STIM1 regulates Ca²⁺ entry via arachidonate‐regulated Ca²⁺‐selective (ARC) channels without store depletion or translocation to the plasma membrane

Abstract

Recent studies have indicated a critical role for STIM (stromal interacting molecule) proteins in the regulation of the store-operated mode of receptor-activated Ca 2+ entry. Current models emphasize the role of STIM located in the endoplasmic reticulum membrane, where a Ca 2+ -binding EF-hand domain within the N-terminal of the protein lies within the lumen and is thought to represent the sensor for the depletion of intracellular Ca 2+ stores. Dissociation of Ca 2+from this domain induces the aggregation of STIM to regions of the ER immediately adjacent to the plasma membrane where it acts to regulate the activity of store-operated Ca 2+ channels. However, the possible effects of STIM on other modes of receptor-activated Ca 2+ entry have not been examined. Here we show that STIM1 also regulates the arachidonic-acid-regulated Ca 2+ -selective (ARC) channels -receptor-activated Ca 2+ entry channels whose activation is entirely independent of store depletion. Regulation of the ARC channels by STIM1 does not involve dissociation of Ca 2+ from the EF-hand, or any translocation of STIM1. Instead, a critical role of STIM1 resident in the plasma membrane is indicated. Thus, exposure of intact cells to an antibody targeting the extracellular N-terminal domain of STIM1 inhibits ARC channel activity without significantly affecting the store-operated channels. A similar specific inhibition of the ARC channels is seen in cells expressing a STIM1 construct in which the N -linked glycosylation sites essential for the constitutive cell surface expression of STIM1, were mutated. We conclude that, in contrast to store-operated channels, regulation of ARC channels by STIM1 depends exclusively on the pool of STIM1 constitutively residing in the plasma membrane. These data demonstrate that STIM1 is a more universal regulator of Ca 2+ entry pathways than previously thought, and appears to have multiple modes of action.

TRPC3 Regulates Agonist-stimulated Ca2+ Mobilization by Mediating the Interaction between Type I Inositol 1,4,5-Trisphosphate Receptor, RACK1, and Orai1

“…In addition, impairment of this complex by shTRPC3 was without effect on TG-evoked SOCE. The role of STIM1 in non-capacitative receptor-regulated Ca 2ϩ entry pathways, such as Ca 2ϩ entry via arachidonate-regulated calcium (ARC) channels (59,60) has previously been demonstrated. Our results reporting the association of STIM1 with type I IP 3 R upon stimulation with ATP or CCh also shows the involvement of STIM1 in ROCE, further suggesting that STIM1 might be a universal regulator of Ca 2ϩ entry.…”

Store-Operated Calcium Channels: New Perspectives on Mechanism and Function

“…STIM1 is necessary for their activation, but only the fraction of STIM1 that is constitutively present in the PM (comprising about 10% -20% of the total STIM1 pool in most cells) (Mignen et al 2007). Concatemer studies suggest that ARC channels form as a pentamer of Orai subunits (3 Â Orai1 þ 2 Â Orai3), and glutamine substitutions for glutamates at E106 in Orai1 or the corresponding location in Orai3 (E81) both inhibit conductance, suggesting the formation of a pentameric glutamatergic selectivity filter (Mignen et al 2009).…”

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

“…The unusually long coiled-coil domain of STIM1 likely provides the structural features needed for connection between the two membranes to transfer the signal from the ER to the PM that activates CRAC channel. A likely candidate for such interactions is PM-STIM1 (6,11,13,14). However, direct interactions with Orai1 are also possible.…”

“…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.…”