Toll-like Receptor 4 Ligands Down-regulate Fcγ Receptor IIb (FcγRIIb) via MARCH3 Protein-mediated Ubiquitination
Toll-like Receptor 4 Ligands Down-regulate Fcγ Receptor IIb (FcγRIIb) via MARCH3 Protein-mediated Ubiquitination
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DOI：
10.1074/jbc.m115.701151
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发表时间：
2016-02-19
影响因子：
4.8
通讯作者：
Butchar, Jonathan P.
中科院分区：
文献类型：
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作者：
Fatehchand, Kavin;Ren, Li;Butchar, Jonathan P.
单核细胞和巨噬细胞对单抗治疗的有效性至关重要。对抗体包被的肿瘤细胞的反应在很大程度上是由Fc受体(Fcr)介导的，Fcr在与免疫复合体结合后被激活。FcRIIb是一种抑制性FCR，负向调节这些反应，它在单核细胞和巨噬细胞上表达。因此，该受体的缺失或下调可能会显著提高治疗效果。在这里，我们筛选了一组Toll样受体(TLR)激动剂，发现对TLR4和TLR8具有选择性的激动剂可以显著下调FcRIIb的表达。进一步研究发现，用TLR4激动剂处理单核细胞可导致FcRIIb蛋白泛素化。对我们早期用TLR7/8激动剂R-848激活的单核细胞微阵列数据库(其中FcRIIb下调)显示，膜相关环指(C3HC4)3(MARCH3)上调，这是一种E3泛素连接酶。因此，我们检测了内毒素是否能上调单核细胞中MARCH3的表达，以及这种E3连接酶是否参与了内毒素介导的FcRIIb下调。结果表明，内毒素激活TLR4可显著增加MARCH3的表达，而针对MARCH3的siRNA可阻止内毒素处理后FcRIIb的减少。这些数据表明，单核细胞上TLR4的激活可以诱导FcRIIb蛋白的快速下调，这涉及泛素化。
Monocytes and macrophages are critical for the effectiveness of monoclonal antibody therapy. Responses to antibody-coated tumor cells are largely mediated by Fc receptors (FcRs), which become activated upon binding to immune complexes. FcRIIb is an inhibitory FcR that negatively regulates these responses, and it is expressed on monocytes and macrophages. Therefore, deletion or down-regulation of this receptor may substantially enhance therapeutic outcomes. Here we screened a panel of Toll-like receptor (TLR) agonists and found that those selective for TLR4 and TLR8 could significantly down-regulate the expression of FcRIIb. Upon further examination, we found that treatment of monocytes with TLR4 agonists could lead to the ubiquitination of FcRIIb protein. A search of our earlier microarray database of monocytes activated with the TLR7/8 agonist R-848 (in which FcRIIb was down-regulated) revealed an up-regulation of membrane-associated ring finger (C3HC4) 3 (MARCH3), an E3 ubiquitin ligase. Therefore, we tested whether LPS treatment could up-regulate MARCH3 in monocytes and whether this E3 ligase was involved with LPS-mediated FcRIIb down-regulation. The results showed that LPS activation of TLR4 significantly increased MARCH3 expression and that siRNA against MARCH3 prevented the decrease in FcRIIb following LPS treatment. These data suggest that activation of TLR4 on monocytes can induce a rapid down-regulation of FcRIIb protein and that this involves ubiquitination.