The cell-surface-expressed nucleolin is associated with the actin cytoskeleton

Exp Cell Res. 2000 Dec 15;261(2):312-28. doi: 10.1006/excr.2000.5071.


Nucleolin is a RNA- and protein-binding multifunctional protein. Mainly characterized as a nucleolar protein, nucleolin is continuously expressed on the surface of different types of cells along with its intracellular pool within the nucleus and cytoplasm. By confocal and electron microscopy using specific antibodies against nucleolin, we show that cytoplasmic nucleolin is found in small vesicles that appear to translocate nucleolin to the cell surface. Translocation of nucleolin is markedly reduced at low temperature or in serum-free medium, whereas conventional inhibitors of intracellular glycoprotein transport have no effect. Thus, translocation of nucleolin is the consequence of an active transport by a pathway which is independent of the endoplasmic reticulum-Golgi complex. The cell-surface-expressed nucleolin becomes clustered at the external side of the plasma membrane when cross-linked by the nucleolin-specific monoclonal antibody mAb D3. This clustering, occurring at 20 degrees C and in a well-organized pattern, is dependent on the existence of an intact actin cytoskeleton. At 37 degrees C, mAb D3 becomes internalized, thus illustrating that surface nucleolin can mediate intracellular import of specific ligands. Our results point out that nucleolin should also be considered a component of the cell surface where it could be functional as a cell surface receptor for various ligands reported before.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / metabolism*
  • Amino Acid Sequence
  • Animals
  • Antibodies, Monoclonal / immunology
  • Antibodies, Monoclonal / metabolism
  • Cell Division
  • Cell Membrane / metabolism
  • Cell Membrane / ultrastructure
  • Cells, Cultured
  • Cytoskeleton / metabolism*
  • Endocytosis
  • Humans
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Mice
  • Microscopy, Confocal
  • Microscopy, Fluorescence
  • Microscopy, Immunoelectron
  • Molecular Sequence Data
  • Nuclear Proteins / metabolism
  • Nucleolin
  • Phosphoproteins / genetics
  • Phosphoproteins / immunology
  • Phosphoproteins / metabolism*
  • Protein Transport
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / immunology
  • RNA-Binding Proteins / metabolism*
  • Sequence Homology
  • Tumor Cells, Cultured


  • Actins
  • Antibodies, Monoclonal
  • Membrane Proteins
  • Nuclear Proteins
  • Phosphoproteins
  • RNA-Binding Proteins