STIM1 has a plasma membrane role in the activation of store-operated Ca ²⁺ channels

Abstract

Receptor-induced Ca 2؉ signals are key to the function of all cells and involve release of Ca 2؉ from endoplasmic reticulum (ER) stores, triggering Ca 2؉ entry through plasma membrane (PM) ''storeoperated channels'' (SOCs). The identity of SOCs and their coupling to store depletion remain molecular and mechanistic mysteries. The single transmembrane-spanning Ca 2؉ -binding protein, STIM1, is necessary in this coupling process and is proposed to function as an ER Ca 2؉ sensor to provide the trigger for SOC activation. Here we reveal that, in addition to being an ER Ca 2؉ sensor, STIM1 functions within the PM to control operation of the Ca 2؉ entry channel itself. Increased expression levels of STIM1 correlate with a gain in function of Ca 2؉ release-activated Ca 2؉ (CRAC) channel activity. Point mutation of the N-terminal EF hand transforms the CRAC channel current (I CRAC) into a constitutively active, Ca 2؉ store-independent mode. Mutants in the EF hand and cytoplasmic C terminus of STIM1 alter operational parameters of CRAC channels, including pharmacological profile and inactivation properties. Last, Ab externally applied to the STIM1 N-terminal EF hand blocks both I CRAC in hematopoietic cells and SOC-mediated Ca 2؉ entry in HEK293 cells, revealing that STIM1 has an important functional presence within the PM. The results reveal that, in addition to being an ER Ca 2؉ sensor, STIM1 functions within the PM to exert control over the operation of SOCs. As a cell surface signaling protein, STIM1 represents a key pharmacological target to control fundamental Ca 2؉ -regulated processes including secretion, contraction, metabolism, cell division, and apoptosis.calcium signaling ͉ calcium channel ͉ patch-clamp ͉ mast cells ͉ T lymphocytes

Voltage Gating at the Selectivity Filter of the Ca2+ Release-activated Ca2+ Channel Induced by Mutation of the Orai1 Protein

“…The luminal/extracellular N terminus contains a helix-rich sterile ␣-motif in addition to an EF-hand Ca 2ϩ sensor (6,18). The cytoplasmic C terminus contains two prominent coiled-coil regions followed by a flexible proline-rich domain (6,18). Based on the protein structure and several studies on STIM1, we hypothesize that two distinct types of interactions are likely important in the function of STIM1.…”

“…Although STIM1 resides predominantly in the ER and the plasma membrane (PM) (11), Orai1 is almost exclusively expressed in the PM (12). STIM1 functions as the Ca 2ϩ sensor in the ER that triggers the CRAC channel activation (5,6,11). However, its translocation to the PM upon activation (11,13) and functional role in the PM have also been demonstrated (6,14).…”

“…STIM1 functions as the Ca 2ϩ sensor in the ER that triggers the CRAC channel activation (5,6,11). However, its translocation to the PM upon activation (11,13) and functional role in the PM have also been demonstrated (6,14). Even though a report by Mignen et al (14) revealed that PM-STIM1 regulates another Ca 2ϩ channel (arachidonate-regulated Ca 2ϩ channels), the same group later revealed that arachidonate-regulated Ca 2ϩ channels have the same molecular identity as CRAC channels (Ref.…”

“…STIM1 contains one transmembrane domain and a number of potential protein-interacting domains on its N and C termini. The luminal/extracellular N terminus contains a helix-rich sterile ␣-motif in addition to an EF-hand Ca 2ϩ sensor (6,18). The cytoplasmic C terminus contains two prominent coiled-coil regions followed by a flexible proline-rich domain (6,18).…”

Calcium dependence of T cell proliferation following focal stimulation

“…A similar conclusion was independently reached by others [15][16][17][18], who in addition showed that ORAI1 increased CRAC currents if expressed with the CRAC activator STIM1. STIM1 has been previously shown to mediate CRAC activation after Ca 2+ store depletion [19][20][21][22].…”