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Redox-assisted regulation of Ca2+ homeostasis in the endoplasmic reticulum by disulfide reductase ERdj5

  1. Kazuhiro Nagataa,b,c,2
  1. aLaboratory of Molecular and Cellular Biology, Department of Molecular Biosciences, Faculty of Life Sciences, Kyoto Sangyo University, Kyoto 603-8555, Japan;
  2. bInstitute for Protein Dynamics, Kyoto Sangyo University, Kyoto 603-8555, Japan;
  3. cCore Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Saitama 332-0012, Japan;
  4. dLaboratory for Developmental Neurobiology, RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan;
  5. eInstitute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan;
  6. fLaboratory of Protein Synthesis and Expression, Institute for Protein Research, Osaka University, Suita 565-0871, Osaka, Japan

  1. Edited by Jonathan S. Weissman, University of California, San Francisco, CA, and approved August 15, 2016 (received for review April 11, 2016)

Significance

Ca2+ is one of the most important second messengers regulating numerous cellular functions; therefore, the regulation of Ca2+ release from and its uptake into the endoplasmic reticulum (ER) are both critical for calcium signaling. The activity of sarco/endoplasmic reticulum Ca2+-ATPase isoform 2b (SERCA2b), a calcium pump on the ER membrane, was reported to be negatively regulated by the oxidation of two cysteines in its ER-luminal portion, and it is expected to be activated by its reduction. However, no molecules responsible for this reduction have been identified. Here, we showed for the first time that ERdj5, the reductase in the ER of mammalian cells, activates SERCA2b by reducing its disulfide bonds in a [Ca2+]ER-dependent manner.

Abstract

Calcium ion (Ca2+) is an important second messenger that regulates numerous cellular functions. Intracellular Ca2+ concentration ([Ca2+]i) is strictly controlled by Ca2+ channels and pumps on the endoplasmic reticulum (ER) and plasma membranes. The ER calcium pump, sarco/endoplasmic reticulum calcium ATPase (SERCA), imports Ca2+ from the cytosol into the ER in an ATPase activity-dependent manner. The activity of SERCA2b, the ubiquitous isoform of SERCA, is negatively regulated by disulfide bond formation between two luminal cysteines. Here, we show that ERdj5, a mammalian ER disulfide reductase, which we reported to be involved in the ER-associated degradation of misfolded proteins, activates the pump function of SERCA2b by reducing its luminal disulfide bond. Notably, ERdj5 activated SERCA2b at a lower ER luminal [Ca2+] ([Ca2+]ER), whereas a higher [Ca2+]ER induced ERdj5 to form oligomers that were no longer able to interact with the pump, suggesting [Ca2+]ER-dependent regulation. Binding Ig protein, an ER-resident molecular chaperone, exerted a regulatory role in the oligomerization by binding to the J domain of ERdj5. These results identify ERdj5 as one of the master regulators of ER calcium homeostasis and thus shed light on the importance of cross talk among redox, Ca2+, and protein homeostasis in the ER.

Footnotes

  • ↵1R.U. and A.M. contributed equally to this work.

  • ↵2To whom correspondence should be addressed. Email: nagata{at}cc.kyoto-su.ac.jp.

  • Author contributions: R.U., K.I., K.M., and K.N. designed research; R.U., A.M., M.I., M.O., K.-i.M., K.U., S.F., and Y.F. performed research; M.U. and J.T. contributed new reagents/analytic tools; R.U. and S.W. analyzed data; and R.U., K.I., K.M., and K.N. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1605818113/-/DCSupplemental.

Freely available online through the PNAS open access option.

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