Cytokine-induced translocation of GRP78 to the plasma membrane triggers a pro-apoptotic feedback loop in pancreatic beta cells

Cell Death Dis. 2019 Apr 5;10(4):309. doi: 10.1038/s41419-019-1518-0.

Abstract

The 78-kDa glucose-regulated protein (GRP78) is an ubiquitously expressed endoplasmic reticulum chaperone, with a central role in maintaining protein homeostasis. Recently, an alternative role for GRP78 under stress conditions has been proposed, with stress-induced extracellular secretion and translocation of GRP78 to the cell surface where it acts as a multifunctional signaling receptor. Here we demonstrate translocation of GRP78 to the surface of human EndoC-βH1 cells and primary human islets upon cytokine exposure, in analogy to observations in rodent INS-1E and MIN6 beta cell lines. We show that GRP78 is shuttled via the anterograde secretory pathway, through the Golgi complex and secretory granules, and identify the DNAJ homolog subfamily C member 3 (DNAJC3) as a GRP78-interacting protein that facilitates its membrane translocation. Evaluation of downstream signaling pathways, using N- and C-terminal anti-GRP78 blocking antibodies, demonstrates that both GRP78 signaling domains initiate pro-apoptotic signaling cascades in beta cells. Extracellular GRP78 itself is identified as a ligand for cell surface GRP78 (sGRP78), increasing caspase 3/7 activity and cell death upon binding, which is accompanied by enhanced Chop and Bax mRNA expression. These results suggest that inflammatory cytokines induce a self-destructive pro-apoptotic feedback loop through the secretion and membrane translocation of GRP78. This proapoptotic function distinguishes the role of sGRP78 in beta cells from its reported anti-apoptotic and proliferative role in cancer cells, opening the road for the use of compounds that block sGRP78 as potential beta cell-preserving therapies in type 1 diabetes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / drug effects*
  • Cell Line
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism*
  • Cell Membrane / ultrastructure
  • Cytokines / metabolism
  • Cytokines / pharmacology*
  • Endoplasmic Reticulum / drug effects
  • Endoplasmic Reticulum / metabolism
  • Feedback, Physiological / drug effects
  • Golgi Apparatus / drug effects
  • Golgi Apparatus / metabolism
  • Golgi Apparatus / ultrastructure
  • HSP40 Heat-Shock Proteins / genetics
  • HSP40 Heat-Shock Proteins / metabolism
  • Heat-Shock Proteins / antagonists & inhibitors
  • Heat-Shock Proteins / genetics
  • Heat-Shock Proteins / metabolism*
  • Humans
  • Insulin-Secreting Cells / drug effects
  • Insulin-Secreting Cells / immunology
  • Insulin-Secreting Cells / metabolism*
  • Islets of Langerhans / drug effects
  • Islets of Langerhans / metabolism
  • Mice
  • Molecular Chaperones / metabolism
  • Rats

Substances

  • Cytokines
  • DNAJC3 protein, human
  • HSP40 Heat-Shock Proteins
  • Heat-Shock Proteins
  • Molecular Chaperones
  • molecular chaperone GRP78