The genetic basis for inactivation of Wnt pathway in human osteosarcoma

Abstract

BackgroundOsteosarcoma is a highly genetically unstable tumor with poor prognosis. We performed microarray-based comparative genomic hybridization (aCGH), transcriptome sequencing (RNA-seq), and pathway analysis to gain a systemic view of the pathway alterations of osteosarcoma.MethodsaCGH experiments were carried out on 10 fresh osteosarcoma samples. The output data (Gene Expression Omnibus Series accession number GSE19180) were pooled with published aCGH raw data (GSE9654) to determine recurrent copy number changes. These were analyzed using Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis to identify altered pathways in osteosarcoma. Transcriptome sequencing of six osteosarcomas was performed to detect the expression profile of Wnt signaling pathway genes. Protein expression of WNT1, β-catenin, c-myc, and cyclin D1 in the Wnt pathway was detected by immunohistochemistry (IHC) in an independent group of 46 osteosarcoma samples.ResultsKEGG pathway analysis identified frequent deletions of Wnt and other Wnt signaling pathway genes. At the mRNA level, transcriptome sequencing found reduced levels of mRNA expression of Wnt signaling pathway transcripts. While WNT1 protein expression was detected by IHC in 69.6% (32/46) of the osteosarcomas, no β-catenin protein was detected in the nucleus. β-catenin protein expression was, however, detected in the membrane and cytoplasm of 69.6% (32/46) of the osteosarcomas. c-myc protein expression was detected in only 47.8% (22/46) and cyclin D1 protein expression in 52.2% (24/46) of osteosarcoma samples. Kaplan-Meier survival analysis showed that WNT1-negative patients had a trend towards longer disease free survival than WNT1-positive patients. Interestingly, in WNT1-negative patients, those who were also cyclin D1-negative had significantly longer disease free survival than cyclin D1-positive patients. However, there was no significant association between any of the investigated proteins and overall survival of human osteosarcoma patients.ConclusionsFrequent deletions of Wnt and other Wnt signaling pathway genes suggest that the Wnt signaling pathway is genetically inactivated in human osteosarcoma.

Genome-Informed Targeted Therapy for Osteosarcoma

“…And although osteosarcoma tumors show a great deal of SV, SVs were found within only 81 of the druggable genes (30 recurrently). The most common genes with an SV were TP53 (29), LRP1B (14), RB1 (8), and FHIT (8). No potentially in-frame gene fusions were detected in more than 2 patients.…”

“…Previous studies have analyzed CN alterations in an attempt to identify candidate osteosarcoma driver oncogenes or tumor suppressors (9)(10)(11)(12)(13)(14)(15). These studies have focused on the identification of recurrent changes.…”

Mesenchymal Tumors Can Derive from Ng2/Cspg4-Expressing Pericytes with β-Catenin Modulating the Neoplastic Phenotype

“…However, its role in sarcomas has been controversial, with some studies suggesting activated β-catenin signaling is important to drive the neoplastic phenotype, while others found an opposite effect (Cai et al, 2014; Cai et al, 2010; Du et al, 2014; Matushansky et al, 2007; Wan et al, 2014). In mesenchymal cell development, β-catenin is precisely regulated at different stages for normal differentiation, raising the possibility that either high or low β-catenin leads to pathology (Chen et al, 2007; Hoffman and Benoit, 2013; Li et al, 2008; Wan et al, 2013).…”

Immuno-genomic landscape of osteosarcoma

“…Recent whole genome sequencing (WGS) and molecular profiling studies undertaken in predominantly pediatric populations have shown high levels of chromosome structural variations, rearrangements resulting from chromothripsis (20-89%) as well as mutation clusters known as kataegis (50-85% of cases) that result in significant disease heterogeneity but few recurrent clinically actionable alterations [5][6][7] . These studies have yielded insights into aberrant signaling pathways such as PI3K/mTOR (24%) 7 , IGF signaling (7%) 6 , and Wnt signaling 8 . However, the efficacy of targeted therapies such as mTOR inhibitors in unselected patient populations with relapsed osteosarcoma has been limited 9,10 .…”