Export of galectin-3 from nuclei of digitonin-permeabilized mouse 3T3 fibroblasts.
Galectin-3 is a galactose-/lactose-binding protein (M(r) approximately 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 (approximately 650 and approximately 60 kDa), both of which can be disrupted by lactose.
Tsay
Y G
YG
Department of Biochemistry, Michigan State University, East Lansing, Michigan, 48824, USA.
Lin
N Y
NY
Voss
P G
PG
Patterson
R J
RJ
Wang
J L
JL
D016475:3T3 Cells; D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism*; D001692:Biological Transport; D002463:Cell Membrane Permeability; D002467:Cell Nucleus / Q000378:metabolism*; D004072:Digitonin; D005347:Fibroblasts / Q000378:metabolism*; D037502:Galectin 3; D007202:Indicators and Reagents; D037102:Lectins; D051379:Mice
D000943:Antigens, Differentiation; D037502:Galectin 3; D007202:Indicators and Reagents; D037102:Lectins; D004072:Digitonin