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W. Li, N. B. Caberoy, D. Maiguel, Y. Kim; Identification of ATP-Binding Cassette Sub-Family F Member 1 (ABCF1) as a Phagocytic Ligand in RPE Cells. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4441. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
RPE phagocytosis plays a key role in the clearance of shed photoreceptor outer segment and is critical to maintain the viability and excitability of the photoreceptors. However, the molecular mechanism of RPE phagocytosis is poorly defined with no phagocytic protein ligands reported. This study is to identify and characterize RPE phagocytic ligands.
A T7 phage display cDNA library has been generated from mouse eye, and a novel functional cloning strategy of phage display has been developed to screen the cDNA library. Phage clones with phagocytic activities were enriched in human ARPE-19 cell line with 4 rounds of selection. Individual phage clones with higher phagocytic activity than control phage were isolated from the enriched phage pool, identified by DNA sequencing, and characterized by phage-based phagocytic assay.
Among several identified phagocytic protein ligands was ABCF129-176 with ~1,000-fold increase in phagocytic activity vs. control phage. Unlike all other members of the ABC protein family, ABCF1 is not a membrane transporter and its function has not been determined. ABCF1 phagocytic activity was demonstrated in ARPE-19 cells, but not in HeLa cells, suggesting its activity is RPE-specific. Its phagocytic activity was further verified independently with florescence-labeled ABCF1 in APRE-19 cells by flow cytometry.
ABCF1 is identified as a RPE-specific phagocytic ligand. The novel functional cloning strategy of phage display described in this study provides a powerful tool to investigate phagocytic mechanisms in RPE cells by identifying phagocytic ligands, receptors and signal pathways.
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