Submitted on August 11, 2005
Accepted on October 15, 2005
Bi-polar assembly of caveolae in Retinal Pigment Epithelium
Rosalia C Mora1, Vera L Bonilha2, Bo-Chul Shin3, Jane Hu4, Leona Cohen-Gould5, Dean Bok6, and Enrique J Rodriguez-Boulan1*
1 Department of Ophthalmology, Weill Medical College of Cornell University, M. Dyson Vision Research Institute, New York, NY, USA
2 The Cleveland Clinic Foundation, The Cole Eye Institute, Cleveland, OH, USA
3 David Geffen School of Medicine, University of California, Department of Pediatrics, Los Angeles, CA, USA
4 David Geffen School of Medicine, University of California, Department of Ophthalmology, Los Angeles, CA, USA
5 and Cell & Developmental Biology, Weill Medical College of Cornell University, Departments of Biochemistry, New York, NY, USA
6 Brain Research Institute and Department of Neurobiology, David Geffen School of Medicine, University of California, Jules Stein Eye Institute, Los Angeles, CA, USA
* To whom correspondence should be addressed. E-mail: boulan{at}med.cornell.edu.
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 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 caveolins 1 and 2. The bi-polar 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 may be related to the nonpolar distribution of both caveolin 1 and 2 in RPE, as caveolin 2 is basolateral and caveolin 1 non polar in other epithelial cells. The bi-polar localization of plasmalemmal caveolae in RPE cells may reflect specialized roles in signaling and trafficking important for visual function.
