title: Localization of multidrug resistance-associated protein 2 in the nonpigmented ciliary epithelium of the eye.
abstract: The nonpigmented epithelium (NPE) of the ciliary body represents an important component of the blood-aqueous barrier of the eye. Many therapeutic drugs penetrate poorly across the NPE into the aqueous humor of the eye interior. Several of these therapeutic drugs, such as methotrexate, vincristine, and etoposide, are substrates of the multidrug resistance-associated protein 2 (MRP2). Abundant MRP2 protein was detected by Western blot in homogenates of human ciliary body and freshly dissected porcine NPE. In cultured porcine NPE, the intracellular accumulation of the MRP2 substrates calcein (1.8-fold), 5-(and-6)-carboxy-2',7'-dichlorofluorescein (22.1-fold), and doxorubicin (1.9-fold) was significantly increased in the presence of 50 microM MK571 ((E)-3-[[[3-[2-(7-chloro-2-quinolinyl)-ethenyl]phenyl]-[[3-dimethylamino)-3-oxopropyl]thio]methyl]thio]-propanoic acid), an MRP inhibitor. In addition, the intracellular accumulation of the MRP2 substrate glutathione methylfluorescein was increased by 50 microM MK571 (4.3-fold), 500 microM indomethacin (2.6-fold), and 50 microM cyclosporin A (2.1-fold) but not by 500 microM sulfinpyrazone. These data are consistent with MRP2-mediated transport activity in cultured NPE, and MRP2 mRNA (reverse transcriptase-polymerase chain reaction) and protein (Western blot) were detected in the cultured cells. Immunolocalization studies in native human and porcine eyes showed MRP2 protein at the apical interface of the NPE and pigmented cell layers. Close examination of MRP2 immunoreactivity supported the conclusion that MRP2 is localized in the apical membrane of the NPE. MRP2 at the apical membrane of NPE cells may be involved in protecting intraocular tissues from exposure to potentially harmful toxins.
authors.affiliation: Department of Physiology, University of Arizona, College of Medicine, Tucson, Arizona, USA. ryan.pelis@novartis.com
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Pelis
authors.forename: Mohammad
authors.initials: M
authors.lastname: Shahidullah
authors.forename: Sikha
authors.initials: S
authors.lastname: Ghosh
authors.forename: Miguel
authors.initials: M
authors.lastname: Coca-Prados
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Wright
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Delamere
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000096:biosynthesis*; D000818:Animals; D015153:Blotting, Western; D002924:Ciliary Body / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004848:Epithelium / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D021381:Protein Transport; D012313:RNA / Q000302:isolation & purification; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013552:Swine; D000097202:ATP-Binding Cassette Sub-Family B Member 4
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D012313:RNA; D000097202:ATP-Binding Cassette Sub-Family B Member 4