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Cell Biology International (2002) 26, 327–335 (Printed in Great Britain)

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RECEPTOR-BOUND uPA IS REVERSIBLY PROTECTED FROM INHIBITION BY LOW MOLECULAR WEIGHT INHIBITORS

Kimberly D Dyer^a,f1, Laura A Linz‑Mcgillem^b, Mary Anne Alliegro^b and Mark C Alliegro^b

^aLaboratory of Host Defenses, NIAID, Bethesda, MD, U.S.A.
^bDepartment of Cell Biology and Anatomy, Louisiana State University Health Sciences Center, New Orleans, LA, U.S.A.

Abstract

Urokinase-type plasminogen activator (uPA) plays a ubiquitous role in cell migration and invasiveness. Amiloride, a competitive inhibitor of uPA, can inhibit endothelial cell (EC) outgrowth during angiogenesis. To address the question of whether amiloride blocked angiogenesis by inhibiting uPA, we undertook a study of uPA expression in sprouting EC in vitro and the effects of amiloride on both enzymatic and morphogenetic activity. As expected, amiloride inhibited soluble uPA (suPA) with an IC50 of 45–85μm , however, receptor-bound uPA (rbuPA) from the sprouting EC was insensitive to amiloride. Removal of uPA from its receptors confers sensitivity to inhibition by amiloride suggesting that a reversible conformational change may mediate the insensitivity of rbuPA to amiloride and its analogs. In summary, we found no evidence to support the hypothesis that amiloride blocks capillary outgrowth by inhibition of uPA, but were able to successfully demonstrate a functional difference between two physiological forms of this important matrix-degrading enzyme.

Key words: angiogenesis, urokinase-type plasminogen activator, uPA, amiloride, endothelial cell, urokinase, urokinase receptor.

^f1Address correspondence to: Dr Kimberly D. Dyer, Laboratory of Host Defenses, 10 Center Drive MSC 1886, Bethesda, MD 2092-1886, U.S.A.; Fax: 301-402-4369; E-mail: kdyer@niaid.nih.gov

Received 8 May 2001; accepted 12 December 2001