Caveolin - an integral membrane protein - is the principal component of caveolae membranes in vivo. Multiple forms of caveolin have been identified: caveolin-1α, caveolin-1β, caveolin-2 and caveolin-3. They differ in their specific properties and tissue distribution. When we studied the lysate of resident and elicited macrophages isolated from rat peritoneal cavity by Western blot analysis, we identified two different proteins (~ 29 kDa and ~ 20 kDa) which were labelled with anti-caveolin antibodies. The ~ 20-kDa protein was labelled specifically only by anti-VIP21/caveolin-1, while the ~ 29-kDa protein was labelled by anti-VIP21/caveolin-1 and anti-caveolin-2. The presence of the ~ 29-kDa protein was characteristic of resident macrophages, and only a small amount of the ~ 20-kDa protein was detected in these cells. Elicitation resulted in a significant increase in the amount of the ~ 20-kDa protein labelled by anti-VIP21/caveolin-1 only. According to its molecular mass and antibody-specificity, this protein might be identical with the caveolin-1β isoform. Our morphological (confocal and electron microscopical) studies have shown that in resident cells caveolin was present in the cytoplasm, in smaller vesicles and multivesicular bodies around the Golgi area. Only a very small amount of caveolae was found on the surface of these cells. In elicited macrophages, caveolae (labelled with the anti-VIP21/caveolin-1 antibody) appeared in large numbers on the cell surface, but caveolin detected by anti-caveolin-2 was also found in small vesicles and multivesicular bodies in the cytoplasm. According to these results, the absence of caveolae in resident cells can be explained by the absence of caveolin-1. The expression of the ~ 29-kDa (caveolin-related) protein in resident macrophages seems to be insufficient for caveolae formation. Elicitation significantly increased the expression of caveolin-1, and the increased amount of caveolin-1 resulted in caveolae formation on the cell surface.
ASJC Scopus subject areas
- Pathology and Forensic Medicine
- Cell Biology