Macromolecular component of the subendothelium. Major component of the Descemet's membrane (basement membrane) of corneal endothelial cells. Also a component of the endothelia of blood vessels. Necessary for migration and proliferation of vascular smooth muscle cells and thus, has a potential role in the maintenance of vessel wall integrity and structure, in particular in atherogenesis. Vastatin, the C-terminal fragment comprising the NC1 domain, inhibits aortic endothelial cell proliferation and causes cell apoptosis. Homotrimers, or heterotrimers in association with alpha 2(VIII) type collagens. Four homotrimers can form a tetrahedron stabilized by central interacting C-terminal NC1 trimers. Expressed primarily in the subendothelium of large blood vessels. Also expressed in arterioles and venules in muscle, heart, kidney, spleen, umbilical cord, liver and lung and is also found in connective tissue layers around hair follicles, around nerve bundles in muscle, in the dura of the optic nerve, in cornea and sclera, and in the perichondrium of cartilaginous tissues. In the kidney, expressed in mesangial cells, glomerular endothelial cells, and tubular epithelial cells. Also expressed in mast cells, and in astrocytes during the repair process. Expressed in Descemet's membrane. Specifically expressed in peritoneal fibroblasts and mesothelial cells. Up-regulated during vascular injury, in atherosclerosis and in diabetes. Prolines at the third position of the tripeptide repeating unit (G-X-Y) are hydroxylated in some or all of the chains. Proteolytically cleaved by neutrophil elastase, in vitro. Proteolytic processing produces the C-terminal NC1 domain fragment, vastatin. Four consecutive Gly-Pro-Pro triplets are present at the C-terminus of the triple-helical region. These may provide the high thermal stability of this region.