The alpha-chemokine, stromal cell-derived factor-1alpha, binds to the transmembrane G-protein-coupled CXCR-4 receptor and activates multiple signal transduction pathways

Central actions of the chemokine stromal cell-derived factor 1 contribute to neurohumoral excitation in heart failure rats

The ample expression of chemokines and their receptors by neurons in the brain suggests that they play a functional role beyond the coordination of inflammatory and immune responses. Growing evidence implicates brain chemokines in the regulation of neuronal activity and neurohormonal release. This study examined the potential role of brain chemokines in regulating hemodynamic, sympathetic, and neuroendocrine mechanisms in rats with ischemia-induced heart failure (HF). Immunohistochemical analysis revealed that the chemokine stromal cell-derived factor 1 (SDF-1)/CXCL12 was highly expressed in the hypothalamic paraventricular nucleus and subfornical organ and that SDF-1 expression was significantly increased in HF rats compared with sham-operated (SHAM) control rats. ICV injection of SDF-1 induced substantial and long-lasting increases in blood pressure, heart rate, and renal sympathetic nerve activity in both SHAM and HF rats, but responses were exaggerated in HF rats. Bilateral microinjection of SDF-1 into the paraventricular nucleus also elicited exaggerated increases in blood pressure, heart rate, and renal sympathetic nerve activity in the HF rats. A 4-hour ICV infusion of SDF-1 increased plasma levels of arginine vasopressin, adrenocorticotropic hormone, and norepinephrine in normal rats, responses that were prevented by pretreatment with ICV SDF-1 short-hairpin RNA (shRNA). ICV administration of SDF-1 shRNA also reduced plasma arginine vasopressin, adrenocorticotropic hormone, and norepinephrine levels in HF rats. These data suggest that the chemokine SDF-1, acting within the brain, plays an important role in regulating sympathetic drive, neuroendocrine release, and hemodynamic function in normal and pathophysiological conditions and so may contribute to the neural and humoral activation in HF.

The SDF-1/CXCR4 axis in stem cell preconditioning

We review the pivotal role of the stromal derived factor (SDF)-1 chemokine in tissue ischaemia and how it orchestrates the rapid revascularization of injured, ischaemic, and regenerating tissues via the CXC chemokine receptors CXCR4 and CXCR7. Furthermore, we discuss the effects of preconditioning (PC), which is a well-known protective phenomenon for tissue ischaemia. The positive effect of both hypoxic and acidic PC on progenitor cell therapeutic potential is reviewed, while stressing the role of the SDF-1/CXCR4 axis in this process.

Hematopoietic Stem Cell Mobilization and Homing after Transplantation: The Role of MMP-2, MMP-9, and MT1-MMP

Hematopoietic stem/progenitor cells (HSPCs) are used in clinical transplantation to restore hematopoietic function. Here we review the role of the soluble matrix metalloproteinases MMP-2 and MMP-9, and membrane type (MT)1-MMP in modulating processes critical to successful transplantation of HSPC, such as mobilization and homing. Growth factors and cytokines which are employed as mobilizing agents upregulate MMP-2 and MMP-9. Recently we demonstrated that MT1-MMP enhances HSPC migration across reconstituted basement membrane, activates proMMP-2, and contributes to a highly proteolytic bone marrow microenvironment that facilitates egress of HSPC. On the other hand, we reported that molecules secreted during HSPC mobilization and collection, such as hyaluronic acid and thrombin, increase MT1-MMP expression in cord blood HSPC and enhance (prime) their homing-related responses. We suggest that modulation of MMP-2, MMP-9, and MT1-MMP expression has potential for development of new therapies for more efficient mobilization, homing, and engraftment of HSPC, which could lead to improved transplantation outcomes.

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.

Grouper (Epinephelus coioides) CXCR4 is expressed in response to pathogens infection and early stage of development

Chemokine (C-X-C motif) receptor 4 (CXCR4) from orange-spotted grouper (Epinephelus coioides) was identified and characterized in this study. gCXCR4 shared common features in protein sequence and predicted structure of CXCR4 family. This suggested that gCXCR4 is a member of G protein-coupled receptors with seven transmembrane domains. The expression patterns revealed that gCXCR4 may play a key role in early development of grouper. Furthermore, overexpression of gCXCR4-GFP for 48 h had significant effects on the GF-1 cell viability. gCXCR4 protein was mainly expressed in the marginal zone of head kidney and on the surface of intestinal villi. gCXCR4 expression can be detected in all the examined tissues and significantly up-regulated in eye and brain, which are the main targets for nervous necrosis virus (NNV) infection and replication. gCXCR4 gene expression can be induced in the spleen and eye by lipopolysaccharide and NNV, respectively. Our data suggested that gCXCR4 may not only play a role in the early immune response to microbial infection but also restrain to the immune system and central nervous system.

CXCR4 expression correlates with the degree of tumor infiltration and BRAF status in papillary thyroid carcinomas

Emerging evidence indicates that interactions between chemokine receptors and their ligands may have a critical role in several steps of tumor development, including tumor growth, progression, and metastasis. In this report, we retrospectively evaluated CXCR4 expression in a consecutive series of 200 papillary thyroid carcinomas. We investigated the relationship between the clinicopathological features of the tumors and mutations in the BRAF gene to verify whether overexpression of CXCR4 is linked to more aggressive behavior in thyroid tumors. CXCR4 protein expression was evaluated by immunohistochemical staining. A final staining score was calculated by adding the score representing the percentage of positive cells to the intensity score. The CXCR4 expression of each papillary thyroid carcinoma sample was normalized by calculating the z score for each final staining score. Univariate analysis was used to correlate CXCR4 expression with the papillary thyroid carcinoma variant, the degree of neoplastic infiltration, the American Joint Commission on Cancer stage, the presence of lymphocytic thyroiditis and the mutation status of the BRAF gene. Multiple regression analysis confirmed a strong association between CXCR4, BRAF mutation and the degree of neoplastic infiltration. These data clearly indicate that the chemokine receptor expression induced by oncogenic activation could be the major determinant of the local aggressiveness of neoplastic cells. In conclusion, our data indicate that CXCR4 expression and BRAF mutation status could cooperatively induce and promote a more aggressive phenotype in papillary thyroid carcinoma through several pathways and specifically increase the tumors' spread outside of the thyroid gland.

Salvianolic acid B inhibits SDF-1α-stimulated cell proliferation and migration of vascular smooth muscle cells by suppressing CXCR4 receptor

Salvianolic acid B (Sal B), a bioactive compound from Salvia miltiorrhiza, widely used to treat cardiovascular diseases, and stromal cell-derived factor-1α (SDF-1α)/CXCR4 pathway has been correlated with balloon angioplasty-induced neointimal formation. The purposes of the present study were to investigate whether Sal B can inhibit SDF-1α/CXCR4-mediated effects on the cell proliferation and migration of vascular smooth muscle cells (VSMCs) and to examine its possible molecular mechanisms. Under 0.5% FBS medium, all of the cellular studies were investigated on VSMCs (A10 cells) stimulated with 10 ng/ml SDF-1α alone or co-treated with 0.075 mg/ml Sal B. Our results showed that SDF-1α markedly stimulated the cell growth and migration of A10 cells, whose effects can be significantly reversed by co-incubation of Sal B. Similarly, Sal B also obviously down-regulated the SDF-1α-stimulated up-regulation of CXCR4 (total and cell-surface levels), Raf-1, MEK, ERK1/2, phospho-ERK1/2, FAK and phospho-FAK as well as an increase of the promoter activity of NF-κB. Besides, Sal B also effectively attenuated balloon angioplasty-induced neointimal hyperplasia. In conclusion, suppressing the expression levels of CXCR4 receptor and downstream molecules of SDF-1α/CXCR4 axis could possibly explain one of the pharmacological mechanisms of Sal B on prevention of cell proliferation, migration and subsequently neointimal hyperplasia.

Targeting the bone marrow in Waldenstrom macroglobulinemia

Waldenstrom macroglobulinemia (WM) is a low-grade B-cell lymphoma characterized by widespread involvement of the bone marrow with lymphoplasmacytic cells. In approximately 20% of patients, the malignant clone also involves the lymph nodes and induces hepatosplenomegaly. The mechanisms by which the tumor cells home to the bone marrow and preferentially reside in the marrow niches are not fully elucidated. In this review, we examine the role of the bone marrow microenvironment in the regulation of cell growth, survival and cell dissemination in WM. We also summarize specific regulators of niche-dependent tumor proliferation in WM. These include chemokines, adhesion molecules, Src/PI3K/Akt/mTOR signaling, NF-kB activation, and micro-RNA regulation in WM. Targeting these pathways in clinical trials could lead to significant responses in this rare disease.

The role of PI3K/protein kinase B (PKB/c-akt) in migration and homing of hematopoietic stem and progenitor cells

PURPOSE OF REVIEW

Hematopoietic stem cell (HSC) transplantation is the most powerful treatment modality for a variety of hematological disorders. Successful hematopoietic recovery after transplantation depends on optimal homing of HSCs to the bone marrow and subsequent lodging in the HSC niche. The molecular mechanisms underlying bone marrow homing are, thus far, incompletely understood. This review focuses on recent studies that extended our understanding of how the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (PKB/c-akt) signaling module can regulate migration and homing of HSCs.

RECENT FINDINGS

In addition to regulation of HSC maintenance and lineage development, it has recently become apparent that the PI3K/PKB signaling module plays a critical role in regulation of migration and adhesion of hematopoietic stem and progenitor cells. Activation of this signaling pathway enhances firm adhesion, reduces migration and inhibits bone marrow homing, whereas inhibition of PKB conversely induces bone marrow homing.

SUMMARY

These findings clearly implicate the PI3K/PKB signaling module in playing a critical role in regulation of bone marrow homing, suggesting that pharmacological modulation of this signaling molecule prior to transplantation may provide a clinical means of improving engraftment levels and accelerating hematopoietic recovery.

CXCR7 mediated Giα independent activation of ERK and Akt promotes cell survival and chemotaxis in T cells

Chemokine receptors CXCR7 and CXCR4 bind to the same ligand stromal cell derived factor-1alpha (SDF-1α/CXCL12). We assessed the downstream signaling pathways mediated by CXCL12-CXCR7 interaction in Jurkat T cells. All experiments were carried out after functionally blocking the CXCR4 receptor. CXCL12, on binding CXCR7, induced phosphorylation of extra cellular regulated protein kinases (ERK 1/2) and Akt. Selective inhibition of each signal demonstrated that phosphorylated ERK 1/2 is essential for chemotaxis and survival of T cells whereas activation of Akt promotes only cell survival. Another interesting finding of this study is that CXCL12-CXCR7 interaction under normal physiological conditions does not activate the p38 pathway. Furthermore, we observed that the CXCL12 signaling via CXCR7 is Giα independent. Our findings suggest that CXCR7 promotes cell survival and does not induce cell death in T cells. The CXCL12 signaling via CXCR7 may be crucial in determining the fate of the activated T cells.

Regulation of ROCKII membrane localization through its C-terminus

RhoA activated kinases (ROCKs) are potent effectors of RhoA signaling for regulation of the cytoskeleton. ROCKs have been shown to be localized to several different subcellular locations, suggesting that its localization is context specific and regulated. However, the signaling mechanisms that control ROCK localization have not been clearly described. In this study we measured ROCKII localization following stimulation with the chemokine CXCL12 or adhesion to collagen 1. Strikingly, each of these extracellular signals targeted ROCKII to membrane protrusions. We further determined that both RhoA and PI3-kinase signaling are required for these stimuli to induce efficient membrane localization. Furthermore, we used a mutational approach to show that two separate domains predicted to respond to these localization signals, the Rho Binding Domain (RBD) and the Pleckstrin Homology domain (PH). Unexpectedly, we found that these two domains work synergistically to lead to membrane localization. This suggests a novel mechanism for controlling ROCKII localization at the membrane, in which the ROCKII C-terminus acts as a coincidence detector for spatial regulatory signals. In other words, efficient membrane targeting requires the ROCKII RBD to receive the RhoA signal and the PH domain to receive the phospholipid signal.

Interleukin-10 deficiency impairs bone marrow-derived endothelial progenitor cell survival and function in ischemic myocardium

RATIONALE

Endothelial progenitor cell (EPC) survival and function in the injured myocardium is adversely influenced by hostile microenvironment such as ischemia, hypoxia, and inflammatory response, thereby compromising full benefits of EPC-mediated myocardial repair.

OBJECTIVE

We hypothesized that interleukin-10 (IL-10) modulates EPC biology leading to enhanced survival and function after transplantation in the ischemic myocardium.

METHODS AND RESULTS

Myocardial infarction (MI)-induced mobilization of bone marrow EPC (Sca-1+Flk1+cells) into the circulation was significantly impaired in IL-10 knockout (KO) mice. Bone marrow transplantation to replace IL-10 KO marrow with wild-type (WT) marrow attenuated these effects. Impaired mobilization was associated with lower stromal cell-derived factor (SDF)-1 expression levels in the myocardium of KO mice. Interestingly, SDF-1 administration reversed mobilization defect in KO mice. In vitro, hypoxia-mediated increases in CXCR4 expression and cell survival were lower in IL-10-deficient EPCs. Furthermore, SDF-1-induced migration of WT EPCs was inhibited by AMD3100, an inhibitor of CXCR4. To further study the effect of IL-10 on in vivo EPC survival and engraftment into vascular structures, GFP-labeled EPC were injected intramyocardially after induction of MI, and the mice were treated with either saline or recombinant IL-10. The IL-10-treated group showed increased retention of transplanted EPCs in the myocardium and was associated with significantly reduced EPC apoptosis after MI. Interestingly, increased EPC retention and their association with the vascular structures was observed in IL-10-treated mice. Increased EPC survival and angiogenesis in the myocardium of IL-10-treated mice corroborated with improved left ventricular function, reduced infarct size, and fibrosis in the myocardium. In vitro, IL-10-induced increase in VEGF expression in WT EPC was abrogated by STAT3 inhibitor, suggesting IL-10 signals through STAT3 activation.

CONCLUSIONS

Taken together, our studies demonstrate that MI-induced EPC mobilization was impaired in IL-10 KO mice and that IL-10 increases EPC survival and function possibly through activation of STAT3/VEGF signaling cascades, leading to attenuation of MI-induced left ventricular dysfunction and remodeling.

Differential roles for the p101 and p84 regulatory subunits of PI3Kγ in tumor growth and metastasis

Phosphoinositide 3-kinase γ (PI3Kγ) consists of a catalytic subunit p110γ, which forms mutually exclusive dimers with one of the regulatory subunits called p101 and p84/p87(PIKAP). Recently, PI3Kγ emerged as being a potential oncogene because overexpression of the catalytic subunit p110γ or the regulatory subunit p101 leads to oncogenic cellular transformation and malignancy. However, the contribution of the individual subunits to tumor growth and metastasis and the mechanisms involved are not understood. We therefore individually knocked down the PI3Kγ subunits (p84, p101 and p110γ) in MDA-MB-231 cells, which reduced in vitro migration of the cell lines. Knockdown of p110γ or p101 inhibited apoptosis, Akt phosphorylation and lung colonization in SCID mice. Similarly, the knockdown of p110γ and p101 in murine epithelial carcinoma 4T1.2 cells inhibited primary tumor growth and spontaneous metastasis, as well as lung colonization. In contrast, knockdown of p84 in MDA-MB-231 cells enhanced Akt phosphorylation and lung colonization. These findings are the first to implicate differential functions of the two PI3Kγ regulatory subunits in the process of oncogenesis, and indicate that loss of p101 is sufficient to reduce in vivo tumor growth and metastasis to the same extent as that of p110γ.

The CXC chemokine receptor 4 ligands ubiquitin and stromal cell-derived factor-1α function through distinct receptor interactions

Recently, we identified extracellular ubiquitin as an endogenous CXC chemokine receptor (CXCR) 4 agonist. However, the receptor selectivity and molecular basis of the CXCR4 agonist activity of ubiquitin are unknown, and functional consequences of CXCR4 activation with ubiquitin are poorly defined. Here, we provide evidence that ubiquitin and the cognate CXCR4 ligand stromal cell-derived factor (SDF)-1α do not share CXCR7 as a receptor. We further demonstrate that ubiquitin does not utilize the typical two-site binding mechanism of chemokine-receptor interactions, in which the receptor N terminus is important for ligand binding. CXCR4 activation with ubiquitin and SDF-1α lead to similar Gα(i)-responses and to a comparable magnitude of phosphorylation of ERK-1/2, p90 ribosomal S6 kinase-l and Akt, although phosphorylations occur more transiently after activation with ubiquitin. Despite the similarity of signal transduction events after activation of CXCR4 with both ligands, ubiquitin possesses weaker chemotactic activity than SDF-lα in cell migration assays and does not interfere with productive entry of HIV-1 into P4.R5 multinuclear activation of galactosidase indicator cells. Unlike SDF-1α, ubiquitin lacks interactions with an N-terminal CXCR4 peptide in NMR spectroscopy experiments. Binding and signaling studies in the presence of antibodies against the N terminus and extracellular loops 2/3 of CXCR4 confirm that the ubiquitin CXCR4 interaction is independent of the N-terminal receptor domain, whereas blockade of extracellular loops 2/3 prevents receptor binding and activation. Our findings define ubiquitin as a CXCR4 agonist, which does not interfere with productive cellular entry of HIV-1, and provide new mechanistic insights into interactions between CXCR4 and its natural ligands.

Quantitative phosphoproteomics of CXCL12 (SDF-1) signaling

CXCL12 (SDF-1) is a chemokine that binds to and signals through the seven transmembrane receptor CXCR4. The CXCL12/CXCR4 signaling axis has been implicated in both cancer metastases and human immunodeficiency virus type 1 (HIV-1) infection and a more complete understanding of CXCL12/CXCR4 signaling pathways may support efforts to develop therapeutics for these diseases. Mass spectrometry-based phosphoproteomics has emerged as an important tool in studying signaling networks in an unbiased fashion. We employed stable isotope labeling with amino acids in cell culture (SILAC) quantitative phosphoproteomics to examine the CXCL12/CXCR4 signaling axis in the human lymphoblastic CEM cell line. We quantified 4,074 unique SILAC pairs from 1,673 proteins and 89 phosphopeptides were deemed CXCL12-responsive in biological replicates. Several well established CXCL12-responsive phosphosites such as AKT (pS473) and ERK2 (pY204) were confirmed in our study. We also validated two novel CXCL12-responsive phosphosites, stathmin (pS16) and AKT1S1 (pT246) by Western blot. Pathway analysis and comparisons with other phosphoproteomic datasets revealed that genes from CXCL12-responsive phosphosites are enriched for cellular pathways such as T cell activation, epidermal growth factor and mammalian target of rapamycin (mTOR) signaling, pathways which have previously been linked to CXCL12/CXCR4 signaling. Several of the novel CXCL12-responsive phosphoproteins from our study have also been implicated with cellular migration and HIV-1 infection, thus providing an attractive list of potential targets for the development of cancer metastasis and HIV-1 therapeutics and for furthering our understanding of chemokine signaling regulation by reversible phosphorylation.

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.

Chemokine CXCL12 uses CXCR4 and a signaling core formed by bifunctional Akt, extracellular signal-regulated kinase (ERK)1/2, and mammalian target of rapamycin complex 1 (mTORC1) proteins to control chemotaxis and survival simultaneously in mature dendritic cells

Chemokines control several cell functions in addition to chemotaxis. Although much information is available on the involvement of specific signaling molecules in the control of single functions controlled by chemokines, especially chemotaxis, the mechanisms used by these ligands to regulate several cell functions simultaneously are completely unknown. Mature dendritic cells (maDCs) migrate through the afferent lymphatic vessels to the lymph nodes, where they regulate the initiation of the immune response. As maDCs are exposed to chemokine CXCL12 (receptors CXCR4 and CXCR7) during their migration, its functions are amenable to be regulated by this ligand. We have used maDCs as a model system to analyze the mechanisms whereby CXCL12 simultaneously controls chemotaxis and survival in maDCs. We show that CXCL12 uses CXCR4, but not CXCR7, and the components of a signaling core that includes G(i)/Gβγ, PI3K-α/-δ/-γ, Akt, ERK1/2 and mammalian target of rapamycin complex 1 (mTORC1), which organize hierarchically to control both functions. Downstream of Akt, Forkhead box class O (FOXO) regulates CXCL12-dependent survival, but not chemotaxis, suggesting that downstream of the aforementioned signaling core, additional signaling molecules may control more selectively CXCL12-dependent chemotaxis or survival. Finally, the data obtained also show that CXCR4 uses a signaling signature that is different from that used by CCR7 to control similar functions.

Characterization of CXCR4 expression in chondrosarcoma of bone

CONTEXT

Alterations in molecular elements derived from the CXC chemokine receptor 4 (CXCR4)/stromal-derived factor 1 (SDF-1) cytokine system have been found to strongly correlate with neoplastic progression leading to metastasis in a number of tumors, including osteosarcoma. Excluding hematologic malignancies, chondrosarcoma of bone is the most common primary malignant tumor of bone in adults in the United States. Like osteosarcoma, chondrosarcoma preferentially metastasizes to lung, bone, and very rarely to regional lymph nodes. However, the role of the signal pathway(s) driving neoplastic progression in chondrosarcoma has not yet been clearly elucidated.

OBJECTIVE

To test whether CXCR4 was detectable in chondrosarcoma and whether CXCR4 expression levels correlated with chondrosarcoma grade.

DESIGN

Twenty-two chondrosarcoma samples banked at our institution between 2001 and 2006 were retrieved for study. By using invasive ductal carcinoma of the breast and osteosarcoma as the positive controls, immunohistochemistry was performed on paraffin-embedded tissue sections and the intensity of the tumor cells was analyzed by morphometric techniques.

RESULTS

All chondrosarcoma cases (22 of 22) were immunoreactive for CXCR4. However, the staining intensity of the CXCR4 between the low- and high-grade groups was significantly different. There was a higher staining intensity in high-grade chondrosarcoma cells (P < .001).

CONCLUSION

CXCR4 is expressed in chondrosarcomas. CXCR4 expression levels were higher in high-grade chondrosarcoma cells than in low-grade specimens. A larger number of cases will be required to confirm these results and expand the observation, but preliminary data would argue for CXCR4 immunohistochemistry as a potential marker for biologic aggressiveness in chondrosarcoma of bone.

Chemokines: key players in cancer progression and metastasis

Instructed cell migration is a fundamental component of various biological systems and is critical to the pathogenesis of many diseases including cancer. Role of chemokines in providing navigational cues to migrating cancer cells bearing specific receptors is well established. However, functional mechanisms of chemokine are not well implicit, which is crucial for designing new therapeutics to control tumor growth and metastasis. Multiple functions and mode of actions have been advocated for chemokines and their receptors in the progression of primary and secondary tumors. In this review, we have discussed current advances in understanding the role of the chemokines and their corresponding receptor in tumor progression and metastasis.

Targeting SDF-1/CXCR4 to inhibit tumour vasculature for treatment of glioblastomas

Local recurrence of glioblastomas is a major cause of patient mortality after definitive treatment. This review discusses the roles of the chemokine stromal cell-derived factor-1 and its receptor CXC chemokine receptor 4 (CXCR4) in affecting the sensitivity of glioblastomas to irradiation. Blocking these molecules prevents or delays tumour recurrence after irradiation by inhibiting the recruitment of CD11b+ monocytes/macrophages that participate in revascularising the tumour. We review the literature pertaining to the mechanism by which revascularisation occurs following tumour irradiation using experimental models. Areas of interest and debate in the literature include the process by which endothelial cells die after irradiation and the identity/origin of the cells that reconstitute the tumour blood vessels after injury. Understanding the processes that mediate tumour revascularisation will guide the improvement of clinical strategies for preventing recurrence of glioblastoma after irradiation.

β2-Adrenergic receptor signaling in the cardiac myocyte is modulated by interactions with CXCR4

Chemokines are small secreted proteins with chemoattractant properties that play a key role in inflammation, metastasis, and embryonic development. We previously demonstrated a nonchemotactic role for one such chemokine pair, stromal cell-derived factor-1α and its G-protein coupled receptor, CXCR4. Stromal cell-derived factor-1/CXCR4 are expressed on cardiac myocytes and have direct consequences on cardiac myocyte physiology by inhibiting contractility in response to the nonselective β-adrenergic receptor (βAR) agonist, isoproterenol. As a result of the importance of β-adrenergic signaling in heart failure pathophysiology, we investigated the underlying mechanism involved in CXCR4 modulation of βAR signaling. Our studies demonstrate activation of CXCR4 by stromal cell-derived factor-1 leads to a decrease in βAR-induced PKA activity as assessed by cAMP accumulation and PKA-dependent phosphorylation of phospholamban, an inhibitor of SERCA2a. We determined CXCR4 regulation of βAR downstream targets is β2AR-dependent. We demonstrated a physical interaction between CXCR4 and β2AR as determined by coimmunoprecipitation, confocal microscopy, and BRET techniques. The CXCR4-β2AR interaction leads to G-protein signal modulation and suggests the interaction is a novel mechanism for regulating cardiac myocyte contractility. Chemokines are physiologically and developmentally relevant to myocardial biology and represent a novel receptor class of cardiac modulators. The CXCR4-β2AR complex could represent a hitherto unknown target for therapeutic intervention.

Evaluation of the combined expression of chemokine SDF-1α and its receptor CXCR4 as a prognostic marker for gastric cancer

Chemokine stromal cell-derived factor (SDF)-1α and its receptor CXC chemokine receptor 4 (CXCR4) have been shown to impact cancer progression. Accumulating evidence suggests that CXCR4 and SDF-1α expression is useful for evaluating the risk of gastric cancer progression. Thus, combined analysis of SDF-1α and CXCR4 should have high prognostic potential as a molecular marker for gastric cancer. We investigated the expression of SDF-1α and CXCR4 using immunohistochemistry in relation to prognosis, clinicopathological features and clinical outcomes in 221 cases of primary gastric cancer. Patients were categorized into three groups according to CXCR4 and SDF-1α expression: high CXCR4/high SDF-1α, low CXCR4/low SDF-1α, and high CXCR4/low SDF-1α - low CXCR4/high SDF-1α. No significant differences were noted in age, gender, histology, tumor location, lymphovascular invasion or proportion of tumor size >5 cm among the three groups. However, high CXCR4/high SDF-1α expression in tumor cells was significantly associated with depth of invasion of the tumor, lymph node involvement, and higher tumor stage compared to tumors with low CXCR4/low SDF-1α expression or high CXCR4/low SDF-1α - low CXCR4/high SDF-1α expression. Furthermore, patients with high CXCR4/high SDF-1α expression had the worst patient prognosis, whereas patients who had low CXCR4/low SDF-1α expression showed the most favorable prognosis. In conclusion, CXCR4 and SDF-1α are useful prognostic factors in gastric cancer, and the combination of high CXCR4 protein expression with high SDF-1α expression suggests a dismal prognosis.

Stromal-derived factor-1/CXCR4 signaling: indispensable role in homing and engraftment of hematopoietic stem cells in bone marrow

Homing and engraftment of hematopoietic stem/progenitor cells (HSPCs) in bone marrow is the major determining factor in success of hematopoietic stem cell transplantation. This is a complex, multistep process orchestrated by the coordinated interplay between adhesion molecules, cytokines, growth factors, and regulatory cofactors, many of which remain to be defined. Recent studies have highlighted the pivotal role of unique stromal-derived factor-1 (SDF-1)/CXCR4 signaling in the regulation of HSPC homing and subsequent engraftment. In addition, studies suggest that SDF-1/CXCR4 signaling acts as an essential survival-promoting factor of transplanted HSPCs as well as maintenance of quiescent HSCs in bone marrow niche. These pleiotropic effects exerted by SDF-1/CXCR4 axis make this unique signaling initiator very promising, not only for optimal hematopoietic reconstitution but also for the development of innovative approaches to achieve restoration, regeneration, or repair of other damaged tissues potentially amendable to reversal by stem cell transplantation. This goal can only be achieved when the role of SDF-1/CXCR4 axis in hematopoietic transplantation is clearly defined. Hence, this review presents current knowledge of the mechanisms through which SDF-1/CXCR4 signaling promotes restoration of hematopoiesis by regulating the homing and engraftment of HSPCs.

Conformational HIV-1 envelope on particulate structures: a tool for chemokine coreceptor binding studies

The human immunodeficiency virus type 1 (HIV-1) external envelope glycoprotein gp120 presents conserved binding sites for binding to the primary virus receptor CD4 as well as the major HIV chemokine coreceptors, CCR5 and CXCR4.

Concerted efforts are underway to understand the specific interactions between gp120 and coreceptors as well as their contribution to the subsequent membrane fusion process.

The present review summarizes the current knowledge on this biological aspect, which represents one of the key and essential points of the HIV-host cell interplay and HIV life cycle. The relevance of conformational HIV-1 Envelope proteins presented on Virus-like Particles for appropriate assessment of this molecular interaction, is also discussed.

Selective labelling of stromal cell-derived factor 1α with carboxyfluorescein to study receptor internalisation

SDF1α plays an important role in the regeneration of injured tissue after ischemia or stroke by inducing the migration of progenitor cells. In order to study the function of this therapeutically relevant chemokine site-specific protein labelling is of great interest. However, modification of SDF1α is complicated because of its complex tertiary structure. Here, we describe the first site-specific fluorescent modification of SDF1α by EPL. We recombinantly expressed SDF1α (1-49) by intein-mediated protein expression. The C-terminal peptide SDF1α (50-68) was synthesised by SPPS and selectively labelled with carboxyfluorescein at Lys(56). In a cell migration assay, M-[K(56)(CF)]SDF1α showed a clear potency to induce chemotaxis of human T-cell leukaemia cells. Microscopic analysis on HEK293 cells transfected with the CXCR4 revealed specific binding of the fluorescent ligand. Furthermore, receptor-induced internalisation of the ligand could be visualised. These results show that site-specific modification of SDF1α yields in a biologically functional molecule that allows the characterisation of CXCR4 production of cells on a molecular level.

[New prospects for chemokines]

Chemokines are small secreted proteins belonging to the cytokine family which were initially discovered for their chemoattractant properties for immune cells. Recently it was shown that chemokines and their G-protein-coupled receptors can be constitutively expressed or induced in several organs and different cell types. Thus chemokines have been shown to regulate immune functions involving infection and inflammation, stem cell migration during development, to be implicated in oncogenic, neovascularization and atherosclerosis processes, to modulate neuronal excitability regulating neurotransmitter release, and to play a key role in the pathogenesis of various neurodegenerative diseases such as Parkinson's disease or age-related-macular degeneration and in pain. Some of these recent advances concerning chemokine functions will be highlighted in this broad appeal symposium which aims to introduce this emerging field. This introductory chapter will examine the basic properties of the various chemokine systems and their receptors.

The chemokine CXCL12 regulates monocyte-macrophage differentiation and RUNX3 expression

Monocytes are versatile cells that can express different functional programs in response to microenvironmental signals. We show that primary blood monocytes secrete the CXCL12 chemokine, and express the CXCR4 and CXCR7 receptors, leading to an autocrine/paracrine loop that contribute to shape monocyte differentiation to a distinct type of macrophages, with an enhanced expression of CD4, CD14, and CD163, or dendritic cells, with a reduced functional ability to stimulate antigen-specific T-lymphocyte responses. The in vivo relevance of CXCL12 production by mononuclear phagocytes was studied in metastatic melanoma tissues by a thoroughly immunofluorescence phenotyping of CXCL12(high) expressing cells, which were CD45(+), coexpressed the macrophage antigens CD68, CD163, and CD209 and constituted the 60%-90% of tumor-associated macrophages. Microarray analysis of primary monocytes revealed that the vascular endothelial growth factor and the angiogenic chemokine CCL1 mRNA levels were up-regulated in response to CXCL12, leading to enhanced expression of both proteins. In addition, we found that CXCL12 autocrine/paracrine signaling down-regulates the expression of the transcription factor RUNX3 and contributes to maintain the long-term CD4 and CD14 expression in monocytes/macrophages. Together, these results suggest that autocrine CXCL12 production modulates differentiation of monocytes toward a distinct program with proangiogenic and immunosuppressive functions.

Epithelial and mesenchymal phenotypic switchings modulate cell motility in metastasis

The most ominous stage of cancer progression is metastasis, or the dissemination of carcinoma cells from the primary site into distant organs. Metastases are often resistant to current extirpative therapies and even the newest biological agents cure only a small subset of patients. Therefore a greater understanding of tumor biology that integrates properties intrinsic to carcinomas with tissue environmental modulators of behavior is needed. In no aspect of tumor progression is this more evident than the acquisition of cell motility that is critical for both escape from the primary tumor and colonization. In this overview, we discuss how this behavior is modified by carcinoma cell phenotypic plasticity that is evidenced by reversible switching between epithelial and mesenchymal phenotypes. The presence or absence of intercellular adhesions mediate these switches and dictate the receptivity towards signals from the extracellular milieu. These signals, which include soluble growth factors, cytokines, and extracellular matrix embedded with matrikines and matricryptines will be discussed in depth. Finally, we will describe a new mode of discerning the balance between epithelioid and mesenchymal movement.

Genomics of Acute Lung Injury and Vascular Barrier Dysfunction

Acute lung injury (ALI) is a devastating ­syndrome of diffuse alveolar damage that develops via a variety of local and systemic insults such as sepsis, trauma, ­pneumonia, and aspiration. It is interestingly to note that only a subset of individuals exposed to potential ALI-inciting insults develop the disorder and the severity of the disease varies from complete resolution to death. In addition, ALI susceptibility and severity are also affected by ethnicity as evidenced by the higher mortality rates observed in African-American ALI patients compared with other ethnic groups in the USA. Moreover, marked differences in strain-specific ALI responses to inflammatory and injurious agents are observed in preclinical animal models. Together, these observations strongly indicate genetic components to be involved in the pathogenesis of ALI. The identification of genes contributing to ALI would potentially provide a better understanding of ALI pathobiology, yield novel biomarkers, identify individuals or populations at risk, and prove useful for the development of novel and individualized therapies. Genome-wide searches in animal models have identified a number of quantitative trait loci that associate with ALI susceptibility. In this chapter, we utilize a systems biology approach combining cellular signaling pathway analysis with population- based association studies to review established and suspected candidate genes that contribute to dysfunction of endothelial cell barrier integrity and ALI susceptibility.

Role of endothelial chemokines and their receptors during inflammation

Chemokines are a large group of small cytokines known for their chemotactic ability to regulate the recruitment of leukocytes to sites of inflammation. This occurs through the binding of chemokines to their receptors located on the leukocyte that results in cellular changes such as actin rearrangement and cell shape, which allow for the migration of the leukocyte. In addition to regulating leukocyte function, it is now becoming apparent that other nonhematopoetic cells, such as smooth muscle cells and endothelial cells, can also be regulated by chemokines. Studies within the past 10 years has demonstrated the presence of various chemokine receptors on endothelial cells as well as the ability of chemokines to activate these receptors resulting in various cellular responses including migration, proliferation, and cellular activation. The purpose of this review is to highlight the research that has been done to date demonstrating the important role for chemokines in regulating endothelial function during various inflammatory conditions associated with angiogenesis, homeostasis, and leukocyte transmigration. This review will focus specifically on the role of the endothelium in mediating chemokine effects associated with wound healing, atherosclerosis, and autoimmune diseases, conditions where leukocyte recruitment and angiogenesis play a major role. Recent progress in the development and implementation of therapeutics agents against these small molecules, or their receptors, will also be addressed.

CXCR4 antagonist 4F-benzoyl-TN14003 inhibits leukemia and multiple myeloma tumor growth

OBJECTIVE

The chemokine receptor CXCR4 and its ligand CXCL12 are involved in the progression and dissemination of a diverse number of solid and hematological malignancies. Binding CXCL12 to CXCR4 activates a variety of intracellular signal transduction pathways that regulate cell chemotaxis, adhesion, survival, proliferation, and apoptosis.

MATERIALS AND METHODS

Here, we demonstrate that the CXCR4 antagonist, 4F-benzoyl-TN14003 (BKT140), but not AMD3100, exhibits a CXCR4-dependent preferential cytotoxicity toward malignant cells of hematopoietic origin. BKT140 significantly and preferentially stimulated multiple myeloma apoptotic cell death. BKT140 treatment induced morphological changes, phosphatidylserine externalization, decreased mitochondrial membrane potential, caspase-3 activation, sub-G1 arrest, and DNA double-stranded breaks.

RESULTS

In vivo, subcutaneous injections of BKT140 significantly reduced, in a dose-dependent manner, the growth of human acute myeloid leukemia and multiple myeloma xenografts. Tumors from animals treated with BKT140 were smaller in size and weights, had larger necrotic areas and high apoptotic scores.

CONCLUSIONS

Taken together, these results suggest a potential therapeutic use for BKT140 in multiple myeloma and leukemia patients.

The tetraspanin CD9 regulates migration, adhesion, and homing of human cord blood CD34+ hematopoietic stem and progenitor cells

The stromal cell-derived factor-1 (SDF-1)/chemokine C-X-C receptor 4 (CXCR4) axis plays a critical role in homing and engraftment of hematopoietic stem/progenitor cells (HSCs) during bone marrow transplantation. To investigate the transcriptional regulation provided by this axis, we performed the first differential transcriptome profiling of human cord blood CD34(+) cells in response to short-term exposure to SDF-1 and identified a panel of genes with putative homing functions. We demonstrated that CD9, a member of the tetraspanin family of proteins, was expressed in CD34(+)CD38(-/lo) and CD34(+)CD38(+) cells. CD9 levels were enhanced by SDF-1, which simultaneously down-regulated CXCR4 membrane expression. Using specific inhibitors and activators, we demonstrated that CD9 expression was modulated via CXCR4, G-protein, protein kinase C, phospholipase C, extracellular signal-regulated kinase, and Janus kinase 2 signals. Pretreatment of CD34(+) cells with the anti-CD9 monoclonal antibody ALB6 significantly inhibited SDF-1-mediated transendothelial migration and calcium mobilization, whereas adhesion to fibronectin and endothelial cells was enhanced. Pretreatment of CD34(+) cells with ALB6 significantly impaired their homing to bone marrow and spleen of sublethally irradiated NOD/SCID (nonobese diabetic/severe combined immune-deficient) mice. Sorted CD34(+)CD9(-) cells displayed lower bone marrow homing capacity compared with that of total CD34(+) cells. CD9 expression on homed CD34(+) cells was significantly up-regulated in vivo. Our results indicate that CD9 might possess specific functions in HSC homing.

Basal and steroid hormone-regulated expression of CXCR4 in human endometrium and endometriosis

Endometriosis is associated with activation of local and systemic inflammatory mechanisms, including increased levels of chemokines and other proinflammatory cytokines. We have previously reported increased gene expression of chemokine receptor 4 (CXCR4), the receptor for CXCL12, in lesions of the rat model of endometriosis. The CXCR4-CXCL12 axis has been shown to have both immune (HIV infection, lymphocyte chemotaxis) and nonimmune functions, including roles in tissue repair, angiogenesis, invasion, and migration. There is evidence indicating that these mechanisms are also at play in endometriosis; therefore, we hypothesized that activation of the CXCR4-CXCL12 axis could be responsible, at least in part, for the survival and establishment of endometrial cells ectopically. Immunohistochemistry (IHC) showed that CXCR4 protein levels were significantly higher in endometriotic lesions compared to the endometrium of controls. Next, we determined basal gene and protein expression of CXCR4 and CXCL12 and regulation by estradiol (E2) and/or progesterone (P4) in endometrial cell lines using quantitative polymerase chain reaction (qPCR), and Western blots. Basal CXCR4 gene expression levels were higher in epithelial versus stromal cells; conversely, CXCL12 was expressed at higher levels in stromal vs epithelial cells. CXCR4 gene expression was significantly downregulated by ovarian steroid hormones in endometrial epithelial. These data suggest that steroid modulation of CXCR4 is defective in endometriosis, although the specific mechanism involved remains to be elucidated. These findings have implications for future therapeutic strategies specifically targeting the inflammatory component in endometriosis.

SDF-1/CXCR4-mediated migration of transplanted bone marrow stromal cells toward areas of heart myocardial infarction through activation of PI3K/Akt

Stromal cell-derived factor-1 (SDF-1) and its receptor, CXCR4, are crucial for homing and migration of multiple stem cell types. Their potential role in mediating bone marrow-derived mesenchymal stem cell (BMSC) migration in areas of myocardial infarction (MI) has not been demonstrated. In this study, rat heart MI was created by left coronary artery ligation, and green fluorescent protein-labeled BMSCs were directly infused into the left ventricular cavity. Reverse transcriptase-polymerase chain reaction and Western blot analysis showed that SDF-1 was predominantly localized in the MI lesion, and its levels peaked by 3 to 7 days and were maintained at least 14 days. Additionally, this was matched with increased accumulation of BMSCs and an improvement in cardiac function. Furthermore, this effect was blocked by the phosphoinositide 3-kinase inhibitor, LY294002. In vitro experiments showed that CXCR4 expression by BMSCs was elevated during hypoxia and SDF-1 induced a concentration-dependent migration of BMSCs. This migration was CXCR4-dependent as confirmed by its total inhibition by AMD3100, a CXCR4-specific antagonist. Migration was also almost completely blocked by LY294002. Analysis showed that phosphorylated Akt was highly increased in SDF-1-treated BMSCs. Together these results demonstrated that SDF-1/CXCR4 may mediate the migration of BMSCs toward heart MI through activation of PI3K/Akt.

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.

Integrating chemotaxis and contact-inhibition during collective cell migration: Small GTPases at work

For directional cell migration to occur cells must interpret guiding cues present in their environment. Chemotaxis based on negative or positive signals has been long thought as the main driving force of guided cell migration. However during collective cell migration cells do receive information from external signals but also upon interactions with their direct neighbours. These multiple inputs must be translated into intracellular reorganisation in order to promote efficient directional migration. Small GTPases, being involved in establishing cell polarity and regulating protrusive activity, are likely to play a central role in signal integration. Indeed, recent findings from our laboratory indicate that Contact-Inhibition of Locomotion controlled by N-Cadherin and chemotaxis dependent on Sdf1/Cxcr4 signaling converge towards regulation of the localized activity of RhoA and Rac1. All together they establish cell polarity and select well-oriented cell protrusions to ensure directional cell migration.

HIV-1 inhibits autophagy in bystander macrophage/monocytic cells through Src-Akt and STAT3

Autophagy is a homeostatic mechanism of lysosomal degradation. Defective autophagy has been linked to various disorders such as impaired control of pathogens and neurodegeneration. Autophagy is regulated by a complex array of signaling pathways that act upstream of autophagy proteins. Little is known about the role of altered regulatory signaling in disorders associated with defective autophagy. In particular, it is not known if pathogens inhibit autophagy by modulation of upstream regulatory pathways. Cells infected with HIV-1 blocked rapamycin-induced autophagy and CD40-induced autophagic killing of Toxoplasma gondii in bystander (non-HIV-1 infected) macrophage/monocytic cells. Blockade of autophagy was dependent on Src-Akt and STAT3 triggered by HIV-1 Tat and IL-10. Neutralization of the upstream receptors VEGFR, beta-integrin or CXCR4, as well as of HIV-1 Tat or IL-10 restored autophagy in macrophage/monocytic cells exposed to HIV-1-infected cells. Defective autophagic killing of T. gondii was detected in monocyte-derived macrophages from a subset of HIV-1(+) patients. This defect was also reverted by neutralization of Tat or IL-10. These studies revealed that a pathogen can impair autophagy in non-infected cells by activating counter-regulatory pathways. The fact that pharmacologic manipulation of cell signaling restored autophagy in cells exposed to HIV-1-infected cells raises the possibility of therapeutic manipulation of cell signaling to restore autophagy in HIV-1 infection.

CXCL12-induced glioblastoma cell migration requires intermediate conductance Ca2+-activated K+ channel activity

The activation of ion channels is crucial during cell movement, including glioblastoma cell invasion in the brain parenchyma. In this context, we describe for the first time the contribution of intermediate conductance Ca2+-activated K (IKCa) channel activity in the chemotactic response of human glioblastoma cell lines, primary cultures, and freshly dissociated tissues to CXC chemokine ligand 12 (CXCL12), a chemokine whose expression in glioblastoma has been correlated with its invasive capacity. We show that blockade of the IKCa channel with its specific inhibitor 1-[(2-chlorophenyl) diphenylmethyl]-1 H-pyrazole (TRAM-34) or IKCa channel silencing by short hairpin RNA (shRNA) completely abolished CXCL12-induced cell migration. We further demonstrate that this is not a general mechanism in glioblastoma cell migration since epidermal growth factor (EGF), which also activates IKCa channels in the glioblastoma-derived cell line GL15, stimulate cell chemotaxis even if the IKCa channels have been blocked or silenced. Furthermore, we demonstrate that both CXCL12 and EGF induce Ca2+ mobilization and IKCa channel activation but only CXCL12 induces a long-term upregulation of the IKCa channel activity. Furthermore, the Ca2+-chelating agent BAPTA-AM abolished the CXCL12-induced, but not the EGF-induced, glioblastoma cell chemotaxis. In addition, we demonstrate that the extracellular signal-regulated kinase (ERK)1/2 pathway is only partially implicated in the modulation of CXCL12-induced glioblastoma cell movement, whereas the phosphoinositol-3 kinase (PI3K) pathway is not involved. In contrast, EGF-induced glioblastoma migration requires both ERK1/2 and PI3K activity. All together these findings suggest that the efficacy of glioblastoma invasiveness might be related to an array of nonoverlapping mechanisms activated by different chemotactic agents.

The omentum is a site of stromal cell-derived factor 1alpha production and reservoir for CXC chemokine receptor 4-positive cell recruitment

BACKGROUND

The mechanism of the omental response to injury remains poorly defined. This study investigates the omental reaction to a foreign body, examining the role of a chemokine ligand/receptor pair known to play a crucial role in angiogenesis and wound healing.

METHODS

A ventral hernia, surgically created in the abdominal wall of 6 swine, was repaired with silicone sheeting to activate the omentum. Omental thickness was determined by ultrasonography. Serial stromal cell-derived factor 1alpha (SDF-1alpha) concentrations were measured in blood, wound, and peritoneal fluids by enzyme-linked immunosorbent assay.

RESULTS

During the 14-day study period, serial ultrasonography showed a 20-fold increase in omental thickness, and enzyme-linked immunosorbent assay revealed a 4-fold increase in SDF-1alpha concentration in local wound fluid. Omental vessel count and vascular surface area were 8- to 10-fold higher in reactive omentum. Immunohistochemistry showed nearly complete replacement of control omental fat with CXC chemokine receptor 4 (CXCR4)-positive cells by day 14.

CONCLUSIONS

Activated omentum, important in the SDF-1alpha/CXCR4 axis, may serve as an intraperitoneal reservoir for recruitment of circulating bone marrow-derived cells vital to healing.

The chemokine SDF-1/CXCL12 contributes to the 'homing' of umbilical cord blood cells to a hypoxic-ischemic lesion in the rat brain

Previous studies have shown that transplanted human umbilical cord blood (hUCB)-derived mononuclear cells exert therapeutic effects in various animal models of CNS impairments, including those of perinatal hypoxic-ischemic brain injury. However, the mechanisms of how transplanted cells exert their beneficial effects on the damaged tissue are still unclear. As detection of hUCB cells at the lesion site coincides with the therapeutic effects observed in our model, we investigated the role of the chemokine stromal derived factor (SDF)-1 (CXCL12) as a possible candidate for chemotaxis-mediated 'homing' of transplanted hUCB cells to a hypoxic-ischemic lesion in the perinatal rat brain. Following the hypoxic-ischemic insult expression of SDF-1 significantly increased in lesioned brain hemispheres and was mainly associated with astrocytes. Transplanted hUCB cells expressing the SDF-1 receptor CXCR4 migrated to the lesion site within one day. Inhibition of SDF-1 by application of neutralizing antibodies in vivo resulted in a significantly reduced number of hUCB cells at the lesioned area. The increase in glial SDF-1 expression shortly after induction of the lesion and hUCB cells expressing the corresponding receptor makes SDF-1 a potential chemotactic factor for hUCB cell migration. The reduction of hUCB cells present at the lesion site upon functional inhibition of SDF-1 strengthens the view that the SDF-1/CXCR4 axis is of major importance for cell 'homing'.

Protein kinase B (PKB/c-akt) regulates homing of hematopoietic progenitors through modulation of their adhesive and migratory properties

Limited number of hematopoietic stem cells in umbilical cord blood (UCB) presents a problem when using UCB for stem cell transplantation. Improving their homing capacity could reduce the need for high initial cell numbers during transplantation procedures. Although it is evident that protein kinase B (PKB/c-Akt) plays an important role in regulation of migration of various cell types, a role for PKB in regulation of migration and homing of human hematopoietic stem and progenitor cells remains to be determined. PKB activity was found to be required for induction of adhesion to bone marrow-derived stromal cells and detrimental for migration of UCB-derived CD34(+) hematopoietic progenitors. In addition, PKB activity was found to positively regulate integrin expression. CD34(+) hematopoietic progenitors, and their capacity to form colonies in vitro, were not affected by transient inhibition of PKB. Finally, transplantation of β2-microglobulin(-/-) nonobese diabetic/severe combined immunodeficient mice with CD34(+) cells ectopically expressing constitutively active PKB resulted in reduced migration to the bone marrow, whereas inhibition of PKB activity resulted in an induction in bone marrow homing and engraftment. These results indicate that transient inhibition of PKB activity may provide a means for ex vivo stem cell manipulation to improve bone marrow transplantation regimes.