Glycosylation in cancer and infection : the role of sialic acid

Sammanfattning: Sialic acids (SA), a group of nine-carbon backbone monosaccharides are abundantly expressed in vertebrates. They are usually linked to the terminal of glycan chains and play crucial roles in many biological processes, including cell adhesion, cell-cell interactions, immune modulation, cancer cell migration and invasion, as well as viral infections. To analyze and monitor SA expression, antibodies and glycan-binding lectins are typically used. However, high costs and poor stability limit the application in SA analysis. To overcome these drawbacks, an imprinting technique was used to synthesize an alternative SA receptor – SA molecularly imprinted polymers (SA-MIPs). Fluorescent molecules are embedded into the MIPs, facilitating the detection of MIPs binding to cells by flow cytometry and fluorescence microscopy. Firstly, core-shell SA imprinted MIPs were used to analyze SA expression in a panel of breast cancer cell lines. The SA expression of these cell lines was also tested by using the two glycan-binding lectins, MAL andSNA, which recognize α2,3 and α2,6 SA, respectively. Our results show that breast cancer cell lines express α2,3 and α2,6 SA dissimilarly, and hence present different SA-MIP binding patterns. The specificity of SA-MIPs was further verified by an inhibition assay using two pentavalent SA conjugates that interfere with the SAMIPs.Furthermore, the SA-MIP synthesis protocol has been improved by using silica-coated polystyrene particles. The polystyrene core particles are lighter and smaller, increasing MIP suspensibility and augmenting MIP-cancer cell interactions. The cancer cell binding properties and the specificity have been verified by using thirteen different cancer cell lines, showing that the SA-MIPs can be used as effective tools for SA expression analysis. The SA-MIPs were used to analyze the SA expression of in vitro cultured cells treated with soluble cytokines to mimic the tumor microenvironment. The SA expression of two cancer cell lines stimulated with soluble cytokines was analyzed by using lectins and SA-MIPs. The MIPbinding data correlated well with lectin staining results, demonstrating the potential of SA-MIPs to be used in the analysis of overexpressed SA in the tumor microenvironment. Furthermore, the involvement of SA in the infection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was assessed. The viral surface receptor-binding domain (RBD) recognizes and conjugates with receptors on host cells, triggering the infection. Although the interaction between the RBD and host cells has been extensively studied, the mechanism behind this reaction is not fully determined. In this study, the interaction between the viral RBD and a panel of human cell lines from tissues susceptible to viral infection was tested. Moreover, the role of SA in this interaction has also been tested and evaluated.