Plasminogen Receptors in Human Malignancies: Effects on Prognosis and Feasibility as Targets for Drug Development.

The major proteases that constitute the fibrinolysis system are tightly regulated. Protease inhibitors target plasmin, the protease responsible for fibrin degradation, and the proteases that convert plasminogen into plasmin, including tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA). A second mechanism by which fibrinolysis is regulated involves exosite interactions, which localize plasminogen and its activators to fibrin, extracellular matrix (ECM) proteins, and cell surfaces. Once plasmin is generated in association with cell surfaces, it may cleave transmembrane proteins, activate growth factors, release growth factors from ECM proteins, remodel ECM, activate metalloproteases, and trigger cell-signaling by cleaving receptors in the Proteaseactivated Receptor (PAR) family. These processes are all implicated in cancer. It is thus not surprising that a family of structurally diverse but functionally similar cell-surface proteins, called Plasminogen Receptors (PlgRs), which increase the catalytic efficiency of plasminogen activation, have received attention for their possible function in cancer and as targets for anticancer drug development. In this review, we consider four previously described PlgRs, including: α-enolase, annexin-A2, Plg-RKT, and cytokeratin-8, in human cancer. To compare the PlgRs, we mined transcriptome profiling data from The Cancer Genome Atlas (TCGA) and searched for correlations between PlgR expression and patient survival. In glioma, the expression of specific PlgRs correlates with tumor grade. In a number of malignancies, including glioblastoma and liver cancer, increased expression of α-enolase or annexin-A2 is associated with an unfavorable prognosis. Whether these correlations reflect the function of PlgRs as receptors for plasminogen or other activities is discussed.

Evidence for functional PAR-4 thrombin receptor expression in cardiac fibroblasts and its regulation by high glucose: PAR-4 in cardiac fibroblasts.

BACKGROUND: Thrombin promotes cardiac fibroblast proliferation and fibrosis via protease-activated receptor (PAR-1). PAR-4 is reportedly absent in cardiac fibroblasts. In smooth muscle cells, PAR-4 expression is also low but increases upon hyperglycemia and contributes to vascular remodelling in diabetic mice. We examined if PAR-4 is a glucose-responsive gene with remodelling-related functions in cardiac fibroblasts. METHODS AND RESULTS: Cardiac PAR-4 increased in mice with streptozotocin- or diabetogenic diet (DD)-induced diabetes. PAR-4 mRNA and protein were detectable in cardiac fibroblasts from chow-fed mice and increased in high (HG, 25mM) vs. low glucose (LG; 5.5mM) cultures. Conversely PAR-4 mRNA was higher in fibroblasts from DD-fed mice but reduced in LG cultures. Cardiac fibroblasts in HG culture responded more strongly to thrombin or PAR-4 activating peptide in terms of migration (wound-scratch assay), remodelling-associated gene expression (interleukin 6, alpha smooth muscle actin) and oxidative stress (dihydroethidium fluorescence). CONCLUSION: PAR-4 is expressed in mouse cardiac fibroblasts and is dynamically regulated by extracellular glucose in vitro and diabetes in vivo, thereby impacting on fibroblast functions relevant for cardiac remodelling. These findings add further evidence for the usefulness of the recently developed PAR-4 antagonists in clinical settings.

[Expressions of protease-activated receptors in human gingival fibroblasts and its functions in periodontitis].

OBJECTIVE: To investigate the expression types of protease-activated receptors(PAR) in human gingival fibroblasts(HGF) and the functions of PAR in periodontitis. METHODS: Primary HGF were cultured.Reverse transcription PCR(RT-PCR) was used to detect the expression of PAR in HGF. Recombinant gingipain R (rRgp) was applied to HGF. The change of PAR expression on the cell surface was analyzed by real-time quantitative RT-PCR, and enzyme-linked immunosorbent assay (ELISA) was used to detect the change of the interleukin (IL)-6 production from HGF. The results of RT-PCR and ELISA were statistically analyzed using the two independent samples t-test of SPSS10.0 software. RESULTS: HGF expressed PAR-1 and PAR-3. The expression of PAR-1 and PAR-3 changed after two rRgp treatment with HGF cells. The relative expression of PAR-1 was decreased from 1.04 ± 0.31 to 0.67 ± 0.11 and 0.31 ± 0.11. The relative expression of PAR-3 was decreased from 1.01 ± 0.44 to 0.79 ± 0.13 and 0.44 ± 0.12(P < 0.05). The level of IL-6 was increased after rRgp treatment for 8 h. The control group was (18.77 ± 4.09) µg/L, the rRgp treatment groups were (179.36 ± 15.81) and (320.56 ± 26.19) µg/L respectively. CONCLUSIONS: HGF expressed PAR-1 and PAR-3 and were involved in periodontal inflammation.

Valproate alters dopamine signaling in association with induction of Par-4 protein expression.

Chromatin remodeling through histone modifications has emerged as a key mechanism in the pathophysiology of psychiatric disorders. Valproate (VPA), a first-line medication for bipolar disorder, is known to have histone deacetylase (HDAC) inhibitor activity, but the relationship between its efficacy as a mood stabilizer and HDAC inhibitory activity is unclear. Here we provide evidence that prostate apoptosis response-4 (Par-4), an intracellular binding partner of dopamine D2 receptors (DRD2), plays a role in mediating the effectiveness of VPA. We found that chronic VPA treatment enhanced the expression of Par-4 in cultured neurons and adult mouse brains. This Par-4 induction phenomenon occurred at the transcriptional level and was correlated with an increase in histone H3 and H4 acetylation of the Par-4 promoter regions. Furthermore, chronic VPA treatment potentiated the suppression of the cAMP signaling cascade upon dopamine stimulation, which was blocked by sulpiride treatment. These results indicate that VPA potentiates DRD2 activity by enhancing Par-4 expression via a chromatin remodeling mechanism.

Expression of coagulation factors and their receptors in tumor tissue and coagulation factor upregulation in peripheral blood of patients with cerebral carcinoma metastases.

BACKGROUND: Patients with malignancies often suffer from thrombembolic events that complicate the course of cancer disease and reduce the patients' quality of life or shorten the survival time in severe cases. This phenomenon is also known for patients with primary or secondary brain tumors; but the reasons are not identified. METHODS: We performed a prospective case-controlled study of patients with brain metastases but without any active peripheral tumor site. Blood of patients was collected perioperatively and investigated for coagulation factor activities. Moreover, we analyzed the expression of coagulation factors and their receptors within the tumor material of brain metastases from clear-cell renal cell carcinomas and small-cell carcinomas of the lung. RESULTS: Here, we show that even patients without an active peripheral tumor disease that means without any tumor masses outside the central nervous system after anticancer treatment by surgery, radiation therapy, or chemotherapy but with symptomatic brain metastasis develop an increased systemic activation of multiple coagulation factors. The pro-coagulatory state is expressed preoperatively, but also can be observed in the early postoperative period. Additionally to that, intracerebral metastases of clear-cell renal cell carcinomas and of small-cell carcinomas of the lung express prothrombin, thrombin, factor X, and the protease-activated receptors type 1, 2, 3, and 4. CONCLUSIONS: These observations support the hypothesis of a link between the hemostatic system in the periphery and the malignant tumor disease even when the tumor is an intracerebral metastasis and the affected patient currently is free of a systemically active tumor. The results of this study support the hypothesis that the concerted action of coagulation factors and their receptors within the metastasis tissue itself and the systemic coagulation system could control the malignant behavior of tumor disease and make larger prospective trials mandatory.

Analysis of properties and proinflammatory functions of cockroach allergens Per a 1.01s.

Cockroaches have been identified as one of the major indoor allergens inducing perennial rhinitis and asthma. Per a 1s are a group of the major allergens from American cockroach. Although Per a 1s are major allergens from American cockroach, factors contributing to the allergenicity of Per a 1s are still poorly defined. To investigate the effects of Per a 1s on the expression of PARs and the release of proinflammatory cytokines from mast cells. Per a 1.0101 and Per a 1.0104 were cloned from American cockroach and then expressed in Eschericia coli. The purified allergens were used to stimulate P815 mast cells, and the expression of protease-activated receptors (PARs) was determined by real-time RT-PCR and flow cytometry. The levels of IL-4 and IL-13 in culture media were detected with ELISA. Sera from 80 and 77.3% of cockroach allergy patients reacted to recombinant Per a (rPer a) 1.0101 and rPer a 1.0104, confirming they are major allergens. Both rPer a 1.0101 and rPer a 1.0104 had no enzymatic activity, but rPer a 1.0101 upregulated the expression of PAR-1 and PAR-2, and rPer a 1.0104 enhanced the expression of PAR-1 and PAR-4 proteins. Both recombinant allergens were able to increase the release of IL-4 and IL-13 from P815 mast cells. This is the first study aiming to investigate functions of group 1 allergens of American cockroach. rPer a 1.0101 and rPer a 1.0104 have the capacity to upregulate the expression of PARs and to enhance Th2 cytokine production in mast cells.

Cancer resistance in transgenic mice expressing the SAC module of Par-4.

Prostate apoptosis response-4 (Par-4) is a tumor-suppressor protein that induces apoptosis in cancer cells, but not in normal/immortalized cells. The cancer-specific proapoptotic action of Par-4 is encoded in its centrally located SAC domain. We report here the characterization of a novel mouse model with ubiquitous expression of the SAC domain. Although SAC transgenic mice displayed normal development and life span, they were resistant to the growth of spontaneous, as well as oncogene-induced, autochthonous tumors. Resistance to tumorigenesis was linked to inhibition of nuclear factor-kappaB activity and induction of apoptosis by the SAC domain. Collectively, our findings provide genetic evidence that the SAC domain of Par-4 confers cancer resistance in transgenic mice without compromising normal viability or aging, and may have therapeutic significance.

Protease-activated receptors in the brain: receptor expression, activation, and functions in neurodegeneration and neuroprotection.

Protease-activated receptors (PARs) are G protein-coupled receptors that regulate the cellular response to extracellular serine proteases, like thrombin, trypsin, and tryptase. The PAR family consists of four members: PAR-1, -3, and -4 as thrombin receptors and PAR-2 as the trypsin/tryptase receptor, which are abundantly expressed in the brain throughout development. Recent evidence has supported the direct involvement of PARs in brain development and function. The expression of PARs in the brain is differentially upregulated or downregulated under pathological conditions in neurodegenerative disorders, like Parkinson's disease, Alzheimer's disease, multiple sclerosis, stroke, and human immunodeficiency virus-associated dementia. Activation of PARs mediates cell death or cell survival in the brain, depending on the amplitude and the duration of agonist stimulation. Interference or potentiation of PAR activation is beneficial in animal models of neurodegenerative diseases. Therefore, PARs mediate either neurodegeneration or neuroprotection in neurodegenerative diseases and represent attractive therapeutic targets for treatment of brain injuries. Here, we review the abnormal expression of PARs in the brain under pathological conditions, the functions of PARs in neurodegenerative disorders, and the molecular mechanisms involved.

A novel therapeutic target in various lung diseases: airway proteases and protease-activated receptors.

Protease-activated receptors (PAR), which are G protein-coupled receptors, have 4 members, PAR-1 to PAR-4. PARs are activated by proteolysis of a peptide bond at the N-terminal domain of the receptor. PARs are widely distributed throughout the airways. Their activity is modulated by airway proteases of endogenous and exogenous origin, which can either activate or disable the receptors. The regulation of PAR activity by proteases is important under pathological conditions when the activity of proteases is increased. Moreover, various inflammatory mediators, such as cytokines, growth factors, or prostanoids, alter the PAR expression level. Elevated PAR levels are observed in various lung disorders, and their significance in the development of pathological situations in the lung is currently intensively investigated. Consequences of PAR activation can be either beneficial or deleterious, depending on the PAR subtype. PAR-1 has been shown to be an important player in the development of pulmonary fibrosis. Thus, PAR-1 represents an exciting target for clinical intervention in fibrotic diseases. PAR-2 contributes to allergic airway inflammation. However, the question whether the impact of PAR-2 is beneficial or deleterious is still under intensive discussion. Therefore, precise information concerning the participation of PAR-2 in various lesions is required. Moreover, it is necessary to generate selective PAR- and organ-targeted approaches for treating the diseases. A thorough understanding of PAR-induced cellular events and the consequences of receptor blockade may help in the development of novel therapeutic strategies targeted to prevent lung destruction and to avoid deterioration of conditions of patients with inflammatory or fibrotic lung diseases.

Expression and function of protease-activated receptor 4 in human myometrium.

OBJECTIVE: Little is known about the presence or functional effects of protease-activated receptor subtypes in human uterine tissues. The aims of this study were as follows: (1) to investigate for protease-activated receptor-4 messenger RNA and protein expression in human myometrium, (2) to evaluate the effects of a specific protease-activated receptor-4 activating peptide (AYPGKF-NH2) on spontaneous human myometrial contractility in vitro, and (3) to examine the effects of a protease-activated receptor-4 antagonist (tcYPGKF-NH2) on thrombin-mediated uterine contractility. STUDY DESIGN: Reverse transcriptase-polymerase chain reaction and Immunofluorescence studies were used to investigate for protease-activated receptor-4 messenger RNA and protein expression, respectively. Isometric tension recordings were used to examine the functional effects on contractility. RESULTS: Reverse transcriptase-polymerase chain reaction demonstrated messenger RNA expression for protease-activated receptor-4 in pregnant and non-pregnant myometrium. Immunofluorescence confocal microscopy demonstrated the presence of protease-activated receptor-4 protein in myometrial cells. With the use of isometric recordings, protease-activated receptor 4-activating peptide elicited a stimulatory effect on spontaneous human pregnant myometrial contractility (13.1% +/- 2.7 SEM; n = 6; P < .05). Protease-activated receptor-4 antagonism alone elicited a significant uterorelaxant effect (14.7% +/- 2.4; n = 6; P < .05). The observed thrombin-mediated uterotonic effect was similar in the absence (46.1% +/- 12.8; n = 6) and presence (48.8% +/- 12.6; n = 6) of the protease-activated receptor-4 antagonist (P = .91). CONCLUSIONS: This study outlines protease-activated receptor-4 messenger RNA and protein expression in human myometrium. Protease-activated receptor-4 activation exerts a mild uterotonic effect, whereas protease-activated receptor-4 antagonism results in a mild uterorelaxant effect. The potent human uterotonic effect of thrombin is not apparently mediated to any great extent by protease-activated receptor-4.

Expression of protease-activated receptors and tissue factor in human liver.

Thrombin, acting via protease-activated receptors (PARs), and tissue factor (TF) are involved in inflammation, tissue repair and tumorigenesis. Hepatocellular carcinomas (HCCs) usually complicate chronic liver diseases characterised by inflammation and fibrosis. The aim of this study was to describe the expression of PARs and TF in normal liver, cirrhosis and HCCs. We performed an immunohistochemical detection of PAR-1, PAR-3, PAR-4 and human TF in human tissue samples from 19 subnormal livers, 33 cirrhosis and 30 HCCs. PAR-1 was found on endothelial cells of sinusoids and larger vessels. In cirrhosis, spindle-shaped cells within septa and T lymphocytes were PAR-1 positive. A few PAR-1-positive tumour cells were found in 10% of HCCs. PAR-4 expression was restricted to macrophages, B lymphocytes and nerves. PAR-3 expression was rare. Unexpectedly, TF was expressed in 95% of normal livers and in 94% of cirrhosis but only in 50% of HCCs (p<0.001). Staining was mostly hepatocellular. No association existed between TF labelling and clinicopathological characteristics of HCCs. In conclusion, the pattern of expression of PARs is compatible with its role in chronic liver disease by promoting inflammation via immune cells and neurogenic stimulation. However, our data do not support a role for PARs or TF in HCC progression.

Expression of proteinase-activated receptors in mouse microglial cells.

Microglia are the resident immune cells of the CNS: they are activated rapidly by CNS damage and perform the function of tissue macrophages. The first steps during microglial activation are currently under intense study, and it is widely believed that substances released from damaged brain tissue can trigger this process. We recently reported that the blood coagulation factor thrombin, which enters the CNS during breakdown of the blood-brain barrier, activates microglial cells. The cellular effects of thrombin and trypsin-like proteases are mediated by proteinase-activated receptors (PARs). Based on our prior data we hypothesized that microglial cells express these receptors. Using RT-PCR and flow cytometry, we report that primary mouse microglial cells, as well as the murine microglial cell lines BV-2 and N9, indeed express PARs, albeit at different levels. Demonstrating multiple PARs on microglia may enhance the attractiveness of PARs as therapeutic targets in neuroinflammatory disorders.