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

Abstract

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.

Expression of Chemokines and Chemokine Receptors in Brain Tumor Tissue Derived Cells

“…Consistently it has been reported that CXCR4 and CXCR7 receptors are different in both expression patterns and functional roles in Neuroblastoma (Liberman et al, 2012). These variations were also addressed in meningiomas.…”

β-Arrestin1 and Distinct CXCR4 Structures Are Required for Stromal Derived Factor-1 to Downregulate CXCR4 Cell-Surface Levels in Neuroblastoma

“…Thus, future therapies designed to specifically enhance expression of b-arrestin1 may be able to selectively inhibit CXCR4 cell-surface expression and function in neuroblastoma. Our results additionally suggest that b-arrestin1 expression, together with GRK2, may serve as useful markers in combination with CXCR4 for predicting metastatic risk in neuroblastoma, helping to regulate the migration, proliferation, invasion, and metastasis of neuroblastoma that is dependent on CXCR4 (Raffaghello et al, 2009;Liberman et al, 2012). Other b-arrestin1 binding proteins might also modulate CXCR4 expression and function in neuroblastoma, for example, ESCRT-0, STAM-1, and/or AIP-4 (Bhandari et al, 2007;Malik and Marchese, 2010).…”

“…In addition to MYCN gene amplification, DNA ploidy changes, and expression of neurotrophin receptors (Vasudevan et al, 2005;Raffaghello et al, 2009;Huang et al, 2011;Davidoff, 2012), elevated expression of the CXCR4 CXC chemokine receptor is a marker and proposed drug target for high-risk neuroblastoma (Shim et al, 2009). CXCR4 expression is associated with neuroblastoma metastatic growth (Liberman et al, 2012), clinical presentation in bone marrow and liver (Geminder et al, 2001;Russell et al, 2004;Meier et al, 2007;Raffaghello et al, 2009;Zhao et al, 2012), and poor prognosis (Russell et al, 2004). Unfortunately, pharmacological targeting of CXCR4 is complicated by the widespread expression of CXCR4 on normal cells.…”

Chemokines and Their Receptors Are Key Players in the Orchestra That Regulates Wound Healing

“…67 However, this chemokine has also been associated with cancer progression and tumor metastasis. 68,69 In contrast to the more homeostatic effects of CXCL12a, the majority of the remaining CXC chemokines are considered to be proinflammatory. For example, CXCL8 is not constitutively expressed, but exhibits inducible expression in multiple cell types, including neutrophils, epithelial cells, endothelial cells, fibroblasts, and specific cancer cells, largely in response to proinflammatory stimuli such as TNF-a, IL-1, bacterial products, and thrombin.…”