Export of Galectin-3 from Nuclei of Digitonin-Permeabilized Mouse 3T3 Fibroblasts |
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Authors: | Yeou-Guang Tsay Nancy Y Lin Patricia G Voss Ronald J Patterson John L Wang |
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Institution: | Department of Biochemistry, Michigan State University, East Lansing, Michigan, 48824, USA. |
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Abstract: | 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. |
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Keywords: | lectins pre-mRNA splicing factors nucleocytoplasmic transport |
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