Nuclear localisation of wild type and mutant galectin-3 in transfected cells

Galectin-3, a member of a family of carbohydrate-binding proteins, is prese nt generally in the cytoplasm of cells. However, galectin 3 can also be loc ated in nuclei under certain conditions although it lacks any known nuclear localisation signal and the mechanism by which the protein is sequestered in nuclei is unknown. Here we describe that Cos-7 cells or rabbit smooth mu scle lib-l cells transfected with cDNA encoding hamster galectin-3 sequeste r the protein in nuclei whereas untransfected BHK cells expressing the endo genous hamster lectin or transfected BHK cells over-expressing the protein, do not. Confocal immunofluorescence microscopy of Cos-7 cells or rabbit sm ooth muscle Rb-l cells transfected with cDNAs encoding mutants of hamster g alectin-3 containing N-terminal or internal deletions shows that nuclear lo calisation does not require the first 103 amino acid residues of the protei n. Further deletion of residues 104-110 dramatically prevents sequestration in nuclei. However, the sequence A(104)PTGALT(110) by itself is not obliga tory for nuclear localisation and can be substituted by other unrelated seq uences. A truncated galectin-3 protein, that is blocked in nuclear expressi on, retains carbohydrate-binding activity, making less likely the possibili ty that severe N-terminal truncations of galectin-3 induce mis-folding lead ing to aggregation and cytoplasmic sequestration and an incidental effect o n nuclear trafficking. These studies indicate that nuclear import and reten tion of galectin-3 is a property of the CRD domain and is independent of N- terminal domains that others have shown to contain binding domains for vari ous nuclear components. 2000 (C) Editions scientifiques et medicales Elsevi er SAS.