Inhibition of chemokine (CXC motif) ligand 12/chemokine (CXC motif) receptor 4 axis (CXCL12/CXCR4)-mediated cell migration by targeting mammalian target of rapamycin (mTOR) pathway in human gastric carcinoma cells

CXCL12/CXCR4 plays an important role in metastasis of gastric carcinoma. Rapamycin has been reported to inhibit migration of gastric cancer cells. However, the role of mTOR pathway in CXCL12/CXCR4-mediated cell migration and the potential of drugs targeting PI3K/mTOR pathway remains unelucidated. We found that CXCL12 activated PI3K/Akt/mTOR pathway in MKN-45 cells. Stimulating CHO-K1 cells expressing pEGFP-C1-Grp1-PH fusion protein with CXCL12 resulted in generation of phosphatidylinositol (3,4,5)-triphosphate, which provided direct evidence of activating PI3K by CXCL12. Down-regulation of p110β by siRNA but not p110α blocked phosphorylation of Akt and S6K1 induced by CXCL12. Consistently, p110β-specific inhibitor blocked the CXCL12-activated PI3K/Akt/mTOR pathway. Moreover, CXCR4 immunoprecipitated by anti-p110β antibody increased after CXCL12 stimulation and G(i) protein inhibitor pertussis toxin abrogated CXCL12-induced activation of PI3K. Further studies demonstrated that inhibitors targeting the PI3K/mTOR pathway significantly blocked the chemotactic responses of MKN-45 cells triggered by CXCL12, which might be attributed primarily to inhibition of mTORC1 and related to prevention of F-actin reorganization as well as down-regulation of active RhoA, Rac1, and Cdc42. Furthermore, rapamycin inhibited the secretion of CXCL12 and the expression of CXCR4, which might form a positive feedback loop to further abolish upstream signaling leading to cell migration. Finally, we found cells expressing high levels of cxcl12 were sensitive to rapamycin in its activity inhibiting migration as well as proliferation. In summary, we found that the mTOR pathway played an important role in CXCL12/CXCR4-mediated cell migration and proposed that drugs targeting the mTOR pathway may be used for the therapy of metastatic gastric cancer expressing high levels of cxcl12.     

CXCR6/CXCL16 functions as a regulator in metastasis and progression of cancer

Metastasis is considered the obvious mark for most aggressive cancers. However, little is known about the molecular mechanism of the regulation of cancer metastasis. Recent evidence increasingly suggests that the interaction between chemokines and chemokine receptors is pivotal in the process of metastasis. The chemokine receptor CXCR4 and its ligand CXCL12, for example, have been reported to play a vital role in cancer metastasis. Another chemokine and chemokine receptor pair, the CXCL16/CXCR6 axis, has been studied by several independent research groups. Here, we summarize recent advances in our knowledge of the function of CXC chemokine receptor CXCR6 and its ligand CXCL16 in regulating metastasis and invasion of cancer. CXCR6 and CXCL16 are up-regulated in multiple cancer tissue types and cancer cell lines relative to normal tissues and cell lines. In addition, both CXCR6 and CXCL16 levels increase as tumor malignancy increases. Trans-membranous CXCL16 chemokine reduces proliferation while soluble CXCL16 chemokine enhances proliferation and migration. TM-CXCL16 functions as an inducer for lymphocyte build-up around tumor sites. High trans-membranous CXCL16 expression correlates with a good prognosis. Moreover, the Akt/mTOR signal pathway is involved in activating the CXCR6/CXCL16 axis. These findings suggest multiple opportunities for blocking the CXCR6/CXCL16 axis and the Akt/mTOR signal pathway in novel cancer therapies.     

PI3Kγ activation by CXCL12 regulates tumor cell adhesion and invasion

Tumor dissemination is a complex process, in which certain steps resemble those in leukocyte homing. Specific chemokine/chemokine receptor pairs have important roles in both processes. CXCL12/CXCR4 is the most commonly expressed chemokine/chemokine receptor pair in human cancers, in which it regulates cell adhesion, extravasation, metastatic colonization, angiogenesis, and proliferation. All of these processes require activation of signaling pathways that include G proteins, phosphatidylinositol-3 kinase (PI3K), JAK kinases, Rho GTPases, and focal adhesion-associated proteins. We analyzed these pathways in a human melanoma cell line in response to CXCL12 stimulation, and found that PI3Kγ regulates tumor cell adhesion through mechanisms different from those involved in cell invasion. Our data indicate that, following CXCR4 activation after CXCL12 binding, the invasion and adhesion processes are regulated differently by distinct downstream events in these signaling cascades.     

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.     

CXCR4/CXCL12 在肿瘤中的研究进展

研究表明趋化因子及其受体在胚胎发育、干细胞迁移以及各种免疫反应中发挥重要作用,是许多生理及病理过程中细胞运动的重要因素。趋化因子受体CXCR4是一个由352个氨基酸构成的、7次跨膜的G蛋白偶联受体。趋化因子CXCL12为其特异性受体。研究发现,CXCR4/CXCL12在多种肿瘤中都有表达,在肿瘤的生长、血管生成、转移等方面发挥着重要作用。与正常组织相比,肿瘤组织及转移灶CXCR4高表达。因此,对CXCR4/CXCL12轴在肿瘤病生理中的作用机制进行进一步研究,很可能为肿瘤的治疗及对肿瘤转移的预防提供一个新的思路。我们现在就对其在肿瘤病生理中的作用做一综述。     

Diverse signaling pathways through the SDF-1/CXCR4 chemokine axis in prostate cancer cell lines leads to altered patterns of cytokine secretion and angiogenesis

The establishment of metastatic bone lesions in prostate cancer (CaP) is a process partially dependent on angiogenesis. Previously we demonstrated that the stromal-derived factor-1 (SDF-1 or CXCL12)/CXCR4 chemokine axis is critical for CaP cell metastasis. In this investigation, cell lines were established in which CXCR4 expression was knocked down using siRNA technology. When CaP cells were co-transplanted with human vascular endothelial cells into SCID mice, significantly fewer human blood vessels were observed paralleling the reductions in CXCR4 levels. Likewise, the invasive behaviors of the CaP cells were inhibited in vitro. From these functional observations we explored angiogenic and signaling mechanisms generated following SDF-1 binding to CXCR4. Differential activation of the MEK/ERK and PI3K/AKT pathways that result in differential secretion IL-6, IL-8, TIMP-2 and VEGF were seen contingent on the cell type examined; VEGF and TIMP-2 expression in PC3 cells are dependent on AKT activation and ERK activation in LNCaP and LNCaP C4-2B cells leads to IL-6 or IL-8 secretion. At the same time, expression of angiostatin levels were inversely related to CXCR4 levels, and inhibited by SDF-1 stimulation. These data link the SDF-1/CXCR4 pathway to changes in angiogenic cytokines by different signaling mechanisms and, suggest that the delicate equilibrium between proangiogenic and antiangiogenic factors may be achieved by different signal transduction pathways to regulate the angiogenic phenotype of prostate cancers. Taken together, our results provide new information regarding expression of functional CXCR4 receptor-an essential role and potential mechanism of angiogenesis upon SDF-1 stimulation.     

Involvement of the CXCR7/CXCR4/CXCL12 Axis in the Malignant Progression of Human Neuroblastoma

Neuroblastoma (NB) is a typical childhood and heterogeneous neoplasm for which efficient targeted therapies for high-risk tumors are not yet identified. The chemokine CXCL12, and its receptors CXCR4 and CXCR7 have been involved in tumor progression and dissemination. While CXCR4 expression is associated to undifferentiated tumors and poor prognosis, the role of CXCR7, the recently identified second CXCL12 receptor, has not yet been elucidated in NB. In this report, CXCR7 and CXCL12 expressions were evaluated using a tissue micro-array including 156 primary and 56 metastatic NB tissues. CXCL12 was found to be highly associated to NB vascular and stromal structures. In contrast to CXCR4, CXCR7 expression was low in undifferentiated tumors, while its expression was stronger in matured tissues and specifically associated to differentiated neural tumor cells. As determined by RT-PCR, CXCR7 expression was mainly detected in N-and S-type NB cell lines, and was slightly induced upon NB cell differentiation in vitro. The relative roles of the two CXCL12 receptors were further assessed by overexpressing CXCR7 or CXCR4 receptor alone, or in combination, in the IGR-NB8 and the SH-SY5Y NB cell lines. In vitro functional analyses indicated that, in response to their common ligand, both receptors induced activation of ERK1/2 cascade, but not Akt pathway. CXCR7 strongly reduced in vitro growth, in contrast to CXCR4, and impaired CXCR4/CXCL12-mediated chemotaxis. Subcutaneous implantation of CXCR7-expressing NB cells showed that CXCR7 also significantly reduced in vivo growth. Moreover, CXCR7 affected CXCR4-mediated orthotopic growth in a CXCL12-producing environment. In such model, CXCR7, in association with CXCR4, did not induce NB cell metastatic dissemination. In conclusion, the CXCR7 and CXCR4 receptors revealed specific expression patterns and distinct functional roles in NB. Our data suggest that CXCR7 elicits anti-tumorigenic functions, and may act as a regulator of CXCR4/CXCL12-mediated signaling in NB.     

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.     

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。     

CXCL12–CXCR7 Signaling Activates ERK and Akt Pathways in Human Choriocarcinoma Cells

Abstract

CXCL12 acts as a physiological ligand for the chemokine receptor CXCR7. Chemokine receptor expression by human trophoblast and other placental cells have important implications for understanding the regulation of placental growth and development. We had previously reported the differential expression of CXCR7 in different stages of the human placenta suggesting its possible role in regulation of placental growth and development. In this study, we determined the expression of CXCR7 in human choriocarcinoma JAR cells at the mRNA level and protein level and the downstream signaling pathway mediated by CXCL12–CXCR7 interaction. We observed that binding of CXCL12 to CXCR7 activates the ERK and Akt cell-survival pathways in JAR cells. Inhibition of the ERK and Akt pathways using specific inhibitors (Wortmanin & PD98509) led to the activation of the p38 pathway. Our findings suggest a possible role of CXCR7 in activating the cell survival pathways ERK and Akt in human choriocarcinoma JAR cells.     

PI3K/PTEN/AKT signaling regulates prostate tumor angiogenesis

PI3K pathway exerts its function through its downstream molecule AKT in regulating various cell functions including cell proliferation, cell transformation, cell apoptosis, tumor growth and angiogenesis. PTEN is an inhibitor of PI3K, and its loss or mutation is common in human prostate cancer. But the direct role and mechanism of PI3K/PTEN signaling in regulating angiogenesis and tumor growth in vivo remain to be elucidated. In this study, by using chicken chorioallantoic membrane (CAM) and in nude mice models, we demonstrated that inhibition of PI3K activity by LY294002 decreased PC-3 cells-induced angiogenesis. Reconstitution of PTEN, the molecular inhibitor of PI3K in PC-3 cells inhibited angiogenesis and tumor growth. Immunohistochemical staining indicated that PTEN expression suppressed HIF-1, VEGF and PCNA expression in the tumor xenographs. Similarly, expression of AKT dominant negative mutant also inhibited angiogenesis and tumor growth, and decreased the expression of HIF-1 and VEGF in the tumor xenographs. These results suggest that inhibition of PI3K signaling pathway by PTEN inhibits tumor angiogenesis and tumor growth. In addition, we found that AKT is the downstream target of PI3K in controlling angiogenesis and tumor growth, and PTEN could inhibit angiogenesis by regulating the expression of HIF-1 and VEGF expression through AKT activation in PC-3 cells.     

Increasing matrix stiffness upregulates vascular endothelial growth factor expression in hepatocellular carcinoma cells mediated by integrin β1

Matrix stiffness as a novel regulation factor involves in modulating the pathogenesis of hepatocellular carcinoma (HCC) invasion or metastasis. However, the mechanism by which matrix stiffness modulates HCC angiogenesis remains unknown. Here, using buffalo rat HCC models with different liver matrix stiffness backgrounds and an in vitro cell culture system of mechanically tunable Collagen1 (COL1)-coated polyacrylamide gel, we investigated the effects of different matrix stiffness levels on vascular endothelial growth factor (VEGF) expression in HCC cells and explored its regulatory mechanism for controlling HCC angiogenesis. Tissue microarray analysis showed that the expression levels of VEGF and CD31 were gradually upregulated in tumor tissues with increasing COL1 and lysyl oxidase (LOX) expression, indicating a positive correlation between tumor angiogenesis and matrix rigidity. The expression of VEGF and the phosphorylation levels of PI3K and Akt were all upregulated in HCC cells on high-stiffness gel than on low-stiffness gel. Meanwhile, alteration of intergrin β1 expression was found to be the most distinctive, implying that it might mediate the response of HCC cells to matrix stiffness simulation. After integrin β1 was blocked in HCC cells using specific monoclonal antibody, the expression of VEGF and the phosphorylation levels of PI3K and Akt at different culture times were accordingly suppressed and downregulated in the treatment group as compared with those in the control group. All data suggested that the extracellular matrix stiffness stimulation signal was transduced into HCC cells via integrin β1, and this signal activated the PI3K/Akt pathway and upregulated VEGF expression. This study unveils a new paradigm in which matrix stiffness as initiators to modulate HCC angiogenesis.     

Chemokine receptor trio: CXCR3, CXCR4 and CXCR7 crosstalk via CXCL11 and CXCL12

Although chemokines are well established to function in immunity and endothelial cell activation and proliferation, a rapidly growing literature suggests that CXC Chemokine receptors CXCR3, CXCR4 and CXCR7 are critical in the development and progression of solid tumors. The effect of these chemokine receptors in tumorigenesis is mediated via interactions with shared ligands I-TAC (CXCL11) and SDF-1 (CXCL12). Over the last decade, CXCR4 has been extensively reported to be overexpressed in most human solid tumors and has earned considerable attention toward elucidating its role in cancer metastasis. To enrich the existing armamentarium of anti-cancerous agents, many inhibitors of CXCL12–CXCR4 axis have emerged as additional or alternative agents for neo-adjuvant treatments and even many of them are in preclinical and clinical stages of their development. However, the discovery of CXCR7 as another receptor for CXCL12 with rather high binding affinity and recent reports about its involvement in cancer progression, has questioned the potential of “selective blockade” of CXCR4 as cancer chemotherapeutics. Interestingly, CXCR7 can also bind another chemokine CXCL11, which is an established ligand for CXCR3. Recent reports have documented that CXCR3 and their ligands are overexpressed in different solid tumors and regulate tumor growth and metastasis. Therefore, it is important to consider the interactions and crosstalk between these three chemokine receptors and their ligand mediated signaling cascades for the development of effective anti-cancer therapies. Emerging evidence also indicates that these receptors are differentially expressed in tumor endothelial cells as well as in cancer stem cells, suggesting their direct role in regulating tumor angiogenesis and metastasis. In this review, we will focus on the signals mediated by this receptor trio via their shared ligands and their role in tumor growth and progression.     

Hepatocyte growth factor enhances CXCR4 expression favoring breast cancer cell invasiveness

Microenvironmental factors affect different aspects of tumor cell biology, including cell survival, invasion, and metastasis. Here, we report that hepatocyte growth factor and hypoxia may contribute to breast carcinoma cell invasiveness by inducing the chemokine receptor CXCR4. Hepatocyte growth factor enhanced CXCR4 mRNA and protein expression exclusively in MCF-7 (low invasive) carcinoma cells, while in response to hypoxia, CXCR4 induction was observed in both MCF-7 and MDA-MB 231 (highly invasive) carcinoma cells. The receptor induction had a functional role in cancer cells, as demonstrated by the fact that hepatocyte growth factor pretreatment promoted MCF-7 cell migration toward the CXCR4-specific ligand CXCL12. Extracellular signal-regulated protein kinase 1/2 (ERK1/2) and phosphoinositide-3-kinase (PI3K) transduction pathways seemed to be differently implicated in the early induction of CXCR4 by hepatocyte growth factor or hypoxia in the two breast carcinoma cells examined.     

Sp1 is involved in Akt-mediated induction of VEGF expression through an HIF-1-independent mechanism

Increased expression of vascular endothelial growth factor (VEGF) contributes to the growth of many tumors by increasing angiogenesis. Although hypoxia is a potent inducer of VEGF, we previously showed that epidermal growth factor receptor amplification and loss of PTEN, both of which can increase phosphatidylinositol-3-kinase (PI3K) activity, increase VEGF expression. Using both adenoviral vectors and a cell line permanently expressing constitutively active myristoylated Akt (myrAkt), we show that activation of Akt, which is downstream of PI3K, increases VEGF expression in vitro and increases angiogenesis in a Matrigel plug assay. Transient transfection experiments using reporter constructs containing the VEGF promoter showed that up-regulation of VEGF by Akt is mediated through Sp1 binding sites located in the proximal promoter. Small interfering RNA directed against Sp1 prevented the induction of VEGF mRNA in response to myrAkt but not to hypoxia. Expression of myrAkt is associated with increased phosphorylation of Sp1 and its increased binding to a probe corresponding to the -88/-66 promoter region. In conclusion, our results indicate that Sp1 is required for transactivation of the VEGF by Akt. Others have proposed that the PI3K/Akt pathway can increase VEGF expression via the hypoxia-inducible factor 1 (HIF-1); however, our results suggest an alternative mechanism can also operate.     

Lactate Engages Receptor Tyrosine Kinases Axl,Tie2, and Vascular Endothelial Growth Factor Receptor 2 to Activate Phosphoinositide 3-Kinase/Akt and Promote Angiogenesis

Although a high level of lactate is quintessential to both tumors and wound healing, the manner by which lactate impacts endothelial cells to promote angiogenesis and thereby create or restore vascular perfusion to growing tissues has not been fully elucidated. Here we report that lactate activated the PI3K/Akt pathway in primary human endothelial cells. Furthermore, activating this signaling pathway was required for lactate-stimulated organization of endothelial cells into tubes and for sprouting of vessels from mouse aortic explants. Lactate engaged the PI3K/Akt pathway via ligand-mediated activation of the three receptor tyrosine kinases Axl, Tie2, and VEGF receptor 2. Neutralizing the ligands for these receptor tyrosine kinases, pharmacologically inhibiting their kinase activity or suppressing their expression largely eliminated the ability of cells and explants to respond to lactate. Elucidating the mechanism by which lactate communicates with endothelial cells presents a previously unappreciated opportunity to improve our understanding of the angiogenic program and to govern it.     

Proteomic studies of rat tibialis anterior muscle during postnatal growth and development

Phosphoinositide 3-kinase (PI3K) pathway exerts its effects through Akt, its downstream target molecule, and thereby regulates various cell functions including cell proliferation, cell transformation, apoptosis, tumor growth, and angiogenesis. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) has been implicated in regulating cell survival signaling through the PI3K/Akt pathway. However, the mechanism by PI3K/PTEN signaling regulates angiogenesis and tumor growth in vivo remains to be elucidated. Vascular endothelial growth factor (VEGF) plays a pivotal role in tumor angiogenesis. The effect of PTEN on VEGF-mediated signal in pancreatic cancer is unknown. This study aimed to determine the effect of PTEN on both the expression of VEGF and angiogenesis. Toward that end, we used the siRNA knockdown method to specifically define the role of PTEN in the expression of VEGF and angiogenesis. We found that siRNA-mediated inhibition of PTEN gene expression in pancreatic cancer cells increase their VEGF secretion, up-modulated the proliferation, and migration of co-cultured vascular endothelial cell and enhanced tubule formation by HUVEC. In addition, PTEN modulated VEGF-mediated signaling and affected tumor angiogenesis through PI3K/Akt/VEGF/eNOS pathway.