Charcot-Leyden Crystal Protein/Galectin-10 Interacts with Cationic Ribonucleases and is Required for Eosinophil Granulogenesis

Abstract Background The human eosinophil Charcot-Leyden Crystal (CLC) protein is a member of the Galectin superfamily and is also known as Galectin-10 (Gal-10). CLC/Gal-10 forms the distinctive hexagonal bipyramidal crystals considered hallmarks of eosinophil participation in allergic responses and related inflammatory reactions; however, the glycan-containing ligands of CLC/Gal-10, its cellular function(s), and its role(s) in allergic diseases are unknown. Objective We sought to determine the binding partners of CLC/Gal-10 and elucidate its role in eosinophil biology. Methods Intracellular binding partners were determined by ligand blotting with CLC/Gal-10, followed by co-immunoprecipitation and co-affinity purifications. The role of CLC/Gal-10 in eosinophil function was determined by employing enzyme activity assays, confocal microscopy, and shRNA knock-out of CLC/Gal-10 expression in human CD34+ cord blood hematopoietic progenitors differentiated to eosinophils. Results CLC/Gal-10 interacts with both human eosinophil granule cationic ribonucleases, eosinophil-derived neurotoxin (EDN, RNS2) and eosinophil cationic protein (ECP, RNS3) , and with murine eosinophil-associated ribonucleases. The interaction is independent of glycosylation and is not inhibitory toward endoribonuclease activity. Activation of eosinophils with INF-γ induces the rapid co-localization of CLC/Gal-10 with EDN/RNS2 and CD63. ShRNA knock-down of CLC/Gal-10 in human cord blood-derived CD34+ progenitor cells impairs eosinophil granulogenesis. Conclusions CLC/Gal-10 functions as a carrier for the sequestration and vesicular transport of the potent eosinophil granule cationic ribonucleases during both differentiation and degranulation, enabling their intracellular packaging and extracellular functions in allergic inflammation.