The galectin family is phylogenically conserved in metazoans,
presently consisting of 14 identified members in
mammals, and galectin-3 is one of the most abundant,
widely distributed, and well-studied members. It is present
intracellularly in nuclear and cytoplasmic compartments,
but is also secreted through an unconventional
mechanism that involves vesicles and exosomes and,
consequently, present outside the cell. While galectin-3
shares many features with other galectins, including cellular
compartmentalization and functions, it appears to
be unique in its structural constituency in the N-terminal
domain, which is rich in proline, glycine, and alanine. It is
through this domain that galectin-3 is able to form
oligomers, and this may be one feature that functionally
differentiates it from other galectins. Galectin-3 has been
associated with several intracellular and extracellular
functions, and recent investigations have uncovered proteins
through which this lectin mediates its activities. The
availability of targeted mutant mice deficient in galectin-
3 and other proteins has also contributed to our appreciation
of the breadth of processes in which this protein is
involved. Among cell functions attributable to galectin-3
are some that are associated with neoplastic transformation
and invasiveness, but the most extensively documented
ones are those related to the immune and inflammatory
responses.