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

The subcellular plurilocalization of some lectins (galectin-1, galectin-3, galectin-10, calreticulin, etc.) is an intriguing problem, implying differe nt partners according to their localization, and involvement in a variety o f cellular activities. For example, the well known lectin, galectin-3, a la ctose-binding protein, can act inside the nucleus in splicing events, and a t 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-a cetylglucosamine residues. This lectin, first isolated from the nucleus of HL60 cells, was also localized in the cytoplasm. It has been demonstrated t hat CBP70 is a glycosylated lectin, with different types of glycosylation, comparing cytoplasmic and nuclear forms. In this article, we have studied t he localization of CBP70 in undifferentiated HL60 cells by electron microsc opy, immunofluorescence analysis, and subcellular fractionation. The result s 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 reticul um and the Golgi apparatus where the glycosylation take place, it raised th e question: where does the glycosylation of nuclear proteins occur? J. Cell . Biochem. 78:638-649, 2000. (C) 2000 Wiley-Liss, Inc.