BASIC RESEARCH TO EXPLOIT PROPERTIES OF ENDOTHELIAL CAVEOLAE FOR DEVELOPMENT OF PREVENTIVE AND/OR TREATING MEASURES FOR VASCULAR DISEASES

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Caveolae are small invaginations of the plasma membrane found in many cell types, and caveolins (caveolin-1,2,3) are a family of integral membrane proteins forming the framework of caveolae. Caveolae and caveolins have been revealed to have diverse functions, including endocytosis, signal transduction, cholesterol transport, and tumor suppression. To understand caveolae and caveolins in molecular terms, we have done several lines of research using various cell biological techniques.Caveolin-1 is heavily phosphorylated in tyrosine in v-Src-expressing cells, but consequences of the phosphorylation has not been known. We generated a polyclonal antibody specific for tyrosine-phosphorylated caveolin-1 (PY14). In v-Src-expressing cells, PY14 labeled caveolae, flat plasmalemmal areas of various sizes and shapes, and intracellular vesicles that are significantly larger than caveolae ; biochemical properties of caveolin-1, including detergent insolubility and oligomerization, were not different from the non-phosphorylated counterpart. In normal rat tissues in vivo, the endothelium of the continuous capillary was labeled by PY14, whereas the endothelium of other vessels was not. In the cultured endothelium, tyrosine phosphatase inhibitors as well as oxidative stress induced tyrosine phosphorylation of caveolin-1, and caused vesiculation of caveolae. These results suggest that tyrosine phosphorylation of caveolin-1 induces vesiculation and/or aggregation of caveolae.We used freeze-fracture immunoelectron microscopy to examine distribution of the two isoforms (α, β) of caveolin-1. Antibodies specific to the α isoform decorated deep caveolae preferentially, whereas those reacting with both α and β isoforms labeled deep and shallow caveolae with similar efficiency. The result indicates that the α/β ratio is different among caveolae, and may suggest that caveolae of different depths is not be convertible each other.