Key result
Wild-type CSQ1 overexpression reduces STIM1 clustering and store-operated Ca2+ entry versus mutants in HeLa cells.
Why the study?
The mechanism by which calsequestrin-1 (CSQ1) regulates store-operated Ca2+ entry (SOCE) through interaction with STIM1 and inhibition of STIM1 aggregation was not fully understood.
CSQ1 monomers suppress store-operated Ca2+ entry by interacting with STIM1 and attenuating its aggregation via the C-terminal amino acid 362-396.
No immediate clinical implications; leaves open CSQ1-STIM1 role in cardiac Ca2+ disorders.
BACKGROUND/AIMS: Stromal interacting molecule-1 (STIM1) aggregation and redistribution to plasma membrane to interact with Orai1 constitute the core mechanism of store-operated Ca2+ entry (SOCE). Previous study has revealed that calsequestrin-1 (CSQ1) regulates SOCE in HEK293 cells through interacting with STIM1 and inhibiting STIM1/Orai1 interaction. Here, we further investigate how CSQ1/STIM1 interaction affects SOCE. METHODS: Using confocal microscopy, STIM1 aggregation and co-localizations with CSQ1 or Orai1 upon Ca2+ store depletion by thapsigargin were measured and quantified by Imaris software in HeLa cells transfected with different CSQ1 mutants. The interactions of CSQ1/STIM1 and STIM1/Orai1, and internal Ca2+ changes were detected by co-immunoprecipitation and Fura2, respectively. RESULTS: Wt-CSQ1 overexpression significantly reduced STIM1 clustering in the perimembrane and cytosolic regions, whereas over-expression of a C-terminal amino acid 362-396 deletion mutant (C35) did not. Consistently, a significant depression of SOCE, increased CSQ1 monomerization and CSQ1/STIM1 interaction, and a reduced STIM1/Orai1 association were observed in wt-CSQ1 but not in C35-transfected cells. Additionally, mutant lacking C-terminal AA 388-396 deletion exerted weaker potency in inhibiting STIM1 aggregation and association with Orai1 than wt-CSQ1. CONCLUSIONS: Our results demonstrate that CSQ1 monomers suppress SOCE by interacting with STIM1 and attenuating STIM1 aggregation via its C-terminal amino acid 362-396.
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Zhang et al. (2016) studied this question. Wt-CSQ1 overexpression vs. C-terminal amino acid 362-396 deletion mutant (C35) was evaluated on STIM1 aggregation and co-localizations with CSQ1 or Orai1 upon Ca2+ store depletion. Wild-type CSQ1 overexpression significantly reduced STIM1 clustering and depressed store-operated Ca2+ entry compared to a C-terminal deletion mutant in HeLa cells.
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