探討DcR3參與脂多醣在巨噬細胞誘導免疫反應及ALIS之角色

Abstract

第三誘餌受體，別名腫瘤壞死因子受體超家族成員6b，是一個多效性的可溶因子，藉由誘餌及非誘餌兩種不同方式調節細胞的功能。過去在癌症及發炎性疾病的研究中，第三誘餌受體展示其抗細胞凋亡與抗發炎的作用。類鐸受體(TLRs)屬於模式辨認受體，參與啟動發炎反應以對抗病原體。目前關於第三誘餌受體在TLR4引起的發炎反應中是否扮演角色仍不是很清楚。在這篇研究中，我們發現在骨髓源性巨噬細胞，第三誘餌受體並不影響脂多醣引起的COX-2、iNOS、NLRP3 及 pro-IL-1 蛋白表現。先前報導指出脂多醣刺激巨噬細胞會形成一種稱為aggresome-like induced structures (ALIS) 的結構。ALIS含有泛素化蛋白的聚集，屬於一種壓力引起的反應，參與第一型主要組織相容性複合體的抗原呈現。我們的結果顯示，第三誘餌受體會藉由抑制活性氧化物及p38 MAPK的磷酸化來減少脂多醣所引起的ALIS生成。除了脂多醣外，我們還發現第三誘餌受體也會抑制ZnPP、 bafilomycin A1與MG132引起的泛素化蛋白。已知ALIS會受到自噬作用的調控，我們發現rapamycin會減少脂多醣引起的ALIS生成，而在WT與DcR3表現的巨噬細胞中，bafilomycin A1會增加相同程度的LC3-II累積。不過，DcR3不改變脂多醣引起的p62與HO-1表現。整體而言，儘管第三誘餌受體不影響脂多醣引起的發炎反應，我們的結果顯示第三誘餌受體在ALIS的生成中扮演全新的角色。

Decoy receptor 3 (DcR3), also known as tumor necrosis factor receptor (TNFR) superfamily member 6b (TNFRSF6B), is a pleiotropic factor which modulates cell functions via decoy and non-decoy actions. DcR3 has been shown its anti-apoptotic and anti-inflammatory effects on cancers and inflammatory diseases. Toll-like receptors (TLRs), which are the members of pattern recognition receptors (PRRs), trigger inflammatory response against invading pathogens. However, it remains unclear whether DcR3 plays a role in TLR4-induced inflammatory response. In this study, we demonstrated that in bone marrow-derived macrophages (BMDMs) DcR3 did not affect lipopolysaccharide (LPS)-induced COX-2, iNOS, NLRP3 and pro-IL-1 protein expression. It has been reported that aggresome-like induced structures (ALIS) are formed in response to LPS in macrophages. ALIS, which containing ubiquitinated protein aggregates, are stress-induced response involved in MHC class I antigen presentation. Our findings illustrated that DcR3 can decrease LPS-induced ALIS formation via inhibiting cellular ROS production and p38 MAPK phosphorylation. In addition to LPS, ZnPP-, bafilomycin A1- and MG132-induced ubiquitinated protein expression were blocked by DcR3. Confirming the notion that ALIS is controlled by autophagy, we found that rapamycin can decrease LPS-induced ALIS formation, while bafilomycin A1 can increase LC3-II accumulation with similar extent in WT and DcR3 macrophages. Nevertheless, DcR3 expression does not change p62 and HO-1 expression induced by LPS. Taken together, despite the fact that DcR3 does not alter LPS-induced inflammatory response, our data suggest novel roles of DcR3 in ALIS formation.