Cell-type and Tissue-specific Expression of Caveolin-2
CAVEOLINS 1 AND 2 CO-LOCALIZE AND FORM A STABLE HETERO-OLIGOMERIC COMPLEX IN VIVO*
- Philipp E. Scherer‡,
- Renée Y. Lewis‡,
- Daniela Volont駶,
- Jeffrey A. Engelman§¶,
- Ferruccio Galbiati§¶,
- Jacques Couet‖,
- D. Stave Kohtz**,
- Elly van Donselaar‡,
- Peter Peters‡ and
- Michael P. Lisanti§§§
- From the Departments of ‡Cell Biology and§Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461, the ‖Laval Hospital Research Center, Sainte-Foy, Quebec, Canada, the **Mount Sinai School of Medicine, Department of Pathology, New York, New York 10029, and the‡Faculty of Medicine, Cell Biology, Heidelberglaan100 - H02., 3143584 CX Utrecht, The Netherlands
Abstract
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 membranein 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.
Footnotes
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↵* This work was supported by a National Institutes of Health FIRST Award (to M. P. L.), a grant from the Elsa U. Pardee Foundation (to M. P. L.), a grant from the G. Harold and Leila Y. Mathers Charitable Foundation (to M. P. L. and P. E. S.), and a Scholarship in the Medical Sciences from the Charles E. Culpeper Foundation (to M. P. L.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵¶ Contributed equally to this work.
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↵§§ To whom correspondence should be addressed: 1300 Morris Park Ave., Bronx, NY 10461. Tel: 718-430-8828; Fax: 718-430-8830; E-mail:lisanti{at}aecom.yu.edu.
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↵1 The abbreviations used are: mAb, monoclonal antibody; pAb, polyclonal antibody; GDI, GDP dissociation inhibitor; PAGE, polyacrylamide gel electrophoresis; PBS, phosphate-buffered saline; CHO, Chinese hamster ovary; IPTG, isopropyl-1-thio-β-d-galactopyranoside; Mes, 4-morpholineethanesulfonic acid.
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↵2 M. P. Lisanti, unpublished observations.
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- Received August 6, 1997.
- Revision received September 10, 1997.
