The galectins constitute a large family of carbohydrate-binding proteins with specificity for N-acetyl-lactosamine-containing glycoproteins. At least 14 mammalian galectins, which share structural similarities in their carbohydrate recognition domains (CRD), have been identified to date. The galectins have been classified into the prototype galectins (-1, -2, -5, -7, -10, -11, -13, -14), which contain one CRD and exist either as a monomer or a noncovalent homodimer. The chimera galectins (Galectin-3) containing one CRD linked to a nonlectin domain, and the tandem-repeat Galectins (-4, -6, -8, -9, -12) consisting of two CRDs joined by a linker peptide. Galectins lack a classical signal peptide and can be localized to the cytosolic compartments where they have intracellular functions. However, via one or more as yet unidentified non-classical secretory pathways, galectins can also be secreted to function extracellularly. Individual members of the galectin family have different tissue distribution profiles and exhibit subtle differences in their carbohydrate-binding specificities. Each family member may preferentially bind to a unique subset of cell-surface glycoproteins (1‑4).
Galectin-8, also known as prostate carcinoma tumor antigen 1 (PCTA1) in human, is a tandem repeat-type galectin. Prototype (single CRD) isoforms arising through alternate gene splicing have also been identified (5). Galectin-8 is highly expressed in lung carcinomas, certain forms of prostate carcinomas, as well as other tumor cells. It binds to a subset of cell surface integrins to modulate ECM-integrin interactions. As a soluble ligand, Galectin-8 can inhibit cell adhesion (6). Immobilized Galectin-8, however, has also been shown to promote cell adhesion (7). Human and mouse Galectin-8 share approximately 80% amino acid homology (4).
