Abstract
Glioblastoma multiforme (GBM) is a fast growing brain tumor characterized by extensive infiltration into the surrounding tissue and one of the most aggressive cancers. GBM is the most common glioma (originating from glial-derived cells) that either evolves from a low grade astrocytoma or appears de novo. Wnt/β-catenin and Hepatocyte Growth Factor (HGF)/c-Met signaling are hyperactive in human gliomas, where they regulate cell proliferation, migration and stem cell behavior. We previously demonstrated that β-catenin is phosphorylated at Y142 by recombinant c-Met kinase and downstream of HGF signaling in neurons. Here we studied phosphoY142 (PY142) β-catenin and dephospho S/T β-catenin (a classical Wnt transducer) in glioma biopsies, GBM cell lines and biopsy-derived glioma cell cultures. We found that PY142 β-catenin mainly localizes in the nucleus and signals through transcriptional activation in GBM cells. Tissue microarray analysis confirmed strong nuclear PY142 β-catenin immunostaining in astrocytoma and GBM biopsies. By contrast, active β-catenin showed nuclear localization only in GBM samples. Western blot analysis of tumor biopsies further indicated that PY142 and active β-catenin accumulate independently, correlating with the expression of Snail/Slug (an epithelial-mesenchymal transition marker) and Cyclin-D1 (a regulator of cell cycle progression), respectively, in high grade astrocytomas and GBMs. Moreover, GBM cells stimulated with HGF showed increasing levels of PY142 β-catenin and Snail/Slug. Importantly, the expression of mutant Y142F β-catenin decreased cell detachment and invasion induced by HGF in GBM cell lines and biopsy-derived cell cultures. Our results identify PY142 β-catenin as a nuclear β-catenin signaling form that downregulates adhesion and promotes GBM cell invasion.