Leukocyte chemoattractant peptides from the serpin heparin cofactor II

The Tissue Factor Pathway in Cancer: Overview and Role of Heparan Sulfate Proteoglycans

Historically, the only focus on tissue factor (TF) in clinical pathophysiology has been on its function as the initiation of the extrinsic coagulation cascade. This obsolete vessel-wall TF dogma is now being challenged by the findings that TF circulates throughout the body as a soluble form, a cell-associated protein, and a binding microparticle. Furthermore, it has been observed that TF is expressed by various cell types, including T-lymphocytes and platelets, and that certain pathological situations, such as chronic and acute inflammatory states, and cancer, may increase its expression and activity. Transmembrane G protein-coupled protease-activated receptors can be proteolytically cleaved by the TF:FVIIa complex that develops when TF binds to Factor VII (PARs). The TF:FVIIa complex can activate integrins, receptor tyrosine kinases (RTKs), and PARs in addition to PARs. Cancer cells use these signaling pathways to promote cell division, angiogenesis, metastasis, and the maintenance of cancer stem-like cells. Proteoglycans play a crucial role in the biochemical and mechanical properties of the cellular extracellular matrix, where they control cellular behavior via interacting with transmembrane receptors. For TFPI.fXa complexes, heparan sulfate proteoglycans (HSPGs) may serve as the primary receptor for uptake and degradation. The regulation of TF expression, TF signaling mechanisms, their pathogenic effects, and their therapeutic targeting in cancer are all covered in detail here.

Suggestions on leading an academic research laboratory group

This commentary is about running an academic research laboratory group, including some reflections, memories, and tips on effectively managing such a group of scientists focused on one’s research. The author’s academic career has spanned from 1982 to 2022, including postdoctoral research associate through the rank of professor with tenure. Currently, the author is in the final year of 3 years of phased retirement. One must be willing to work hard at running a research laboratory. Also, stay focused on funding the laboratory tasks and publishing one’s work. Recruit the best people possible with advice from the collective laboratory group. Laboratory group members felt more like they were a part of a collective family than simply employees; however, what works best for the researcher is what matters. Several other points to discuss will include managing university roles, recruiting laboratory personnel, getting recognition, dealing with intellectual property rights, and publishing work. In closing, there are many more positives than negatives to leading a research laboratory group. Finally, one cannot replace the unforgettable memories and the legacy of a research laboratory group.

Discovery of novel bladder cancer biomarkers by comparative urine proteomics using iTRAQ technology

A urine sample preparation workflow for the iTRAQ (isobaric tag for relative and absolute quantitation) technique was established. The reproducibility of this platform was evaluated and applied to discover proteins with differential levels between pooled urine samples from nontumor controls and three bladder cancer patient subgroups with different grades/stages (a total of 14 controls and 23 cancer cases in two multiplex iTRAQ runs). Combining the results of two independent clinical sample sets, a total of 638 urine proteins were identified. Among them, 55 proteins consistently showed >2-fold differences in both sample sets. Western blot analyses of individual urine samples confirmed that the levels of apolipoprotein A-I (APOA1), apolipoprotein A-II, heparin cofactor 2 precursor and peroxiredoxin-2 were significantly elevated in bladder cancer urine specimens (n = 25-74). Finally, we quantified APOA1 in a number of urine samples using a commercial ELISA and confirmed again its potential value for diagnosis (n = 126, 94.6% sensitivity and 92.0% specificity at a cutoff value of 11.16 ng/mL) and early detection (n = 71, 83.8% sensitivity and 94.0% specificity). Collectively, our results provide the first iTRAQ-based quantitative profile of bladder cancer urine proteins and represent a valuable resource for the discovery of bladder cancer markers.

Decreased heparin cofactor II activity is associated with impaired endothelial function determined by brachial ultrasonography and predicts cardiovascular events

BACKGROUND

Heparin cofactor II (HCII) could inactivate thrombin after binding to dermatan sulfate at injured arterial walls, and has been shown to be a novel and independent antiatherosclerotic factor. However, the relation between plasma HCII activity and peripheral vascular endothelial function remains unclear.

METHODS

A total of 199 patients (mean age, 63+/-14 years) were enrolled and followed up for a median period of 24 months. Endothelial function was assessed using brachial ultrasonography to determine endothelium dependent flow-mediated vasodilation (FMD). Cox regression analyses were conducted for the 199 subjects, with cardiovascular events being defined as myocardial infarction (MI), percutaneous coronary intervention (PCI), coronary artery bypass grafting (CABG), ischemic stroke, and peripheral artery revascularization.

RESULTS

A total of 31 patients (16%) had cardiovascular events. Patients with cardiovascular events had significantly lower HCII activity (112+/-34 versus 127+/-34%, p=0.027) and lower antithrombin III (ATIII) activity (82+/-12 versus 88+/-13%, p=0.014) than those without events. By multivariate analysis, age (p=0.012), hsCRP (p=0.020) and HCII activity (p=0.035) were correlated with FMD. Kaplan-Meier analysis was performed and showed plasma HCII (p=0.036) and ATIII activities (p=0.005) were predictors of cardiovascular events. By Cox regression analysis, plasma HCII activity (p=0.026) could be an independent predictor of future cardiovascular events, but not ATIII.

CONCLUSIONS

The present study demonstrates that plasma HCII activity is positively correlated with endothelial vasodilator function. Furthermore, plasma HCII activity could be a predictor of future cardiovascular events in patients with suspected coronary artery disease, suggesting its role in atherosclerosis.

Ovarian cancer, the coagulation pathway, and inflammation

Epithelial ovarian cancer (EOC) represents the most frequent cause of death in the United States from a cancer involving the female genital tract. Contributing to the overall poor outcome in EOC patients, are the metastases to the peritoneum and stroma that are common in this cancer. In one study, cDNA microarray analysis was performed on fresh tissue to profile gene expression in patients with EOC. This study showed a number of genes with significantly altered expression in the pelvic peritoneum and stroma, and in the vicinity of EOC implants. These genes included those encoding coagulation factors and regulatory proteins in the coagulation cascade and genes encoding proteins associated with inflammatory responses. In addition to promoting the formation of blood clots, coagulation factors exhibit many other biologic functions as well as tumorigenic functions, the later including tumor cell proliferation, angiogenesis, invasion, and metastasis. Coagulation pathway proteins involved in tumorigenesis consist of factor II (thrombin), thrombin receptor (protease-activated receptors), factor III (tissue factor), factor VII, factor X and factor I (fibrinogen), and fibrin and factor XIII. In a recent study we conducted, we found that factor XII, factor XI, and several coagulation regulatory proteins, including heparin cofactor-II and epithelial protein C receptor (EPCR), were also upregulated in the peritoneum of EOC. In this review, we summarize evidence in support of a role for these factors in promoting tumor cell progression and the formation of ascites. We also discuss the different roles of coagulation factor pathways in the tumor and peritumoral microenvironments as they relate to angiogenesis, proliferation, invasion, and metastasis. Since inflammatory responses are another characteristic of the peritoneum in EOC, we also discuss the linkage between the coagulation cascade and the cytokines/chemokines involved in inflammation. Interleukin-8, which is considered an important chemokine associated with tumor progression, appears to be a linkage point for coagulation and inflammation in malignancy. Lastly, we review findings regarding the inflammatory process yielded by certain clinical trials of agents that target members of the coagulation cascade in the treatment of cancer. Current data suggest that disrupting certain elements of the coagulation and inflammation processes in the tumor microenvironment could be a new biologic approach to cancer therapeutics.

Mechanisms of glycosaminoglycan activation of the serpins in hemostasis

Serpins are the predominant protease inhibitors in the higher organisms and are responsible, in humans, for the control of many highly regulated processes including blood coagulation and fibrinolysis. The serpin inhibitory mechanism has recently been revealed by the solution of a crystallographic structure of the final serpin-protease complex. The serpin mechanism, in contrast to the classical lock-and-key mechanism, involves dramatic conformational change in both the inhibitor and the inhibited protein. The final result is a stable covalent complex in which the properties of each component are altered so as to allow clearance from the circulation. Several serpins are involved in hemostasis: antithrombin (AT) inhibits many coagulation proteases, most importantly factor Xa and thrombin; heparin cofactor II (HCII) inhibits thrombin; protein C inhibitor (PCI) inhibits activated protein C and thrombin bound to thrombomodulin; plasminogen activator inhibitor 1 inhibits tissue plasminogen activator; and alpha2-antiplasmin inhibits plasmin. Nearly all of these reactions are accelerated through interactions with glycosaminoglycans (GAGs) such as heparin or heparan sulfate. Recent structures of AT, HCII and PCI have revealed how in each case the serpin mechanism has been fine-tuned by evolution to bring about high levels of regulatory control, and how seemingly disparate mechanisms of GAG binding and activation can share critical elements. By considering the serpins involved in hemostasis together it is possible to develop a deeper understanding of their complex individual roles.

What is all that thrombin for?

The hemostatic process initiated by the exposure of tissue factor to blood is a threshold limited reaction which occurs in two distinct phases. During an initiation phase, small amounts of factor (F)Xa, FIXa and thrombin are generated. The latter activates the procofactors FV and FVIII to the activated cofactors which together with their companion serine proteases form the intrinsic FX activator (FVIIIa-FIXa) and prothrombinase (FVa-FXa) which generate the bulk of FXa and thrombin during a propagation phase. The clotting process (fibrin formation) occurs at the inception of the propagation phase when only 5-10 nM thrombin has been produced. Consequently, the vast majority (greater than 95%) of thrombin is produced after clotting during the propagation phase of thrombin generation. The blood of individuals with either hemophilia A or hemophilia B has no ability to generate the intrinsic FXase, and hence is unable to support the propagation phase of the reaction. Since clot based assays conclude before the propagation phase they are not sensitive to hemophilia A and B. The inception and magnitude of the propagation phase of thrombin generation is influenced by genetic polymorphisms associated with thrombotic and hemorrhagic disease, by the natural abundance of pro- and anticoagulants in healthy individuals and by pharmacologic interventions which influence thrombotic pathology. Therefore, it is our suspicion that the performance of the entire process of thrombin generation from initiation through propagation and termination phases of the reaction are relevant with respect to both hemorrhagic and thrombotic pathology.

Crystal structures of native and thrombin-complexed heparin cofactor II reveal a multistep allosteric mechanism

The serine proteases sequentially activated to form a fibrin clot are inhibited primarily by members of the serpin family, which use a unique beta-sheet expansion mechanism to trap and destroy their targets. Since the discovery that serpins were a family of serine protease inhibitors there has been controversy as to the role of conformational change in their mechanism. It now is clear that protease inhibition depends entirely on rapid serpin beta-sheet expansion after proteolytic attack. The regulatory advantage afforded by the conformational mobility of serpins is demonstrated here by the structures of native and S195A thrombin-complexed heparin cofactor II (HCII). HCII inhibits thrombin, the final protease of the coagulation cascade, in a glycosaminoglycan-dependent manner that involves the release of a sequestered hirudin-like N-terminal tail for interaction with thrombin. The native structure of HCII resembles that of native antithrombin and suggests an alternative mechanism of allosteric activation, whereas the structure of the S195A thrombin-HCII complex defines the molecular basis of allostery. Together, these structures reveal a multistep allosteric mechanism that relies on sequential contraction and expansion of the central beta-sheet of HCII.

A bacteria-induced, intracellular serpin in granular hemocytes of Manduca sexta

Serine proteinase inhibitors from the serpin superfamily have been identified as hemolymph proteins from several groups of arthropods, including horseshoe crabs, crayfish, and insects. In the tobacco hornworm, Manduca sexta, one group of serpins present in plasma is generated by alternate exon splicing from serpin gene-1. We have identified a second serpin gene from this insect, M. sexta serpin-2. A serpin-2 DNA clone was isolated from a fifth instar larval cDNA library. The full-length cDNA is 1.5 kb long and encodes a protein of 381 amino acid residues. Amino acid sequence comparisons with other invertebrate serpins reveal approximately 25-40% identity with serpin-2. An expressed sequence tag from Bombyx mori, which is very similar to M. sexta serpin-2, was identified, and the corresponding full-length cDNA sequence was determined. This silkworm homolog of serpin-2 is 57% identical to M. sexta serpin-2. Recombinant M. sexta serpin-2 was used as an antigen to generate a rabbit polyclonal antiserum. This antiserum recognized a 43 kDa protein present in hemocytes but absent from plasma. Western and Northern blot results revealed that serpin-2 gene expression increased dramatically after larvae were injected with bacteria. In situ hybridization showed that the serpin-2 mRNA is present in granular hemocytes of immune-stimulated larvae. Serpin-2 purified from hemocytes obtained 24 h after injection of larvae with bacteria lacked inhibitory activity for all proteinases tested except for human cathepsin G. The intracellular location of serpin-2 suggests a function for serpin-2 different from the plasma serpin-1 proteins.

Cell-surface heparan sulfate proteoglycan-mediated regulation of human neutrophil migration by the serpin antithrombin III

The serpin antithrombin III (AT III) is reported to have hemostasis-regulating and anti-inflammatory properties. To determine its ability to influence thrombin-independent leukocyte responses, the direct effects of the AT III concentrate Kybernin P and a monoclonal antibody-purified AT III on neutrophil migration were studied. Chemotactic activity of human neutrophils isolated from the blood of healthy donors was determined in modified Boyden microchemotaxis chambers, and binding studies were performed according to standard experimental protocols. Preincubation in vitro of neutrophils with Kybernin P or immune-adsorbed AT III significantly deactivated migration toward fMet-Leu-Phe, or interleukin-8 (IL-8), in a concentration-dependent manner. In the absence of additional attractants, neutrophils exhibited a migratory response toward gradients of AT III preparations. True chemotaxis was confirmed in checkerboard assays. Analyses revealed that the AT III heparin-binding site interacts with neutrophil membrane-associated heparan sulfate proteoglycan receptors. Mechanisms of intracellular signaling differed; the deactivation of IL-8-induced chemotaxis resulted from tyrphostin-sensitive interactions of AT III-signaling with the IL-8 signal transduction pathway, whereas AT III-induced chemotaxis involved protein kinase C and phosphodiesterases. Signaling similarities between AT III and the proteoglycan syndecan-4 may suggest the binding of AT III to this novel type of membrane receptor. Under physiological conditions, AT III may prevent neutrophils from premature activation. Moreover, the systemic administration of AT III concentrate could have beneficial effects in combating systemic inflammation.

Thrombin inhibition by HCII in the presence of elastase-cleaved HCII and thrombin-HCII complex

The rate of thrombin inhibition by heparin cofactor II (HCII) is facilitated by heparin or dermatan sulfate in vitro. The distributions of these glycosaminoglycans (GAGs) in vivo are not the same; heparin-like substance is rich on the surface of endothelial cells and dermatan sulfate is relatively dominant in the extravascular region. When inflammation takes place, at least two other possible existent forms of HCII, the complexed form with thrombin and the cleaved form by leukocyte elastase, are assumed to be present at relatively high concentrations in a local circumstance. We examined the interactions of HCII with the two forms of HCII on thrombin inhibition in the presence of the GAGs. By HCII in complex with thrombin or cleaved by leukocyte elastase, the affinity of HCII moiety for heparin increases and that for dermatan sulfate decreases. The two forms possibly occur at relatively high concentrations in a local pathological situation, although the heparin cofactor activity for thrombin inhibition by HCII decreases and dermatan sulfate determines the cofactor activity. These results indicate efficient thrombin inhibitory activity of HCII in the extravascular region.

Limited proteolysis and physiological regulation: an example from thyrotropin-releasing hormone metabolism

Proteases like trypsin, elastase, and many others play important regulatory functions by generating new biologically active molecules through limited proteolysis of larger proteins and peptides. The limited proteolysis of thyrotropin-releasing hormone (TRH) by Pyroglutamate aminopeptidase yields cyclo(His-Pro) or CHP, a new biopeptide associated with a variety of pharmacological activities, including regulation of body temperature, inhibition of prolactin secretion, and modulation of motor functions. Although the mechanism by which CHP elicits these biological activities is not well understood, it appears that the cyclic peptide may function at least in part by modulating central amine transport mechanisms.

Interaction of thrombin with antithrombin, heparin cofactor II, and protein C inhibitor

alpha-Thrombin is a trypsin-like serine proteinase involved in blood coagulation and wound repair processes. Thrombin interacts with many macromolecular substrates, cofactors, cell-surface receptors, and blood plasma inhibitors. The three-dimensional structure of human alpha-thrombin shows multiple surface "exosites" for interactions with these macromolecules. We used these coordinates to probe the interaction of thrombin's active site and two exosites, anion-binding exosite-I and -II, with the blood plasma serine proteinase inhibitors (serpins) antithrombin (AT), heparin cofactor II (HC), and protein C inhibitor (PCI). Heparin, a widely used anticoagulant drug, accelerates the rate of thrombin inhibition by AT, PCI, and HC. Thrombin Quick II is a dysfunctional thrombin mutant with a Gly 226-->Val substitution in the substrate specificity pocket. We found that thrombin Quick II was inhibited by HC, but not by AT or PCI. Molecular modeling studies suggest that the larger Val side chain protrudes into the specificity pocket, allowing room for the smaller P1 side chain of HC (Leu) but not the larger P1 side chain of AT and PCI (both with Arg). gamma T-Thrombin and thrombin Quick I (Arg 67-->Cys) are both altered in anion-binding exosite-I, yet bind to heparin-Sepharose and can be inhibited by AT, HC, and PCI in an essentially normal manner in the absence of heparin. In the presence of heparin, inhibition of these altered thrombins by HC is greatly reduced compared to both AT and PCI. alpha-Thrombin with chemically modified lysines in both anion-binding exosite-I and -II has no heparin accelerated thrombin inhibition by either AT or HC. Thrombin lysine-modified in the presence of heparin has protected residues in anion-binding exosite-II and the loss of heparin-accelerated inhibition by HC is greater than that by AT. Collectively, these results suggest differences in serpin reactive site recognition by thrombin and a more complicated mechanism for heparin-accelerated inhibition by HC compared to either AT or PCI.

The effects of heparin cofactor II-derived chemotaxins on neutrophil actin conformation and cyclic AMP levels

The serine proteinase inhibitor heparin cofactor II (HC) can be cleaved by polymorphonuclear leukocyte (PMN) elastase (LE) to yield potent chemotactic activity for PMN and monocytes. In contrast to the bacterially-derived chemotaxin formyl-Met-Leu-Phe (fMLP), the HC-derived chemotaxin does not stimulate PMN degranulation or oxidative burst activity. We compared the effects of HC-derived chemotaxins to the effects of fMLP on PMN actin conformation and on the cAMP levels. Both the HC chemotaxins and fMLP rapidly induced an increase in F-actin which was similar in magnitude and time-course. However, in contrast to fMLP, HC-derived chemotaxins did not elevate cAMP levels. HC-derived chemotaxins may be useful probes of chemotactic responses, since they do not have the mixed biological activities of fMLP.