Galectin-8 binding to integrins inhibits cell adhesion and induces apoptosis

The interaction of cells with the extracellular matrix regulates cell adhesion, motility, growth, survival and differentiation through integrin-mediated signal transduction, Here we demonstrate that galectin-8, a secreted mammalian beta-galactoside binding protein, inhibits adhesion of human carcinoma (1299) cells to plates coated with integrin ligands, and induces cell apoptosis, Pretreatment of the cells with Mn2+, which increases the affinity of integrins for their ligands, abolished the inhibitory effects of galectin-8, The inhibitory effects of galectin-8 were specific and were not mimicked by plant lectins or other galectins (galectin-1 and galectin-3). In accordance with its anti-adhesive effects, transfection of galectin-8 cDNA into 1299 cells significantly reduced (by 75%) colony formation, when compared to the number of colonies formed by cells transfected With an empty vector. Affinity chromatography over immobilized galectin-8 indicated that few membrane proteins interacted with galectin-8 in a sugar-dependent manner. Microsequencing and western immunoblotting revealed that alpha(3)beta(1) integrin derived from 1299 as well as other cells (e.g. HeLa and human endothelial cells) is a major galectin-8 binding-protein. Furthermore, immunoprecipitation and immunohistochemical studies suggested that endogenous galectin-8, secreted from 1299 cells, forms complexes with alpha(3)beta(1) integrins expressed on the surface of 1299 cells. Galectin-8 also interacts with other members of the integrin family, like alpha(6)beta(1) integrins, In contrast, galectin-8 only minimally interacts with alpha(4) or beta(3) integrins, We propose that galectin-8 is an integrin binding-protein that interacts to a different extent with several, but not all members of the integrin family. Binding of galectin-8 modulates integrin interactions with the extracellular matrix and thus regulates cell adhesion and cell survival.