The selective post-translational processing of transcription factor Nrf1 yields distinct isoforms that dictate its ability to differentially regulate gene expression

Sci Rep. 2015 Aug 13:5:12983. doi: 10.1038/srep12983.

Abstract

Upon translation, the N-terminal homology box 1 (NHB1) signal anchor sequence of Nrf1 integrates it within the endoplasmic reticulum (ER) whilst its transactivation domains [TADs, including acidic domain 1 (AD1), the flanking Asn/Ser/Thr-rich (NST) domain and AD2] are transiently translocated into the ER lumen, whereupon the NST domain is glycosylated to yield an inactive 120-kDa glycoprotein. Subsequently, these TADs are retrotranslocated into extra-luminal subcellular compartments, where Nrf1 is deglycosylated to yield an active 95-kDa isoform. Herein, we report that AD1 and AD2 are required for the stability of the 120-kDa Nrf1 glycoprotein, but not that of the non-glycosylated/de-glycosylated 95-kDa isoform. Degrons within AD1 do not promote proteolytic degradation of the 120-kDa Nrf1 glycoprotein. However, repositioning of AD2-adjoining degrons (i.e. DSGLS-containing SDS1 and PEST2 sequences) into the cyto/nucleoplasm enables selective topovectorial processing of Nrf1 by the proteasome and/or calpains to generate a cleaved active 85-kDa Nrf1 or a dominant-negative 36-kDa Nrf1γ. Production of Nrf1γ is abolished by removal of SDS1 or PEST2 degrons, whereas production of the cleaved 85-kDa Nrf1 is blocked by deletion of the ER luminal-anchoring NHB2 sequence (aa 81-106). Importantly, Nrf1 activity is positively and/or negatively regulated by distinct doses of proteasome and calpain inhibitors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence / genetics
  • Animals
  • COS Cells
  • Calpain / genetics*
  • Calpain / metabolism
  • Chlorocebus aethiops
  • Endoplasmic Reticulum / genetics
  • Gene Expression Regulation
  • Humans
  • Nuclear Respiratory Factor 1 / biosynthesis
  • Nuclear Respiratory Factor 1 / genetics*
  • Proteasome Endopeptidase Complex / genetics
  • Protein Isoforms / biosynthesis
  • Protein Isoforms / genetics*
  • Protein Processing, Post-Translational / genetics*
  • Proteolysis
  • Sequence Homology, Amino Acid
  • Transcriptional Activation / genetics*

Substances

  • NRF1 protein, human
  • Nuclear Respiratory Factor 1
  • Protein Isoforms
  • Calpain
  • Proteasome Endopeptidase Complex