Tissue factor is the receptor for plasminogen type 1 on 1-LN human prostate cancer cells

Proteoform-Resolved Profiling of Plasminogen Activation Reveals Novel Abundant Phosphorylation Site and Primary N-Terminal Cleavage Site

Plasminogen (Plg), the zymogen of plasmin (Plm), is a glycoprotein involved in fibrinolysis and a wide variety of other physiological processes. Plg dysregulation has been implicated in a range of diseases. Classically, human Plg is categorized into two types, supposedly having different functional features, based on the presence (type I) or absence (type II) of a single N-linked glycan. Using high-resolution native mass spectrometry, we uncovered that the proteoform profiles of human Plg (and Plm) are substantially more extensive than this simple binary classification. In samples derived from human plasma, we identified up to 14 distinct proteoforms of Plg, including a novel highly stoichiometric phosphorylation site at Ser339. To elucidate the potential functional effects of these post-translational modifications, we performed proteoform-resolved kinetic analyses of the Plg-to-Plm conversion using several canonical activators. This conversion is thought to involve at least two independent cleavage events: one to remove the N-terminal peptide and another to release the active catalytic site. Our analyses reveal that these processes are not independent but are instead tightly regulated and occur in a step-wise manner. Notably, N-terminal cleavage at the canonical site (Lys77) does not occur directly from intact Plg. Instead, an activation intermediate corresponding to cleavage at Arg68 is initially produced, which only then is further processed to the canonical Lys77 product. Based on our results, we propose a refined categorization for human Plg proteoforms. In addition, we reveal that the proteoform profile of human Plg is more extensive than that of rat Plg, which lacks, for instance, the here-described phosphorylation at Ser339.

Biophysical Mechanisms Mediating Fibrin Fiber Lysis

The formation and dissolution of blood clots is both a biochemical and a biomechanical process. While much of the chemistry has been worked out for both processes, the influence of biophysical properties is less well understood. This review considers the impact of several structural and mechanical parameters on lytic rates of fibrin fibers. The influences of fiber and network architecture, fiber strain, FXIIIa cross-linking, and particle transport phenomena will be assessed. The importance of the mechanical aspects of fibrinolysis is emphasized, and future research avenues are discussed.

Preferential Acquisition and Activation of Plasminogen Glycoform II by PAM Positive Group A Streptococcal Isolates

Plasminogen (Plg) circulates in the host as two predominant glycoforms. Glycoform I Plg (GI-Plg) contains glycosylation sites at Asn289 and Thr346, whereas glycoform II Plg (GII-Plg) is exclusively glycosylated at Thr346. Surface plasmon resonance experiments demonstrated that Plg binding group A streptococcal M protein (PAM) exhibits comparative equal affinity for GI- and GII-Plg in the "closed" conformation (for GII-Plg, KD = 27.4 nM; for GI-Plg, KD = 37.0 nM). When Plg was in the "open" conformation, PAM exhibited an 11-fold increase in affinity for GII-Plg (KD = 2.8 nM) compared with that for GI-Plg (KD = 33.2 nM). The interaction of PAM with Plg is believed to be mediated by lysine binding sites within kringle (KR) 2 of Plg. PAM-GI-Plg interactions were fully inhibited with 100 mM lysine analogue ε-aminocaproic acid (εACA), whereas PAM-GII-Plg interactions were shown to be weakened but not inhibited in the presence of 400 mM εACA. In contrast, binding to the KR1-3 domains of GII-Plg (angiostatin) by PAM was completely inhibited in the presence 5 mM εACA. Along with PAM, emm pattern D GAS isolates express a phenotypically distinct SK variant (type 2b SK) that requires Plg ligands such as PAM to activate Plg. Type 2b SK was able to generate an active site and activate GII-Plg at a rate significantly higher than that of GI-Plg when bound to PAM. Taken together, these data suggest that GAS selectively recruits and activates GII-Plg. Furthermore, we propose that the interaction between PAM and Plg may be partially mediated by a secondary binding site outside of KR2, affected by glycosylation at Asn289.

High turnover of tissue factor enables efficient intracellular delivery of antibody-drug conjugates

Antibody-drug conjugates (ADC) are emerging as powerful cancer treatments that combine antibody-mediated tumor targeting with the potent cytotoxic activity of toxins. We recently reported the development of a novel ADC that delivers the cytotoxic payload monomethyl auristatin E (MMAE) to tumor cells expressing tissue factor (TF). By carefully selecting a TF-specific antibody that interferes with TF:FVIIa-dependent intracellular signaling, but not with the procoagulant activity of TF, an ADC was developed (TF-011-MMAE/HuMax-TF-ADC) that efficiently kills tumor cells, with an acceptable toxicology profile. To gain more insight in the efficacy of TF-directed ADC treatment, we compared the internalization characteristics and intracellular routing of TF with the EGFR and HER2. Both in absence and presence of antibody, TF demonstrated more efficient internalization, lysosomal targeting, and degradation than EGFR and HER2. By conjugating TF, EGFR, and HER2-specific antibodies with duostatin-3, a toxin that induces potent cytotoxicity upon antibody-mediated internalization but lacks the ability to induce bystander killing, we were able to compare cytotoxicity of ADCs with different tumor specificities. TF-ADC demonstrated effective killing against tumor cell lines with variable levels of target expression. In xenograft models, TF-ADC was relatively potent in reducing tumor growth compared with EGFR- and HER2-ADCs. We hypothesize that the constant turnover of TF on tumor cells makes this protein specifically suitable for an ADC approach.

Plasminogen receptors and their role in the pathogenesis of inflammatory, autoimmune and malignant disease

Plasminogen is the proenzyme of plasmin, the key protease of the fibrinolytic system, but its role is not limited to fibrinolysis regulation. Plasminogen binds not only to fibrin, but also to different receptors on cell surfaces, including the heterotetrameric complex Annexin A2-S100A10, enolase-1, histone H2B and the plasminogen receptor Plg-R(KT) . These receptors localize plasmin generation to the cell surface and provide a broad spectrum of reactions including proteolytic activity, cell migration and recruitment as well as signaling pathway activation. These plasminogen-binding proteins are involved in both physiologic and pathologic processes such as inflammation, thrombosis and cancer. Thus, plasminogen is at the center of a complex tightly controlled and regulated system where plasminogen-binding proteins have a crucial role, suggesting new therapeutic and diagnostic strategies. This review will discuss currently available information on plasminogen receptors, particularly their mechanisms of action and their roles in inflammatory, autoimmune and malignant disease.

The voltage-dependent anion channel (VDAC) binds tissue-type plasminogen activator and promotes activation of plasminogen on the cell surface

The voltage-dependent anion channel (VDAC), a major pore-forming protein in the outer membrane of mitochondria, is also found in the plasma membrane of a large number of cells where in addition to its role in regulating cellular ATP release and volume control it is important for maintaining redox homeostasis. Cell surface VDAC is a receptor for plasminogen kringle 5, which promotes partial closure of the channel. In this study, we demonstrate that VDAC binds tissue-type plasminogen activator (t-PA) on human neuroblastoma SK-N-SH cells. Binding of t-PA to VDAC induced a decrease in K(m) and an increase in the V(max) for activation of its substrate, plasminogen (Pg). This resulted in accelerated Pg activation when VDAC, t-PA, and Pg were bound together. VDAC is also a substrate for plasmin; hence, it mimics fibrin activity. Binding of t-PA to VDAC occurs between a t-PA fibronectin type I finger domain located between amino acids Ile(5) and Asn(37) and a VDAC region including amino acids (20)GYGFG(24). These VDAC residues correspond to a GXXXG repeat motif commonly found in amyloid β peptides that is necessary for aggregation when these peptides form fibrillar deposits on the cell surface. Furthermore, we also show that Pg kringle 5 is a substrate for the NADH-dependent reductase activity of VDAC. This ternary complex is an efficient proteolytic complex that may facilitate removal of amyloid β peptide deposits from the normal brain and cell debris from injured brain tissue.

Prostasomes are mediators of intercellular communication: from basic research to clinical implications

Prostasomes are nanosized microvesicles secreted by acinar epithelial cells of the prostate gland. Furthermore, they are intracellular microvesicles inside another larger vesicle, a so-called storage vesicle, equivalent to multivesicular bodies of late endosomal origin. Prostasomes are thought to play an important role in intercellular communication by direct interaction primarily between the immobile acinar cells of the prostate gland and the mobile spermatozoa. Prostasomes transfer not only membrane components but also genetic material to spermatozoa. They are rich in various transferable bioactive molecules (e.g., receptors and enzymes) that promote the fertilizing ability of spermatozoa. In this review, the pleiotropic biological effects of prostasomes that are relevant for successful fertilization will be discussed. The ability to synthesize and export prostasomes to the extracellular space is observed not only in normal prostate epithelial cells but also in malignant prostate cells. Release of prostasomes by prostate cancer cells suggests a role in malignant cell growth and proliferation. These findings may provide new therapeutic and diagnostic strategies.

An overview of coagulation disorders in cancer patients

A diversity of coagulation disorders in cancer patients arise from tumor-specific growth characteristics, neoangiogenesis with impaired endothelial lining, defective myelopoiesis, hypoproteinemia or metastatic lesions growth with organ dysfunction. Recent investigations have found a clinically relevant correlation of coagulation disorders and tumor growth. These prompted new therapeutic strategies focused on growth factors with the aim to control tumor metastasis, particularly if used for the treatment of micrometastatic disease. However, such treatment may lead to the life threatening coagulation imbalance. A coagulation homeostasis may become further impaired after nonsurgical cancer therapy, especially after preoperative irradiation, which produces lesions precipitating both bleeding and thrombosis. Anticancer chemotherapy may affect liver function and decrease the synthesis of both procoagulation and anticoagulation factors. The most of chemotherapeutic protocols affect platelet synthesis, which arises as a principal dose-limiting side effect. It was observed both during combined systemic chemotherapy and local antitumor therapy. Although the side effects produced by chemotherapy are reversible, endothelial lesions may persist for many years after the anticancer treatment. Instead of cancer patients, there's a growing cohort of patients with nonmalignant diseases who use cytostatics in the perioperative period, and are candidates for surgical procedures not related to their malignant disease, i.e. hernia repair. In this patient population a special attention must be paid to the preoperative evaluation of coagulation status and thromboprophylaxis. This overview reminds the most common coagulation disorders in cancer patients in the perioperative period. It emphasizes the need for proper patient monitoring which may facilitate the diagnostics and treatment of cancer-related coagulation disorders in the perioperative setting.

Prothrombotic effect of prostasomes of metastatic cell and seminal origin

BACKGROUND

Prostasomes are secretory granules produced by the glandular epithelial cells of the prostate. Seminal prostasomes contain high amounts of Tissue Factor (TF) but no studies of TF on malignant cell prostasomes have been made. Here we compare the expression, phosphorylation, and function of TF on prostasomes of different origin.

METHODS

TF was detected on prostasomes isolated from seminal fluid and human prostate cancer cell lines (PC-3, DU145, and LNCaP) using FACS and enzyme immunoassay (EIA). Incubation of prostasomes with radioactive ATP under conditions favoring protein kinase A activity led to phosphorylation of TF as detected by immunoprecipitation and SDS-PAGE. The prothrombotic effect of prostasomes was investigated in whole blood and recalcified plasma. Blocking experiments were performed using anti-TF antibodies and corn trypsin inhibitor.

RESULTS

TF was expressed on all tested prostasome preparations with lowest values found for seminal ones. Prostasomal TF was the main endogenous substrate for prostasomal protein kinase A. All tested prostasome preparations greatly enhanced the rate of clot formation in a dose-dependent fashion, that is, the clotting capability of prostasomes seemed to be related to the extent of their expression of TF. In addition, the density of the clot varied between different prostasome preparations. When incubated in whole blood, prostasomes were found to associate to WBC thereby inducing them to express and release TF.

CONCLUSIONS

These data show that TF is overexpressed and also subjected to phosphorylation by malignant cell prostasomes. This suggests major roles for prostasomes in thrombotic events that occur in some advanced cases of prostate cancer.

Tissue factor haploinsufficiency during endotoxin induced coagulation and inflammation in mice

Intervention studies blocking tissue factor (TF) driven coagulation show beneficial effects on survival in endotoxemia models by reducing cytokine production. It is unknown, however, if moderately reduced TF levels influence endotoxemia. The objective was to investigate whether TF haploinsufficiency reduces endotoxin-induced cytokine production in murine cells or in mice. We analyzed the intrinsic capacity of heterozygous TF deficient (TF+/-) leukocytes to produce cytokines. In addition, we determined the consequences of TF haploinsufficiency on endotoxin-induced inflammation during murine endotoxemia. Endotoxin induced the production of tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-6 and keratinocyte-derived chemokine (KC) in both whole blood and macrophages. Heterozygous TF deficiency reduced endotoxin induced IL-6 and KC levels about two-fold, while TNF-alpha levels were indistinguishable between TF+/- and wild-type cells. In vivo, endotoxin induced a biphasic coagulant response and significant increases in cytokine levels. Surprisingly, both the inflammatory and the coagulant responses were indistinguishable between wild-type and TF+/- mice. At baseline tissues of TF+/- mice showed a 50% reduction in TF activity compared to wild type. Upon endotoxin administration, TF activity increased and the difference between TF+/- and wild-type mice disappeared after 4 h. After 12 h the baseline difference in TF activity was re-established. TF deficiency reduces cytokine production in vitro, but an enhanced induction of TF during murine endotoxemia eliminates this effect in vivo.

Oncogenic events regulate tissue factor expression in colorectal cancer cells: implications for tumor progression and angiogenesis

Tissue factor (TF) is the primary cellular initiator of blood coagulation and a modulator of angiogenesis and metastasis in cancer. Indeed, systemic hypercoagulability in patients with cancer and TF overexpression by cancer cells are both closely associated with tumor progression, but their causes have been elusive. We now report that in human colorectal cancer cells, TF expression is under control of 2 major transforming events driving disease progression (activation of K-ras oncogene and inactivation of the p53 tumor suppressor), in a manner dependent on MEK/mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3'-kinase (PI3K). Furthermore, the levels of cell-associated as well as circulating (microvesicle-associated) TF activity are linked to the genetic status of cancer cells. Finally, RNA interference experiments suggest that TF expression is an important effector of the K-ras-dependent tumorigenic and angiogenic phenotype in vivo. Thus, this study establishes a causal link between cancer coagulopathy, angiogenesis, and genetic tumor progression.

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

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

Characterization of plasminogen as an adhesive ligand for integrins alphaMbeta2 (Mac-1) and alpha5beta1 (VLA-5)

Plasminogen (Pg) has been implicated in many biologic processes involving extracellular proteolysis. We investigated whether Pg, by virtue of its capacity to be deposited within the extracellular matrix, can serve as a ligand for cell surface integrins. We report here that Pg supports cell adhesion by engaging integrins alphaMbeta2 and alpha5beta1. The immobilized Glu-Pg, but not its derivatives with the N-terminal peptide lacking, plasmin and Lys-Pg, supported efficient adhesion that was abolished by anti-alphaMbeta2 and anti-alpha5beta1 integrin-specific monoclonal antibodies (mAbs). In addition, lysine binding sites of Glu-Pg contributed to cell adhesion inasmuch as tranexamic acid and epsilon-aminocaproic acid inhibited cell adhesion. The involvement of alphaMbeta2 and alpha5)beta1 in adhesion to Glu-Pg was demonstrable with blood neutrophils, U937 monocytoid cells, and genetically engineered alphaMbeta2-transfected human embryonic kidney (HEK) 293 cells. In alphaMbeta2, the alphaMI-domain is the binding site for Glu-Pg because the "I-less" form of alphaMbeta2 did not support cell adhesion and the recombinant alphaMI-domain bound Glu-Pg directly. In comparison with cell adhesion, the binding of soluble Glu-Pg to cells and the concomitant generation of plasmin activity was inhibited by anti-alpha5beta1 but not by anti-alphaMbeta2. These findings identify Glu-Pg as an adhesive ligand for integrins alphaMbeta2 and alpha5beta1 and suggest that alpha5beta1 may participate in the binding of soluble Glu-Pg and assist in its activation.

The Janus-faced nature of prostasomes: their pluripotency favours the normal reproductive process and malignant prostate growth

Prostasomes are submicron secretory granules synthesized, stored and secreted by the epithelial cells of the human prostate gland. They are membrane-surrounded also in their extracellular appearance and the membrane architecture is composite. They are believed to be life-giving and act as protectors of the spermatozoa in the lower and upper female genital tract on their way to the ovum. Hence, the prostasomes are immunosuppressive and inhibitory of complement activation. Further, they promote sperm's forward motility and have antioxidant and antibacterial capacities. The prostasomes with their many composite abilities seem to turn against the host cell after the age of 50 y being conducive to the transition of the normal prostate epithelial cell into a neoplastic cell and therewith lay the foundations of the very high prevalence of prostate cancer of men of more than 50 y of age.