Suggested by treatment of HEK293 cells with the specific membrane-permeable IP
Suggested by treatment of HEK293 cells with the specific membrane-permeable IP3 receptor antagonist, 2-APB [17]. 2-APB is able to completely abolish the Echinacea-induced calcium release from internal stores. 2-APB has been reported to enhance leakage of Ca2+ from the ER and inhibit SERCA activity, resulting in enhancement of Ca 2+ signaling [27]. This PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/28607003 Lurbinectedin chemical information complex action of 2-APB is consistent with the small initial intracellular calcium increase we observed in HEK293 cells after 2-APB application. This model predicts that the Echinacea-induced release of Ca2 from internal stores may be coupled to a subsequent activation of the SOCE process. In many cell types, depletion of intracellular Ca2+ stores results in the opening of SOCE in the plasma membrane [16]. SOCE, thought to mediate aspects of cell secretion and motility, cell proliferation and gene expression by altering cellular Ca2+ [16], is considered a promising target for therapeutic treatment in inflammatory diseases [28]. The nature of SOCE, andthe mechanism linking Ca2+-store content to the opening of this Ca2+ channel, remains unclear. Two proteins have been implicated in SOCE function: Orai1, a pore-forming subunit of the SOCE, and stromal interaction molecule 1 (STIM1), thought to be an ER-based Ca2+ sensor that activates SOCE by an as yet undefined mechanism [16]. Therefore we propose that the resultant decrease of Ca2+ in ER after Echinacea treatment would in turn activate the plasma membrane SOCE through a mechanism that involves STIM1. Taken together, this model predicts that in HEK293 cells, the level of cytosolic Ca2+ associated with Echinacea treatment increases through two mechanisms: initially the release of Ca2+ from ER Ca2+ stores, and subsequently Ca2+ influx via SOCE. The physiological events downstream of a cytosolic Ca2+ increase, whether Echinacea-induced or otherwise, are complex and highly dependent on the cell type and context in which they occur. Longer range effects of changes in cytosolic levels of Ca2+ regulate a wide variety of cellular processes [20]. In T-cells, for example, elevated intracellular Ca2+ activate Ca2+-dependent enzymes, such as calcineurin, and thereby transcription factors, such as nuclear factor of activated T cells (NFAT) and nuclear factor-B (NF-B). These transcription factors modulate the activation of T-cells and generation of cytokines, which in turn regulate the expression of many target genes in inflammation and pain transmission [20]. Studies using animal and human models indicate that Echinacea extracts enhance the cyclooxygenase 2 andWu et al. BMC Complementary and Alternative Medicine 2010, 10:72 http://www.biomedcentral.com/1472-6882/10/Page 11 ofCa2+R PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/27488460 plasma membraneSOCE2-APBU-73122 PLC PIP2 2-APB IP3 IP3R Ca2+ ERSERCACa2+ Ca2+Ca2+cytoplasmCa2+Ca2+thapsigarginFigure 8 Proposed metabotropic mechanism for Ca2+ signaling in HEK293 cells underlying the modulation of some of the cellular responses induced by Echinacea extracts. Green arrows indicate steps proposed from data in this paper. Purple lines indicate inhibitors used in this study. In this model, lipophilic constituents in Echinacea extracts bind to unidentified surface membrane receptor(s) (R), resulting in the activation of PLC. PLC-activation catalyzes the production of IP3 from PIP2. IP3 binds to and opens IP3R in the membrane of the ER, resulting in the release of Ca2+ from ER Ca2+ store. The decrease in the Ca2+ content of the ER is sensed by STIM1, which in turn.