Abstract 5031: R-spondin potentiates Wnt/β-catenin signaling in Ewing sarcoma cells.

Abstract

Abstract Proper regulation of Wnt signaling is highly context-dependent and critical for growth and cellular maintenance. It is well-established that dysregulation of the canonical Wnt/β-catenin pathway contributes to the development and progression of numerous malignancies. Despite this, there has been little evidence to support a role for canonical Wnt signaling in Ewing sarcoma (ES) pathogenesis. Recent studies have shown that when members of the leucine-rich G-protein coupled receptor (LGR) family, namely LGR4 and LGR5, are bound by their ligands, R-spondins, they potentiate Wnt/β-catenin activity. Importantly, recent studies from our lab have shown that some ES tumors and cell lines express high levels of LGR5. In addition, R-spondin is highly expressed in the developing bone, which is the primary site of ES in children. Since ES cells do not exhibit canonical Wnt/β-catenin activity in standard culture conditions, we hypothesized that cues from the tumor microenvironment may be required for activation of this pathway. In particular, we hypothesized that R-spondins would potentiate Wnt activity in LGR-expressing ES cells. To test this hypothesis, ES cells were cultured in the presence of WNT3A and/or R-spondin 2 (Rspo2). Immunocytochemistry was used to determine β-catenin nuclear localization, and Wnt transcriptional activity was determined by flow cytometry and luciferase activity using cell lines transduced with lentiviral 7xTCF-GFP and 7xTCF-luciferase reporters, respectively. qRT-PCR was used to confirm transcription of the Wnt target gene AXIN2. Our results show that exogenous WNT3A induces β-catenin nuclear localization in ES cells and is associated with induction of TCF-mediated transcriptional activity and AXIN2 expression. Furthermore, Wnt/β-catenin activation is potentiated in the presence of Rspo2, and ES cells lines with the highest expression of LGRs show the strongest potentiation. Interestingly, however, exogenous WNT3A and Rspo2 did not induce Wnt activity in all cells. Together these data confirm that in the presence of exogenous ligand, Wnt/β-catenin signaling can be robustly activated in a subpopulation of ES cells and that signaling is potently enhanced in the presence of Rspo2 and LGRs. To our knowledge, this is the first evidence of R-spondins influencing Wnt activity in a non-epithelial cancer. These studies support the concept that R-spondin expression in the tumor microenvironment may contribute to ES pathogenesis by modulating Wnt/β-catenin signaling. Citation Format: Elisabeth A. Pedersen, Christopher A. Scannell, Elizabeth R. Lawlor. R-spondin potentiates Wnt/β-catenin signaling in Ewing sarcoma cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5031. doi:10.1158/1538-7445.AM2013-5031