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BG Kennedy, NJ Mangini; Native and Cultured Human RPE Express P-glycoprotein . Invest. Ophthalmol. Vis. Sci. 2002;43(13):903.
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Purpose: The retinal pigment epithelium (RPE) is a transporting epithelial monolayer that controls hydration and composition of the subretinal space. P-glycoprotein (PGP) is an ATP-binding cassette transport protein known to confer multi-drug resistance in neoplastic cells. The expression of PGP in barrier epithelial cells suggests that it could have a normal protective function, possibly serving to clear a variety of xenobiotics. The present study is designed to determine the expression and function of PGP in normal human RPE. Methods: PGP specific antibodies were used to localize the protein in frozen, formaldehyde-fixed sections of native human RPE/choroid by immunohistochemistry. PGP specific antibodies were also employed in Western blotting to identify PGP expressed in cultured human RPE and in an established RPE cell line (D407). Finally, cDNA was obtained by performing RT-PCR on total RNA isolated from cultured human RPE and from D407 cells. cDNA was amplified using PGP (isoform mdr-1) specific primers, with the products purified and sequenced. Results: PGP protein is expressed in native human RPE tissue that had not been exposed to any inducers. Localization is predominantly, though not exclusively apical. Western blotting demonstrated specific bands at ∼220 and 160 kD. RT-PCR yielded a 546 bp product that was 100% identical to published data for the mdr-1 isoform of human PGP. Conclusion: RPE, not exposed to inducer treatment, does express PGP. Presence of the protein on both apical and basal surfaces raises the possibility that PGP serves multiple functions in the RPE.
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