A calreticulin-dependent nuclear export signal is involved in the regulation of liver receptor homologue-1 protein folding

Feng Ming Yang, Shan Jung Feng, Tsai Chun Lai, Meng Chun Hu

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

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/importindependent. 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 regionmaintenance 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 aggresomelike 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 misfoldinginduced aggregation.

Original languageEnglish
Pages (from-to)199-209
Number of pages11
JournalBiochemical Journal
Volume471
Issue number2
DOIs
Publication statusPublished - Oct 15 2015
Externally publishedYes

Keywords

  • Aggresome
  • Autophagy
  • Calreticulin
  • Heat shock protein 70
  • Liver receptor homologue-1 (LRH-1)
  • Nuclear export signal

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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