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 specificit y for type I and II ABH blood group epitopes and polylactosamine glyca ns expressed on cell surface and extracellular matrix glycoproteins su ch as laminin. Cell lines propagated from human normal mammary epithel ia and from benign or infiltrating components of primary breast tumour s express low levels of galectin-3 in the cytoplasm. However, galectin -3 when added exogenously in solution or when bound within a three-dim ensional matrix markedly enhanced the migration of the primary tumour cell lines through a Matrigel barrier. Galectin-3 expression in the cy toplasm 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 th e Matrigel assay and exogenous galectin-3 had no enhancing effect on i nvasiveness. These results suggest that galectin-3 could play multiple roles in cell metastasis at an early invasive stage by acting in a pa racrine manner to stimulate cell migration through an extracellular ma trix, and in later stage cancers in synergy with other mediators of ce ll-cell aggregation. However,endogenous galectin-3 expression in human breast cancers is not correlated directly with their invasive potenti al in vitro. (C) 1996 Wiley-Liss, Inc.