As an orphan member of the nuclear receptor family, liver receptor homologue-1 (LRH-1) controls a tremendous range of transcriptional programmes that are essential for metabolism and hormone synthesis. Our previous studies have shown that nuclear localization of the LRH-1 protein is mediated by two nuclear localization signals (NLSs) that are karyopherin/importin-dependent. It is unclear whether LRH-1 can be actively exported from the nucleus to the cytoplasm. In the present study, we describe a nuclear export domain containing two leucine-rich motifs [named nuclear export signal (NES)1 and NES2] within the ligand-binding domain (LBD). Mutation of leucine residues in NES1 or NES2 abolished nuclear export, indicating that both NES1 and NES2 motifs are essential for full nuclear export activity. This NES-mediated nuclear export was insensitive to the chromosomal region maintenance 1 (CRM1) inhibitor leptomycin B (LMB) or to CRM1 knockdown. However, knockdown of calreticulin (CRT) prevented NES-mediated nuclear export. Furthermore, our data show that CRT interacts with LRH-1 and is involved in the nuclear export of LRH-1. With full-length LRH-1, mutation of NES1 led to perinuclear accumulation of the mutant protein. Immunofluorescence analysis showed that these perinuclear aggregates were co-localized with the centrosome marker, microtubule-associated protein 1 light chain 3 (LC3), ubiquitin and heat shock protein 70 (Hsp70), indicating that the mutant was misfolded and sequestered into aggresome-like structures via the autophagic clearance pathway. Our study demonstrates for the first time that LRH-1 has a CRT-dependent NES which is not only required for cytoplasmic trafficking, but also essential for correct protein folding to avoid misfolding-induced aggregation.
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Research Article|
October 02 2015
A calreticulin-dependent nuclear export signal is involved in the regulation of liver receptor homologue-1 protein folding
Feng-Ming Yang;
Feng-Ming Yang
*Graduate Institute of Physiology, National Taiwan University College of Medicine, Taipei 100, Taiwan
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Shan-Jung Feng;
Shan-Jung Feng
*Graduate Institute of Physiology, National Taiwan University College of Medicine, Taipei 100, Taiwan
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Tsai-Chun Lai;
Tsai-Chun Lai
*Graduate Institute of Physiology, National Taiwan University College of Medicine, Taipei 100, Taiwan
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Meng-Chun Hu
Meng-Chun Hu
1
*Graduate Institute of Physiology, National Taiwan University College of Medicine, Taipei 100, Taiwan
1To whom correspondence should be addressed (email mengchun@ntu.edu.tw).
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Publisher: Portland Press Ltd
Received:
March 03 2015
Revision Received:
July 27 2015
Accepted:
August 12 2015
Accepted Manuscript online:
August 12 2015
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 2015 Authors; published by Portland Press Limited
2015
Biochem J (2015) 471 (2): 199–209.
Article history
Received:
March 03 2015
Revision Received:
July 27 2015
Accepted:
August 12 2015
Accepted Manuscript online:
August 12 2015
Citation
Feng-Ming Yang, Shan-Jung Feng, Tsai-Chun Lai, Meng-Chun Hu; A calreticulin-dependent nuclear export signal is involved in the regulation of liver receptor homologue-1 protein folding. Biochem J 15 October 2015; 471 (2): 199–209. doi: https://doi.org/10.1042/BJ20150252
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