Cell-type and tissue-specific expression of caveolin-2. Caveolins 1 and 2 co-localize and form a stable hetero-oligomeric complex in vivo.
Caveolae are microdomains of the plasma membrane that have been implicated in organizing and compartmentalizing signal transducing molecules. Caveolin, a 21-24-kDa integral membrane protein, is a principal structural component of caveolae membrane in vivo. Recently, we and other laboratories have identified a family of caveolin-related proteins; caveolin has been re-termed caveolin-1. Here, we examine the cell-type and tissue-specific expression of caveolin-2. For this purpose, we generated a novel mono-specific monoclonal antibody probe that recognizes only caveolin-2, but not caveolins-1 and -3. A survey of cell and tissue types demonstrates that the caveolin-2 protein is most abundantly expressed in endothelial cells, smooth muscle cells, skeletal myoblasts (L6, BC3H1, C2C12), fibroblasts, and 3T3-L1 cells differentiated to adipocytes. This pattern of caveolin-2 protein expression most closely resembles the cellular distribution of caveolin-1. In line with these observations, co-immunoprecipitation experiments with mono-specific antibodies directed against either caveolin-1 or caveolin-2 directly show that these molecules form a stable hetero-oligomeric complex. The in vivo relevance of this complex was further revealed by dual-labeling studies employing confocal laser scanning fluorescence microscopy. Our results indicate that caveolins 1 and 2 are strictly co-localized within the plasma membrane and other internal cellular membranes. Ultrastructurally, this pattern of caveolin-2 localization corresponds to caveolae membranes as seen by immunoelectron microscopy. Despite this strict co-localization, it appears that regulation of caveolin-2 expression occurs independently of the expression of either caveolin-1 or caveolin-3 as observed using two different model cell systems. Although caveolin-1 expression is down-regulated in response to oncogenic transformation of NIH 3T3 cells, caveolin-2 protein levels remain unchanged. Also, caveolin-2 protein levels remain unchanged during the differentiation of C2C12 cells from myoblasts to myotubes, while caveolin-3 levels are dramatically induced by this process. These results suggest that expression levels of caveolins 1, 2, and 3 can be independently up-regulated or down-regulated in response to a variety of distinct cellular cues.
Scherer
P E
PE
Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Lewis
R Y
RY
Volonte
D
D
Engelman
J A
JA
Galbiati
F
F
Couet
J
J
Kohtz
D S
DS
van Donselaar
E
E
Peters
P
P
Lisanti
M P
MP
D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism; D000818:Animals; D001704:Biopolymers; D051242:Caveolin 1; D051243:Caveolin 2; D022461:Caveolins; D002461:Cell Line, Transformed; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure; D008565:Membrane Proteins / Q000096:biosynthesis / Q000378:metabolism*; D051379:Mice; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data
D001704:Biopolymers; C495540:CAV1 protein, human; C495541:Cav1 protein, mouse; D051242:Caveolin 1; D051243:Caveolin 2; D022461:Caveolins; D008565:Membrane Proteins