Caveolin-1 in cytokine-induced enhancement of intracellular Ca²⁺ in human airway smooth muscle

Abstract

Diseases such as asthma are characterized by airway hyperresponsiveness. Enhanced airway smooth muscle (ASM) intracellular Ca(2+) ([Ca(2+)](i)) response to agonist stimulation leading to increased airway constriction has been suggested to contribute to airway hyperresponsiveness. Caveolae are flask-shaped plasma membrane invaginations that express the scaffolding protein caveolin and contain multiple proteins important in [Ca(2+)](i) signaling (e.g., agonist receptors, ion channels). We recently demonstrated that caveolae and caveolin-1 are important in [Ca(2+)](i) regulation in human ASM. Proinflammatory cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-13 modulate [Ca(2+)](i) in ASM. We hypothesized that cytokine upregulation of caveolar signaling in ASM contributes to enhanced agonist-induced [Ca(2+)](i) in inflammation. Enzymatically dissociated human ASM cells were exposed to medium (control), 20 ng/ml TNF-α, or 50 ng/ml IL-13 for 24 h. Caveolae-enriched membrane fractions displayed substantial increase in caveolin-1 and -2 expressions by TNF-α and IL-13. Transfection with caveolin-1-mRed DNA substantially accelerated and increased plasma membrane caveolin-1 expression by TNF-α and to a lesser extent by IL-13. Caveolin-1 enhancement was inhibited by nuclear factor-κB and mitogen-activated protein kinase inhibitors. In fura 2-loaded ASM cells, [Ca(2+)](i) responses to 1 μM ACh, 10 μM histamine, or 10 nM bradykinin were all exaggerated by TNF-α as well as IL-13 exposure. However, disruption of caveolae using caveolin-1 suppression via small-interfering RNA resulted in significant blunting of agonist-induced [Ca(2+)](i) responses of vehicle and TNF-α-exposed cells. These functional data were correlated to the presence of TNFR(1) receptor (but not the IL-4/IL-13 receptor) within caveolae. Overall, these results indicate that caveolin-1 plays an important role in airway inflammation by modulating the effect of specific cytokines on [Ca(2+)](i).

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 or IL-13 Enhances SOCE in Human ASM Cells SOCE was measured in untransfected cells or those cells transfected with STIM1 constructs, followed by cytokine exposure. TNF-a or IL-13 significantly increased SOCE in untreated cells ( Figure 6; P , 0.05), consistent with previous findings (31). Importantly, SOCE was enhanced in cells overexpressing WT-STIM1 and STIM1-D76A, after exposure to TNF-a or IL-13 ( Figure 6; P , 0.05).…”

“…These effects involve enhanced SR Ca 21 release, which should deplete SR Ca 21 stores. We also previously demonstrated that TNF-a and IL-13 enhance SOCE (22,31). Accordingly, the effects of TNF-a and IL-13 on STIM1 aggregation were examined.…”

“…The proinflammatory cytokines TNF-a and IL-13 have been shown to enhance the [Ca 21 ] i response to agonist stimulation in human ASM cells (3,31). These effects involve enhanced SR Ca 21 release, which should deplete SR Ca 21 stores.…”

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

“…These data point to a potentially novel avenue for addressing increases in [Ca 2ϩ ] i or even downstream effects such as ER stress and function, proliferation/migration, and cellular metabolism in the context of ASM structure and function. ] i and contractile responses to inflammation (265). In this regard, it appears that caveolae may differentially modulate ASM responses to cytokines such as TNF-␣ vs. IL-13, at least in part due to caveolar vs. noncaveolar expression of their respective receptors (265).…”

“…i and contractile responses to inflammation (265). In this regard, it appears that caveolae may differentially modulate ASM responses to cytokines such as TNF-␣ vs. IL-13, at least in part due to caveolar vs. noncaveolar expression of their respective receptors (265). In contrast to these [Ca 2ϩ ] i /contraction data, reduced caveolin-1 expression has been reported to facilitate ASM proliferation (89,91,93).…”