Generation of the neutrophil-activating peptide NAP-2 from platelet basic protein or connective tissue-activating peptide III through monocyte proteases

The role of CXC chemokines and receptors in breast cancer

CXC chemokines are a class of cytokines possessing chemotactic properties. Studies indicate that CXC chemokines exhibit dysregulation in miscellaneous cancer categories and are significantly associated with the advancement of tumors. Breast cancer is a commonly diagnosed and fatal cancer among the female population. Breast cancer pathogenesis and progression involve various mechanisms, including invasion, metastasis, angiogenesis, and inflammation. Chemokines and their receptors are involved in all of these processes. The CXC chemokine receptors (CXCRs) and their related ligands have attracted considerable attention due to their multifaceted functions in facilitating and controlling tumor proliferation. CXCRs are expressed by both cancer cells and immune cells, and they play a crucial role in regulating the tumor microenvironment and the immune response. This review aims to assess the potential of CXCRs and CXC chemokines as therapeutic targets or biomarkers for personalized therapy. Additionally, it provides an overview of the current understanding of the expression, function, and prognostic relevance of CXCRs in breast cancer. Furthermore, the challenges and potential prospects pertaining to CXCR investigation in breast cancer are deliberated.

Early-Stage Lung Cancer Diagnosis by a Point-of-Care Electrochemical Aptamer-Based Sensor of NAP2 in Human Serum

The target neutrophil-activating peptide-2, NAP2, is a potential biomarker for early lung cancer diagnosis, whereas there are currently no precise techniques for differentiating NAP2 from its precursors. To overcome this difficulty, we created an electrochemical aptamer-based sensor (E-AB) consisting of the 33-mer aptamer domain, a 2-bp three-junction region, and two conductive signal reporter stems. Whereas E-AB-AT and E-AB-RAN sensors with two (AT)6 or N12 stems, respectively, were unable to distinguish between platelet basic protein (PBP) (94 aa) and NAP2 (70 aa). However, in contrast, the E-AB-GC sensor with two (GC)6 stems could selectively detect NAP2 but hardly recorded PBP. Here, we developed an E-AB-GC point-of-care test (POCT) technique to detect NAP2 away from its precursors in 10 μL of human serum and provide concentration data in 5 min. Interestingly, serum NAP2 levels in human samples, as determined by the E-AB-GC sensor, were roughly 30-50% lower than those obtained by ELISA. Results also showed that E-AB-GC analysis of serum NAP2 in patients in stages I through IV revealed statistical significance and an excellent guiding function in the early diagnosis of lung cancer, particularly for patients in stage I cancer (p = 0.0054, area under the curve, 0.95). Importantly, this E-AB-GC POCT platform has shown potential as an on-site quick diagnostic tool, which can also be used to detect other lung cancer markers. Our research on the impacts of stem sequencing on sensing capabilities might assist in the future development of E-AB biomarker sensors.

Understanding Platelet Activation in the Aeson Bioprosthetic Total Artificial Heart: Insights From Aspirin Treatment and Outcomes

This study aimed to assess platelet activation following implantation of the Aeson bioprosthetic total artificial heart (A-TAH). We monitored plasma levels of platelet activation markers in patients receiving A-TAH support (n = 16) throughout the follow-up period. Before implantation, soluble CD40 ligand (sCD40L) levels averaged 3,909.06 pg/ml (standard deviation [SD] = 3,772.37), remaining stable postimplantation at 3,964.56 pg/ml (SD = 2,198.85) during months 1-3 and at 3,519.27 pg/ml (SD = 1,647.04) during months 3-6. Similarly, P-selectin (sP-sel) levels were 35,235.36 pg/ml (SD = 14,940.47) before implantation, stabilizing to 33,158.96 pg/ml (SD = 9,023.11) (1-3 months) and 31,022.58 pg/ml (SD = 9,249.95) (3-6 months). Preimplantation platelet factor 4 (PF4) measured 2,593.47 ng/ml (SD = 2,167.85), remaining consistent at 2,136.10 ng/ml (SD = 1,264.47) (1-3 months) and 1,991.26 ng/ml (SD = 1,234.16) (3-6 months). Levels of neutrophil-activating peptide 2 (NAP2) were also steady, measuring 785.63 ng/ml (SD = 605.26) preimplantation, 935.10 ng/ml (SD = 517.73) at 1-3 months, and 907.21 ng/ml (SD = 501.96) at 3-6 months postimplantation. Importantly, neither aspirin nor heparin treatment affected these platelet biomarker levels. No correlation was observed between platelet activation marker levels and clinical outcomes such as pericardial effusion, nor with the timing of aspirin initiation and drain removal. Our findings confirm that A-TAH does not trigger platelet activation. The lack of association between aspirin, platelet activation, and clinical outcomes suggests the possibility of discontinuing antiplatelet therapy following A-TAH implantation in the future.

The Immune Nature of Platelets Revisited

Platelets are the primary cellular mediators of hemostasis and this function firmly acquaints them with a variety of inflammatory processes. For example, platelets can act as circulating sentinels by expressing Toll-like receptors (TLR) that bind pathogens and this allows platelets to effectively kill them or present them to cells of the immune system. Furthermore, activated platelets secrete and express many pro- and anti-inflammatory molecules that attract and capture circulating leukocytes and direct them to inflamed tissues. In addition, platelets can directly influence adaptive immune responses via secretion of, for example, CD40 and CD40L molecules. Platelets are also the source of most of the microvesicles in the circulation and these miniscule elements further enhance the platelet’s ability to communicate with the immune system. More recently, it has been demonstrated that platelets and their parent cells, the megakaryocytes (MK), can also uptake, process and present both foreign and self-antigens to CD8+ T-cells conferring on them the ability to directly alter adaptive immune responses. This review will highlight several of the non-hemostatic attributes of platelets that clearly and rightfully place them as integral players in immune reactions.

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Platelets can act as circulating sentinels by expressing pathogen-associated molecular pattern receptors that bind pathogens and induce their killing and elimination.

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Activated platelets secrete and express a multitude of pro- and anti-inflammatory molecules that attract and capture circulating leukocytes and direct them to inflamed tissues.

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Platelets express and secrete many critical immunoregulatory molecules that significantly affect both innate and adaptive immune responses.

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Platelets are the primary source of microparticles in the circulation and these augment the platelet’s ability to communicate with the immune system.

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Platelets and megakaryocytes can act as antigen presenting cells and present both foreign- and self-peptides to T-cells.

Mouse Mast Cell Protease-4 Recruits Leukocytes in the Inflammatory Phase of Surgically Wounded Skin

Objective: Mouse mast cell protease-4 (mMCP-4, also known as chymase) has both pro- and anti-inflammatory roles depending on the disease model. However, its effects have not been studied in surgically wounded skin. Given the significant clinical applications of modulating the inflammatory response in wound healing, we examined the role of mMCP-4 and the effect of its inhibitor chymostatin on leukocyte and polymorphonuclear cell (PMN) recruitment in our skin model. Approach: Recruitment was assessed on day-1 postwounding of three groups of mice (n = 10 each): mMCP-4 null mice, wild-type (WT) mice treated with the mMCP-4 inhibitor chymostatin, and WT with no other intervention. Leukocytes were stained with CD-45 cell marker, and PMN cells were stained with chloroacetate esterase. Results: The WT mice had 27 ± 9 leukocytes per field compared with 11 ± 6 for the mMCP-4 nulls, a decrease of 60% (p = 0.03), whereas the chymostatin-injected group had a count comparable with the uninjected WT controls at 24 ± 9. The WT group had a PMN count of 96 ± 12 cells, compared with just 24 ± 8 in the mMCP-4 null group, a decrease of 75% (p = 0.001), whereas the chymostatin-treated group had 60 ± 18 cells, a decrease of 38% compared with the WT group (p = 0.03). Innovation: We showed that the inflammatory process can be influenced by impeding the arrival of PMNs into the surgically injured site using the mMCP-4 inhibitor chymostatin. Conclusion: Chymase contributes to the recruitment of white blood cells in surgically wounded skin.

The Platelet Napoleon Complex-Small Cells, but Big Immune Regulatory Functions

Platelets have dual physiologic roles as both cellular mediators of thrombosis and immune modulatory cells. Historically, the thrombotic function of platelets has received significant research and clinical attention, but emerging research indicates that the immune regulatory roles of platelets may be just as important. We now know that in addition to their role in the acute thrombotic event at the time of myocardial infarction, platelets initiate and accelerate inflammatory processes that are part of the pathogenesis of atherosclerosis and myocardial infarction expansion. Furthermore, it is increasingly apparent from recent studies that platelets impact the pathogenesis of many vascular inflammatory processes such as autoimmune diseases, sepsis, viral infections, and growth and metastasis of many types of tumors. Therefore, we must consider platelets as immune cells that affect all phases of immune responses.

CTAPIII/CXCL7: a novel biomarker for early diagnosis of lung cancer

It is desirable to have a biomarker which can facilitate low-dose CT in diagnosis of early stage lung cancer. CTAPIII/CXCL7 is reported to be a potential biomarker for diagnosis of early lung cancer. In this study, we investigated the serum level of CTAPIII/CXCL7 in patients at different stage of lung cancer and the diagnostic efficacy of CTAPIII/CXCL7 in NSCLC. The plasma level of CTAPIII/CXCL7 was assayed by ELISA. CEA, SCCAg, and Cyfra211 were measured using a commercial chemiluminescent microparticle immunoassay. A total of 419 subjects were recruited, including 265 NSCLC patients and 154 healthy individuals. The subjects were randomly assigned to a training set and a test set. Receiver operating characteristic (ROC) and binary logistic regression analyses were conducted to evaluate the diagnostic efficacy and establish diagnostic mathematical model. Plasma CTAPIII/CXCL7 levels were significantly higher in NSCLC patients than in controls, which was independent of the stage of NSCLC. The diagnostic efficiency of CTAPIII/CXCL7 in NSCLC (training set: area under ROC curve (AUC) 0.806, 95% CI: 0.748-0.863; test set: AUC 0.773, 95% CI: 0.711-0.835) was greater than that of SCCAg, Cyfra21-1, or CEA. The model combining CTAPIII/CXCL7 with CEA, SCCAg, and Cyfra21-1 was more effective for NSCLC diagnosis than CTAPIII/CXCL7 alone. In addition, plasma level of CTAPIII/CXCL7 may contribute to the early diagnosis of NSCLC. CTAPIII/CXCL7 can be used as a plasma biomarker for the diagnosis of NSCLCs, particularly early stage lung cancer, with relatively high sensitivity and specificity.

Platelet-Derived Chemokine CXCL7 Dimer Preferentially Exists in the Glycosaminoglycan-Bound Form: Implications for Neutrophil-Platelet Crosstalk

Platelet-derived chemokine CXCL7 (also known as NAP-2) plays a crucial role in orchestrating neutrophil recruitment in response to vascular injury. CXCL7 exerts its function by activating the CXC chemokine receptor 2 (CXCR2) receptor and binding sulfated glycosaminoglycans (GAGs) that regulate receptor activity. CXCL7 exists as monomers, dimers, and tetramers, and previous studies have shown that the monomer dominates at lower and the tetramer at higher concentrations. These observations then raise the question: what, if any, is the role of the dimer? In this study, we make a compelling observation that the dimer is actually the favored form in the GAG-bound state. Further, we successfully characterized the structural basis of dimer binding to GAG heparin using solution nuclear magnetic resonance (NMR) spectroscopy. The chemical shift assignments were obtained by exploiting heparin binding-induced NMR spectral changes in the WT monomer and dimer and also using a disulfide-linked obligate dimer. We observe that the receptor interactions of the dimer are similar to the monomer and that heparin-bound dimer is occluded from receptor interactions. Cellular assays also show that the heparin-bound CXCL7 is impaired for CXCR2 activity. We conclude that the dimer–GAG interactions play an important role in neutrophil–platelet crosstalk, and that these interactions regulate gradient formation and the availability of the free monomer for CXCR2 activation and intrathrombus neutrophil migration to the injury site.

Platelet-Specific Chemokines Contribute to the Pathogenesis of Acute Lung Injury

Platelets and neutrophils contribute to the development of acute lung injury (ALI). However, the mechanism by which platelets make this contribution is incompletely understood. We investigated whether the two most abundant platelet chemokines, CXCL7, which induces neutrophil chemotaxis and activation, and CXCL4, which does neither, mediate ALI through complementary pathogenic pathways. To examine the role of platelet-derived chemokines in the pathogenesis of ALI using Cxcl7^-/- and Cxcl4^-/- knockout mice and mice that express human CXCL7 or CXCL4, we measured levels of chemokines in these mice. ALI was then induced by acid aspiration, and the severity of injury was evaluated by histology and by the presence of neutrophils and protein in the bronchoalveolar lavage fluid. Pulmonary vascular permeability was studied in vivo by measuring extravasation of fluorescently labeled dextran. Murine CXCL7, both recombinant and native protein released from platelets, can be N-terminally processed by cathepsin G to yield a biologically active CXCL7 fragment. Although Cxcl7^-/- mice are protected from lung injury through the preservation of endothelial/epithelial barrier function combined with impaired neutrophils transmigration, Cxcl4^-/- mice are protected through improved barrier function without affecting neutrophils transmigration to the airways. Sensitivity to ALI is restored by transgenic expression of CXCL7 or CXCL4. Platelet-derived CXCL7 and CXCL4 contribute to the pathogenesis of ALI through complementary effects on neutrophil chemotaxis and through activation and vascular permeability.

CD26/dipeptidylpeptidase IV-chemokine interactions: double-edged regulation of inflammation and tumor biology

Review of how chemokine processing by CD26/DPP IV regulates leukocyte trafficking.

Post‐translational modification of chemokines is an essential regulatory mechanism to enhance or dampen the inflammatory response. CD26/dipeptidylpeptidase IV, ubiquitously expressed in tissues and blood, removes NH₂‐terminal dipeptides from proteins with a penultimate Pro or Ala. A large number of human chemokines, including CXCL2, CXCL6, CXCL9, CXCL10, CXCL11, CXCL12, CCL3L1, CCL4, CCL5, CCL11, CCL14, and CCL22, are cleaved by CD26; however, the efficiency is clearly influenced by the amino acids surrounding the cleavage site and although not yet proven, potentially affected by the chemokine concentration and interactions with third molecules. NH₂‐terminal cleavage of chemokines by CD26 has prominent effects on their receptor binding, signaling, and hence, in vitro and in vivo biologic activities. However, rather than having a similar result, the outcome of NH₂‐terminal truncation is highly diverse. Either no difference in activity or drastic alterations in receptor recognition/specificity and hence, chemotactic activity are observed. Analogously, chemokine‐dependent inhibition of HIV infection is enhanced (for CCL3L1 and CCL5) or decreased (for CXCL12) by CD26 cleavage. The occurrence of CD26‐processed chemokine isoforms in plasma underscores the importance of the in vitro‐observed CD26 cleavages. Through modulation of chemokine activity, CD26 regulates leukocyte/tumor cell migration and progenitor cell release from the bone marrow, as shown by use of mice treated with CD26 inhibitors or CD26 knockout mice. As chemokine processing by CD26 has a significant impact on physiologic and pathologic processes, application of CD26 inhibitors to affect chemokine function is currently explored, e.g., as add‐on therapy in viral infection and cancer.

Chemokine-Derived Peptides: Novel Antimicrobial and Antineoplasic Agents

Chemokines are a burgeoning family of chemotactic cytokines displaying a broad array of functions such as regulation of homeostatic leukocyte traffic and development, as well as activating the innate immune system. Their role in controlling early and late inflammatory stages is now well recognized. An improper balance either in chemokine synthesis or chemokine receptor expression contributes to various pathological disorders making chemokines and their receptors a useful therapeutic target. Research in this area is progressing rapidly, and development of novel agents based on chemokine/chemokine receptors antagonist functions are emerging as attractive alternative drugs. Some of these novel agents include generation of chemokine-derived peptides (CDP) with potential agonist and antagonist effects on inflammation, cancer and against bacterial infections. CDP have been generated mainly from N- and C-terminus chemokine sequences with subsequent modifications such as truncations or elongations. In this review, we present a glimpse of the different pharmacological actions reported for CDP and our current understanding regarding the potential use of CDP alone or as part of the novel therapies proposed in the treatment of microbial infections and cancer.

Emerging roles for platelets as immune and inflammatory cells

Despite their small size and anucleate status, platelets have diverse roles in vascular biology. Not only are platelets the cellular mediator of thrombosis, but platelets are also immune cells that initiate and accelerate many vascular inflammatory conditions. Platelets are linked to the pathogenesis of inflammatory diseases such as atherosclerosis, malaria infection, transplant rejection, and rheumatoid arthritis. In some contexts, platelet immune functions are protective, whereas in others platelets contribute to adverse inflammatory outcomes. In this review, we will discuss platelet and platelet-derived mediator interactions with the innate and acquired arms of the immune system and platelet-vessel wall interactions that drive inflammatory disease. There have been many recent publications indicating both important protective and adverse roles for platelets in infectious disease. Because of this new accumulating data, and the fact that infectious disease continues to be a leading cause of death globally, we will also focus on new and emerging concepts related to platelet immune and inflammatory functions in the context of infectious disease.

Role of platelet chemokines, PF-4 and CTAP-III, in cancer biology

With the recent addition of anti-angiogenic agents to cancer treatment, the angiogenesis regulators in platelets are gaining importance. Platelet factor 4 (PF-4/CXCL4) and Connective tissue activating peptide III (CTAP-III) are two platelet-associated chemokines that modulate tumor angiogenesis, inflammation within the tumor microenvironment, and in turn tumor growth. Here, we review the role of PF-4 and CTAP-III in the regulation of tumor angiogenesis; the results of clinical trial using recombinant PF-4 (rPF-4); and the use of PF-4 and CTAP-III as cancer biomarkers.

Serum proteomics reveals systemic dysregulation of innate immunity in type 1 diabetes

Proteomics analysis identifies human serum proteins involved with innate immune responses, complement activation, and blood coagulation that are diagnostic for type 1 diabetes.

Using global liquid chromatography-mass spectrometry (LC-MS)–based proteomics analyses, we identified 24 serum proteins that were significantly variant between those with type 1 diabetes (T1D) and healthy controls. Functionally, these proteins represent innate immune responses, the activation cascade of complement, inflammatory responses, and blood coagulation. Targeted verification analyses were performed on 52 surrogate peptides representing these proteins, with serum samples from an antibody standardization program cohort of 100 healthy control and 50 type 1 diabetic subjects. 16 peptides were verified as having very good discriminating power, with areas under the receiver operating characteristic curve ≥0.8. Further validation with blinded serum samples from an independent cohort (10 healthy control and 10 type 1 diabetics) demonstrated that peptides from platelet basic protein and C1 inhibitor achieved both 100% sensitivity and 100% specificity for classification of samples. The disease specificity of these proteins was assessed using sera from 50 age-matched type 2 diabetic individuals, and a subset of proteins, C1 inhibitor in particular, were exceptionally good discriminators between these two forms of diabetes. The panel of biomarkers distinguishing those with T1D from healthy controls and those with type 2 diabetes suggests that dysregulated innate immune responses may be associated with the development of this disorder.

Overview of the mechanisms regulating chemokine activity and availability

Physiological leukocyte homing and extravasation of leukocytes during inflammatory processes is directed by a number of proteins including adhesion molecules, proteases, cytokines and chemokines. Tight regulation of leukocyte migration is essential to ensure appropriate migration. A number of mechanisms exist that regulate leukocyte migration including up- or down-regulation of chemokine or chemokine receptor gene expression. However, chemokine availability in vivo also depends on the interaction of chemokines with specific glycosaminoglycans such as heparan sulfate on the surface of endothelial layers. Modification of the interaction of chemokines with these glycosaminoglycans alters the presentation of chemokines to chemokine receptors on circulating leukocytes. On top, binding of chemokines to atypical chemokine receptors that do not signal through G proteins affects chemokine availability on the endothelial layers. In addition to mechanisms that modulate chemokine availability, this review summarizes mechanisms that fine-tune chemokine function. These include synergy or antagonism between chemokines and alternative splicing of chemokine genes. Moreover, chemokines may be posttranslationally modified leading to molecules with enhanced or reduced potency to bind to G protein-coupled receptors or GAGs or generating chemokines with altered receptor specificity. Cross-talk between these different mechanisms generates a complex regulatory network that allows the organism to modulate leukocyte migration in a highly specific manner.

Touch of chemokines

Chemoattractant cytokines or chemokines constitute a family of structurally related proteins found in vertebrates, bacteria, or viruses. So far, 48 chemokine genes have been identified in humans, which bind to around 20 chemokine receptors. These receptors belong to the seven transmembrane G-protein-coupled receptor family. Chemokines and their receptors were originally studied for their role in cellular trafficking of leukocytes during inflammation and immune surveillance. It is now known that they exert different functions under physiological conditions such as homeostasis, development, tissue repair, and angiogenesis but also under pathological disorders including tumorigenesis, cancer metastasis, inflammatory, and autoimmune diseases. Physicochemical properties of chemokines and chemokine receptors confer the ability to homo- and hetero-oligomerize. Many efforts are currently performed in establishing new therapeutically compounds able to target the chemokine/chemokine receptor system. In this review, we are interested in the role of chemokines in inflammatory disease and leukocyte trafficking with a focus on vascular inflammatory diseases, the operating synergism, and the emerging therapeutic approaches of chemokines.

Native thrombocidin-1 and unfolded thrombocidin-1 exert antimicrobial activity via distinct structural elements

Chemokines (chemotactic cytokines) can have direct antimicrobial activity, which is apparently related to the presence of a distinct positively charged patch on the surface. However, chemokines can retain antimicrobial activity upon linearization despite the loss of their positive patch, thus questioning the importance of this patch for activity. Thrombocidin-1 (TC-1) is a microbicidal protein isolated from human blood platelets. TC-1 only differs from the chemokine NAP-2/CXCL7 by a two-amino acid C-terminal deletion, but this truncation is crucial for antimicrobial activity. We assessed the structure-activity relationship for antimicrobial activity of TC-1. Reduction of the charge of the TC-1-positive patch by replacing lysine 17 with alanine reduced the activity against bacteria and almost abolished activity against the yeast Candida albicans. Conversely, augmentation of the positive patch by increasing charge density or size resulted in a 2-3-fold increased activity against Staphylococcus aureus, Escherichia coli, and Bacillus subtilis but did not substantially affect activity against C. albicans. Reduction of TC-1 resulted in loss of the folded conformation, but this disruption of the positive patch did not affect antimicrobial activity. Using overlapping 15-mer synthetic peptides, we demonstrate peptides corresponding to the N-terminal part of TC-1 to have similar antimicrobial activity as intact TC-1. Although we demonstrate that the positive patch is essential for activity of folded TC-1, unfolded TC-1 retained antimicrobial activity despite the absence of a positive patch. This activity is probably exerted by a linear peptide stretch in the N-terminal part of the molecule. We conclude that intact TC-1 and unfolded TC-1 exert antimicrobial activity via distinct structural elements.

iTRAQ-based proteomic profiling of human serum reveals down-regulation of platelet basic protein and apolipoprotein B100 in patients with hematotoxicity induced by chronic occupational benzene exposure

Benzene is an important industrial chemical and an environmental contaminant, but the pathogenesis of hematotoxicity induced by chronic occupational benzene exposure (HCOBE) remains to be elucidated. To gain an insight into the molecular mechanisms and developmental biomarkers for HCOBE, isobaric tags for relative and absolute quantitation (iTRAQ) combined with two-dimensional liquid chromatography-tandem mass spectrometry (2D-LC-MS/MS) were utilized. Identification and quantitation of differentially expressed proteins between HCOBE cases and healthy control were thus made. Expressions of selected proteins were confirmed by western blot and further validated by ELISA. A total of 159 unique proteins were identified (≥95% confidence), and relative expression data were obtained for 141 of these in 3 iTRAQ experiments, with fifty proteins found to be in common among 3 iTRAQ experiments. Plasminogen (PLG) was found to be significantly up-regulated, whereas platelet basic protein (PBP) and apolipoprotein B100 (APOB100) were significantly down-regulated in the serum of HCOBE cases. Additionally, the altered proteins were associated with the molecular functions of binding, catalytic activity, enzyme regulator activity and transporter activity, and involved in biological processes of apoptosis, developmental and immune system process, as well as response to stimulus. Furthermore, differential expressions of PLG, PBP and APOB100 were confirmed by western blot, and the clinical relevance of PBP and APOB100 with HCOBE was validated by ELISA. Overall, our results showed that lowered expression of PBP and APOB100 proteins served as potential biomarkers of HCOBE, and may play roles in the benzene-induced immunosuppressive effects and disorders in lipid metabolism.

The expression and role of CXC chemokines in colorectal cancer

Cancer is a life-threatening disease world-wide and colorectal cancer is the second common cause of cancer mortality. The interaction between tumor cells and stromal cells plays a crucial role in tumor initiation and progression and is partially mediated by chemokines. Chemokines predominantly participate in the chemoattraction of leukocytes to inflammatory sites. Nowadays, it is clear that CXC chemokines and their receptors (CXCR) may also modulate tumor behavior by several important mechanisms: regulation of angiogenesis, activation of a tumor-specific immune response by attracting leukocytes, stimulation of tumor cell proliferation and metastasis. Here, we review the expression and complex roles of CXC chemokines (CXCL1 to CXCL16) and their receptors (CXCR1 to CXCR6) in colorectal cancer. Overall, increased expression levels of CXC chemokines correlate with poor prognosis.

Biological activity of CXCL8 forms generated by alternative cleavage of the signal peptide or by aminopeptidase-mediated truncation

Background

Posttranslational modification of chemokines is one of the mechanisms that regulate leukocyte migration during inflammation. Multiple natural NH₂-terminally truncated forms of the major human neutrophil attractant interleukin-8 or CXCL8 have been identified. Although differential activity was reported for some CXCL8 forms, no biological data are available for others.

Methodology/Principal Findings

Aminopeptidase-cleaved CXCL8(2-77) and CXCL8(3-77), the product of alternative cleavage of the signal peptide CXCL8(-2-77) and the previously studied forms containing 77 and 72 amino acids, CXCL8(1-77) and CXCL8(6-77), were prepared by solid-phase peptide synthesis, purified and folded into active proteins. No differences in binding and calcium signaling potency were detected between CXCL8(1-77), CXCL8(-2-77), CXCL8(2-77) and CXCL8(3-77) on cells transfected with one of the human CXCL8 receptors, i.e. CXCR1 and CXCR2. However, CXCL8(-2-77) was more potent compared to CXCL8(1-77), CXCL8(2-77) and CXCL8(3-77) in signaling and in vitro chemotaxis of peripheral blood-derived human neutrophils. Moreover, CXCL8(-2-77) was less efficiently processed by plasmin into the more potent CXCL8(6-77). The truncated forms CXCL8(2-77) and CXCL8(3-77) had higher affinity for heparin than CXCL8(1-77), a property important for the presentation of CXCL8 on endothelial layers. Upon intraperitoneal injection in mice, elongated, truncated and intact CXCL8 were equally potent to recruit neutrophils to the peritoneal cavity.

Conclusions

In terms of their ability to induce neutrophil recruitment in vivo, the multiple CXCL8 forms may be divided in three groups. The first group includes CXCL8 proteins consisting of 75 to 79 amino acids, cleaved by aminopeptidases, with intermediate activity on neutrophils. The second group, generated through proteolytic cleavage (e.g. by Ser proteases), contains 69 to 72 amino acid forms which are highly potent neutrophil attractants in vivo. A third category is generated through the modification of the arginine in the NH₂-terminal region into citrulline by peptidylarginine deiminases and has weak potency to induce neutrophil extravasation.

Exploring platelet chemokine antimicrobial activity: nuclear magnetic resonance backbone dynamics of NAP-2 and TC-1

The platelet chemokines neutrophil-activating peptide-2 (NAP-2) and thrombocidin-1 (TC-1) differ by only two amino acids at their carboxy-terminal ends. Nevertheless, they display a significant difference in their direct antimicrobial activities, with the longer NAP-2 being inactive and TC-1 being active. In an attempt to rationalize this difference in activity, we studied the structure and the dynamics of both proteins by nuclear magnetic resonance (NMR) spectroscopy. Using 15N isotope-labeled protein, we confirmed that the two monomeric proteins essentially have the same overall structure in aqueous solution. However, NMR relaxation measurements provided evidence that the negatively charged carboxy-terminal residues of NAP-2 experience a restricted motion, whereas the carboxy-terminal end of TC-1 moves in an unrestricted manner. The same behavior was also seen in molecular dynamic simulations of both proteins. Detailed analysis of the protein motions through model-free analysis, as well as a determination of their overall correlation times, provided evidence for the existence of a monomer-dimer equilibrium in solution, which seemed to be more prevalent for TC-1. This finding was supported by diffusion NMR experiments. Dimerization generates a larger cationic surface area that would increase the antimicrobial activities of these chemokines. Moreover, these data also show that the negatively charged carboxy-terminal end of NAP-2 (which is absent in TC-1) folds back over part of the positively charged helical region of the protein and, in doing so, interferes with the direct antimicrobial activity.

Platelet-derived chemokines: pathophysiology and therapeutic aspects

The identification of chemokines in blood platelets has strengthened our view of these cells as participants in immune host defense. Platelet chemokines representing prestored and rapidly releasable proteins may play a major role as first-line inflammatory mediators. This is evident from their capability to recruit early inflammatory cells such as neutrophil granulocytes and monocytes and even to exhibit direct antimicrobial activity. However, insight is growing that platelet chemokines may be also long-term regulators, e.g., by activating T lymphocytes, by modulating the formation of endothelium and even thrombocytopoiesis itself. This review deals with the individual and cooperative functionality of platelet chemokines, as well as their potential as a basis for therapeutic intervention in the pathology of inflammation, infection, allergy and tumors. Within this context, therapeutic strategies based on the use of antibodies, modified chemokines, chemokine-binding proteins and chemokine receptor antagonists as well as first clinical studies will be addressed.

Immunohistochemical analysis of ocular platelet basic protein expression during infection with Pseudomonas aeruginosa

Platelet basic protein (PBP) and several of its derivatives are known to express a wide range of biological characteristics. It is the precursor of connective tissue activating peptide (CTAP-III), beta thromboglobulin (beta-TG) and neutrophil activating peptide (NAP-2), which is the proteolytic derived end product. The temporal ocular expression of the chemokine PBP before and during corneal infection over several days by Pseudomonas aeruginosa was examined by immunohistochemistry. Prior to corneal infection, immunohistochemical staining demonstrated the constitutive expression of PBP in the cornea, lens and retina. PBP expression was present in the corneal epithelium, stromal fibroblasts and endothelium. There was a temporal increase in PBP expression in the cornea after infection. The entire cornea exhibited extensive cellular infiltration by positive PBP staining infiltrating cells within 6 days post-infection. The cornea, lens and retina underwent extensive degradation within 5-6 days post-infection with some apparent selective increase in PBP staining in the lens and retina.

Chapter 1. Isolation, identification, and production of posttranslationally modified chemokines

Chemokines attract cells during the development of lymphoid tissues, leukocyte homing, and pathologic processes such as cancer and inflammation. Limited posttranslational modification of chemokines may significantly alter the glycosaminoglycan and/or receptor binding properties and signaling potency of these chemotactic proteins. To compare the in vitro and in vivo biologic activities of posttranslationally modified chemokine isoforms, considerable amounts of pure chemokine isoforms are required. This chapter describes a number of chromatographic techniques that are useful for the isolation of natural, posttranslationally modified chemokines from primary human cell cultures. In addition, combination of immunologic assays and biochemical techniques such as automated Edman degradation and mass spectrometry are used for the identification of modifications. Alternate methods for the generation of specific chemokine isoforms are discussed such as modification of chemokines by specific enzymes and total chemical syntheses and folding of chemokine isoforms. In particular, in vitro processing of chemokines by the protease aminopeptidase N/CD13 and citrullination or deamination of chemokines by peptidyl arginine deiminases (PAD) are described as methods for the confirmation or generation of posttranslationally modified chemokine isoforms.

The role of CXC chemokines and their receptors in cancer

Chemokines, or chemotactic cytokines, and their receptors have been discovered as essential and selective mediators in leukocyte migration to inflammatory sites and to secondary lymphoid organs. Besides their functions in the immune system, they also play a critical role in tumor initiation, promotion and progression. There are four subgroups of chemokines: CXC, CC, CX(3)C, and C chemokine ligands. The CXC or alpha subgroup is further subdivided in the ELR(+) and ELR(-) chemokines. Members that contain the ELR motif bind to CXC chemokine receptor 2 (CXCR2) and are angiogenic. In contrast, most of the CXC chemokines without ELR motif bind to CXCR3 and are angiostatic. An exception is the angiogenic ELR(-)CXC chemokine stromal cell-derived factor-1 (CXCL12/SDF-1), which binds to CXCR4 and CXCR7 and is implicated in tumor metastasis. This review is focusing on the role of CXC chemokines and their receptors in tumorigenesis, including angiogenesis, attraction of leukocytes to tumor sites and induction of tumor cell migration and homing in metastatic sites. Finally, their therapeutic use in cancer treatment is discussed.

Detection and identification of NAP-2 as a biomarker in hepatitis B-related hepatocellular carcinoma by proteomic approach

BACKGROUND

A lack of sensitive and specific biomarkers is a major reason for the high rate of Primary hepatocellular carcinoma (HCC)-related mortality. The aim of this study was to investigate potential proteomic biomarkers specific for HCC.

METHODS

81 patients with hepatitis B-related HCC and 33 healthy controls were randomly divided into a training set (33 HCC, 33 controls) and a testing set (48 HCC, 33 controls). Serum proteomic profiles were measured using Surface-enhanced laser desorption/ionization-time-of-flight mass spectroscopy (SELDI-TOF-MS).) A classification tree was established by Biomarker Pattern Software (BPS). Candidate SELDI peaks were isolated by tricine-SDS-PAGE, identified by HPLC-MS/MS and validated by immunohistochemistry (IHC) in liver tissues.

RESULTS

A total of 6 proteomic peaks (3157.33 m/z, 4177.02 m/z, 4284.79 m/z, 4300.80 m/z, 7789.87 m/z, and 7984.14 m/z) were chosen by BPS to establish a classification tree with the highest discriminatory power in the training set. The sensitivity and specificity of this classification tree were 95.92%, and 100% respectively in the testing set. A candidate marker of about 7984 m/z was isolated and identified as neutrophil-activating peptide 2 (NAP-2). IHC staining showed that NAP-2 signals were positive in HCC tissues but negative in adjacent tissues.

CONCLUSION

The NAP-2 may be a specific proteomic biomarker of hepatitis B-related HCC.

Proteolytic processing of CXCL11 by CD13/aminopeptidase N impairs CXCR3 and CXCR7 binding and signaling and reduces lymphocyte and endothelial cell migration

CXCR3 ligands were secreted by tissue fibroblasts and peripheral blood-derived mononuclear leukocytes in response to interferon-gamma (IFN-gamma) and Toll-like receptor (TLR) ligands. Subsequent purification and identification revealed the presence of truncated CXCL11 variants missing up to 6 amino acids. In combination with CD26/dipeptidyl peptidase IV, the metalloprotease aminopeptidase N (APN), identical to the myeloid cell marker CD13, rapidly processed CXCL11, but not CXCL8, to generate truncated CXCL11 forms. Truncated CXCL11 had reduced binding, signaling, and chemotactic properties for lymphocytes and CXCR3- or CXCR7-transfected cells. CD13/APN-truncated CXCL11 failed to induce an intracellular calcium increase but was still able to bind and desensitize CXCR3 for intact CXCL11 signaling. CXCL11 efficiently bound to CXCR7, but CXCL11 was not able to induce calcium signaling or ERK1/2 or Akt phosphorylation through CXCR7. CD26-truncated CXCL11 failed to attract lymphocytes but still inhibited microvascular endothelial cell (HMVEC) migration. However, further processing of CXCL11 by CD13 resulted in significant reduction of inhibition of HMVEC migration. Taken together, during inflammation or cancer, CXCL11 processing by CD13 may lead to a reduced number of tumor-infiltrating lymphocytes and in a more angiogenic environment.

Serum proteome profiling detects myelodysplastic syndromes and identifies CXC chemokine ligands 4 and 7 as markers for advanced disease

Myelodysplastic syndromes (MDS) are among the most frequent hematologic malignancies. Patients have a short survival and often progress to acute myeloid leukemia. The diagnosis of MDS can be difficult; there is a paucity of molecular markers, and the pathophysiology is largely unknown. Therefore, we conducted a multicenter study investigating whether serum proteome profiling may serve as a noninvasive platform to discover novel molecular markers for MDS. We generated serum proteome profiles from 218 individuals by MS and identified a profile that distinguishes MDS from non-MDS cytopenias in a learning sample set. This profile was validated by testing its ability to predict MDS in a first independent validation set and a second, prospectively collected, independent validation set run 5 months apart. Accuracy was 80.5% in the first and 79.0% in the second validation set. Peptide mass fingerprinting and quadrupole TOF MS identified two differential proteins: CXC chemokine ligands 4 (CXCL4) and 7 (CXCL7), both of which had significantly decreased serum levels in MDS, as confirmed with independent antibody assays. Western blot analyses of platelet lysates for these two platelet-derived molecules revealed a lack of CXCL4 and CXCL7 in MDS. Subtype analyses revealed that these two proteins have decreased serum levels in advanced MDS, suggesting the possibility of a concerted disturbance of transcription or translation of these chemokines in advanced MDS.

Proteomic analysis of factors released from p21-overexpressing tumour cells

The p21Waf1/Cip1/Sdi1 cyclin-dependent kinase inhibitor is a key regulator of cell cycle progression and has also been observed to influence the expression of genes associated with several age-related disorders. Previous work has shown that expression of p21 in tumour cells mediates an antiapoptotic and mitogenic paracrine effect, which is in contrast to the arrested state of p21-expressing cells. Here, we have employed SELDI-MS technology to characterise, at a proteomic level, factors released from HT-1080 human fibrosarcoma cells displaying inducible p21 expression. Conditioned media from induced and noninduced cells were profiled on a range of diverse ProteinChip arrays and subjected to SELDI-MS analysis. Evaluation of proteins binding onto IMAC, Q10 or CM10 surfaces led to the discovery of a number of putative p21-regulated factors. We further validated three p21-regulated proteins observed at 10.2, 11.7 and 13.4 kDa. Using Q Ceramic HyperD fractionation columns, we were able to selectively enrich for each of these three proteins. Subsequent SDS-PAGE and MS analysis of tryptic digests identified the 13.4 kDa protein as cystatin C and the 10.2 kDa protein as pro-platelet basic protein (PPBP). Judging by the apparent MW and the pI of the 11.7 kDa protein, we reasoned that it may be beta-2-microglobulin, which was confirmed by subsequent identification. Increased levels of cystatin C and beta-2-microglobulin in conditioned media from p21-expressing cells was confirmed by antibody capture experiments using anticystatin C and anti-beta-2-microglobulin antibodies on preactivated PS-20 arrays. Western blot analysis demonstrated increased expression of intracellular and extracellular cystatin C and beta-2-microglobulin in p21-expressing cells, compared to noninduced controls. Increased levels of PPBP were validated in cell lysates from p21-expressing cells. The three secreted factors that we have identified in this study, have all been shown previously to have growth modulating effects and, as such, may contribute to the observed mitogenic and anti-apoptotic paracrine activity of p21-expressing [corrected] cells.

Increased Levels of Neutrophil-Activating Peptide-2 in Acute Coronary Syndromes

OBJECTIVES

We sought to investigate the role of the CXC chemokine neutrophil-activating peptide-2 (NAP-2) in atherogenesis and plaque destabilization.

BACKGROUND

Chemokines are involved in atherogenesis, but the role of NAP-2 in atherosclerotic disorders is unclear. Based on its potential pro-atherogenic properties, we hypothesized a pathogenic role for NAP-2 in coronary artery disease.

METHODS

We tested this hypothesis by differential experimental approaches including studies in patients with stable (n = 40) and unstable angina (n = 40) and healthy control subjects (n = 20).

RESULTS

The following results were discovered: 1) patients with stable, and particularly those with unstable, angina had markedly raised plasma levels of NAP-2 compared with control subjects, accompanied by increased expression of CXC receptor 2 in monocytes; 2) platelets, but also peripheral blood mononuclear cells (PBMCs), released large amounts of NAP-2 upon stimulation, with a particularly prominent PBMC response in unstable angina; 3) NAP-2 protein was detected in macrophages and smooth muscle cells of atherosclerotic plaques and in monocytes and platelets of coronary thrombi; 4) in vitro, recombinant and platelet-derived NAP-2 increased the expression of adhesion molecules and chemokines in endothelial cells; and 5) whereas aspirin reduced plasma levels of NAP-2, statin therapy increased NAP-2 with stimulating effects both on platelets and leukocytes.

CONCLUSIONS

Our findings suggest that NAP-2 has the potential to induce inflammatory responses within the atherosclerotic plaque. By its ability to promote leukocyte and endothelial cell activation, such a NAP-2-driven inflammation could promote plaque rupture and acute coronary syndromes.

Mast cells and neutrophils proteolytically activate chemokine precursor CTAP-III and are subject to counterregulation by PF-4 through inhibition of chymase and cathepsin G

The CXC chemokines platelet factor 4 (PF-4/CXCL4) and connective tissue-activating peptide III (CTAP-III) are released by activated human platelets in micromolar concentrations. So far, neutrophils have been recognized to cleave the precursor CTAP-III to form the active chemokine neutrophil-activating peptide 2 (NAP-2/CXCL7) through limited proteolysis by membrane-associated cathepsin G. Here we show for the first time that activated human skin mast cells (MCs) convert CTAP-III into biologically active NAP-2 through proteolytic cleavage by released chymase. A direct comparison on a cell number basis revealed that unstimulated MCs exceed the CTAP-III–processing potency of neutrophils about 30-fold, whereas MCs activated by IgE cross-linking exhibit even 1000-fold higher CTAP-III–processing capacity than fMLP-stimulated neutrophils. Intriguingly, PF-4 counteracted MC- as well as neutrophil-mediated NAP-2 generation at physiologically relevant concentrations. Addressing the underlying mechanism, we obtained evidence that PF-4 acts as an inhibitor of the CTAP-III–processing enzymes cathepsin G and chymase without becoming cleaved itself as a competitive substrate. Because cleavage of the CTAP-III–unrelated substrate substance P was also affected by PF-4, our results suggest a regulatory role for PF-4 not only in NAP-2 generation but also in neutrophil- and MC-mediated processing of other physiologically relevant inflammatory mediators.

Chemokine-protease interactions in cancer

Solid tumour and leukemic cells expressing chemokine receptors, metastasize to chemokine-secreting organs. Chemokines indirectly affect tumour development by attracting immunocompetent cells with pro- or anti-tumoral activities. Various membrane-associated and soluble proteases selectively cleave specific chemokines. Precursor plasma chemokines (CXCL7, CCL14) need to be proteolytically processed to obtain receptor affinity. Angiogenic CXC chemokines (CXCL1, CXCL8) have increased CXCR1/CXCR2 affinity after limited NH2-terminal processing, whereas truncated angiostatic chemokines (CXCL10) show lower CXCR3 affinity without loss of angiostatic potential. NH2-terminally cleaved monocyte chemotactic proteins (CCL2, CCL7, CCL8) have impaired capacity to attract tumour-associated macrophages and function as receptor antagonists for intact CC chemokines. Migration of Th1/CCR5+ and Th2/CCR4+ effector lymphocytes toward CCR5 (CCL5, CCL3L1) and CCR4 (CCL22) ligands is affected by cleavage. Although proteolytical processing of chemokines is well studied in vitro, the direct or indirect effects on tumour invasion and metastasis are only poorly evaluated.

Rapamycin attenuates vascular wall inflammation and progenitor cell promoters after angioplasty

Rapamycin combines antiproliferative and antiinflammatory properties and reduces neointima formation after angioplasty in patients. Its effect on transcriptional programs governing neointima formation has not yet been investigated. Here, we systematically analyzed the effect of rapamycin on gene expression during neointima formation in a human organ culture model. After angioplasty, renal artery segments were cultured for 21 or 56 days in absence or presence of 100 ng/ml rapamycin. Gene expression analysis of 2312 genes revealed 264 regulated genes with a peak alteration after 21 days. Many of those were associated with recruitment of blood cells and inflammatory reactions of the vessel wall. Likewise, chemokines and cytokines such as M-CSF, IL-1beta, IL-8, beta-thromboglobulin, and EMAP-II were found up-regulated in response to vessel injury. Markers indicative for a facilitated recruitment and stimulation of hematopoetic progenitor cells (HPC), including BST-1 and SDF-1, were also induced. In this setting, rapamycin suppressed the coordinated proadhesive and proinflammatory gene expression pattern next to down-regulation of genes related to metabolism, proliferation, and apoptosis. Our study shows that mechanical injury leads to induction of a proinflammatory, proadhesive gene expression pattern in the vessel wall even in absence of leukocytes. These molecular events could provide a basis for the recruitment of leukocytes and HPC. By inhibiting the expression of such genes, rapamycin may lead to a reduced recruitment of leukocytes and HPC after vascular injury, an effect that may play a decisive role for its effectiveness in reducing restenosis.

Induction and antimicrobial activity of platelet basic protein derivatives in human monocytes

The antimicrobial activity of a number of chemokines has recently come into focus of research about innate immunity. We have previously shown that platelet basic protein (PBP), which gives rise to several antimicrobial peptides of platelets, is also expressed in human monocytes. In the present studies, we show that exposure of human monocytes to bacteria or microbial components (lipopolysaccharide and zymosan) induces a several-fold greater expression of derivates of PBP. Also, activation of proteinase-activated receptors (PARs) by thrombin or the synthetic peptide ligand SFLLRN of PAR-1 significantly increased PBP expression, presumably on the transcriptional level, as evidenced by higher mRNA levels. Derivates of PBP appeared to reach phago-lysosomes, as higher concentration was found in latex phagosomes isolated by a flotation method. By the gel-overlay technique, two bactericidal derivatives of PBP could be visualized, which were immunoreactive with anti-PBP antibody in Western blots. By matrix-assisted laser desorption/ionization time of flight and surface-enhanced laser desorption and ionization techniques, it was confirmed that the bands corresponded to PBP derivates. After immunofixation with a monoclonal antibody to PBP, the major peptide in zymosan-stimulated monocytes was identified to correspond by molecular weight to connective tissue-activating peptide III, which has been reported to be a major antimicrobial PBP derivate also in platelets. Our observations indicate that PBP and its derivates are constituents of the antimicrobial arsenal of human monocytes. Their increased expression after exposure to microorganisms allows a rapid host response to pathogens.

Constitutive and regulated expression of platelet basic protein in human monocytes

Platelet basic protein (PBP) and several of its derivatives are known for their broad range of functions as signaling molecules and cationic antimicrobial peptides and were considered hitherto megakaryocyte- and platelet-specific. In search of glucocorticoid-regulated antimicrobial systems of monocytes, we found a 15-fold down-regulation of PBP mRNA by differential display. Regulation was confirmed in vivo even at low prednisone doses. Quantitative mRNA analyses confirmed down-regulation also for platelets. Western blotting and immunostains showed down-regulation at the protein level. Pro-PBP derivatives were in the size range of 7.5-14 kD and in immunostains, gave granular cytoplasmatic patterns. Interleukin (IL)-4 and IL-10 induced a similar down-regulation. Phagocytosis resulted in an increase of smaller derivatives in the range of 7.5 kD. Stimulation with interferon-gamma and lipopolysaccharide did decrease expression of PBP and affected derivatization. Expression of PBP and its derivatives is not restricted to the megakaryocytic cell lineage. PBP and some of its derivatives might contribute to the antimicrobial armamentarium of mononuclear phagocytes or have monokine functions. Our studies define PBPs as one among the many immunosuppressive targets of glucocorticoids.

Platelet factor 4 enhances the binding of oxidized low-density lipoprotein to vascular wall cells

Accumulation of low-density lipoprotein (LDL)-derived cholesterol by macrophages in vessel walls is a pathogenomic feature of atherosclerotic lesions. Platelets contribute to lipid uptake by macrophages through mechanisms that are only partially understood. We have previously shown that platelet factor 4 (PF4) inhibits the binding and degradation of LDL through its receptor, a process that could promote the formation of oxidized LDL (ox-LDL). We have now characterized the effect of PF4 on the binding of ox-LDL to vascular cells and macrophages and on the accumulation of cholesterol esters. PF4 bound to ox-LDL directly and also increased ox-LDL binding to vascular cells and macrophages. PF4 did not stimulate ox-LDL binding to cells that do not synthesize glycosaminoglycans or after enzymatic cleavage of cell surface heparan and chondroitin sulfates. The effect of PF4 on binding ox-LDL was dependent on specific lysine residues in its C terminus. Addition of PF4 also caused an approximately 10-fold increase in the amount of ox-LDL esterified by macrophages. Furthermore, PF4 and ox-LDL co-localize in atherosclerotic lesion, especially in macrophage-derived foam cells. These observations offer a potential mechanism by which platelet activation at sites of vascular injury may promote the accumulation of deleterious lipoproteins and offer a new focus for pharmacological intervention in the development of atherosclerosis.

Platelet-derived chemokines CXC chemokine ligand (CXCL)7, connective tissue-activating peptide III, and CXCL4 differentially affect and cross-regulate neutrophil adhesion and transendothelial migration

In this study, we have examined the major platelet-derived CXC chemokines connective tissue-activating peptide III (CTAP-III), its truncation product neutrophil-activating peptide 2 (CXC chemokine ligand 7 (CXCL7)), as well as the structurally related platelet factor 4 (CXCL4) for their impact on neutrophil adhesion to and transmigration through unstimulated vascular endothelium. Using monolayers of cultured HUVEC, we found all three chemokines to promote neutrophil adhesion, while only CXCL7 induced transmigration. Induction of cell adhesion following exposure to CTAP-III, a molecule to date described to lack neutrophil-stimulating capacity, depended on proteolytical conversion of the inactive chemokine into CXCL7 by neutrophils. This was evident from experiments in which inhibition of the CTAP-III-processing protease and simultaneous blockade of the CXCL7 high affinity receptor CXCR-2 led to complete abrogation of CTAP-III-mediated neutrophil adhesion. CXCL4 at substimulatory dosages modulated CTAP-III- as well as CXCL7-induced adhesion. Although cell adhesion following exposure to CTAP-III was drastically reduced, CXCL7-mediated adhesion underwent significant enhancement. Transendothelial migration of neutrophils in response to CXCL7 or IL-8 (CXCL8) was subject to modulation by CTAP-III, but not CXCL4, as seen by drastic desensitization of the migratory response of neutrophils pre-exposed to CTAP-III, which was paralleled by selective down-modulation of CXCR-2. Altogether our results demonstrate that there exist multiple interactions between platelet-derived chemokines in the regulation of neutrophil adhesion and transendothelial migration.

Scintigraphy of acute inflammatory lesions in rats with radiolabelled recombinant human neutrophil-activating peptide-2

Radiolabelled recombinant human interleukin-8 (IL-8) with its homologue neutrophil-activating peptide-2 (NAP-2) have been compared for imaging acute sterile inflammatory lesions in rats. 125I-IL-8 and 125I-NAP-2 were prepared by reaction with chloramine-T and injected intravenously into male rats bearing subcutaneous carrageenan abscesses in their left hindlimbs. Left hindlimb and right hindlimb activities were determined from serial total-body scintigrams between 1 h and 96 h post-injection as regional per cent injected activity corrected for physical decay (%IA). Time-activity curves for 125I-IL-8 and 125I-NAP-2 in the carrageenan-containing left hindlimbs were similar in that both peaked at 1-3 h post-injection (IL-8, 4.9+/-0.5%IA; NAP-2, 4.8+/-1.9%IA) and decreased exponentially thereafter. However, while the lesioned-to-control limb activity ratio (L/C) for 125I-IL-8 only approximately doubled during the imaging period (1.7+/-0.3 at 1 h vs 3.7+/-1.0 at 24 h post-injection), L/C for 125I-NAP-2 more than tripled, rising from 1.5+/-0.4 at 1 h to 5.3+/-0.7 by 72 h post-injection. It is concluded that while both radiolabelled IL-8 and NAP-2 may prove useful for clinical imaging, radiolabelled NAP-2 may provide better discrimination of inflammatory lesions from normal tissue at later times post-injection.

Matrix metalloproteinase activity inactivates the CXC chemokine stromal cell-derived factor-1

Chemokines provide directional cues for leukocyte migration and activation that are essential for normal leukocytic trafficking and for host responses during processes such as inflammation, infection, and cancer. Recently we reported that matrix metalloproteinases (MMPs) modulate the activity of the CC chemokine monocyte chemoattractant protein-3 by selective proteolysis to release the N-terminal tetrapeptide. Here we report the N-terminal processing, also at position 4-5, of the CXC chemokines stromal cell-derived factor (SDF)-1alpha and beta by MMP-2 (gelatinase A). Robustness of the MMP family for chemokine cleavage was revealed from identical cleavage site specificity of MMPs 1, 3, 9, 13, and 14 (MT1-MMP) toward SDF-1; selectivity was indicated by absence of cleavage by MMPs 7 and 8. Efficient cleavage of SDF-1alpha by MMP-2 is the result of a strong interaction with the MMP hemopexin C domain at an exosite that overlaps the monocyte chemoattractant protein-3 binding site. The association of SDF-1alpha with different glycosaminoglycans did not inhibit cleavage. MMP cleavage of SDF-1alpha resulted in loss of binding to its cognate receptor CXCR-4. This was reflected in a loss of chemoattractant activity for CD34(+) hematopoietic progenitor stem cells and pre-B cells, and unlike full-length SDF-1alpha, the MMP-cleaved chemokine was unable to block CXCR-4-dependent human immunodeficiency virus-1 infection of CD4(+) cells. These data suggest that MMPs may be important regulatory proteases in attenuating SDF-1 function and point to a deep convergence of two important networks, chemokines and MMPs, to regulate leukocytic activity in vivo.

Functional expression of CCR1, CCR3, CCR4, and CXCR4 chemokine receptors on human platelets

Platelets are known to contain platelet factor 4 and β-thromboglobulin, α-chemokines containing the CXC motif, but recent studies extended the range to the β-family characterized by the CC motif, including RANTES and Gro-α. There is also evidence for expression of chemokine receptors CCR4 and CXCR4 in platelets. This study shows that platelets have functional CCR1, CCR3, CCR4, and CXCR4 chemokine receptors. Polymerase chain reaction detected chemokine receptor messenger RNA in platelet RNA. CCR1, CCR3, and especially CCR4 gave strong signals; CXCR1 and CXCR4 were weakly positive. Flow cytometry with specific antibodies showed the presence of a clear signal for CXCR4 and weak signals for CCR1 and CCR3, whereas CXCR1, CXCR2, CXCR3, and CCR5 were all negative. Immunoprecipitation and Western blotting with polyclonal antibodies to cytoplasmic peptides clearly showed the presence of CCR1 and CCR4 in platelets in amounts comparable to monocytes and CCR4 transfected cells, respectively. Chemokines specific for these receptors, including monocyte chemotactic protein 1, macrophage inflammatory peptide 1α, eotaxin, RANTES, TARC, macrophage-derived chemokine, and stromal cell–derived factor 1, activate platelets to give Ca++ signals, aggregation, and release of granule contents. Platelet aggregation was dependent on release of adenosine diphosphate (ADP) and its interaction with platelet ADP receptors. Part, but not all, of the Ca++ signal was due to ADP release feeding back to its receptors. Platelet activation also involved heparan or chondroitin sulfate associated with the platelet surface and was inhibited by cleavage of these glycosaminoglycans or by heparin or low molecular weight heparin. These platelet receptors may be involved in inflammatory or allergic responses or in platelet activation in human immunodeficiency virus infection.

Functional expression of CCR1, CCR3, CCR4, and CXCR4 chemokine receptors on human platelets

Platelets are known to contain platelet factor 4 and β-thromboglobulin, α-chemokines containing the CXC motif, but recent studies extended the range to the β-family characterized by the CC motif, including RANTES and Gro-α. There is also evidence for expression of chemokine receptors CCR4 and CXCR4 in platelets. This study shows that platelets have functional CCR1, CCR3, CCR4, and CXCR4 chemokine receptors. Polymerase chain reaction detected chemokine receptor messenger RNA in platelet RNA. CCR1, CCR3, and especially CCR4 gave strong signals; CXCR1 and CXCR4 were weakly positive. Flow cytometry with specific antibodies showed the presence of a clear signal for CXCR4 and weak signals for CCR1 and CCR3, whereas CXCR1, CXCR2, CXCR3, and CCR5 were all negative. Immunoprecipitation and Western blotting with polyclonal antibodies to cytoplasmic peptides clearly showed the presence of CCR1 and CCR4 in platelets in amounts comparable to monocytes and CCR4 transfected cells, respectively. Chemokines specific for these receptors, including monocyte chemotactic protein 1, macrophage inflammatory peptide 1α, eotaxin, RANTES, TARC, macrophage-derived chemokine, and stromal cell–derived factor 1, activate platelets to give Ca++ signals, aggregation, and release of granule contents. Platelet aggregation was dependent on release of adenosine diphosphate (ADP) and its interaction with platelet ADP receptors. Part, but not all, of the Ca++ signal was due to ADP release feeding back to its receptors. Platelet activation also involved heparan or chondroitin sulfate associated with the platelet surface and was inhibited by cleavage of these glycosaminoglycans or by heparin or low molecular weight heparin. These platelet receptors may be involved in inflammatory or allergic responses or in platelet activation in human immunodeficiency virus infection.

Stimulation of cellular sphingomyelin import by the chemokine connective tissue-activating peptide III

The selective import of phospholipids into cells could be mediated by proteins secreted from the cells into the extracellular compartment. We observed that the supernatants obtained from suspensions of thrombin-activated platelets stimulated the exchange of pyrene (py)-labeled sphingomyelin between lipid vesicles in vitro. The proteins with sphingomyelin transfer activity were purified and identified as the chemokine connective tissue-activating peptide III (CTAP-III) and platelet basic protein. Isolated CTAP-III stimulated the exchange of py-sphingomyelin between lipid vesicles but did not affect the translocations of py-labeled phosphatidylcholine and phosphatidylethanolamine. CTAP-III rapidly increased the transfer of py-sphingomyelin from low density lipoproteins into peripheral blood lymphocytes, other immune cells, and fibroblasts. In the presence of heparin, CTAP-III was unable to insert sphingomyelin into the peripheral blood lymphocytes. The activation energy of the py-sphingomyelin transfer suggested that the translocation proceeded entirely in a hydrophobic environment. [(3)H]Sphingomyelin transferred to the cells by CTAP-III was hydrolyzed to [(3)H]ceramide and [(3)H]sphingosine after activation with tumor necrosis factor alpha. The generation of the [(3)H]sphingolipid messengers was catalyzed by acid sphingomyelinase. Our results identify CTAP-III as the first mediator of the selective (endocytosis-independent) cellular import of sphingomyelin allowing the paracrine modulation of the sphingolipid signaling.

Down-regulation of neutrophil functions by the ELR+CXC chemokine platelet basic protein

The platelet-derived neutrophil-activating peptide 2 (NAP-2, 70 amino acids) belongs to the ELR+ CXC subfamily of chemokines. Similar to other members of this group, such as IL-8, NAP-2 activates chemotaxis and degranulation in neutrophils (polymorphonuclear [PMN]) through chemokine receptors CXCR-1 and CXCR-2. However, platelets do not secrete NAP-2 as an active chemokine but as the C-terminal part of several precursors that lack PMN-stimulating capacity. As we have previously shown, PMN themselves may liberate NAP-2 from the precursor connective tissue-activating peptide III (CTAP-III, 85 amino acids) by proteolysis. Instead of inducing cell activation, continuous accumulation of the chemokine in the surroundings of the processing cells results in the down-regulation of specific surface-expressed NAP-2 binding sites and in the desensitization of chemokine-induced PMN degranulation. Thus, NAP-2 precursors may be regarded as indirect mediators of functional desensitization in neutrophils. In the current study we investigated the biologic impact of another major NAP-2 precursor, the platelet basic protein (PBP, 94 amino acids). We show that PBP is considerably more potent than CTAP-III to desensitize degranulation and chemotaxis in neutrophils. We present data suggesting that the high desensitizing capacity of PBP is based on its enhanced proteolytic cleavage into NAP-2 by neutrophil-expressed cathepsin G and that it involves efficient down-regulation of surface-expressed CXCR-2 while CXCR-1 is hardly affected. Correspondingly, we found PBP and, less potently, CTAP-III to inhibit CXCR-2– but not CXCR-1– dependent chemotaxis of neutrophils toward NAP-2. Altogether our findings demonstrate that the anti-inflammatory capacity of NAP-2 is governed by the species of its precursors.

Down-regulation of neutrophil functions by the ELR+CXC chemokine platelet basic protein

The platelet-derived neutrophil-activating peptide 2 (NAP-2, 70 amino acids) belongs to the ELR+ CXC subfamily of chemokines. Similar to other members of this group, such as IL-8, NAP-2 activates chemotaxis and degranulation in neutrophils (polymorphonuclear [PMN]) through chemokine receptors CXCR-1 and CXCR-2. However, platelets do not secrete NAP-2 as an active chemokine but as the C-terminal part of several precursors that lack PMN-stimulating capacity. As we have previously shown, PMN themselves may liberate NAP-2 from the precursor connective tissue-activating peptide III (CTAP-III, 85 amino acids) by proteolysis. Instead of inducing cell activation, continuous accumulation of the chemokine in the surroundings of the processing cells results in the down-regulation of specific surface-expressed NAP-2 binding sites and in the desensitization of chemokine-induced PMN degranulation. Thus, NAP-2 precursors may be regarded as indirect mediators of functional desensitization in neutrophils. In the current study we investigated the biologic impact of another major NAP-2 precursor, the platelet basic protein (PBP, 94 amino acids). We show that PBP is considerably more potent than CTAP-III to desensitize degranulation and chemotaxis in neutrophils. We present data suggesting that the high desensitizing capacity of PBP is based on its enhanced proteolytic cleavage into NAP-2 by neutrophil-expressed cathepsin G and that it involves efficient down-regulation of surface-expressed CXCR-2 while CXCR-1 is hardly affected. Correspondingly, we found PBP and, less potently, CTAP-III to inhibit CXCR-2– but not CXCR-1– dependent chemotaxis of neutrophils toward NAP-2. Altogether our findings demonstrate that the anti-inflammatory capacity of NAP-2 is governed by the species of its precursors.