Functions of Galectins in Cell Adhesion and Chemotaxis

Abstract

This chapter focuses on the role of galectins in cell adhesion and chemotaxis, which is mostly attributable to the extracellular functions of galectins. The capability of galectins of binding to β-galactoside-containing glycoproteins present on the cell surface and also in extracellular matrices allows the galectin family to be categorized as cell-adhesion molecules. Galectin ligands relevant to cell adhesion functions are tabulated. The involvement of galectins in cell–cell and cell–matrix adhesion has been described in various aspects. The levels of expression of galectin-1 in T cells and B cells are elevated when these cells are activated. Galectin-1 is also expressed in thymic epithelial cells. Galectin-1 has been involved in myoblast detachment from laminin during muscle development, as it inhibits myoblast adhesion to laminin. Galectin-1 also inhibits the attachment of smooth muscle cells (SMC) to laminin through binding to the α1β1 integrin on SMC and to laminin. Similar to galectin-1, galectin-3 has been recognized as a laminin-binding protein and was initially regarded as a laminin receptor. In tumor cells, endogenous or transfected galectin-3 may be secreted andbind to the extracellular matrices or cell surface ligands and affect the cells by an autocrine or paracrine mechanism. So, galectin-3 can influence the cells both intra- and extra-cellularly. For the neutrophil activation by galectin-3 that results in a respiratory burst, the extravasation process has been suggested to render the cells more sensitive to the lectin. Galectin-8 has been shown to interact with integrins and modulate cell adhesion. Findings that galectin-3 and -9 are novel chemoattractants for monocytes/ macrophages and eosinophils are discussed.