Abstract 3406: Prognostic relevance of Wnt-beta catenin signaling in Ewing's sarcoma (2010)

Abstract Wnt signaling pathway is involved in normal embryonic development and has a majoir role in development and progression of cancer. If the role of wnt pathway is well characterized in carcinoma, its involvement is under study in sarcoma. Starting from an experimental model constituted by stable transfectants of short-hairpin RNA of CD99, characterized by reduced malignancy, real Time PCR analysis suggested a down-modulation of Wnt signaling. In fact, TC-71 cells deprived of CD99 showed increased expression of some inhibitors of the Wnt pathway (DKK1, sFRP1) and reduction in some ligands (Wnt 2 and 11). Since TCsiCD99 are less malignant than parental cells, these preliminary data indicated a possible relationship between Wnt pathway and EWS aggressiveness. Gene expression profiling of 30 primary EWS tumors confirmed these indications: low expression of Frizzled (Fzd) 2,3, LRP5/6 and low expression of some Wnt ligands (Wnt3, 11) are significantly associated with better prognosis. Validations of these associations at protein level by evaluation of Fzd2, Fzd3 and beta-catenin in EWS tissue arrays confirmed that lower levels of Fzds are associated with better prognosis, while no beta-catenin nuclear localization was found in any of the 103 cases examined. In contrast, around 40% of patients showed high expression of beta-catenin at the membrane level and these patients showed better prognosis. No activation of canonical-wnt pathway was confirmed also in the experimental model, with non nuclear localization of the protein. It is well known that beta-catenin is an essential co-activator of the canonical Wnt pathway but it also plays a critical structural role in cadherin-based adhesions. In EWS, beta-catenin membrane associated localization suggested its major role in cell-cell adhesion. Indeed, direct and significant associations were observed with other adhesion proteins, such as ZO-1, desmoplakin and desmoglein (p&amp;lt;0.05, Fisher t test). Higher expression of these proteins is also associated with better prognosis, indicating the positive value of adherence and tight junctions in limiting EWS aggressiveness. LLack of nuclear beta-catenin in EWS samples suggested that the Wnt canonical pathway is not activated. However, Frzs and Wnts are also involved in the delivery of a beta-catenin independent signaling, which is dependent on cytoskeleton organization and intracellular Ca+ release. Genetic expression of mediators of these non-canonical signaling pathways (CAMK, RAC1) are also associated with EWS prognosis. In conclusion, 1. canonical Wnt pathway is not activated in EWS, whereas non-canonical Wnt pathways are and they show prognostic relevance. 2. beta-catenin functions are more related to regulation of cell-cell adhesion than activating Wnt target genes transcription (grants from EU project Eurobonet and Italian Association for Cancer Research). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3406.