Urokinase links plasminogen activation and cell adhesion by cleavage of the RGD motif in vitronectin

Abstract

Components of the plasminogen activation system including urokinase (uPA), its inhibitor (PAI-1) and its cell surface receptor (uPAR) have been implicated in a wide variety of biological processes related to tissue homoeostasis. Firstly, the binding of uPA to uPAR favours extracellular proteolysis by enhancing cell surface plasminogen activation. Secondly, it promotes cell adhesion and signalling through binding of the provisional matrix protein vitronectin. We now report that uPA and plasmin induces a potent negative feedback on cell adhesion through specific cleavage of the RGD motif in vitronectin. Cleavage of vitronectin by uPA displays a remarkable receptor dependence and requires concomitant binding of both uPA and vitronectin to uPAR. Moreover, we show that PAI-1 counteracts the negative feedback and behaves as a proteolysis-triggered stabilizer of uPAR-mediated cell adhesion to vitronectin. These findings identify a novel and highly specific function for the plasminogen activation system in the regulation of cell adhesion to vitronectin. The cleavage of vitronectin by uPA and plasmin results in the release of N-terminal vitronectin fragments that can be detected in vivo, underscoring the potential physiological relevance of the process.

Novel LRAP‐binding partner revealing the plasminogen activation system as a regulator of cementoblast differentiation and mineral nodule formation in vitro

“…Similar results were reported in muscle cells, where treatment with EACA or monoclonal antibody against α‐enolase (MAb11G1) inhibited the differentiation ratio and altered the cell morphology of differentiated myocytes (Días‐Ramos et al, ). We speculate that changes in OCCM‐30 cell morphology promoted by EACA may have occurred as the result of modulation of PAS‐mediated signaling, which has been reported to affect cell‐cell adhesion and cell‐matrix (De Lorenzi et al, ). In the current study, the effect of different concentrations of plasmin, the active form of plasminogen, on cell morphology, mineral nodule formation and expression of cementoblast differentiation markers was assessed.…”

Mechanisms of plasminogen activator inhibitor 1 action in stromal remodeling and related diseases

“…In the initial stage, a significant increase of PAI-1 and u-PA were seen at the outermost edge of the wound, particularly in the newly deposited matrix as matrix-bound proteins. Concomitant increase of u-PA and u-PA receptor (u-PAR) is observed on migrating cells at their leading edge [15][16][17] . PAI-1 is shown to be prominent molecule of the early G0 to G1 transition transcriptome of human keratinocytes cell line, while the keratinocyte growth factor, secreted by the stromal fibroblasts during wound closure, is a powerful stimulator of PAI-1 expression 15 .…”

“…Urokinase initiated plasminogen activation is mainly required for pericellular proteolysis. Binding of u-PA to u-PAR at the cell surface activates plasminogen and enhances extracellular proteolysis 16 . At the same time, through the u-PA initiated conformational change of u-PAR, and associated adapter proteins, intracellular signaling is initiated, specifically -mechanical force transmission to the cytoskeleton.…”

“…PAI-1 was shown to counteract this function by stabilizing u-PAR mediated cell adhesion to VN (ref. 16 ). Several studies potentiate PAI-1 inhibitory effect on cell migration and its contribution to delay in wound closure.…”

“…Physiologically, elevated PAI-1 expression in the initial phase expedite wound healing by protecting ECM proteins. PAI-1 blocks u-PA/t-PA activation and consequently plasminogen, MMPs, and TGF-β activation, thus retarding ECM turnover 3,15,16,57 . However, pathologically prolonged low ECM degradation leads to the excessive collagen accumulation.…”