Tissue-specific expression of the relaxed conformation of plasminogen activator inhibitor-2 and low-density lipoprotein receptor-related protein in human term gestational tissues

MicroRNA-590-3p inhibits trophoblast-dependent maternal spiral artery remodeling by repressing low-density lipoprotein receptor-related protein 6

Background

The remodeling of maternal spiral artery following embryo implantation, which relies on well‐regulated trophoblast functions, is a pivotal process to ensure a successful pregnancy. Low‐density lipoprotein receptor‐related protein 6 (LRP6) and microRNAs (miRNAs, miRs) are suggested to be involved in angiogenesis and several vascular diseases; however, their functions in the control of trophoblast remain elusive. We therefore aimed to examine the roles of LRP6 and miR‐590‐3p in the regulation of trophoblast during the remodeling of maternal spiral artery.

Methods

HTR‐8/SVneo cell, a trophoblast cell line, was utilized to study the effects of LRP6 and miR‐590‐3p on apoptosis, cell proliferation, migration, invasion, as well as tube formation. Expression of angiogenic factors placental growth factor (PlGF), matrix metalloproteinases (MMPs), vascular endothelial growth factor (VEGF), and activities of canonical Wnt/β‐catenin signaling pathway, which were implicated in the process of artery remodeling, were also examined.

Results

MiR‐590‐3p directly targeted 3′ untranslated region (3′‐UTR) of LRP6 mRNA and repressed LRP6 expression, which in turn inhibited proliferation, migration, invasion, as well as tube formation, and resulted in apoptosis in HTR‐8/SVneo cells. Further, inhibition of LRP6 through miR‐590‐3p significantly suppressed the expression of PlGF, MMPs, and VEGF and reduced the activation of Wnt/β‐catenin signaling pathway.

Conclusion

MicroRNAs‐590‐3p may inhibit trophoblast‐dependent maternal spiral artery remodeling, via both trophoblast invasion and endovascular formation, by repressing LRP6.

Human extravillous trophoblasts bind but do not internalize antiphospholipid antibodies

INTRODUCTION

Obstetric morbidity in women with antiphospholipid antibodies (aPLs) may reflect the adverse effects of aPLs on placental cells such as extravillous trophoblasts and the syncytiotrophoblast. Antiphospholipid antibodies may affect the syncytiotrophoblast after being internalised by members of the Low-density lipoprotein receptor (LDLR) family and the antigen of aPLs, β2 glycoprotein I.

AIM

This study aimed to determine whether aPL internalization was a mechanism by which aPLs adversely affect extravillous trophoblasts.

METHOD

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STUDY

Fluorescently-labelled monoclonal aPLs IIC5 or ID2 were incubated with first trimester extravillous trophoblast outgrowths and visualized by microscopy. The subcellular expression of β2 glycoprotein I and LDLR family members was investigated by live/permeabilised immunocytochemistry.

RESULTS

Unlike the syncytiotrophoblast of anchoring villi, monoclonal aPLs were not internalised by extravillous trophoblasts, which expressed LDLR family members intracellularly. The aPL IIC5 bound to the surface of extravillous trophoblasts in a pattern similar to the extracellular expression of β2 glycoprotein I.

CONCLUSIONS

The mechanisms of action of aPLs are different in extravillous trophoblasts and the syncytiotrophoblast. The interaction of aPLs with the extravillous trophoblast surface, which may involve β2 glycoprotein I, is consistent with reports that aPLs trigger intracellular signaling cascades through cell-surface receptors.

Revisiting the biological roles of PAI2 (SERPINB2) in cancer

Tumour expression of the urokinase plasminogen activator correlates with invasive capacity. Consequently, inhibition of this serine protease by physiological inhibitors should decrease invasion and metastasis. However, of the two main urokinase inhibitors, high tumour levels of the type 1 inhibitor actually promote tumour progression, whereas high levels of the type 2 inhibitor decrease tumour growth and metastasis. We propose that the basis of this apparently paradoxical action of two similar serine protease inhibitors lies in key structural differences controlling interactions with components of the extracellular matrix and endocytosis-signalling co-receptors.

Maspin retards cell detachment via a novel interaction with the urokinase-type plasminogen activator/urokinase-type plasminogen activator receptor system

It is well documented that tumor suppressive maspin inhibits tumor cell invasion and extracellular matrix remodeling. Maspin is a cytosolic, cell surface-associated, and secreted protein in the serine protease inhibitor superfamily. Although several molecules have been identified as candidate intracellular maspin targets, the extracellular maspin target(s) remains elusive. Although maspin does not directly inhibit urokinase-type plasminogen activator (uPA) activity, we have shown evidence that maspin may block the pericellular proteolysis mediated by cell surface-associated uPA. In the current study, maspin significantly inhibited the Ca2+ reduction-induced detachment of DU145 cells. This maspin effect was associated with increased and sustained levels of mature focal adhesion contacts (FAC). We noted that maspin (a) colocalized with uPA and uPA receptor (uPAR), (b) enhanced the interaction between uPAR and low-density lipoprotein receptor related protein, and (c) induced rapid internalization of uPA and uPAR. The maspin effects on surface-associated uPA and uPAR required the interaction between uPA and uPAR. Further biochemical and biophysical analyses revealed that maspin specifically bound to pro-uPA with a deduced K(d) of 270 nmol/L and inhibited the plasmin-mediated pro-uPA cleavage. Interestingly, substitution of maspin p1' site Arg340 in the reactive site loop (RSL) with alanine not only abolished the binding to pro-uPA but also diminished the maspin effects on pro-uPA cleavage and cell detachment. These data show an important role of maspin RSL in regulating the uPA/uPAR-dependent cell detachment. Together, our data led to a new hypothesis that maspin may stabilize mature FACs by quenching localized uPA/uPAR complex before uPA activation.

Tumor suppressive maspin and epithelial homeostasis

Maspin is a 42-kDa novel serine protease inhibitor (serpin) with multifaceted tumor suppressive activities. To date, the consensus that maspin expression predicts a better prognosis still largely holds for breast, prostate, colon, and oral squamous cancers. Interestingly, however, more detailed analyses revealed a biphasic expression pattern of maspin in early steps of tumorigenicity and re-expression of maspin in dormant cancer metastatic revertants. These data suggest a sensitivity of maspin expression to changes of epithelial microenvironments, and a role of maspin in epithelial homeostasis. Experimental evidence consistently showed that maspin suppresses tumor growth, invasion and metastasis, induces tumor redifferentiation, and enhances tumor cell sensitivity to apoptosis. Maspin protein isolated from biological sources is a monomer, which is present as a secreted, a cytoplasmic, a nuclear, as well as a cell surface-associated protein. Nuclear maspin is associated with better prognoses of cancer. It is further noted that extracellular maspin is sufficient to block tumor induced extracellular matrix degradation, tumor cell motility and invasion, whereas intracellular maspin is responsible for the increased cellular sensitivity to apoptosis. Despite these exciting developments, the mechanistic studies of maspin have proven challenging primarily due to the lack of a prototype molecular model. Although the maspin sequence has overall homologies with other members in the serpin superfamily, it does not behave like a typical serpin, that is, non-inhibitory toward active serine proteases in solution. This novel feature is in line with the X-ray crystallographic evidence. Several recent studies dedicated to finding the maspin partners support a paradigm shift. The current review is intended to summarize these recent findings and discuss a new perspective of maspin in epithelial homeostasis.

Endothelial and lipoprotein lipases in human and mouse placenta

Placenta expresses various lipase activities. However, a detailed characterization of the involved genes and proteins is lacking. In this study, we compared the expression of endothelial lipase (EL) and LPL in human term placenta. When placental protein extracts were separated by heparin-Sepharose affinity chromatography, the EL protein eluted as a single peak without detectable phospholipid or triglyceride (TG) lipase activity. The major portion of LPL protein eluted slightly after EL. This peak also had no lipase activity and most likely contained monomeric LPL. Fractions eluting at a higher NaCl concentration contained small amounts of LPL protein (most likely dimeric LPL) and had substantial TG lipase activity. In situ hybridization studies showed EL mRNA expression in syncytiotrophoblasts and endothelial cells and LPL mRNA in syncytiotrophoblasts. In contrast, immunohistochemistry showed EL and LPL protein associated with both cell types. In mouse placentas, lack of LPL expression resulted in increased EL mRNA expression. These results suggest that the cellular expression of EL and LPL in human placenta is different. Nevertheless, the two lipases might have overlapping functions in the mouse placenta. Our data also suggest that the major portions of both proteins are stored in an inactive form in human term placenta.

Urokinase plasminogen activator (uPA) and its receptor (uPAR) in gestational tissues; Measurements and clinical implications

BACKGROUND

Urokinase plasminogen activator (uPA) and urokinase plasminogen activator receptor (uPAR) are central molecules for uPA/uPAR/plasmin-dependent proteolysis, which is thought to play a significant role in the development of pregnancy, as well as its many complications.

OBJECTIVE

To measure the levels of uPA and uPAR in the placenta and myometrium, as well as in the foetal membranes and amniotic fluid.

STUDY DESIGN

The study group consisted of 35 women with normal course of pregnancy, but with complications arising during delivery, which led to Caesarean section. Samples of placenta, myometrium, foetal membranes, amniotic fluid and blood were obtained at the time of operation. Tissue extracts were prepared. Measurements were made by the ELISA method.

RESULTS

uPA and uPAR concentration in gestational tissues, including amniotic fluid, is 100-200 times higher than in plasma. Among tissues, the highest uPA level was found in placenta ( 1.32 +/- 0.48 ng/mg of protein), and the highest uPAR level in foetal membranes (3.33 +/- 1.20 ng/mg of protein).

CONCLUSIONS

uPA and uPAR are present in all gestational tissues, in some in relatively high concentrations. Our results support the modern clinical hypothesis that fibrinolytic system can participate in mechanisms of such obstetric complications as pre-term pre-mature rupture of foetal membranes and placental abruption.

The role of the plasminogen activation cascade in glioma cell invasion: a review

Tumour cell invasion is a dynamic process that depends on a co-ordinated series of biochemical events. This review discusses the role of the proteolytic enzyme system, the plasminogen activation cascade, in glioma cell invasion.

Evidence for intracellular cleavage of plasminogen activator inhibitor type 2 (PAI-2) in normal epidermal keratinocytes

Plasminogen activator inhibitor type 2 (PAI-2) is a serine proteinase inhibitor (serpin), present in high quantities in stratified squamous epithelia. Detergent extracts of human epidermis or cultured keratinocytes contain primarily active, nonglycosylated PAI-2. In keratinocytes, the vast majority of PAI-2 is retained within the cell, supporting the hypothesis that PAI-2 may serve specific intracellular function(s) through interaction with an unknown cytoplasmic proteinase. During interaction with the target proteinase, cleavage of PAI-2 within its reactive site loop leads to the formation of a more stable, "relaxed" conformation (PAI-2r). Using a monoclonal antibody specific for PAI-2r, we demonstrate here that PAI-2r is present in keratinocytes of the granular and basal layers of normal human epidermis. In addition, PAI-2r is detectable in cultured human epidermal keratinocytes, where it is concentrated in a detergent-insoluble fraction within differentiating cells. These data provide evidence for the presence of an endogenous, keratinocyte-derived proteinase that constitutively cleaves intracellular PAI-2 in normal human epidermal keratinocytes. Cleavage of PAI-2 by this proteinase may reflect specific intracellular action of PAI-2 in normal cells. Finally, we demonstrate that a commercially available anti-PAI-2 monoclonal antibody (#3750, American Diagnostica, Greenwich, CT), under native experimental conditions, preferentially recognizes the uncleaved, active form of PAI-2 and does not efficiently detect PAI-2r.

Localization and significance of urokinase plasminogen activator and its receptor in placental tissue from intrauterine, ectopic and molar pregnancies

Urokinase plasminogen activator receptor (uPAR) is a membrane-anchored protein with urokinase plasminogen activator (uPA) as the ligand. This complex induces proteolysis and remodelling of maternal decidua during placental implantation. The presence of uPAR on trophoblasts is supposed to promote adhesion, migration and invasion. In cancer tissue, high levels of uPAR are correlated with a poor prognosis. This immunohistochemical study shows the localization of uPA and uPAR in a prospective design with stereological sampling of fetal and maternal tissue from normal, ectopic and hydatidiform molar (HM) pregnancies. Cytokeratin and Ki67 were used as markers for trophoblasts and proliferating cells. Membrane-bound uPAR was observed on villous non-proliferating intermediate trophoblasts (IT) within cell columns in intrauterine and ectopic pregnancies. The corresponding proliferating IT with cytological atypia sprouting from the chorionic villi in HM was uPAR-negative. uPA but not uPAR was observed in anchoring distal IT at the attachment-point to the basal plate. In the placental bed, extravillous interstitial trophoblasts were uPA-positive but uPAR-negative. The trophoblast giant cells were both uPA- and uPAR-negative. In relation to the maternal vessels, a focal distribution for uPA and uPAR was present in the endovascular and perivascular trophoblasts. The intraluminal trophoblasts overlying endothelial cells were uPAR-positive only. In maternal tissue from intrauterine and molar pregnancies, uPAR was seen in the decidual cells in a zone facing the anchoring villi and the fibrinoid lesions with embedded trophoblasts. In contrast, the stromal cells of the fallopian tube without a decidual reaction facing the implanted gestation were uPAR-negative. Non-invaded decidual, myometrial and muscular tissue of the pregnant uterus and fallopian tube was extensively positive for uPA whereas 'pseudodecidual' cells from the intrauterine evacuate in patients with an ectopic pregnancy only showed a focal and scanty reaction for uPA. When trophoblast invasion of the decidua was present, the decidual cells were uPA-negative. A semi-quantitative assessment of the receptor was estimated in villous IT within cell columns in normal and molar pregnancies but, in conclusion, quantitative evaluation of uPAR cannot be used to predict development of post-molar persistent trophoblastic disease (PTD).

Immunological detection of conformational neoepitopes associated with the serpin activity of plasminogen activator inhibitor type-2

The physiological roles of plasminogen activator inhibitor-2 (PAI-2) are not yet well understood. Kinetic studies suggest a role in the regulation of plasminogen activator-driven proteolysis in many cell types. This study describes a monoclonal antibody (2H5), which uniquely recognizes neoepitope determinants on PAI-2 appearing after thermodynamic relaxation of the molecule. Enzyme-linked immunosorbent assays and native polyacrylamide gel electrophoresis immunoblotting confirmed the specificity of 2H5 for urokinase type plasminogen activator.PAI-2 complexes. Examination of the affinity of 2H5 for complexes formed between PAI-2 and a synthetic 14-mer reactive site loop peptide, PAI-2 treated with tissue plasminogen activator, or thrombin suggests that the 2H5 epitope is determined exclusively by sequences found only on PAI-2 following proteolytic cleavage of the Arg380-Thr381 bond and insertion of the reactive site loop into beta-sheet A. Peptides lacking both the P13 (Glu368) and P14 (Thr367) residues did not induce a conformational change or affect the inhibitory activity of PAI-2, indicating that one or both of these residues are critical for PAI-2 function. To our knowledge, this is the first description of a monoclonal antibody that can distinguish conformational changes in PAI-2 related specifically to its potential biological function(s).