Format

Send to

Choose Destination
J Biol Chem. 2004 Mar 5;279(10):8867-72. Epub 2003 Dec 18.

Identification of novel nuclear export and nuclear localization-related signals in human heat shock cognate protein 70.

Author information

1
Department of Pharmacology, Tokyo Women's Medical University, School of Medicine, 8-1 Kawada-cho, Shinjuku-ku, Tokyo 162-8666, Japan. fuji@research.twmu.ac.jp

Abstract

Heat shock cognate protein 70 (Hsc70) serves nuclear transport of several proteins as a molecular chaperone. We have recently identified a novel variant of human Hsc70, heat shock cognate protein 54 (Hsc54), that lacks amino acid residues 464-616 in the protein binding and variable domains of Hsc70. In the present study, we examined nucleocytoplasmic localization of Hsc70 and Hsc54 by using green fluorescent protein (GFP) fusions. GFP-Hsc70 is localized in both the cytoplasm and the nucleus at 37 degrees C and accumulated into the nucleolus/nucleus after heat shock, whereas GFP-Hsc54 always remained exclusively in the cytoplasm under these conditions. Mutation studies indicated that 20 amino acid residues of nuclear localization-related signals, which are missing in Hsc54 but are retained in Hsc70, are required for proper nuclear localization of Hsc70. We further found that Hsc54 contains a functional leucine-rich nuclear export signal (NES, (394)LDVTPLSL(401)) which is differently situated from the previously proposed NES in Saccharomyces cerevisiae Ssb1p. The cytoplasmic localization of Hsc54 was impaired by a mutation in NES as well as by a nuclear export inhibitor, leptomycin B, suggesting that Hsc54 is actively exported from the nucleus to the cytoplasm through a CRM1-dependent mechanism. In contrast, the nucleocytoplasmic localization of Hsc70 was not affected by the same mutation of NES or leptomycin B. These results suggest that the nuclear localization-related signal could functionally mask NES leading to prolonged retention of Hsc70 in the nucleus. An additional mechanism for unmasking the NES may regulate nucleocytoplasmic trafficking of Hsc70.

PMID:
14684748
DOI:
10.1074/jbc.M308848200
[Indexed for MEDLINE]
Free full text

Supplemental Content

Full text links

Icon for HighWire
Loading ...
Support Center