Expression of cadherins and their undercoat proteins (α-, β-, and γ-catenins and p120) and accumulation of β-catenin with no gene mutations in synovial sarcoma
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E-cadherin, the major intercellular adhesion molecule of epithelial cells, is important in determining the architecture of sarcomas, especially those showing epithelioid features. In addition to its role in cell adhesion, β-catenin, a cadherin undercoat protein, has been shown to function as a downstream transcriptional activator of the Wnt/Wingless signaling pathway. In order to evaluate the significance of the cadherin cell adhesion system and the Wnt/Wingless signaling pathway in the morphogenesis and/or tumorigenesis of synovial sarcoma (a major type of sarcoma with epithelioid features), immunoreactivity for pan-cadherin, E-cadherin, and their undercoat proteins (α-, β- ,and γ-catenins and p120) was evaluated in 15 synovial sarcomas. Immunoreactivity for pan-cadherin, E-cadherin, α-catenin, β-catenin, and p120 was observed in all 15 specimens. Immunoreactivity for pan-cadherin was stronger than that for E-cadherin. Expression of γ-catenin was detected in ten specimens. Although β-catenin was observed only at the cell–cell boundaries in four specimens, it was present in the nucleus and cytoplasm and at the cell–cell boundaries in the other 11, suggesting constitutional activation of the Wnt/Wingless signaling pathway in synovial sarcoma. Direct sequencing for exon 3 of the β-catenin gene, however, revealed no mutations in any of the 15 specimens. In conclusion, other types of cadherin besides E-cadherin, together with cadherin undercoat proteins, may play a role in cell adhesion in synovial sarcoma. Furthermore, mechanisms other than mutation of exon 3 of the β-catenin gene may activate the Wnt/Wingless signaling pathway in this type of tumor.
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