Molecular Analysis of Hybrid Neurofibroma/Schwannoma Identifies Common Monosomy 22 and α-T-Catenin/CTNNA3 as a Novel Candidate Tumor Suppressor

Neurofibromas and schwannomas are benign Schwann cell-derived peripheral nerve sheath tumors arising sporadically and within neurofibromatoses. Multiple tumors are a hallmark of neurofibromatosis type 1 (NF1) and type 2 (NF2) and schwannomatosis. Neurofibromas in NF1 and schwannomas in NF2 or schwannomatosis are defined by distinctive molecular hits. Among these, multiple hybrid neurofibromas/schwannomas may also appear, not yet being defined by a molecular background. We therefore performed molecular analysis of 22 hybrid neurofibromas/schwannomas using array comparative genomic hybridization, immunohistochemistry, quantitative RT-PCR, and functional analyses of cultured Schwann cells. Furthermore, we analyzed SMARCB1 by fluorescence in situ hybridization and multiplex ligation-dependent probe. Monosomy 22 was identified in 44% of tumors of tested patients with hybrid neurofibromas/schwannomas. In addition, in a single case, we detected focal deletion of the α-T-catenin/CTNNA3 gene (10q21.3). To further characterize this candidate, transient knockdown of α-T-catenin in Schwann cells was performed. CTNNA3 depleted cells showed cytoskeletal abnormalities and reduced E-cadherin expression, indicating epithelial-mesenchymal transition-like abnormalities. To conclude, we uncovered loss of chromosome 22 in almost half of all cases with hybrid neurofibromas/schwannomas of patients with multiple peripheral nerve sheath tumors. We tagged α-T-catenin/CTNNA3 as a novel candidate gene. Our functional investigations might indicate involvement of α-T-catenin/CTNNA3 in the biology of peripheral nerve sheath tumors.