Véronique Masson

The pro- or antiangiogenic effect of plasminogen activator inhibitor 1 is dose dependent

Plasminogen activator inhibitor 1 (PAI‐1) is believed to control proteolytic activity and cell migration during angiogenesis. We previously demonstrated in vivo that this inhibitor is necessary for optimal tumor invasion and vascularization. We also showed that PAI‐1 angiogenic activity is associated with its control of plasminogen activation but not with the regulation of cell‐matrix interaction. To dissect the role of the various components of the plasminogen activation system during angiogenesis, we have adapted the aortic ring assay to use vessels from gene‐inactivated mice. The single deficiency of tPA, uPA, or uPAR, as well as combined deficiencies of uPA and tPA, did not dramatically affect microvessel formation. Deficiency of plasminogen delayed microves‐sel outgrowth. Lack of PAI‐1 completely abolished angio‐genesis, demonstrating its importance in the control of plasmin‐mediated proteolysis. Microvessel outgrowth from PAI‐1‐/‐ aortic rings could be restored by adding exogenous PAI‐1 (wild‐type serum or purified recombi‐nant PAI‐1). Addition of recombinant PAI‐1 led to a bell‐shaped angiogenic response clearly showing that PAI‐1 is proangiogenic at physiological concentrations and antiangiogenic at higher levels. Using specific PAI‐1 mutants, we could demonstrate that PAI‐1 promotes an‐giogenesis at physiological (nanomolar) concentrations through its antiproteolytic activity rather than by interacting with vitronectin.—Devy, L., Blacher, S., Grignet‐Debrus, C., Bajou, K., Masson, V., Gerard, R. D., Gils, A., Carmeliet, G., Carmeliet, P., Declerck, P. J., Noèl, A., Foidart, J. M. The pro‐ or antiangiogenic effect of plasminogen activator inhibitor 1 is dose dependent. FASEB J. 16, 147–154 (2002)

Contribution of host MMP-2 and MMP-9 to promote tumor vascularization and invasion of malignant keratinocytes

The matrix metalloproteinases (MMPs) play a key role in normal and pathological angiogenesis by mediating extracellular matrix degradation and/or controlling the biological activity of growth factors, chemokines, and/or cytokines. Specific functions of individual MMPs as anti‐ or proangiogenic mediators remain to be elucidated. In the present study, we assessed the impact of single or combined MMP deficiencies in in vivo and in vitro models of angiogenesis (malignant keratinocyte transplantation and the aortic ring assay, respectively). MMP‐9 was predominantly expressed by neutrophils in tumor transplants, whereas MMP‐2 and MMP‐3 were stromal. Neither the single deficiency of MMP‐2, MMP‐3, or MMP‐9, nor the combined absence of MMP‐9 and MMP‐3 did impair tumor invasion and vascularization in vivo. However, there was a striking cooperative effect in double MMP‐2:MMP‐9‐deficient mice as demonstrated by the absence of tumor vascularization and invasion. In contrast, the combined lack of MMP‐2 and MMP‐9 did not impair the in vitro capillary outgrowth from aortic rings. These results point to the importance of a cross talk between several host cells for the in vivo tumor promoting and angiogenic effects of MMP‐2 and MMP‐9. Our data demonstrate for the first time in an experimental model that MMP‐2 and MMP‐9 cooperate in promoting the in vivo invasive and angiogenic phenotype of malignant keratinocytes.

Mouse aortic ring assay: A new approach of the molecular genetics of angiogenesis

Angiogenesis, a key step in many physiological and pathological processes, involves proteolysis of the extracellular matrix. To study the role of two enzymatic families, serine-proteases and matrix metalloproteases in angiogenesis, we have adapted to the mouse, the aortic ring assay initially developed in the rat. The use of deficient mice allowed us to demonstrate that PAI-1 is essential for angiogenesis while the absence of an MMP, MMP-11, did not affect vessel sprouting. We report here that this model is attractive to elucidate the cellular and molecular mechanisms of angiogenesis, to identify, characterise or screen “pro- or anti-angiogenic agents that could be used for the treatment of angiogenesis-dependent diseases. Approaches include using recombinant proteins, synthetic molecules and adenovirus-mediated gene transfer.

Role of plasminogen activator-plasmin system in tumor angiogenesis

Abstract: New blood formation or angiogenesis has become a key target in therapeutic strategies aimed at inhibiting tumor growth and other diseases associated with neovascularization. Angiogenesis is associated with important extracellular remodeling involving different proteolytic systems among which the plasminogen system plays an essential role. It belongs to the large serine proteinase family and can act directly or indirectly by activating matrix metalloproteinases or by liberating growth factors and cytokines sequestered within the extracellular matrix. Migration of endothelial cells is associated with significant upregulation of proteolysis and, conversely, immunoneutralization or chemical inhibition of the system reduces angiogenesis in vitro. On the other hand, genetically altered mice developed normally without overt vascular anomalies indicating the possibility of compensation by other proteases in vivo. Nevertheless, they have in some experimental settings revealed unanticipated roles for previously characterized proteinases or their inhibitors. In this review, the complex mechanisms of action of the serine proteases in pathological angiogenesis are summarized alongside possible therapeutic applications.

Molecular interactions involving urokinase plasminogen activator (uPA), its receptor (uPAR) and its inhibitor, plasminogen activator inhibitor-1 (PAI-1), as new targets for tumour therapy

In the promotion of cancer progression, a classical role had previously been ascribed to the plasminogen activation system on the basis of urokinase plasminogen activator (uPA) proteolytic activity and plasminogen activation triggering a focalised pericellular activation cascade involving matrix metalloproteinases (MMPs). As a result, many pharmaceutical companies have undertaken the development of synthetic uPA inhibitors. However, during the last few years, data have accumulated that uPA, as well as urokinase-type plasminogen activator receptor (uPAR) and plasminogen activator inhibitor-1 (PAI-1), are likely to play an essential role in tumour progression through non-proteolysis-related activities. Such activities endow them with new and likely key functions in tumour progression-associated events, such as cellular adhesion, migration, invasion and angiogenesis. Since these activities essentially depend upon protein-protein interactions, they represent new therapeutic targets.