The Effect Of Polysialic Acid (PSA) On The Neural Cell Adhesion Molecule(NCAM) During Epithelial-Mesenchymal Transition

Sialic acids(Sias), a monosaccharide with a nine-carbon backbone, frequently terminate the carbohydrate chains of glycoproteins and glycolipids. As the aberrant expression have been reported in various cancer cells, Sias could be served as a potential tumor marker. Its homopolymer, composed of α-(2,8)-linked sialic acid residues, was named as polysialic acid(PSA). Owing to their negative electric charge, PSA is crucial in cellular functions, such as cell-cell interaction, influencing conformation of glycoproteins on cell membranes, and masking antigenic determinants on receptor molecules. PSA, catalyzed synergistically by two polysialyltransferases, ST8 Sia II(STX) and ST8 Sia IV(PST), was mainly attached to the neural cell adhesion molecule(NCAM) resulting in PSA-NCAM. PSA-NCAM was barely expressed in adult, but re-expressed in lung cancer, pancreatic cancer, neuroblastoma and glioma, where it modulates cell adhesion, migration, and invasion. NCAM level in human malignant breast cancer(BC) is dramatically increased in advanced stage associated with dysregulation of Sias; however, NCAM and PSA expression and their biological functions in human BC remain were unknown. Therefore, study on PSA and PSA-NCAM to understand their effects during tumorigenesis and metastasis in malignant tumor will provide the basic theory for cancer therapy.In this study, epithelial–mesenchymal transition(EMT) model using mammary epithelial cells was established using mouse and human breast cells, and functional roles of PSA and PSA-NCAM in during EMT progression were explored. The main results are as follows:(1) Expression of NCAM and PSA-NCAM in human BC clinical specimens. Increased expression of NCAM or PST was found and was correlated with the TNM stage in human BC specimens(n=24). High expression of NCAM and low expression of PSA-NCAM was showed in high-grad tissue using tissue microarrays(TMAs) of BC(n=60). Expression of NCAM related to the positive rate of TMAs score accounts approximate 93%(TNM I, 87.5%; TNM II, 92%; TNM III, 100%). It indicated that expression of NCAM is positively correlated with BC tumor tissue grade. On the contrast, high expression of PSA-NCAM were found in TNM I stage(75%), resulting that the aberrant polysialylation occurred in the initial stage during BC progression. However, survival analysis showed that expression of NCAM have no relationship with BC patient. This suggested that NCAM and PSA-NCAM may play different roles in breast tumor tumorigenesis and progression.(2) Expression of NCAM and PSA-NCAM in cells undergoing EMT. The expression of NCAM and PSA-NCAM was increased in normal mouse and human breast cell lines undergoing TGF-β1-induced EMT.(3) Effect of PSA in modulating NCAM on cell behaviors. The overexpression of NCAM-140 increased cell proliferation, migration, but not in motility, which fulfilled the EMT-like process based on the “cadherin-switch”. While, the overexpression of PSA increased cell motility and decreased cell adhesion; Otherwise, PSA increased NCAM-mediated cell proliferation and migration and decreased NCAM-mediated cell adhesion, indicating that PSA can promote cell potential metastasis.(4) The different cell signaling pathways mediated by NCAM and PSA. PSA activated EGFR/STAT3 pathway while NCAM induced β-catenin/slug pathway. Moreover, NCAM-140 induced β-catenin/slug signaling in cell by decreasing CK1α expression involved in upregulation of axin 2, slug, c-myc and ccnd1 and regulated cell proliferation and migration; While PSA induced EGFR/STAT3 signaling in cell by increasing GSK 3β expression in favor of cell motility. This result indicated that NCAM and PSA mediated different cell signaling pathway in modulating cell behaviors during breast cancer progression.In conclusion, we demonstrated that increased expression of NCAM and its high polysialylation were found in BC. Overexpression of NCAM-140 induced the occurrence of EMT. PSA further increased NCAM-mediated cell proliferation and migration and decreased NCAM-mediated cell adhesion. Meanwhile, PSA and NCAM mediated different cell behaviors through a different cell signaling pathways.