CXCR7 transcription in human non-small cell lung cancer and tumor-free lung tissues; possible regulation upon chemotherapy

Atypical chemokine receptors in tumor cell growth and metastasis

Atypical chemokine receptors (ACKRs) are seven-transmembrane cell surface protein receptors expressed in immune cells, normal mesenchymal cells, and several tumor cells. As of this writing, six ACKRs have been characterized by diverse activities. They bind both cysteine-cysteine (CC) type and cysteine-X-cysteine (CXC)-type chemokines, either alone, or together with a ligand bound-functional G-protein coupled (typical) chemokine receptor. The major structural difference between ACKRs and typical chemokine receptors is the substituted DRYLAIV amino acid motif in the second intracellular loop of the ACKR. Due to this substitution, these receptors cannot bind Gαi-type G-proteins responsible for intracellular calcium mobilization and cellular chemotaxis. Although initially characterized as non-signaling transmembrane receptors (decoy receptors) that attenuate ligand-induced signaling by GPCRs, studies of all ACKRs have shown ligand-independent and ligand-dependent transmembrane signaling in both non-tumor and tumor cells. The precise function and mechanism of the differential expression of ACKRs in many tumors are not understood well. The use of antagonists of ACKRs ligands has shown limited antitumor potential; however, depleting ACKR expression resulted in a reduction in experimental tumor growth and metastasis. The ACKRs represent a unique class of transmembrane signaling proteins that regulate growth, survival, and metastatic processes in tumor cells, affecting multiple pathways of tumor growth. Therefore, closer investigations of ACKRs have a high potential for identifying therapeutics which affect the intracellular signaling, preferentially via the ligand-independent mechanism.

The Role of ACKR3 in Breast, Lung, and Brain Cancer

Recent reports regarding the significance of chemokine receptors in disease have put a spotlight on atypical chemokine receptor 3 (ACKR3). This atypical chemokine receptor is overexpressed in numerous cancer types and has been involved in the modulation of tumor cell proliferation and migration, tumor angiogenesis, or resistance to drugs, thus contributing to cancer progression and metastasis occurrence. Here, we focus on the clinical significance and potential mechanisms underlying the pathologic role of ACKR3 in breast, lung, and brain cancer and discuss its possible relevance as a prognostic factor and potential therapeutic target in these contexts.

A multi-targeted approach to suppress tumor-promoting inflammation

Cancers harbor significant genetic heterogeneity and patterns of relapse following many therapies are due to evolved resistance to treatment. While efforts have been made to combine targeted therapies, significant levels of toxicity have stymied efforts to effectively treat cancer with multi-drug combinations using currently approved therapeutics. We discuss the relationship between tumor-promoting inflammation and cancer as part of a larger effort to develop a broad-spectrum therapeutic approach aimed at a wide range of targets to address this heterogeneity. Specifically, macrophage migration inhibitory factor, cyclooxygenase-2, transcription factor nuclear factor-κB, tumor necrosis factor alpha, inducible nitric oxide synthase, protein kinase B, and CXC chemokines are reviewed as important antiinflammatory targets while curcumin, resveratrol, epigallocatechin gallate, genistein, lycopene, and anthocyanins are reviewed as low-cost, low toxicity means by which these targets might all be reached simultaneously. Future translational work will need to assess the resulting synergies of rationally designed antiinflammatory mixtures (employing low-toxicity constituents), and then combine this with similar approaches targeting the most important pathways across the range of cancer hallmark phenotypes.

A differential role for CXCR4 in the regulation of normal versus malignant breast stem cell activity

C-X-C chemokine receptor type 4 (CXCR4) is known to regulate lung, pancreatic and prostate cancer stem cells. In breast cancer, CXCR4 signalling has been reported to be a mediator of metastasis, and is linked to poor prognosis. However its role in normal and malignant breast stem cell function has not been investigated. Anoikis resistant (AR) cells were collected from immortalised (MCF10A, 226L) and malignant (MCF7, T47D, SKBR3) breast cell lines and assessed for stem cell enrichment versus unsorted cells. AR cells had significantly higher mammosphere forming efficiency (MFE) than unsorted cells. The AR normal cells demonstrated increased formation of 3D structures in Matrigel compared to unsorted cells. In vivo, SKBR3 and T47D AR cells had 7- and 130-fold enrichments for tumour formationrespectively, compared with unsorted cells. AR cells contained significantly elevated CXCR4 transcript and protein levels compared to unsorted cells. Importantly, CXCR4 mRNA was higher in stem cell-enriched CD44+/CD24- patient-derived breast cancer cells compared to non-enriched cells. CXCR4 stimulation by its ligand SDF-1 reduced MFE of the normal breast cells lines but increased the MFE in T47D and patient-derived breast cancer cells. CXCR4 inhibition by AMD3100 increased stem cell activity but reduced the self-renewal capacity of the malignant breast cell line T47D. CXCR4+ FACS sorted MCF7 cells demonstrated a significantly increased MFE compared with CXCR4- cells. This significant increase in MFE was further demonstrated in CXCR4 over-expressing MCF7 cells which also had an increase in self-renewal compared to parental cells. A greater reduction in self-renewal following CXCR4 inhibition in the CXCR4 over-expressing cells compared with parental cells was also observed. Our data establish for the first time that CXCR4 signalling has contrasting effects on normal and malignant breast stem cell activity. Here, we demonstrate that CXCR4 signalling specifically regulates breast cancer stem cell activities and may therefore be important in tumour formation at the sites of metastases.

Expression of stromal cell-derived factor 1 and CXCR7 ligand receptor system in pancreatic adenocarcinoma

BACKGROUND

Stromal cell-derived factor 1 (SDF-1) is a chemokine that is expressed in some cancer cells and is involved in tumor cell migration and metastasis. CXCR7, a novel receptor for SDF-1, has been identified recently. Research has demonstrated that SDF-1/CXCR7 interaction could play an important role in cancer progression. In this study, we aimed to investigate the expression of the SDF-1/CXCR7 ligand receptor system and the relationship between this expressions and clinicopathological characteristics in pancreatic adenocarcinoma.

METHODS

Expressions of SDF-1 and CXCR7 in 64 cases of pancreatic adenocarcinoma tissue and 24 cases of normal pancreatic tissue were detected immunohistochemically.

RESULTS

Expressions of SDF-1 and CXCR7 were negative in normal pancreatic tissues. Respectively, positive expression rates of SDF-1 and CXCR7 in pancreatic adenocarcinoma were 45.3% and 51.6%. The expression of SDF-1 correlated with histological grades; the expression rate in moderate to low differentiation was higher than in high differentiation (P<0.05). The expression of CXCR7 positively correlated with lymph node metastasis (P<0.05). A log-rank test showed that the expression of SDF-1+/CXCR7+ correlated with poor prognosis (P<0.05).

CONCLUSIONS

The SDF-1/CXCR7 receptor ligand system may take part in invasive progression and metastasis of pancreatic adenocarcinoma, and might be useful as an index for evaluating invasiveness and prognosis.

CXCR4 and CXCR7 transduce through mTOR in human renal cancer cells

Treatment of metastatic renal cell carcinoma (mRCC) has improved significantly with the advent of agents targeting the mTOR pathway, such as temsirolimus and everolimus. However, their efficacy is thought to be limited by feedback loops and crosstalk with other pathways leading to the development of drug resistance. As CXCR4-CXCL12-CXCR7 axis has been described to have a crucial role in renal cancer; the crosstalk between the mTOR pathway and the CXCR4-CXCL12-CXCR7 chemokine receptor axis has been investigated in human renal cancer cells. In SN12C and A498, the common CXCR4-CXCR7 ligand, CXCL12, and the exclusive CXCR7 ligand, CXCL11, activated mTOR through P70S6K and 4EBP1 targets. The mTOR activation was specifically inhibited by CXCR4 antagonists (AMD3100, anti-CXCR4-12G5 and Peptide R, a newly developed CXCR4 antagonist) and CXCR7 antagonists (anti-CXCR7-12G8 and CCX771, CXCR7 inhibitor). To investigate the functional role of CXCR4, CXCR7 and mTOR in human renal cancer cells, both migration and wound healing were evaluated. SN12C and A498 cells migrated toward CXCL12 and CXCL11; CXCR4 and CXCR7 inhibitors impaired migration and treatment with mTOR inhibitor, RAD001, further inhibited it. Moreover, CXCL12 and CXCL11 induced wound healing while was impaired by AMD3100, the anti CXCR7 and RAD001. In SN12C and A498 cells, CXCL12 and CXCL11 promoted actin reorganization characterized by thin spikes at the cell periphery, whereas AMD3100 and anti-CXCR7 impaired CXCL12/CXCL11-induced actin polymerization, and RAD001 treatment further reduced it. In addition, when cell growth was evaluated in the presence of CXCL12, CXCL11 and mTOR inhibitors, an additive effect was demonstrated with the CXCR4, CXCR7 antagonists and RAD001. RAD001-resistant SN12C and A498 cells recovered RAD001 sensitivity in the presence of CXCR4 and CXCR7 antagonists. In conclusion, the entire axis CXCR4-CXCL12-CXCR7 regulates mTOR signaling in renal cancer cells offering new therapeutic opportunities and targets to overcome resistance to mTOR inhibitors.

Expression of stromal cell-derived factor 1 and CXCR7 in papillary thyroid carcinoma

Stromal cell-derived factor 1 (SDF-1) is a chemokine that is expressed in some cancer cells and is involved in tumor cell migration and metastasis. CXCR7, a novel receptor for SDF-1, has been identified recently. Researches demonstrated that interaction between SDF-1 and CXCR7 could play an important role in cancer progression. In this study, we aimed to investigate the expressions of SDF-1 and CXCR7 and the relationship between their expressions and clinicopathological characteristics in papillary thyroid carcinoma (PTC). Expressions of SDF-1 and CXCR7 in 33 cases of thyroid benign lesion tissue and 79 cases of PTC tissue and peritumoral non-malignant tissue were detected by immunohistochemical staining. Expressions of SDF-1 and CXCR7 were negative in peritumoral non-malignant tissues. Respectively, positive expression rates of SDF-1 and CXCR7 were 69.6 and 65.8 % in PTC, 12.1 and 30.3 % in thyroid benign tissue. The expression of SDF-1 and CXCR7 were positively correlated with lymph node metastasis. SDF-1 and CXCR7 expressions were related with the lymph nodes metastasis of PTC.

CXCL12 receptor preference, signal transduction, biological response and the expression of 5T4 oncofoetal glycoprotein

CXCL12 is a pleiotropic chemokine capable of eliciting multiple signal transduction cascades and functions, via interaction with either CXCR4 or CXCR7. Factors that determine CXCL12 receptor preference, intracellular signalling route and biological response are poorly understood but are of central importance in the context of therapeutic intervention of the CXCL12 axis in multiple disease states. We have recently demonstrated that 5T4 oncofoetal glycoprotein facilitates functional CXCR4 expression leading to CXCL12 mediated chemotaxis in mouse embryonic cells. Using wild type (WT) and 5T4 knockout (5T4KO) murine embryonic fibroblasts (MEFs), we now show that CXCL12 binding to CXCR4 activates both the ERK and AKT pathways within minutes, but while these pathways are intact, they are non-functional in 5T4KO cells treated with CXCL12. Importantly, in the absence of 5T4 expression, CXCR7 is upregulated and becomes the predominant receptor for CXCL12, activating a distinct signal transduction pathway with slower kinetics involving transactivation of the epidermal growth factor receptor (EGFR), eliciting proliferation rather than chemotaxis. Thus the surface expression of 5T4 marks the use of the CXCR4 rather than the CXCR7 receptor, with distinct consequences for CXCL12 exposure, relevant to the spread and growth of a tumour. Consistent with this hypothesis, we have identified human small cell lung carcinoma cells with similar 5T4/CXCR7 reciprocity that is predictive of biological response to CXCL12 and determined that 5T4 expression is required for functional chemotaxis in these cells.

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.

CXCR7 and syndecan-4 are potential receptors for CXCL12 in human cytotrophoblasts

The placenta forms the interface between the mother and the fetus. During placental development cytotrophoblasts differentiate to form the syncytium or to invade the decidual wall to breach maternal vessels and establish the blood flow in the intervillous space. This process is still not well understood but it is proposed that chemokines and their receptors are involved in guiding cytotrophoblasts to the decidua and maternal vessels as well as attracting immunocompetent cells to the implantation site. CXCL12 is a chemokine expressed by cytotrophoblasts and is involved in cytotrophoblast invasion, differentiation and survival. One of its receptors, CXCR4, has been detected on cytotrophoblasts. Recent data show that CXCR7 and syndecan-4 might partially mediate CXCL12 function in other cell types. In this study, we examined CXCR7 and syndecan-4 expression at the maternal-fetal interface via immmunolocalization in placental tissue sections and in isolated cytotrophoblasts. We further used immunoblot analyses to confirm the data. We were able to show that cytotrophoblasts express both receptors and that upregulation occurs during the differentiation process of cytotrophoblasts towards the invasive phenotype. On a functional level CXCR7 seems not to be involved in JAR cell chemotaxis, suggesting a different function of this receptor. In conclusion, we propose that CXCL12 binds to CXCR4, but also to CXCR7 and syndecan-4. These three receptors could mediate different functions of CXCL12, such as cell migration, directed invasion, proliferation and survival. The latter molecules might also be involved in the development of placental pathologies, such as preeclampsia or choriocarcinoma growth.

Overlapping and distinct role of CXCR7-SDF-1/ITAC and CXCR4-SDF-1 axes in regulating metastatic behavior of human rhabdomyosarcomas

We have demonstrated that the α-chemokine stromal-derived factor (SDF)-1-CXCR4 axis plays an important role in rhabdomyosarcoma (RMS) metastasis. With the recent description of CXCR7, a new receptor for SDF-1 that also binds the interferon-inducible T-cell α chemoattractant (ITAC) chemokine, we became interested in the role of the CXCR7-SDF-1/ITAC axis in RMS progression. To address this issue, we evaluated 6 highly metastatic alveolar (A)RMS and 3 less metastatic embryonal (E)RMS cell lines and found that all these cell lines express CXCR7. Although CXCR4 was expressed at a much higher level by highly metastatic ARMS lines, CXCR7 was present at a high level on ERMS lines. We also noticed that CXCR7 expression on RMS cells was downregulated in hypoxic conditions. More importantly, the CXCR7 receptor on RMS cell lines was functional after stimulation with ITAC and SDF-1 as evidenced by mitogen-activated protein kinase (MAPK)p42/44 and AKT phosphorylation as well as CXCR7 internalization, chemotaxis, cell motility and adhesion assays. Similarly to CXCR4, signaling from activated CXCR7 was not associated with increased RMS proliferation or cell survival. Moreover, CXCR7(+) RMS cells responded to SDF-1 and I-TAC in the presence of CXCR4 antagonists (T140, AMD3100). Furthermore, while intravenous injection of RMS cells with overexpressed CXCR7 resulted in increased seeding efficiency of tumor cells to bone marrow, CXCR7 downregulation showed the opposite effect. In conclusion, the CXCR7-SDF-1/ITAC axis is involved in the progression of RMS; targeting of the CXCR4-SDF-1 axis alone without simultaneous blockage of CXCR7 will be an inefficient strategy for inhibiting SDF-1-mediated prometastatic responses of RMS cells.

High levels of expression of human stromal cell-derived factor-1 are associated with worse prognosis in patients with stage II pancreatic ductal adenocarcinoma

BACKGROUND

Stromal cell-derived factor-1 (SDF-1) and its receptor, CXCR4, have been shown to mediate invasiveness and metastatic behavior in a number of cancers, including ovarian, prostate, bladder, breast, and pancreatic cancers. The expression and significance of SDF-1 in pancreatic ductal adenocarcinoma (PDA) have not been systematically studied.

METHODS

We examined the expression of SDF-1 by immunohistochemistry using a mouse anti-human SDF-1/CXCL12 antibody (dilution 1:300) and a tissue microarray consisting of 72 stage II PDAs from pancreaticoduodenectomy specimens. The staining results were categorized as SDF-1-high (SDF-1-H; cytoplasmic staining of ≥10% of tumor cells) or SDF-1-low (SDF-1-L; no staining or staining of <10% of tumor cells). The results of SDF-1 expression were correlated with clinicopathologic parameters and survival. Statistical analyses were done using SPSS software.

RESULT

Of the 72 stage II PDAs, 25 (35%) showed high levels of SDF-1 expression. The median overall and recurrence-free survival for patients with SDF-1-H PDAs were 26.1 and 11.1 months, respectively, compared with 44.3 and 22.3 months for patients with SDF-1-L tumors (log-rank test, P = 0.047 and P = 0.021). In multivariate analysis, high SDF-1 expression correlated with poor overall and disease-free survival (P = 0.02 and P = 0.02) independent of tumor size, differentiation, and lymph node status.

CONCLUSION

High levels of SDF-1 expression were associated with poor overall and disease-free survival in patients with stage II PDA. SDF-1 may serve as a useful prognostic marker for stage II PDA.

IMPACT

Our results suggest that SDF-1-CXCR4 or SDF-1-CXCR7 pathways may represent a potential target for therapeutic intervention as well as prediction of prognosis in PDA.

The role of stromal-derived factor-1--CXCR7 axis in development and cancer

Cancer metastasis is a major clinical problem that contributes to unsuccessful therapy. Augmenting evidence indicates that metastasizing cancer cells employ several mechanisms that are involved in developmental trafficking of normal stem cells. Stromal-derived factor-1 (SDF-1) is an important alpha-chemokine that binds to the G-protein-coupled seven-transmembrane span CXCR4. The SDF-1-CXCR4 axis regulates trafficking of normal and malignant cells. SDF-1 is an important chemoattractant for a variety of cells including hematopoietic stem/progenitor cells. For many years, it was believed that CXCR4 was the only receptor for SDF-1. However, several reports recently provided evidence that SDF-1 also binds to another seven-transmembrane span receptor called CXCR7, sharing this receptor with another chemokine family member called Interferon-inducible T-cell chemoattractant (I-TAC). Thus, with CXCR7 identified as a new receptor for SDF-1, the role of the SDF-1-CXCR4 axis in regulating several biological processes becomes more complex. Based on the available literature, this review addresses the biological significance of SDF-1's interaction with CXCR7, which may act as a kind of decoy or signaling receptor depending on cell type. Augmenting evidence suggests that CXCR7 is involved in several aspects of tumorogenesis and could become an important target for new anti-metastatic and anti-cancer drugs.

Chemokines in neuroectodermal cancers: the crucial growth signal from the soil

Although chemokines and their receptors were initially identified as regulators of cell trafficking during inflammation and immune response, they have emerged as crucial players in all stages of tumor development, primary growth, migration, angiogenesis, and establishment as metastases in distant target organs. Neuroectodermal tumors regroup neoplasms originating from the embryonic neural crest cells, which display clinical and biological similarities. These tumors are highly malignant and rapidly progressing diseases that disseminate to similar target organs such as bone marrow, bone, liver and lungs. There is increasing evidence that interaction of several chemokine receptors with corresponding chemokine ligands are implicated in the growth and invasive characteristics of these tumors. In this review we summarize the current knowledge on the role of CXCL12 chemokine and its CXCR4 and CXCR7 receptors in the progression and survival of neuroectodermal tumors, with particular emphasis on neuroblastoma, the most typical and enigmatic neuroectodermal childhood tumor.

Differential expression of RDC1/CXCR7 in the human placenta

INTRODUCTION

Chemokine receptor expression by human trophoblast and other placental cells have important implications for understanding the regulation of placental growth, development, and their role in maternofetal HIV transmission. CXCR7, now a deorphanized G protein coupled receptor that has been recently shown to bind to the ligands ITAC and CXCL12 has been proposed to act as a co-receptor for HIV-1, HIV-2, and SIV strains. The differential expression of CXCR7 in the human placenta is not yet reported.

METHODS

The expression of CXCR7 was studied in 45 different human placental tissues, of which 20 were from early placental tissues (8-10 week old) obtained from medically terminated pregnancies and 25 were placenta from normal term deliveries.

RESULTS

Immunohistochemistry and RT-PCR analysis revealed a greater expression of CXCR7 in term human placenta as compared to the early stage. This was further confirmed by real-time PCR.

CONCLUSION

Our study reveals, for the first time, the differential expression of CXCR7 in early (8-10 weeks) and term human placenta. The precise role of CXCR7 in the human placenta needs to be determined. HIV vertical transmission is reported to occur mainly during the end stages of pregnancy. Our finding of increased CXCR7 expression in the term human placenta therefore warrants future studies to assess its role in the vertical transmission of HIV-1.

CXCR7, CXCR4 and CXCL12: an eccentric trio?

CXCR7, formerly called RDC1 is a recently deorphanized G-protein coupled receptor which binds with high affinity the inflammatory and homing chemokines CXCL11/ITAC and CXCL12/SDF-1. Despite its phylogenetic relation and ligand binding properties CXCR7 does not mediate typical chemokine receptor responses such as leukocyte trafficking. Recent findings in zebrafish indicate that a critical activity of the receptor is scavenging of CXCL12 thereby generating guidance cues for CXCR4-dependent migration. The observations do not exclude the possibility that the receptor is capable of inducing signal transduction which is suggestive from studies of tumor growth and survival. The pronounced expression in central and peripheral nervous tissue and the absence of a brain phenotype in CXCR7(-/-) mice suggest a subtle activity of the receptor.