Regulation of calcium homeostasis and flux between the endoplasmic reticulum and the cytosol

J Biol Chem. 2022 May 21;298(7):102061. doi: 10.1016/j.jbc.2022.102061. Online ahead of print.

Abstract

The concentration of Ca2+ in the endoplasmic reticulum (ER) is critically important for maintaining its oxidizing environment as well as for maintaining luminal ATP levels required for chaperone activity. Therefore, local luminal Ca2+ concentrations and the dynamic Ca2+ flux between the different subcellular compartments are tightly controlled. Influx of Ca2+ into the ER is enabled by a reductive shift, which opens the sarcoendoplasmic reticulum calcium transport ATPase pump, building the Ca2+ gradient across the ER membrane required for ATP import. Meanwhile, Ca2+ leakage from the ER has been reported to occur via the Sec61 translocon following protein translocation. In this review, we provide an overview of the complex regulation of Ca2+ homeostasis, Ca2+ flux between subcellular compartments, and the cellular stress response (the unfolded protein response) induced upon dysregulated luminal Ca2+ metabolism. We also provide insight into the structure and gating mechanism at the Sec61 translocon and examine the role of ER-resident cochaperones in assisting the central ER-resident chaperone BiP in the control of luminal Ca2+ concentrations.

Keywords: BiP/Grp78/HspA5; DnaJ; J-proteins; UPR; chaperone; diabetes; stress; thioredoxin; translocon.

Publication types

  • Review