Secretion of the galectin family of mammalian carbohydrate-binding proteins

Galectins are cytosolic proteins that lack any signal sequence for transpor t into the endoplasmic reticulum and are not glycosylated, although several galectins contain consensus sites for N-glycosylation, indicating that the se proteins do not traverse the ER-Golgi network. However, there is abundan t evidence for the extracellular localisation of some galectins at cell sur faces, in the extracellular matrix and in cell secretions consistent with o ther evidence for extracellular roles of galectins as modulators of cell ad hesion and signalling. How then are galectins secreted if not through the c lassical secretory pathway? Do all galectins share the same secretory pathw ay? Can a particular galectin utilise more than one secretory pathway? If g alectins play important extracellular roles how is their secretion regulate d in relation to function? These are still largely unanswered questions but recent studies are beginning to give glimpses into some novel aspects of t he secretion of these intriguing proteins. (C) 1999 Elsevier Science B.V. A ll rights reserved.