPE-19 cells (P=.003). Exposure to anti-EMP2 diabody resulted in a 75% reduction in EMP2 protein levels. Concordant decreases in basal levels of activated FAK were also observed. Anti-EMP2 diabody treatment reduced VEGF expression by 50% in ARPE-19 (P=.04) and by 40% in the ARPE-19/EMP2 cells(P=.03). VEGF secretion was reduced by 64% in cells treated with PP2.
This study establishes a novel connection between levels of EMP2 and VEGF and may reflect either a direct effect through the tetraspan web or an indirect change through FAK activation. In addition to the direct use of anti-VEGF antibodies, EMP2 may be an additional therapeutic target for the treatment of neovascular AMD.
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