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

Abstract

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 Mn(2+), 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.

Galectins in Endothelial Cell Biology and Angiogenesis: The Basics

“…In line with this, Hadari et al showed that endothelial cell binding to vitronectin was hardly enhanced by galectin-8 since this adhesion is mediated through integrinαVβ3, which only shows limited interaction with galectin-8 [100]. Instead, galectin-8 was shown to interact with other integrin subunits present in endothelial cells, including α3, α5, and β1 [100,101]. As such, galectin-8 can be expected to differentially mediate cell adhesion and migration, depending on the presence of specific extracellular matrix components as well as certain endothelial cell surface molecules.…”

“…In the latter, CD166 (ALCAM) was identified as a binding partner suggesting that the interaction of galectin-8 with specific endothelial cell surface molecules determines the angioregulatory function of the protein. In line with this, Hadari et al showed that endothelial cell binding to vitronectin was hardly enhanced by galectin-8 since this adhesion is mediated through integrinαVβ3, which only shows limited interaction with galectin-8 [100]. Instead, galectin-8 was shown to interact with other integrin subunits present in endothelial cells, including α3, α5, and β1 [100,101].…”

Galectin-8, cytokines, and the storm

“…The underlying mechanism involves binding of Gal-8 to a complex of cell surface receptors that include LRP1, uPAR, and MRC2; activation of AKT, ERK, JNK, and NFkB signaling pathways; and induction of cytokine/chemokine production (Figure 2). Receptors such as CD44 [7] or members of the integrin family [9,10] are additional candidates to mediate the effects of Gal-8 on cytokine secretion as these receptors are binding partners of Gal-8 and were reported to trigger signaling pathways that converge upon activation of the NF-κB pathway [141][142][143]. Importantly, cytokine expression is mediated by different signaling pathways.…”

“…uPAR co-immunoprecipitates with integrins and integrin-associated signaling molecules such as FAK and Src family kinases (reviewed in [ 78 ]) to modulate the affinity of β 1 , β 2 , and β 3 integrins [ 79 ]. Integrins, including β 1 , αM, α 3 β 1 , and α 6 β 1 , as well as other ECM proteins, also serve as binding partners to Gal-8 that functions as a matricellular protein [ 9 , 11 , 13 , 80 ]. Complex formation between extracellular Gal-8 and integrins triggers integrin-mediated signaling cascades such as Tyr phosphorylation of FAK and paxillin, and a robust and sustained activation of the ERK and PI3K pathways [ 9 , 10 , 81 , 82 ].…”

“…synovial fluids of RA patients (25-60 nM) [7] or serum of breast (4.7-233.2 ng/ ml) and colon (5.6-178.2 ng/ml) cancer patients [8]). Extracellular Gal-8 promotes cell adhesion upon binding to cell adhesion molecules such as integrins [9][10][11][12][13], CD44 [7], CD166 [14], and Podoplanin [15].…”