Caveolin-1 regulation of store-operated Ca²⁺influx in human airway smooth muscle

Abstract

Caveolae, plasma membrane invaginations with constitutive caveolin proteins, harbour proteins involved in intracellular calcium ([Ca2+]i) regulation. In human airway smooth muscle (ASM), store-operated Ca2+ entry (SOCE) is a key component of [Ca2+]i regulation, and contributes to increased [Ca2+]i in inflammation. SOCE involves proteins Orai1 and stromal interaction molecule (STIM)1. We investigated the link between caveolae, SOCE and inflammation in ASM. [Ca2+]i was measured in human ASM cells using fura-2. Small interference RNA (siRNA) or overexpression vectors were used to alter expression of caveolin-1 (Cav-1), Orai1 or STIM1. Tumour necrosis factor (TNF)-α was used as a representative pro-inflammatory cytokine. TNF-α increased SOCE following sarcoplasmic reticulum Ca2+ depletion, and increased whole-cell and caveolar Orai1 (but only intracellular STIM1). Cav-1 siRNA decreased caveolar and whole-cell Orai1 (but not STIM1) expression, and blunted SOCE, even in the presence of TNF-α. STIM1 overexpression substantially enhanced SOCE: an effect only partially reversed by Cav-1 siRNA. In contrast, Orai1 siRNA substantially blunted SOCE even in the presence of TNF-α. Cav-1 overexpression significantly increased Orai1 expression and SOCE, especially in the presence of TNF-α. These results demonstrate that caveolar expression and regulation of proteins such as Orai1 are important for [Ca2+]i regulation in human ASM cells and its modulation during inflammation.

Impairment of TRPC1–STIM1 channel assembly and AQP5 translocation compromise agonist-stimulated fluid secretion in mice lacking caveolin1

“…These data suggest that both channel assemblies are likely to involve lipid raft domains, with TRPC1-STIM1 channel assembly occurring in caveolar microdomains and Orai1-STIM1 association likely in non-caveolar raft microdomains. Although Cav1 was recently shown to affect Orai1 trafficking (Sathish et al, 2012;Yu et al, 2010), we did not find evidence of any alteration in STIM1-Orai1 interaction in Cav1 2/2 cells. We suggest that Orai1-STIM1 channel or other Ca 2+ channels, e.g.…”

“…2C). Although Cav1 was recently shown to affect Orai1 trafficking (Sathish et al, 2012;Yu et al, 2010), our data indicate that Orai1-STIM1 interaction is not affected in Cav1 2/2 acinar cells and could thus account for the residual Ca 2+ influx. Further, channels including other TRPC subtypes could also contribute toward this residual Ca 2+ entry in Cav1 2/2 cells and thus cannot be excluded.…”

“…TRPC1 associates with Cav1 which serves as scaffold to retain the channel in the plasma membrane region and facilitate its interaction with STIM1 Sundivakkam et al, 2009). Recent studies also suggest a role of lipid rafts domains (LRD) and Cav1 in regulation of Orai1 (Sathish et al, 2012;Yu et al, 2010). However, direct physiological evidence for Cav1 in regulation of Orai1-STIM1 channel assembly remains to be determined.…”

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

“…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).…”

“…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).…”