Selective localization of receptors for urokinase amino-terminal fragment at substratum contact sites of an in vitro-established line of human epidermal cells

• Published in: Experimental cell research Vol. 203; no. 2; p. 427
• Main Authors: Del Rosso, M, Pedersen, N, Fibbi, G, Pucci, M, Dini, G, Anichini, E, Blasi, F
• Format: Journal Article
• Language: English
• Published: United States 01-12-1992
• Subjects: Binding Sites; Cell Adhesion; Cell Line; Cell Membrane - chemistry; Cell Membrane - ultrastructure; Cross-Linking Reagents - pharmacology; Epidermis - chemistry; Epidermis - ultrastructure; Humans; Microscopy, Electron; Peptide Fragments - metabolism; Phosphatidylinositol Diacylglycerol-Lyase; Phosphoinositide Phospholipase C; Phosphoric Diester Hydrolases - pharmacology; Receptors, Cell Surface - analysis; Receptors, Urokinase Plasminogen Activator; Succinimides - pharmacology; Urokinase-Type Plasminogen Activator - metabolism
• ISSN: 0014-4827
• DOI: 10.1016/0014-4827(92)90017-3

We have shown the presence of surface receptors for the amino-terminal fragment (ATF) of human urokinase-type plasminogen activator (u-PA) on an in vitro-established cell line of human epidermal origin by both radio-binding assays with human 125I-u-PA-ATF and transmission electron microscopy of a gold-u-PA complex. On the basis of cross-linking experiments with 125I-u-PA-ATF and subsequent autoradiography of the gels we have observed that such receptors are not spontaneously released into the culture medium. The treatment with phosphatidylinositol-specific phospholipase C induces the release of the receptor, which behaves as a glycosyl phosphatidyl inositol(GPI)-anchored protein. Phase-partitioning experiments on cell lysates have shown that the receptor partitions into the detergent phase. By detaching cell monolayers with the chelating agent EDTA we have prepared the cell-substratum contact sites of these cells, which represent only the 3.5% of the surface membrane of monolayered cells. Such plasma membrane remnants are highly selected since they contain about 43% of total u-PA-ATF binding sites. Such binding sites show the same biochemical and morphological characteristics of u-PA-ATF receptors observed in the monolayered cells, thus indicating that u-PA is selectively concentrated at the level of cell-substratum contacts. This is likely to enable directional proteolysis for cell migration and invasion.