Abstract
Cytoplasmic Ca(2+) oscillations constitute a widespread signaling mode and are often generated in response to stimulation of G protein-coupled receptors that activate phospholipase C. In mast cells, repetitive Ca(2+) oscillations can be evoked by modest activation of cysteinyl leukotriene type I receptors by the physiological trigger, leukotriene C4. The Ca(2+) oscillations arise from regenerative Ca(2+) release from inositol 1,4,5-trisphosphate-sensitive stores followed by Ca(2+) entry through store-operated Ca(2+) channels, and the latter selectively activate the Ca(2+)-dependent transcription factor NFAT. The cysteinyl leukotriene type I receptors desensitize through negative feedback by protein kinase C, which terminates the oscillatory Ca(2+) response. Here, we show that the scaffolding protein caveolin-1 has a profound effect on receptor-driven Ca(2+) signals and downstream gene expression. Overexpression of caveolin-1 increased receptor-phospholipase C coupling, resulting in initially larger Ca(2+) release transients of longer duration but which then ran down quickly. NFAT-activated gene expression, triggered in response to the Ca(2+) signal, was also reduced by caveolin-1. Mutagenesis studies revealed that these effects required a functional scaffolding domain within caveolin-1. Mechanistically, the increase in Ca(2+) release in the presence of caveolin-1 activated protein kinase C, which accelerated homologous desensitization of the leukotriene receptor and thereby terminated the oscillatory Ca(2+) response. Our results reveal that caveolin-1 is a bimodal regulator of receptor-dependent Ca(2+) signaling, which fine-tunes the spatial and temporal profile of the Ca(2+) rise and thereby its ability to activate the NFAT pathway.
Highlights
The scaffolding protein caveolin-1 coordinates membrane signaling clusters, but how this affects Ca2ϩ oscillations is unknown
Endogenous levels of caveolin-1 were virtually undetectable in Western blots from RBL-1 cells, so we overexpressed the GFP-tagged protein to study its impact on Ca2ϩ oscillations
Stimulation of CysLT1 receptors with leukotriene C4 (LTC4) leads to repetitive Ca2ϩ oscillations, which reflect regenerative Ca2ϩ release followed by transient Ca2ϩ entry through CRAC channels [11]
Summary
The scaffolding protein caveolin-1 coordinates membrane signaling clusters, but how this affects Ca2ϩ oscillations is unknown. Conclusion: Caveolin-1 increases receptor desensitization through Ca2ϩ-dependent stimulation of protein kinase C. The cysteinyl leukotriene type I receptors desensitize through negative feedback by protein kinase C, which terminates the oscillatory Ca2؉ response. We show that the scaffolding protein caveolin-1 has a profound effect on receptor-driven Ca2؉ signals and downstream gene expression. The increase in Ca2؉ release in the presence of caveolin-1 activated protein kinase C, which accelerated homologous desensitization of the leukotriene receptor and thereby terminated the oscillatory Ca2؉ response. Our results reveal that caveolin-1 is a bimodal regulator of receptor-dependent Ca2؉ signaling, which fine-tunes the spatial and temporal profile of the Ca2؉ rise and thereby its ability to activate the NFAT pathway. 1 Y-C.Y. was a recipient of National Science Council Fellowship 100-2911-
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