Ca 2+ mobilization-dependent reduction of the endoplasmic reticulum lumen is due to influx of cytosolic glutathione

BMC Biol. 2020 Feb 26;18(1):19. doi: 10.1186/s12915-020-0749-y.

Abstract

Background: The lumen of the endoplasmic reticulum (ER) acts as a cellular Ca2+ store and a site for oxidative protein folding, which is controlled by the reduced glutathione (GSH) and glutathione-disulfide (GSSG) redox pair. Although depletion of luminal Ca2+ from the ER provokes a rapid and reversible shift towards a more reducing poise in the ER, the underlying molecular basis remains unclear.

Results: We found that Ca2+ mobilization-dependent ER luminal reduction was sensitive to inhibition of GSH synthesis or dilution of cytosolic GSH by selective permeabilization of the plasma membrane. A glutathione-centered mechanism was further indicated by increased ER luminal glutathione levels in response to Ca2+ efflux. Inducible reduction of the ER lumen by GSH flux was independent of the Ca2+-binding chaperone calreticulin, which has previously been implicated in this process. However, opening the translocon channel by puromycin or addition of cyclosporine A mimicked the GSH-related effect of Ca2+ mobilization. While the action of puromycin was ascribable to Ca2+ leakage from the ER, the mechanism of cyclosporine A-induced GSH flux was independent of calcineurin and cyclophilins A and B and remained unclear.

Conclusions: Our data strongly suggest that ER influx of cytosolic GSH, rather than inhibition of local oxidoreductases, is responsible for the reductive shift upon Ca2+ mobilization. We postulate the existence of a Ca2+- and cyclosporine A-sensitive GSH transporter in the ER membrane. These findings have important implications for ER redox homeostasis under normal physiology and ER stress.

Keywords: Calcium; Calreticulin; Cyclophilins; Cyclosporine A; Endoplasmic reticulum; Endoplasmic reticulum stress; Glutathione; Membrane transport proteins; Redox homeostasis; Sec61 translocon.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calcium / metabolism*
  • Calreticulin / metabolism
  • Cytosol / metabolism*
  • Endoplasmic Reticulum / metabolism*
  • Glutathione / metabolism*
  • Humans
  • Protein Binding

Substances

  • CALR protein, human
  • Calreticulin
  • Glutathione
  • Calcium