Privileged coupling between Ca(2+) entry through plasma membrane store-operated Ca(2+) channels and the endoplasmic
María Teresa Alonso1, Isabel M Manjarrés, Javier García-Sancho
1Instituto de Biología y Genética Molecular, Universidad de Valladolid y Consejo Superior de Investigaciones Científicas, c/ Sanz y Forés s/n, 47003 Valladolid, Spain.
Molecular and Cellular Endocrinology
|September 1, 2011
Summary
The sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) efficiently refills the endoplasmic reticulum (ER) with calcium entering through store-operated calcium channels (SOC). Stoichiometry of STIM, Orai, and SERCA proteins critically impacts this calcium entry-calcium refilling (CECR) coupling.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Capacitative calcium entry (CCE) is crucial for cellular calcium homeostasis.
- The sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) plays a key role in calcium reuptake into the ER.
- STIM1 and Orai1 form store-operated calcium channels (SOC) at the plasma membrane.
Purpose of the Study:
- To investigate the role of SERCA in coupling with SOC for efficient ER calcium refilling.
- To determine how the stoichiometry of STIM1, Orai1, and SERCA affects calcium entry and ER refilling.
- To elucidate the mechanisms governing calcium distribution between the ER and mitochondria following SOC activity.
Main Methods:
- Immunofluorescence microscopy to visualize colocalization of SERCA, STIM1, and Orai1.
- Calcium imaging techniques to measure intracellular calcium dynamics.
- Biochemical assays to assess protein stoichiometry and activity.
Main Results:
- SERCA colocalizes with STIM1 and Orai1 at puncta, facilitating calcium entry-calcium refilling (CECR).
- CECR efficiency is comparable to excitation-response mechanisms, limiting calcium wave progression.
- Altered STIM1, Orai1, and SERCA stoichiometry, particularly excess Orai1, impairs ER refilling.
- The ER preferentially takes up calcium from SOC, with mitochondria capturing a minimal fraction due to spatial and affinity differences.
Conclusions:
- SERCA is integral to the functional unit of CCE, directly coupling plasma membrane SOC to ER calcium uptake.
- The efficiency of CECR is highly sensitive to the relative abundance of STIM1, Orai1, and SERCA.
- Spatial organization and differential calcium affinities dictate the preferential sequestration of calcium by the ER over mitochondria.
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