Selective localization of receptors for urokinase amino-terminal fragment at substratum contact sites of an in vitro-established line of human epidermal cells.
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.
Del Rosso
M
M
Istituto di Patologia Generale, Università di Firenze, Italy.
Pedersen
N
N
Fibbi
G
G
Pucci
M
M
Dini
G
G
Anichini
E
E
Blasi
F
F
D001665:Binding Sites; D002448:Cell Adhesion; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry / Q000648:ultrastructure; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004817:Epidermis / Q000737:chemistry* / Q000648:ultrastructure; D006801:Humans; D008854:Microscopy, Electron; D010446:Peptide Fragments / Q000378:metabolism*; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D010727:Phosphoric Diester Hydrolases / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000032:analysis*; D055293:Receptors, Urokinase Plasminogen Activator; D013388:Succinimides / Q000494:pharmacology; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism*
D003432:Cross-Linking Reagents; C524898:PLAUR protein, human; D010446:Peptide Fragments; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D013388:Succinimides; D010727:Phosphoric Diester Hydrolases; D054801:Phosphoinositide Phospholipase C; D014568:Urokinase-Type Plasminogen Activator; D043265:Phosphatidylinositol Diacylglycerol-Lyase; C019358:disuccinimidyl suberate