A serine/threonine-rich motif is one of three nuclear localization signals that determine unidirectional transport of the mineralocorticoid receptor to the nucleus.
The mineralocorticoid receptor (MR) is a tightly regulated nuclear hormone receptor that selectively transmits corticosteroid signals. Steroid treatment transforms MR from a transcriptionally inert state, in which it is distributed equally between the nucleus and cytoplasm, to an active completely nuclear transcription factor. We report here that MR is an atypical nuclear hormone receptor that moves unidirectionally from the cytoplasm to the nucleus. We show that nuclear import of MR is controlled through three nuclear localization signals (NLSs) of distinct types. Nuclear localization of naive MR was mediated primarily through a novel serine/threonine-rich NLS (NL0) in the receptor N terminus. Specific amino acid substitutions that mimicked phosphorylation selectively enhanced or repressed NL0 activity, highlighting the potential for active regulation of this new type of NLS. The second NLS (NL2) within the ligand-binding domain also lacks a recognizable basic motif. Nuclear transfer through this signal was strictly dependent on steroid agonist, but was independent of the interaction of MR with coactivator proteins. The third MR NLS (NL1) is a bipartite basic motif localized to the C terminus of the MR DNA-binding domain with properties distinct from those of NL1 of the closely related glucocorticoid receptor. NL1 acted in concert with NL0 and NL2 to stimulate nuclear uptake of the agonist-treated receptor, but also directed the complete nuclear localization of MR in response to treatment with steroid antagonist. These results present MR as a nuclear hormone receptor whose unidirectional transfer to the nucleus may be regulated through multiple pathways.
Walther
Rhian F
RF
Department of Medicine and Biochemistry, Graduate Program in Biochemistry, Ottawa Health Research Institute, Ottawa Hospital, University of Ottawa, Ontario, Canada.
Atlas
Ella
E
Carrigan
Amanda
A
Rouleau
Yanouchka
Y
Edgecombe
Allison
A
Visentin
Laura
L
Lamprecht
Claudia
C
Addicks
Gregory C
GC
Haché
Robert J G
RJ
Lefebvre
Yvonne A
YA
D021581:Active Transport, Cell Nucleus; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D019556:COS Cells; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D036681:Fluorescence Recovery After Photobleaching; D019084:Fluorescent Antibody Technique, Indirect; D005982:Glutathione Transferase / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D015530:Nuclear Matrix / Q000378:metabolism; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D018161:Receptors, Mineralocorticoid / Q000378:metabolism*; D012694:Serine / Q000737:chemistry*; D013256:Steroids / Q000378:metabolism; D013912:Threonine / Q000737:chemistry*; D013997:Time Factors; D014162:Transfection
D008024:Ligands; D019913:Nuclear Localization Signals; D011965:Receptors, Glucocorticoid; D018161:Receptors, Mineralocorticoid; D013256:Steroids; D049452:Green Fluorescent Proteins; D013912:Threonine; D012694:Serine; D005982:Glutathione Transferase