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Mechanisms and Physiological Significance of the Transport of the Glutathione Conjugate of 4-Hydroxynonenal in Human Lens Epithelial Cells

¹From the Departments of Human Biological Chemistry and Genetics and ²Pathology, University of Texas Medical Branch, Galveston, Texas; and the ³Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, Texas.

PURPOSE. To study the mechanism and physiological significance of the transport of the glutathione (GSH) conjugate of 4-hydroxynonenal (4-HNE) from lens epithelial cells.

METHODS. HLE B-3 cells were treated with [³H] 4-HNE and efflux of its GSH conjugate, [³H] GS-HNE, into the medium was quantitated and characterized by HPLC and mass spectrometry. Inside-out vesicles (IOVs) were prepared from HLE B-3 cell membranes. The kinetics of adenosine triphosphate (ATP)-dependent uptake of GS-HNE and dinitrophenyl S-glutathione (DNP-SG) by these IOVs and inhibition of GS-HNE uptake by anti-RLIP76 IgG was studied. Localization of RLIP76 was studied by immunogold electron microscopy and kinetics of the adenosine triphosphatase (ATPase) activity of purified RLIP76 was determined. 4-HNE–induced apoptosis was compared in HLE-B3 cells coated with anti-RLIP76 IgG or preimmune IgG, by caspase activation assay.

RESULTS. The results showed the presence of RLIP76 in plasma membranes of HLE B-3 cells and that it mediated ATP-dependent transport of GS-HNE as well as of DNP-SG. The transport was saturable with respect to GS-HNE (K_m = 8.4 µM), DNP-SG (100 µM) as well as to ATP (K_m 0.45 mM) and was sensitive to temperature and osmolarity of the medium. Anti-RLIP76 IgG inhibited approximately 65% of the transport of GS-HNE and DNP-SG, indicating that most of the transport was mediated by RLIP76. Compatible with its transport function, the EGTA- and ouabain-insensitive ATPase activity of purified RLIP76 was stimulated by DNP-SG and GS-HNE. 4-HNE–induced caspase activation in HLE-B3 cells was exacerbated when the transport of GS-HNE from these cells was blocked by anti-RLIP76 IgG.

CONCLUSIONS. RLIP76 provides a defense against the deleterious effects of 4-HNE by transporting GS-HNE and can modulate apoptotic signaling by regulating the intracellular concentrations of 4-HNE.

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