Abstract
Background
Neural cell adhesion molecule (NCAM), a common mammalian cell surface glycoprotein, is the major substrate of polysialic acid (polySia). Polysialylated NCAM occurs in many types of cancer, but rarely in normal adult tissues. Epithelial-mesenchymal transition (EMT) is an important process contributing to tumor metastasis. The functional role of NCAM hypersialylation in EMT is unclear.
Method
Expression of NCAM and polysialylated NCAM in breast cancer progression were evaluated by western blot (WB), immunohistochemistry, semi-quantitative PCR and immunoprecipitation (IP). Overexpression of NCAM-140 and ST8SiaII were performed to assess the functional role of NCAM hypersialylation by liposome transfection. Cell proliferation ability was investigated with MTT assay. Transwell and wound closure assay were conducted to evaluate cell migratory ability. Phagokinetic gold sol assay and cell adhesion assay were performed to assess cell motility ability and cell adhesion ability, respectively. Furthermore, WB and IP were used to reveal the activated signaling pathway.
Results
The present study indicates that NCAM and attached polysialic acid affect behaviors of breast epithelial cells through differential signaling pathways, based on the following observations: (i) NCAM and polysialylated NCAM were aberrantly regulated in breast cancer cells; (ii) NCAM and polysialylated NCAM expression were upregulated in normal breast epithelial cells undergoing EMT; (iii) NCAM overexpression induced EMT in breast epithelial cells; (iv) NCAM promoted cell proliferation and migration through activation of a β-catenin/slug signaling pathway; (v) modification of polySia attached to NCAM inhibited cell adhesion and promoted cell motility through activation of an EGFR/STAT3 pathway.
Conclusion
This study demonstrates that NCAM and polysialylated NCAM facilitate different signaling pathway and affect different cell behaviors. Switching between the NCAM-mediated pathways appeared to depend on polySia decoration.
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