A functional overlap of plasminogen and MMPs regulates vascularization during placental development

Reduced metastasis of transgenic mammary cancer in urokinase-deficient mice

A prominent phenotype of plasmin deficiency in mice is reduced metastasis in the MMTV-PymT transgenic breast cancer model. Proteolytically active plasmin is generated from inactive plasminogen by one of 2 activators, uPA or tPA. We now find that uPA deficiency alone significantly reduces metastasis >7-fold in the MMTV-PymT model. We studied a cohort of 55 MMTV-PymT transgenic mice, either uPA-deficient or wild-type controls. Tumor incidence, latency, growth rate and final primary tumor burden were not significantly affected by uPA deficiency. In contrast, average lung metastasis volume was reduced from 1.58 mm(3) in wild-type controls to 0.21 mm(3) in uPA-deficient mice (p = 0.023). Tumor cell dissemination to brachial lymph nodes was also reduced from 53% (28/53) in wild-type controls to 31% (17/54) in uPA-deficient mice (p = 0.032). Mice without plasminogen display a severe pleiotropic phenotype. By comparison, spontaneous phenotypes are modest in uPA-deficient mice, probably because they still have active tPA. We show that metastasis is strongly and selectively decreased in uPA-deficient mice, suggesting that uPA-directed antimetastatic therapy would be efficacious and have limited side effects.

Serine protease HtrA1 is developmentally regulated in trophoblast and uterine decidual cells during placental formation in the mouse

Development of a hemochorial placenta involves trophoblast proliferation, differentiation, and invasion into the uterus to promote blood flow to the embryo. Trophoblast invasion is tightly controlled by expression of specific proteases in the trophoblast and highly coordinated activities in the uterus. One uterine event essential for placentation is the developmentally regulated formation and regression of the decidua. In mice, decidual regression takes place in a temporal- and spatial-specific manner that is coordinated with placental development. In this study, we identified that the serine protease HtrA1 (high temperature requirement factor A1) was specifically expressed in differentiated trophoblast cells, especially the giant cells, during the early stages of placental development. A high level of HtrA1 expression was also detected in decidua capsularis specifically at the decidual-trophoblast interface where active involution occurs. Thus, we have identified a previously unknown role for HtrA1 as a protease potentially important for trophoblast differentiation/invasion and uterine decidual regression during placental development.

The urokinase receptor (uPAR) and the uPAR-associated protein (uPARAP/Endo180): membrane proteins engaged in matrix turnover during tissue remodeling

The breakdown of the barriers formed by extracellular matrix proteins is a pre-requisite for all processes of tissue remodeling. Matrix degradation reactions take part in specific physiological events in the healthy organism but also represent a crucial step in cancer invasion. These degradation processes involve a highly organized interplay between proteases and their cellular binding sites as well as specific substrates and internalization receptors. This review article is focused on two components, the urokinase plasminogen activator receptor (uPAR) and the uPAR-associated protein (uPARAP, also designated Endo180), that are considered crucially engaged in matrix degradation. uPAR and uPARAP have highly diverse functions, but on certain cell types they interact with each other in a process that is still incompletely understood. uPAR is a glycosyl-phosphatidylinositol-anchored glycoprotein on the surface of various cell types that serves to bind the urokinase plasminogen activator and localize the activation reactions in the proteolytic cascade system of plasminogen activation. uPARAP is an integral membrane protein with a pronounced role in the internalization of collagen for intracellular degradation. Both receptors have additional functions that are currently being unraveled. The present discussion of uPAR and uPARAP is centered on their protein structure and molecular and cellular function.

Human cytomegalovirus interleukin-10 downregulates metalloproteinase activity and impairs endothelial cell migration and placental cytotrophoblast invasiveness in vitro

At the uterine-placental interface, fetal cytotrophoblasts invade the decidua, breach maternal blood vessels, and form heterotypic contacts with uterine microvascular endothelial cells. In early gestation, differentiating- invading cytotrophoblasts produce high levels of matrix metalloproteinase 9 (MMP-9), which degrades the extracellular matrix and increases the invasion depth. By midgestation, when invasion is complete, MMP levels are reduced. Cytotrophoblasts also produce human interleukin-10 (hIL-10), a pleiotropic cytokine that modulates immune responses, helping to protect the fetal hemiallograft from rejection. Human cytomegalovirus (CMV) is often detected at the uterine-placental interface. CMV infection impairs cytotrophoblast differentiation and invasion, altering the expression of the cell adhesion and immune molecules. Here we report that infection with a clinical CMV strain, VR1814, but not a laboratory strain, AD169, downregulates MMP activity in uterine microvascular endothelial cells and differentiating-invading cytotrophoblasts. Infected cytotrophoblasts expressed CMV IL-10 (cmvIL-10) mRNA and secreted the viral cytokine, which upregulated hIL-10. Functional analyses showed that cmvIL-10 treatment impaired migration in endothelial cell wounding assays and cytotrophoblast invasion of Matrigel in vitro. Comparable changes occurred in cells that were exposed to recombinant hIL-10 or cmvIL-10. Our results show that cmvIL-10 decreases MMP activity and dysregulates the cell-cell and/or cell-matrix interactions of infected cytotrophoblasts and endothelial cells. Reduced MMP activity early in placental development could impair cytotrophoblast remodeling of the uterine vasculature and eventually restrict fetal growth in affected pregnancies.