Galectins typically bind β-galactose-containing glycoconjugates and share primary structural homology in their carbohydrate-recognition domains (CRDs), representing a group of proteins that are the most widely expressed class of lectins in all organisms. Three galectins that have shown importance in cancer progression and metastasis are galectin-1, -3, and -9.

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An Overview of Galectin

Endogenous lectin Galectin is a kind of soluble protein which exists in the cell chamber or secretes to the extracellular, and widely distributes in organism, from nematodes to human. Galectin is divided into three types: prototype, chimeric and tandem repeats. Galectins has a special amino acid sequence and has high affinity with sugar conjugates containing β-galactoside residues. It binds to the β-galactoside on the surface of the cell to regulate cell survival and signal transduction, and it acts as a specific adhesion between cells, between cell and matrix, within tumor metastasis and infiltration. Growth and adhesion are involved in cell proliferation, differentiation, local immune regulation and apoptosis. Galectins also mediates the adhesion of macrophages and dendritic cells to other lectin activated lymphocytes and produces an IgG mediated immune response. Galectin-1,3 both have the role of promotion and anti-adhesion, which has features of double regulation.

Inhibition of Galectin

Galectin can be inhibited by some pharmacological drugs in multiple steps. Carbohydrates, antibodies and peptides are inhibitors of galectin. Citrus pectin is a kind of natural polysaccharide extracted from plant cell wall and modified citrus pectin (MCP) is obtained after specific pH and humidity treatment. The MCP acts as a high affinity ligand of Galectin-3 and CRD of Galectin-3, which competes with Galectin-3 ligand in vivo. When the MCP reaches a certain concentration, the galectin-3 site on the tumor cell surface is almost occupied by it, thus blocking the mutual recognition and aggregation of the cells, preventing the tumor cells from obtaining nutrients from the blood vessels and inhibiting the growth of tumor.

Galectin and Diseases

Galectin-3 in galectin can promote nerve axon growth, induce endothelial cell differentiation and vascular growth, leading to tumor onset and metastasis. The expression of Galectin-3 is increased in some malignant tumors (lymphoma, hepatocellular carcinoma, etc.). It is found that galectin-3 can be used as a reliable marker for thyroid neoplasms and can better differentiate benign and malignant thyroid tumors since Galectin-3 is not expressed in benign or normal thyroid tissues, but in malignant tumors. The further study of Galectins and all the complex conjugates outside cells is of great significance in the field of tumor immunotherapy.