Plasminogen activator inhibitor type 2: a regulator of monocyte proliferation and differentiation

Glycolytic reprogramming fuels myeloid cell-driven hypercoagulability

BACKGROUND

Myeloid cell metabolic reprogramming is a hallmark of inflammatory disease; however, its role in inflammation-induced hypercoagulability is poorly understood.

OBJECTIVES

We aimed to evaluate the role of inflammation-associated metabolic reprogramming in regulating blood coagulation.

METHODS

We used novel myeloid cell-based global hemostasis assays and murine models of immunometabolic disease.

RESULTS

Glycolysis was essential for enhanced activated myeloid cell tissue factor expression and decryption, driving increased cell-dependent thrombin generation in response to inflammatory challenge. Similarly, inhibition of glycolysis enhanced activated macrophage fibrinolytic activity through reduced plasminogen activator inhibitor 1 activity. Macrophage polarization or activation markedly increased endothelial protein C receptor (EPCR) expression on monocytes and macrophages, leading to increased myeloid cell-dependent protein C activation. Importantly, inflammation-dependent EPCR expression on tissue-resident macrophages was also observed in vivo. Adipose tissue macrophages from obese mice fed a high-fat diet exhibited significantly enhanced EPCR expression and activated protein C generation compared with macrophages isolated from the adipose tissue of healthy mice. Similarly, the induction of colitis in mice prompted infiltration of EPCR+ innate myeloid cells within inflamed colonic tissue that were absent from the intestinal tissue of healthy mice.

CONCLUSION

Collectively, this study identifies immunometabolic regulation of myeloid cell hypercoagulability, opening new therapeutic possibilities for targeted mitigation of thromboinflammatory disease.

The role of plasminogen activator inhibitor-2 in pneumococcal meningitis

Pneumococcal meningitis is associated with dysregulation of the coagulation cascade. Previously, we detected upregulation of cerebral plasminogen activator inhibitor-2 (PAI-2) mRNA expression during pneumococcal meningitis. Diverse functions have been ascribed to PAI-2, but its role remains unclear. We analyzed the function of SERPINB2 (coding for PAI-2) in patients with bacterial meningitis, in a well-established pneumococcal meningitis mouse model, using Serpinb2 knockout mice, and in vitro in wt and PAI-2-deficient bone marrow-derived macrophages (BMDMs). We measured PAI-2 in cerebrospinal fluid of patients, and performed functional, histopathological, protein and mRNA expression analyses in vivo and in vitro. We found a substantial increase of PAI-2 concentration in CSF of patients with pneumococcal meningitis, and up-regulation and increased release of PAI-2 in mice. PAI-2 deficiency was associated with increased mortality in murine pneumococcal meningitis and cerebral hemorrhages. Serpinb2−/− mice exhibited increased C5a levels, but decreased IL-10 levels in the brain during pneumococcal infection. Our in vitro experiments confirmed increased expression and release of PAI-2 by wt BMDM and decreased IL-10 liberation by PAI-2-deficient BMDM upon pneumococcal challenge. Our data show that PAI-2 is elevated during in pneumococcal meningitis in humans and mice. PAI-2 deficiency causes an inflammatory imbalance, resulting in increased brain pathology and mortality.

Evi1 involved in benzene-induced haematotoxicity via modulation of PI3K/mTOR pathway and negative regulation Serpinb2

Benzene is a widely used chemical and an environmental pollutant. Exposure to benzene can cause blood diseases, but the mechanisms underlying benzene haematotoxicity have not been fully clarified. Ecotropic virus integration site-1 (Evi1), a transcription factor, plays important roles in normal haematopoiesis and haematological diseases. In this study, we investigated the role and mechanism of Evi1 in benzene-induced haematotoxicity. We found that benzene exposure significantly increased Evi1 level in white blood cells (WBCs) in occupational benzene workers as well as mouse bone marrow cells. Further in vitro results demonstrated that compared with control cells exposed to same 1,4-benzoquinone (1,4-BQ, an important active metabolite of benzene) concentration, Evi1 downregulation significantly reduced cell proliferation, and disrupted cell viability, apoptosis, erythroid and megakaryotic cell differentiation and cell cycle. Additionally, down-regulation of Evi1 suppressed phosphoinositide 3-kinase (PI3K)/mTOR signalling pathway and elevated its target gene Serpinb2 following 1,4-BQ exposure. Moreover, the PI3K activator could partially relieve the inhibitory effect of down-regulation of Evi1 on cell proliferation and increase cell arrest in in G2/M phase. What's more, downregulation of Serpinb2 could partially alleviate proliferation inhibition and reverse cell cycle changes in G0/G1 phase and S phase induced by Evi1 inhibition. In conclusion, our data revealed that Evi1 downregulation aggravated the inhibition of cell proliferation and arrested cells in the G0/G1 phase when exposed to 1,4-BQ, potentially by inactivating the PI3K/mTOR pathway and upregulating downstream target gene Serpinb2. Our study provides novel insights on mechanism by which Evi1 participates in benzene-induced haematotoxicity.

The Fibrinolytic System: Mysteries and Opportunities

The deposition and removal of fibrin has been the primary role of coagulation and fibrinolysis, respectively. There is also little doubt that these 2 enzyme cascades influence each other given they share the same serine protease family ancestry and changes to 1 arm of the hemostatic pathway would influence the other. The fibrinolytic system in particular has also been known for its capacity to clear various non-fibrin proteins and to activate other enzyme systems, including complement and the contact pathway. Furthermore, it can also convert a number of growth factors into their mature, active forms. More recent findings have extended the reach of this system even further. Here we will review some of these developments and also provide an account of the influence of individual players of the fibrinolytic (plasminogen activating) pathway in relation to physiological and pathophysiological events, including aging and metabolism.

Trps1 transcription factor represses phosphate-induced expression of SerpinB2 in osteogenic cells

Serine protease inhibitor SerpinB2 is one of the most upregulated proteins following cellular stress. This multifunctional serpin has been attributed a number of pleiotropic activities, including roles in cell survival, proliferation, differentiation, immunity and extracellular matrix (ECM) remodeling. Studies of cancer cells demonstrated that expression of SerpinB2 is directly repressed by the Trps1 transcription factor, which is a regulator of skeletal and dental tissues mineralization. In our previous studies, we identified SerpinB2 as one of the novel genes highly upregulated by phosphate (P_i) at the initiation of the mineralization process, however SerpinB2 has never been implicated in formation nor homeostasis of mineralized tissues. The aim of this study was to establish, if SerpinB2 is involved in function of cells producing mineralized ECM and to determine the interplay between P_i signaling and Trps1 in the regulation of SerpinB2 expression specifically in cells producing mineralized ECM. Analyses of the SerpinB2 expression pattern in mouse skeletal and dental tissues detected high SerpinB2 protein levels specifically in cells producing mineralized ECM. qRT-PCR and Western blot analyses demonstrated that SerpinB2 expression is activated by elevated P_i specifically in osteogenic cells. However, the P_i-induced SerpinB2 expression was diminished by overexpression of Trps1. Decreased SerpinB2 levels were also detected in osteoblasts and odontoblasts of 2.3Col1a1-Trps1 transgenic mice. Chromatin immunoprecipitation assay (ChIP) revealed that the occupancy of Trps1 on regulatory elements in the SerpinB2 gene changes in response to P_i. In vitro functional assessment of the consequences of SerpinB2 deficiency in cells producing mineralized ECM detected impaired mineralization in SerpinB2-deficient cells in comparison with controls. In conclusion, high and specific expression of SerpinB2 in cells producing mineralized ECM, the impaired mineralization of SerpinB2-deficient cells and regulation of SerpinB2 expression by two molecules regulating formation of mineralized tissues suggest involvement of SerpinB2 in physiological mineralization.

Plasminogen activator Inhibitor-2 inhibits pulmonary arterial smooth muscle cell proliferation in pulmonary arterial hypertension via PI3K/Akt and ERK signaling

BACKGROUND

The proliferation of pulmonary arterial smooth muscle cells (PASMCs) and subsequent pulmonary vascular remodeling leads to pulmonary arterial hypertension (PAH). Understanding the underlying mechanisms and identifying molecules that can suppress PASMCs proliferation is critical for developing effective pharmacological treatment. We previously showed that plasminogen activator inhibitor-2 (PAI-2) inhibited human PASMC (hPASMCs) proliferation in vitro. However, its inhibitory effect on PAH remains to be determined, and the mechanism remains to be illustrated.

METHODS

We compared serum PAI-2 levels between PAH patients and healthy controls, and examined the correlation between PAI-2 level and disease severity. In monocrotaline-induced PAH rats, we examined the effects of exogenous PAI-2 administration on pulmonary vascular remodeling and PAH development. The effect of PAI-2 and potential mechanisms was further examined in cultured hPASMCs.

RESULTS

The serum PAI-2 was decreased in PAH patients compared with controls. PAI-2 level was negatively correlated with mean pulmonary arterial pressure and estimated systolic pulmonary arterial pressure in ultrasonic cardiogram, while positively correlated with 6-min walking distance. In rats, administration of exogenous PAI-2 significantly reversed monocrotaline-induced PAH, as indicated by the decrease in right ventricle systolic pressure, right ventricular hypertrophy index and percent media thickness of pulmonary arterioles. Further mechanistic investigation in hPASMCs showed that PAI-2 inhibited cell proliferation by preventing the activation of PI3K/Akt and ERK pathways.

CONCLUSION

PAI-2 is downregulated in PAH patients. PAI-2 attenuates PAH development by suppressing hPASMCs proliferation via the inhibition of PI3K/Akt and ERK pathways. PAI-2 may serve as a potential biomarker and therapeutic target for PAH.

Molecular imaging of the urokinase plasminogen activator receptor: opportunities beyond cancer

The urokinase plasminogen activator receptor (uPAR) plays a multifaceted role in almost any process where migration of cells and tissue-remodeling is involved such as inflammation, but also in diseases as arthritis and cancer. Normally, uPAR is absent in healthy tissues. By its carefully orchestrated interaction with the protease urokinase plasminogen activator and its inhibitor (plasminogen activator inhibitor-1), uPAR localizes a cascade of proteolytic activities, enabling (patho)physiologic cell migration. Moreover, via the interaction with a broad range of cell membrane proteins, like vitronectin and various integrins, uPAR plays a significant, but not yet completely understood, role in differentiation and proliferation of cells, affecting also disease progression. The implications of these processes, either for diagnostics or therapeutics, have received much attention in oncology, but only limited beyond. Nonetheless, the role of uPAR in different diseases provides ample opportunity to exploit new applications for targeting. Especially in the fields of oncology, cardiology, rheumatology, neurology, and infectious diseases, uPAR-targeted molecular imaging could offer insights for new directions in diagnosis, surveillance, or treatment options.

An Integrative Synthetic Biology Approach to Interrogating Cellular Ubiquitin and Ufm Signaling

Global identification of substrates for PTMs (post-translational modifications) represents a critical but yet dauntingly challenging task in understanding biology and disease pathology. Here we presented a synthetic biology approach, namely ‘YESS’, which coupled Y2H (yeast two hybrid) interactome screening with PTMs reactions reconstituted in bacteria for substrates identification and validation, followed by the functional validation in mammalian cells. Specifically, the sequence-independent Gateway^® cloning technique was adopted to afford simultaneous transfer of multiple hit ORFs (open reading frames) between the YESS sub-systems. In proof-of-evidence applications of YESS, novel substrates were identified for UBE3A and UFL1, the E3 ligases for ubiquitination and ufmylation, respectively. Therefore, the YESS approach could serve as a potentially powerful tool to study cellular signaling mediated by different PTMs.

SerpinB2 inhibits migration and promotes a resolution phase signature in large peritoneal macrophages

SerpinB2 (plasminogen activator inhibitor type 2) has been called the "undecided serpin" with no clear consensus on its physiological role, although it is well described as an inhibitor of urokinase plasminogen activator (uPA). In macrophages, pro-inflammatory stimuli usually induce SerpinB2; however, expression is constitutive in Gata6+ large peritoneal macrophages (LPM). Interrogation of expression data from human macrophages treated with a range of stimuli using a new bioinformatics tool, CEMiTool, suggested that SerpinB2 is most tightly co- and counter-regulated with genes associated with cell movement. Using LPM from SerpinB2-/- and SerpinB2R380A (active site mutant) mice, we show that migration on Matrigel was faster than for their wild-type controls. Confocal microscopy illustrated that SerpinB2 and F-actin staining overlapped in focal adhesions and lamellipodia. Genes associated with migration and extracellular matrix interactions were also identified by RNA-Seq analysis of migrating RPM from wild-type and SerpinB2R380A mice. Subsequent gene set enrichment analyses (GSEA) suggested SerpinB2 counter-regulates many Gata6-regulated genes associated with migration. These data argue that the role of SerpinB2 in macrophages is inhibition of uPA-mediated plasmin generation during cell migration. GSEA also suggested that SerpinB2 expression (likely via ensuing modulation of uPA-receptor/integrin signaling) promotes the adoption of a resolution phase signature.

The sGC activator inhibits the proliferation and migration, promotes the apoptosis of human pulmonary arterial smooth muscle cells via the up regulation of plasminogen activator inhibitor-2

BACKGROUND

Different types of pulmonary hypertension (PH) share the same process of pulmonary vascular remodeling, the molecular mechanism of which is not entirely clarified by far. The abnormal biological behaviors of pulmonary arterial smooth muscle cells (PASMCs) play an important role in this process.

OBJECTIVES

We investigated the regulation of plasminogen activator inhibitor-2 (PAI-2) by the sGC activator, and explored the effect of PAI-2 on PASMCs proliferation, apoptosis and migration.

METHODS

After the transfection with PAI-2 overexpression vector and specific siRNAs or treatment with BAY 41-2272 (an activator of sGC), the mRNA and protein levels of PAI-2 in cultured human PASMCs were detected, and the proliferation, apoptosis and migration of PASMCs were investigated.

RESULTS

BAY 41-2272 up regulated the endogenous PAI-2 in PASMCs, on the mRNA and protein level. In PAI-2 overexpression group, the proliferation and migration of PASMCs were inhibited significantly, and the apoptosis of PASMCs was increased. In contrast, PAI-2 knockdown with siRNA increased PASMCs proliferation and migration, inhibited the apoptosis.

CONCLUSIONS

PAI-2 overexpression inhibits the proliferation and migration and promotes the apoptosis of human PASMCs. Therefore, sGC activator might alleviate or reverse vascular remodeling in PH through the up-regulation of PAI-2.

Dysregulation in microRNA expression in peripheral blood mononuclear cells of sepsis patients is associated with immunopathology

Sepsis is a major cause of death worldwide. It triggers systemic inflammation, the role of which remains unclear. In the current study, we investigated the induction of microRNA (miRNA) during sepsis and their role in the regulation of inflammation. Patients, on days 1 and 5 following sepsis diagnosis, had reduced T cells but elevated monocytes. Plasma levels of IL-6, IL-8, IL-10 and MCP-1 dramatically increased in sepsis patients on day 1. T cells from sepsis patients differentiated primarily into Th2 cells, whereas regulatory T cells decreased. Analysis of 1163 miRNAs from PBMCs revealed that miR-182, miR-143, miR-145, miR-146a, miR-150, and miR-155 were dysregulated in sepsis patients. miR-146a downregulation correlated with increased IL-6 expression and monocyte proliferation. Bioinformatics analysis uncovered the immunological associations of dysregulated miRNAs with clinical disease. The current study demonstrates that miRNA dysregulation correlates with clinical manifestations and inflammation, and therefore remains a potential therapeutic target against sepsis.

Tumor cell-expressed SerpinB2 is present on microparticles and inhibits metastasis

Expression of SerpinB2 (plasminogen activator inhibitor type 2/PAI-2) by certain cancers is associated with a favorable prognosis. Although tumor-associated host tissues can express SerpinB2, no significant differences in the growth of a panel of different tumors in SerpinB2(-/-) and SerpinB2(+/+) mice were observed. SerpinB2 expression by cancer cells (via lentiviral transduction) also had no significant effect on the growth of panel of mouse and human tumor lines in vivo or in vitro. SerpinB2 expression by cancer cells did, however, significantly reduce the number of metastases in a B16 metastasis model. SerpinB2-expressing B16 cells also showed reduced migration and increased length of invadopodia-like structures, supporting the classical view that that tumor-derived SerpinB2 is inhibiting extracellular urokinase. Importantly, although SerpinB2 is usually poorly secreted, we found that SerpinB2 effectively reaches the extracellular milieu on the surface of 0.5-1 μm microparticles (MPs), where it was able to inhibit urokinase. We also provide evidence that annexins mediate the binding of SerpinB2 to phosphatidylserine, a lipid characteristically exposed on the surface of MPs. The presence of SerpinB2 on the surface of MPs provides a physiological mechanism whereby cancer cell SerpinB2 can reach the extracellular milieu and access urokinase plasminogen activator (uPA). This may then lead to inhibition of metastasis and a favorable prognosis.

TLR-induced PAI-2 expression suppresses IL-1β processing via increasing autophagy and NLRP3 degradation

The NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome, a multiprotein complex, triggers caspase-1 activation and maturation of the proinflammatory cytokines IL-1β and IL-18 upon sensing a wide range of pathogen- and damage-associated molecules. Dysregulation of NLRP3 inflammasome activity contributes to the pathogenesis of many diseases, but its regulation remains poorly defined. Here we show that depletion of plasminogen activator inhibitor type 2 (PAI-2), a serine protease inhibitor, resulted in NLRP3- and ASC (apoptosis-associated Speck-like protein containing a C-terminal caspase recruitment domain)-dependent caspase-1 activation and IL-1β secretion in macrophages upon Toll-like receptor 2 (TLR2) and TLR4 engagement. TLR2 or TLR4 agonist induced PAI-2 expression, which subsequently stabilized the autophagic protein Beclin 1 to promote autophagy, resulting in decreases in mitochondrial reactive oxygen species, NLRP3 protein level, and pro-IL-1β processing. Likewise, overexpressing Beclin 1 in PAI-2-deficient cells rescued the suppression of NLRP3 activation in response to LPS. Together, our data identify a tier of TLR signaling in controlling NLRP3 inflammasome activation and reveal a cell-autonomous mechanism which inversely regulates TLR- or Escherichia coli-induced mitochondrial dysfunction, oxidative stress, and IL-1β-driven inflammation.

Global Identification of EVI1 Target Genes in Acute Myeloid Leukemia

The ecotropic virus integration site 1 (EVI1) transcription factor is associated with human myeloid malignancy of poor prognosis and is overexpressed in 8-10% of adult AML and strikingly up to 27% of pediatric MLL-rearranged leukemias. For the first time, we report comprehensive genomewide EVI1 binding and whole transcriptome gene deregulation in leukemic cells using a combination of ChIP-Seq and RNA-Seq expression profiling. We found disruption of terminal myeloid differentiation and cell cycle regulation to be prominent in EVI-induced leukemogenesis. Specifically, we identified EVI1 directly binds to and downregulates the master myeloid differentiation gene Cebpe and several of its downstream gene targets critical for terminal myeloid differentiation. We also found EVI1 binds to and downregulates Serpinb2 as well as numerous genes involved in the Jak-Stat signaling pathway. Finally, we identified decreased expression of several ATP-dependent P2X purinoreceptors genes involved in apoptosis mechanisms. These findings provide a foundation for future study of potential therapeutic gene targets for EVI1-induced leukemia.

The transcription factor C/EBP-β mediates constitutive and LPS-inducible transcription of murine SerpinB2

SerpinB2 or plasminogen activator inhibitor type 2 (PAI-2) is highly induced in macrophages in response to inflammatory stimuli and is linked to the modulation of innate immunity, macrophage survival, and inhibition of plasminogen activators. Lipopolysaccharide (LPS), a potent bacterial endotoxin, can induce SerpinB2 expression via the toll-like receptor 4 (TLR4) by ∼1000-fold over a period of 24 hrs in murine macrophages. To map the LPS-regulated SerpinB2 promoter regions, we transfected reporter constructs driven by the ∼5 kb 5'-flanking region of the murine SerpinB2 gene and several deletion mutants into murine macrophages. In addition, we compared the DNA sequence of the murine 5′ flanking sequence with the sequence of the human gene for homologous functional regulatory elements and identified several regulatory cis-acting elements in the human SERPINB2 promoter conserved in the mouse. Mutation analyses revealed that a CCAAT enhancer binding (C/EBP) element, a cyclic AMP response element (CRE) and two activator protein 1 (AP-1) response elements in the murine SerpinB2 proximal promoter are essential for optimal LPS-inducibility. Electrophoretic mobility shift (EMSA) and chromatin immunoprecipitation (ChIP) assays demonstrated that LPS induces the formation of C/EBP-β containing complexes with the SerpinB2 promoter. Importantly, both constitutive and LPS-induced SerpinB2 expression was severely abrogated in C/EBP-β-null mouse embryonic fibroblasts (MEFs) and primary C/EBP-β-deficient peritoneal macrophages. Together, these data provide new insight into C/EBP-β-dependent regulation of inflammation-associated SerpinB2 expression.

Variant screening of the serum amyloid A1 gene and functional study of the p.Gly90Asp variant for its role in atherosclerosis

OBJECTIVES

Serum amyloid A1 (SAA1) is a major acute-phase protein that is increasingly used as a reliable predictor of coronary artery disease (CAD). In this study we aim to screen the SAAI promoter and exons for genetic variants and to determine their association with CAD. In addition, we also carried out functional study on a variant of p.Gly90Asp encoded by the SAA1 gene.

METHODS

Variant screening of SAA1 was performed using high resolution melting (HRM) analysis. Genetic association of p.Gly90Asp with CAD was determined in 800 CAD patients and 773 Chinese control subjects. Functional study of p.Gly90Asp was carried out using THP-1-derived macrophages and HL-60 promyelocytic leukemia cells.

RESULTS

A total of 6 SNPs were identified, of which 2 were found to be novel (c.-913G > A and c.92-5T > G). The rare allele of p.Gly90Asp has a lower frequency of 0.013 in the CAD patients although this is not statistically significant. Functional studies of p.Gly90Asp revealed that the variant has decreased upregulation of key cytokines such as IL-8, MCP-1 and TNF-α as well as SERPINB2.

CONCLUSIONS

We found the variant p.Gly90Asp SAA1 protein eliciting significantly reduced inflammatory responses in macrophages through a reduction in the secretion of inflammatory cytokines. Despite strong functional effects, the minor allele frequency is too low in the population to attain statistical significance difference between cases and controls.

Natural and engineered plasmin inhibitors: applications and design strategies

The serine protease plasmin is ubiquitously expressed throughout the human body in the form of the zymogen plasminogen. Conversion to active plasmin occurs through enzymatic cleavage by plasminogen activators. The plasminogen activator/plasmin system has a well-established function in the removal of intravascular fibrin deposition through fibrinolysis and the inhibition of plasmin activity; this has found widespread clinical use in reducing perioperative bleeding. Increasing evidence also suggests diverse, although currently less defined, roles for plasmin in a number of physiological and pathological processes relating to extracellular matrix degradation, cell migration and tissue remodelling. In particular, dysregulation of plasmin has been linked to cancer invasion/metastasis and various chronic inflammatory conditions; this has prompted efforts to develop inhibitors of this protease. Although a number of plasmin inhibitors exist, they commonly suffer from poor potency and/or specificity of inhibition that either results in reduced efficacy or prevents clinical use. Consequently, there is a need for further development of high-affinity plasmin inhibitors that maintain selectivity over other serine proteases. This review summarises clearly defined and potential applications for plasmin inhibition. The properties of naturally occurring and engineered plasmin inhibitors are discussed in the context of current knowledge regarding plasmin structure, specificity and function. This includes design strategies to obtain the potency and specificity of inhibition in addition to controlled temporal and spatial distribution tailored for the intended use.

The urokinase system in the pathogenesis of atherosclerosis

Atherogenesis refers to the development of atheromatous plaques in the inner lining of the arteries. These atherosclerotic lesions are characterized by accumulation of monocyte-derived macrophage-foam cells loaded with cholesterol, which eventually undergo apoptotic death, leading finally to formation of the necrotic core of the plaque. Atheroma formation also involves the recruitment of smooth muscle cells (SMC) from the media into the intima, where they proliferate and form the neointima in a process called "remodeling". Cells in the advanced atherosclerotic plaques express high levels of the serine protease urokinase-type plasminogen activator (uPA) and its receptor (uPAR). uPA is a multi-functional multi-domain protein that is not only a regulator of fibrinolysis, but it is also associated with several acute and chronic pathologic conditions. uPA mediate the extracellular matrix (ECM) degradation, and plays a pivotal role in cell adhesion, migration and proliferation, during tissue remodeling. On cell surface uPA binds to the high affinity urokinase receptor, providing a strictly localized proteolysis of ECM proteins. The uPA/uPAR complex also activates intracellular signaling, thus regulating cellular function. An imbalance in the uPA/uPAR system leads to dis-orders in tissue structure and function. This review summarizes recent progress in understanding the role and mechanisms of the uPA/uPAR system in atherogenesis.

Association of plasminogen activator inhibitor type 2 (PAI-2) with proteasome within endothelial cells activated with inflammatory stimuli

Quiescent endothelial cells contain low concentrations of plasminogen activator inhibitor type 2 (PAI-2). However, its synthesis can be rapidly stimulated by a variety of inflammatory mediators. In this study, we provide evidence that PAI-2 interacts with proteasome and affects its activity in endothelial cells. To ensure that the PAI-2·proteasome complex is formed in vivo, both proteins were coimmunoprecipitated from endothelial cells and identified with specific antibodies. The specificity of this interaction was evidenced after (a) transfection of HeLa cells with pCMV-PAI-2 and coimmunoprecipitation of both proteins with anti-PAI-2 antibodies and (b) silencing of the PAI-2 gene using specific small interfering RNA (siRNA). Subsequently, cellular distribution of the PAI-2·proteasome complexes was established by immunogold staining and electron microscopy analyses. As judged by confocal microscopy, both proteins appeared in a diffuse cytosolic pattern, but they also could be found in a dense perinuclear and nuclear location. PAI-2 was not polyubiquitinated, suggesting that it bound to proteasome not as the substrate but rather as its inhibitor. Consistently, increased PAI-2 expression (a) abrogated degradation of degron analyzed after cotransfection of HeLa cells with pCMV-PAI-2 and pd2EGFP-N1, (b) prevented degradation of p53, as evidenced both by confocal microscopy and Western immunoblotting, and (c) inhibited proteasome cleavage of specific fluorogenic substrate. This suggests that PAI-2, in endothelial cells induced with inflammatory stimuli, can inhibit proteasome and thus tilt the balance favoring proapoptotic signaling.

Plasminogen activator inhibitor type 2: still an enigmatic serpin but a model for gene regulation

Plasminogen activator inhibitor type-2 (PAI-2; SERPINB2) is an atypical member of the Ov-serpin family of serine protease inhibitors. While it is an undisputed inhibitor of urokinase and tissue-type plasminogen activator in the extracellular space and on the cell surface, the weight of circumstantial evidence suggests that PAI-2 also fulfills an intracellular role which is independent of plasminogen activator inhibition and indeed may not even involve protease inhibition at all. More and more data continue to implicate a role for PAI-2 in many settings, the most recent associating it as a modulator of the innate immune response. Further to the debates concerning its physiological role, there are few genes, if any, that display the regulation profile of the PAI-2 gene: PAI-2 protein and mRNA levels can be induced in the order of, not hundred-, but thousand-folds in a process that is controlled at many levels including gene transcription and mRNA stability while an epigenetic component is also likely. The ability of some cells, including monocytes, fibroblasts, and neurons to have the capacity to increase PAI-2 synthesis to such high levels is intriguing enough. So why do these cells have the capacity to synthesize so much of this protein? While tantalizing clues continue to be revealed to the field, an understanding of how this gene is regulated so profoundly has provided insights into the broader mechanics of gene expression and regulation.

Proteome changes in human monocytes upon interaction with calcium oxalate monohydrate crystals

Monocytic infiltration in renal interstitium is commonly found surrounding the site of calcium oxalate (CaOx) crystal deposition in the kidney. Monocytes are supposed to eliminate the deposited crystals. However, effects of CaOx crystals on the infiltrating monocytes remain unknown. Therefore, this study investigated the altered cellular proteome of human monocytes in response to interaction with CaOx monohydrate (COM) crystals. After 24-h culture with or without 100 microg/mL COM crystals, U937 cells were harvested and subjected to 2-DE analysis with Deep Purple fluorescence staining (n = 5 gels/group; each was derived from independent culture). Spot matching, quantitative intensity analysis, and statistics revealed 22 differentially expressed proteins (9 up-regulated and 13 down-regulated proteins), which were successfully identified by Q-TOF MS and MS/MS analyses, including those involved in cell cycle, cellular structure, carbohydrate metabolism, lipid metabolism, mRNA processing, and protein synthesis, stabilization, and degradation. Randomly selected changes [up-regulated ALG-2 interacting protein 1 (Alix), elongation factor-2 (EF-2), and down-regulated beta-actin] were confirmed by Western blot analysis. Our data may help to understand how monocytes interact with COM crystals. These processes are proposed to cause subsequent inflammatory response in kidney stone disease through oxidative stress pathway(s).

Human papilloma virus transformed CaSki cells constitutively express high levels of functional SerpinB2

Many malignant tissues, including human papilloma virus (HPV)-associated cancers, express SerpinB2, also known as plasminogen activator inhibitor type-2 (PAI-2). Whether SerpinB2 is expressed by the HPV-transformed cancer cells, and if so, whether SerpinB2 is mutated or behaves aberrantly remains unclear. Here we show that HPV-transformed CaSki cells express high levels of constitutive wild-type SerpinB2, with cellular distribution, glycosylation, secretion, cleavage, induction and urokinase binding similar to that reported for primary cells. Neutralization of secreted SerpinB2 failed to affect CaSki cell migration or growth. Lentivirus-based over-expression of SerpinB2 also had no effect on growth, and we were unable to confirm a role for SerpinB2 in binding or regulating expression of the retinoblastoma protein. CaSki cells thus emerge as a useful tool for studying SerpinB2, with the physiological function of SerpinB2 expression by tumor cells remaining controversial. Using CaSki cells as a source of endogenous SerpinB2, we confirmed that SerpinB2 efficiently binds the proteasomal subunit member β1.

The plasminogen activator inhibitor 2 transcript is destabilized via a multi-component 3' UTR localized adenylate and uridylate-rich instability element in an analogous manner to cytokines and oncogenes

Plasminogen activator inhibitor type 2 (PAI-2; SERPINB2) is a highly-regulated gene that is subject to both transcriptional and post-transcriptional control. For the latter case, inherent PAI-2 mRNA instability was previously shown to require a nonameric adenylate-uridylate element in the 3' UTR. However, mutation of this site was only partially effective at restoring complete mRNA stabilization. In the present study, we have identified additional regulatory motifs within the 3' UTR that cooperate with the nonameric adenylate-uridylate element to promote mRNA destabilization. These elements are located within a 74 nucleotide U-rich stretch (58%) of the 3' UTR that flanks the nonameric motif; deletion or substitution of this entire region results in complete mRNA stabilization. These new elements are conserved between species and optimize the destabilizing capacity with the nonameric element to ensure complete mRNA instability in a manner analogous to some class I and II adenylate-uridylate elements present in transcripts encoding oncogenes and cytokines. Hence, post-transcriptional regulation of the PAI-2 mRNA transcript involves an interaction between closely spaced adenylate-uridylate elements in a manner analogous to the post-transcriptional regulation of oncogenes and cytokines.

A physiological function of inflammation-associated SerpinB2 is regulation of adaptive immunity

SerpinB2 (plasminogen activator inhibitor-2) is widely described as an inhibitor of urokinase plasminogen activator; however, SerpinB2(-/-) mice show no detectable increase in urokinase plasminogen activator activity. In this study, we describe an unexpected immune phenotype in SerpinB2(-/-) mice. After immunization with OVA in CFA, SerpinB2(-/-) mice made approximately 6-fold more IgG2c and generated approximately 2.5-fold more OVA-specific IFN-gamma-secreting T cells than SerpinB2(+/+) littermate controls. In SerpinB2(+/+) mice, high inducible SerpinB2 expression was seen at the injection site and in macrophages low levels in draining lymph nodes and conventional dendritic cells, and no expression was seen in plasmacytoid dendritic, B, T, or NK cells. SerpinB2(-/-) macrophages promoted greater IFN-gamma secretion from wild-type T cells in vivo and in vitro and, when stimulated with anti-CD40/IFN-gamma or cultured with wild-type T cells in vitro, secreted more Th1-promoting cytokines than macrophages from littermate controls. Draining lymph node SerpinB2(-/-) myeloid APCs similarly secreted more Th1-promoting cytokines when cocultured with wild-type T cells. Regulation of Th1 responses thus appears to be a physiological function of inflammation-associated SerpinB2; an observation that may shed light on human inflammatory diseases like pre-eclampsia, lupus, asthma, scleroderma, and periodontitis, which are associated with SerpinB2 polymorphisms or dysregulated SerpinB2 expression.

FES kinases are required for oncogenic FLT3 signaling

The closely related non-receptor tyrosine kinases FEline Sarcoma (FES) and FEs Related (FER) are activated by cell surface receptors in hematopoietic cells. Despite the early description of oncogenic viral forms of fes, v-fes, and v-fps, the implication of FES and FER in human pathology is not known. We have recently shown that FES but not FER is necessary for oncogenic KIT receptor signaling. Here, we report that both FES and FER kinases are activated in primary acute myeloid leukemia (AML) blasts and in AML cell lines. FES and FER activation is dependent on FLT3 in cell lines harboring constitutively active FLT3 mutants. Moreover, both FES and FER proteins are critical for FLT3-internal tandem duplication (ITD) signaling and for cell proliferation in relevant AML cell lines. FER is required for cell cycle transitions, whereas FES seems necessary for cell survival. We concluded that FES and FER kinases mediate essential non-redundant functions downstream of FLT3-ITD.

Genotype Ser413/Ser ofPAI‐2 polymorphism Ser413/Cys is associated with anti‐phospholipid syndrome and systemic lupus erythematosus in a familial case: comparison with healthy controls

BACKGROUND

We describe a family with a 7-year-old proband case diagnosed with systemic lupus erythematosus (SLE) plus secondary anti-phospholipid syndrome (APS) as well as two affected paternal aunts. We compared the frequency of these polymorphisms with healthy controls.

OBJECTIVES

To evaluate the mode of inheritance in this familial case of APS and SLE and the possible association of plasminogen activator inhibitor-1 (PAI-1) -675 4G/5G and PAI-2 Ser(413)/Cys polymorphisms. To compare the genotype frequency of these polymorphisms with the results found in a Mexican Mestizo population.

METHODS

PAI-1 -675 4G/5G and PAI-2 Ser(413)/Cys were determined by the polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) technique using Bsl I and Mwo I on four generations of the family studied. PAI-2 Ser(413)/Cys polymorphism was also determined in 50 healthy individuals of Mexican Mestizo origin.

RESULTS

The family pedigree demonstrated that this family did not follow a Mendelian inheritance pattern. When the PAI-2 Ser(413)/Cys polymorphism was examined, we found that 60% (3/5) of the relatives homozygous to Ser(413)/Ser were affected with SLE and/or APS (p = 0.027). The proband case was 4G/5G genotype for the PAI-1 -675 4G/5G polymorphism. No differences between healthy controls of the Mexican Mestizo population and the family studied for the PAI-2 Ser(413)/Cys polymorphism or PAI-1 -675 4G/5G polymorphisms were found.

CONCLUSIONS

Our data indicate that this family did not follow the Mendelian inheritance pattern. The Ser(413)/Ser genotype demonstrated in 60% of the affected members (3/5) of this family might increase the risk for autoimmune syndromes such as APS or SLE.

Identification of molecular distinctions between normal breast-associated fibroblasts and breast cancer-associated fibroblasts

Stromal fibroblasts influence the behavior of breast epithelial cells. Fibroblasts derived from normal breast (NAF) inhibit epithelial growth, whereas fibroblasts from breast carcinomas (CAF) have less growth inhibitory capacity and can promote epithelial growth. We sought to identify molecules that are differentially expressed in NAF versus CAF and potentially responsible for their different growth regulatory abilities. To determine the contribution of soluble molecules to fibroblast–epithelial interactions, NAF were grown in 3D, transwell or direct contact co-cultures with MCF10AT epithelial cells. NAF suppressed proliferation of MCF10AT in both direct contact and transwell co-cultures, but this suppression was significantly greater in direct co-cultures, indicating involvement of both soluble and contact factors. Gene expression profiling of early passage fibroblast cultures identified 420 genes that were differentially expressed in NAF versus CAF. Of the eight genes selected for validation by real-time PCR, FIBULIN 1, was overexpressed in NAF, and DICKKOPF 1, NEUREGULIN 1, PLASMINOGEN ACTIVATOR INHIBITOR 2, and TISSUE PLASMINOGEN ACTIVATOR were overexpressed in CAF. A higher expression of FIBULIN 1 in normal- than cancer-associated fibroblastic stroma was confirmed by immunohistochemistry of breast tissues. Among breast cancers, stromal expression of Fibulin 1 protein was higher in estrogen receptor α-positive cancers and low stromal expression of Fibulin 1 correlated with a higher proliferation of cancer epithelial cells. In conclusion, expression profiling of NAF and CAF cultures identified many genes with potential relevance to fibroblast–epithelial interactions in breast cancer. Furthermore, these early passage fibroblast cultures can be representative of gene expression in stromal fibroblasts in vivo.

Estrogen-induced uterine abnormalities in TIMP-1 deficient mice are associated with elevated plasmin activity and reduced expression of the novel uterine plasmin protease inhibitor serpinb7

Tissue inhibitor of metalloproteinase-1 (TIMP-1) is a multifunctional protein capable of regulating a variety of biological processes in a wide array of tissue and cell types. We have previously demonstrated that TIMP-1 deficient mice exhibit alterations in normal uterine morphology and physiology. Most notably, absence of TIMP-1 is associated with an altered uterine phenotype characterized by profound branching of the uterine lumen and altered adenogenesis. To begin to assess the mechanism by which TIMP-1 may control these uterine events, we utilized steroid-treated ovariectomized wild-type and TIMP-1 null mice exposed to estrogen for 72 hr. Administration of estrogen to TIMP-1 deficient mice resulted in development of an abnormal uterine histo-architecture characterized by increased endometrial gland density, luminal epithelial cell height, and abnormal lumen structure. To determine the mediators which may contribute to the abnormal uterine morphology in the TIMP-1 deficient mice, cDNA microarray analysis was performed. Analysis revealed that expression of two plasmin inhibitors (serpbinb2 and serbinb7) was significantly reduced in the TIMP-1 null mice. Associated with the reduction in expression of these inhibitors was a significant increase in plasmin activity. Localization of the novel uterine serpinb7 revealed that expression was confined to the luminal and glandular epithelial cells. Further, expression of uterine serpinb7 was decreased by estrogen and showed an inverse relationship with plasmin activity. We conclude from these studies that in addition to controlling MMP activity, TIMP-1 may also control activity of serine proteases through modulation of serine protease inhibitors such as serpinb7.

Serpins in T cell immunity

Serine protease inhibitors (serpins) are a family of proteins that are important in the regulation of several biological processes. This mainly involves the inhibition of serine proteases, although some serpins inhibit a different class of proteases or even function without inhibitory activity. In contrast to other protease inhibitor families, serpins inhibit their target proteases by a specific mechanism, which depends on a change in conformation. This review primarily focuses on one subgroup of serpins--ovalbumin (ov)-serpins. Different than most members of the family, this group of serpins lacks secretion signal sequences and therefore, mainly functions intracellularly. In addition to expression in most normal tissues, ov-serpins can be found in multiple different cells of the immune system. Interestingly, expression of ov-serpins in these cells is tightly regulated, indicating a role for these serpins in the regulation of immune responses. The role of serpins in the immune response will be the topic of this review.

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.

Immunomodulatory effects of plasminogen activators on hepatic fibrogenesis

Tissue-type plasminogen activators (tPA) and urokinase-type plasminogen activators (uPA) are involved in liver repair. We examined the potential immunomodulatory actions of uPA, tPA and uPA-receptor (uPAR) in carbon-tetrachloride-induced hepatic fibrosis in wild-type (WT), tPA-/-, uPA-/- and uPAR-/- mice. Carbon-tetrachloride treatment increased fibrosis in four groups but significantly less in three knock-out models. Serum cytokines and intrahepatic T cells elevated significantly following fibrosis process in WT animals but not in the knock-out groups. In culture, uPA increased lymphocyte proliferation significantly in WT and uPA-/- but not uPAR-/- animals. Following uPA exposure in vivo, there was CD8 predominance. To isolate uPA's effect on lymphocytes, WT mice were irradiated sublethally and then reconstituted with WT or uPA-/- lymphocytes. In these animals fibrosis was decreased and T cells were reduced in the uPA-/- recipients. Based on these data we postulate that plasminogen activators affect fibrosis in part by liver-specific activation of CD8 subsets that govern the fibrogenic activity of hepatic stellate cells.

A role for caspases in the differentiation of erythroid cells and macrophages

Several cysteine proteases of the caspase family play a central role in many forms of cell death by apoptosis. Other enzymes of the family are involved in cytokine maturation along inflammatory response. In recent years, several caspases involved in cell death were shown to play a role in other cellular processes such as proliferation and differentiation. In the present review, we summarize the current knowledge of the role of caspases in the differentiation of erythroid cells and macrophages. Based on these two examples, we show that the nature of involved enzymes, the pathways leading to their activation in response to specific growth factors, and the specificity of the target proteins that are cleaved by the activated enzymes strongly differ from one cell type to another. Deregulation of these pathways is thought to play a role in the pathophysiology of low-grade myelodysplastic syndromes, characterized by excessive activation of caspases and erythroid precursor apoptosis, and that of chronic myelomonocytic leukemia, characterized by a defective activation of caspases in monocytes exposed to M-CSF, which blocks their differentiation.

Fibrinolysis, inflammation, and regulation of the plasminogen activating system

The maintenance of a given physiological process demands a coordinated and spatially regulated pattern of gene regulation. This applies to genes encoding components of enzyme cascades, including those of the plasminogen activating system. This family of proteases is vital to fibrinolysis and dysregulation of the expression pattern of one or more of these proteins in response to inflammatory events can impact on hemostasis. Gene regulation occurs on many levels, and it is apparent that the genes encoding the plasminogen activator (fibrinolytic) proteins are subject to both direct transcriptional control and significant post-transcriptional mechanisms. It is now clear that perturbation of these genes at either of these levels can dramatically alter expression levels and have a direct impact on the host's response to a variety of physiological and pharmacological challenges. Inflammatory processes are well known to impact on the fibrinolytic system and to promote thrombosis, cancer and diabetes. This review discusses how inflammatory and other signals affect the transcriptional and post-transcriptional expression patterns of this system, and how this modulates fibrinolysis in vivo.

SerpinB2 Is an Inducible Host Factor Involved in Enhancing HIV-1 Transcription and Replication

The serine protease inhibitor SerpinB2 (plasminogen activator inhibitor-2) is a major product of activated monocytes and macrophages and is substantially induced during most inflammatory processes. Distinct from its widely described extracellular role as an inhibitor of urokinase plasminogen activator, SerpinB2 has recently been shown to have an intracellular role as a retinoblastoma protein (Rb)-binding protein that inhibits Rb degradation. Here we show that HIV-1 infection and gp120 treatment of human peripheral blood mononuclear cells resulted in induction of SerpinB2. Furthermore, SerpinB2 expression in THP-1 monocyte/macrophage, Jurkat T, and HeLa cell lines increased replication of HIV-1 and enhanced transcription from the HIV-1 long terminal repeat (LTR) promoter by 3-10-fold. Increased HIV-1 gene expression and transcription was also observed in activated macrophages from SerpinB2+/+ mice compared with macrophages from SerpinB2-/- mice. The SerpinB2-mediated elevation of Rb protein levels appeared to be responsible for enhancing transcription from the core promoter region of the LTR by relieving HDM2-mediated inhibition of Sp1 and/or by increasing the Sp1/Sp3 expression ratios. This is the first report associating HIV-1 replication with SerpinB2 expression and illustrates that SerpinB2 is a potentially important inducible host factor that significantly promotes HIV-1 replication.

Altered hemostatic balance and endothelial activation in pregnant women with familial hypercholesterolemia

INTRODUCTION

Patients with familial hypercholesterolemia (FH) are prone to premature cardiovascular disease. During pregnancy plasma lipids reach higher absolute values in FH than in healthy women. Pregnancy is associated with activation of coagulation and possibly also of vascular endothelium, which might further increase the risk of cardiovascular disease in FH. However, whether hemostatic and endothelial activation markers are increased in pregnant FH women compared with non-FH pregnancies, is unknown.

MATERIALS AND METHODS

Activation markers of hemostasis and endothelium were analyzed in blood samples collected prospectively from 22 heterozygous FH women during pregnancy and compared with those of a reference group of 149 healthy, pregnant women.

RESULTS

A procoagulant pattern was detected in both groups, but was more evident among FH women at least partly due to their enhanced thrombin generation, and because tissue factor pathway inhibitor type 1 increased in the reference group only. Furthermore, plasminogen activator inhibitor type 2 antigen increased more in FH than in the reference group. Whereas C-reactive protein, intercellular adhesion marker-1 and E-selectin did not change appreciably, vascular endothelial cell adhesion molecule 1 rose markedly in FH.

CONCLUSION

Increased lipid levels as well as a net procoagulant activity and an enhanced endothelial activation possibly confer additional risks of cardiovascular disease among pregnant FH women.

Identification of proteins cleaved downstream of caspase activation in monocytes undergoing macrophage differentiation

We have shown previously that caspases were specifically involved in the differentiation of peripheral blood monocytes into macrophages while not required for monocyte differentiation into dendritic cells. To identify caspase targets in monocytes undergoing macrophagic differentiation, we used the human monocytic leukemic cell line U937, whose macrophagic differentiation induced by exposure to 12-O-tetradecanoylphorbol 13-acetate (TPA) can be prevented by expression of the baculovirus caspase-inhibitory protein p35. A comparative two-dimensional gel proteomic analysis of empty vector- and p35-transfected cells after 12 h of exposure to 20 nm TPA, followed by mass spectrometry analysis, identified 38 differentially expressed proteins. Those overexpressed in p35-expressing cells (n = 16) were all full-length, whereas half of those overexpressed in control cells (n = 22) were N- or C-terminal cleavage fragments. The cleavage or degradation of seven of these proteins was confirmed in peripheral blood monocytes undergoing macrophage colony-stimulating factor-induced macrophagic differentiation. In U937 cells exposed to TPA, these proteolytic events can be inhibited by expression of a caspase-8 dominant negative mutant or the cowpox virus CrmA caspase inhibitor. These cleavages provide new insights to analyze the role of caspases in this specific differentiation program.

Genetic Dissection of Vasculitis, Myeloperoxidase-Specific Antineutrophil Cytoplasmic Autoantibody Production, and Related Traits in Spontaneous Crescentic Glomerulonephritis-Forming/Kinjoh Mice

The spontaneous crescentic glomerulonephritis-forming/Kinjoh (SCG/Kj) mouse is a model of human crescentic glomerulonephritis and vasculitis associated with the production of the myeloperoxidase (MPO)-specific antineutrophil cytoplasmic autoantibody (MPO-ANCA). Although the disease is mediated initially by mutation of the Fas gene (lpr), SCG/Kj mice also have non-Fas predisposing genetic factors. To define these factors, genome-wide quantitative trait locus (QTL) mapping was performed on female (B(6)x SCG/Kj) F(2) intercross mice. Fourteen non-Fas QTLs were identified. QTLs of glomerulonephritis were located on chromosomes 1, 10, 13, 16, and 17, vasculitis on chromosomes 1 and 17, splenomegaly on chromosome 1, hypergammaglobulinemia on chromosomes 1, 2, 4, 6, 7, 11, 13, and 17, antinuclear Ab on chromosomes 1, 8, 10, and 12, and MPO-ANCA production on chromosomes 1 and 10. Significant QTLs derived from SCG/Kj on chromosomes 1, 2, 7, and 13 were designated Scg-1 to Scg-5, respectively, and those derived from B(6) on chromosomes 4, 6, 17, and 10 were designated Sxb-1 to Sxb-4, respectively. Two loci linked to MPO-ANCA production on chromosomes 1 and 10 were designated Man-1 and Man-2 (for MPO-ANCA), respectively. Although both Scg-1 and Scg-2 were on chromosome 1 and shared several functions, it was of interest that aberrant MPO-ANCA production was exclusively controlled by Man-1, the centromeric half region of the Scg-2 chromosomal segment. We also examined the epistatic effects between the lpr mutation and non-Fas susceptibility genes. QTLs are discussed in relation to previously described loci, with emphasis on their candidate genes.

Cytoplasmic and nuclear interaction between Rb family proteins and PAI-2: a physiological crosstalk in human corneal and conjunctival epithelial cells

Extracellular plasminogen activator inhibitor type-2 (PAI-2) is a potent inhibitor of urokinase-type plasminogen activator (u-PA) and also acts as a multifunctional protein. However, the biological activity of intracellular PAI-2, as well as its intracellular targets, until now remain an enigma. Here, we show that pRb2/p130 and Rb1/p105, but not p107, interact with PAI-2 in both the cytoplasm and nucleus of normal primary human corneal and conjunctival epithelial cells. We provided the first in vivo evidence that a specific fragment of the PAI-2 promoter is bound simultaneously by pRb2/ p130, PAI-2, E2F5, histone deacetylase 1 (HDAC1), DNA methyltransferase 1 (DNMT1), and histone methyltransferase (SUV39H1), in normal primary human corneal epithelial cells, and by pRb2/p130, PAI-2, E2F5, HDAC1, and DNMT1, in normal primary human conjunctiva epithelial cells. Our results strongly indicate a physiological interaction between pRb family members and PAI-2, suggesting the hypothesis that pRb2/p130 and PAI-2 may cooperate in modulating PAI-2 gene expression by chromatin remodeling, in normal corneal and conjunctival cells.

The undecided serpin

Plasminogen activator inhibitor type-2 (PAI-2) is a nonconventional serine protease inhibitor (serpin) with unique and tantalizing properties that is generally considered to be an authentic and physiological inhibitor of urokinase. However, the fact that only a small percentage of PAI-2 is secreted has been a long-standing argument for alternative roles for this serpin. Indeed, PAI-2 has been shown to have a number of intracellular roles: it can alter gene expression, influence the rate of cell proliferation and differentiation, and inhibit apoptosis in a manner independent of urokinase inhibition. Despite these recent advances in defining the intracellular function of PAI-2, it still remains one of the most mysterious and enigmatic members of the serpin superfamily.

Silencing of integrated human papillomavirus type 18 oncogene transcription in cells expressing SerpinB2

The serine protease inhibitor SerpinB2 (PAI-2), a major product of differentiating squamous epithelial cells, has recently been shown to bind and protect the retinoblastoma protein (Rb) from degradation. In human papillomavirus type 18 (HPV-18)-transformed epithelial cells the expression of the E6 and E7 oncoproteins is controlled by the HPV-18 upstream regulatory region (URR). Here we illustrate that PAI-2 expression in the HPV-18-transformed cervical carcinoma line HeLa resulted in the restoration of Rb expression, which led to the functional silencing of transcription from the HPV-18 URR. This caused loss of E7 protein expression and restoration of multiple E6- and E7-targeted host proteins, including p53, c-Myc, and c-Jun. Rb expression emerged as sufficient for the transcriptional repression of the URR, with repression mediated via the C/EBPbeta-YY1 binding site (URR 7709 to 7719). In contrast to HeLa cells, where the C/EBPbeta-YY1 dimer binds this site, in PAI-2- and/or Rb-expressing cells the site was occupied by the dominant-negative C/EBPbeta isoform liver-enriched transcriptional inhibitory protein (LIP). PAI-2 expression thus has a potent suppressive effect on HPV-18 oncogene transcription mediated by Rb and LIP, a finding with potential implications for prognosis and treatment of HPV-transformed lesions.

N-Ras–Induced Growth Suppression of Myeloid Cells Is Mediated by IRF-1

Activating mutations in ras oncogenes occur at high frequency in human malignancies and expression of activated ras in immortalized cells lines is generally transforming. However, somewhat paradoxically, ectopic expression of ras in some myeloid cell lines has been shown to induce growth suppression associated with up-regulation of the cyclin-dependent kinase inhibitor p21CIP1/WAF1 in a p16INK4a, p15INK4b, and p53 independent fashion. We have used cDNA array technology to compare the expression profile induced by activated N-ras (N-rasG13R) in growth-suppressed myeloid cells with that induced in myeloid cells, which are transformed by N-rasG13R. The expression profile induced in growth suppressed cells was consistent with differentiation and included the up-regulation of the transcription factor IFN regulatory factor-1 (IRF-1), a known transcriptional activator of p21CIP/WAF1 expression and a target of oncogenic mutations associated with myeloid leukemia. Antisense suppression of IRF-1 prevented N-rasG13R–associated growth arrest and up-regulation of p21CIP1/WAF1. These results define a novel tumor suppressive response to oncogenic signaling and provide a mechanistic link between growth suppression and differentiation in myeloid cells.

The plasmin system in airway remodeling

Recent studies suggest that the plasmin system plays an active role in tissue remodeling. Plasmin degrades the extracellular matrix (ECM), either directly removing glycoproteins from ECM or by activating matrix metalloproteinases (MMPs). PAI-1 blocking MMPs may prevent ECM degradation, but inhibiting fibrinolysis leads to fibrin accumulation and fibrosis. Components of the plasmin system including tissue plasminogen activator (t-PA), urokinase plasminogen activator (u-PA), and plasminogen activator inhibitors PAI-1 and PAI-2 are synthesised by airway cells, and inflammatory mediators affect their expression. The plasmin system, in turn, actively influences the production of inflammatory mediators and growth factors, extending pathological structural changes in the airway. Modulation of the plasmin system might be a new pharmacological strategy that could inhibit the development of airway remodeling.

Interrelationships between the fibrinolytic system and lipoproteins in the pathogenesis of coronary atherosclerosis

The fibrinolytic system is comprised of a series of serine proteases and serine protease inhibitors which are involved in the dissolution of fibrin in the vascular lumen, but also in the migration of cells and in the remodeling of the extracellular matrix of the vascular wall. The transcription, expression and degradation of the various fibrinolytic enzymes by cells in the vascular wall is influenced by lipoproteins and this interrelationship may play a significant role in the development of the atherosclerotic plaque: the transcription of plasminogen activator inhibitor-1 is influenced by very low-density lipoproteins, the expression of both tissue plasminogen activator and plasminogen activator inhibitor-1 is influenced by low-density lipoproteins and lipoprotein(a) (Lp(a)) and the internalization of the urokinase: plasminogen activator inhibitor-1 complex occurs via the low-density lipoprotein related protein. Several clinical studies have shown correlations between fibrinolytic parameters and lipoproteins in healthy populations and in patients with dyslipidemia, but the correlation between single plasma fibrinolytic enzymes and the severity of coronary atherosclerosis is less well documented. The reduction of plasma lipids with lipid-lowering drugs also affects the concentration of fibrinolytic enzymes, although this may also be due to direct effects of the drugs on the expression of the various fibrinolytic enzymes. The reduction of fibrinolytic and proteolytic activity in the atherosclerotic plaque by their lipid-lowering effect and by their direct action on the fibrinolytic system may be one of the mechanisms by which some lipid-lowering drugs achieve plaque stabilization.

Induction of plasminogen activator inhibitor-2 is associated with suppression of invasive activity in TPA-mediated differentiation of human prostate cancer cells

We previously reported that 12-O-tetra-decanoylphorbol-13-acetate (TPA) induces microglia-like differentiation and decreases malignancy in human prostate cancer TSU-Pr1 cells. To investigate the mechanism underlying differentiation and decrease of malignancy in TSU-Pr1 cells treated with TPA, we attempted to identify genes expressed differentially during the differentiation using differential display. We successfully detected plasminogen activator inhibitor type-2 (PAI-2) as one gene up-regulated by TPA treatment. The change in expression of PAI-2 by TPA was blocked by treatment with protein kinase C or mitogen-activated protein kinase inhibitors. We also found that secretion of PAI-2 protein was increased by TPA treatment. Moreover, we demonstrated that suppression of invasive activity of TSU-Pr1 cells by TPA treatment was blocked by co-treatment with anti-PAI-2 antibody. These results suggest that induction of PAI-2 is associated with suppression of invasive activity in TSU-Pr1 cells treated with TPA.