Promotion of the release of 11-cis-retinal from cultured retinal pigment epithelium by interphotoreceptor retinoid-binding protein.
This study investigates whether the interphotoreceptor retinoid-binding protein (IRBP) is necessary for the release of 11-cis-retinaldehyde (RAL) or if the retinoid is constitutively released from the retinal pigment epithelium (RPE) following synthesis. The strategic location of IRBP in the interphotoreceptor matrix (IPM) and its retinoid-binding ability make it a candidate for a role in 11-cis-RAL release. Fetal bovine RPE cells were grown in permeable chambers, and their apical surfaces were incubated with medium containing either apo-IRBP, the apo form of cellular retinaldehyde-binding protein (CRALBP), the apo form of serum retinol-binding protein (RBP), or bovine serum albumin (BSA) or with medium devoid of binding proteins. [3H]-all-trans-Retinol (ROL) was delivered to the basal surface of the cells by RBP. High-performance liquid chromatography demonstrated that [3H]-11-cis-RAL was optimally released into the apical medium when apo-IRBP was present. The most surprising result was the diminished level of [3H]-11-cis-RAL when apo-CRALBP was in the apical medium. Circular dichroism demonstrated that CRALBP had not been denatured by the photobleaching required for endogenous ligand removal. Therefore, apo-CRALBP should have been able to bind [3H]-11-cis-RAL if it was constitutively released into the apical medium. In addition, when proteins other than apo-IRBP were present, or if the cells were incubated with medium alone, the observed decrease in apical [3H]-11-cis-RAL was concomitant with a buildup of intracellular [3H]-all-trans-retinyl palmitate and [3H]-all-trans-ROL in the basal culture medium.(ABSTRACT TRUNCATED AT 250 WORDS)
Carlson
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Department of Anatomy and Cell Biology, Jules Stein Eye Institute, Los Angeles, California 90024.
Bok
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D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D002942:Circular Dichroism; D005136:Eye Proteins / Q000378:metabolism*; D066298:In Vitro Techniques; D008854:Microscopy, Electron; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D011487:Protein Conformation; D012172:Retinaldehyde / Q000378:metabolism*; D012177:Retinol-Binding Proteins / Q000378:metabolism*; D000099214:Retinol-Binding Proteins, Interstitial
D005136:Eye Proteins; D012172:Retinaldehyde; D012177:Retinol-Binding Proteins; D000099214:Retinol-Binding Proteins, Interstitial