Potential CanonicalWntPathway Activation in High-Grade Astrocytomas
Aberrantwntpathway activation through cytoplasmic stabilization ofβ-catenin is crucial for the development of various human malignancies. In gliomagenesis, the role of canonical (i.e.,β-catenin-dependent) signalling is largely unknown. Here, we studied canonicalwntpathway activation in 15 short-term cultures from high-grade gliomas and potential pathomechanisms leading to cytoplasmicβ-catenin accumulation. Furthermore, we assessed the prognostic relevance ofβ-catenin expression in a tissue microarray comprising 283 astrocytomas. Expression ofβ-catenin, its transcriptional cofactors TCF-1 and TCF-4 as well as GSK-3βand APC, constituents of theβ-catenin degradation complex was confirmed by RT-PCR in all cultures. A cytoplasmicβ-catenin pool was detectable in 13/15 cultures leading to some transcriptional activity assessed by luciferase reporter gene assay in 8/13. Unlike other malignancies, characteristic mutations ofβ-catenin and APC leading to cytoplasmic stabilization ofβ-catenin were excluded by direct sequencing or protein truncation test. In patient tissues,β-catenin expression was directly and its degradation product's (β-catenin-P654) expression was inversely correlated with WHO grade. Increasedβ-catenin expression and lowβ-catenin-P654 expression were associated with shorter survival. Altogether, we report on potential canonicalwntpathway activation in high-grade gliomas and demonstrate thatβ-catenin expression in astrocytomas is associated with increased malignancy and adverse outcome.