Extracellular functions of galectin-3.

Galectin-3 has been suspected of modulating cell to extracellular matrix interactions in a novel fashion ever since it was first described. However, the rapid accumulation of research data in just the last 8 years alone has completely changed our perspective of this multifunctional protein. Its chimeric nature (consists of carbohydrate recognition and collagen like domains) somehow makes it suited to interact with a plethora of interesting extracellular matrix proteins some of which might enable it to cross the plasma membrane despite its lack of appropriate signal peptides. It is now becoming established as a mediator of signal transduction events on the cell surface as well as a mediator of a variety of extra-cellular processes such as kidney development, angiogenesis, neuronal functions, tumor metastasis, autoimmune disorders, endocytosis and possibly exocytosis. Nevertheless, it still retains its unique position as a mediator/modulator of cell to extracellular matrix adhesive interactions. Cells, particularly epithelial cells which lack galectin-3 expression, interact poorly with their extracellular matrices. In some of these processes, it functions as a matricellular protein, displaying both pro- and anti-adhesive properties.