Cellular characteristics of neuroblastoma cells: regulation by the ELR--CXC chemokine CXCL10 and expression of a CXCR3-like receptor

The role of CXCR3 and its ligands in cancer

Chemokines are a class of small cytokines or signaling proteins that are secreted by cells. Owing to their ability to induce directional chemotaxis of nearby responding cells, they are called chemotactic cytokines. Chemokines and chemokine receptors have now been shown to influence many cellular functions, including survival, adhesion, invasion, and proliferation, and regulate chemokine levels. Most malignant tumors express one or more chemokine receptors. The CXC subgroup of chemokine receptors, CXCR3, is mainly expressed on the surface of activated T cells, B cells, and natural killer cells, and plays an essential role in infection, autoimmune diseases, and tumor immunity by binding to specific receptors on target cell membranes to induce targeted migration and immune responses. It is vital to treat infections, autoimmune diseases, and tumors. CXCR3 and its ligands, CXCL9, CXCL10, and CXCL11, are closely associated with the development and progression of many tumors. With the elucidation of its mechanism of action, CXCR3 is expected to become a new indicator for evaluating the prognosis of patients with tumors and a new target for clinical tumor immunotherapy. This article reviews the significance and mechanism of action of the chemokine receptor CXCR3 and its specific ligands in tumor development.

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.

Bone Marrow Environment in Metastatic Neuroblastoma

The study of the interactions occurring in the BM environment has been facilitated by the peculiar nature of metastatic NB. In fact: (i) metastases are present at diagnosis; (ii) metastases are confined in a very specific tissue, the BM, suggestive of a strong attraction and possibility of survival; (iii) differently from adult cancers, NB metastases are available because the diagnostic procedures require morphological examination of BM; (iv) NB metastatic cells express surface antigens that allow enrichment of NB metastatic cells by immune-magnetic separation; and (v) patients with localized disease represent an internal control to discriminate specific alterations occurring in the metastatic niche from generic alterations determined by the neoplastic growth at the primary site. Here, we first review the information regarding the features of BM-infiltrating NB cells. Then, we focus on the alterations found in the BM of children with metastatic NB as compared to healthy children and children with localized NB. Specifically, information regarding all the BM cell populations and their sub-sets will be first examined in the context of BM microenvironment in metastatic NB. In the last part, the information regarding the soluble factors will be presented.

Beyond Cell Motility: The Expanding Roles of Chemokines and Their Receptors in Malignancy

The anti-tumor activities of some members of the chemokine family are often overcome by the functions of many chemokines that are strongly and causatively linked with increased tumor progression. Being key leukocyte attractants, chemokines promote the presence of inflammatory pro-tumor myeloid cells and immune-suppressive cells in tumors and metastases. In parallel, chemokines elevate additional pro-cancerous processes that depend on cell motility: endothelial cell migration (angiogenesis), recruitment of mesenchymal stem cells (MSCs) and site-specific metastasis. However, the array of chemokine activities in cancer expands beyond such “typical” migration-related processes and includes chemokine-induced/mediated atypical functions that do not activate directly motility processes; these non-conventional chemokine functions provide the tumor cells with new sets of detrimental tools. Within this scope, this review article addresses the roles of chemokines and their receptors at atypical levels that are exerted on the cancer cell themselves: promoting tumor cell proliferation and survival; controlling tumor cell senescence; enriching tumors with cancer stem cells; inducing metastasis-related functions such as epithelial-to-mesenchymal transition (EMT) and elevated expression of matrix metalloproteinases (MMPs); and promoting resistance to chemotherapy and to endocrine therapy. The review also describes atypical effects of chemokines at the tumor microenvironment: their ability to up-regulate/stabilize the expression of inhibitory immune checkpoints and to reduce the efficacy of their blockade; to induce bone remodeling and elevate osteoclastogenesis/bone resorption; and to mediate tumor-stromal interactions that promote cancer progression. To illustrate this expanding array of atypical chemokine activities at the cancer setting, the review focuses on major metastasis-promoting inflammatory chemokines—including CXCL8 (IL-8), CCL2 (MCP-1), and CCL5 (RANTES)—and their receptors. In addition, non-conventional activities of CXCL12 which is a key regulator of tumor progression, and its CXCR4 receptor are described, alongside with the other CXCL12-binding receptor CXCR7 (RDC1). CXCR7, a member of the subgroup of atypical chemokine receptors (ACKRs) known also as ACKR3, opens the gate for discussion of atypical activities of additional ACKRs in cancer: ACKR1 (DARC, Duffy), ACKR2 (D6), and ACKR4 (CCRL1). The mechanisms involved in chemokine activities and the signals delivered by their receptors are described, and the clinical implications of these findings are discussed.

Differential expression profile of CXCR3 splicing variants is associated with thyroid neoplasia. Potential role in papillary thyroid carcinoma oncogenesis?

Papillary thyroid cancer (PTC) is the most prevalent endocrine neoplasia. The increased incidence of PTC in patients with thyroiditis and the frequent immune infiltrate found in PTC suggest that inflammation might be a risk factor for PTC development. The CXCR3-ligand system is involved in thyroid inflammation and CXCR3 has been found upregulated in many tumors, suggesting its pro-tumorigenic role under the inflammatory microenvironment. CXCR3 ligands (CXCL4, CXCL9, CXCL10 and CXCL11) trigger antagonistic responses partly due to the presence of two splice variants, CXCR3A and CXCR3B. Whereas CXCR3A promotes cell proliferation, CXCR3B induces apoptosis. However, the relation between CXCR3 variant expression with chronic inflammation and PTC development remains unknown. Here, we characterized the expression pattern of CXCR3 variants and their ligands in benign tumors and PTC. We found that CXCR3A and CXCL10 mRNA levels were increased in non-metastatic PTC when compared to non-neoplastic tissue. This increment was also observed in a PTC epithelial cell line (TPC-1). Although elevated protein levels of both isoforms were detected in benign and malignant tumors, the CXCR3A expression remained greater than CXCR3B and promoted proliferation in Nthy-ori-3-1 cells. In non-metastatic PTC, inflammation was conditioning for the CXCR3 ligands increased availability. Consistently, CXCL10 was strongly induced by interferon gamma in normal and tumor thyrocytes.

Our results suggest that persistent inflammation upregulates CXCL10 expression favoring tumor development via enhanced CXCR3A-CXCL10 signaling. These findings may help to further understand the contribution of inflammation as a risk factor in PTC development and set the basis for potential therapeutic studies.

A CXCL ortholog from Hippocampus abdominalis: Molecular features and functional delineation as a pro-inflammatory chemokine

Chemokines are a family of chemotactic cytokines that regulate leukocyte migration. They are classified into four groups namely, CXC, CC, C and CX₃C, based on the formation of a disulfide bridge. Among these, CXC chemokines have been identified as the largest group of chemokines in humans. In this study, we identified and functionally characterized a homolog of CXC chemokine from the big-belly seahorse, Hippocampus abdominalis, and designated it as ShCXCL. The cDNA of ShCXCL composed of a 342-bp open reading frame encoding 113 amino acids (aa). The CXC family-specific small cytokine domain (SCY) was identified from the mature peptide region, which comprised of a conserved CXC motif. As ShCXCL lacks an ELR (Glutamic acid-Leucine-Arginine) motif, it belongs to ELR^- subfamily. The recombinant ShCXCL protein strongly induced the nitric oxide (NO) production in macrophage cells (RAW 264.7 cell line) and showed the chemotactic effect on flounder peripheral blood leukocytes. Tissue profiling showed a ubiquitous expression pattern in all examined tissues, with a high abundance in spleen. The up-regulated mRNA expression pattern of ShCXCL was observed in blood and kidney tissues after immune stimulation by live bacteria, such as Streptococcus iniae and Edwardsiella tarda, and mitogens, such as lipopolysaccharides (LPS) and polyinosinic:polycytidylic acid (poly I:C), suggesting its important role in host immune defense against microbial infection.

Evaluation of bone marrow as a metastatic site of human neuroblastoma

Arising from neural crest cells, neuroblastoma (NB) is the most common extracranial pediatric solid tumor. The clinical presentation of NB is heterogeneous, ranging from patients with asymptomatic tumor masses, who require minimal treatment, to patients with metastatic disease who are treated with multimodal therapies. Clinical outcome is also variable, with overall survival ranging from 98% to 100% in infants with stage 1 NB, to less than 30% in patients with stage 4 MYCN-amplified NB. More than 50% of patients show metastasis at diagnosis, with the involvement of different vascularized tissues, including the bone marrow (BM). In this paper, we focus on BM infiltration by NB cells, which is considered an adverse prognostic factor. In particular, we discuss the role of different biological factors that may favor the dissemination of NB cells in the BM, such as chromosomic abnormalities, gene amplification, transcription factors, cell-surface receptors, products of oncogenes, and, more importantly, cytokines and chemokines. In addition, we analyze different techniques to evaluate BM infiltration by malignant cells (i.e., flow cytometry, immunocytochemistry, and quantitative reverse transcriptase polymerase chain reaction). Finally, we review recent data regarding phenotypic and genetic characterization of BM-infiltrating malignant cells and characterization of the BM microenvironment in NB patients compared to healthy subjects.

The role of chemoattractant receptors in shaping the tumor microenvironment

Chemoattractant receptors are a family of seven transmembrane G protein coupled receptors (GPCRs) initially found to mediate the chemotaxis and activation of immune cells. During the past decades, the functions of these GPCRs have been discovered to not only regulate leukocyte trafficking and promote immune responses, but also play important roles in homeostasis, development, angiogenesis, and tumor progression. Accumulating evidence indicates that chemoattractant GPCRs and their ligands promote the progression of malignant tumors based on their capacity to orchestrate the infiltration of the tumor microenvironment by immune cells, endothelial cells, fibroblasts, and mesenchymal cells. This facilitates the interaction of tumor cells with host cells, tumor cells with tumor cells, and host cells with host cells to provide a basis for the expansion of established tumors and development of distant metastasis. In addition, many malignant tumors of the nonhematopoietic origin express multiple chemoattractant GPCRs that increase the invasiveness and metastasis of tumor cells. Therefore, GPCRs and their ligands constitute targets for the development of novel antitumor therapeutics.

The emerging role of CXC chemokines and their receptors in cancer

Chemokines and their receptors have a multifaceted role in tumor biology and are implicated in nearly all aspects of cancer growth, survival and dissemination. Modulation of the interaction between chemokines and their cell surface receptor is, therefore, a promising area for the development of new cancer medicines. In this review, we look at the compelling evidence that is emerging to support targeting CXC chemokines, also known as family α chemokines, as novel therapeutic strategies in the treatment of cancer.

Mesenchymal stromal cells may enhance metastasis of neuroblastoma via SDF-1/CXCR4 and SDF-1/CXCR7 signaling

Bone marrow metastasis is frequently observed in patients with high-risk neuroblastoma. Mesenchymal stromal cells (MSCs) in bone marrow may enhance tumor metastasis through secreting stromal cell-derived factor-1 (SDF-1). Here we investigated neuroblastoma cell behaviors under the influence of MSCs and explored the function of SDF-1 signaling during metastasis. Neuroblastoma expressed both of the SDF-1 receptors CXCR4 and CXCR7. shRNA knockdown showed that these receptors were responsible for the migration of neuroblastoma towards MSCs. CXCR4 also supported neuroblastoma invasion. These effects could be effectively blocked by AMD3100, a potent SDF-1 antagonist. Our study suggests that MSCs are important for neuroblastoma metastasis via the secretion of SDF-1 and that such effect can be inhibited by AMD3100 or shRNA knockdown.

Lung-residing metastatic and dormant neuroblastoma cells

The mechanism by which dormant tumor cells can begin growing after long periods of inactivity and accelerate disease recurrence is poorly understood. The present study characterizes dormant neuroblastoma (NB) cells, as well as metastatic cells, which reside in the same organ microenvironment. A xenograft model of human NB consisting of variants that generate nonmetastatic local tumors in the orthotopic inoculation site and variants that generate lung metastatic NB (MetNB) cells was developed in our laboratory. The present study shows that lungs of mice inoculated with nonmetastatic NB variants contain disseminated neuroblastoma (DisNB) human cells. Both DisNB and MetNB variants expressed a similar tumorigenicty phenotype in vivo, whereas the MetNB variants produced a heavy metastatic load and the DisNB variants produced no or little metastasis. A comparative in vitro characterization of MetNB and DisNB cells revealed similarities and differences. DisNB, but not MetNB cells, expressed the minimal residual disease markers PHOX2B and TH. MetNB cells demonstrated higher migratory capacity, an elevated matrix metalloproteinase (MMP) secretion, and a higher constitutive phosphorylation of extracellular signal-regulated kinase (ERK) than DisNB cells. We suggest that characteristics common to both MetNB and DisNB cells were acquired relatively early in the metastatic process and the characteristics that differ between these variants were acquired later. We hypothesize that the DisNB cells are metastasis precursors, which may progress toward metastasis under certain microenvironmental conditions.

Chemokine-chemokine receptor axes in melanoma brain metastasis

Brain metastasis confers an extremely unfavorable prognosis upon melanoma patients. The mechanisms underlying the homing of metastatic melanoma to the brain and survival of metastatic melanoma cells in the brain are unknown. Tumor cells, including melanoma, use chemokine receptor-ligand axes to home to specific organ sites. To identify chemokine receptors that might be involved in brain-targeted melanoma metastasis, we first established a chemokine receptor profile of cultured melanoma cells (3 cell lines of cutaneous melanoma and 5 cell lines of melanoma brain metastasis). The expression of the membrane-bound chemokine CX3CL1 by these lines was also determined. We show that out of 19 receptors tested, cultured melanoma cells express CCR3, CCR4, CXCR3, CXCR7, CX3CR1 and membrane CX3CL1. Utilizing cells from newly created variants of human melanoma xenografts, we found that the expression of CCR4 was significantly higher in one brain metastatic variant compared to its expression in the corresponding local variant. Local and metastatic variants stimulated with the CCR4 ligand, CCL22, showed a differential AKT phosphorylation pattern. These findings may suggest the involvement of CCR4 in the process of brain metastasis in human melanoma, and that CCR4 may be a novel molecular biomarker for the identification of melanoma cells likely to metastasize to the brain.

Antagonism of chemokine receptor CXCR3 inhibits osteosarcoma metastasis to lungs

Metastasis continues to be the leading cause of mortality for patients with cancer. Several years ago, it became clear that chemokines and their receptors could control the tumor progress. CXCR3 has now been identified in many cancers including osteosarcoma and CXCR3 ligands were expressed by lungs that are the primary sites to which this tumor metastasize. This study tested the hypothesis that disruption of the CXCR3/CXCR3 ligands complexes could lead to a decrease in lungs metastasis. The experimental design involved the use of the CXCR3 antagonist, AMG487 and 2 murine models of osteosarcoma lung metastases. After tail vein injection of osteosarcoma cells, mice that were systematically treated with AMG487 according to preventive or curative protocols had a significant reduction in metastatic disease. Treatment of osteosarcoma cells in vitro with AMG487 led to decreased migration, decreased matrix metalloproteinase activity, decreased proliferation/survival and increased caspase-independent death. Taken together, our results support the hypothesis that CXCR3 and their ligands intervene in the initial dissemination of the osteosarcoma cells to the lungs and stimulate the growth and expansion of the metastatic foci in later stages. Moreover, these studies indicate that targeting CXCR3 may specifically inhibit tumor metastasis without adversely affecting antitumoral host response.

CXCR3 expression is associated with poor survival in breast cancer and promotes metastasis in a murine model

Breast tumor cells express the chemokine receptor CXCR3, which binds the ligands CXCL9, CXCL10, and CXCL11. CXCR3 and other chemokine receptors may mediate tumor metastasis by supporting migration of tumor cells to sites of ligand expression including the lymph nodes, lungs, and bone marrow. We examined the relationship of CXCR3 expression to clinical outcome in 75 women diagnosed with early-stage breast cancer. We detected CXCR3 in malignant epithelium from all tumors. Twelve percent were weakly positive and 64% had moderate levels of CXCR3. Strong CXCR3-positive staining was observed in 24% of tumors. Kaplan-Meier survival curves showed that high CXCR3 expression was associated with poorer overall survival; the unadjusted hazard ratio was 1.56 and it was marginally significant (P=0.07). When interactions between lymph node status and CXCR3 were considered, the adjusted hazard ratio for CXCR3 was 2.62 (P=0.02) for women with node-negative disease at diagnosis, whereas the hazard ratio for CXCR3 was not significant for those with node-positive disease. CXCR3 gene silencing inhibited lung colonization and spontaneous lung metastasis from mammary gland-implanted tumors in a murine model. The size or growth rate of the locally growing tumors was not affected. The antimetastatic effect of CXCR3 gene silencing was compromised in mice depleted of Natural Killer cells or with mutations in IFN-gamma, suggesting that the role of CXCR3 is not simply to mediate tumor cell trafficking. These studies support the continued examination of CXCR3 as a potential therapeutic target in patients with breast cancer.

Chemokines in neuroectodermal tumour progression and metastasis

Chemokines and their receptors have emerged as pivotal regulators of tumour growth, progression, and metastasis. Here we review the current knowledge on chemokines and receptors likely involved in the development of metastasis of neuroectodermal tumours, with emphasis on neuroblastoma. In this respect, we discuss the controversial role of the CXCR4/CXCL12 axis in bone marrow localization of neuroblastoma cells. In addition, we focus on the ability of neuroblastoma-derived chemokines such as CCL2 and CX3CL1 to attract lymphoid cells to the tumour site. Finally, chemokine receptor and function in other neuroectodermal tumours of adulthood (i.e. melanoma and small cell lung cancer) are discussed.

Chemokines in neuroectodermal cancers: the crucial growth signal from the soil

Although chemokines and their receptors were initially identified as regulators of cell trafficking during inflammation and immune response, they have emerged as crucial players in all stages of tumor development, primary growth, migration, angiogenesis, and establishment as metastases in distant target organs. Neuroectodermal tumors regroup neoplasms originating from the embryonic neural crest cells, which display clinical and biological similarities. These tumors are highly malignant and rapidly progressing diseases that disseminate to similar target organs such as bone marrow, bone, liver and lungs. There is increasing evidence that interaction of several chemokine receptors with corresponding chemokine ligands are implicated in the growth and invasive characteristics of these tumors. In this review we summarize the current knowledge on the role of CXCL12 chemokine and its CXCR4 and CXCR7 receptors in the progression and survival of neuroectodermal tumors, with particular emphasis on neuroblastoma, the most typical and enigmatic neuroectodermal childhood tumor.

Generation and characterization of novel local and metastatic human neuroblastoma variants

Neuroblastoma (NB) is the most commonly occurring solid tumor in children. The disease usually arises in the adrenal medulla, and it is characterized by a remarkable heterogeneity in its progression. Most NB patients with an advanced disease have massive bone marrow infiltration at diagnosis. Lung metastasis represents a widely disseminated stage and is typically considered to be a terminal event. Much like other malignancies, NB progression is a complex, multistep process. The expression, function, and significance of the various factors involved in NB progression must be studied in relevant in vivo and in vitro models. Currently, models consisting of metastatic and nonmetastatic cell variants of the same genetic background exist for several types of cancer; however, none exists for NB. In the present study, we describe the generation of a NB metastasis model. SH-SY5Y and MHH-NB-11 NB cells were inoculated orthotopically into the adrenal glands of athymic nude mice. Neuroblastoma cells metastasizing to the lungs were isolated from mice bearing adrenal tumors. Lung metastatic variants were generated by repeated cycles of in vivo passage. Characterization of these variants included cellular morphology and immunophenotyping in vitro, aggressiveness in vivo, and various biologic parameters in vitro. The NB metastatic variant in each model displayed unique properties, and both metastatic variants demonstrated a metastatic phenotype in vivo. These reproducible models of human NB metastasis will serve as an unlimited source of transcriptomic and proteomic material. Such models can facilitate future studies on NB metastasis and the identification of novel NB biomarkers and targets for therapy.

The involvement of the fractalkine receptor in the transmigration of neuroblastoma cells through bone-marrow endothelial cells

Transendothelial migration (TEM) of tumor cells is a crucial step in metastasis formation. The prevailing paradigm is that the mechanism underlying TEM of tumor cells is similar to that of leukocytes involving adhesion molecules and chemokines. Fractalkine (CX3CL1) is a unique membrane-bound chemokine that functions also as an adhesion molecule. CX3CL1 can be cleaved to a soluble fragment, capable of attracting fractalkine receptor (CX3CR1)-expressing cells. In the present study, we asked if CX3CR1 is involved in the TEM of neuroblastoma cells. We demonstrated that biologically functional CX3CR1 is expressed by several neuroblastoma cell lines. Most importantly, CX3CR1-expressing neuroblastoma cells were stimulated by CX3CL1 to transmigrate through human bone-marrow endothelial cells. A dose dependent phosphorylation of ERK1/2 and AKT was induced in CX3CR1-expressing neuroblastoma cells by soluble CX3CL1. In addition to CX3CR1, neuroblastoma cells also express the CX3CL1 ligand. Membrane CX3CL1 expression was downregulated and the shedding of soluble CX3CL1 was upregulated by PKC activation. Taken together, the results of this study indicate that CX3CR1 plays a functional role in transmigration of neuroblastoma cells through bone-marrow endothelium. These results led us to hypothesize that the CX3CR1-CX3CL1 axis takes part in bone-marrow metastasis of neuroblastoma.

Bone marrow microenvironment and tumor progression

The bone marrow constitutes an unique microenvironment for cancer cells in three specific aspects. First, the bone marrow actively recruits circulating tumor cells where they find a sanctuary rich in growth factors and cytokines that promote their proliferation and survival. When in the bone marrow, tumor cells profoundly affect the homeostasis of the bone and the balance between osteogenesis and osteolysis. As a consequence, growth and survival factors normally sequestered into the bone matrix are released, further fueling cancer progression. Second, tumor cells actively recruit bone marrow-derived precursor cells into their own microenvironment. When in the tumors, these bone marrow-derived cells contribute to an inflammatory reaction and to the formation of the tumor vasculature. Third, bone marrow-derived cells can home in distant organs, where they form niches that attract circulating tumor cells. Our understanding of the contribution of the bone marrow microenvironment to cancer progression has therefore dramatically improved over the last few years. The importance of this new knowledge cannot be underestimated considering that the vast majority of cancer treatments such as cytotoxic and myeloablative chemotherapy, bone marrow transplantation and radiation therapy inflict a trauma to the bone marrow microenvironment. How such trauma affects the influence that the bone marrow microenvironment exerts on cancer is still poorly understood. In this article, the reciprocal relationship between the bone marrow microenvironment and tumor cells is reviewed, and its potential impact on cancer therapy is discussed.

CXCR5 may be involved in the attraction of human metastatic neuroblastoma cells to the bone marrow

INTRODUCTION

Up-regulation of some chemokine receptors on tumor cells is associated with increased metastatic potential. In this respect, limited information is available on chemokine receptor in human neuroblastoma (NB).

OBJECTS

Purpose of the study was to identify chemokines/chemokine receptors involved in bone marrow (BM) localization of metastatic NB cells in view of the development of targeted therapeutic strategies. CD45- metastatic NB cells were isolated from the BM of six patients by immunomagnetic bead manipulation. Some experiments were carried out using a panel of human neuroblastoma cell lines (GI-ME-N, GI-LI-N, LAN-5, HTLA-230, SH-SY-5Y and IMR-32). Immunophenotypic analyses were performed by flow cytometry. Cell migration assays were carried out using transwell systems. Calcium ion mobilization, chemokine receptor internalization and cell proliferation were investigated by flow cytometry.

RESULTS

In all BM samples, CXCR5 was expressed by the majority of primary neuroblasts and mediated their chemotaxis in response to CXCL13. Primary metastatic NB cells from all BM samples expressed CXCR6, but were not attracted by soluble CXCL16. Studies performed with two CXCR6+ NB cell lines showed that the mechanism whereby neuroblasts did not migrate to CXCL16 was likely related to defective calcium ion mobilization.

CONCLUSIONS

CXCR5 is the first chemokine receptor so far identified able to attract in vitro primary metastatic NB cells. CXCR6 may be involved in retention of metastatic neuroblasts in the BM through interaction with CXCL16 expressing stromal cells in the absence of signal transduction.

Pathophysiology of tumor neovascularization

Neovascularization is essential to the process of development and differentiation of tissues in the vertebrate embryo, and is also involved in a wide variety of physiological and pathological conditions in adults, including wound repair, metabolic diseases, inflammation, cardiovascular disorders, and tumor progression. Thanks to cumulative studies on vasculature, new therapeutic approaches have been opened for us to some life-threatening diseases by controlling angiogenesis in the affected organs. In cancer therapy, for example, modulation of factors responsible for tumor angiogenesis may be beneficial in inhibiting of tumor progression. Several antiangiogenic approaches are currently under preclinical trial. However, the mechanisms of neovascularization in tumors are complicated and each tumor shows unique features in its vasculature, depending on tissue specificity, angiogenic micromilieu, grades and stages, host immunity, and so on. For better understanding and effective therapeutic approaches, it is important to clarify both the general mechanism of angiogenic events and the disease-specific mechanism of neovascularization. This review discusses the general features of angiogenesis under physiological and pathological conditions, mainly in tumor progression. In addition, recent topics such as contribution of the endothelial progenitor cells, tumor vasculogenic mimicry, markers for tumor-derived endothelial cells and pericytes, and angiogenic/angiostatic chemokines are summarized.

The multifaceted roles of chemokines in malignancy

Tumor development and progression are multifactorial processes, regulated by a large variety of intrinsic and microenvironmental factors. A key role in cancer is played by members of the chemokine superfamily. Chemokines and their receptors are expressed by tumor cells and by host cells, in primary tumors and in specific metastatic loci. The effects of chemokines on tumorigenesis are diverse: While some members of the superfamily significantly support this process, others inhibit fundamental events required for tumor establishment and metastasis. The current review describes the multifaceted roles of chemokines in malignancy, addressing four major aspects of their activities: (1) inducing leukocyte infiltration to tumors and regulating immune functions, with emphasis on tumor-associated macrophages (and the chemokines CCL2, CCL5), T cells (and the chemokines CXCL9, CXCL10) and dendritic cells (and the chemokines CCL19, CCL20, CCL21); (2) directing the homing of tumor cells to specific metastatic sites (the CXCL12-CXCR4 axis); (3) regulating angiogenic processes (mainly the ELR(+)-CXC and non-ELR-CXC chemokines); (4) acting directly on the tumor cells to control their malignancy-related functions. Together, these different chemokine functions establish a net of interactions between the tumor cells and their microenvironment, and partly dictate the fate of the malignancy cascade.

Antagonism of CXCR3 inhibits lung metastasis in a murine model of metastatic breast cancer

Tumor cells aberrantly express chemokines and/or chemokine receptors, and some may promote tumor growth and metastasis. We examined the expression and function of chemokine receptor CXCR3 in a syngeneic murine model of metastatic breast cancer. By flow cytometry, CXCR3 was detected in all murine mammary tumor cell lines examined. All human breast cancer cell lines examined also expressed CXCR3, as did the immortalized but nontumorigenic MCF-10A cell line. Interaction of CXCR3 ligands, CXCL9, CXCL10, and CXCL11, with CXCR3 on the highly malignant murine mammary tumor cell line 66.1 resulted in intracellular calcium mobilization and chemotaxis in vitro. To test the hypothesis that tumor metastasis is facilitated by CXCR3 expressed by tumor cells, we employed a small molecular weight antagonist of CXCR3, AMG487. 66.1 tumor cells were pretreated with AMG487 prior to i.v. injection into immune-competent female mice. Antagonism of CXCR3 on 66.1 tumor cells inhibited experimental lung metastasis, and this antimetastatic activity was compromised in mice depleted of natural killer cells. Systemic administration of AMG487 also inhibited experimental lung metastasis. In contrast to the antimetastatic effect of AMG487, local growth of 66.1 mammary tumors was not affected by receptor antagonism. These studies indicate that murine mammary tumor cells express CXCR3 which facilitates the development of lung metastases. These studies also indicate for the first time that a small molecular weight antagonist of CXCR3 has the potential to inhibit tumor metastasis.

The Pyst2-L phosphatase is involved in cell-crowding

The dual-specificity phosphatase Pyst2-L was found to be over expressed in leukocytes derived from AML and ALL patients as well as in certain other solid tumors and lymphoblastoid cell lines. Pyst2-L, binds and dephosphorylates both pERKs and pJNKs proteins, and thus, plays a role in regulating the MAP kinase signaling pathway. In the present study, a comparative genomic application was used and sequence analysis of multi-organisms databases were searched in order to identify genes homologous to Pyst2-L. The Xenopus laevis MAP kinase phosphatase X17c gene and the Yeast nitrogen starvation-induced protein phosphatase Yvh1p gene were revealed to be highly homologous with Pyst2-L. Both X17c and Yvh1p genes play a role in cell cycle regulation. A down regulated expression of the Yvh1p gene occurred in Saccharomyces cerevisiae that were synchronized to the G2-phase of the cell cycle by alpha-factor. In conformity with this result, a reduction in Pyst2-L expression levels was observed in G2-phase-synchronized Human K562 cells. Finally, we were able to show that cells in highly crowded cultures express high levels of the Pyst2-L phosphatase. These observations may indicate that low levels of the Pyst2-L phosphatase are essential for the G2-phase of the cell cycle and that this phosphatase might play a role in signaling cascades induced by cellular crowding.