Effects of the Inflammatory Cytokines TNF-α and IL-13 on Stromal Interaction Molecule–1 Aggregation in Human Airway Smooth Muscle Intracellular Ca²⁺ Regulation

Abstract

(20,21). STIM1 has been demonstrated to constitute a transmembrane protein predominantly localized in the SR membrane (22). The luminal N-terminal region of STIM1 contains an EF-hand domain and a sterile a motif (SAM) domain. Beyond a transmembrane region, STIM1 also contains a long cytoplasmic C-terminal domain, which is proposed to be the site of interactions with Orai1 to trigger SOCE (23). STIM1 senses the depletion of SR Ca 21 through its low-affinity Ca 21 -binding EF-hand domain. Upon sensing SR Ca 21 depletion, STIM1 oligomerizes with adjacent STIM1 proteins via the SAM domain, and moves within the SR membrane to enhance its proximity to the PM, where STIM1 interacts with Orai1 and transient receptor potential cation channels to form clusters, thus activating these PM channels to induce SOCE (24). Although much of the information on STIM1 was derived from nonexcitable cells and expression systems, STIM1 has been demonstrated in human ASM cells, and is implicated in the regulation of [Ca 21 ] i responses (11,21,22). The knockdown of STIM1 results in reduced SOCE after store depletion, whereas the overexpression of STIM1 dramatically increases SOCE in human ASM cells (21). However, the dynamics of STIM1 in ASM cells in the context of SOCE have not been examined. CLINICAL RELEVANCEInflammation cytokines induce a constitutive increase in the stromal interaction molecule-1 (STIM1) aggregation that contributes to enhanced store-operated Ca 21 entry in human airway smooth muscle after inflammation. Such effects of inflammation on STIM1 aggregation may contribute to airway hyperresponsiveness.TNF-a and IL-13 are proinflammatory cytokines abundantly produced in inflamed airways (2, 4). TNF-a has been known to increase agonist-induced [Ca 21 ] i response and contractility in ASM (1,6,22,25). Our recent studies also showed that TNF-a increases SOCE in human ASM cells (11,22). Similarly, IL-13 enhances agonist-induced [Ca 21 ] i responses in human ASM (26), and increases airway contractility in mouse and rat tracheas (27). Increased [Ca 21 ] i is clearly a key component of airway hyperreactivity, and contributes to the pathophysiology of asthma and chronic obstructive pulmonary disease (5,16,28). However, the contributions of specific [Ca 21 ] i regulatory mechanisms and their modulation by inflammation remain under investigation.In the present study, we hypothesized that inflammatory cytokines increase [Ca 21 ] i and SOCE by depleting the SR Ca 21 content via enhanced STIM1 aggregation. We used real-time fluorescence imaging techniques to assess the dynamics of STIM1 aggregation triggered by intracellular SR Ca

Arachidonate-Regulated Ca2+ Influx in Human Airway Smooth Muscle

“…Accordingly, the limited but interesting data that asthmatic ASM cells have a higher amplitude of [Ca 21 ] i responses to AA raise the question of whether ARC channels are potentially contributory to increased [Ca 21 ] i in asthmatic ASM. Although the mechanisms for such up-regulation were beyond the scope of this study, enhanced Orai3 expression (or activation) may be involved, and would be consistent with previous findings that related mechanisms, such as STIM1, Orai1, and even caveolin-1, are upregulated in human ASM after inflammation (11,24,25). Furthermore, inflammation can result in enhanced expression of SR Ca 21 proteins and functionality, and AA-induced influx could produce greater SR Ca 21 responses, leading to greater contraction.…”

“…In this regard, capacitative Ca 21 entry in response to intracellular store depletion (i.e., SOCE) is an important mechanism in ASM (9)(10)(11)25). However, there is increasing evidence in nonexcitable cells for an additional noncapacitative Ca 21 influx mechanism regulated by AA (13,33).…”

“…Furthermore, the ARC channel pore is thought to be formed by assembly of three plasma membrane proteins, Orai1 and two Orai3 subunits (18). There is now substantial evidence that plasma membrane Orai1, and STIM1 at the level of the SR, are mediators of SOCE in ASM (10,11,(20)(21)(22)(23)(24)(25). However, there is currently no information on the role of ARC channels in ASM, their molecular identity, or the mechanisms that may regulate such channels.…”

Airway smooth muscle in airway reactivity and remodeling: what have we learned?

“…In PC12 cells, changes in extracellular pH can influence store-operated Ca 2ϩ influx that is dependent on the SR Ca 2ϩ protein stromal interacting molecule 1 (STIM1) (299). Given the important role of STIM1/Orai1 in human ASM (80,137,225,264,292,357), it is possible that OGR1 could modulate store-operated Ca 2ϩ entry (SOCE) by enhancing STIM1 interactions with Orai1 or other channels that contribute to Ca 2ϩ influx, particularly canonical transient receptor potentials (TRPCs) (80,338). Furthermore, the limited data in human ASM suggest that OGR1 can further result in p42/44 MAPK phosphorylation (269) and IL-6 production (122) and therefore have more complex effects in the setting of disease.…”

Orai channel-mediated Ca2+ signals in vascular and airway smooth muscle

“…They reported that rat airway SMC proliferation in response to serum and TGF␤1 was partly reduced by 10 M SKF-96365 (27). Jia et al (37) showed that IL-13 and TNF␣ enhance puncta formation of ectopically expressed fluorescently tagged STIM1 and increased SOCE in airway SMCs, suggesting that inflammatory cytokines might contribute to airway hyperresponsiveness through increased SOCE in human airway SMCs during disease.…”