Abstract 1978: The tyrosine kinase Syk plays a role in the maintenance of intercellular adhesive junctions in human breast cancer cells

The non-receptor spleen tyrosine kinase Syk has mainly been studied in hematopoietic cells in which it plays a key role in the immune-response signalling. We previously demonstrated that Syk is also present in mammary epithelial cells and that its expression is lost during malignant progression of breast cancer cell lines. Clinical studies confirmed loss of Syk expression, not only in breast tumors but also in other carcinomas and melanoma. Xenotransplantation animal experiments evidenced that Syk acts as a tumor and metastasis suppressor in breast cancer and melanoma. The mechanisms by which Syk exerts its anti-oncogenic activity remain, however, unrevealed. Using a quantitative phospho-proteomic SILAC approach in breast cancer cells, we identified new potential Syk substrates involved in intercellular adhesion and epithelial cell polarity, both characters of cell differentiation that are lost during tumor progression. Using in vitro kinase assays, we demonstrated that E-cadherin and various catenins are direct Syk substrates. The tyrosine residues phosphorylated by Syk were identified by mass spectrometry and phospho-peptide-specific antibodies were generated. By immunofluorescence, we observed that endogenous Syk and E-cadherin colocalize at adherens junctions and that transient DsRed-Syk transfection induces phospho-E-cadherin- and phospho-catenin epitopes at cell-cell contacts. Immunoprecipitation experiments indicate that phosphorylated E-cadherin and catenins are associated in a complex. Syk-mediated phosphorylation of E-cadherin seems to be important for the proper localization of p120-catenin at adherens junctions. Syk knockdown in breast cancer cells partially inhibits the re-aggregation of cells and increases invasion in Matrigel. Using Syk knockdown and overexpression we explored its potential role in the maintenance of an epithelial phenotype, preventing EMT. In conclusion, Syk might play a role in the establishment and maintenance of intercellular junctions via the phosphorylation of the E-cadherin/catenin complex. Loss of Syk expression or function might lead to the destabilization of these complexes and promote invasion (supported by Fondation ARC SL220110603480) Citation Format: Toufic Kassouf, Philippe Montcourrier, Romain Larive, Nadir Bettache, Anne Morel, Fabrice Merezegue, Serge Urbach, Peter J. Coopman. The tyrosine kinase Syk plays a role in the maintenance of intercellular adhesive junctions in human breast cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1978. doi:10.1158/1538-7445.AM2014-1978