Novel Role for STIM1 as a Trigger for Calcium Influx Factor Production

Abstract

STIM1 has been recently identified as a Ca 2؉ sensor in endoplasmic reticulum (ER) and an initiator of the store-operated Ca 2؉ entry (SOCE) pathway, but the mechanism of SOCE activation remains controversial. Here we focus on the early ERdelimited steps of the SOCE pathway and demonstrate that STIM1 is critically involved in initiating of production of calcium influx factor (CIF), a diffusible messenger that can deliver the signal from the stores to plasma membrane and activate SOCE. We discovered that CIF production is tightly coupled with STIM1 expression and requires functional integrity of its intraluminal sterile ␣-motif (SAM) domain. We demonstrate that 1) molecular knockdown or overexpression

Mutations of the Ca2+-sensing Stromal Interaction Molecule STIM1 Regulate Ca2+ Influx by Altered Oligomerization of STIM1 and by Destabilization of the Ca2+ Channel Orai1

“…On the other hand, both Ca 2ϩ influx and CD of the double mutant N131Q/N171Q (STIM1 QQ) were significantly smaller than wild type (STIM WT) (Fig. 1, B and C), consistent with work by Csutora et al (28).…”

“…Although mutation of a conserved tryptophan adjacent to Asn-131, namely W132R, had little effect on the quaternary structure and oligomerization of the EF SAM domain, mutation of T172R, adjacent to Asn-171, led to persistent EF-SAM aggregation (34). In contrast to earlier work, which showed either reduced STIM1 function upon mutation of the consensus glycosylation site asparagines to glutamines N131Q/N171Q (28) or an unaltered endogenous SOCE (35), we were able to show that prevention of glycosylation does not reduce function per se and that a particular mutant combination, namely N131D/ N171Q (DQ), instead created a strong gain of function mutant. In comparison with the ␣9 helix destabilizing mutation T172R, which leads to constitutive activation combined with Tg insensitivity of Mn 2ϩ quench rates (34), STIM1 DQ mutants display Tg sensitivity, do not show constitutive currents in patch clamp recordings, and thus do not lead to permanently activated Orai1 channels.…”

Store-operated Ca2+ Entry-associated Regulatory factor (SARAF) Plays an Important Role in the Regulation of Arachidonate-regulated Ca2+ (ARC) Channels

“…In an attempt to confirm the essential role of STIM1 in storeoperated Ca 2ϩ (SOC) and ARC channel activation we repeated the maneuver depicted in Fig. 2A in NG115-401L cells, a neuroblastoma cell line that expresses a negligible amount of endogenous STIM1 (13,16). As depicted in Fig.…”

The STIM/Orai coupling machinery

“…1C), a yet unidentified Ca 2+ influx factor (CIF) might additionally be involved. STIM1 has been proposed to trigger the production of CIF, 60 which could contribute to signal transmission from STIM1 to Orai1. 61 CIF has been suggested to displace calmodulin (CaM) from phospholipase A2 (iPLA 2 ), stimulating lysophospholipid generation that in turn activates CRAC.…”