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The IL-8-regulated chemokine receptor CXCR7 stimulates EGFR signaling to promote prostate cancer growth.

ABSTRACT: The proinflammatory chemokine receptor CXCR7 that binds the ligands CXCL11 and CXCL12 (SDF-1a) is elevated in a variety of human cancers, but its functions are not understood as it does not elicit classical chemokine receptor signaling. Here we report that the procancerous cytokine IL-8 (interleukin-8) upregulates CXCR7 expression along with ligand-independent functions of CXCR7 that promote the growth and proliferation of human prostate cancer cells (CaP cells). In cell culture, ectopic expression or addition of IL-8 selectively increased expression of CXCR7 at the level of mRNA and protein production. Conversely, suppressing IL-8 signaling abolished the ability of IL-8 to upregulate CXCR7. RNAi-mediated knockdown of CXCR7 in CaP cells caused multiple antitumor effects, including decreased cell proliferation, cell-cycle arrest in G(1) phase, and decreased expression of proteins involved in G(1) to S phase progression. In contrast, addition of the CXCR7 ligand SDF-1a and CXCL11 to CaP cells did not affect cell proliferation. Over expression of CXCR7 in normal prostate cells increased their proliferation in a manner associated with increased levels of phospho-EGFR (epidermal growth factor receptor; pY1110) and phospho-ERK1/2. Notably, coimmunoprecipitation studies established a physical association of CXCR7 with EGFR, linking CXCR7-mediated cell proliferation to EGFR activation. Consistent with these findings, CXCR7-depleted CaP tumors grew more slowly than control tumors, expressing decreased tumor-associated expression of VEGF, cyclin D1, and p-EGFR. Together, these results reveal a novel mechanism of ligand-independent growth promotion by CXCR7 and its coregulation by the proinflammatory factor IL-8 in prostate cancer.

SUBMITTER: Singh RK

PROVIDER: S-EPMC3085571 | biostudies-literature | 2011 May

REPOSITORIES: biostudies-literature

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The IL-8-regulated chemokine receptor CXCR7 stimulates EGFR signaling to promote prostate cancer growth.

Singh Rajendra Kumar RK Lokeshwar Bal L BL

Cancer research 20110311 9

The proinflammatory chemokine receptor CXCR7 that binds the ligands CXCL11 and CXCL12 (SDF-1a) is elevated in a variety of human cancers, but its functions are not understood as it does not elicit classical chemokine receptor signaling. Here we report that the procancerous cytokine IL-8 (interleukin-8) upregulates CXCR7 expression along with ligand-independent functions of CXCR7 that promote the growth and proliferation of human prostate cancer cells (CaP cells). In cell culture, ectopic express ...[more]

PMID: 21398406

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Project description:BackgroundRecent advances have revealed a significant contribution of chemokines and their receptors in tumor growth, survival after chemotherapy, and organ-specific metastasis. The CXC chemokine receptor-7 (CXCR7) is the latest chemokine receptor implicated in cancer. Although over expressed in breast cancer cell lines and tumor tissues, its mechanism of action in breast cancer (BrCa) growth and metastasis is unclear. Studies in other cancers have implicated CXCR7 in cell proliferation, anti-apoptotic activity and cell-cell adhesion. The present study was initiated to examine the pattern of CXCR7 expression and its role in regulation of growth signaling in breast cancer.MethodsThe contribution of CXCR7 in BrCa cell proliferation was investigated in representative cell lines using real time quantitative PCR (q-PCR), proliferation assays, immunohistochemistry and immunoblotting. Phenotypic changes were examined after CXCR7 specific cDNA and siRNA transfection and expression levels were monitored by q-PCR. Further, the association of CXCR7 with epidermal growth factor receptor (EGFR) and modulation of its activity were investigated by western blotting, immunofluorescence, and in-situ proximity ligation assays in human BrCa cells and tissues.ResultsCXCR7 was expressed in both, estrogen receptor (ER) positive and negative BrCa cell lines. CXCR7 was also expressed unevenly in normal breast tissues and to a much higher extent in ER + cancer tissues. Depletion of CXCR7 in MCF7 BrCa cells by RNA interference decreased proliferation and caused cell cycle arrest. Further, proximity ligation assay (PLA) revealed colocalization of CXCR7 with EGFR in cancer tissues and cancer cell lines. CXCR7 depletion reduced levels of phospho-EGFR at Tyrosine1110 after EGF-stimulation and also reduced phosphorylation of ERK1/2, indicating a potentially direct impact on mitogenic signaling in MCF7 cells. Using siRNA to knockdown ?-arrestin2 in cells with EGFR over expression we were able to nearly deplete the CXCR7-EGFR colocalization events, suggesting that ?-arrestin2 acts as a scaffold to enhance CXCR7 dependent activation of EGFR after EGF stimulation.ConclusionsThese results demonstrate coupling of CXCR7 with EGFR to regulate proliferation of BrCa cells and suggest an important ligand-independent role of CXCR7 in BrCa growth. Thus, the CXCR7-EGFR axis is a promising target for breast cancer therapy.

Project description:The CXCL12/CXCR4 axis has been posited widely to have significant roles in many primary tumors and metastases. It is known that CXCR7 can also be engaged by CXCL12, but the exact function of CXCR7 is controversial. This prompted us to investigate the expression, specific function and signal transduction of CXCR7 in hepatocellular carcinoma (HCC). In this study, CXCR7 and CXCR4 were differentially expressed in nine cell lines of HCC, and that elevated expression of both CXCR7 and CXCL4 were correlated with highly metastatic ability of HCC cells. Moreover, CXCR7 expression was significantly upregulated in metastatic HCC samples compared with the non-metastatic ones by staining of high-density tissue microarrays constructed from a cohort of 48 human HCC specimens. CXCR7 overexpression enhanced cell growth and invasiveness in vitro, and tumorigenicity and lung metastasis in vivo. By contrast, CXCR7 stable knockdown markedly reduced these malignant behaviors. In addition, it was observed that alterations in CXCR7 expression were positively correlated with the phosphorylation levels of mitogen-activated protein kinase (MAPK) pathway proteins. Targeting extracellular regulated kinase pathway by using U0126 inhibitor or using CCX771, a selective CXCR7 antagonist, drastically reduced CXCR7-mediated cell proliferation. Importantly, by using human biotin-based antibody arrays, several differentially expressed proteins were identified in CXCR7-overexpression and depletion groups. Comparative analysis indicated that upstream regulators including TP53 and IL-6 were involved in CXCR7 signal transduction. CXCR7 expression was further proved to regulate expression of vascular endothelial growth factor A and galectin-3, which may contribute to tumor angiogenesis and invasiveness. Consequently, elevated expression of CXCR7 contributes to HCC growth and invasiveness via activation of MAPK and angiogenesis signaling pathways. Targeting CXCR7 may prevent metastasis and provide a potential therapeutic strategy for HCC.

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The IL-8-regulated chemokine receptor CXCR7 stimulates EGFR signaling to promote prostate cancer growth.

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The IL-8-regulated chemokine receptor CXCR7 stimulates EGFR signaling to promote prostate cancer growth.

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