Regulation of CXCR4-mediated chemotaxis and chemoinvasion of breast cancer cells

Antimetastatic effect of nobiletin through the down-regulation of CXC chemokine receptor type 4 and matrix metallopeptidase-9

CONTEXT

Nobiletin is one of the citrus bioflavonoids and can be found in citrus fruits such as lemons, oranges, tangerines, and grapefruits. The most studied properties of nobiletin are its anti-inflammatory and anticancer activities.

OBJECTIVE

The exact mechanisms of how nobiletin inhibits tumor metastasis and invasion are still not fully understood. In this study, we screened various natural compounds to down-modulate the CXC chemokine receptor-4 (CXCR4) and matrix metallopeptidase-9 (MMP-9).

MATERIALS AND METHODS

The effect of nobiletin on the constitutive expressions of CXCR4 and MMP-9, MMP-9 enzymatic activity, associated nuclear factor κB (NF-κB) and mitogen-activated protein kinases (MAPKs) activation, and tumor cell invasion in human breast cancer cells was investigated. CXCR4 and MMP-9 expression were evaluated via reverse transcription polymerase chain reaction (RT-PCR) and western blotting. NF-κB activation was also evaluated by electrophoretic mobility shift assay (EMSA). In addition, the antimetastatic effects of nobiletin were determined by gelatin zymography and invasion assay.

RESULTS

Nobiletin down-regulated both the constitutive expressions of CXCR4 and MMP-9 in human breast cancer cells with IC(50) values of 32 and 24 µM, respectively. Nobiletin also suppressed MMP-9 enzymatic activity and tumor cell invasion under noncytotoxic concentrations. Neither proteasome inhibition nor lysosomal stabilization had any effect on the nobiletin-induced decrease in CXCR4 expression. A detailed study of the underlying molecular mechanisms revealed that the regulation of the down-regulation of CXCR4 and MMP-9 were at the transcriptional level, as indicated by the down-regulation of mRNA expression and the suppression of the constitutive NF-κB and MAPKs activation.

DISCUSSION AND CONCLUSION

Our results indicate, for the first time, that nobiletin is a novel blocker of CXCR4 and MMP-9 expressions and thus has the potential to suppress metastasis of breast cancer.

The janus face of lipids in human breast cancer: how polyunsaturated Fatty acids affect tumor cell hallmarks

For several years, lipids and especially n - 3 and n - 6 polyunsaturated fatty acids (PUFAs) receive much attention in human health. Epidemiological studies tend to correlate a PUFA-rich diet with a reduced incidence of cancer, including breast cancer. However, the molecular and cellular mechanisms supporting the effect of PUFAs in breast cancer cells remain relatively unknown. Here, we review some recent progress in understanding the impact that PUFA may have on breast cancer cell proliferation, apoptosis, migration, and invasion. While most of the results obtained with docosahexaenoic acid and/or eicosapentaenoic acid show a decrease of tumor cell proliferation and/or aggressivity, there is some evidence that other lipids, which accumulate in breast cancer tissues, such as arachidonic acid may have opposite effects. Finally, lipids and especially PUFAs appear as potential adjuvants to conventional cancer therapy.

Chemokine (C-X-C motif) ligand 12 is associated with gallbladder carcinoma progression and is a novel independent poor prognostic factor

PURPOSE

Although recent studies have suggested that chemokine (C-X-C motif) ligand 12 (CXCL12) is important in the progression of various malignancies, its role in gallbladder carcinoma (GBC) remains unknown. We investigated CXCL12 expression in GBC and its biologic and prognostic role in GBC tumorigenesis.

EXPERIMENTAL DESIGN

We examined CXCL12 expression in tumor specimens from 72 patients with GBC by immunohistochemistry and analyzed the correlation between CXCL12 expression and clinicopathologic factors or survival. The functional significance of CXCL12 expression was investigated by CXCL12 treatment and suppression of CXCR4, a major receptor of CXCL12, as well as by CXCL12 overexpression in in vitro and in vivo studies.

RESULTS

CXCL12 was differentially expressed in GBC tissues. CXCL12 expression was significantly associated with a high histologic grade (P = 0.042) and nodal metastasis (P = 0.015). Multivariate analyses showed that CXCL12 expression (HR, 8.675; P = 0.014) was an independent risk factor for patient survival. CXCL12 significantly increased anchorage-dependent and -independent growth, migration, invasion, adhesiveness, and survival of GBC cells in vitro, and these effects were dependent on CXCR4. Consistent with these results, overexpression of CXCL12 significantly promoted GBC tumorigenicity in a xenograft model.

CONCLUSIONS

Our results indicate that GBC cells express both CXCL12 and its receptor CXCR4, and CXCL12 may have a role in GBC progression through an autocrine mechanism. In addition, CXCL12 is a novel independent poor prognostic factor in patients with GBCs. Thus, targeting CXCL12 and CXCR4 may provide a novel therapeutic strategy for GBC treatment.

Rapid generation of multiplexed cell cocultures using acoustic droplet ejection followed by aqueous two-phase exclusion patterning

The development of tools for patterning cocultures of cells is a fundamental interest among cell biologists and tissue engineers. Although a variety of systems exist for micropatterning cells, the methods used to generate cell micropatterns are often cumbersome and difficult to adapt for tissue engineering purposes. This study combines acoustic droplet ejection and aqueous two-phase system exclusion patterning to introduce a method for patterning cocultures of cells in multiplexed arrays. This new method uses focused acoustic radiation pressure to eject discrete droplets of uniform size from the surface of a dextran solution containing cells. The size of droplets is controlled by adjusting ultrasound parameters, such as pulse, duration, and amplitude. The ejected dextran droplets are captured on a cell culture substrate that is manipulated by a computer-controlled 3D positioning system according to predesigned patterns. Polyethylene glycol solution containing an additional cell type is then added to the culture dish to produce a two-phase system capable of depositing different types of cells around the initial pattern of cells. We demonstrate that our method can produce patterns of islands or lines with two or more cell types. Further, we demonstrate that patterns can be multiplexed for studies involving combinations of multiple cell types. This method offers a tool to transfer cell-containing samples in a contact-free, nozzle-less manner, avoiding sample cross-contamination. It can be used to pattern cell cocultures without complicated fabrication of culture substrates. These capabilities were used to examine the response of cancer cells to the presence of a ligand (CXCL12) secreted from surrounding cocultured cells.

High expression of IL-13 receptor α2 in colorectal cancer is associated with invasion, liver metastasis, and poor prognosis

Autocrine secretion of cytokines by metastatic colorectal cancer cells and their role during invasion and liver homing has been poorly characterized. In this study, we used cytokine arrays to analyze the secretomes of poorly and highly metastatic colorectal cancer cells. Compared with poorly metastatic cancer cells, highly metastatic cells expressed increased levels of the immunosuppressive cytokines interleukin (IL)-4 and IL-13 in addition to increased surface expression of the high affinity IL-13 receptor IL-13Rα2, suggesting that IL-13Rα2 mediates IL-13 effects in colorectal cancer cells. Silencing of IL-13Rα2 in highly metastatic cells led to a decrease in adhesion capacity in vitro and a reduction in liver homing and increased survival in vivo, revealing a role for this receptor in cell adhesion, migration, invasion, and metastatic colonization. In support of this, IL-13 signaling activated the oncogenic signaling molecules phosphoinositide 3-kinase, AKT, and SRC in highly metastatic cells. Clinically, high expression of IL-13Rα2 was associated with later stages of disease progression and poor outcome in patients with colorectal cancer. Our findings therefore support a critical role for IL-13Rα2 expression in colon cancer invasion and metastasis.

Protein kinases: emerging therapeutic targets in chronic lymphocytic leukemia

INTRODUCTION

Although protein kinases are primary targets for inhibition in hematological malignancies, until recently their contribution to chronic lymphocytic leukemia (CLL) was poorly understood. Insights into B-cell receptor signaling and its role in regulating key cellular functions have shed light on candidate protein kinases that are aberrantly activated in CLL. In this regard, protein kinases are now considered as potential drug targets in CLL.

AREA COVERED

This review has covered signaling pathways and associated protein kinases in CLL and the kinase inhibitors currently available in preclinical and clinical investigations. Individual protein kinases that are abnormally active in CLL and the functional consequences of their inhibition are discussed.

EXPERT OPINION

A growing body of evidence suggests that protein kinases are druggable targets for patients with CLL. The emergence of novel and bio-available kinase inhibitors and their promising clinical activity in CLL underscore the oncogenic role of kinases in leukemogenesis. Further investigations directed towards their role as single agents or in combinations may provide insight into understanding the substantial role of kinase-mediated signal transduction pathways and their inhibition in B- CLL.

Stromal-Cell-Derived Factor-1 (SDF-1)/CXCL12 as Potential Target of Therapeutic Angiogenesis in Critical Leg Ischaemia

In the Western world, peripheral vascular disease (PVD) has a high prevalence with high morbidity and mortality. In a large percentage of these patients, lower limb amputation is still required. Studies of ischaemic skeletal muscle disclosed evidence of endogenous angiogenesis and adaptive skeletal muscle metabolic changes in response to hypoxia. Chemokines are potent chemoattractant cytokines that regulate leukocyte trafficking in homeostatic and inflammatory processes. More than 50 different chemokines and 20 different chemokine receptors have been cloned. The chemokine stromal-cell-derived factor-1 (SDF-1 aka CXCL12) is a constitutively expressed and inducible chemokine that regulates multiple physiological processes, including embryonic development and organ homeostasis. The biologic effects of SDF-1 are mediated by chemokine receptor CXCR4, a 352 amino acid rhodopsin-like transmembrane-specific G protein-coupled receptor (GPCR). There is evidence that the administration of SDF-1 increases blood flow and perfusion via recruitment of endothelial progenitor cells (EPCs). This review will focus on the role of the SDF-1/CXCR4 system in the pathophysiology of PVD and discuss their potential as therapeutic targets for PVD.

Inhibition of CD26/DPP-IV enhances donor muscle cell engraftment and stimulates sustained donor cell proliferation

BACKGROUND

Transplantation of myogenic stem cells possesses great potential for long-term repair of dystrophic muscle. In murine-to-murine transplantation experiments, CXCR4 expression marks a population of adult murine satellite cells with robust engraftment potential in mdx mice, and CXCR4-positive murine muscle-derived SP cells home more effectively to dystrophic muscle after intra-arterial delivery in mdx5cv mice. Together, these data suggest that CXCR4 plays an important role in donor cell engraftment. Therefore, we sought to translate these results to a clinically relevant canine-to-canine allogeneic transplant model for Duchenne muscular dystrophy (DMD) and determine if CXCR4 is important for donor cell engraftment.

METHODS

In this study, we used a canine-to-murine xenotransplantation model to quantitatively compare canine muscle cell engraftment, and test the most effective cell population and modulating factor in a canine model of DMD using allogeneic transplantation experiments.

RESULTS

We show that CXCR4 expressing cells are important for donor muscle cell engraftment, yet FACS sorted CXCR4-positive cells display decreased engraftment efficiency. However, diprotin A, a positive modulator of CXCR4-SDF-1 binding, significantly enhanced engraftment and stimulated sustained proliferation of donor cells in vivo. Furthermore, the canine-to-murine xenotransplantation model accurately predicted results in canine-to-canine muscle cell transplantation.

CONCLUSIONS

Therefore, these results establish the efficacy of diprotin A in stimulating muscle cell engraftment, and highlight the pre-clinical utility of a xenotransplantation model in assessing the relative efficacy of muscle stem cell populations.

Contribution of CXCL12 secretion to invasion of breast cancer cells

INTRODUCTION

Neu (HER2/ErbB2) is overexpressed in 25% to 30% of human breast cancer, correlating with a poor prognosis. Researchers in previous studies who used the mouse mammary tumor virus Neu-transgenic mouse model (MMTV-Neu) demonstrated that the Neu-YB line had increased production of CXCL12 and increased metastasis, whereas the Neu-YD line had decreased metastasis. In this study, we examined the role of increased production of CXCL12 in tumor cell invasion and malignancy.

METHODS

We studied invasion in the tumor microenvironment using multiphoton intravital imaging, in vivo invasion and intravasation assays. CXCL12 signaling was altered by using the CXCR4 inhibitor AMD3100 or by increasing CXCL12 expression. The role of macrophage signaling in vivo was determined using a colony-stimulating factor 1 receptor (CSF-1R) blocking antibody.

RESULTS

The Neu-YD strain was reduced in invasion, intravasation and metastasis compared to the Neu-YB and Neu deletion mutant (activated receptor) strains. Remarkably, in the Neu-YB strain, in vivo invasion to epidermal growth factor was dependent on both CXCL12-CXCR4 and CSF1-CSF-1R signaling. Neu-YB tumors had increased macrophage and microvessel density. Overexpression of CXCL12 in rat mammary adenocarcinoma cells increased in vivo invasion as well as microvessel and macrophage density.

CONCLUSIONS

Expression of CXCL12 by tumor cells results in increased macrophage and microvessel density and in vivo invasiveness.

Emodin inhibits invasion and migration of prostate and lung cancer cells by downregulating the expression of chemokine receptor CXCR4

Emodin (ED), an anthraquinone derivative, has been found to inhibit proliferation, induce apoptosis, suppress angiogenesis, impede metastasis, and enhance chemotherapy. However, the detailed mechanism of ED related to the regulation of CXC chemokine receptor-4 (CXCR4) gene expression that affects cellular migration and invasion in prostate and lung cancer cells are not fully understood. Recent evidence indicates that the CXCR4/CXCL12 axis is involved in promoting invasion and metastasis in tumors. Thus, novel agents that can downregulate CXCR4 expression have therapeutic potential in repressing cancer metastasis. Among ED and its derivatives, it is found that ED downregulated the expression of both CXCR4 and HER2 without affecting cell viability in tumor cells. The suppression of CXCR4 expression by ED was found to correlate with the inhibition of CXCL12-induced migration and invasion of both DU145 and A549 cells. Besides, neither proteasome inhibition nor lysosomal stabilization had any effect on ED-induced decrease in CXCR4 expression. The basic molecular mechanisms unveiled that the downregulation of CXCR4 was at the transcriptional level, as indicated by downregulation of mRNA expression and suppression of NF-κB activation. Overall, our findings suggest that ED is a novel blocker of CXCR4 expression and, thus, has enormous potential as a powerful therapeutic agent for metastatic cancer.

CXCR4/CXCL12 participate in extravasation of metastasizing breast cancer cells within the liver in a rat model

INTRODUCTION

Organ-specific composition of extracellular matrix proteins (ECM) is a determinant of metastatic host organ involvement. The chemokine CXCL12 and its receptor CXCR4 play important roles in the colonization of human breast cancer cells to their metastatic target organs. In this study, we investigated the effects of chemokine stimulation on adhesion and migration of different human breast cancer cell lines in vivo and in vitro with particular focus on the liver as a major metastatic site in breast cancer.

METHODS

Time lapse microscopy, in vitro adhesion and migration assays were performed under CXCL12 stimulation. Activation of small GTPases showed chemokine receptor signalling dependence from ECM components. The initial events of hepatic colonisation of MDA-MB-231 and MDA-MB-468 cells were investigated by intravital microscopy of the liver in a rat model and under shRNA inhibition of CXCR4.

RESULTS

In vitro, stimulation with CXCL12 induced increased chemotactic cell motility (p<0.05). This effect was dependent on adhesive substrates (type I collagen, fibronectin and laminin) and induced different responses in small GTPases, such as RhoA and Rac-1 activation, and changes in cell morphology. In addition, binding to various ECM components caused redistribution of chemokine receptors at tumour cell surfaces. In vivo, blocking CXCR4 decreased extravasation of highly metastatic MDA-MB-231 cells (p<0.05), but initial cell adhesion within the liver sinusoids was not affected. In contrast, the less metastatic MDA-MB-468 cells showed reduced cell adhesion but similar migration within the hepatic microcirculation.

CONCLUSION

Chemokine-induced extravasation of breast cancer cells along specific ECM components appears to be an important regulator but not a rate-limiting factor of their metastatic organ colonization.

Progenitor cell mobilization and recruitment: SDF-1, CXCR4, α4-integrin, and c-kit

Progenitor cell retention and release are largely governed by the binding of stromal-cell-derived factor 1 (SDF-1) to CXC chemokine receptor 4 (CXCR4) and by α4-integrin signaling. Both of these pathways are dependent on c-kit activity: the mobilization of progenitor cells in response to either CXCR4 antagonism or α4-integrin blockade is impaired by the loss of c-kit kinase activity; and c-kit-kinase inactivation blocks the retention of CXCR4-positive progenitor cells in the bone marrow. SDF-1/CXCR4 and α4-integrin signaling are also crucial for the retention of progenitor cells in the ischemic region, which may explain, at least in part, why clinical trials of progenitor cell therapy have failed to display the efficacy observed in preclinical investigations. The lack of effectiveness is often attributed to poor retention of the transplanted cells and, to date, most of the trial protocols have mobilized cells with injections of granulocyte colony-stimulating factor (G-CSF), which activates extracellular proteases that irreversibly cleave cell-surface adhesion molecules, including α4-integrin and CXCR4. Thus, the retention of G-CSF-mobilized cells in the ischemic region may be impaired, and the mobilization of agents that reversibly disrupt SDF-1/CXCR4 binding, such as AMD3100, may improve patient response. Efforts to supplement SDF-1 levels in the ischemic region may also improve progenitor cell recruitment and the effectiveness of stem cell therapy.

Inhibition of CXCR4/CXCL12 signaling axis by ursolic acid leads to suppression of metastasis in transgenic adenocarcinoma of mouse prostate model

Increasing evidences indicate that CXCR4/CXCL12 signaling pathway plays a pivotal role in the process of distant site metastasis that accounts for more than 90% of prostate cancer related deaths in patients. Thus, novel drugs that can downregulate CXCR4/CXCL12 axis have a great potential in the treatment of metastatic prostate cancer. In this report, we tested an agent, ursolic acid (UA) for its ability to modulate CXCR4 expression in prostate cancer cell lines and inhibit metastasis in vivo in transgenic adenocarcinoma of mouse prostate (TRAMP) model. We observed that UA downregulated the expression of CXCR4 in prostate cancer cells irrespective of their HER2 status in a dose- and time-dependent manner. Neither proteasome inhibitor nor lysosomal stabilization had any effect on UA-induced decrease in CXCR4 expression. When investigated for the molecular mechanisms, it was observed that the downregulation of CXCR4 was due to transcriptional regulation as indicated by downregulation of mRNA expression, inhibition of NF-κB activation and modulation of chromatin immunoprecipitation activity. Suppression of CXCR4 expression by UA further correlated with the inhibition of CXCL12-induced migration and invasion in prostate cancer cells. Finally, we also found that UA treatment can inhibit metastasis of prostate cancer to distal organs, including lung and liver and suppress CXCR4 expression levels in the prostate tissues of TRAMP mice. Overall, our experimental findings suggest that UA exerts its antimetastatic effects through the suppression of CXCR4 expression in prostate cancer both in vitro and in vivo.

Crosstalk between chemokine receptor CXCR4 and cannabinoid receptor CB2 in modulating breast cancer growth and invasion

Background

Cannabinoids bind to cannabinoid receptors CB₁ and CB₂ and have been reported to possess anti-tumorigenic activity in various cancers. However, the mechanisms through which cannabinoids modulate tumor growth are not well known. In this study, we report that a synthetic non-psychoactive cannabinoid that specifically binds to cannabinoid receptor CB₂ may modulate breast tumor growth and metastasis by inhibiting signaling of the chemokine receptor CXCR4 and its ligand CXCL12. This signaling pathway has been shown to play an important role in regulating breast cancer progression and metastasis.

Methodology/Principal Findings

We observed high expression of both CB₂ and CXCR4 receptors in breast cancer patient tissues by immunohistochemical analysis. We further found that CB₂-specific agonist JWH-015 inhibits the CXCL12-induced chemotaxis and wound healing of MCF7 overexpressing CXCR4 (MCF7/CXCR4), highly metastatic clone of MDA-MB-231 (SCP2) and NT 2.5 cells (derived from MMTV-neu) by using chemotactic and wound healing assays. Elucidation of the molecular mechanisms using various biochemical techniques and confocal microscopy revealed that JWH-015 treatment inhibited CXCL12-induced P44/P42 ERK activation, cytoskeletal focal adhesion and stress fiber formation, which play a critical role in breast cancer invasion and metastasis. In addition, we have shown that JWH-015 significantly inhibits orthotopic tumor growth in syngenic mice in vivo using NT 2.5 cells. Furthermore, our studies have revealed that JWH-015 significantly inhibits phosphorylation of CXCR4 and its downstream signaling in vivo in orthotopic and spontaneous breast cancer MMTV-PyMT mouse model systems.

Conclusions/Significance

This study provides novel insights into the crosstalk between CB₂ and CXCR4/CXCL12-signaling pathways in the modulation of breast tumor growth and metastasis. Furthermore, these studies indicate that CB₂ receptors could be used for developing innovative therapeutic strategies against breast cancer.

Plumbagin inhibits invasion and migration of breast and gastric cancer cells by downregulating the expression of chemokine receptor CXCR4

Background

Increasing evidence indicates that the interaction between the CXC chemokine receptor-4 (CXCR4) and its ligand CXCL12 is critical in the process of metastasis that accounts for more than 90% of cancer-related deaths. Thus, novel agents that can downregulate the CXCR4/CXCL12 axis have therapeutic potential in inhibiting cancer metastasis.

Methods

In this report, we investigated the potential of an agent, plumbagin (5-hydroxy-2-methyl-1, 4-naphthoquinone), for its ability to modulate CXCR4 expression and function in various tumor cells using Western blot analysis, DNA binding assay, transient transfection, real time PCR analysis, chromatin immunoprecipitation, and cellular migration and invasion assays.

Results

We found that plumbagin downregulated the expression of CXCR4 in breast cancer cells irrespective of their HER2 status. The decrease in CXCR4 expression induced by plumbagin was not cell type-specific as the inhibition also occurred in gastric, lung, renal, oral, and hepatocellular tumor cell lines. Neither proteasome inhibition nor lysosomal stabilization had any effect on plumbagin-induced decrease in CXCR4 expression. Detailed study of the underlying molecular mechanism(s) revealed that the regulation of the downregulation of CXCR4 was at the transcriptional level, as indicated by downregulation of mRNA expression, inhibition of NF-κB activation, and suppression of chromatin immunoprecipitation activity. In addition, using a virtual, predictive, functional proteomics-based tumor pathway platform, we tested the hypothesis that NF-κB inhibition by plumbagin causes the decrease in CXCR4 and other metastatic genes. Suppression of CXCR4 expression by plumbagin was found to correlate with the inhibition of CXCL12-induced migration and invasion of both breast and gastric cancer cells.

Conclusions

Overall, our results indicate, for the first time, that plumbagin is a novel blocker of CXCR4 expression and thus has the potential to suppress metastasis of cancer.

EGF and bFGF promote invasion that is modulated by PI3/Akt kinase and Erk in vestibular schwannoma

OBJECTIVES

Vestibular schwannomas (VSs) are slow-growing benign tumors but, on rare occasion, can invade adjacent cranial nerves, causing significant morbidity, especially in association with neurofibromatosis 2 (NF2). We aimed to determine the role of the growth factors EGF, bFGF, and the hormone, Epo, in promoting such invasive behavior in VS, as well as their mechanisms of action.

METHODS

Immunohistochemical staining showed expression of EGFR, bFGF, Epo, EpoR in archived VS tissue. Western blots and immunofluorescence showed expression of EGFR, EpoR and FGF in HEI-193, an immortalized cell line derived from human NF2-related VS. Matrigel invasion assays were used to study the effect of Epo, FGF and bFGF on invasive behavior in HEI-193. Western blotting showed levels of phospho-Akt and phospho-Erk in HEI-193 upon addition of growth factors plus PI3K or MEK inhibitors. Quantitative RT-PCR was performed to determine the expression of MMP2 and MMP9 after treatment with growth factors.

RESULTS

EGFR, bFGF, Epo and EpoR were expressed in VS tissue and HEI193. Addition of EGF and bFGF increased cellular invasion by 10 and 3.5-fold, respectively. Epo had minimal effect on invasion. Results indicated that Erk is involved in bFGF but not EGF-induced invasion, while Akt is involved in both pathways. EGF treatment moderately induced MMP9, but is unlikely to account for the observed invasion.

CONCLUSION

Activation of EGFR and FGFR may promote invasive behavior in VS through ERK and Akt signaling pathways. Further investigation will be necessary to elucidate their potential as useful targets in the treatment of VS.

Testicular germ cell tumours: predisposition genes and the male germ cell niche

Testicular germ cell tumours (TGCTs) of adults and adolescents are putatively derived from primordial germ cells or gonocytes. Recently reported genome-wide association studies implicate six gene loci that predispose to TGCT development. Remarkably, the functions of proteins encoded by genes within these regions bridge our understanding between the pathways involved in primordial germ cell physiology, male germ cell development and the molecular pathology of TGCTs. Furthermore, this improved understanding of the mechanisms underlying TGCT development and dissemination has clinical relevance for the management of patients with these tumours.

Inhibition of breast cancer cell invasion by melatonin is mediated through regulation of the p38 mitogen-activated protein kinase signaling pathway

INTRODUCTION

The pineal gland hormone, melatonin, has been shown by numerous studies to inhibit the proliferation of estrogen receptor α (ERα)-positive breast cancer cell lines. Here, we investigated the role of melatonin in the regulation of breast cancer cell invasion.

METHODS

Three invasive MCF-7 breast cancer cell clones - MCF-7/6, MCF-7/Her2.1, and MCF-7/CXCR4 cells - were employed in these studies. All three cell lines exhibited elevated phosphorylation of the ERK1/2 and p38 mitogen-activated protein kinase (MAPK) as determined by Western blot analysis. The effect of melatonin on the invasive potential of these human breast cancer cells was examined by matrigel invasion chamber assays. The expression and proteinase activity of two matrix metalloproteinases (MMPs), MMP-2 and MMP-9, were analyzed by Western blot analysis and gelatin zymography, respectively.

RESULTS

Melatonin (10-9 M) significantly suppressed the invasive potential of MCF-7/6 and MCF-7/Her2.1 cells as measured by matrigel invasion chamber assays, and significantly repressed the proteinase activity of MMP-2 and MMP-9. In MCF-7/CXCR4 cells, melatonin significantly inhibited stromal-derived factor-1 (SDF-1/CXCL12) induced cell invasion and activity of MMP-9. Elevated expression of the MT1 melatonin receptor further enhanced, while luzindole, an MT1/MT2 antagonist, abrogated melatonin's anti-invasive effect, suggesting that melatonin's effect on invasion is mediated, principally, through the MT1 receptor. Furthermore, melatonin repressed the phosphorylation of p38 MAPK in MCF-7/Her2.1 cells and blocked stromal-derived factor-1 (SDF-1) induced p38 phosphorylation in MCF-7/CXCR4 cells. SB230580, a p38 inhibitor, was able to mimic, while transfection of the cells with a constitutively-active MKK6b construct blocked melatonin's effect on cell invasion, suggesting that the anti-invasive action of melatonin is mediated through the p38 pathway.

CONCLUSIONS

Melatonin exerts an inhibitory effect on breast cancer cell invasion through down-regulation of the p38 pathway, and inhibition of MMP-2 and MMP-9 expression and activity.

CXCR4 and cancer

The chemokine receptor CXCR4 belongs to the large superfamily of G protein-coupled receptors and has been identified to play a crucial role in a number of biological processes, including the trafficking and homeostasis of immune cells such as T lymphocytes. CXCR4 has also been found to be a prognostic marker in various types of cancer, including leukemia and breast cancer, and recent evidence has highlighted the role of CXCR4 in prostate cancer. Furthermore, CXCR4 expression is upregulated in cancer metastasis, leading to enhanced signaling. These observations suggest that CXCR4 is important for the progression of cancer. The CXCR4-CXCL12 (stromal cell-derived factor 1 (SDF-1)) axis has additionally been identified to have a role in normal stem cell homing. Interestingly, cancer stem cells also express CXCR4, indicating that the CXCR4-SDF-1 axis may direct the trafficking and metastasis of these cells to organs that express high levels of SDF-1, such as the lymph nodes, lungs, liver, and bone. This review focuses on the current knowledge of CXCR4 regulation and how deregulation of this protein may contribute to the progression of cancer.

PI3 kinase-dependent stimulation of platelet migration by stromal cell-derived factor 1 (SDF-1)

Platelets have been regarded as static cells that do not move once they adhere to a matrix. The present study explored, whether platelets are able to migrate. In contrast to the current opinion, we found that platelets were mobile, able to migrate over a surface, and transmigrate through a transwell membrane and endothelium toward a source of stromal cell-derived factor 1 (SDF-1). Platelet migration was stimulated by SDF-1, which led to the downstream activation and phosphorylation of Wiskott-Aldrich syndrome protein. SDF-1 signaling and subsequent platelet migration could be inhibited by CXCR4-receptor blocker AMD3100, pertussis toxin, inhibition of phosphoinositol 3-kinase (PI3 kinase) with LY294002 or wortmannin, and disruption of actin polymerization with cytochalasin B. The potential of platelets to migrate in an SDF-1-mediated fashion may redefine the role of platelets in the pathophysiology of vascular inflammation, subsequent atherosclerotic degeneration, and vascular regeneration.

Multiple functions of CXCL12 in a syngeneic model of breast cancer

Background

A growing body of work implicates chemokines, in particular CXCL12 and its receptors, in the progression and site-specific metastasis of various cancers, including breast cancer. Various agents have been used to block the CXCL12-CXCR4 interaction as a means of inhibiting cancer metastasis. However, as a potent chemotactic factor for leukocytes, CXCL12 also has the potential to enhance anti-cancer immunity. To further elucidate its role in breast cancer progression, CXCL12 and its antagonist CXCL12_(P2G) were overexpressed in the syngeneic 4T1.2 mouse model of breast carcinoma.

Results

While expression of CXCL12_(P2G) significantly inhibited metastasis, expression of wild-type CXCL12 potently inhibited both metastasis and primary tumor growth. The effects of wild-type CXCL12 were attributed to an immune response characterized by the induction of CD8⁺ T cell activity, enhanced cell-mediated cytotoxicity, increased numbers of CD11c⁺ cells in the tumor-draining lymph nodes and reduced accumulation of myeloid-derived suppressor cells in the spleen.

Conclusions

This study highlights the need to consider carefully therapeutic strategies that block CXCL12 signaling. Therapies that boost CXCL12 levels at the primary tumor site may prove more effective in the treatment of metastatic breast cancer.

ITF2 is a target of CXCR4 in MDA-MB-231 breast cancer cells and is associated with reduced survival in estrogen receptor-negative breast cancer

CXCR4, a chemokine receptor, plays an important role in breast cancer growth, invasion, and metastasis. The transcriptional targets of CXCR4 signaling are not known. Microarray analysis of CXCR4-enriched and CXCR4-low subpopulations of the MDA-MB-231 breast cancer cell line, which has a constitutively active CXCR4 signaling network, revealed differential expression of ∼ 200 genes in the CXCR4-enriched subpopulation. ITF2, upregulated in CXCR4-enriched cells, was investigated further. Expression array datasets of primary breast tumors revealed higher ITF2 expression in estrogen receptor negative tumors, which correlated with reduced progression free and overall survival and suggested its relevance in breast cancer progression. CXCL12, a CXCR4 ligand, increased ITF2 expression in MDA-MB-231 cells. ITF2 is a basic helix-loop-helix transcription factor that controls the epithelial-to-mesenchymal transition and the function of the ID family (inhibitor-of-differentiation) of transcription factors, such as ID2. ID2 promotes differentiation of breast epithelial cells and its reduced expression in breast cancer is associated with an unfavorable prognosis. Both CXCR4 and ITF2 repressed ID2 expression. In xenograft studies, CXCR4-enriched cells formed large tumors and exhibited significantly elevated lung metastasis. Short interfering RNA against ITF2 reduced invasion of the CXCR4-enriched MDA-MB-231 subpopulation, whereas ITF2 overexpression restored the invasive capacity of MDA-MB-231 cells expressing CXCR4shRNA. Furthermore, overexpression of ITF2 in these cells enhanced tumor growth. We propose that ITF2 is one of the CXCR4 targets, which is involved in CXCR4-dependent tumor growth and invasion of breast cancer cells.

Butein downregulates chemokine receptor CXCR4 expression and function through suppression of NF-κB activation in breast and pancreatic tumor cells

The CXC chemokine receptor-4 (CXCR4), a Gi protein-coupled receptor for the ligand CXCL12/stromal cell-derived factor-1α (SDF-1α), is known to be expressed in various tumors. This receptor mediates homing of tumor cells to specific organs that express the ligand CXCL12 for this receptor and plays an important role in tumor growth, invasion, metastasis, and angiogenesis. Thus, a priori, agents that can downregulate CXCR4/CXCL12 signaling cascade have potential against cancer metastasis. In this study, we report the identification of butein (3, 4, 2', 4'-tetrahydroxychalcone) as a novel regulator of CXCR4 expression and function. We found that butein downregulated the expression of CXCR4 in HER2-overexpressing breast cancer cells in a dose- and time-dependent manner. The decrease in CXCR4 expression induced by butein was not cell type-specific as the inhibition also occurred in pancreatic, prostate, multiple myeloma, head and neck, and hepatocellular cancer cell lines. When investigated for the molecular mechanism(s), it was found that the downregulation of CXCR4 was not due to proteolytic degradation but rather to transcriptional regulation as indicated by downregulation of mRNA expression, inhibition of NF-κB activation evident by both DNA binding, and reporter assays, and suppression of chromatin immunoprecipitation activity. Suppression of CXCR4 expression by butein correlated with the inhibition of CXCL12-induced migration and invasion of both breast and pancreatic cancer cells. Overall, our results demonstrate for the first time that butein is a novel inhibitor of CXCR4 expression and thus has a potential in suppressing metastasis of cancer.

Evaluation of a CXCR4 antagonist in a xenograft mouse model of inflammatory breast cancer

CXCL12/CXCR4 signaling, being important in the homing of cancer cells to lungs, bone and other organs, is a promising therapeutic target. Our purpose was to determine whether a peptide-based antagonist of CXCR4 would reduce primary tumor growth and/or metastasis in a preclinical mouse model of inflammatory breast cancer. We improved an existing model of inflammatory breast cancer for this study by luciferase transfection of SUM149 cells and the monitoring of such cells in mice by imaging and the luciferase assay. We implanted 2 x 10(6) SUM49-Luc cells along with matrigel into the left thoracic mammary fat pad of nude mice to produce tumors. Our mouse model exhibited important features of inflammatory breast cancer, namely, aggressive local disease, local metastases and distant metastases. To evaluate the efficacy of a CXCR4 antagonist CTCE-9908, by itself or in combination with paclitaxel, we treated groups of ten mice each with CTCE-9908 (25 mg/kg, injected subcutaneously 5 days/week), control peptide SC-9908, paclitaxel (10 mg/kg, injected subcutaneously twice a week), and CTCE-9908 plus paclitaxel concurrently. We assessed all mice weekly by whole-body luciferase imaging to quantify relative primary tumor burden and distant metastases. At the end of the experiment, we quantified primary tumors by weight and lung metastases by luciferase activity assay on tissue lysates. Paclitaxel, a known chemotherapeutic, inhibited primary tumor growth in our model (P < 0.05). CTCE-9908 did not significantly inhibit primary tumor growth or lung metastases as compared to control groups, without or with paclitaxel (P > 0.05). However, CTCE-9908 as a single therapy inhibited organ-specific metastasis to leg (P < 0.05 by chi-squared test and by two-sample t-test).

Nuclear factor-kappaB activation regulates cyclooxygenase-2 induction in human astrocytes in response to CXCL12: role in neuronal toxicity

Neurodegenerative and neuroinflammatory disorders are commonly associated with local chemokine release. In other way, emerging data indicate that the prostaglandin E2 (PGE(2)), one of the major prostaglandins produced in the brain, play a central role in several pathological diseases. In this study, we investigated the relationship between CXCL12, cyclooxygenase (COX)-2 and PGE(2) in human brain cells. CXCL12 induced COX-2 and secretion of PGE(2) in a dose-dependent manner in human astrocytes. This induction was abolished by treatment with pertussis toxin and AMD3100, confirming the role of CXCR4 signaling. The nuclear factor-kappaB involvement was confirmed by using pyrrolidine dithiocarbamate, and with transient transfection assays. Over-expression of inhibitory proteins of nuclear factor-kappaB abrogated COX-2 induction, and CXCL12 induced p65/relA translocation. Culture supernatants from CXCL12-treated astrocytes reduced viability of neuroblastoma cells, and COX inhibitors abrogated this toxicity. Therefore, the relationship between chemokines and PGs could differentially influence the pathogenic network responsible for neurodegeneration.

Cell aggregation induces phosphorylation of PECAM-1 and Pyk2 and promotes tumor cell anchorage-independent growth

BACKGROUND

Apoptosis caused by inadequate or inappropriate cell-matrix interactions is defined as anoikis. Although transformed cells are known to be anoikis-resistant, the underlying mechanisms have not been well understood. We investigated the mechanisms of anoikis resistance of tumor cells.

RESULTS

We observed that cell aggregation in suspension promoted cell survival and proliferation. We demonstrated a correlation between tumor cell aggregation in suspension and cell growth in soft agar. Analysis of tyrosine kinase-mediated cell survival and growth signaling pathways revealed increased levels of tyrosine-phosphorylation of PECAM-1 and Pyk2 in cell aggregates. We also showed that PECAM-1 and Pyk2 physically interact with each other, and that PECAM-1 carrying a deletion of exons 11-16 could no longer bind to Pyk2. Furthermore, RNA interference-mediated reduction of Pyk2 and PECAM-1 protein levels reduced cell aggregation and inhibited the growth of tumor cells in soft agar.

CONCLUSIONS

The data demonstrated that Pyk2 and PECAM-1 were critical mediators of both anchorage-independent growth and anoikis resistance in tumor cells.

Expression pattern of stromal cell-derived factor-1 chemokine in invasive breast cancer is correlated with estrogen receptor status and patient prognosis

Chemokine receptor CXCR4 is known to be crucially involved in tumor progression, but the role of its ligand, stromal cell-derived factor-1 (SDF-1), remains unclear. The present study was conducted to clarify the clinicopathological and prognostic impact of SDF-1 expression in invasive breast cancers. Expression of SDF-1 mRNA and protein was examined in five breast cancer cell lines with or without estradiol treatment. In 52 surgically resected breast cancers, the level of SDF-1 mRNA in frozen samples and the pattern of SDF-1 protein immunoreactivity in formalin-fixed paraffin-embedded tissue sections were compared. In another cohort of 223 breast cancers, the correlation between SDF-1 immunoreactivity and clinicopathological parameters was examined using a tissue microarray. Estradiol treatment markedly increased the expression of SDF-1 mRNA and protein in the estrogen receptor (ER)-positive cell lines, MCF-7 and T47D. Among the 52 resected breast cancers, those with a cytoplasmic-dominant pattern of SDF-1 expression showed higher SDF-1 mRNA levels (median 27.4) than those with a membrane-dominant or negative pattern (median 13.6, P = 0.0017). Accordingly, the cytoplasmic-dominant pattern was defined as "high SDF-1 expression," and other patterns were defined as "low SDF-1 expression." Among the cohort of 223 tumors, "high SDF-1 expression" was detected in 158 (70.9%) and was significantly correlated with ER positivity (P < 0.0001), HER2 negativity (P = 0.021), and lower grade (P < 0.0001). Univariate analysis demonstrated that "high SDF-1 expression" was a significant indicator of better clinical outcome in both the entire patient cohort (P = 0.017) and the 133 patients with ER-positive tumors (P = 0.036), but not in the 90 patients with ER-negative tumors. Multivariate analysis showed that SDF-1 status was an independent factor related to overall survival in patients with ER-positive tumors (P = 0.046). SDF-1 status is a significant prognostic factor and may be clinically useful for assigning adjuvant therapy to patients with ER-positive invasive breast cancers.

Site-specific metastasis formation: chemokines as regulators of tumor cell adhesion, motility and invasion

The metastatic spread of tumors is a well-coordinated process in which different types of cancers tend to form metastases in defined organs. The formation of site-specific metastases requires full compatibility between the intrinsic properties of the tumor cells and the tumor microenvironment. It was recently found that chemokines which are expressed in specific loci promote the adhesion, migration and invasion of tumor cells that express the corresponding receptor(s). Of the different members of the family, the CXCL12 chemokine and its cognate CXCR4 receptor are the prototypes of this process, although other members of the family (e.g. CCR7 and CCR10) also play a role in determination of the metastatic spread. This commentary addresses the fundamental roles of chemokines and their receptors in site-specific metastasis, with emphasis on CXCL12-CXCR4. The article also describes some of the efforts that were performed thus far in order to identify the intracellular components involved in this process. The focus is put on the roles played by proteins that regulate adhesion and migration of tumor cells in response to CXCL12, including mainly focal adhesion kinase (FAK), Pyk2/RAFTK and members of the Rho family of GTPases (RhoA, Rac, Cdc42). This is followed by discussion of open questions that need to be addressed in future research, and of the potential therapeutic implications of the findings that are available to date in this field.

CXCR4 regulates the early extravasation of metastatic tumor cells in vivo

Recent studies have demonstrated that the chemokine receptor CXCR4 plays a crucial role in organ-specific metastasis formation. Although a variety of studies showed the expression of chemokine receptors, in particular, CXCR4, by gastrointestinal tumors, the precise mechanisms of chemokine receptor-mediated homing of cancer cells to specific sites of metastasis remained elusive. Here, we used liver metastatic human HEP-G2 hepatoma and HT-29LMM colon cancer cells expressing functional CXCR4 to dissect the metastatic cascade by intravital fluorescence microscopy. Immunohistochemistry revealed that the CXCR4 ligand CXCL12 is expressed by endothelial cells and likely Kupffer cells lining the liver sinusoids. Tumor cell adhesion and extravasation in vivo was quantitatively analyzed using intravital fluorescence microscopy. Treatment of cells with an anti-CXCR4 antibody did not affect cell adhesion but significantly impaired tumor cell extravasation (HEP-G2; isotype control: 22.3% +/- 4.3% vs anti-CXCR4: 6.0% +/- 5.0%, P < .001). In addition, pretreatment of tumor cells with the ligand CXCL12 enhanced the activation of the small GTPases Rho, Rac, and cdc42 as well as tumor cell extravasation without affecting tumor cell adhesion within liver sinusoids. Taken together, the findings of the present study provide first in vivo insights into the early events of chemokine ligand/receptor-mediated liver metastasis formation of tumor cells and define tumor cell extravasation rather than tumor cell arrest as the rate-limiting event.

CD26 expression on T cell lines increases SDF-1-alpha-mediated invasion

BACKGROUND

CD26 is a multifunctional membrane-bound glycoprotein that regulates tumour growth in addition to its other activities. Because disease aggressiveness is correlated with CD26 expression in several T-cell malignancies, we decided to investigate the invasiveness of cells expressing different levels of CD26.

METHODS

To assess CD26 involvement in cell invasion, we performed in vitro invasion assays with human T cell lines expressing different levels of CD26. These included the parental CD26-positive T-lymphoblast cell line HSB-2 and clones infected with a retrovirus expressing siRNA vectors that either targeted CD26 or encoded a missense siRNA, and the parental CD26-negative T-leukaemia cell line Jurkat and clones expressing CD26. CD26 expression in these cell lines was evaluated by flow cytometry and western immunoblotting. CXCR4 expression, phosphorylation of signalling kinases, and MMP-9 secretion were also evaluated by western immunoblotting, whereas MMP-9 activity and the effect of kinase and CD45 inhibitors on activity were measured by zymography of conditioned media.

RESULTS

The presence of CD26 enhanced stromal-cell-derived factor-1-alpha (SDF-1-alpha)-mediated invasion of T cell lines. This process was regulated in part by the PI-3K and MEK1 pathways, as indicated by increased phosphorylation of p44/42 MAP kinase and Akt in the presence of SDF-1-alpha and the effect of their respective inhibitors on MMP-9 secretion and in vitro invasion. In addition, CD26-associated enhancement of SDF-1-alpha-induced invasion was decreased when CD45 was inhibited.

CONCLUSIONS

Our results indicate that the expression of CD26 in T cell lines leads to increased SDF-1-alpha-mediated invasion in an in vitro system and that this is controlled in part by the PI-3K and MEK1 pathways. The data also suggest that CD26 enhancement of invasion may be mediated by CD45, however, more studies are required to confirm this involvement.

Prognostic significance of CXCL12 expression in patients with colorectal carcinoma

The present study investigated the protein expression level of CXCL12 in colorectal cancer and aimed to elucidate its association with prognosis. CXCL12 positivity in 50% or more of tumor cells was defined as high expression and that in less than 50% of the tumor cells as low expression. CXCL12+ tumor budding at the invasive front was divided into 2 grades: high with 10 or more budding foci per x200 field of view and low grade with fewer than 10 budding foci. Patients with high expression (72.7%) and high grade CXCL12+ tumor budding (43.0%) had significantly shorter survival than patients with low expression (P = .014) and low grade (P = .003), respectively. Patients with a combination of high expression and high grade had the worst outcome (P < .001). Our study demonstrated that CXCL12 expression in colorectal cancer cells and at sites of budding were significant prognostic factors. Furthermore, together with lymph node metastasis, a combination of both expression patterns was a more powerful independent prognostic factor.

Shp2 acts downstream of SDF-1alpha/CXCR4 in guiding granule cell migration during cerebellar development

Shp2 is a non-receptor protein tyrosine phosphatase containing two Src homology 2 (SH2) domains that is implicated in intracellular signaling events controlling cell proliferation, differentiation and migration. To examine the role of Shp2 in brain development, we created mice with Shp2 selectively deleted in neural stem/progenitor cells. Homozygous mutant mice exhibited early postnatal lethality with defects in neural stem cell self-renewal and neuronal/glial cell fate specification. Here we report a critical role of Shp2 in guiding neuronal cell migration in the cerebellum. In homozygous mutants, we observed reduced and less foliated cerebellum, ectopic presence of external granule cells and mispositioned Purkinje cells, a phenotype very similar to that of mutant mice lacking either SDF-1alpha or CXCR4. Consistently, Shp2-deficient granule cells failed to migrate toward SDF-1alpha in an in vitro cell migration assay, and SDF-1alpha treatment triggered a robust induction of tyrosyl phosphorylation on Shp2. Together, these results suggest that although Shp2 is involved in multiple signaling events during brain development, a prominent role of the phosphatase is to mediate SDF-1alpha/CXCR4 signal in guiding cerebellar granule cell migration.

Neuropilin-2 expression in breast cancer: correlation with lymph node metastasis, poor prognosis, and regulation of CXCR4 expression

BACKGROUND

Neuropilin-2 (Nrp2) is a receptor for vascular endothelial growth factor-C (VEGF-C), which is a well-known lymphangiogenic factor and plays an important role in lymph node metastasis of various human cancers, including breast cancer. Recently, Nrp2 was shown to play a role in cancer by promoting tumor cell metastasis. CXC chemokine receptor 4 (CXCR4) also promotes tumor metastasis. In the previous studies, we demonstrated that VEGF-C and cytoplasmic CXCR4 expressions were correlated with poorer patient prognosis (BMC Cancer 2008,8:340; Breast Cancer Res Treat 2005, 91:125-132).

METHODS

The relationship between Nrp2 expression and lymph node metastasis, VEGF-C expression, CXCR4 expression, and other established clinicopathological variables (these data were cited in our previous papers), including prognosis, was analyzed in human breast cancer. Effects of neutralizing anti-Nrp2 antibody on CXCR4 expression and chemotaxis were assessed in MDA-MB-231 breast cancer cells.

RESULTS

Nrp2 expression was observed in 53.1% (60 of 113) of the invasive breast carcinomas. Nrp2 expression was significantly correlated with lymph node metastasis, VEGF-C expression, and cytoplasmic CXCR4 expression. Survival curves determined by the Kaplan-Meier method showed that Nrp2 expression was associated with reduced overall survival. In multivariate analysis, Nrp2 expression emerged as a significant independent predictor for overall survival. Neutralizing anti-Nrp2 antibody blocks cytoplasmic CXCR4 expression and CXCR4-induced migration in MDA-MB-231 cells.

CONCLUSION

Nrp2 expression was correlated with lymph node metastasis, VEGF-C expression, and cytoplasmic CXCR4 expression. Nrp2 expression may serve as a significant prognostic factor for long-term survival in breast cancer. Our data also showed a role for Nrp2 in regulating cytoplasmic CXCR4 expression in vitro.

Cyclic stretch upregulates SDF-1alpha/CXCR4 axis in human saphenous vein smooth muscle cells

Cyclic stretch (CS) mediates different cellular functions in vascular smooth muscle cells and involves in neointimal hyperplasia and subsequent atherosclerosis of vein grafts. Here, we investigated whether CS can modulate stromal cell-derived factor-1alpha (SDF-1alpha)/CXCR4 axis in human saphenous vein smooth muscle cells. We found CS induced the upregulation of SDF-1alpha and CXCR4 in human saphenous vein smooth muscle cells in vitro, which was dependent on PI3K/Akt/mTOR pathway. Furthermore, CS augmented human saphenous vein smooth muscle migration and focal adhesion kinase (FAK) activation by PI3K/Akt/mTOR pathway. Interestingly, the upregulation of SDF-1alpha/CXCR4 axis was instrumental in CS-induced saphenous vein smooth muscle cell migration and FAK activation, as showed by AMD3100, an inhibitor of SDF-1alpha/CXCR4 axis, partially but significantly blocked the CS-induced cellular effects. Thus, those data suggested SDF-1alpha/CXCR4 axis involves in CS-mediated cellular functions in human saphenous vein smooth muscle cells.

Laminin-421 produced by lymphatic endothelial cells induces chemotaxis for human melanoma cells

Melanoma has a high tendency to metastasize to lymph nodes, which is one of the clinicopathological factors to indicate poor prognosis. Recent investigations have shown the importance of lymphangiogenesis in lymph node metastasis in a variety of human tumors including melanoma. However, molecular mechanism of lymphatic metastasis is still poorly defined. We examined influence of interactions between normal lymphatic endothelial cells (LECs) and melanoma cells on cell migration. Medium conditioned with LEC (LEC-CM) contained chemotactic and chemokinetic activities for human melanoma cell lines. The chemotactic activity was fractionated in more than 100 kDa, and inactivated by heat-treatment. The chemotactic activity of LEC-CM was abolished by immunodepletion with anti-laminin-1 antibody. And immunoprecipitation and Western blot analyses revealed that LEC-CM contained laminin-421. When melanoma C8161 cells were treated with function-blocking antibodies to integrin alpha3 or alpha6, their chemotactic responses to LEC-CM were markedly reduced. Furthermore, the knock-down of tetraspanin CD151 weakened the chemotactic responses of C8161 and MeWo cells to LEC-CM. These data suggest that laminin-421 secreted by LEC possibly facilitates lymphatic metastasis through the induction of chemotaxis of melanoma cells.

Chemokine receptors in advanced breast cancer: differential expression in metastatic disease sites with diagnostic and therapeutic implications

BACKGROUND

We investigated the expression of CXCR4, CCR7, estrogen receptor (ER), progesterone receptor (PR) and HER2-neu in human metastatic breast cancers to determine whether these biological biomarkers were preferentially expressed in any organ-specific metastases.

MATERIALS AND METHODS

CXCR4, CCR7, ER, PR and HER2-neu expression levels were evaluated by immunohistochemical staining using paraffin-embedded tissue sections of metastatic breast cancers (n = 41) obtained by either diagnostic biopsy or surgical resection.

RESULTS

The metastatic sites included the following: bone (n = 15), brain (n = 14), lung (n = 6), liver (n = 2), and omental metastases (n = 2). CXCR4 was expressed in 41% of cases, CCR7 expression was demonstrated in 10%, and HER2-neu overexpression was present in 27%. CXCR4 was more likely to be expressed in bone metastases than visceral metastases (67% versus 26%, P = 0.020). Visceral sites demonstrated a lower rate of CXCR4 positivity (33% and 23%, respectively, for lung and brain metastases). Similarly, CCR7 was more likely to be found in bone metastases than visceral sites (27% versus 0%, P = 0.037).

CONCLUSIONS

These results indicate that CXCR4 can contribute to the homing of breast cancer cells to the bone. This finding might have important clinical implications since patients with metastatic bone disease may achieve the highest benefit from a CXCR4-targeted therapy.

Human mesenchymal stem cells (hMSCs) target osteosarcoma and promote its growth and pulmonary metastasis

In an effort to study the interaction between MSCs and osteosarcoma, we established an animal model of primary osteosarcoma in nude mice using Saos-2 cells. hMSCs, labeled with adv-GFP, were injected through the caudal vein. We observed that exogenous hMSCs targeted the osteosarcoma site and promoted its growth and pulmonary metastasis in vivo. To elucidate the underlying mechanisms, we employed transwell, neutralization antibody and MTT assays in vitro. hMSCs migrated toward the conditioned medium from Saos-2 cells, and SDF-1 was involved in this migration. Likewise, Saos-2 cells migrated toward the conditioned medium from hMSCs and CCL5 played an important role in this migration. Furthermore, proliferation of Saos-2 cells was enhanced by the conditioned medium from hMSCs and CCL5 was at least partly responsible for this enhancement.

The CXCR4/SDF-1 chemokine receptor axis: a new target therapeutic for non-small cell lung cancer

Chemokines are proinflammatory chemoattractant cytokines that regulate cell trafficking and adhesion. The CXCR4 chemokine receptor and its ligand, stromal cell derived factor (SDF-1), constitute a chemokine/receptor axis that has attracted great interest because of an increasing understanding of its role in cancer, including lung cancer. The CXCR4/SDF-1 complex activates several pathways that mediate chemotaxis, migration and secretion of angiopoietic factors. Neutralization of SDF-1 by anti-SDF-1 or anti-CXCR4 monoclonal antibody in preclinical in vivo studies results in a significant decrease of non-small cell lung cancer metastases. Since anti-SDF-1/CXCR4 strategies have already been developed for use in combating human immunodeficiency virus infections, it is likely that these approaches will be used in clinical trials in non-small cell lung cancer in the very near future.

Clinical and biological significance of CXCL12 and CXCR4 expression in adult testes and germ cell tumours of adults and adolescents

Interaction between the chemokine CXCL12 (SDF1) and the G-protein coupled receptor CXCR4 is responsible for the maintenance of adult stem cell niches and is known to play an important role in utero in the migration of primordial germ cells. We demonstrate expression of CXCL12 by Sertoli cells and confirm CXCR4 expression by the germ cell population of the adult human testes. CXCR4 is also known to mediate organ-specific patterns of metastases in a range of common cancers. We identify consistent expression of CXCR4 mRNA and protein in testicular germ cell tumours (TGCT) that accounts for their patterns of relapse in sites of known CXCL12 expression. Extragonadal primary germ cell tumours express CXCR4 and their sites of occurrence are coincident with areas of known CXCL12 expression in utero. We show that CXCL12 stimulates the invasive migration of a TGCT cell line in vitro in a CXCR4-dependent fashion and activates ERK. Furthermore, we demonstrate that expression of CXCL12 in stage I non-seminomas is significantly associated with organ-confined disease post-orchidectomy and reduced risk of relapse (p = 0.003). This may be through the loss of CXCL12 gradients that might otherwise attract cells away from the primary tumour. We propose CXCL12 expression as a potential predictor of subsequent relapse that could lead to avoiding unnecessary treatment and associated late toxicities. Our observations support a role for CXCL12/CXCR4 in the adult germ cell population and demonstrate pathological function in germ cell tumour development and metastasis that may have clinical utility.

Zerumbone down-regulates chemokine receptor CXCR4 expression leading to inhibition of CXCL12-induced invasion of breast and pancreatic tumor cells

CXC chemokine receptor 4 (CXCR4), initially linked with leukocyte trafficking, is now known to be expressed in various tumors including breast, ovary, prostate, gastrointestinal, head and neck, bladder, brain, and melanoma. This receptor mediates homing of tumor cells to specific organs that express the ligand CXCL12 for this receptor. Thus, agents that can down-regulate CXCR4 expression have potential against cancer metastasis. In this study, we report the identification of zerumbone, a component of subtropical ginger (Zingiber zerumbet), as a regulator of CXCR4 expression. This sesquiterpene down-regulated the expression of CXCR4 on HER2-overexpressing breast cancer cells in a dose- and time-dependent manner. The decrease in CXCR4 by zerumbone was found to be not cell type specific as its expression was abrogated in leukemic, skin, kidney, lung, and pancreatic cancer cell lines. The down-regulation of CXCR4 was not due to proteolytic degradation but rather to transcriptional regulation, as indicated by down-regulation of mRNA expression, inhibition of nuclear factor-kappaB activity, and suppression of chromatin immunoprecipitation activity. Suppression of CXCR4 expression by zerumbone correlated with the inhibition of CXCL12-induced invasion of both breast and pancreatic cancer cells. An analogue of zerumbone, alpha-humulene, which lacks the carbonyl group, was found to be inactive in inducing CXCR4 down-regulation. Overall, our results show that zerumbone is a novel inhibitor of CXCR4 expression and thus has a potential in the suppression of cancer metastasis.

Suppression of neuroblastoma growth by dipeptidyl peptidase IV: relevance of chemokine regulation and caspase activation

Imbalanced protease expression and activities may contribute to the development of cancers, including neuroblastoma (NB). NB is a fatal childhood cancer of the sympathetic nervous system that frequently overexpresses mitogenic peptides, chemokines and their receptors. Dipeptidyl peptidase IV (DPPIV), a cell surface serine protease, inactivates or degrades some of these bioactive peptides and chemokines, thereby regulating cell proliferation and survival. Our studies show that DPPIV is expressed in normal neural crest-derived structures, including superior cervical and dorsal root ganglion cells, sciatic nerve, and in adrenal glands, but its expression is greatly decreased or lost in cells derived from NB, their malignant counterpart. Restoration of DPPIV expression in NB cells led to their differentiation in association with increased expression of the neural marker MAP2 and decreased expression of chemokines, including stromal-derived factor 1 (SDF1) and its receptor CXCR4. Furthermore, DPPIV promoted apoptosis, and inhibited SDF1-mediated in vitro cell migration and angiogenic potential. These changes were accompanied by caspase activation and decreased levels of phospho-Akt and MMP9 activity, which are downstream effectors of SDF1-CXCR4 signaling. Importantly, DPPIV suppressed the tumorigenic potential of NB cells in a xenotransplantation mouse model. These data support a potential role for DPPIV in inhibiting NB growth and progression.