Abstract：
The high-affinity IgE receptor FcεRI is the mast cell (MC) receptor responsible for the involvement of MCs in IgE-associated allergic disorders. Activation of the FcεRI is achieved via crosslinking by multivalent antigen (Ag) recognized by IgE resulting in degranulation and proinflammatory cytokine production. In comparison to the T- and B-cell receptor complexes, for which several co-receptors orchestrating the initial signaling events have been described, information is scarce about FcεRI-associated proteins. Additionally, it is unclear how FcεRI signaling synergizes with input from other receptors and how regulators affect this synergistic response. We found that the HDL receptor SR-BI (gene name: Scarb1/SCARB1) is expressed in MCs, functionally associates with FcεRI, and regulates the plasma membrane cholesterol content in cholesterol-rich plasma membrane nanodomains. This impacted the activation of MCs upon co-stimulation of the FcεRI with receptors known to synergize with FcεRI signaling. Amongst them, we investigated the co-activation of the FcεRI with the receptor tyrosine kinase KIT, the IL-33 receptor, and GPCRs activated by adenosine or PGE2. Scarb1-deficient bone marrow-derived MCs showed reduced cytokine secretion upon co-stimulation conditions suggesting a role for plasma membrane-associated cholesterol regulating respective MC activation. Mimicking Scarb1 deficiency by cholesterol depletion employing MβCD, we identified PKB and PLCγ1 as cholesterol-sensitive proteins downstream of FcεRI activation in bone marrow-derived MCs. When MCs were co-stimulated with stem cell factor (SCF) and Ag, PLCγ1 activation was boosted, which could be mitigated by cholesterol depletion and SR-BI inhibition. Similarly, SR-BI inhibition attenuated the synergistic response to PGE2 and anti-IgE in the human ROSAKIT WT MC line, suggesting that SR-BI is a crucial regulator of synergistic MC activation.
摘要：
高亲和力IgE受体FcεRI是肥大细胞（MC）受体，负责MC参与IgE相关的过敏性疾病。FcεRI的活化通过由IgE识别的多价抗原(Ag)交联实现,导致脱粒和促炎细胞因子产生。与T细胞和B细胞受体复合物相比，已经描述了几种协调初始信号事件的共受体，关于FcεRI相关蛋白的信息很少。此外,目前尚不清楚FcεRI信号如何与其他受体的输入协同作用，以及调节剂如何影响这种协同反应。我们发现HDL受体SR-BI（基因名称：Scarb1/SCARB1）在MC中表达，与FcεRI功能相关，并调节富含胆固醇的质膜纳米结构域中的质膜胆固醇含量。这在FcεRI与已知与FcεRI信号传导协同的受体共刺激时影响MC的活化。在他们当中,我们研究了FcεRI与受体酪氨酸激酶试剂盒的共激活，IL-33受体，和由腺苷或PGE2激活的GPCRs。Scarb1缺陷的骨髓来源的MC在共刺激条件下显示出细胞因子分泌减少，这表明质膜相关胆固醇调节各自的MC活化。通过使用MβCD消耗胆固醇来模拟Scarb1缺乏症，我们确定PKB和PLCγ1是骨髓来源的MC中FcεRI激活下游的胆固醇敏感蛋白。当MC与干细胞因子（SCF）和Ag共同刺激时，PLCγ1激活得到加强，这可以通过胆固醇消耗和SR-BI抑制来缓解。同样，SR-BI抑制减弱了人ROSAKITWTMC细胞系中对PGE2和抗IgE的协同反应，表明SR-BI是协同MC激活的关键调节因子。
