CXCR1 and CXCR2 enhances human melanoma tumourigenesis, growth and invasion

The aggressiveness of malignant melanoma is associated with differential expression of CXCL-8 and its receptors, CXCR1 and CXCR2. However, the precise functional role of these receptors in melanoma progression remains unclear. In this study, we investigate the precise functional role of CXCR1 and CXCR2 in melanoma progression. CXCR1 or CXCR2 were stably overexpressed in human melanoma cell lines, SBC-2 (non-tumourigenic) and A375P (low-tumourigenic) exhibiting low endogenous expression of receptors. Functional assays were performed to study the resulting changes in cell proliferation, motility and invasion, and in vivo tumour growth using a mouse xenograft model. Our data demonstrated that CXCR1- or CXCR2-overexpressing SBC-2 and A375P melanoma cells had enhanced proliferation, chemotaxis and invasiveness in vitro. Interestingly, CXCR1 or CXCR2 overexpression in SBC-2 cells induced tumourigenicity, and A375P cells significantly enhanced tumour growth as examined in vivo. Immunohistochemical analyses showed significantly increased tumour cell proliferation and microvessel density and reduced apoptosis in tumours generated from CXCR1- or CXCR2-overexpressing melanoma cells. CXCR1- or CXCR2-induced modulation of melanoma cell proliferation and migration was observed to be mediated through the activation of ERK1/2 phosphorylation. Together, these studies demonstrate that CXCR1 and CXCR2 play essential role in growth, survival, motility and invasion of human melanoma.     

Functional activity of CXCL8 receptors, CXCR1 and CXCR2, on human malignant melanoma progression

We examined the autocrine/paracrine role of interleukin-8 (CXCL8) and the functional significance of CXCL8 receptors, CXCR1 and CXCR2, in human malignant melanoma proliferation, migration, invasion and angiogenesis. We found that a panel of seven cell lines, even though at different extent, secreted CXCL8 protein, and expressed CXCR1 and CXCR2 independently from the CXCL8 expression, but depending on the oxygen level. In fact, hypoxic exposure increases the expression of CXCR1 and CXCR2. The cell proliferation of both M20 and A375SM lines, expressing similar levels of both CXCR1 and CXCR2 but secreting low and high amounts of CXCL8, respectively, was significantly enhanced by CXCL8 exposure and reduced by CXCL8, CXCR1 and CXCR2 neutralising antibodies, indicating the autocrine/paracrine role of CXCL8 in melanoma cell proliferation. Moreover, an increased invasion and migration in response to CXCL8 was observed in several cell lines, and a further enhancement evidenced under hypoxic conditions. A CXCL8-dependent in vivo vessel formation, evaluated through a matrigel assay, was also demonstrated. Furthermore, when neutralising antibodies against CXCR1 or CXCR2 were used, only the involvement of CXCR2, but not CXCR1 was observed on cell migration and invasion, while both receptors played a role in angiogenesis.In summary, our data demonstrate that CXCL8 induces cell proliferation and angiogenesis through both receptors and that CXCR2 plays an important role in regulating the CXCL8-mediated invasive and migratory behaviour of human melanoma cells. Thus, blocking the CXCL8 signalling axis promises an improvement for the therapy of cancer and, in particular, of metastatic melanoma.     

CXCL12–CXCR7 axis is important for tumor endothelial cell angiogenic property

We reported that tumor endothelial cells (TECs) differ from normal endothelial cells (NECs) in many aspects, such as gene expression profiles. Although CXCR7 is reportedly highly expressed in blood vessels of several tumors, its function in TECs is still unknown. To investigate this role, we isolated TECs from mouse tumor A375SM xenografts, and compared them with NECs from normal mouse dermis. After confirming CXCR7 upregulation in TECs, we analyzed its function using CXCR7 siRNA and CXCR7 inhibitor; CCX771. CXCR7 siRNA and CCX771 inhibited migration, tube formation and resistance to serum starvation in TECs but not in NECs. ERK1/2 phosphorylation was inhibited by CXCR7 knockdown in TECs. These results suggest that CXCR7 promotes angiogenesis in TECs via ERK1/2 phosphorylation. Using ELISA, we also detected CXCL12, a ligand of CXCR7, in conditioned medium from TECs, but not from NECs. CXCL12 neutralizing antibody significantly inhibited TEC random motility. VEGF stimulation upregulated CXCR7 expression in NECs, implying that VEGF mediates CXCR7 expression in endothelial cells. A CXCR7 inhibitor, CCX771 also inhibited tumor growth, lung metastasis and tumor angiogenesis in vivo. Taken together, the CXCL12–CXCR7 autocrine loop affects TEC proangiogenic properties, and could be the basis for an antiangiogenic therapy that specifically targets tumor blood vessels rather than normal vessels.     

Effects of Triptolide on Cell Proliferation and CXCR4 Expression in Burkitt＇s Lymphoma Raji Cells In Vitro

Objective： To investigate the inhibitory effects of triptolide on cell proliferation and CXCR4 expression in Burkitt＇s lymphoma cell line Raji cells. Methods： The effects of triptolide on the growth of Raji cells were studied by 3-（4, 5-Dimethyl-2-thiazolyl）-2, 5-diphenyl-2H-tetrazolium（MTT） assay. The effects of triptolide on CXCR4 expression on Raji cells were studied by flow cytometric analysis. Chemotaxis assays were performed to observe the effects of triptolide on migration of Raji cells towards recombinant human SDF-1α （rhSDF-1α） in vitro. Results： Triptolide inhibited the proliferation of Raji cells in a dose- and time-dependent way with a 24-h IC50 value of 43.06 nmol/L and a 36-h IC50 value of 25.08 nmol/L. Triptolide could downregulate the CXCR4 expression on Raji cells in a dose-dependent manner. Furthermore, chemotaxis assays showed that triptolide could block the migration of Raji cells to rhSDF-1α in vitro, and the inhibition was dose-dependent. Conclusion： Triptolide could inhibit the proliferation and migration of Raji cells in vitro. The underlying anti-tumor mechanism of triptolide might be related to the anti-proliferative effect and the blockage of SDF-1/CXCR4 axis.     

The role of CXCR3 and CXCR4 in colorectal cancer metastasis

Chemokines and their receptors play key roles in leukocyte trafficking and are also implicated in cancer metastasis. We previously demonstrated that forced expression of CXCR3 promotes colon cancer metastasis preferentially to the draining lymph nodes (LNs), with poor prognosis. Using clinical colorectal cancer (CRC) samples, here, we show that expressions of CXCR3 and CXCR4 are significantly higher in metastatic foci within LNs and liver compared to primary tumors, whereas ligands for CXCR3 and CXCR4 are not. We also have demonstrated that some human CRC cell lines constitutively express both CXCR3 and CXCR4, and that activation of CXCR3 strengthens the CXCR4‐mediated cell migration in vitro in a synergistic manner. By constructing SW620 cell lines with reduced expression of CXCR3 and/or CXCR4 using microRNA, we investigated in vivo metastatic activities in a mouse rectal transplantation model. Six weeks after inoculation, CXCR3‐, CXCR4‐, and CXCR3/CXCR4 double‐knockdowns significantly reduced metastasis to LNs, liver and lungs, compared to the control (p < 0.05). Importantly, its suppressive effect on LN metastasis was significantly stronger in CXCR3‐ and CXCR3/CXCR4 double‐knockdowns. In addition, CXCR3‐ and CXCR3/CXCR4 double‐knockdowns significantly decreased the dissemination of cancer cells to liver and lungs, even after 2 weeks. These results indicate that targeting CXCR3 and CXCR4 can be a promising therapy against CRC metastasis.     

Correlation between CXCR4/CXCR7/CXCL12 chemokine axis expression and prognosis in lymph‐node‐positive lung cancer patients

The CXCR4/CXCR7/CXCL12 chemokine axis plays important roles in the migration of tumor cells during cancer development by modulating site‐specific distant metastasis including to regional lymph nodes. We investigated the correlation of these chemokine expressions to prognosis in lymph‐node‐positive non‐small‐cell lung cancer (NSCLC) patients. A total of 140 surgically resected specimens of primary site (PS) and metastatic lymph nodes (MLN) of NSCLC involving hilar and/or mediastinal lymph nodes (N1‐2) were collected. CXCR4, CXCR7 and CXCL12 expressions were evaluated. Cox regression analysis was performed to determine whether these chemokines were independent prognostic factors in N1‐2 NSCLC. High expression of CXCR4 in PS and CXCL12 in MLN was associated with poor overall survival (OS) (P = .025 and .033, respectively). Significant correlations between CXCR4 expression in PS and CXCL12 expression in MLN were observed (P = .040). There was significant difference in OS between 2 groups according to expressions of CXCR4 in PS and CXCL12 in MLN (P = .0033). Expression of CXCL12 in MLN was identified as an independent prognostic factor (HR 1.79, 95% CI 1.08‐3.04, P = .023). CXCL12 in MLN was mainly expressed by tumor cells compared with stromal cells (56% vs 25%, respectively, P < .0001). CXCR4/CXCL12 may play roles in tumor progression in MLN and is associated with poor prognosis of lymph‐node‐positive NSCLC patients.     

Blockade of CXCR4 in oral squamous cell carcinoma inhibits lymph node metastases

We have previously demonstrated that a stromal cell-derived factor-1 (SDF-1; CXCL12)/CXCR4 system is involved in the establishment of lymph node metastasis in oral squamous cell carcinoma (OSCC). In this study, we investigated whether the blockade of CXCR4 inhibits lymph node metastasis in B88 OSCC cells. These cells harbour a functional CXCR4 and have the potential to metastasise to the lymph node in vivo. Following introduction of a vector that expresses short hairpin small interfering RNA (shRNA) against CXCR4, we isolated three clones (shCXCR4-16, -17 and -21) that showed decreased expression of CXCR4 mRNA. These clones also had reduced CXCR4 protein levels and showed impairments in calcium flux and cell migration in response to SDF-1. These cells were orthotopically inoculated into the masseter muscle of nude mice. Lymph node metastases, loss in body weight and tumour volumes were significantly inhibited in mice inoculated with shCXCR4-17 cells compared to mice inoculated with control cells. SDF-1-induced migration of B88 cells was significantly inhibited in vitro by the treatment with 1,1′-[1,4-phenylenebis(methylene)]bis-1,4,8,11-tetraazacyclotetradecane octahydrochloride (AMD3100), a CXCR4 antagonist. Subcutaneous administration of AMD3100 significantly inhibited the lymph node metastases of B88 cells when they were orthotopically inoculated into the masseter muscle of nude mice. Moreover, the enhanced production of interleukin (IL)-6 and IL-8 in response to SDF-1 was inhibited by shRNA against CXCR4 or by treatment with AMD3100. These results suggest that blockade of CXCR4 may be a potent anti-metastatic therapy against lymph node metastases in cases of CXCR4-related OSCC.     

TRAIL Suppresses Human Breast Cancer Cell Migration via MADD/CXCR7

Background: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can specifically induceapoptosis limited to various cancer cells, so this reagent is considered a promising medicine for cancer therapy.TRAIL also exerts effects on non-apoptotic signals, relevant to processes such as metastasis, autophagy andproliferation in cancer cells. However, the mechanisms of TRAIL-regulated non-apoptotic signals are unclear.The purpose of this study was to investigate MADD/CXCR7 effects in TRAIL-mediated breast cancer cellmigration. Materials and Methods: The ability of MADD/CXCR7 to regulate MVP signaling in TRAIL-mediatedbreast cancer cells migration was evaluated by transwell migration assay, quantitative RT-PCR, Westernblotting and knock down experiments. Results: In this study, we found that treatment with TRAIL resultedin induced expression levels of MADD and CXCR7 in breast cancer cells. Knock down of MADD followed bytreatment with TRAIL resulted in increased cell migration compared to either treatment alone. Similarly, throughoverexpression and knockdown experiments, we demonstrated that CXCR7 also positively regulated TRAILinhibitedmigration. Surprisingly, knock down of MADD lead to inhibition of TRAIL-induced CXCR7 mRNAand protein expression and overexpression of CXCR7 lead to the reduction of MADD expression, indicatingthat MADD is an upstream regulatory factor of TRAIL-triggered CXCR7 production and a negative feedbackmechanism between MADD and CXCR7. Furthermore, we showed that CXCR7 is involved in MADD-inhibitedmigration in breast cancer cells. Conclusions: Our work defined a novel signaling pathway implicated in thecontrol of breast cancer migration.     

C‐X‐C chemokine receptor 7

BACKGROUND:

C‐X‐C chemokine receptor 4 (CXCR4) and CXCR7 are 7‐transmembrane chemokine receptors of the stroma‐derived factor (SDF‐1). CXCR4, but not CXCR7, has been examined in bladder cancer (BCa). This study examined the functional and clinical significance of CXCR7 in BCa.

METHODS:

CXCR4 and CXCR7 levels were measured in BCa cell lines, tissues (normal = 25; BCa = 44), and urine specimens (n = 186) by quantitative polymerase chain reaction and/or immunohistochemistry. CXCR7 function in BCa cells were examined by transient transfections using a CXCR7 expression vector or small interfering RNA.

RESULTS:

In BCa cell lines, CXCR7 messenger RNA levels were 5‐ to 37‐fold higher than those for CXCR4. Transient overexpression of CXCR7 in BCa cell lines promoted growth and chemotactic motility. CXCR7 colocalized and formed a functional complex with epidermal growth factor receptor, phosphoinositide 3‐kinase/Akt, Erk, and src and induced their phosphorylation. CXCR7 also induced up‐regulation of cyclin‐D1 and bcl‐2. Suppression of CXCR7 expression reversed these effects and induced apoptosis. CXCR7 messenger RNA levels and CXCR7 staining scores were significantly (5‐ to 10‐fold) higher in BCa tissues than in normal tissues (P < .001). CXCR7 expression independently associated with metastasis (P = .019) and disease‐specific mortality (P = .03). CXCR7 was highly expressed in endothelial cells in high‐grade BCa tissues when compared to low‐grade BCa and normal bladder. CXCR7 levels were elevated in exfoliated urothelial cells from high‐grade BCa patients (P = .0001; 90% sensitivity; 75% specificity); CXCR4 levels were unaltered.

CONCLUSIONS:

CXCR7 promotes BCa cell proliferation and motility plausibly through epidermal growth factor receptor receptor and Akt signaling. CXCR7 expression is elevated in BCa tissues and exfoliated cells and is associated with high‐grade and metastasis. Cancer 2013. © 2012 American Cancer Society.     

CXCL16/CXCR6 chemokine signaling mediates breast cancer progression by pERK1/2-dependent mechanisms

Our previous studies demonstrate that CXCL6/CXCR6 chemokine axis induces prostate cancer progression by the AKT/mTOR signaling pathway; however, its role and mechanisms underlying invasiveness and metastasis of breast cancer are yet to be elucidated. In this investigation, CXCR6 protein expression was examined using high-density tissue microarrays and immunohistochemistry. Expression of CXCR6 shows a higher epithelial staining in breast cancer nest site and metastatic lymph node than the normal breast tissue, suggesting that CXCR6 may be involved in breast cancer (BC) development. In vitro and in vivo experiments indicate that overexpression of CXCR6 in BC cells has a marked effect on increasing cell migration, invasion and metastasis. In contrast, reduction of CXCR6 expression by shRNAs in these cells greatly reduce its invasion and metastasis ability. Mechanistic analyses show that CXCL16/CXCR6 chemokine axis is capable of modulating activation of RhoA through activating ERK1/2 signaling pathway, which then inhibits the activity of cofilin, thereby enhancing the stability of F-actin, responsible for invasiveness and metastasis of BC.Taken together, our data shows for the first time that the CXCR6 / ERK1/2/ RhoA / cofilin /F-actin pathway plays a central role in the development of BC. Targeting the signaling pathway may prove beneficial to prevent metastasis and provide a more effective therapeutic strategy for BC.     

趋化因子受体CXCR7及其与肿瘤的关系

CXCR7是继CXCR4之后发现的趋化因子CXCL12的新受体.目前研究表明,CXCL12/CXCR7生物轴对多种肿瘤的发展有重要影响,与CXCL12/CXCR4生物轴的作用有一定相似性.CXCR7广泛表达于多种肿瘤组织及肿瘤细胞,在肿瘤细胞的生长增殖、黏附迁徙中起重要作用.抑制CXCR7表达或阻断其信号传导通路可能为肿瘤治疗提供新策略.     

Clinical significance of CXCR3 and CXCR4 expression in primary melanoma

Tumor cell migration involved in metastases is a tightly regulated, nonrandom process. Chemokines have been identified as critical molecules guiding cell migration. We performed a prospective study to analyze a possible association between the expression of chemokine receptors CXCR3 and CXCR4 by primary melanoma and clinical outcome. Forty primary melanomas were available for analysis; 57% of the tumors expressed CXCR3 and 35% expressed CXCR4 by melanoma cells. At initial diagnosis, 5 patients had subclinical lymph node involvement and after a median follow-up time of 32 months, 2 additional patients developed regional lymph node metastases and 5 patients developed distant metastases. The expression of CXCR4, but not CXCR3, by melanoma cells in primary lesions was significantly associated with the presence of ulceration, increased tumor thickness, a greater risk of developing regional and distant metastases and a higher mortality rate. Our study underscores the value of CXCR4 expression as a useful marker for predicting outcome in patients with localized melanoma. In addition, our findings support that, among chemokine receptors, CXCR4 might be an appropriate therapeutic target for adjuvant therapy in patients at risk for metastatic disease.     

RNAi‐mediated MEK1 knock‐down prevents ERK1/2 activation and abolishes human hepatocarcinoma growth in vitro and in vivo

The mitogen‐activated protein kinases MEK/ERK pathway regulates fundamental processes in malignant cells and represents an attractive target in the development of new cancer treatments especially for human hepatocarcinoma highly resistant to chemotherapy. Although gene extinction experiments have suggested distinct roles for these proteins, the MEK/ERK cascade remains widely considered as exhibiting an overlap of functions. To investigate the functionality of each kinase in tumorigenesis, we have generated stably knock‐down clones for MEK1/2 and ERK1/2 isoforms in the human hepatocellular carcinoma line HuH7. Our results have shown that RNAi strategy allows a specific disruption of the targeted kinases and argued for the critical function of MEK1 in liver tumor growth. Transient and stable extinction experiments demonstrated that MEK1 isoform acts as a major element in the signal transduction by phosphorylating ERK1 and ERK2 after growth factors stimulation, whereas oncogenic level of ERK1/2 phosphorylation appears to be MEK1 and MEK2 dependent in basal condition. In addition, silencing of MEK1 or ERK2 abolished cell proliferation and DNA replication in vitro as well as tumor growth in vivo after injection in rodent. In contrast, targeting MEK2 or ERK1 had no effect on hepatocarcinoma progression. These results strongly corroborate the relevance of targeting the MEK cascade as attested by pharmacologic drugs and support the potential application of RNAi in future development of more effective cancer therapies. Our study emphasizes the importance of the MEK/ERK pathway in human hepatocarcinoma cell growth and argues for a crucial role of MEK1 and ERK2 in this regulation.     

Chemokine receptor CXCR4 expression is correlated with VEGF expression and poor survival in soft‐tissue sarcoma

The expression of chemokine receptor CXCR4 has been associated with poor prognosis and VEGF expression in several kinds of human malignancy. We measured CXCR4 expression levels in soft‐tissue sarcoma and compared them with VEGF expression or microvessel density (MVD). We used real‐time quantitative PCR to examine the CXCR4 and VEGF expression levels in a total 176 tumors, including 24 intermediate tumors, 24 malignant round‐cell tumors (MRCTs) and 128 malignant non‐round‐cell tumors (MNRCTs). We also assessed their immunohistochemical expression of CXCR4 and VEGF, MVD and proliferative activities, as measured by the MIB‐1‐labeling index (LI). Furthermore, we evaluated their significance with respect to patient survival rates in MNRCTs, using the Cox regression model. Within the different types of tumor tissue, the expression levels of CXCR4 (p < 0.0001) and VEGF (p < 0.0001) in MNRCTs were significantly higher than those in intermediate tumors or MRCTs. Immunohistochemical expression levels of CXCR4 and VEGF were significantly correlated with their mRNA expression levels (p < 0.0001). Significant positive correlation was found between CXCR4 and VEGF expression in 112 primary MNRCTs (r = 0.434, p < 0.0001). Moreover, both univariate (p < 0.0001) and Cox multivariate analysis (p = 0.0001) revealed that overexpression of CXCR4 was an independent adverse prognostic factor, in addition to high stage according to the American Joint Committee on Cancer and a high MIB‐1‐LI. Determination of the CXCR4 expression level as a novel marker can provide useful prognostic information for patients and it could be a candidate for molecular targeting therapy in MNRCTs of soft‐tissue sarcomas. © 2008 Wiley‐Liss, Inc.     

CXCR2‐mediated tumor‐associated neutrophil recruitment is regulated by IFN‐β

The chemokine receptor CXCR2 and its ligands CXCL1, CXCL2 and CXCL5 play an important role in homing of tumor‐associated neutrophils (TANs) into developing tumors. TANs are known to support the development of blood vessels in growing solid tumors, hence contributing to tumor growth. Here, we show that the migration of neutrophils is influenced by endogenous interferon‐beta (IFN‐β) via regulation of such chemokines and their receptor. We could demonstrate that CXCL1 and CXCL2 gradients are formed in tumor‐bearing mice, i.e., low chemokine level in bone marrow (BM) and high level in the tumor. This supports migration of neutrophils into the tumor. Moreover, expression of CXCR2 was highest on neutrophils from BM and lowest in TANs. Importantly, although IFN‐β appears to have only a minor influence on the expression of CXCR2, it strongly regulates the CXCR2 ligands. In the absence of endogenous IFN‐β, they were expressed significantly higher in tumor‐infiltrating neutrophils. Treatment of such neutrophils from tumor‐bearing Ifnb1^?/? mice with recombinant IFN‐β downregulated CXCR2 ligand expression to wild‐type levels. This explains the reduced migration of neutrophils into tumors and the diminished tumor angiogenesis in IFN‐β‐sufficient mice. Our results add a novel functional aspect of the type I IFN system as effector molecules of natural cancer surveillance and open interesting possibilities for antineutrophil therapies against cancer.