AFFINITY-PURIFICATION AND CHARACTERIZATION OF CAVEOLINS FROM THE BRAIN - DIFFERENTIAL EXPRESSION OF CAVEOLIN-1, CAVEOLIN-2, AND CAVEOLIN-3 IN BRAIN ENDOTHELIAL AND ASTROGLIAL CELL-TYPES

Caveolins 1, 2 and 3 are the principal protein components of caveolae organelles. It has been proposed that caveolae play a vital role in a number of essential cellular functions including signal transduction, lipid metabolism, cellular growth control and apoptotic cell death. Th us, a major focus of caveolae-related research has been the identifica tion of novel caveolins, caveolae-associated proteins and caveolin-int eracting proteins. However, virtually nothing is known about the expre ssion of caveolins in brain tissue. Here, we report the purification a nd characterization of caveolins from brain tissue under non-denaturin g conditions. As a final step in the purification, we employed immune- affinity chromatography using rabbit polyclonal anti-caveolin IgG and specific elution at alkaline pH. The final purified brain caveolin fra ctions contained three bands with molecular masses of 52 kDa, 24 kDa a nd 22 kDa as visualized by silver staining. Sequencing by ion trap mas s spectrometry directly identified the major 24-kDa component of this hetero-oligomeric complex as caveolin 1. Further immunocyto- and histo chemical analyses demonstrated that caveolin 1 was primarily expressed in brain endothelial cells. Caveolins 2 and 3 were also detected in p urified caveolin fractions and brain cells. The cellular distribution of caveolin 2 was similar to that of caveolin 1. In striking contrast, caveolin 3 was predominantly expressed in brain astroglial cells. Thi s finding was surprising as our previous studies have suggested that t he expression of caveolin 3 is confined to striated (cardiac and skele tal) and smooth muscle cells. Electron-microscopic analysis revealed t hat astrocytes possess numerous caveolar invaginations of the plasma m embrane. Our results provide the first biochemical and histochemical e vidence that caveolins 1, 2 and 3 are expressed in brain endothelial a nd astroglial cells. (C) 1998 Elsevier Science B.V. All rights reserve d.