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PROTEIN AND VESICLE TRAFFICKING, CYTOSKELETON

Bipolar assembly of caveolae in retinal pigment epithelium

¹M. Dyson Vision Research Institute, Department of Ophthalmology, Weill Medical College of Cornell University, New York; ²The Cole Eye Institute, The Cleveland Clinic Foundation, Cleveland, Ohio; ³Department of Pediatrics and ⁴Department of Ophthalmology, David Geffen School of Medicine, University of California, Los Angeles; ⁵Departments of Biochemistry and Cell and Developmental Biology, Weill Medical College of Cornell University, New York, New York; and ⁶Jules Stein Eye Institute, Brain Research Institute, and Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California

Submitted 11 August 2005 ; accepted in final form 15 October 2005

Caveolae and their associated structural proteins, the caveolins, are specialized plasmalemmal microdomains involved in endocytosis and compartmentalization of cell signaling. We examined the expression and distribution of caveolae and caveolins in retinal pigment epithelium (RPE), which plays key roles in retinal support, visual cycle, and acts as the main barrier between blood and retina. Electron microscopic observation of rat RPE, in situ primary cultures of rat and human RPE and a rat RPE cell line (RPE-J) demonstrated in all cases the presence of caveolae in both apical and basolateral domains of the plasma membrane. Caveolae were rare in RPE in situ but were frequent in primary RPE cultures and in RPE-J cells, which correlated with increased levels in the expression of caveolin-1 and -2. The bipolar distribution of caveolae in RPE is striking, as all other epithelial cells examined to date (liver, kidney, thyroid, and intestinal) assemble caveolae only at the basolateral side. This might be related to the nonpolar distribution of both caveolin-1 and 2 in RPE because caveolin-2 is basolateral and caveolin-1 nonpolar in other epithelial cells. The bipolar localization of plasmalemmal caveolae in RPE cells may reflect specialized roles in signaling and trafficking important for visual function.

caveolin; raft microdomains; membrane traffic; normal rat kidney