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Ligand-dependent nuclear import is crucial for the function of the androgen receptor (AR) in both health and disease. The unliganded AR is retained in the cytoplasm but, on binding 5alpha-dihydrotestosterone, it translocates into the nucleus and alters transcription of its target genes. Nuclear import of AR is mediated by the nuclear import factor importin-alpha, which functions as a receptor that recognises and binds to specific nuclear localisation signal (NLS) motifs on cargo proteins. We show here that the AR binds to importin-alpha directly, albeit more weakly than the NLS of SV40 or nucleoplasmin. We describe the 2.6-angstroms-resolution crystal structure of the importin-alpha-AR-NLS complex, and show that the AR binds to the major NLS-binding site on importin-alpha in a manner different from most other NLSs. Finally, we have shown that pathological mutations within the NLS of AR that are associated with prostate cancer and androgen-insensitivity syndrome reduce the binding affinity to importin-alpha and, subsequently, retard nuclear import; surprisingly, however, the transcriptional activity of these mutants varies widely. Thus, in addition to its function in the nuclear import of AR, the NLS in the hinge region of AR has a separate, quite distinct role on transactivation, which becomes apparent once nuclear import has been achieved.

Original publication

DOI

10.1242/jcs.022103

Type

Journal article

Journal

J Cell Sci

Publication Date

01/04/2008

Volume

121

Pages

957 - 968

Keywords

Active Transport, Cell Nucleus, Amino Acid Sequence, Animals, Binding Sites, Blotting, Western, COS Cells, Cell Nucleus, Cercopithecus aethiops, Crystallography, X-Ray, Humans, Models, Biological, Molecular Sequence Data, Nuclear Localization Signals, Protein Binding, Protein Structure, Secondary, Receptors, Androgen, Sequence Homology, Amino Acid, alpha Karyopherins