Human Cancer Biology The Activation of theWNT Signaling Pathway Is a Hallmark in Neurofibromatosis Type 1 Tumorigenesis

Purpose: The hallmark of neurofibromatosis type 1 (NF1) is the onset of dermal or plexiform neurofibromas,mainly composedof Schwann cells. Plexiformneurofibromas can transform intomalignant peripheral nerve sheath tumors (MPNST) that are resistant to therapies. Experimental Design: The aim of this study was to identify an additional pathway in the NF1 tumorigenesis. We focused our work on Wnt signaling that is highly implicated in cancer, mainly in regulating the proliferation of cancer stem cells. We quantifiedmRNAs of 89Wnt pathway genes in 57NF1associated tumors including dermal and plexiform neurofibromas and MPNSTs. Expression of two major stem cell marker genes and five major epithelial–mesenchymal transition marker genes was also assessed. The expression of significantly deregulated Wnt genes was then studied in normal human Schwann cells, fibroblasts, endothelial cells, and mast cells and in seven MPNST cell lines. Results: The expression of nine Wnt genes was significantly deregulated in plexiform neurofibromas in comparison with dermal neurofibromas. Twenty Wnt genes showed altered expression in MPNST biopsies and cell lines. Immunohistochemical studies confirmed the Wnt pathway activation in NF1-associated MPNSTs. We then confirmed that the knockdown of NF1 in Schwann cells but not in epithelial cells provoked the activation ofWnt pathway by functional transfection assays. Furthermore, we showed that the protein expression of active b-catenin was increased inNF1-silenced cell lines. Wnt pathway activation was strongly associated to both cancer stem cell reservoir and Schwann–mesenchymal transition. Conclusion: We highlighted the implication of Wnt pathway in NF1-associated tumorigenesis. Clin Cancer Res; 20(2); 358–71. 2013 AACR.