This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Del Rosso, M. Articles by Fibbi, G. Search for Related Content PubMed PubMed Citation Articles by Del Rosso, M. Articles by Fibbi, G.

Receptors for Plasminogen Activator, Urokinase, in Normal and Rous Sarcoma Virus-transformed Mouse Fibroblasts¹

Institute of General Pathology, University of Florence, Viale Morgagni, 50, 50134, Florence, Italy

We have prepared a conjugate of the plasminogen activator urokinase (UK) and ferritin, which maintains fibrinolytic activity. Monolayers of BALB/c-3T3 cells and of Rous sarcoma virus-transformed highly malignant line AA12-3T3, subcultured in plasminogen-free serum, were incubated with UK-ferritin at 0° and processed for transmission electron microscopy. Under these conditions, both of the lines showed specific receptors on the cell surface that were distributed in singlets, in small or large clusters. In the presence of excess native UK, the binding of ferritin was reduced by 99%, indicating the interaction of UK:ferritin with a specific receptor. The ligand-receptor interaction involves the catalytic site of UK, since the binding was completely impaired by preincubation of UK:ferritin with p-aminobenzamidine, a competitive inhibitor of the catalytic site of UK. The number and density of receptors decreased about one order of magnitude on the membrane of AA12 cells when compared with normal 3T3 cells. Saturation kinetics, using ¹²⁵I-labeled UK, indicate the presence of 4 x 10⁴ and 2.5 x 10³ receptors on the membrane of 3T3 and AA12 cells, respectively. At 37°, UK:ferritin redistributed on the plane of the membrane, in a process which was faster in malignant than in normal cells. Ferritin particles clustered in large groups on coated areas of the surface and were internalized by adsorptive pinocytosis. After 10 min at 37°, the vesicles showed a progressively deeper internalization and a fusion with lysosomes, and some were observed in the Golgi complex area. Since the experiments were planned in order to exclude the presence of protease-nexin in the incubation medium, these data suggest the existence of a plasminogen-independent novel receptor for the catalytic site of plasminogen activators, the number on the cell surface of which decreases in Rous sarcoma virus-transformed mouse fibroblasts.

¹ This work was supported by a grant from Ministero Pubblica Istruzione (DPR 382/80, 40% and 60%).

² To whom requests for reprints should be addressed.

Received 2/ 9/84. Accepted 10/16/84.

This article has been cited by other articles:

				Y. Zhang, A. Wisner, Y. Xiong, and C. Bon A Novel Plasminogen Activator from Snake Venom J. Biol. Chem., April 28, 1995; 270(17): 10246 - 10255. [Abstract] [Full Text] [PDF]

				M. Pucci, G. Fibbi, L. Magnelli, and M. Del Rosso Regulation of Urokinase/Urokinase Receptor Interaction by Heparin-like Glycosaminoglycans J. Biol. Chem., February 9, 2001; 276(7): 4756 - 4765. [Abstract] [Full Text] [PDF]