Effects of the carbohydrate-binding protein galectin-3 on the invasiveness of human breast carcinoma cells.

Galectin-3 is a Mr 30,000 protein with carbohydrate-binding specificity for type I and II ABH blood group epitopes and polylactosamine glycans expressed on cell surface and extracellular matrix glycoproteins such as laminin. Cell lines propagated from human normal mammary epithelia and from benign or infiltrating components of primary breast tumours express low levels of galectin-3 in the cytoplasm. However, galectin-3 when added exogenously in solution or when bound within a three-dimensional matrix markedly enhanced the migration of the primary tumour cell lines through a Matrigel barrier. Galectin-3 expression in the cytoplasm and intercellularly on surface membranes was greatly increased in cell lines propagated from malignant ascites and pleural effusions of late stage breast cancer. These cell lines were non-invasive in the Matrigel assay and exogenous galectin-3 had no enhancing effect on invasiveness. These results suggest that galectin-3 could play multiple roles in cell metastasis at an early invasive stage by acting in a paracrine manner to stimulate cell migration through an extracellular matrix, and in later stage cancers in synergy with other mediators of cell-cell aggregation. However, endogenous galectin-3 expression in human breast cancers is not correlated directly with their invasive potential in vitro.