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.