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

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.