Inhibition of Human Umbilical Vein Endothelial Cell Proliferation by the CXC Chemokine, Platelet Factor 4 (PF4), Is Associated With Impaired Downregulation of p21Cip1/WAF1

Platelet factors ameliorate thoracic aortic aneurysm and dissection by inhibiting the FGF-FGFR cascade activation in aortic-endothelial cell

Thoracic aortic aneurysm and dissection (TAAD) is closely associated with vascular endothelial dysfunction. Platelet factor 4 (PF4) is crucial for maintaining vascular endothelial cell homeostasis. However, whether PF4 can influence the progression of TAAD remains unknown. In the present study, we constructed a liposome-encapsulated PF4 nanomedicine and verified its effect on BAPN-induced TAAD in vivo. We found that liposome PF4 nanoparticles (Lipo-PF4), more effectively than PF4 alone, inhibited the formation of TAAD. In vitro, PF4 improved endothelial cell function under pathological conditions by inhibiting migratory and angiogenic abilities of human aortic endothelial cells (HAECs). Mechanically, PF4 inhibited the development of TAAD and improved HAECs function by combining with heparin sulfate and blocking fibroblast growth factor-fibroblast growth factor receptor (FGF-FGFR) signaling. Taken together, we developed a nano-drug (Lipo-PF4) that effectively ameliorates the progression of TAAD by improving endothelial function. Lipo-PF4 is expected to be a therapeutic option for TAAD in the future.

Contribution of CXCR3-mediated signaling in the metastatic cascade of solid malignancies

Metastasis is a significant cause of the mortality resulting from solid malignancies. The process of metastasis is complex and is regulated by numerous cancer cell-intrinsic and -extrinsic factors. CXCR3 is a chemokine receptor that is frequently expressed by cancer cells, endothelial cells and immune cells. CXCR3A signaling in cancer cells tends to promote the invasive and migratory phenotype of cancer cells. Indirectly, CXCR3 modulates the anti-tumor immune response resulting in variable effects that can permit or inhibit metastatic progression. Finally, the activity of CXCR3B in endothelial cells is generally angiostatic, which limits the access of cancer cells to key conduits to secondary sites. However, the interaction of these activities within a tumor and the presence of opposing CXCR3 splice variants clouds the picture of the role of CXCR3 in metastasis. Consequently, thorough analysis of the contributions of CXCR3 to cancer metastasis is necessary. This review is an in-depth examination of the involvement of CXCR3 in the metastatic process of solid malignancies.

Chemokines and Chemokine Receptors: Orchestrating Tumor Metastasization

Metastasis still represents the primary cause of cancer morbidity and mortality worldwide. Chemokine signalling contributes to the overall process of cancer growth and metastasis, and their expression in both primary tumors and metastatic lesions correlate with prognosis. Chemokines promote tumor metastasization by directly supporting cancer cell survival and invasion, angiogenesis, and by indirectly shaping the pre-metastatic niches and antitumor immunity. Here, we will focus on the relevant chemokine/chemokine receptor axes that have been described to drive the metastatic process. We elaborate on their role in the regulation of tumor angiogenesis and immune cell recruitment at both the primary tumor lesions and the pre-metastatic foci. Furthermore, we also discuss the advantages and limits of current pharmacological strategies developed to target chemokine networks for cancer therapy.

Anti-CXCL4 monoclonal antibody accelerates telogen to anagen transition and attenuates apoptosis of the hair follicle in mice

Although hair loss or alopecia is a common disease, its exact mechanisms are not yet well understood. The present study investigated the hypothesis that the homeostatic regulation of genes during hair regeneration may participate in hair loss, based on the cyclicity of hair growth. A cluster of such genes was identified by an expression gene-array from the dorsal skin in a depilated mouse model, and CXCL4 was identified as a significantly regulated gene during the hair regeneration process. To elucidate the function of CXCL4 in hair growth, CXCL4 activity was blocked by the administration of an anti-CXCL4 monoclonal antibody (mAb). Histomorphometric analysis indicated that anti-CXCL4 mAb induced an earlier anagen phase and delayed hair follicle regression, in contrast with that in the control group. Moreover, CXCL4 mAb upregulated the transcription levels of several hair growth-related genes, including Lef1, Wnt10b, Bmp4 and Bmp2. In addition, CXCL4 mAb increased the levels of the proliferation-related protein PCNA and Bcl-2 during the anagen phase, while it reduced the expression of pro-apoptotic protein Bax and cleaved caspase-3 during the catagen phase. These findings reveal that CXCL4 plays an important role in hair growth, and that blockade of CXCL4 activity promotes hair growth.

Effects of Co-Culture Media on Hepatic Differentiation of hiPSC with or without HUVEC Co-Culture

The derivation of hepatocytes from human induced pluripotent stem cells (hiPSC) is of great interest for applications in pharmacological research. However, full maturation of hiPSC-derived hepatocytes has not yet been achieved in vitro. To improve hepatic differentiation, co-cultivation of hiPSC with human umbilical vein endothelial cells (HUVEC) during hepatic differentiation was investigated in this study. In the first step, different culture media variations based on hepatocyte culture medium (HCM) were tested in HUVEC mono-cultures to establish a suitable culture medium for co-culture experiments. Based on the results, two media variants were selected to differentiate hiPSC-derived definitive endodermal (DE) cells into mature hepatocytes with or without HUVEC addition. DE cells differentiated in mono-cultures in the presence of those media variants showed a significant increase (p < 0.05) in secretion of α-fetoprotein and in activities of cytochrome P450 (CYP) isoenzymes CYP2B6 and CYP3A4 as compared with cells differentiated in unmodified HCM used as control. Co-cultivation with HUVEC did not further improve the differentiation outcome. Thus, it can be concluded that the effect of the used medium outweighed the effect of HUVEC co-culture, emphasizing the importance of the culture medium composition for hiPSC differentiation.

Angiostatic, tumor inflammatory and anti-tumor effects of CXCL4(47-70) and CXCL4L1(47-70) in an EGF-dependent breast cancer model

CXCL4 and CXCL4L1, platelet-derived CXC chemokines, and their carboxy-terminal peptides CXCL4^47–70 and CXCL4L1^47–70 previously displayed angiostatic and anti-tumoral activity in a melanoma model. Here, we found CXCL4^47–70 and CXCL4L1^47–70 to inhibit lymphatic endothelial cell proliferation in vitro. Furthermore, the angiostatic potential of CXCL4^47–70 and CXCL4L1^47–70 was tested against different angiogenic stimuli (FGF1, FGF2, FGF8, EGF and VEGF). Besides reducing FGF2-induced vascular endothelial cell growth, CXCL4^47–70 and CXCL4L1^47–70 efficiently counteracted EGF. Consequently, we considered their anti-tumoral potential in EGF-dependent MDA-MB-231 breast tumors. In tumor-bearing mice, CXCL4^47–70 reduced tumor growth better than CXCL4L1^47–70. In CXCL4^47–70-treated tumors significantly more intratumoral monocytes/macrophages and dendritic cells were present and higher expression levels of CCL5 and IFN-γ were detected by qPCR on tumor lysates. Because neither peptide was able to specifically bind CXCR3A or CXCR3B, differential glycosaminoglycan binding and direct interaction with cytokines (EGF and CCL5) might explain any differences in anti-tumoral effects. Notably, CCL5-induced monocyte chemotaxis in vitro was increased by addition of CXCL4^47–70 or CXCL4L1^47–70. Finally, CXCL4^47–70 and CXCL4L1^47–70 inhibited proliferation of MDA-MB-231 cells. Our results suggest a tumor type-dependent responsiveness to either CXCL4^47–70 or CXCL4L1^47–70 treatment, defined by anti-proliferative, angiostatic and inflammatory actions, and substantiate their therapeutic potential.

Platelet factor 4 protects bone marrow mesenchymal stem cells from acute radiation injury

OBJECTIVE

The aim of this study was to find a new radiation protector, platelet factor 4 (PF4) and to identify its effect on haemopoietic microenvironment in vitro and in vivo.

METHODS

Radiation damage on bone marrow mesenchymal stem cells ex and in vitro was set up as models. Growth curve analysis, clonogenic survival assay, FACSCalibur™ (BD Immunocytometry Systems, San Jose, CA), 5-ethynyl-2'-deoxyuridine immunofluorescence staining and quantitative reverse transcription-polymerase chain reaction were employed to assess the characterization of bone marrow mesenchymal stem cells (BMSCs), proliferation, apoptosis, cell cycle and gene expression.

RESULTS

A dose- and time-dependent enhancement of cell viability and survival was observed for PF4 treatment along with 500 cGy γ-radiation in vitro. The same phenomena were noted in vivo, including enhancement of adherence and proliferation ability while inhibition of cell apoptosis, which were associated with a short-term decrease in the G0/G1 ratio owing to S phase arrest. These were accompanied with enhanced Bcl-2 expression and p53/p21 loss.

CONCLUSION

These results uncover that PF4 might be a novel therapeutic approach, which could reduce DNA damage and increase survival of BMSCs, in part, by inhibiting p53/p21 axis and facilitating DNA damage repair.

ADVANCES IN KNOWLEDGE

This study explores the feasibility of a new radioprotector and hence may be clinically important.

Anti-angiogenic gene therapy in the treatment of malignant gliomas

More than four decades ago, Dr. Judah Folkman hypothesized that angiogenesis was a critical process in tumor growth. Since that time, there have been significant advances in understanding tumor biology and groundbreaking research in cancer therapy that have validated his hypothesis. However, in spite of extensive research, glioblastoma multiforme (GBM), the most common and malignant primary brain tumor, has gained little in the way of improved median survival. There have been several angiogenesis targets that have resulted in drugs that are in clinical trials or FDA approved for clinical use in several cancers. GBM is a highly angiogenic tumor and several drugs are showing promise in clinical trials with one (bevacizumab), clinically approved for use. We will review several possible angiogenic targets in GBM as well as the vector methodologies used for delivery. In addition, GBMs present several therapeutic challenges related to structure, tumor immune microenvironment and resistance to angiogenesis. To overcome these challenges will require novel approaches to improve therapeutic gene expression and vector biodistribution in the glioma.

IL-12-dependent innate immunity arrests endothelial cells in G0-G1 phase by a p21(Cip1/Waf1)-mediated mechanism

Innate immunity may activate paracrine circuits able to entail vascular system in the onset and progression of several chronic degenerative diseases. In particular, interleukin (IL)-12 triggers a genetic program in lymphomononuclear cells characterized by the production of interferon-γ and specific chemokines resulting in an angiostatic activity. The aim of this study is to identify molecules involved in the regulation of cell cycle in endothelial cells co-cultured with IL-12-stimulated lymphomonuclear cells. By using a transwell mediated co-culture system we demonstrated that IL-12-stimulated lymphomonuclear cells induce an arrest of endothelial cells cycle in G1, which is mainly mediated by the up-regulation of p21(Cip1/Waf1), an inhibitor of cyclin kinases. This effect requires the activation of STAT1, PKCδ and p38 MAPK, while p53 is ineffective. In accordance, siRNA-dependent silencing of these molecules in endothelial cells inhibited the increase of p21(Cip1/Waf1) and the modification in cell cycle promoted by IL-12-stimulated lymphomonuclear cells. These results indicate that the angiostatic action of IL-12-stimulated lymphomononuclear cells may lie in the capability to arrest endothelial cells in G1 phase through a mechanisms mainly based on the specific up-regulation of p21(Cip1/Waf1) induced by the combined activity of STAT1, PKCδ and p38 MAPK.

Megakaryocytes, malignancy and bone marrow vascular niches

Dynamic interactions between hematopoietic cells and their specialized bone marrow microenvironments, namely the vascular and osteoblastic 'niches', regulate hematopoiesis. The vascular niche is conducive for thrombopoiesis and megakaryocytes may, in turn, regulate the vascular niche, especially in supporting vascular and hematopoietic regeneration following irradiation or chemotherapy. A role for platelets in tumor growth and metastasis is well established and, more recently, the vascular niche has also been implicated as an area for preferential homing and engraftment of malignant cells. This article aims to provide an overview of the dynamic interactions between cellular and molecular components of the bone marrow vascular niche and the potential role of megakaryocytes in bone marrow malignancy.

Regulation of angiostatic chemokines driven by IL-12 and IL-27 in human tumors

Chemokines have pleiotropic effects in regulating immunity, angiogenesis, and tumor growth. CXC and CC chemokine families members and their receptors are able to exert a proangiogenic or an antiangiogenic effect in experimental models and in human tumors. In this review article, we have summarized literature data and our studies concerning the angiostatic activity of chemokines. Their angiostatic activity may be a result of a direct effect on the biological functions of endothelial cells and/or an effect on tumor cells inhibiting their capability to stimulate new blood vessel formation. Moreover, chemokines have a pro- and antitumor effect within the tumor microenvironment by regulating immune cell infiltration and its antitumor activities. We have focused our interest on the role of IL-12 and IL-27 in solid and hematological tumors, and we have suggested and discussed their potential use as antiangiogenic agents in the treatment of such tumors.

CXCL4L1 inhibits angiogenesis and induces undirected endothelial cell migration without affecting endothelial cell proliferation and monocyte recruitment

BACKGROUND AND OBJECTIVES

The non-allelic variant of CXCL4/PF4, CXCL4L1/PF4alt, differs from CXCL4 in three amino acids of the C-terminal α-helix and has been characterized as a potent anti-angiogenic regulator. Although CXCL4 structurally belongs to the chemokine family, it does not behave like a 'classical' chemokine, lacking significant chemotactic properties. Specific hallmarks are its angiostatic, anti-proliferative activities, and proinflammatory functions, which can be conferred by heteromer-formation with CCL5/RANTES enhancing monocyte recruitment.

METHODS AND RESULTS

Here we show that tube formation of endothelial cells was inhibited by CXCL4L1 and CXCL4, while only CXCL4L1 triggered chemokinesis of endothelial cells. The chemotactic response towards VEGF and bFGF was attenuated by both variants and CXCL4L1-induced chemokinesis was blocked by bFGF or VEGF. Endothelial cell proliferation was inhibited by CXCL4 (IC(50) 6.9 μg mL(-1)) but not by CXCL4L1, while both chemokines bound directly to VEGF and bFGF. Moreover, CXCL4 enhanced CCL5-induced monocyte arrest in flow adhesion experiments and monocyte recruitment into the mouse peritoneal cavity in vivo, whereas CXCL4L1 had no effect. CXCL4L1 revealed lower affinity to CCL5 than CXCL4, as quantified by isothermal fluorescence titration. As evidenced by the reduction of the activated partial thromboplastin time, CXCL4L1 showed a tendency towards less heparin-neutralizing activity than CXCL4 (IC(50) 2.45 vs 0.98 μg mL(-1)).

CONCLUSIONS

 CXCL4L1 may act angiostatically by causing random endothelial cell locomotion, disturbing directed migration towards angiogenic chemokines, serving as a homeostatic chemokine with a moderate structural distinction yet different functional profile from CXCL4.

The role of the CXC chemokines platelet factor-4 (CXCL4/PF-4) and its variant (CXCL4L1/PF-4var) in inflammation, angiogenesis and cancer

Chemokines are chemotactic cytokines which recruit leukocytes to inflammatory sites. They also affect tumor development and metastasis by acting as growth factor, by attracting pro- or anti-tumoral leukocytes or by influencing angiogenesis. Platelet factor-4 (CXCL4/PF-4) was the first chemokine shown to inhibit angiogenesis. CXCL4L1/PF-4var, recently isolated from thrombin-stimulated platelets, differing from authentic CXCL4/PF-4 in three carboxy-terminally located amino acids, was found to be more potent than CXCL4/PF-4 in inhibiting angiogenesis and tumor growth. Both glycosaminoglycans (GAG) and CXCR3 are implicated in the activities of the PF-4 variants. This report reviews the current knowledge on the role of CXCL4/PF-4 and CXCL4L1/PF-4var in physiological and pathological processes. In particular, the role of CXCL4/PF-4 in cancer, heparin-induced thrombocytopenia and atherosclerosis is described.

CXC chemokine ligand 4 (CXCL4) down-regulates CC chemokine receptor expression on human monocytes

During acute inflammation, monocytes are essential in abolishing invading micro-organisms and encouraging wound healing. Recruitment by CC chemokines is an important step in targeting monocytes to the inflamed tissue. However, cell surface expression of the corresponding chemokine receptors is subject to regulation by various endogenous stimuli which so far have not been comprehensively identified. We report that the platelet-derived CXC chemokine ligand 4 (CXCL4), a known activator of human monocytes, induces down-regulation of CC chemokine receptors (CCR) 1, -2, and -5, resulting in drastic impairment of monocyte chemotactic migration towards cognate CC chemokine ligands (CCL) for these receptors. Interestingly, CXCL4-mediated down-regulation of CCR1, CCR2 and CCR5 was strongly dependent on the chemokine's ability to stimulate autocrine/paracrine release of TNF-α. In turn, TNF-α induced the secretion CCL3 and CCL4, two chemokines selective for CCR1 and CCR5, while the secretion of CCR2-ligand CCL2 was TNF-α-independent. Culture supernatants of CXCL4-stimulated monocytes as well as chemokine-enriched preparations thereof reproduced CXCL4-induced CCR down-regulation. In conclusion, CXCL4 may act as a selective regulator of monocyte migration by stimulating the release of autocrine, receptor-desensitizing chemokine ligands. Our results stress a co-ordinating role for CXCL4 in the cross-talk between platelets and monocytes during early inflammation.

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.

Tumor angiogenesis: insights and innovations

Angiogenesis is a vital process resulting in the formation of new blood vessels. It is normally a highly regulated process that occurs during human development, reproduction, and wound repair. However, angiogenesis can also become a fundamental pathogenic process found in cancer and several other diseases. To date, the inhibition of angiogenesis has been researched at both the bench and the bedside. While several studies have found moderate improvements when treating with angiogenesis inhibitors, greater success is being seen when the inhibition of angiogenesis is combined with other traditional forms of available therapy. This review summarizes several important angiogenic factors, examines new research and ongoing clinical trials for such factors, and attempts to explain how this new knowledge may be applied in the fight against cancer and other angiogenic-related diseases.

The COOH-terminal peptide of platelet factor-4 variant (CXCL4L1/PF-4var47-70) strongly inhibits angiogenesis and suppresses B16 melanoma growth in vivo

Chemokines influence tumor growth directly or indirectly via both angiogenesis and tumor-leukocyte interactions. Platelet factor-4 (CXCL4/PF-4), which is released from alpha-granules of activated platelets, is the first described angiostatic chemokine. Recently, it was found that the variant of CXCL4/PF-4 (CXCL4L1/PF-4var) could exert a more pronounced angiostatic and antitumoral effect than CXCL4/PF-4. However, the molecular mechanisms of the angiostatic activities of the PF-4 forms remain partially elusive. Here, we studied the biological properties of the chemically synthesized COOH-terminal peptides of CXCL4/PF-4 (CXCL4/PF-4(47-70)) and CXCL4L1/PF-4var (CXCL4L1/PF-4var(47-70)). Both PF-4 peptides lacked monocyte and lymphocyte chemotactic activity but equally well inhibited (25 nmol/L) endothelial cell motility and proliferation in the presence of a single stimulus (i.e., exogenous recombinant fibroblast growth factor-2). In contrast, when assayed in more complex angiogenesis test systems characterized by the presence of multiple mediators, including in vitro wound-healing (2.5 nmol/L versus 12.5 nmol/L), Matrigel (60 nmol/L versus 300 nmol/L), and chorioallantoic membrane assays, CXCL4L1/PF-4var(47-70) was found to be significantly (5-fold) more angiostatic than CXCL4/PF-4(47-70). In addition, low (7 microg total) doses of intratumoral CXCL4L1/PF-4var(47-70) inhibited B16 melanoma growth in mice more extensively than CXCL4/PF-4(47-70). This antitumoral activity was predominantly mediated through inhibition of angiogenesis (without affecting blood vessel stability) and induction of apoptosis, as evidenced by immunohistochemical and fluorescent staining of B16 tumor tissue. In conclusion, CXCL4L1/PF-4var(47-70) is a potent antitumoral and antiangiogenic peptide. These results may represent the basis for the design of CXCL4L1/PF-4var COOH-terminal-derived peptidomimetic anticancer drugs.

Therapeutic efficacy of recombinant human endostatin combined with chemotherapeutics in mice-transplanted tumors

Endostatin is an endogenous inhibitor of angiogenesis and has been shown to exhibit potent inhibitory activity in certain mice tumor models. In this study, a treatment strategy of combining recombinant human endostatin (rhEndostatin) and chemotherapeutics was implemented to evaluate the therapeutic efficacy of rhEndostatin against solid tumors. The antitumor effect of rhEndostatin in combination with several chemotherapeutic drugs, e.g., 5-fluorouracil, cyclophosphamide, methotrexate, and mitomycin C, on human QGY liver tumor and mice H22 liver tumor was compared with that of rhEndostatin treatment alone. The results showed that the combination of rhEndostatin and chemotherapeutic drugs resulted in a more potent inhibition of tumor growth. The potential advantages of rhEndostatin plus tumor chemotherapy provide a basis for further clinical trials of rhEndostatin.

The CXC-chemokine CXCL4 interacts with integrins implicated in angiogenesis

The human CXC-chemokine CXCL4 is a potent inhibitor of tumor-induced angiogenesis. Considering that CXCL4 is sequestered in platelet alpha-granules and released following platelet activation in the vicinity of vessel wall injury, we tested the hypothesis that CXCL4 might function as a ligand for integrins. Integrins are a family of adhesion receptors that play a crucial role in angiogenesis by regulating early angiogenic processes, such as endothelial cell adhesion and migration. Here, we show that CXCL4 interacts with alphavbeta3 on the surface of alphavbeta3-CHO. More importantly, human umbilical vein endothelial cells adhere to immobilized CXCL4 through alphavbeta3 integrin, and also through other integrins, such as alphavbeta5 and alpha5beta1. We further demonstrate that CXCL4-integrin interaction is of functional significance in vitro, since immobilized CXCL4 supported endothelial cell spreading and migration in an integrin-dependent manner. Soluble CXCL4, in turn, inhibits integrin-dependent endothelial cell adhesion and migration. As a whole, our study identifies integrins as novel receptors for CXCL4 that may contribute to its antiangiogenic effect.

CCR7 signaling inhibits T cell proliferation

CCR7 and its ligands, CCL19 and CCL21, are responsible for directing the migration of T cells and dendritic cells into lymph nodes, where these cells play an important role in the initiation of the immune response. Recently, we have shown that systemic application of CCL19-IgG is able to inhibit the colocalization of T cells and dendritic cells within secondary lymphoid organs, resulting in pronounced immunosuppression with reduced allograft rejection after organ transplantation. In this study, we demonstrate that the application of sustained high concentrations of either soluble or immobilized CCL19 and CCL21 elicits an inhibitory program in T cells. We show that these ligands specifically interfere with cell proliferation and IL-2 secretion of CCR7(+) cells. This could be demonstrated for human and murine T cells and was valid for both CD4(+) and CD8(+) T cells. In contrast, CCL19 had no inhibitory effect on T cells from CCR7 knockout mice, but CCR7(-/-) T cells showed a proliferative response upon TCR-stimulation similar to that of CCL19-treated wild-type cells. Furthermore, the inhibition of proliferation is associated with delayed degradation of the cyclin-dependent kinase (CDK) inhibitor p27(Kip1) and the down-regulation of CDK1. This shows that CCR7 signaling is linked to cell cycle control and that sustained engagement of CCR7, either by high concentrations of soluble ligands or by high density of immobilized ligands, is capable of inducing cell cycle arrest in TCR-stimulated cells. Thus, CCR7, a chemokine receptor that has been demonstrated to play an essential role during activation of the immune response, is also competent to directly inhibit T cell proliferation.

Platelet factor 4 (CXC chemokine ligand 4) differentially regulates respiratory burst, survival, and cytokine expression of human monocytes by using distinct signaling pathways

Platelet factor 4 (PF4; CXCL4) is an abundant platelet alpha-granule CXC chemokine with unique functions. Although lacking a chemotactic activity, PF4 initiates a signal transduction cascade in human monocytes leading to the induction of a broad spectrum of acute and delayed functions including phagocytosis, respiratory burst, survival, and the secretion of cytokines. Surprisingly, although these monocyte functions are well defined, only very limited information exists on the specific signaling pathways that are involved in the regulation of these biological responses. By using specific inhibitors and direct phosphorylation/activation studies, we show in the present study that PF4-mediated respiratory burst is dependent on a very rapid activation of PI3K, Syk, and p38 MAPK. Moreover, monocyte survival and differentiation instead is controlled by a delayed activation of Erk, with an activity peak after 6 h of stimulation. The inhibition of Erk completely reverted PF4-mediated protection against apoptosis. Finally, even though JNK is rapidly activated in PF4-treated monocytes, it is dispensable for the regulation of survival and respiratory burst. However, PF4-induced up-regulation of chemokine and cytokine mRNA and protein requires a sustained activation of JNK and Erk. Taken together, PF4-stimulated immediate monocyte functions (oxygen radical formation) are regulated by p38 MAPK, Syk, and PI3K, whereas delayed functions (survival and cytokine expression) are controlled by Erk and JNK.

Platelets as immune cells: bridging inflammation and cardiovascular disease

Beyond an eminent role in hemostasis and thrombosis, platelets are characterized by expert functions in assisting and modulating inflammatory reactions and immune responses. This is achieved by the regulated expression of adhesive and immune receptors on the platelet surface and by the release of a multitude of secretory products including inflammatory mediators and cytokines, which can mediate the interaction with leukocytes and enhance their recruitment. In addition, platelets are characterized by an enormous surface area and open canalicular system, which in concert with specialized recognition receptors may contribute to the engulfment of serum components, antigens, and pathogens. Platelet-dependent increases in leukocyte adhesion may not only account for an exacerbation of atherosclerosis, for arterial repair processes, but also for lymphocyte trafficking during adaptive immunity and host defense. This review compiles a selection of platelet-derived tools for bridging inflammation and vascular disease and highlights the molecular key components governing platelet-mediated mechanisms operative in immune surveillance, vascular remodeling, and atherosclerosis.

Molecular pathways of angiogenesis inhibition

A large body of evidence now demonstrates that angiostatic therapy represents a promising way to fight cancer. This research recently resulted in the approval of the first angiostatic agent for clinical treatment of cancer. Progress has been achieved in decrypting the cellular signaling in endothelial cells induced by angiostatic agents. These agents predominantly interfere with the molecular pathways involved in migration, proliferation and endothelial cell survival. In the current review, these pathways are discussed. A thorough understanding of the mechanism of action of angiostatic agents is required to develop efficient anti-tumor therapies.

Roles of platelet factor 4 in hematopoiesis and angiogenesis

Platelet factor 4 (PF4) has been recognized as a physiological inhibitor of megakaryocytopoiesis and angiogenesis for two decades. Structure-function studies have shown that the DLQ determinant in position 54-56 is necessary for megakaryocytic inhibition whereas mutations of these residues into ELR sequence and more importantly, into DLR sequence, induce a stronger inhibitory activity of peptide p47-70 on angiogenesis. The alpha-helix region of peptides may participate in the fixation of the effector to its cellular receptor and the other important structural domains would activate the receptor. In vivo, PF4 and its related peptides can protect hematopoiesis from chemotherapy by enhancing cell viability and suppress tumor growth through anti-angiogenic pathway. Several PF4 fragments and modified molecules exhibit antiangiogenesis properties and may become an alternative for further therapeutic angiogenesis.

Oncolytic HSV armed with platelet factor 4, an antiangiogenic agent, shows enhanced efficacy

Oncolytic herpes simplex viruses (HSV) have emerged as a promising platform for cancer therapy. However, efficacy as single agents has thus far been unsatisfactory. Tumor vasculature is critical in supporting tumor growth, but successful antiangiogenic approaches often require maintaining constant levels of antiangiogenic products. We hypothesized that oncolytic HSV has the potential to destroy tumor vasculature and that this effect can be enhanced by combination with antiangiogenic gene transfer. We examined the strategy of arming oncolytic HSV with an antiangiogenic transgene, platelet factor 4 (PF4). The PF4 transgene was inserted into oncolytic HSV G47Delta utilizing a bacterial artificial chromosome construction system. Whereas bG47Delta-empty showed robust cell killing and migration inhibition of proliferating endothelial cells (HUVEC and Py-4-1), the effect was further enhanced by PF4 expression. Importantly, enhanced potency did not impede viral replication. In vivo, bG47Delta-PF4 was more efficacious than its nonexpressing parent bG47Delta-empty at inhibiting tumor growth and angiogenesis in both human U87 glioma and mouse 37-3-18-4 malignant peripheral nerve sheath tumor models. Enhancing the antiangiogenic properties of oncolytic HSV through the expression of antiangiogenic factors such as PF4 is a powerful new strategy that targets both the tumor cells and tumor vasculature.

Influence of angiogenesis inhibitors on endothelial cell morphology in vitro

Human umbilical vein endothelial cells (HUVEC) propagated in co-culture with fibroblasts form capillary-like networks of tubes. Here we characterize the morphology and ultrastructure of HUVEC in such co-cultures and investigate the influence of different angiogenesis inhibitors on endothelial cell morphology. Addition of angiogenesis inhibitors to the co-culture disrupted endothelial network formation and influenced endothelial cell morphology in two distinct ways. Instead of characteristic capillary-like networks, the endothelial cell morphology appeared as either short cords or compact cell clusters of variable size. Electron microscopy (EM) showed that in co-culture untreated HUVEC formed capillary-like tubes with lumina and retained important ultrastructural and physiological properties of endothelial cells in functional vessels as they contained both Weibel-Palade bodies and transport vesicles. Immuno-EM showed that the endothelial cell marker CD 31 stained endothelial membranes at cell-cell contacts, and at the luminal and abluminal side of the capillary-like tubes, although most abundantly at the luminal membranes. No ultrastructural signs of apoptosis were seen in HUVEC in inhibitor-treated co-cultures. Our results demonstrate that treatment with levamisole or anti-VEGF inhibits endothelial cell differentiation into tubes or instead induces formation of compact endothelial cell clusters. Treatment with platelet factor 4, suramin and TNP-470 results in formation of short endothelial cell cords. We discuss the implications of these findings.

Neutrophil adhesion to endothelial cells induced by platelet factor 4 requires sequential activation of Ras, Syk, and JNK MAP kinases

Signal transduction mechanisms associated with neutrophil activation by platelet factor 4 (PF4; CXCL4) are as yet poorly characterized. In a recent report, we showed that PF4-induced neutrophil functions (such as adhesion and secondary granule exocytosis) involve the activation of Src-kinases. By analyzing intracellular signals leading to adherence, we here demonstrate by several lines of evidence that in addition to Src-kinases, PF4 signaling involves the monomeric GTPase Ras, the tyrosine kinase Syk, and the MAP kinase JNK. Furthermore, on stimulation, GTPases Rac2 and RhoA were activated, and each was translocated to a different membrane compartment. As shown by inhibitor studies, Rac2 and JNK are located downstream of Syk and Ras. Most intriguingly, the latter 2 elements appear to control the activity of Rac2 and JNK independently of each other at different phases of the activation process. Although a first phase of Rac2 and JNK activation of up to 5 minutes is initiated by Ras, the second phase (5-30 minutes) depends predominantly on the activity of Syk. In summary, we describe that coordinated activity of Syk, Ras, and JNK mediates neutrophil adhesion to endothelial cells and that PF4 induces sequential activation of these elements.

Inhibition of angiogenesis by vitamin D-binding protein: characterization of anti-endothelial activity of DBP-maf

Angiogenesis is a complex process involving coordinated steps of endothelial cell activation, proliferation, migration, tube formation and capillary sprouting with participation of intracellular signaling pathways. Regulation of angiogenesis carries tremendous potential for cancer therapy. Our earlier studies showed that vitamin D-binding protein-macrophage activating factor (DBP-maf) acts as a potent anti-angiogenic factor and inhibits tumor growth in vivo. The goal of this investigation was to understand the effect of DBP-maf on human endothelial cell (HEC) and the mechanism of angiogenesis inhibition. DBP-maf inhibited human endothelial cell (HEC) proliferation by inhibiting DNA synthesis (IC(50) = 7.8 +/- 0.15 microg/ml). DBP-maf significantly induced S- and G0/G1-phase arrest in HEC in 72 h. DBP-maf potently blocked VEGF-induced migration, tube-formation of HEC in a dose dependent manner. In addition, DBP-maf inhibited growth factor-induced microvessel sprouting in rat aortic ring assay. Moreover, DBP-maf inhibited VEGF signaling by decreasing VEGF-mediated phosphorylation of VEGFR-2 and ERK1/2, a downstream target of VEGF signaling cascade. However, Akt activation was not affected. These studies collectively demonstrate that DBP-maf inhibits angiogenesis by blocking critical steps such as HEC proliferation, migration, tube formation and microvessel sprouting. DBP-maf exerts its effect by inhibiting VEGR-2 and ERK1/2 signaling cascades. Understanding the cellular and molecular mechanisms of anti-endothelial activity of DBP-maf will allow us to develop it as an angiogenesis targeting novel drug for tumor therapy.

CXC chemokines in angiogenesis

CXC chemokines display pleiotropic effects in immunity, regulating angiogenesis, and mediating organ-specific metastases of cancer. In the context of angiogenesis, CXC chemokines are a unique family of cytokines, known for their ability to behave in a disparate manner in the regulation of angiogenesis. Members that contain the 'ELR' motif are potent promoters of angiogenesis, and mediate their angiogenic activity via binding and activating CXCR2 on endothelium. In contrast, members, in general, those are inducible by interferons and lack the ELR motif (ELR-) are potent inhibitors of angiogenesis, and bind to CXCR3 on endothelium. This review will discuss the biology of these angiogenic and angiostatic CXC chemokines and discuss their disparate angiogenic activity in the context of a variety of disorders.

Platelet factor 4 differentially modulates CD4+CD25+ (regulatory) versus CD4+CD25- (nonregulatory) T cells

Active suppression mediated by CD4(+)CD25(+) T regulatory (Tr) cells plays an important role in the down-regulation of T cell responses to both foreign and self-Ags. Platelet factor 4 (PF4), a platelet-derived CXC chemokine, has been shown to strongly inhibit T cell proliferation as well as IFN-gamma and IL-2 release by isolated T cells. In this report we show that human PF4 stimulates proliferation of the naturally anergic human CD4(+)CD25(+) Tr cells while inhibiting proliferation of CD4(+)CD25(-) T cells. In coculture experiments we found that CD4(+)CD25(+) Tr cells exposed to PF4 lose the ability to inhibit the proliferative response of CD4(+)CD25(-) T cells. Our findings suggest that human PF4, by inducing Tr cell proliferation while impairing Tr cell function, may play a previously unrecognized role in the regulation of human immune responses. Because platelets are the sole source of PF4 in the circulation, these findings may be relevant to the pathogenesis of certain immune-mediated disorders associated with platelet activation, such as heparin-induced thrombocytopenia and autoimmune thrombocytopenic purpura.

Platelets release CXCL4L1, a nonallelic variant of the chemokine platelet factor-4/CXCL4 and potent inhibitor of angiogenesis

Platelet factor-4 (PF-4)/CXCL4 was the first chemokine described to inhibit neovascularization. Here, the product of the nonallelic variant gene of CXCL4, PF-4var1/PF-4alt, designated CXCL4L1, was isolated for the first time from thrombin-stimulated human platelets and purified to homogeneity. Although secreted CXCL4 and CXCL4L1 differ in only three amino acids, CXCL4L1 was more potent in inhibiting chemotaxis of human microvascular endothelial cells toward interleukin-8 (IL-8)/CXCL8 or basic fibroblast growth factor (bFGF). In vivo, CXCL4L1 was also more effective than CXCL4 in inhibiting bFGF-induced angiogenesis in rat corneas. Thus, activated platelets release CXCL4L1, a potent regulator of endothelial cell biology, which affects angiogenesis and vascular diseases.

Recent developments in the inhibition of angiogenesis: examples from studies on platelet factor-4 and the VEGF/VEGFR system

Inhibition of angiogenesis is an important strategy to block tumor growth and invasion. We discuss herein results from our ongoing investigations on platelet factor-4 (PF-4) and the VEGF/VEGFR system. Platelet factor-4 (PF-4) is an anti-angiogenic ELR-negative chemokine. PF-4 inhibits endothelial cell proliferation and migration, and angiogenesis in vitro and in vivo. We have studied the structure and anti-angiogenic activities of a C-terminal fragment of PF-4 named PF-4 CTF. This molecule retains anti-angiogenic activity, blocks the interaction of angiogenesis factors with their receptors and may also be improved by mutation or domain-swapping. It seems, therefore, to be a good candidate for further development. Furthermore, we have developed a cyclic vascular endothelial growth inhibitor (Cyclo VEGI) from the structure of VEGF-A. In aqueous solution, cyclo-VEGI adopts an alpha helix conformation. Cyclo-VEGI inhibits binding of iodinated VEGF(165) to endothelial cells and angiogenesis. Furthermore, cyclo-VEGI significantly blocks the growth of established intracranial glioma in nude and syngeneic mice and improves survival.

Platelet factor 4 disrupts the intracellular signalling cascade induced by vascular endothelial growth factor by both KDR dependent and independent mechanisms

The mechanism by which the CXC chemokine platelet factor 4 (PF-4) inhibits endothelial cell proliferation is unclear. The heparin-binding domains of PF-4 have been reported to prevent vascular endothelial growth factor 165 (VEGF(165)) and fibroblast growth factor 2 (FGF2) from interacting with their receptors. However, other studies have suggested that PF-4 acts via heparin-binding independent interactions. Here, we compared the effects of PF-4 on the signalling events involved in the proliferation induced by VEGF(165), which binds heparin, and by VEGF(121), which does not. Activation of the VEGF receptor, KDR, and phospholipase Cgamma (PLCgamma) was unaffected in conditions in which PF-4 inhibited VEGF(121)-induced DNA synthesis. In contrast, VEGF(165)-induced phosphorylation of KDR and PLCgamma was partially inhibited by PF-4. These observations are consistent with PF-4 affecting the binding of VEGF(165), but not that of VEGF(121), to KDR. PF-4 also strongly inhibited the VEGF(165)- and VEGF(121)-induced mitogen-activated protein (MAP) kinase signalling pathways comprising Raf1, MEK1/2 and ERK1/2: for VEGF(165) it interacts directly or upstream from Raf1; for VEGF(121), it acts downstream from PLCgamma. Finally, the mechanism by which PF-4 may inhibit the endothelial cell proliferation induced by both VEGF(121) and VEGF(165), involving disruption of the MAP kinase signalling pathway downstream from KDR did not seem to involve CXCR3B activation.

Molecular targets in the inhibition of angiogenesis

Angiogenesis, the process of blood vessel formation, is crucial for malignant tumour growth and metastases; therefore, it has become an attractive target for anticancer therapy. Theoretically applicable to most solid tumours, this therapy may be advantageous over existing cytotoxic therapy, since it is directed at genetically stable endothelium growing within tumours rather than at malignant cells, which acquire resistance to treatment. Many promising angiogenesis inhibitors have been developed, although their activity has yet to be demonstrated in human clinical trials. To improve therapeutic benefit, this may require further insight into tumour angiogenesis, development of appropriate surrogate markers of activity, treatment of early stage neoplastic disease and probably a combination of different classes of antiangiogenesis agents to overcome redundant mechanisms of angiogenesis control.

An alternatively spliced variant of CXCR3 mediates the inhibition of endothelial cell growth induced by IP-10, Mig, and I-TAC, and acts as functional receptor for platelet factor 4

The chemokines CXCL9/Mig, CXCL10/IP-10, and CXCL11/I-TAC regulate lymphocyte chemotaxis, mediate vascular pericyte proliferation, and act as angiostatic agents, thus inhibiting tumor growth. These multiple activities are apparently mediated by a unique G protein-coupled receptor, termed CXCR3. The chemokine CXCL4/PF4 shares several activities with CXCL9, CXCL10, and CXCL11, including a powerful angiostatic effect, but its specific receptor is still unknown. Here, we describe a distinct, previously unrecognized receptor named CXCR3-B, derived from an alternative splicing of the CXCR3 gene that mediates the angiostatic activity of CXCR3 ligands and also acts as functional receptor for CXCL4. Human microvascular endothelial cell line-1 (HMEC-1), transfected with either the known CXCR3 (renamed CXCR3-A) or CXCR3-B, bound CXCL9, CXCL10, and CXCL11, whereas CXCL4 showed high affinity only for CXCR3-B. Overexpression of CXCR3-A induced an increase of survival, whereas overexpression of CXCR3-B dramatically reduced DNA synthesis and up-regulated apoptotic HMEC-1 death through activation of distinct signal transduction pathways. Remarkably, primary cultures of human microvascular endothelial cells, whose growth is inhibited by CXCL9, CXCL10, CXCL11, and CXCL4, expressed CXCR3-B, but not CXCR3-A. Finally, monoclonal antibodies raised to selectively recognize CXCR3-B reacted with endothelial cells from neoplastic tissues, providing evidence that CXCR3-B is also expressed in vivo and may account for the angiostatic effects of CXC chemokines.

Thrombospondins 1 and 2 function as inhibitors of angiogenesis

Thrombospondins (TSPs) 1 and 2 are matricellular proteins with the well-characterized ability to inhibit angiogenesis in vivo, and the migration and proliferation of cultured microvascular endothelial cells (ECs). Angiogenesis in developing tumors and in various models of wound healing is diminished or delayed by the presence of TSP1 or 2. Sequences within the type I repeats of TSP1 and 2 have been demonstrated to mediate the anti-migratory effects of TSPs on microvascular EC, although, paradoxically, sequences in the N- and C-terminal domains have pro-angiogenic effects. A scavenger receptor, CD36, recognizes the active sequences in the type I repeats, and is required for the anti-angiogenic effects of TSP1 in the corneal neovascularization assay. However, interactions of TSPs with growth factors, proteases, histidine-rich glycoprotein, and other cell-surface receptors on EC have the potential to modulate CD36-mediated effects. Binding of TSP1 to CD36 has been shown to activate apoptosis by inducing p38 and Jun N-terminal kinase, members of the mitogen-activated protein kinase superfamily, and subsequently the cell-surface expression of FasL. Ligation of Fas by FasL then induces a caspase cascade and apoptotic cell death. However, we have recently shown that inhibition of proliferation of microvascular EC by TSPs can occur in the absence of cell death. This finding raises the possibility that TSPs can activate separate cell death and anti-proliferative pathways.

Cell surface heparan sulfate participates in CXCL1-induced signaling

The CXC subfamily of chemokines plays an important role in diverse processes, including inflammation, wound healing, growth regulation, angiogenesis, and tumorigenesis. The ELR-CXC chemokine, CXCL1 or MGSA/GROalpha, is traditionally considered to attract neutrophils to sites of inflammation. The non-ELR-CXC chemokine, CXCL10 or IP-10, is chemotactic for monocytes, B cells, and activated T lymphocytes. In addition to its role in leukocyte migration, CXCL10 inhibits the angiogenic functions of the ELR-CXC chemokines as well as bFGF and VEGF. Heparan sulfate proteoglycans (HSPGs) are required for the interaction of bFGF and vEGF ligands and their receptors. However, the role of HSPGs in regulating the ELR-chemokines signaling and biological functions is poorly understood. We show here that the CXCL1 maximal binding to CXCR2 expressed on HEK293 and CHO-K1 cells is dependent on the presence of cell surface HSPGs. The cell surface HSPGs on cells are required for CXCL1-induced PAK1 activation. Moreover, CXCL10 can inhibit CXCL1-induced PAK1 and ERK activation as well as the CXCL1-induced chemotaxis through decreasing CXCL1 binding to cell surface heparan sulfate. These data indicate that HSPGs are involved in modulating CXCL1-induced PAK1 activation and chemotaxis through regulating CXCL1 binding activity to CXCR2 receptor. CXCL10 inhibits CXCL1-induced PAK1 activation and chemotaxis by interfering with appropriate binding of CXCL1 to CXCR2 receptor.

Analysis of the role of chemokines in angiogenesis

Chemokines, a large family of inflammatory cytokines, have been shown to play a critical role in the regulation of angiogenesis during several pathophysiologic processes, such as tumor growth, wound healing and ischemia. Semiquantitative or quantitative angiogenesis assays are commonly utilized to screen the angiogenic or angiostatic activity of chemokines. These include in vitro endothelial cell activation assays and ex vivo or in vivo models of neovascularization. Chemokines may exert their regulatory activity on angiogenesis directly or as a consequence of leukocyte infiltration and/or the induction of growth factor expression. The effect of chemokines on endothelium can be assessed by performing in vitro assays on purified endothelial cell populations or by in vivo assays. Nevertheless, each model used to evaluate the angiogenic or angiostatic activity of a discrete factor has advantages and limitations. Thus, in order to avoid under- or overestimating the regulatory effect of chemokines on angiogenesis and to evaluate all aspects of the angiogenic process, multiple assays are usually performed. This review summarizes past and recent studies on chemokines as modulators of angiogenesis with particular emphasis on the methods currently used for the assessment of chemokine-mediated angiogenic or angiostatic responses.

Platelet factor 4 inhibits FGF2-induced endothelial cell proliferation via the extracellular signal-regulated kinase pathway but not by the phosphatidylinositol 3-kinase pathway

Platelet factor 4 (PF-4) is a member of the chemokine family with powerful antiangiogenic properties. The mechanism by which PF-4 inhibits endothelial cell proliferation is unclear. We investigated the effects of PF-4 on the intracellular signal transduction induced by basic fibroblast growth factor (FGF2). We found that PF-4 (10 microg/mL) inhibited the FGF2-induced proliferation of adrenal cortex capillary endothelial (ACE) cells. The inhibition of MEK1/2 (mitogen-activated protein kinase kinase) by PD98059 or of PI3K (phosphatidylinositol 3-kinase) by Ly294002 abolished the proliferation induced by FGF2, suggesting that ACE cell proliferation required dual signaling through both the extracellular signal-regulated kinase (ERK) and PI3K pathways. Ly294002 had no significant effect on ERK phosphorylation, whereas PD98059 had a weak effect on the phosphorylation of Akt, suggesting that 2 separate cascades are required for ACE cell proliferation. The addition of PF-4 (10 microg/mL) significantly inhibited ERK phosphorylation (95%), showing that PF-4 acted directly on or upstream from this kinase. Surprisingly, PF-4 did not affect FGF2-induced Akt phosphorylation. This suggests that PF-4 disrupts FGF2 signaling via an intracellular mechanism of inhibition. To exclude the possibility that PF-4 inhibited the binding of FGF2 to only one FGF receptor, preferentially activating the ERK pathway, we investigated the effect of PF-4 on FGF2-induced ERK and Akt phosphorylation, using mutant heparan sulfate-deficient Chinese hamster ovary cells transfected with the FGF-R1 cDNA. The addition of PF-4 (1 microg/mL) significantly inhibited ERK phosphorylation (90%), with no effect on Akt phosphorylation, suggesting that PF-4 acts downstream from the FGF-R1 receptor. In conclusion, this is the first report showing that PF-4 inhibits FGF2 activity downstream from its receptor.

Guanylate-binding protein-1 expression is selectively induced by inflammatory cytokines and is an activation marker of endothelial cells during inflammatory diseases

During angiogenesis and inflammatory processes, endothelial cells acquire different activation phenotypes, whose identification may help in understanding the complex network of angiogenic and inflammatory interactions in vivo. To this goal we investigated the expression of the human guanylate-binding protein (GBP)-1 that is highly induced by inflammatory cytokines (ICs) and, therefore, may characterize IC-activated cells. Using a new rat monoclonal antibody raised against GBP-1, we show that GBP-1 is a cytoplasmic protein and that its expression in endothelial cells is selectively induced by interferon-gamma, interleukin-1alpha, interleukin-1beta, or tumor necrosis factor-alpha, but not by other cytokines, chemokines, or growth factors. Moreover, we found that GBP-1 expression is highly associated with vascular endothelial cells as confirmed by the simultaneous detection of GBP-1 and the endothelial cell-associated marker CD31 in a broad range of human tissues. Notably, GBP-1 expression was undetectable in the skin, but it was highly induced in vessels of skin diseases with a high-inflammatory component including psoriasis, adverse drug reactions, and Kaposi's sarcoma. These results indicate that GBP-1 is a novel cellular activation marker that characterizes the IC-activated phenotype of endothelial cells.

Increased plasma thrombospondin-1 (TSP-1) levels are associated with the TNF alpha-308A allele in children with juvenile dermatomyositis

Vascular occlusion is more frequent in children with juvenile dermatomyositis (JDM) who have the TNF alpha-308A allele. One of the potent anti-angiogenic factors is thrombospondin-1 (TSP-1). This study investigated the association of the TNF alpha-308A allele with circulating levels of angiogenic mediators, TSP-1, and platelet factor 4 (PF4) using fresh, platelet-poor plasma (PPP). The TNF alpha-308A allele was characterized by PCR amplification and NcoI digestion. Concentrations of TSP-1 and PF4 in PPP from 31 JDM patients and 25 matched pediatric controls were determined by ELISA. The majority of the JDM children with the TNF alpha-308A allele (7/12) produced more TSP-1 than their TNF alpha-308G counterparts (P < 0.05), and their TSP-1 values were inversely related to those for PF4 (P < 0.0006). We conclude that the increased circulating concentrations of TSP-1 associated with the TNF alpha-308A allele suggest that this anti-angiogenic regulator may play a significant role in the augmented vascular occlusion observed in JDM children with this genetic marker.

Signal transduction of chemokine platelet factor 4 in human erythroleukemia cells

Previous data have demonstrated that CXC-chemokine platelet factor 4 (PF4) inhibits the proliferation of the human erythroleukemia cell line (HEL). However, the mechanism of action is unclear at present. The signaling transduction induced by PF4 in the HEL was compared with that induced by transforming growth factor beta1 (TGF-beta1), which is also a potent inhibitor of HEL growth. It was found that PF4 had no inhibitory effect on intracellular calcium levels in resting HEL cells. When HEL cells were stimulated with interleukin-3 (IL-3), a rapid increase in the intracellular level of free calcium occurred within 15 to 20 seconds, and this increase was followed by a sustained increase that gradually declined until resting levels were reached 30 to 40 minutes later. PF4 dramatically decreased the transient rise of [Ca2+] and protein kinase C (PKC) activity of HEL cells induced by IL-3. However, PF4 had no inhibitory effect on PKC activation in resting HEL cells. Furthermore, PF4 was found to down-regulate significantly protein tyrosine kinase (PTK) activity. In contrast, TGF-beta1 induced an increase in intracellular free calcium concentration and PKC and PTK activity in HEL cells. Furthermore, PF4 significantly increased the messenger RNA (mRNA) level of p21waf1 in HEL cells. These data demonstrate that PF4 acts on HEL cells through a signaling transduction pathway, which is different from that of TGF-beta1 and is related to the up-regulatory mRNA level of p21waf1 in HEL cells.

The chemokine CXCL13 (BCA-1) inhibits FGF-2 effects on endothelial cells

Several chemokines, belonging to both the CXC and CC classes, act as positive or negative regulators of angiogenesis. We sought to investigate the role of CXCL13, B cell-attracting chemokine 1 (BCA-1), also known as B-lymphocyte chemoattractant (BLC), on endothelial cell functions. We tested the effect of CXCL13 on HUVEC chemotaxis and proliferation in the presence of fibroblast growth factor (FGF)-2 and found that such chemokine inhibits FGF-2-induced functions, while is not active by itself. To test whether other FGF-2-mediated biological activities may be affected, we evaluated the ability of CXCL13 to rescue HUVEC from starvation-induced apoptosis, as FGF-2 is a survival factor for endothelial cells, and found that CXCL13 partially inhibits such rescue. Multiple mechanisms may be responsible for these biological activities as CXCL13 displaces FGF-2 binding to endothelial cells, inhibits FGF-2 homodimerization, and induces the formation of CXCL13-FGF-2 heterodimers. Our data suggest that CXCL13 may modulate angiogenesis by interfering with FGF-2 activity.

A short peptide domain of platelet factor 4 blocks angiogenic key events induced by FGF-2

Platelet factor 4 (PF-4) is a CXC-chemokine with strong anti-angiogenic properties. We have shown previously that PF-4 inhibits angiogenesis by associating directly with fibroblast growth factor 2 (FGF-2), inhibiting its dimerization, and blocking FGF-2 binding to endothelial cells. We now have characterized a small peptide domain (PF-447-70) derived from the C-terminus of PF-4, which conserves anti-angiogenic effects of the parent protein. PF-447-70 inhibited internalization of 125I-FGF-2 by endothelial cells in a time-dependent manner. The peptide reduced FGF-2-stimulated cell migration to control levels in wounded monolayers of bovine capillary endothelial cells. PF-447-70 also reduced FGF-2 induced phosphorylation of MAP kinases ERK-1 and ERK-2, which are essential for migration and survival of endothelial cells. In a serum-free ex vivo angiogenesis assay, the peptide blocked microvessel outgrowth by 89%. A single amino acid substitution within PF-447-70 abolished all inhibitory activities. To simulate a real anti-angiogenic treatment situation, we administered PF-447-70 systemically to mice implanted subcutaneously with FGF-2 containing gelatin sponges with the result of sparse, scattered, and immature vessel growth. The small peptide fragment derived from the angio-inhibitory CXC-chemokine PF-4 might be used as a starting point to develop anti-angiogenic designer drugs for angiogenesis-dependent pathologies such as cancer, diabetic retinopathy, and rheumatoid arthritis.