SDF-1/CXCL12 regulates cAMP production and ion transport in intestinal epithelial cells via CXCR4

Human colonic epithelial cells express CXCR4, the sole cognate receptor for the chemokine stromal cell-derived factor (SDF)-1/CXC chemokine ligand (CXCL) 12. The aim of this study was to define the mechanism and functional consequences of signaling intestinal epithelial cells through the CXCR4 chemokine receptor. CXCR4, but not SDF-1/CXCL12, was constitutively expressed by T84, HT-29, HT-29/-18C1, and Caco-2 human colon epithelial cell lines. Studies using T84 cells showed that CXCR4 was G protein-coupled in intestinal epithelial cells. Moreover, stimulation of T84 cells with SDF-1/CXCL12 inhibited cAMP production in response to the adenylyl cyclase activator forskolin, and this inhibition was abrogated by either anti-CXCR4 antibody or receptor desensitization. Studies with pertussis toxin suggested that SDF-1/CXCL12 activated negative regulation of cAMP production through G(i)alpha subunits coupled to CXCR4. Consistent with the inhibition of forskolin-stimulated cAMP production, SDF-1/CXCL12 also inhibited forskolin-induced ion transport in voltage-clamped polarized T84 cells. Taken together, these data indicate that epithelial CXCR4 can transduce functional signals in human intestinal epithelial cells that modulate important cAMP-mediated cellular functions.     

The role of CXCR7/RDC1 as a chemokine receptor for CXCL12/SDF-1 in prostate cancer

Several reports have recently documented that CXCR7/RDC1 functions as a chemokine receptor for SDF-1/CXCL12, which regulates a spectrum of normal and pathological processes. In this study, the role of CXCR7/RDC1 in prostate cancer (PCa) was explored. Staining of high density tissue microarrays demonstrates that the levels of CXCR7/RDC1 expression increase as the tumors become more aggressive. In vitro and in vivo studies with PCa cell lines suggest that alterations in CXCR7/RDC1 expression are associated with enhanced adhesive and invasive activities in addition to a survival advantage. In addition, it was observed that CXCR7/RDC1 levels are regulated by CXCR4. Among the potential downstream targets of CXCR7/RDC1 are CD44 and cadherin-11, which are likely to contribute to the invasiveness of PCa cells. CXCR7/RDC1 also regulates the expression of the proangiogenic factors interleukin-8 or vascular endothelial growth factor, which are likely to participate in the regulation of tumor angiogenesis. Finally, we found that signaling by CXCR7/RDC1 activates AKT pathways. Together, these data demonstrate a role for CXCR7/RDC1 in PCa metastasis and progression and suggest potential targets for therapeutic intervention.     

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.     

Grk2 is an Essential Regulator of CXCR7 Signalling in Astrocytes

We previously demonstrated that in astrocytes, SDF-1/CXCL12 exclusively signals through CXCR7 despite the additional presence of the alternate SDF-1/CXCL12 receptor, CXCR4. In addition, we provided evidence that astrocytic CXCR7-signalling involves a G protein-dependent mechanism. This is insofar remarkable as in all other cell types studied to date, CXCR7 either acts as a scavenger chemokine receptor, a modulator of CXCR4, or a non-classical chemokine receptor, signalling through ß-arrestin. To begin to unravel the molecular framework impinging the selective function of CXCR7 on a given cell type, we have now analysed the role of G protein-coupled receptor kinases (Grks) in astrocytic CXCR7 signalling. We demonstrate that Grk2 mediates signalling of SDF-1/CXCL12-bound CXCR7 as suggested by the finding that SDF-1/CXCL12-induced activation of Erk1/2 and Akt is abrogated following RNAi-mediated inhibition of Grk2, but not of Grk3, Grk5, or Grk6. We further unravel that Grk2 additionally controls signalling of SDF-1/CXCL12-bound CXCR7 in astrocytes by mediating internalization and subsequent silencing of CXCR7. Finally, we demonstrate that Grk2 is likewise expressed by microglial cells and Schwann cells, cell types in which CXCR7 does not act as a classical chemokine receptor. In conclusion, our findings establish that Grk2 tightly controls CXCR7 signalling in astrocytes, but does not imprint the cell type-specific function of this chemokine receptor.     

Long-term high-fat diet induces pancreatic injuries via pancreatic microcirculatory disturbances and oxidative stress in rats with hyperlipidemia

Stromal cell-derived factor 1 (CXCL12) is an angiogenic chemokine that is believed to act solely via its cognate receptor CXCR4. Evidence is now provided for the existence of a different CXCL12 binding and signaling receptor on endothelial cells. Bovine aortic endothelial cells (BAECs) strongly expressed CXCR4 and exhibited high binding capacity for fluorescently labeled CXCL12. However, CXCL12 binding was not correlated with the CXCR4 expression level and was virtually unaffected by the specific CXCR4 antagonists AMD3100 or T22. Similar observations were made in endothelial cells of mouse and human origin. Also, AMD3100 failed to block CXCL12 internalization and CXCL12-induced intracellular signal transduction via extracellular signal-regulated kinases 1/2 in BAECs. In contrast, CXCL12 binding and signaling were almost completely inhibited by the CXCR4 antagonist in T-lymphoid SupT1 cells. Together, our data point to the existence of an additional receptor through which CXCL12 exerts its biological effects in endothelial cells.     

The peptidomimetic CXCR4 antagonist TC14012 recruits beta-arrestin to CXCR7: roles of receptor domains

CXCR7 is an atypical chemokine receptor that signals through β-arrestin in response to agonists without detectable activation of heterotrimeric G-proteins. Its cognate chemokine ligand CXCL12 also binds CXCR4, a chemokine receptor of considerable clinical interest. Here we report that TC14012, a peptidomimetic inverse agonist of CXCR4, is an agonist on CXCR7. The potency of β-arrestin recruitment to CXCR7 by TC14012 is much higher than that of the previously reported CXCR4 antagonist AMD3100 and differs only by one log from that of the natural ligand CXCL12 (EC(50) 350 nM for TC14012, as compared with 30 nM for CXCL12 and 140 μM for AMD3100). Moreover, like CXCL12, TC14012 leads to Erk 1/2 activation in U373 glioma cells that express only CXCR7, but not CXCR4. Given that with TC14012 and AMD3100 two structurally unrelated CXCR4 antagonists turn out to be agonists on CXCR7, this likely reflects differences in the activation mechanism of the arrestin pathway by both receptors. To identify the receptor domain responsible for these opposed effects, we investigated CXCR4 and CXCR7 C terminus-swapping chimeras. Using quantitative bioluminescence resonance energy transfer, we find that the CXCR7 receptor core formed by the seven-transmembrane domains and the connecting loops determines the agonistic activity of both TC14012 and AMD3100. Moreover, we find that the CXCR7 chimera bearing the CXCR4 C-terminal constitutively associates with arrestin in the absence of ligands. Our data suggest that the CXCR4 and CXCR7 cores share ligand-binding surfaces for the binding of the synthetic ligands, indicating that CXCR4 inhibitors should be tested also on CXCR7.     

CXCR7 Functions as a Scavenger for CXCL12 and CXCL11

Background

CXCR7 (RDC1), the recently discovered second receptor for CXCL12, is phylogenetically closely related to chemokine receptors, but fails to couple to G-proteins and to induce typical chemokine receptor mediated cellular responses. The function of CXCR7 is controversial. Some studies suggest a signaling activity in mammalian cells and zebrafish embryos, while others indicate a decoy activity in fish. Here we investigated the two propositions in human tissues.

Methodology/Principal Findings

We provide evidence and mechanistic insight that CXCR7 acts as specific scavenger for CXCL12 and CXCL11 mediating effective ligand internalization and targeting of the chemokine cargo for degradation. Consistently, CXCR7 continuously cycles between the plasma membrane and intracellular compartments in the absence and presence of ligand, both in mammalian cells and in zebrafish. In accordance with the proposed activity as a scavenger receptor CXCR7-dependent chemokine degradation does not become saturated with increasing ligand concentrations. Active CXCL12 sequestration by CXCR7 is demonstrated in adult mouse heart valves and human umbilical vein endothelium.

Conclusions/Significance

The finding that CXCR7 specifically scavenges CXCL12 suggests a critical function of the receptor in modulating the activity of the ubiquitously expressed CXCR4 in development and tumor formation. Scavenger activity of CXCR7 might also be important for the fine tuning of the mobility of hematopoietic cells in the bone marrow and lymphoid organs.     

Secreted CXCL12 (SDF-1) forms dimers under physiological conditions

Chemokine CXCL12 (CXC chemokine ligand 12) signalling through CXCR (CXC chemokine receptor) 4 and CXCR7 has essential functions in development and underlies diseases including cancer, atherosclerosis and autoimmunity. Chemokines may form homodimers that regulate receptor binding and signalling, but previous studies with synthetic CXCL12 have produced conflicting evidence for homodimerization. We used bioluminescence imaging with GL (Gaussia luciferase) fusions to investigate dimerization of CXCL12 secreted from mammalian cells. Using column chromatography and GL complementation, we established that CXCL12 was secreted from mammalian cells as both monomers and dimers. Secreted CXCL12 also formed homodimers in the extracellular space. Monomeric CXCL12 preferentially activated CXCR4 signalling through Gαi and Akt, whereas dimeric CXCL12 more effectively promoted recruitment of β-arrestin 2 to CXCR4 and chemotaxis of CXCR4-expressing breast cancer cells. We also showed that CXCR7 preferentially sequestered monomeric CXCL12 from the extracellular space and had minimal effects on dimeric CXCL12 in cell-based assays and an orthotopic tumour xenograft model of human breast cancer. These studies establish that CXCL12 secreted from mammalian cells forms homodimers under physiological conditions. Since monomeric and dimeric CXCL12 have distinct effects on cell signalling and function, our results have important implications for ongoing efforts to target CXCL12 pathways for therapy.     

Characterization of human T cells that regulate neutrophilic skin inflammation

It is unknown whether neutrophilic inflammations can be regulated by T cells. This question was analyzed by studying acute generalized exanthematous pustulosis (AGEP), which is a severe drug hypersensitivity resulting in intraepidermal or subcorneal sterile pustules. Recently, we found that drug-specific blood and skin T cells from AGEP patients secrete high levels of the potent neutrophil-attracting chemokine IL-8/CXCL8. In this study, we characterize the phenotype and function of CXCL8-producing T cells. Supernatants from CXCL8(+) T cells were strongly chemotactic for neutrophils, CXCR1, and CXCR2 transfectants, but not for transfectants expressing CXCR4, CX3CR1, human chemokine receptor, and RDC1. Neutralization experiments indicated that chemotaxis was mainly mediated by CXCL8, but not by granulocyte chemotactic protein-2/CXCL6, epithelial cell-derived neutrophil attractant-78/CXCL5, or growth-related oncogene-alpha,beta,gamma/CXCL1,2,3. Interestingly, approximately 2.5% of CD4(+) T cells in normal peripheral blood also produced CXCL8. In addition to CXCL8, AGEP T cells produced large amounts of the monocyte/neutrophil-activating cytokine GM-CSF, and the majority released IFN-gamma and the proinflammatory cytokine TNF-alpha. Furthermore, apoptosis in neutrophils treated with conditioned medium from CXCL8(+) T cells could be reduced by 40%. In lesional skin, CXCL8(+) T cells consistently expressed the chemokine receptor CCR6, suggesting a prominent role for CCR6 in early inflammatory T cell recruitment. Finally, our data suggest that CXCL8-producing T cells facilitate skin inflammation by orchestrating neutrophilic infiltration and ensuring neutrophil survival, which leads to sterile pustular eruptions found in AGEP patients. This mechanism may be relevant for other T cell-mediated diseases with a neutrophilic inflammation such as Beh?et's disease and pustular psoriasis.     

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.     

Follicular dendritic cell regulation of CXCR4-mediated germinal center CD4 T cell migration

Follicular dendritic cells (FDCs) up-regulate the chemokine receptor CXCR4 on CD4 T cells, and a major subpopulation of germinal center (GC) T cells (CD4(+)CD57(+)), which are adjacent to FDCs in vivo, expresses high levels of CXCR4. We therefore reasoned that GC T cells would actively migrate to stromal cell-derived factor-1 (CXCL12), the CXCR4 ligand, and tested this using Transwell migration assays with GC T cells and other CD4 T cells (CD57(-)) that expressed much lower levels of CXCR4. Unexpectedly, GC T cells were virtually nonresponsive to CXCL12, whereas CD57(-)CD4 T cells migrated efficiently despite reduced CXCR4 expression. In contrast, GC T cells efficiently migrated to B cell chemoattractant-1/CXCL13 and FDC supernatant, which contained CXCL13 produced by FDCs. Importantly, GC T cell nonresponsiveness to CXCL12 correlated with high ex vivo expression of regulator of G protein signaling (RGS), RGS13 and RGS16, mRNA and expression of protein in vivo. Furthermore, FDCs up-regulated both RGS13 and RGS16 mRNA expression in non-GC T cells, resulting in their impaired migration to CXCL12. Finally, GC T cells down-regulated RGS13 and RGS16 expression in the absence of FDCs and regained migratory competence to CXCL12. Although GC T cells express high levels of CXCR4, signaling through this receptor appears to be specifically inhibited by FDC-mediated expression of RGS13 and RGS16. Thus, FDCs appear to directly affect GC T cell migration within lymphoid follicles.     

A naturally occurring splice variant of CXCL12/stromal cell-derived factor 1 is a potent human immunodeficiency virus type 1 inhibitor with weak chemotaxis and cell survival activities

CXCL12/stromal cell-derived factor 1 is a member of the CXC family of chemokines that plays an important role in hematopoiesis and signals through CXCR4 and CXCR7. Two splice variants of human CXCL12 (CXCL12alpha and CXCL12beta) induce chemotaxis of CXCR4(+) cells and inhibit X4 infection. Recent studies described four other novel splice variants of human CXCL12; however, their antiviral activities were not investigated. We constructed and expressed all of the CXCL12 splice variants in Escherichia coli. Recombinant proteins were purified through a His affinity column, and their biological properties were analyzed. All six CXCL12 variants induced chemotaxis of CXCR4(+) and CXCR7(+) cell lines. Enhancement of survival and replating capacity of human hematopoietic progenitor cells were observed with CXCL12alpha, CXCL12beta, and CXCL12epsilon but not with the other variants. CXCL12gamma showed the greatest antiviral activity in X4 inhibition assays and the weakest chemotaxis activity through CXCR4. The order of potency in X4 inhibition assays was as follows: CXCL12gamma > CXCL12beta > CXCL12alpha > CXCL12theta > CXCL12epsilon > CXCL12delta. The order of anti-human immunodeficiency virus (HIV) activity was associated with the number of BBXB motifs present in each variant; the most potent inhibitor was CXCL12gamma, with five BBXB domains. The results suggest that the different C termini of CXCL12 variants may contain important molecular determinants for the observed differences in antiviral effects and other biological functions. These studies implicate CXCL12gamma as a potent HIV-1 entry inhibitor with significantly reduced chemotaxis activity and small or absent effects on progenitor cell survival or replating capacity, providing important insight into the structure-function relationships of CXCL12.     

CXCL14 is no direct modulator of CXCR4

C-X-C motif chemokine 12/C-X-C chemokine receptor type 4 (CXCL12/CXCR4) signaling is involved in ontogenesis, hematopoiesis, immune function and cancer. Recently, the orphan chemokine CXCL14 was reported to inhibit CXCL12-induced chemotaxis – probably by allosteric modulation of CXCR4. We thus examined the effects of CXCL14 on CXCR4 regulation and function using CXCR4-transfected human embryonic kidney (HEK293) cells and Jurkat T cells. CXCL14 did not affect dose–response profiles of CXCL12-induced CXCR4 phosphorylation, G protein-mediated calcium mobilization, dynamic mass redistribution, kinetics of extracellular signal-regulated kinase 1 (ERK1) and ERK2 phosphorylation or CXCR4 internalization. Hence, essential CXCL12-operated functions of CXCR4 are insensitive to CXCL14, suggesting that interactions of CXCL12 and CXCL14 pathways depend on a yet to be identified CXCL14 receptor.     

SDF-1/CXCR4在肿瘤信号转导中作用的分子机制

CXC趋化因子受体4(CXCR4)是最主要的趋化因子受体之一,在多种类型细胞中均有表达,包括淋巴细胞、造血干细胞、内皮细胞和肿瘤细胞。CXCR4与其配体——基质细胞衍生因子1(SDF-1)(也称CXCL12)结合,能介导多种与细胞趋化、细胞存活或增殖相关信号传导通路。CXCR4与SDF-1轴涉及肿瘤的恶性演进、血管生成、转移和存活。因此,阻断CXCR4与SDF-1轴及下游信号通路成为相关治疗的分子靶标。     

The chemokine SDF1a coordinates tissue migration through the spatially restricted activation of Cxcr7 and Cxcr4b

Tissue migration is a collective behavior that plays a key role in the formation of many organ systems. Although tissue movements are guided by extrinsic cues, in many contexts, their receptors need to be active only at the leading edge to ensure morphogenesis. This has led to the prevalent view that extrinsic signals exert their influence by controlling a small number of leader cells. The zebrafish lateral-line primordium is a cohesive cohort of over 100 cells that is guided through CXCR4-SDF1 signaling. Recent work has shown that Cxcr4b activity is only required in cells at the very tip, raising the question of what controls cell behavior within trailing regions. Here, we present the first mutant in zebrafish SDF1a/CXCL12a and show, surprisingly, that the resultant phenotype is stronger than a null mutation in its cognate receptor, Cxcr4b, indicating the involvement of other SDF1a receptors. A candidate approach identified Cxcr7/RDC1, whose expression is restricted to cells behind the leading edge. Morpholino knockdown of Cxcr7 leads to a novel phenotype in which the migration of trailing cells is specifically affected, causing tissue stretching, a defect rescued by the reintroduction of wild-type cells specifically at the back of the primordium. Finally, we present evidence that Cxcr4b and Cxcr7 act independently to regulate group migration. We provide the first example where a single extrinsic guidance cue, SDF1a, directly controls the migration of both leading and trailing edges of a tissue through the activation of two independent receptors, CXCR4b and CXCR7.     

Syndecan-4 is a signaling molecule for stromal cell-derived factor-1 (SDF-1)/ CXCL12

Stromal cell-derived factor-1 (SDF-1)/CXCL12, the ligand for CXCR4, induces signal transduction. We previously showed that CXCL12 binds to high- and low-affinity sites expressed by primary cells and cell lines, and forms complexes with CXCR4 as expected and also with a proteoglycan, syndecan-4, but does not form complexes with syndecan-1, syndecan-2, CD44 or beta-glycan. We also demonstrated the occurrence of a CXCL12-independent heteromeric complex between CXCR4 and syndecan-4. However, our data ruled out the glycosaminoglycan-dependent binding of CXCL12 to HeLa cells facilitating the binding of this chemokine to CXCR4. Here, we demonstrate that CXCL12 directly binds to syndecan-4 in a glycosaminoglycan-dependent manner. We show that upon stimulation of HeLa cells by CXCL12, CXCR4 becomes tyrosine phosphorylated as expected, while syndecan-4 (but not syndecan-1, syndecan-2 or beta-glycan) also undergoes such tyrosine phosphorylation. Moreover, tyrosine-phosphorylated syndecan-4 from CXCL12-stimulated HeLa cells physically coassociates with tyrosine phosphorylated CXCR4. Pretreatment of the cells with heparitinases I and III prevented the tyrosine phosphorylation of syndecan-4, which suggests that the heparan sulfate-dependent binding of SDF-1 to this proteoglycan is involved. Finally, by reducing syndecan-4 expression using RNA interference or by pretreating the cells with heparitinase I and III mixture, we suggest the involvement of syndecan-4 and heparan sulfate in p44/p42 mitogen-activated protein kinase and Jun N-terminal/stress-activated protein kinase activation by action of CXCL12 on HeLa cells. However, these treatments did not modify the calcium mobilization induced by CXCL12 in these cells. Therefore, syndecan-4 behaves as a CXCL12 receptor, selectively involved in some transduction pathways induced by SDF-1, and heparan sulfate plays a role in these events.     

Fluorescent CXCL12AF647 as a novel probe for nonradioactive CXCL12/CXCR4 cellular interaction studies.

BACKGROUND: Chemokines drive the migration of leukocytes via interaction with specific G protein-coupled 7-transmembrane receptors. The chemokine ligand/receptor pair stromal cell-derived factor-1 (SDF-1, CXCL12)/CXCR4 is gaining increasing interest because of its involvement in the metastasis of several types of cancer and in certain inflammatory autoimmune disorders such as rheumatoid arthritis. In addition, CXCR4 serves as an important coreceptor for cellular entry of T-tropic strains of human immunodeficiency virus (HIV). Therefore, potent and specific CXCR4 antagonists may have therapeutic potential as anti-HIV, anti-cancer, and anti-inflammatory drugs. METHODS AND RESULTS: Chemokine receptor antagonists can be identified by their ability to inhibit ligand binding to the receptor protein. Until now, chemokine binding assays were mostly performed with radiolabeled chemokine ligands such as [(125)I]CXCL12. To overcome the practical problems associated with such radioactive chemokine binding assays, we have developed a flow cytometric technique using a new, commercially available Alexa Fluor 647 conjugate of CXCL12 (CXCL12(AF647)). Calcium flux, chemotaxis, and p44/42 mitogen-activated protein kinase phosphorylation assays showed that the agonistic activity of the fluorescent CXCL12 was unchanged as compared with that of unlabeled CXCL12. Human T-lymphoid (CXCR4(+)) SupT1 cells and CXCR4-transfected, but not CCR5- or CXCR3-transfected, human astroglioma U87.CD4 cells specifically bound CXCL12(AF647) in a concentration-dependent manner. Unlabeled CXCL12 and the well-known CXCR4 inhibitors, AMD3100 and T22, blocked the binding of CXCL12(AF647) to SupT1 cells with 50% inhibitory concentrations of 92, 13, and 8 ng/ml, respectively. We have also used this method to evaluate CXCL12 binding and CXCR4 expression level in different subsets of human peripheral blood mononuclear cells. CONCLUSION: CXCL12(AF647) is a valuable, more convenient alternative for [(125)I]CXCL12 in ligand/receptor interaction studies.     

CXCR4 and CXCL12 are inversely expressed in colorectal cancer cells and modulate cancer cell migration, invasion and MMP-9 activation

Colorectal cancer (CRC) is characterized by a distinct metastatic pattern resembling chemokine-induced leukocyte trafficking. This prompted us to investigate expression, signal transduction and specific functions of the chemokine receptor CXCR4 in CRC cells and metastases. Using RT-PCR analysis and Western blotting, we demonstrated CXCR4 and CXCL12 expression in CRC and CRC metastases. Cell differentiation increases CXCL12 mRNA levels. Moreover, CXCR4 and its ligand are inversely expressed in CRC cell lines with high CXCR4 and low or not detectable CXCL12 expression. CXCL12 activates ERK-1/2, SAPK/JNK kinases, Akt and matrix metalloproteinase-9. These CXCL12-induced signals mediate reorganization of the actin cytoskeleton resulting in increased cancer cell migration and invasion. Moreover, CXCL12 increases vascular endothelial growth factor (VEGF) expression and cell proliferation but has no effect on CRC apoptosis. Therefore, the CXCL12/CXCR4 system is an important mediator of invasion and metastasis of CXCR4 expressing CRC cells.