Glycosylated nuclear lectin CBP70 also associated with endoplasmic reticulum and the golgi apparatus: Does the ?classic pathway? of glycosylation also apply to nuclear glycoproteins?

Abstract

The subcellular plurilocalization of some lectins (galectin-1, galectin-3, galectin-10, calreticulin, etc.) is an intriguing problem, implying different partners according to their localization, and involvement in a variety of cellular activities. For example, the well-known lectin, galectin-3, a lactose-binding protein, can act inside the nucleus in splicing events, and at the plasma membrane in adhesion, and it was demonstrated that galectin-3 interacts in the cytoplasm with Bcl-2, an antiapoptotic protein. Some years ago, our group isolated a nuclear lectin CBP70, capable of recognizing N-acetylglucosamine residues. This lectin, first isolated from the nucleus of HL60 cells, was also localized in the cytoplasm. It has been demonstrated that CBP70 is a glycosylated lectin, with different types of glycosylation, comparing cytoplasmic and nuclear forms. In this article, we have studied the localization of CBP70 in undifferentiated HL60 cells by electron microscopy, immunofluorescence analysis, and subcellular fractionation. The results obtained clearly demonstrated that CBP70 is a plurilocalized lectin that is found in the nucleus, at the endoplasmic reticulum, the Golgi apparatus, and mitochondria, but not at the plasma membrane. Because CBP70, a nuclear glycoprotein, was found to be associated also with the endoplasmic reticulum and the Golgi apparatus where the glycosylation take place, it raised the question: where does the glycosylation of nuclear proteins occur?

The cellular prion protein: A new partner of the lectin CBP70 in the nucleus of NB4 human promyelocytic leukemia cells*

“…Indeed, these data are consistent with the hypothesis that PrP can shuttle into the nucleus via a complex with other protein(s) targeted to this cellular compartment [Jaegly et al, 1998]. It was shown that CBP70, which is present in the nucleus and in the cytoplasm [Hadj‐Sahraoui et al, 1996; Rousseau et al, 2000], is a glycoprotein whose glycosylation differs depending on its subcellular localization(s) [Rousseau et al, 1997]. It was suggested that sugar residues might be nuclear‐targeting signals and could define a new nuclear import mechanism [Duverger et al, 1996].…”

Identification of N-acetyl-d-glucosamine-specific lectins from rat liver cytosolic and nuclear compartments as heat-shock proteins

“…Several parallels can be drawn between the identification of p70, described in the present study as being Hsc-70 and as CBP-70 by Felin et al [13]. Indeed, Rousseau et al [15] demonstrated that CBP-70, initially shown to be localized in the cytosol and the nucleus, is also associated with endoplasmic reticulum and the Golgi apparatus. Interestingly HSPs are ubiquitous and are found in numerous cellular compartments, from the cytosolic to the endoplasmic reticulum compartments (Hsc-70, the cytosolic HSP-70 form, and BiP, the endoplasmic reticulum HSP-70 form, have a similarity of 61.2 %).…”

“…CBP-70 also localized in the cytosol and one 82 kDa ligand was characterized for the nuclear CBP-70 [14]. Rousseau et al [15] demonstrated, using electron microscopy, immunofluorescence analysis and subcellular fractionation, that CBP-70 is a pluri-localized lectin that is also found in the endoplasmic reticulum, Golgi apparatus and mitochondria. The nuclear lectins have mainly been found in ribonucleoprotein complexes [16].…”

Myocilin is associated with mitochondria in human trabecular meshwork cells

“…A variety of mitochondrial proteins are found under physiological conditions in different subcellular compartments (Soltys and Gupta, 1999, 2000). Other examples include p32 (Soltys et al, 2000), tumor necrosis factor receptor‐associated protein 1/TRAP‐1 (Cechetto and Gupta, 2000), 45‐kDa glycoprotein (Chandra et al, 1998), CBP70 (Rousseau et al, 2000), and Wilson's disease protein (Lutsenko and Cooper, 1998). Myocilin now may also add to the list.…”