CONSTITUTIVE AND REGULATED EXPRESSION OF VITRONECTIN

Tissue homeostasis depends on spatially and temporally controlled expr ession of multifunctional adhesive glycoproteins and their cellular co unter receptors, and on a tight regulation of proteolytic enzyme syste ms. The adhesive glycoprotein vitronectin (Vn) not only regulates adhe sive events, but also controls a number of these proteolytic enzyme ca scades, including the complement, coagulation, and fibrinolytic system s. However, understanding of the biological functions of this molecule is complicated due to it's conformationally lability and its tendency to self-associate. While plasma Vn is monomeric and lacks exposure of conformationally sensitive epitopes, platelet and tissue-associated V n are believed to be conformationally altered and multimeric. The latt er forms express a functional repertoire distinct from plasma Vn. Whil e little Vn immunoreactivity is detectable in most normal tissues, inc reased depositions of Vn have been observed in areas of tissue injury and necrosis. Tissue Vn was believed to be plasma-derived, but recent studies indicate that extrahepatic cells have the biosynthetic potenti al to produce Vn and that its synthesis can be regulated under inflamm atory conditions. Here, the constitutive and regulated expression of V n, its locations in tissues and interaction with other matrix molecule s are reviewed and their implications for the functions of this molecu le are discussed.