Transport of galectin-3 between the nucleus and cytoplasm. II. Identification of the signal for nuclear export.
Galectin-3, a factor involved in the splicing of pre-mRNA, shuttles between the nucleus and the cytoplasm. Previous studies have shown that incubation of fibroblasts with leptomycin B resulted in the accumulation of galectin-3 in the nucleus, suggesting that the export of galectin-3 from the nucleus may be mediated by the CRM1 receptor. A candidate nuclear export signal fitting the consensus sequence recognized by CRM1 can be found between residues 240 and 255 of the murine galectin-3 sequence. This sequence was engineered into the pRev(1.4) reporter system, in which candidate sequences can be tested for nuclear export activity in terms of counteracting the nuclear localization signal present in the Rev(1.4) protein. Rev(1.4)-galectin-3(240-255) exhibited nuclear export activity that was sensitive to inhibition by leptomycin B. Site-directed mutagenesis of Leu247 and Ile249 in the galectin-3 nuclear export signal decreased nuclear export activity, consistent with the notion that these two positions correspond to the critical residues identified in the nuclear export signal of the cAMP-dependent protein kinase inhibitor. The nuclear export signal activity was also analyzed in the context of a full-length galectin-3 fusion protein; galectin-3(1-263; L247A) showed more nuclear localization than wild-type, implicating Leu247 as critical to the function of the nuclear export signal. These results indicate that residues 240-255 of the galectin-3 polypeptide contain a leucine-rich nuclear export signal that overlaps with the region (residues 252-258) identified as important for nuclear localization.
Li
Su-Yin
SY
Department of Biochemistry, Michigan State University, East Lansing, MI 48824, USA.
Davidson
Peter J
PJ
Lin
Nancy Y
NY
Patterson
Ronald J
RJ
Wang
John L
JL
Arnoys
Eric J
EJ
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism*; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism; D037502:Galectin 3 / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000032:analysis / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D041681:NIH 3T3 Cells; D049790:Nuclear Export Signals / Q000235:genetics; D011487:Protein Conformation; D017434:Protein Structure, Tertiary / Q000235:genetics
D037502:Galectin 3; D049790:Nuclear Export Signals; D049452:Green Fluorescent Proteins