STUDIES ON THE CELL-SURFACE VERSUS NUCLEAR-LOCALIZATION OF GALECTIN-3

Galectin-3 is a galactose/lactose-specific carbohydrate-binding protei n found in many cell types and tissues. Immunofluorescence analysis us ing antibodies directed against galectin-3 on mouse 3T3 fibroblasts, f ixed with formaldehyde and permeabilized with Triton X-100, yielded pr ominent labeling of the cell nucleus and some staining of the cytoplas m. A similar analysis, carried out on live 3T3 cells, yielded little o r no immunofluorescent staining. These results indicate that the major ity of the galectin-3 of 3T3 cells was intracellular, requiring deterg ent permeabilization for the binding of the antibodies. In contrast, b oth live as well as fixed and permeabilized thioglycollate-elicited mo use macrophages showed galectin-3 immunofluorescent staining, suggesti ng that the protein is expressed at the cell surface of these macropha ges. Inside 3T3 cells, galectin-3 is found in the nuclear matrix, alon g with the small nuclear ribonucleoprotein complexes (snRNPs) involved in the splicing of pre-mRNA. This notion is consistent with the recen t identification of galectin-3 as a required factor in a cell-free ass ay for RNA splicing. During mitosis, galectin-3 and the snRNPs are fou nd throughout the cell except where chromosomal DNA is located.