Abstract 2903: The role of canonical WNT/β-catenin signaling in glial tumors

Introduction: The canonical WNT/β-catenin pathway plays an important role in embryogenesis as well as in carcinogenesis. When soluble WNT factor binds to the transmembrane receptor, the inactivation complex composed of axin/GSK-3/APC becomes instable and free β-catenin translocates from the cytoplasm to the nucleus. It binds to the T-cell factor complex and activates specific target genes including cyclin D1, c-Myc and c-jun, which have been reported to be critical for cancer development. Although β-catenin has been shown to be abnormally expressed in a variety of human cancers, little is known about its involvement in initiation and propagation of glial tumors. In this project the involvement of WNT/β-catenin signaling in tumorigenesis of glial brain tumors, with special focus on the brain tumor stem like cell population has been investigated. Clinical Significance, Experimental Approach and Results: The evaluation of glial tumor samples (WHO grade II-IV) based on histological analysis of tissue micro arrays revealed about 10- 15% of the cases having active WNT/β-catenin signaling, as determined by the presence of intranuclear β-catenin staining. Moreover, recently published wide genomic analysis data (Verhaak et al., 2010) showed that DICKKOPF-1 (DKK-1), a negative feedback regulator of WNT/β-catenin through inhibition of WNTs co-receptor LRP5/6 and a protein down stream of β-catenin activation, is approximately seven fold over-expressed in glioblastoma multiformes (GBM) of the mesenchymal phenotype, supposed to be the most aggressive type of GBMs containing highly motile cell popoulation. Concordantly, Kaplan-Meier survival curves based on the Rembrandt database showed that DKK-1 over-expression is a negative prognostic factor concerning an overall survival of GBM patients. We hypothesize that a more aggressive and infiltrative growth of mesenchymal subtype of GBM might be dependent on the activation of canonical WNT/β-catenin pathway. Therefore, we established a lentiviral gain-of-function dual promoter system with a point-mutated β-catenin (can not be phosphorylated and inactivated) under EF1alpha promoter enabling us to stably genetically modify patient derived glioma cultures and select for β-catenin over-expressing cells based on their eGFP expression (ubiquitin promoter). The comparative quantitative gene expression analyses of the downstream target gene AXIN2, controlled exclusively by canonical WNT/β-catenin pathway showed up to 150-fold expression level increase as compared to wild type control. Cells over-expressing point-mutated β-catenin displayed a higher in vitro migration potential and up to threefold increased invasion in Boyden Chamber based in vitro invasion assays. Furthermore, we developed a human DKK1 overexpression model using a lentiviral construct to test the effect of boosted DKK1 on in vitro proliferation/migration patterns and its influence on WNT/ β-catenin signaling pathway. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2903. doi:10.1158/1538-7445.AM2011-2903