Visualization and manipulation of plasma membrane-endoplasmic reticulum contact sites indicates the presence of additional molecular components within the STIM1-Orai1 Complex.
ABSTRACT STIM1, a recently identified endoplasmic reticulum (ER) protein, rapidly translocates to a plasma membrane-adjacent ER compartment upon depletion of the ER Ca(2+) stores. Here we use a novel means, namely a chemically inducible bridge formation between the plasma and ER membranes, to highlight the plasma membrane-adjacent ER compartment and show that this is the site where STIM1 and its Ca(2+) channel partner, Orai1, form a productive interaction upon store depletion. By changing the length of the linkers connecting the plasma and ER membranes, we show that Orai1 requires a larger space than STIM1 between the two membranes. This finding suggests that Orai1 is part of a larger macromolecular cluster with an estimated 11-14-nm protrusion to the cytoplasm, whereas the cytoplasmic domain of STIM1 fits in a space calculated to be less than 6 nm. We finally show that agonist-induced translocation of STIM1 is rapidly reversible and only partially affects STIM1 in the juxtanuclear ER compartment. These studies are the first to detect juxtaposed areas between the ER and the plasma membrane in live cells, revealing novel details of STIM1-Orai1 interactions.
- SourceAvailable from: Sonal Srikanth[Show abstract] [Hide abstract]
ABSTRACT: The proteins STIM1 and Orai1 are the long sought components of the store-operated channels required in T-cell activation. However, little is known about the interaction of these proteins in T-cells after engagement of the T-cell receptor. We found that T-cell receptor engagement caused STIM1 and Orai1 to colocalize in puncta near the site of stimulation and accumulate in a dense structure on the opposite side of the T-cell. FRET measurements showed a close interaction between STIM1 and Orai1 both in the puncta and in the dense cap-like structure. The formation of cap-like structures did not entail rearrangement of the entire endoplasmic reticulum. Cap formation depended on TCR engagement and tyrosine phosphorylation, but not on channel activity or Ca(2+) influx. These caps were very dynamic in T-cells activated by contact with superantigen pulsed B-cells and could move from the distal pole to an existing or a newly forming immunological synapse. One function of this cap may be to provide preassembled Ca(2+) channel components to existing and newly forming immunological synapses.Molecular biology of the cell 08/2008; 19(7):2802-17. DOI:10.1091/mbc.E08-02-0146 · 5.98 Impact Factor
- Frontiers in Bioscience 01/2012; 17(1):1304. DOI:10.2741/3988 · 4.25 Impact Factor
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ABSTRACT: Mitochondria are the powerhouse of cells as they produce the bulk of ATP which is consumed by the cell. They form a highly interconnected network that is governed by fission and fusion processes. In addition, mitochondria and the endoplasmic reticulum (ER) are found in close proximity to each other and it is thought that they maintain contact sites to exchange molecules. The regulation and the function of these contact sites need to be further explored. The small GTPase Arf1 (ADP-ribosylation factor 1), which is best known for its essential role in the generation of coatomer protein I (COPI)-coated vesicles at the Golgi complex appears to be also essential for the dynamics and maintenance of mitochondrial function, presumably at ER-mitochondrial contact sites.Biochemical Society Transactions 02/2015; 43(1):108-10. DOI:10.1042/BST20140284 · 3.24 Impact Factor