Galectin‐3 type‐C self‐association on neutrophil surfaces; The carbohydrate recognition domain regulates cell function

Galectin‐3 is an endogenous β‐galactoside‐binding lectin comprising a carbohydrate recognition domain (CRD) linked to a collagen‐like N‐domain. Both domains are required for galectin‐3 to induce cellular effects; a C‐terminal fragment of galectin‐3, galectin‐3C, containing the CRD but lacking the N‐domain, binds cell surface glycoconjugates but does not induce cellular effects since cross‐linking promoted by the N‐domain is thought to be required. Instead, galectin‐3C is proposed to antagonize the effects of galectin‐3 by competing for binding sites. The aim of this study was to investigate the effects of galectin‐3C on galectin‐3 interactions with human neutrophils. Recombinant galectin‐3C inhibited galectin‐3‐induced production of reactive oxygen species in primed neutrophils. Surprisingly, this inhibition was not due to competitive inhibition of galectin‐3 binding to the cells. In contrast, galectin‐3C potentiated galectin‐3 binding, in line with emerging evidence that galectin‐3 can aggregate not only through the N‐domain but also through the CRD. The cell surface interaction between galectin‐3C and galectin‐3 was corroborated by colocalization of fluorescently labeled galectin‐3 and galectin‐3C. Galectin‐3C can be generated in vivo through cleavage of galectin‐3 by proteases. Indeed, in circulation, galectin‐3 and galectin‐3C were both attached to the cell surface of neutrophils, which displayed great capacity to bind additional galectin‐3 and galectin‐3C. In conclusion, galectin‐3C enhances galectin‐3 binding to neutrophils by nonactivating type‐C self‐association, in parallel to inhibiting neutrophil activation by galectin‐3 (induced by type‐N self‐association). This implicates type‐C self‐association as a termination system for galectin‐3‐induced cell activation, with the purpose of avoiding oxidant‐dependent tissue damage.