Unconventional secretion factor GRASP55 is increased by pharmacological unfolded protein response inducers in neurons

Sci Rep. 2019 Feb 7;9(1):1567. doi: 10.1038/s41598-018-38146-6.

Abstract

Accumulation of misfolded proteins in the endoplasmic reticulum (ER), defined as ER stress, results in activation of the unfolded protein response (UPR). UPR activation is commonly observed in neurodegenerative diseases. ER stress can trigger unconventional secretion mediated by Golgi reassembly and stacking proteins (GRASP) relocalization in cell lines. Here we study the regulation of GRASP55 by the UPR upon pharmacological induction of ER stress in primary mouse neurons. We demonstrate that UPR activation induces mRNA and protein expression of GRASP55, but not GRASP65, in cortical neurons. UPR activation does not result in relocalization of GRASP55. UPR-induced GRASP55 expression is reduced by inhibition of the PERK pathway of the UPR and abolished by inhibition of the endonuclease activity of the UPR transducer IRE1. Expression of the IRE1 target XBP1s in the absence of ER stress is not sufficient to increase GRASP55 expression. Knockdown of GRASP55 affects neither induction nor recovery of the UPR. We conclude that the UPR regulates the unconventional secretion factor GRASP55 via a mechanism that requires the IRE1 and the PERK pathway of the UPR in neurons.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Astrocytes / drug effects
  • Astrocytes / metabolism
  • Endoplasmic Reticulum Stress
  • Endoribonucleases / genetics
  • Endoribonucleases / metabolism
  • Gene Expression
  • Golgi Matrix Proteins / genetics
  • Golgi Matrix Proteins / metabolism*
  • Humans
  • Neurons / drug effects*
  • Neurons / metabolism*
  • Protein Serine-Threonine Kinases / genetics
  • Protein Serine-Threonine Kinases / metabolism
  • Protein Transport
  • Unfolded Protein Response / drug effects*
  • X-Box Binding Protein 1 / metabolism

Substances

  • GORASP2 protein, human
  • Golgi Matrix Proteins
  • X-Box Binding Protein 1
  • ERN1 protein, human
  • Protein Serine-Threonine Kinases
  • Endoribonucleases