Abstract
Histamine is an important immunomodulator involved in allergic reactions and inflammatory responses. In endothelial cells, histamine induces Ca(2+) mobilization by releasing Ca(2+) from the endoplasmic reticulum and eliciting Ca(2+) entry across the plasma membrane. Herein, we show that histamine-evoked Ca(2+) entry in human umbilical vein endothelial cells (HUVECs) is sensitive to blockers of Ca(2+) release-activated Ca(2+) (CRAC) channels. RNA interference against STIM1 or Orai1, the activating subunit and the pore-forming subunit of CRAC channels, respectively, abolishes this histamine-evoked Ca(2+) entry. Furthermore, overexpression of dominant-negative CRAC channel subunits inhibits while co-expression of both STIM1 and Orai1 enhances histamine-induced Ca(2+) influx. Interestingly, gene silencing of STIM1 or Orai1 also interrupts the activation of calcineurin/nuclear factor of activated T-cells (NFAT) pathway and the production of interleukin 8 triggered by histamine in HUVECs. Collectively, these results suggest a central role of STIM1 and Orai1 in mediating Ca(2+) mobilization linked to inflammatory signaling of endothelial cells upon histamine stimulation.
Highlights
Histamine Triggers Store Release, Followed by Ca2ϩ Entry, in human umbilical vein endothelial cells (HUVECs) with Dose-dependent Manner—HUVECs were loaded with Fura-2 AM and imaged under room temperature to evaluate the effect of histamine on intracellular Ca2ϩ dynamics
Our results indicate that Orai1 and STIM1, the pore-forming and activating subunits, respectively, form the main type of endothelial Ca2؉ release-activated Ca2؉ (CRAC) channels, downstream of H1 receptors, mediating Ca2ϩ mobilization upon histamine stimulation
We have demonstrated that the CRAC channel, formed by STIM1 and Orai1, mediates the histamine-evoked Ca2ϩ entry and the downstream nuclear factor of activated T-cells (NFAT) nuclear translocation, as well as cytokine production, in HUVECs
Summary
STIM1 and Orai in mediating Ca2؉ mobilization linked to inflammatory signaling of endothelial cells upon histamine stimulation. Upon Ca2ϩ release from the ER, STIM1 oligomerizes and subsequently moves to the ER-PM junctions, binding to and activating Orai channels for Ca2ϩ entry (28, 29, 33, 36 – 41) It has not been addressed whether this Ca2ϩ entry pathway contributes to the Ca2ϩ mobilization and function of vascular cells in response to histamine. In the present study, utilizing both pharmacological and molecular tools specific to CRAC channels, we elucidated the contribution of STIM1 and Orai to histamine-evoked intracellular Ca2ϩ mobilization and downstream cytokine production in endothelial cells
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