Tissue fibronectin is an endogenous ligand for galectin-1

A 14K ß-galactoside-binding lecttn (galectin-1) ispresent in many animal tissues. In a search for endogenous ligands,we surveyed galectin-1-binding proteins in human placenta. Extractof human placenta with 2 M urea was applied to a Sepharose 4Bcolumn conjugated with galectin-1 purified from frog (Rana catesbeiana)eggs. Two major proteins eluted with 100 mM lactose from thecolumn-bound fraction showed apparent molecular masses of 220and 180 kDa on SDS-PAGE under reducing conditions. Western blottinganalysis using monoclonal antibodies indicated that these proteinswere fibronectin and laminin, respectively. Most placenta] andamniotic fibronectins bound strongly to the column, whereasalmost all plasma fibronectin passed through the column. Thegalectin-1, fibronectin and laminin were immunohistochemicallyshown to be co-localized in the extracellular matrix of placentaltissue. In a cell attachment assay, rhabdosarcoma cells adheredto a plate coated with placental fibronectin, even in the presenceof GRGDS peptide, if galectin-1 were also present This adhesiveeffect of galectin-1 was inhibited by lactose. These resultsindicate that tissue fibronectin, as well as laminin, serveas endogenous ligands for galectin-1, suggesting that galectin-1may play a role in assembly of the extracellular matrix, orin the control of cell adhesion based on lectin-extracellularmatrix interaction. extracellular matrix fibronectin galectin laminin placenta