Wnt pathway markers in molecular subgroups of glioblastoma.

ABSTRACT

Glioblastoma (GBM) is a highly heterogeneous and aggressive brain tumor. Comprehensive genomic and transcriptomic analyses revealed that GBM segregates into three subgroups with characteristic signaling pathways. The Wnt pathway recently received increasing attention with the recognition of its importance in tumor development and recurrence through the promotion of glioma stem cells. As an extension of our previous translational studies, here we tested the possible interactions between key subgroup markers (IDH-1 R132H, EGFRvIII and both cytoplasmic and nuclear loss [c-/n-] of NF-1 expression) and the canonical (Wnt3a and beta-catenin) and non-canonical (Wnt5a and Fzd2) Wnt pathway markers by immunohistochemistry. These analyses revealed increased expression levels of both Wnt pathway markers with significant quantitative differences within, but not among subgroups. Wnt5a and Fzd2 levels were higher than the canonical marker levels in all subgroups. The strongest evidence for correlation between expression levels of the EGFRvIII subgroup marker and the Fzd2 Wnt marker was found, but weaker correlations also could be noted for IDH-1 R132H and NF-1 and some Wnt markers. The correlations detected between markers of the canonical and non-canonical pathways raised the possibility of cross-talk between the two pathways. Analyses of tumors with various NF-1 expression patterns (c+/n-; c-/n+ combined with c+/n+, and c-/n-) revealed that aberrant nuclear accumulation of NF-1 is accompanied by nuclear accumulation of beta-catenin, suggesting that they may act synergistically to define the tumor's biology. Altogether, our study presents expression characteristics of Wnt ligands and receptors, and suggests complex molecular interactions in subgroups of GBM.