Characterization and visualization of [125I] stromal cell-derived factor-1alpha binding to CXCR4 receptors in rat brain and human neuroblastoma cells

The tumour microenvironment of pituitary neuroendocrine tumours

The tumour microenvironment (TME) includes a variety of non-neoplastic cells and non-cellular elements such as cytokines, growth factors and enzymes surrounding tumour cells. The TME emerged as a key modulator of tumour initiation, progression and invasion, with extensive data available in many cancers, but little is known in pituitary tumours. However, the understanding of the TME of pituitary tumours has advanced thanks to active research in this field over the last decade. Different immune and stromal cell subpopulations, and several cytokines, growth factors and matrix remodelling enzymes, have been characterised in pituitary tumours. Studying the TME in pituitary tumours may lead to a better understanding of tumourigenic mechanisms, identification of biomarkers useful to predict aggressive disease, and development of novel therapies. This review summarises the current knowledge on the different TME cellular/non-cellular elements in pituitary tumours and provides an overview of their role in tumourigenesis, biological behaviour and clinical outcomes.

Structural and Biological Characterizations of Novel High-Affinity Fluorescent Probes with Overlapped and Distinctive Binding Regions on CXCR4

CXC-type chemokine receptor 4 (CXCR4) is well known as a co-receptor for cellular entry and infection of human immunodeficiency virus type 1 (HIV-1). As an important member of the G protein-coupled receptor (GPCR) family, CXCR4 also mediates a variety of cellular processes and functions, such as cell chemotaxis, proliferation, and calcium signal transductions. Identification and characterization of molecular ligands or probes of CXCR4 have been an intensive area of investigations as such ligands or probes are of significant clinical values for the studies and treatments of HIV-1 infection and other human diseases mediated by the receptor. The crystal structures of CXCR4 in complex with different ligands have revealed two distinctive binding regions or subpockets. Thus, understanding the interactions of diverse ligands with these distinctive CXCR4 binding regions has become vital for elucidating the relationship between binding modes and biological mechanisms of ligand actions. Peptidic CVX15 is the only ligand that has been validated to bind one of these distinctive binding regions (or so called the major subpocket) of CXCR4. Therefore, in this study, we developed an efficient probe system including two high-affinity peptidic fluorescent probes, designated as FITC-CVX15 and FITC-DV1, with the aim of targeting distinctive CXCR4 subpockets. We conducted rational design and chemical characterization of the two CXCR4-specific probes and examined their application in biological experiments including competitive binding assays, flow cytometry analysis, and confocal imaging. Especially these two probes were applied in parallel CXCR4 competitive binding assays to detect and analyze potential binding modes of diverse CXCR4 ligands, together with molecular docking and simulations. Our results have indicated that these peptidic fluorescent probe systems provide novel ligand detecting tools, as well as present a new approach for analyzing distinctive binding modes of diverse CXCR4 ligands.

Biomedical applications of radioiodinated peptides

The overexpression of peptide receptors in certain tumors as compared to endogeneous expression levels represents the molecular basis for the design of peptide-based tools for targeted nuclear imaging and therapy. Receptor targeting with radiolabelled peptides became a very important imaging and/or therapeutic approach in nuclear medicine and oncology. A great variety of peptides has been radiolabelled with clinical relevant radionuclides, such as radiometals and radiohalogens. However, to the best of our knowledge concise and updated reviews providing information about the biomedical application of radioiodinated peptides are still missing. This review outlines the synthetic efforts in the preparation of radioiodinated peptides highlighting the importance of radioiodine in nuclear medicine, giving an overview of the most relevant radioiodination strategies that have been employed and describes relevant examples of their use in the biomedical field.

The Role of Chemokines in the Pathophysiology of Major Depressive Disorder

Major depressive disorder (MDD) is a debilitating condition, whose high prevalence and multisymptomatic nature set its standing as a leading contributor to global disability. To better understand this psychiatric disease, various pathophysiological mechanisms have been proposed, including changes in monoaminergic neurotransmission, imbalance of excitatory and inhibitory signaling in the brain, hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, and abnormalities in normal neurogenesis. While previous findings led to a deeper understanding of the disease, the pathogenesis of MDD has not yet been elucidated. Accumulating evidence has confirmed the association between chronic inflammation and MDD, which is manifested by increased levels of the C-reactive protein, as well as pro-inflammatory cytokines, such as Interleukin 1 beta, Interleukin 6, and the Tumor necrosis factor alpha. Furthermore, recent findings have implicated a related family of cytokines with chemotactic properties, known collectively as chemokines, in many neuroimmune processes relevant to psychiatric disorders. Chemokines are small (8-12 kDa) chemotactic cytokines, which are known to play roles in direct chemotaxis induction, leukocyte and macrophage migration, and inflammatory response propagation. The inflammatory chemokines possess the ability to induce migration of immune cells to the infection site, whereas their homeostatic chemokine counterparts are responsible for recruiting cells for their repair and maintenance. To further support the role of chemokines as central elements to healthy bodily function, recent studies suggest that these proteins demonstrate novel, brain-specific mechanisms including the modulation of neuroendocrine functions, chemotaxis, cell adhesion, and neuroinflammation. Elevated levels of chemokines in patient-derived serum have been detected in individuals diagnosed with major depressive disorder, bipolar disorder, and schizophrenia. Furthermore, despite the considerable heterogeneity of experimental samples and methodologies, existing biomarker studies have clearly demonstrated the important role of chemokines in the pathophysiology of psychiatric disorders. The purpose of this review is to summarize the data from contemporary experimental and clinical studies, and to evaluate available evidence for the role of chemokines in the central nervous system (CNS) under physiological and pathophysiological conditions. In light of recent results, chemokines could be considered as possible peripheral markers of psychiatric disorders, and/or targets for treating depressive disorders.

Modulation of the Tumor Microenvironment by CXCR4 Antagonist-Armed Viral Oncotherapy Enhances the Antitumor Efficacy of Dendritic Cell Vaccines against Neuroblastoma in Syngeneic Mice

The induction of antitumor immune responses in tumor-bearing hosts depends on efficient uptake and processing of native or modified tumors/self-antigens by dendritic cells (DCs) to activate immune effector cells, as well as the extent of the immunosuppressive network in the tumor microenvironment (TME). Because the C-X-C motif chemokine receptor 4 (CXCR4) for the C-X-C motif chemokine 12 (CXCL12) is involved in signaling interactions between tumor cells and their TME, we used oncolytic virotherapy with a CXCR4 antagonist to investigate whether targeting of the CXCL12/CXCR4 signaling axis in murine neuroblastoma cells (NXS2)-bearing syngeneic mice affects the efficacy of bone marrow (BM)-derived DCs loaded with autologous tumor cells treated with doxorubicin for induction of immunogenic cell death. Here, we show that CXCR4 antagonist expression from an oncolytic vaccinia virus delivered intravenously to mice with neuroblastoma tumors augmented efficacy of the DC vaccines compared to treatments mediated by a soluble CXCR4 antagonist or oncolysis alone. This study is the first demonstration that modulating the tumor microenvironment by an armed oncolytic virus could have a significant impact on the efficacy of DC vaccines, leading to the generation of effective protection against neuroblastoma challenge.

Development of a novel 99m Tc-labeled small molecular antagonist for CXCR4 positive tumor imaging

The chemokine receptor 4 (CXCR4) has been an attractive molecular target for tumor imaging, because it is overexpressed in many tumor types and involved in tumor progression and metastasis. The purpose of this study is to examine the CXCR4 targeting properties of ^99m Tc-labeled AMD3465, a small molecule antagonist of CXCR4. ^99m Tc-AMD3465 was prepared in high yield (>95%) and stable in mice serum at least for 4 hours. In vitro cell binding experiments were performed with Chinese hamster ovary (CHO), MCF-7 (breast cancer), and CHO-CXCR4 (CHO stably transfected to express CXCR4) cell lines. Small animal single photon emission computed tomography/computed tomography imaging studies in nude mice bearing MCF-7 and CHO xenografts showed that the uptakes of the radiotracer in MCF-7 tumors were significantly higher than those in the CXCR4-negative CHO tumors (P < 0.05), and the MCF-7 tumors uptake could be blocked with an excess of unlabeled AMD3465 (P < 0.05). These results suggested that ^99m Tc-AMD3465 could be a potential single photon emission computed tomography radiotracer for CXCR4 imaging.

AMD3100: A Versatile Platform for CXCR4 Targeting (68)Ga-Based Radiopharmaceuticals

CXCR4 is a G protein-coupled receptor (GPCR), which is overexpressed in numerous diseases, particularly in multiple cancers. Therefore, this receptor represents a valuable target for imaging and therapeutic purposes. Among the different approaches, which were developed for CXCR4 imaging, a CXCR4 antagonist biscyclam system (AMD3100, also called Mozobil), currently used in the clinic for the mobilization of hematopoietic stem cells, was radiolabeled with different radiometals such as (62)Zn, (64)Cu, (67)Ga, or (99m)Tc. However, cyclam is not an ideal chelator for most of these radiometals, and could lead to the release of the radionuclide in vivo. In the current study, a new family of CXCR4 imaging agents is presented, in which AMD3100 is used as a carrier for specific delivery of an imaging reporter, i.e., a (68)Ga complex for PET imaging. AMD3100 was functionalized on the phenyl moiety with different linkers, either ethylenediamine or diamino-polyethylene glycol 3 (PEG3). The resulting AMD3100 analogues were further coupled with two different chelators, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) or 1,4,7-triazacyclononane-1-glutaric acid-4,7-acetic acid (NODAGA). Five potential CXCR4 targeting agents were obtained. The derived AMD3100-based ligands were labeled with (68)Ga, highlighting the influence of the spacer nature on the (68)Ga-labeling yield. The lipophilic character of the different systems was also investigated, as well as their affinity for the CXCR4 receptor. The most promising compound was further evaluated in vivo in H69 tumor xenografts by biodistribution and PET imaging studies, validating the proof of principle of our concept.

Emerging Targets in Pituitary Adenomas: Role of the CXCL12/CXCR4-R7 System

Chemokines are chemotactic regulators of immune surveillance in physiological and pathological conditions such as inflammation, infection, and cancer. Several chemokines and cognate receptors are constitutively expressed in the central nervous system, not only in glial and endothelial cells but also in neurons, controlling neurogenesis, neurite outgrowth, and axonal guidance during development. In particular, the chemokine CXCL12 and its receptors, CXCR4 and CXCR7, form a functional network that controls plasticity in different brain areas, influencing neurotransmission, neuromodulation, and cell migration, and the dysregulation of this chemokinergic axis is involved in several neurodegenerative, neuroinflammatory, and malignant diseases. CXCR4 primarily mediates the transduction of proliferative signals, while CXCR7 seems to be mainly responsible for scavenging CXCL12. Importantly, the multiple intracellular signalling generated by CXCL12 interaction with its receptors influences hypothalamic modulation of neuroendocrine functions, although a direct modulation of pituitary functioning via autocrine/paracrine mechanisms was also reported. Both CXCL12 and CXCR4 are constitutively overexpressed in pituitary adenomas and their signalling induces cell survival and proliferation, as well as hormonal hypersecretion. In this review we focus on the physiological and pathological functions of immune-related cyto- and chemokines, mainly focusing on the CXCL12/CXCR4-7 axis, and their role in pituitary tumorigenesis. Accordingly, we discuss the potential targeting of CXCR4 as novel pharmacological approach for pituitary adenomas.

Current status of chemokines in the adult CNS

Chemokines - chemotactic cytokines - are small secreted proteins that attract and activate immune and non-immune cells in vitro and in vivo. It has been suggested that chemokines and their receptors play a role in the central nervous system (CNS), in addition to their well established role in the immune system. We focus here on three chemokines-CXCL12 (C-X-C motif ligand 12), CCL2 (C-C motif ligand 2), and CX3CL1 (C-X-3C motif ligand 1) - and their principal receptors - CXCR4 (C-X-C motif receptor 4), CCR2 (C-C motif receptor 2) and CX3CR1 (C-X-3C motif receptor 1), respectively. We first introduce the classification of chemokines and their G-protein coupled receptors and the main signaling pathways triggered by receptor activation. We then discuss the cellular distribution of CXCL12/CXCR4, CCL2/CCR2 and CX3CL1/CX3CR1 in adult brain and the neurotransmission and neuromodulation effects controlled by these chemokines in the adult CNS. Changes in the expression of CXCL12, CCL2 and CX3CL1 and their respective receptors are also increasingly being implicated in the pathogenesis of CNS disorders, such as Alzheimer's disease, Parkinson's disease, HIV-associated encephalopathy, stroke and multiple sclerosis, and are therefore plausible targets for future pharmacological intervention. The final section thus discusses the role of these chemokines in these pathophysiological states. In conclusion, the role of these chemokines in cellular communication may make it possible: (i) to identify new pathways of neuron-neuron, glia-glia or neuron-glia communications relevant to both normal brain function and neuroinflammatory and neurodegenerative diseases; (ii) to develop new therapeutic approaches for currently untreatable brain diseases.

Imaging agents for the chemokine receptor 4 (CXCR4)

The interaction between the chemokine receptor 4 (CXCR4) and stromal cell-derived factor-1 (SDF-1, also known as CXCL12) is a natural regulatory process in the human body. However, CXCR4 over-expression is also found in diseases such as cancer, where it plays a role in, among others, the metastatic spread. For this reason it is an interesting biomarker for the field of diagnostic oncology, and therefore, it is gaining increasing interest for applications in molecular imaging. Especially "small-molecule" imaging agents based on T140, FC131 and AMD3100 have been extensively studied. SDF-1, antibodies, pepducins and bioluminescence have also been used to visualize CXCR4. In this critical review reported CXCR4 targeting imaging agents are described based on their affinity, specificity and biodistribution. The level wherein CXCR4 is up-regulated in cancer patients and its relation to the different cell lines and animal models used to evaluate the efficacy of the imaging agents is also discussed (221 references).

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.

The cyclic pentapeptide d-Arg3FC131, a CXCR4 antagonist, induces apoptosis of somatotrope tumor and inhibits tumor growth in nude mice

The interaction between the chemokine stromal cell-derived factor 1 and its receptor CXCR4 plays an important role in GH production and cell proliferation in normal and tumorous pituitary somatotrope cells. Therefore, the chemokine receptor CXCR4 could be an attractive target for antitumor drugs in patients with acromegaly. A synthetic antagonist of CXCR4, cyclic pentapeptide d-Arg3FC131 (c[Gly1-d-Tyr2-d-Arg3-Arg4-Nal5]) significantly inhibited GH production and proliferation of GH3 somatotrope tumor cells in vitro. It also induced apoptosis of GH3 cells through activation of the caspase-3 pathway. Systemic administration of d-Arg3FC131 inhibited the growth of GH3 cell xenografts in immunodeficient nude mice by inducing apoptosis and suppressing the proliferation of tumor cells. These results indicate that d-Arg3FC131 might have potential for the treatment of pituitary tumors producing excess GH in patients with acromegaly.

The CXCR4 antagonist AMD3100 suppresses hypoxia-mediated growth hormone production in GH3 rat pituitary adenoma cells

Pituitary adenomas produce the chemokine stromal cell-derived factor (SDF-1α/CXCL12) and its receptor, CXCR4. A recent study indicated that CXCL12 and CXCR4 are concomitantly up-regulated in hypoxia. The objective of this study was to analyze the molecular mechanism of hypoxia-mediated CXCR4 up-regulation and assess the effect of pharmacological inhibition of CXCR4 by the receptor blocker, AMD3100, on pituitary function. CXCR4 expression in pituitary adenoma tissues was determined by a tissue microarray analysis of 62 pituitary adenoma samples. CXCR4 expression was significantly elevated and positively correlated with Knosp grade in pituitary adenomas (P < 0.005), and was higher in macroadenoma and growth hormone (GH)-producing adenomas. Pre-operative serum GH levels were significantly correlated with CXCR4 levels in the microarray (P < 0.0001). The relative expression of genes/gene categories that were modulated by up-regulated CXCL12/CXCR4 signaling was determined by a comparative transcriptome analysis of wild-type and CXCR4-knockdown cells in normoxia and hypoxia using the rat GH-producing and prolactin-producing pituitary adenoma cell line, GH3. Real-time reverse transcriptase-polymerase chain reaction analysis (RT-PCR) showed that CXCR4 mRNA expression in GH3 cells was increased by hypoxia (1% oxygen), and a cDNA microarray analysis revealed that inhibin β-C expression was diminished. siRNA-mediated CXCR4 knockdown blocked the hypoxia-induced decrease in inhibin β-C mRNA expression, as did inhibition of CXCR4 activity with AMD3100. An ELISA study demonstrated that GH secretion by wild-type GH3 cells was moderately enhanced by hypoxia and further potentiated by exposure to recombinant SDF-1α/CXCL12 protein. Conversely, hypoxia-induced GH secretion was reduced in CXCR4-silenced cells and in cells treated with the CXCR4 antagonist, AMD3100, notwithstanding the presence of SDF-1α/CXCL12 protein. These latter observations reflect the failure of hypoxia to suppress expression of inhibin β-C in cells deficient in CXCR4 or in which CXCR4 signaling was blocked. Together, these results indicate that the SDF-1α/CXCL12-CXCR4 signaling pathway interfaces with the classical endocrine pathway to up-regulate GH production via suppression of inhibin β-C. Because it blocks CXCR4 and prevents hypoxia-induced down-regulation of inhibin β-C expression, AMD3100 has promise as a molecular-targeting agent in the treatment of GH-producing adenomas.

Absence of activating mutations of CXCR4 in pituitary tumours

OBJECTIVE

Mutations of the gsp oncogene are responsible for 30-40% of GH-producing pituitary adenomas and 10% of nonfunctioning pituitary adenomas (NFPAs). However, the pathogenetic mechanism of the remaining pituitary tumours still remains to be identified. Recently, the interaction between the chemokine stromal cell-derived factor 1 and its receptor CXCR4 was found to play an important role in GH production and cell proliferation in various pituitary adenoma cell lines. As CXCR4 is a Gi-coupled chemokine receptor, its constitutive activating mutations may be involved in pituitary tumour formation by cyclic adenosine monophosphate (cAMP)-independent, ERK-related pathways.

PATIENTS AND METHODS

We investigated whether somatic activating-mutations of CXCR4 might be a possible tumourigenic mechanism for gsp-negative GH-secreting pituitary adenomas and NFPAs. Direct sequencing of polymerase chain reaction-amplified products for coding exons of CXCR4 were performed using genomic deoxyribonucleic acid samples from 37 GH-producing pituitary tumour tissues that were negative for the gsp mutation and 14 CXCR4 expressing NFPAs.

RESULTS

Immunohistochemical analyses and double immunofluorescent staining of sectioned paraffin-embedded pituitary tissues revealed that CXCR4 is highly expressed in GH-producing pituitary adenomas and NFPAs. Direct sequencing showed that two synonymous mutations in exon 2 (87 C > T and 414 C > T) were detected in 4 out of 51 pituitary tumours.

CONCLUSION

Our results indicate that an activating mutation of the CXCR4 may not be a common pathogenetic mechanism in GH-producing pituitary tumours and NFPAs.

SDF-1alpha/CXCL12 enhances GABA and glutamate synaptic activity at serotonin neurons in the rat dorsal raphe nucleus

The serotonin (5-hydroxytryptamine; 5-HT) system has a well-characterized role in depression. Recent reports describe comorbidities of mood-immune disorders, suggesting an immunological component may contribute to the pathogenesis of depression as well. Chemokines, immune proteins which mediate leukocyte trafficking, and their receptors are widely distributed in the brain, mediate neuronal patterning, and modulate various neuropathologies. The purpose of this study was to investigate the neuroanatomical relationship and functional impact of the chemokine stromal cell-derived factor-1alpha/CXCL12 and its receptor, CXCR4, on the serotonin dorsal raphe nucleus (DRN) system in the rat using anatomical and electrophysiological techniques. Immunohistochemical analysis indicates that over 70% of 5-HT neurons colocalize with CXCL12 and CXCR4. At a subcellular level, CXCL12 localizes throughout the cytoplasm whereas CXCR4 concentrates to the outer membrane and processes of 5-HT neurons. CXCL12 and CXCR4 also colocalize on individual DRN cells. Furthermore, electrophysiological studies demonstrate CXCL12 depolarization of 5-HT neurons indirectly via glutamate synaptic inputs. CXCL12 also enhances the frequency of spontaneous inhibitory and excitatory postsynaptic currents (sIPSC and sEPSC). CXCL12 concentration-dependently increases evoked IPSC amplitude and decreases evoked IPSC paired-pulse ratio selectively in 5-HT neurons, effects blocked by the CXCR4 antagonist AMD3100. These data indicate presynaptic enhancement of GABA and glutamate release at 5-HT DRN neurons by CXCL12. Immunohistochemical analysis further shows CXCR4 localization to DRN GABA neurons, providing an anatomical basis for CXCL12 effects on GABA release. Thus, CXCL12 indirectly modulates 5-HT neurotransmission via GABA and glutamate synaptic afferents. Future therapies targeting CXCL12 and other chemokines may treat serotonin related mood disorders, particularly depression experienced by immune-compromised individuals.

Secreted trefoil factor 2 activates the CXCR4 receptor in epithelial and lymphocytic cancer cell lines

The secreted trefoil factor family 2 (TFF2) protein contributes to the protection of the gastrointestinal mucosa from injury by strengthening and stabilizing mucin gels, stimulating epithelial restitution, and restraining the associated inflammation. Although trefoil factors have been shown to activate signaling pathways, no cell surface receptor has been directly linked to trefoil peptide signaling. Here we demonstrate the ability of TFF2 peptide to activate signaling via the CXCR4 chemokine receptor in cancer cell lines. We found that both mouse and human TFF2 proteins (at approximately 0.5 microm) activate Ca2+ signaling in lymphoblastic Jurkat cells that could be abrogated by receptor desensitization (with SDF-1alpha) or pretreatment with the specific antagonist AMD3100 or an anti-CXCR4 antibody. TFF2 pretreatment of Jurkat cells decreased Ca2+ rise and chemotactic response to SDF-1alpha. In addition, the CXCR4-negative gastric epithelial cell line AGS became highly responsive to TFF2 treatment upon expression of the CXCR4 receptor. TFF2-induced activation of mitogen-activated protein kinases in gastric and pancreatic cancer cells, KATO III and AsPC-1, respectively, was also dependent on the presence of the CXCR4 receptor. Finally we demonstrate a distinct proliferative effect of TFF2 protein on an AGS gastric cancer cell line that expresses CXCR4. Overall these data identify CXCR4 as a bona fide signaling receptor for TFF2 and suggest a mechanism through which TFF2 may modulate immune and tumorigenic responses in vivo.

Overexpression of stromal cell-derived factor 1 and its receptor CXCR4 induces autocrine/paracrine cell proliferation in human pituitary adenomas

PURPOSE

Hypothalamic or locally produced growth factors and cytokines control pituitary development, functioning, and cell division. We evaluated the expression of the chemokine stromal cell-derived factor 1 (SDF1) and its receptor CXCR4 in human pituitary adenomas and normal pituitary tissues and their role in cell proliferation.

EXPERIMENTAL DESIGN

The expression of SDF1 and CXCR4 in 65 human pituitary adenomas and 4 human normal pituitaries was determined by reverse transcription-PCR, immunohistochemistry, and confocal immunofluorescence. The proliferative effect of SDF1 was evaluated in eight fibroblast-free human pituitary adenoma cell cultures.

RESULTS

CXCR4 mRNA was expressed in 92% of growth hormone (GH)-secreting pituitary adenomas (GHoma) and 81% of nonfunctioning pituitary adenomas (NFPA), whereas SDF1 was identified in 63% and 78% of GHomas and NFPAs, respectively. Immunostaining for CXCR4 and SDF1 showed a strong homogenous labeling in all tumoral cells in both GHomas and NFPAs. In normal tissues, CXCR4 and SDF1 were expressed only in a subset of anterior pituitary cells, with a lower expression of SDF1 compared with its cognate receptor. CXCR4 and SDF1 were not confined to a specific cell population in the anterior pituitary but colocalized with discrete subpopulations of GH-, prolactin-, and adrenocorticorticotropic hormone-secreting cells. Conversely, most of the SDF1-containing cells expressed CXCR4. In six of eight pituitary adenoma primary cultures, SDF1 induced a statistically significant increase in DNA synthesis that was prevented by the treatment with the CXCR4 antagonist AMD3100 or somatostatin.

CONCLUSIONS

CXCR4 and SDF1 are overexpressed in human pituitary adenomas and CXCR4 activation may contribute to pituitary cell proliferation and, possibly, to adenoma development in humans.

Molecular imaging of metastatic potential

If molecular imaging is to prove clinically useful it will have to surpass current, primarily anatomic techniques in terms of sensitivity and the ability to detect minimal changes in tissue. One of the most important tests for molecular imaging is to determine whether it can image the metastatic potential of tumors. Like all predictive endeavors, the imaging of such "potential" is a daunting task, but one that only molecular imaging--rather than standard, anatomic techniques--is likely to solve. Although difficult, imaging of metastatic potential is also arguably the most important task for molecular imaging of cancer because it is generally the dissemination of malignant tissue, not its prolonged residence in an inopportune site, which kills the patient. Below are examples of uses of molecular imaging of metastases as well as of metastatic potential, the former being a far more developed area of clinical inquiry.

CXCR4/SDF-1 system modulates development of GnRH-1 neurons and the olfactory system

Stromal cell-derived factor 1 (SDF-1) and its receptor CXCR4 influence neuronal migration and have been identified in nasal regions. Gonadotropin releasing hormone-1 (GnRH-1) neurons migrate from nasal regions into the developing forebrain, where postnatally they control reproduction. This study examined the role of SDF-1/CXCR4 in development of the GnRH-1/olfactory systems. Migrating GnRH-1 neurons were CXCR4 immunopositive as were the fibers along which they migrate. SDF-1 transcripts were detected in olfactory epithelium and vomeronasal organ, while SDF-1 immunoreactivity highlighted the GnRH-1 migratory pathway. CXCR4-deficient mice showed a decrease in GnRH-1 cells at the nasal forebrain junction and in brain, but the overall migratory pathway remained intact, no ectopic GnRH-1 cells were detected and olfactory axons reached the olfactory bulb. To further characterize the influence of SDF-1/CXCR4 in the GnRH-1 system, nasal explants were used. CXCR4 expression in vitro was similar to that in vivo. SDF-1 was detected in a dorsal midline cell cluster as well as in migrating GnRH-1 cells. Treatment of explants with bicyclam AMD3100, a CXCR4 antagonist, attenuated GnRH-1 neuronal migration and sensory axon outgrowth. Moreover, the number of GnRH-1 neurons in the explant periphery was reduced. The effects were blocked by coincubation with SDF-1. Removal of midline SDF-1 cells did not alter directional outgrowth of olfactory axons. These results indicate that SDF-1/CXCR4 signaling in not necessary for olfactory axon guidance but rather influences sensory axon extension and GnRH-1 neuronal migration, and maintains GnRH-1 neuronal expression as the cells move away from nasal pit regions.

Tissue microenvironment modulates CXCR4 expression and tumor metastasis in neuroblastoma

Neuroblastoma (NB) is derived from intrinsic migratory neural crest cells and has a high potential for distant metastasis. Growing evidence has implicated chemokine receptors, especially CXCR4, which normally control immune and inflammatory cell migration, as having important roles in tumor progression. In this study, we investigated the expression of CXCR4 in eight different NB cell lines and found that CXCR4 expression is dynamically regulated in NB and can be modulated by different tissue stromata. In addition, we demonstrate that IL-5 and IFN-gamma are released from stromal cells and act as differential mediators for CXCR4 expression. We also overexpressed CXCR4 in two NB cell lines, NUB-7 and SK-N-BE(2), and studied the role of CXCR4 in NB metastasis both in vitro and in vivo. In vitro transwell invasion assay showed that CXCR4 overexpression promoted NB cell migration preferentially toward a bone marrow stromal cell-conditioned medium. Using an in vivo xenograft model, CXCR4-overexpressing cells showed an increased incidence of metastasis, most notably bone marrow metastasis. Our studies reveal critical roles for CXCR4 in NB metastasis and provide insights into the regulatory mechanism of chemokine receptors in NB and the importance of the tissue microenvironment in modulating tumor cell behavior.

SDF-1 Controls Pituitary Cell Proliferation through the Activation of ERK1/2 and the Ca2+-Dependent, Cytosolic Tyrosine Kinase Pyk2

Stromal cell-derived factor-1 (SDF-1) is a chemokine of the CXC subfamily that exerts its effects via CXCR4, a G-protein-coupled receptor. CXCR4 is often expressed by tumor cells, and its activation causes tumor cell proliferation. Using GH4C1 cells, here we show that SDF-1 induced cell proliferation in a dose-dependent manner. Thus, we evaluated the intracellular signaling involved in this effect. SDF-1 increased cytosolic [Ca2+] and activated Pyk2, ERK1/2, and BKCa channels. To correlate these intracellular effectors with the proliferative activity of SDF-1, we inhibited their activity using BAPTA-AM (Ca2+ chelator), PD98059 (MEK inhibitor), salicylate (Pyk2 inhibitor), and TEA (K+ channel blocker). All these compounds reverted SDF-1-induced proliferation, suggesting the involvement of multiple intracellular pathways. To identify a possible crosstalk and a molecular ordering among these pathways, we tested these antagonists on SDF-1-dependent activation of ERK1/2, Pyk2, and BKCa channels. We report that the inhibition of [Ca2+]i increase or the blockade of BKCa channel activity did not affect ERK1/2 activation by SDF-1; Pyk2 activation was purely Ca2+-dependent, not involving ERK1/2 or BKCa channels; and BKCa channel activity was antagonized by Pyk2 but not by ERK1/2 inhibitors. These data suggest that SDF-1-dependent increase of [Ca2+]i activates Pyk2, which, in turn, regulates BKCa channel activity. Conversely, ERK1/2 activation is an independent phenomenon. In conclusion, we demonstrate that SDF-1 induces proliferation of GH4C1 cells, suggesting that the activation of CXCR4 may represent a novel regulatory mechanism for pituitary cell proliferation which may contribute to pituitary adenoma development.

Stroma-derived factor (SDF-1/CXCL12) and human tumor pathogenesis

The chemokine stroma-derived factor (SDF-1/CXCL12) plays multiple roles in tumor pathogenesis. It has been demonstrated that CXCL12 promotes tumor growth and malignancy, enhances tumor angiogenesis, participates in tumor metastasis, and contributes to immunosuppressive networks within the tumor microenvironment. Therefore, it stands to reason that the CXCL12/CXCR4 pathway is an important target for the development of novel anti-cancer therapies. In this review, we consider the pathological nature and characteristics of the CXCL12/CXCR4 pathway in the tumor microenvironment. Strategies for therapeutically targeting the CXCL12/CXCR4 axis also are discussed.

Effects of SDF-1alpha and gp120IIIB on apoptotic pathways in SK-N-SH neuroblastoma cells

CXCR4, a chemokine receptor constitutively expressed in the brain, binds both ligands, the chemokine SDF-1alpha and the HIV envelope glycoprotein gp120(IIIB). There seem to be intracellular differences between the neuronal apoptosis induced by SDF-1alpha and that induced by gp120(IIIB), but the apoptotic pathways involved have not been compared in human neuronal cells. In this study, we characterized the apoptotic intracellular pathways activated by neurotoxic concentrations of SDF-1alpha and gp120(IIIB) in human neuroblastoma cells SK-N-SH. SDF-1alpha (10 nM) and gp120(IIIB) (2 nM) induced similar levels of apoptosis after 24 h of incubation (49 +/- 4% and 48 +/- 3%, respectively, of the neurons were apoptotic). SDF1alpha-induced apoptosis was completely abolished by the inhibition of Src phosphorylation by PP2. Exposure to SDF-1alpha (10 nM) triggered an increase in Src phosphorylation, with a maximum after 20 min of incubation (1.80 +/- 0.24 times higher than control, P = 0.01). NMDA calcium flux was enhanced only if cells were incubated with SDF-1alpha for 20 min before applying NMDA. By contrast, gp120(IIIB)-induced apoptosis was not affected by the inhibition of Src phosphorylation. Moreover, gp120(IIIB) enhanced NMDA calcium flux immediately, without modifying Src phosphorylation status. Finally, levels of phospho-JNK increased following exposure to gp120(IIIB) (by a factor of 1.46 +/- 0.4 at 120 min, P = 0.03), but not after exposure to SDF-1alpha. Thus, SDF-1alpha and gp120(IIIB) induced a similar level of neuronal apoptosis, but by activating different intracellular pathways. SDF-1alpha enhanced NMDA activity indirectly via Src phosphorylation, whereas gp120(IIIB) probably activated the NMDA receptor directly and phosphorylated JNK.

Constitutive neuronal expression of CCR2 chemokine receptor and its colocalization with neurotransmitters in normal rat brain: functional effect of MCP-1/CCL2 on calcium mobilization in primary cultured neurons

Chemokines and their receptors are well described in the immune system, where they promote cell migration and activation. In the central nervous system, chemokine has been implicated in neuroinflammatory processes. However, an increasing number of evidence suggests that they have regulatory functions in the normal nervous system, where they could participate in cell communication. In this work, using a semiquantitative immunohistochemistry approach, we provide the first neuroanatomical mapping of constitutive neuronal CCR2 localization. Neuronal expression of CCR2 was observed in the anterior olfactory nucleus, cerebral cortex, hippocampal formation, caudate putamen, globus pallidus, supraoptic and paraventricular hypothalamic nuclei, amygdala, substantia nigra, ventral tegmental area, and in the brainstem and cerebellum. These data are largely in accordance with results obtained using quantitative autoradiography with [(125)I]MCP-1/CCL2 and RT-PCR CCR2 mRNA analysis. Furthermore, using dual fluorescent immunohistochemistry we studied the chemical phenotype of labeled neurons and demonstrated the coexistence of CCR2 with classical neurotransmitters. Indeed, localization of CCR2 immunostaining is observed in dopaminergic neurons in the substantia nigra pars compacta and in the ventral tegmental area as well as in cholinergic neurons in the substantia innominata and caudate putamen. Finally, we show that the preferential CCR2 ligand, MCP-1/CCL2, elicits Ca(2+) transients in primary cultured neurons from various rat brain regions including the cortex, hippocampus, hypothalamus, and mesencephalon. In conclusion, the constitutive neuronal CCR2 expression in selective brain structures suggests that this receptor could be involved in neuronal communication and possibly associated with cholinergic and dopaminergic neurotransmission and related disorders.

Chemokine Stromal Cell-Derived Factor 1α Induces Proliferation and Growth Hormone Release in GH4C1 Rat Pituitary Adenoma Cell Line through Multiple Intracellular Signals

We used GH4C1 cells as a model to study the effects of the chemokine stromal cell-derived factor 1 (SDF1) in pituitary functions. In these cells, SDF1alpha induced proliferation and growth hormone secretion, suggesting a possible regulatory role for this chemokine at pituitary level. We evaluated the intracellular signaling involved in these effects: SDF1alpha increased cytosolic [Ca(2+)] and activated Pyk2, extracellular signal-regulated kinases 1 and 2 (ERK1/2), and large-conductance Ca(2+)-activated K(+) channels (BK(Ca)) channels. To correlate these intracellular effectors with the proliferative and secretory effects, we inhibited their activity using BAPTA-AM (Ca(2+) chelator), 2'-amino-3'-methoxyflavone (PD98059; a mitogen-activated protein kinase kinase inhibitor), salicylate (Pyk2 inhibitor), and tetraethyl ammonium (K(+) channel blocker). All of these compounds reverted SDF1alpha-induced proliferation, suggesting the involvement of multiple intracellular pathways. Conversely, only BAPTA-AM reverted growth hormone secretion. To identify a possible cross-talk and a molecular ordering among these pathways, we tested these antagonists on SDF1alpha-dependent activation of ERK1/2, Pyk2, and BK(Ca) channels. From these experiments, we observed that the inhibition of [Ca(2+)](i) increase or BK(Ca) channel activity did not affect ERK1/2 activation by SDF1alpha; Pyk2 activation was purely Ca(2+)-dependent, not involving ERK1/2 or BK(Ca) channels; and BK(Ca) channel activity was antagonized by Pyk2 but not by ERK1/2 inhibitors. These data suggest that an SDF1alpha-dependent increase of [Ca(2+)](i) activates Pyk2, which in turn regulates BK(Ca) channel activity. Conversely, ERK1/2 activation is an independent phenomenon. In conclusion, we demonstrate that SDF1alpha causes both proliferation and growth hormone release from pituitary adenoma cells, suggesting that the activation of CXCR4 may represent a novel regulatory mechanism for growth hormone secretion and pituitary cell proliferation, which may contribute to pituitary adenoma development.

Fractalkine reduces N-methyl-d-aspartate-induced calcium flux and apoptosis in human neurons through extracellular signal-regulated kinase activation

Our purpose was to investigate in human neurons the neuroprotective pathways induced by Fractalkine (FKN) against glutamate receptor-induced excitotoxicity. CX(3)CR1 and FKN are expressed constitutively in the tested human embryonic primary neurons and SK-N-SH, a human neuroblastoma cell line. Microfluorometry assay demonstrated that CX(3)CR1 was functional in 44% of primary neurons and in 70% of SK-N-SH. Fractalkine induced ERK1/2 phosphorylation within 1 min and Akt phosphorylation after 10 min, and both phosphorylation decreased after 20 min. No p38 and SAPK/JNK activation was observed after FKN treatment. Application of FKN triggered a 53% reduction of the NMDA-induced neuronal calcium influx, which was insensitive to pertussis toxin and LY294002 an inhibitor of Akt pathway, but abolished by PD98059, an ERK1/2 pathway inhibitor. Moreover, FKN significantly reduced neuronal NMDA-induced apoptosis, which was pertussis toxin insensitive and abolished in presence of PD98059 and LY294002. In conclusion, FKN protected human neurons from NMDA-mediated excitotoxicity in at least two ways with different kinetics: (i) an early ERK1/2 activation which reduced NMDA-mediated calcium flux; and (ii), a late Akt activation associated with the previously induced ERK1/2 activation.

Effect of cerebral ischemia on brain mast cells in rats

The purpose of this study was to investigate the effect of transient cerebral ischemia on brain mast cells in rats. The mast cells decreased significantly at 1 h, 2 h, 4 h and 7 days after ischemia. At 1 day following ischemia, the increase of the number of mast cells in the middle aspect of the thalamus (bregma -2.80 to -3.16 mm) was twice as that of other regions in the thalamus. In addition, histamine contents increased significantly in the thalamus and striatum after ischemia. These results indicate that brain mast cells participate in the pathological process after ischemia.

CXCR4 expression in neuroblastoma primary tumors is associated with clinical presentation of bone and bone marrow metastases

BACKGROUND/PURPOSE

The chemokine receptor, CXCR4, has been implicated in the mechanism of tumor cell metastasis to bone and bone marrow. Neuroblastoma, a cancer of children, is well known for its potential to metastasize to these sites. The goal of this study was to investigate whether the degree of expression of CXCR4 on cells from neuroblastoma primary tumors was related to the pattern of metastatic involvement.

METHODS

Archived neuroblastoma primary tumor samples and clinical data were collected from 26 patients with newly diagnosed neuroblastoma. Expression of CXCR4 (12g5 antibody) was evaluated on formalin-fixed paraffin-embedded tumor tissues using standard immunohistochemical techniques. Each tumor was graded (grade 1 through 4) based on the proportion of cells that were positive for the 12g5 antibody. Tumor grades for CXCR4 expression were compared with clinical data from each patient.

RESULTS

Higher grades of expression (grade 3 and 4) were found in tumors from patients with high-stage disease (P < .01) and in patients with bone and bone marrow metastases (P < or = .01). Clinical outcome in patients with tumors highly expressing CXCR4 was significantly worse (P < .01) than in those patients with low-grade CXCR4.

CONCLUSIONS

CXCR4 expression in neuroblastoma primary tumors is significantly correlated with the pattern of metastatic spread.

Dexamethasone downregulates chemokine receptor CXCR4 and exerts neuroprotection against hypoxia/ischemia-induced brain injury in neonatal rats

OBJECTIVE

Hypoxia/ischemia (H/I) induces rapid and massive brain damage in neonatal rat brain, resulting in long-term consequences on structural and functional maturation of the central nervous system. Inflammatory mediators contribute to these permanent pathological changes, which are sensitive to corticoid treatments. Since the chemokine receptor CXCR4, specific for the SDF-1 alpha/CXCL12 ligand, regulates both apoptotic and neuroregeneration processes, this receptor was quantified 2 days following H/I in neonatal rat brain in relation with dexamethasone (DEX) treatment.

METHODS

Seven-day-old male rats were exposed to a 90-min hypoxia following unilateral carotid ligation (H/I) and were sacrificed 48 h later. Glucocorticoid-pretreated animals were injected subcutaneously 5 h prior to hypoxia with 0.5 microg/g DEX. Glial fibrillary acidic protein and cresyl violet staining were used for assessing the extent of brain lesion subdivided into necrotic and penumbra-like areas. The density of CXCR4 receptors was determined by quantitative autoradiography using [(125)I]SDF-1 alpha as a ligand.

RESULTS

The H/I resulted in a massive lesion ipsilateral to the carotid ligation, which was extended to cortical, striatal, hippocampal and thalamic areas, while the contralateral hemisphere remained apparently unaffected. DEX decreased the lesion size by reducing mainly the necrotic area. H/I induced a marked increase in CXCR4 receptor binding in the penumbra-like areas. DEX pretreatment decreased CXCR4 receptor density in the penumbra and attenuated astrocytosis. Furthermore, DEX strongly lowered mortality rate and reduced functional recovery time right after hypoxia.

CONCLUSION

The rapid enhancement in CXCR4 chemokine receptor binding in the affected brain areas suggests that SDF-1 alpha/CXCR4 may play a role in the hypoxia-induced inflammatory reaction in the neonatal brain. Attenuation of CXCR4 expression and astrogliosis could contribute to the neuroprotective effect of DEX pretreatment via influencing the inflammatory cascade induced by H/I in the neonatal brain.

CD4 dependence of gp120IIIB-CXCR4 interaction is cell-type specific

The HIV-1 envelope protein gp120IIIB is selective for the CXCR4 chemokine receptor and has been shown to induce apoptosis in neurons both in vivo and in vitro. We examined the ability of gp120IIIB to signal through the rat CXCR4 (rCXCR4) receptor and its dependence on the presence of the human CD4 (hCD4) protein in a number of cell systems. SDF-1alpha potently inhibited N-type Ca channels in cultured HEK293 cells expressing both the Ca channel subunits and rCXCR4 receptors. However, gp120IIIB was ineffective in producing either Ca channel inhibition or in blocking the effects of SDF-1alpha. However, when hCD4 was coexpressed with rCXCR4 and Ca channel subunits, gp120IIIB also produced Ca channel inhibition. Similarly, in PC12 cells transfected with the rCXCR4, SDF-1alpha produced mobilization of intracellular Ca, while gp120IIIB was only effective when hCD4 was coexpressed. SDF-1alpha induced endocytosis of Yellow Fluorescent Protein (YFP)-tagged rCXCR4 expressed in PC12 cells, as did gp120IIIB, an effect which was enhanced by hCD4 coexpression. When tagged rCXCR4 was expressed in F-11 cells or in rat DRG neurons, SDF-1alpha produced extensive receptor endocytosis. However, the ability of gp120IIIB to produce endocytosis was dependent on the coexpression of hCD4. Our results demonstrate that the degree of hCD4 dependence of the agonist effects of gp120IIIB at the rCXCR4 receptor is cell-type specific.

Role of the alpha-chemokine stromal cell-derived factor (SDF-1) in the developing and mature central nervous system

alpha-chemokines, which control the activation and directed migration of leukocytes, participate in the inflammatory processes in host defense response. One of the alpha-chemokines, CXCL12 or stromal cell-derived factor 1 (SDF-1), not only regulates cell growth and migration of hematopoietic stem cells but may also play a central role in brain development as we discuss here. SDF-1 indeed activates the CXCR4 receptor expressed in a variety of neural cells, and this signaling results in diverse biological effects. It enhances migration and proliferation of cerebellar granule cells, chemoattracts microglia, and stimulates cytokine production and glutamate release by astrocytes. Moreover, it elicits postsynaptic currents in Purkinje cells, triggers migration of cortical neuron progenitors, and produces pain by directly exciting nociceptive neurons. By modulating cell signaling and survival during neuroinflammation, SDF-1 may also play a role in the pathogenesis of brain tumors, experimental allergic encephalitis, and the nervous system dysfunction associated with acquired immunodeficiency syndrome.

Chemokine receptor binding and signal transduction in native cells of the central nervous system

Chemokine receptors belong to the superfamily of seven-transmembrane-spanning, G-protein-coupled receptors, and their expression by central nervous system cells is clearly documented. As this gene family has become the target of novel therapeutic development, the analysis of these receptors requires radioligand binding techniques as well as methods that entail assessing receptor stimulation of signal transduction pathways. Herein, we describe specific protocols for measuring radiolabeled chemokine binding to their cognate receptors on cultured glial cells as well as to receptors expressed in heterologous cell systems. Multiple downstream signaling pathways, including intracellular calcium influx and receptor-dependent kinase activation, are associated with chemokine receptor stimulation. Protocols for measuring these signaling events in chemokine-receptor-expressing cells are also presented.

Signalling pathways involved in the chemotactic activity of CXCL12 in cultured rat cerebellar neurons and CHP100 neuroepithelioma cells

We compared the signal transduction pathways activated by stromal cell-derived factor-1 (CXCL12) chemokine in two different cell systems: primary cultures of rat cerebellar granule neurons (CGN) and human neuroepithelioma CHP100 cells. Both cell types express functional CXC chemokine receptor 4 (CXCR4), which is coupled both to extracellular signal-regulated kinase (ERK) and Akt phosphorylation pathways. The activation of ERK shows different dependency on the phosphatidylinositol 3-kinase (PI3-K) pathway and different sensitivity to pertussis toxin (PTX) treatment, indicative of coupling to different G proteins in the two cell systems considered. We demonstrate that the inhibition of either the ERK kinase or the PI3-K pathways blocks the CXCL12 induced-chemotaxis in CHP100 cells; while only PI3-K activity is stringently necessary for CGN migration.

CXC chemokine receptors in the central nervous system: Role in cerebellar neuromodulation and development

Chemokines and their receptors are constitutively present in the central nervous system (CNS), expressed in neurons and glial cells. Much evidence suggests that, beyond their involvement in neuroinflammation, these proteins play a role in neurodevelopment and neurophysiological signaling. The goal of this review is to summarize recent information concerning expression, signaling, and function of CXC chemokine receptor in the CNS, with the main focus on the developmental and neuromodulatory actions of chemokines in the cerebellum.

Neuroanatomical distribution of CXCR4 in adult rat brain and its localization in cholinergic and dopaminergic neurons

Accumulating evidence supports a role of chemokines and their receptors in brain function. Up to now scarce evidence has been given of the neuroanatomical distribution of chemokine receptors. Although it is widely accepted that chemokine receptors are present on glial cells, especially in pathological conditions, it remains unclear whether they are constitutively present in normal rat brain and whether neurons have the potential to express such chemokine receptors. CXCR4, a G protein-coupled receptor for the chemokine stromal cell-derived factor-1 (SDF-1/CXCL12) was reported to have possible implications in brain development and AIDS-related dementia. By dual immunohistochemistry on brain sections, we clearly demonstrate that CXCR4 is constitutively expressed in adult rat brain, in glial cells (astrocytes, microglia but not oligodendrocytes) as well as in neurons. Neuronal expression of CXCR4 is mainly found in cerebral cortex, caudate putamen, globus pallidus, substantia innominata, supraoptic and paraventricular hypothalamic nuclei, ventromedial thalamic nucleus and substantia nigra. Using confocal microscopy, a differential distribution of CXCR4 in neuronal perikarya and dendrites can be observed according to the brain structure. Furthermore, this work demonstrates for the first time the coexistence of a chemokine receptor with classical neurotransmitters. A localization of CXCR4 is thus observed in neuronal cell bodies expressing choline acetyltransferase-immunoreactivity in the caudate putamen and substantia innominata, as well as in tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta. In conclusion, the constitutive neuronal CXCR4 expression suggests that SDF-1/CXCL12 could be involved in neuronal communication and possibly linked up with cholinergic and dopaminergic neurotransmission and related disorders.

Stimuli from conspecifics influence brain mast cell population in male rats

It is well established that mast cells occur within the brain of many species, and that the brain mast cell population is not static, but changes with the behavioral and physiological state of the animal. In this study, we tested whether exposure to conspecifics alters the number of brain mast cells in male rats, and then investigated the nature of stimuli influencing the changes observed in the number and localization of brain mast cells. Five days of cohabitation with an ovariectomized, estrogen-progesterone (OVX + EP)-treated female resulted in the largest number of thalamic mast cells, while pairing with such a female physically separated by a wire mesh or with a novel male produced a smaller, but significant increase over other pairings (OVX females for 5 days, OVX and OVX + EP females for 1 day, familiar or isolated males for 5 days). In all groups, mast cells were localized within specific dorsal thalamic nuclei, including the paraventricular nucleus, anterior nuclear group, or mediodorsal, ventroposterior, or medial geniculate nuclei. The results suggest that the behavioral and/or endocrine factors associated with cohabitation with conspecifics are sufficient to alter the number of brain mast cell-specific nuclei in the thalami of male rats and thus can provide targeted delivery of neuromodulators to specific regions of the brain that process information concerning the normal physiological state of the animal.

A role for CCN3 (NOV) in calcium signalling

AIMS

In animals and humans increased expression of CCN3 (NOV) is detected in tissues where calcium is a key regulator, such as the adrenal gland, central nervous system, bone and cartilage, heart muscle, and kidney. Because the multimodular structure of the CCN proteins strongly suggests that these cell growth regulators are metalloproteins, this study investigated the possible role of CCN3 in ion flux and transport during development, control of cell proliferation, differentiation, and pathobiology.

METHODS

The isolation of CCN3 partners was performed by means of the two hybrid system. Yeasts were cotransfected with an HL60 cDNA library fused to the transactivation domain of the GAL4 transcription factor, and with a plasmid expressing CCN3 fused to the DNA binding domain of GAL4. Screening of the recombinant clones selected on the basis of leucine, histidine, and tryptophan prototrophy was performed with a beta-galactosidase assay. After the interaction between CCN3 and its putative partners was checked with a GST (glutathione S-transferase) pull down assay, the positive clones were identified by cloning. To establish whether the CCN3 protein affected calcium ion flux, a dynamic imaging microscopy system was used, which allowed the fluorometric measurement of the intracellular calcium concentration. The proteins used in the assays were GST fused with either CCN3 or CCN2 (CTGF) and GST alone as a control.

RESULTS

The two hybrid system identified the S100A4 (mts1) calcium binding protein as a partner of CCN3 and the use of the GST fusion proteins showed that the addition of CCN3 and CCN2 to G59 glioblastoma and SK-N-SH neuroblastoma cells caused a pronounced but transient increase of intracellular calcium, originating from both the entry of extracellular calcium and the mobilisation of intracellular stores.

CONCLUSIONS

The interaction of CCN3 with S100A4 may account, in part, for the association of CCN3 with carcinogenesis and its pattern of expression in normal conditions. The increased intracellular calcium concentrations induced by CCN3 and CCN2 both involve different processes, among which voltage independent calcium channels might be of considerable importance in regulating the calcium flux associated with cell growth control, motility, and spreading. These observations assign for the first time a biological function to the CCN3 protein and point out a broader role for the CCN proteins in calcium ion signalling.

Stimulation of chemokine CXC receptor 4 induces synaptic depression of evoked parallel fibers inputs onto Purkinje neurons in mouse cerebellum

In the present work, we studied the effects of the stimulation of the chemokine CXC receptor 4 (CXCR4) by the stromal-derived cell growth factor-1alpha (SDF-1alpha) on the evoked excitatory postsynaptic current. This was generated in Purkinje neurons (PN) from mouse cerebellar slices by the stimulation of parallel fibers. It was found that the amplitude of EPSC was reversibly reduced by SDF-1alpha application. This effect was dose-dependent (IC(50)=0.34 nM) and was abolished by the anti-CXCR4 monoclonal antibody (mAb) 12G5. This SDF-1alpha-induced synaptic depression was caused by a decrease of evoked glutamate release, rather than a decrease in the postsynaptic glutamate receptor (GluR) sensitivity, as the mean amplitude of the spontaneous EPSCs was not influenced by chemokine application. Moreover, NMDA receptors (NMDARs) are involved in EPSC depression being inhibited by the NMDAR blocker 2-amino-5-phosphonopentanoic acid (AP-5). The mechanisms by which SDF-1alpha modulates neurotransmission in the cerebellar cortex are discussed.

Distribution, cellular localization and functional role of CCR2 chemokine receptors in adult rat brain

Recent studies demonstrated that the chemokine monocyte chemoattractant protein-1 (MCP-1)/CCL2 and its receptor, CCR2, play important roles in various brain diseases. In this study, using quantitative autoradiography, we studied the pharmacological properties of [125l]MCP-1/CCL2 binding in rat brain and we clearly showed the distribution of CCR2 receptors in cerebral cortex, nucleus accumbens, striatum, amygdala, thalamus, hypothalamus, hippocampus, substantia nigra, mammillary bodies and raphe nuclei. Moreover, using double fluorescent immunohistochemistry, we showed that CCR2 receptors were constitutively expressed on neurons and astrocytes. Using RT-PCR methods, we demonstrated that CCR2 mRNA is present in various brain areas described above. Four hours after an acute intraperitoneal lipopolysaccharide injection, we showed that MCP-1/CCL2 binding was up-regulated in several brain structures; this effect took place on both CCR2B labelled neurons and astrocytes and to a lesser extent on activated microglia. To explore neurobiological function of CCR2, actimetric study was carried out. After intracerebroventricular injections of MCP-1/CCL2, we showed that motor activity was markedly decreased. Our results provide the first evidence for constitutive CCR2 receptor expression with precise neuroanatomical and cellular localizations in the brain, and its regulation during an inflammatory process, suggesting that MCP-1/CCL2 and CCR2 play important physiological and pathophysiological role(s) in the CNS.

A possible role for CXCR4 and its ligand, the CXC chemokine stromal cell-derived factor-1, in the development of bone marrow metastases in neuroblastoma

The homing of hemopoietic stem cells to the bone marrow is mediated by specific interactions occurring between CXCR4, which is expressed on hemopoietic stem cells, and its ligand, stromal cell-derived factor-1 (SDF-1), a CXC chemokine secreted by bone marrow stromal cells. In the present study we evaluated the possibility that neuroblastoma cells use a mechanism similar to that used by hemopoietic stem cells to home to the bone marrow and adhere to bone marrow stromal cells. Our study suggests that CXCR4 expression may be a general characteristic of neuroblastoma cells. SH-SY5Y neuroblastoma cells express not only CXCR4, but also its ligand, SDF-1. CXCR4 expression on SH-SY5Y neuroblastoma cells is tightly regulated by tumor cell-derived SDF-1, as demonstrated by the ability of neutralizing Abs against human SDF-1alpha to up-regulate CXCR4 expression on the tumor cells. The reduction in CXCR4 expression following short term exposure to recombinant human SDF-1alpha can be recovered as a result of de novo receptor synthesis. Recombinant human SDF-1alpha induces the migration of CXCR4-expressing SH-SY5Y neuroblastoma cells in CXCR4- and heterotrimeric G protein-dependent manners. Furthermore, SH-SY5Y cells interact at multiple levels with bone marrow components, as evidenced by the fact that bone marrow-derived constituents promote SH-SY5Y cell migration, adhesion to bone marrow stromal cells, and proliferation. These results suggest that SH-SY5Y neuroblastoma cells are equipped with adequate machinery to support their homing to the bone marrow. Therefore, the ability of neuroblastoma tumors to preferentially form metastases in the bone marrow may be influenced by a set of complex CXCR4-SDF-1 interactions.

Pharmacological evidence for complex and multiple site interaction of CXCR4 with SDF-1alpha: implications for development of selective CXCR4 antagonists

The C-X-C chemokine SDF-1 and its receptor CXCR4, mediate a pivotal role in the pathophysiology of HIV-1 infection and vascular inflammatory diseases. In this study, we investigated the pharmacological properties of SDF-1alpha interaction with CXCR4 in human leukemia cell lines. Our data, based on [125I]-SDF-1alpha radioligand binding, SDF-1alpha-induced [35S]-GTPgammaS binding and use of specific CXCR4 antagonist AMD3100 reveals the complex nature of SDF-1alpha-CXCR4 interaction. Firstly, homologous competition with cold SDF-1alpha revealed a bimodal ligand displacement curve and secondly, although AMD3100 inhibited both SDF-1alpha-mediated chemotaxis (IC(50)=4.7 nM) and [35S]-GTPgammaS binding (IC(50)=7.4 nM) with high affinity, it was intriguingly up to 3000-fold less potent (IC(50)=15.2 microM) in the radioligand binding assay. These results provide pharmacological evidence for the recently described two-site model for SDF-1alpha-CXCR4 interaction. Accordingly, inhibition of SDF-1alpha binding to one of the receptor sites is sufficient to antagonize function, without causing its complete displacement from the receptor. Furthermore, these findings have important implications in the development and evaluation of CXCR4-selective small molecule antagonists for therapeutic use.

SDF-1α induces chemotaxis and enhances Sonic hedgehog-induced proliferation of cerebellar granule cells

The chemokine SDF-1α (CXC12) and its receptor CXCR4 have been shown to play a role in the development of normal cerebellar cytoarchitecture. We report here that SDF-1α both induces chemotactic responses in granule precursor cells and enhances granule cell proliferative responses to Sonic hedgehog. Chemotactic and proliferative responses to SDF-1α are greater in granule cells obtained from cerebella of animals in the first postnatal week, coinciding with the observed in vivo peak in cerebellar CXCR4 expression. SDF-1α activation of neuronal CXCR4 differs from activation of CXCR4 in leukocytes in that SDF-1α-induced calcium flux is activity dependent, requiring predepolarization with KCl or pretreatment with glutamate. However, as is the case in leukocytes, neuronal responses to SDF-1α are all abolished by pretreatment of granule cells with pertussis toxin, suggesting they occur through Gαi activation. In conclusion, SDF-1α plays a role in two important processes of granule cell maturation – proliferation and migration – assisting in the achievement of appropriate cell number and position in the cerebellar cortex.