Export of Galectin-3 from Nuclei of Digitonin-Permeabilized Mouse 3T3 Fibroblasts

• Published in: Experimental cell research 1999-11, Vol.252 (2), p.250-261
• Main Authors: Tsay, Yeou-Guang, Lin, Nancy Y., Voss, Patricia G., Patterson, Ronald J., Wang, John L.
• Format: Article
• Language: English
• Subjects: 3T3 Cells; Animals; Antigens, Differentiation - metabolism; Biological Transport; Cell Membrane Permeability; Cell Nucleus - metabolism; Digitonin; Fibroblasts - metabolism; Galectin 3; Indicators and Reagents; Lectins; Mice; nucleocytoplasmic transport; pre-mRNA splicing factors
• ISSN: 0014-4827; 1090-2422
• DOI: 10.1006/excr.1999.4643

Galectin-3 is a galactose-/lactose-binding protein (Mr ∼30,000), identified as a required factor in the splicing of pre-mRNA. Immunofluorescence staining revealed that galectin-3 distributes differentially between the nucleus and the cytoplasm, depending on the proliferative state of the cells under analysis. Using digitonin-permeabilized mouse 3T3 fibroblasts, we provide evidence that galectin-3 is rapidly and selectively exported from the nucleus. Although both phosphorylated and nonphosphorylated isoforms of galectin-3 are found in the nuclear fraction, only phosphorylated galectin-3 is identified in the exported fraction, implying that phosphorylation is important for the nuclear export of the protein. The rate of galectin-3 export is temperature dependent and is decreased by the addition of wheat germ agglutinin. More strikingly, galectin-3 export can be inhibited by the addition of leptomycin B, a drug that disrupts the interaction between the leucine-rich nuclear export signal and its receptor, CRM1 (chromosome maintenance region 1). Indeed, a putative leucine-rich nuclear export signal can be found in residues 241–249 of the murine galectin-3 sequence. Finally, gel filtration of the exported material showed that galectin-3 can be found in at least two high molecular weight complexes (∼650 and ∼60 kDa), both of which can be disrupted by lactose.