AbstractPrion diseases are characterized by the presence of an abnormal isoform of the cellular prion protein (PrPc) whose physiological role still remains elusive. To better understand the function of PrPc, it is important to identify the different subcellular localization(s) of the protein and the different partners with which it might be associated. In this context, the PrPc–lectins interactions are investigated because PrPc is a sialoglycoprotein which can react with lectins which are carbohydrate‐binding proteins. We have previously characterized a nuclear lectin CBP70 able to recognize N‐acetyl‐β‐d‐glucosamine residues in HL60 cells. Using confocal immunofluorescence, flow‐cytofluorometry, and Western‐blotting, we have found that PrPc is expressed in the nucleus of the NB4 human promyelocytic leukemia cell line. It was also found that the lectin CBP70 is localized in NB4 cell nuclei. Moreover, several approaches revealed that PrPc and CBP70 are colocalized in the nucleus. Immunoprecipitation experiments showed that these proteins are coprecipitated and interact via a sugar‐dependent binding moiety. In conclusion, PrPc and CBP70 are colocalized in the nuclear compartment of NB4 cells and this interaction may be important to better understand the biological function and possibly the conversion process of PrPc into its pathological form (PrPsc). J. Cell. Biochem. 84: 408–419, 2002. © 2001 Wiley‐Liss, Inc.