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Insights into the Regulation of Store-operated Calcium Entry Open Access


Other title
store-operated calcium entry
Type of item
Degree grantor
University of Alberta
Author or creator
Prins, Daniel S
Supervisor and department
Michalak, Marek (Biochemistry)
Examining committee member and department
Lytton, Jonathan (Biochemistry & Molecular Biology, University of Calgary)
Eitzen, Gary (Cell Biology)
Touret, Nicolas (Biochemistry)
Fliegel, Larry (Biochemistry)
Department of Biochemistry

Date accepted
Graduation date
Doctor of Philosophy
Degree level
Calcium (Ca2+) ions serve a crucial role in numerous intracellular signaling pathways, controlling physiological functions as diverse as cell proliferation, immune system function, and muscular contraction. As such, the cell has evolved many different mechanisms to precisely control the movement of Ca2+ ions into and out of various cellular compartments. One such pathway is called store-operated Ca2+ entry (SOCE), which couples an initial depletion of endoplasmic reticulum (ER) luminal Ca2+ stores with Ca2+ influx across the plasma membrane into the cytoplasm. SOCE is controlled by two major proteins, STIM1 and Orai1. STIM1 senses ER luminal Ca2+ levels and transduces this signal across the ER membrane by migrating to subplasmalemmal punctae, where it activates Orai1, a plasma membrane Ca2+ channel that allows Ca2+ flux across the plasma membrane. SOCE is of key importance to human health; as such, a more complete understanding of how the cell controls SOCE will yield deeper insights into how the pathway might be manipulated for therapeutic purposes. The research in this thesis focuses on novel cellular mechanisms to control SOCE, specifically focusing on protein-protein interactions of STIM1. We used a variety of biochemical and cell biological techniques to discover novel protein binding partners of STIM1 and to elucidate the functional consequences of these interactions. First, we discovered that ERp57, an ER luminal oxidoreductase, binds to the luminal domain of STIM1. ERp57 binding is dependent upon two highly conserved cysteine residues within STIM1 and this binding serves to inhibit the initiation of SOCE. We hypothesize that ERp57-STIM1 interactions may act as a brake upon SOCE to prevent its overactivation. Importantly, the triggering of SOCE is known to occur within the ER lumen, and our results were the first published description of a protein-protein interaction within the ER luminal domain of STIM1. Second, we discovered that the cytoplasmic domain of STIM1 is subject to calpain cleavage. This cleavage occurs in healthy cells to regulate the abundance of STIM1: inhibition of calpain cleavage increases STIM1 levels. Additionally, STIM1 cleavage is upregulated during programmed cell death. We hypothesize that the interplay between STIM1 and calpains is a mechanism to control the cellular abundance of STIM1 and that perturbations of this mechanism may lead to dysregulation of STIM1 protein levels. Finally, we discovered that a previously described STIM1-calnexin interaction is of key importance in immune cells. Calnexin-deficient T cells exhibit severely impaired SOCE, which may be due to impaired movement of STIM1 to subplasmalemmal punctae or increased susceptibility to calpain cleavage. Calnexin's effects on SOCE seem to be specific to immune cells, suggesting that the calnexin-STIM1 interaction could be one mechanism by which the immune system strengthens SOCE, where a strong, sustained Ca2+ influx is so important. Overall, the research presented in this thesis describes three unique protein binding partners of STIM1 and explains how each interaction serves to regulate SOCE. Any alterations in these interactions may underlie dysregulated SOCE in disease; conversely, interventions targeting these protein binding partners could serve as methods to manipulate SOCE for therapeutic outcomes.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Prins, D., Groenendyk, J., Touret, N. & Michalak, M. Modulation of STIM1 and capacitative Ca2+ entry by the endoplasmic reticulum luminal oxidoreductase ERp57. EMBO Rep 12, 1182-1188, doi:embor2011173 [pii] 10.1038/embor.2011.173.

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