Li Xiaobing, Saitoh Shin-Ichiroh, Shibata Takuma, Tanimura Natsuko, Fukui Ryutaro, Miyake Kensuke
Division of Innate Immunity, Department of Microbiology and Immunology, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan.
Division of Innate Immunity, Department of Microbiology and Immunology, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan Laboratory of Innate Immunity, Center for Experimental Medicine and Systems Biology, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan
Int Immunol. 2015 Feb;27(2):83-94. doi: 10.1093/intimm/dxu086. Epub 2014 Sep 19.
Toll-like receptor 7 (TLR7) and TLR9 sense microbial single-stranded RNA (ssRNA) and ssDNA in endolysosomes. Nucleic acid (NA)-sensing in endolysosomes is thought to be important for avoiding TLR7/9 responses to self-derived NAs. Aberrant self-derived NA transportation to endolysosomes predisposes to autoimmune diseases. To restrict NA-sensing in endolysosomes, TLR7/9 trafficking is tightly controlled by a multiple transmembrane protein Unc93B1. In contrast to TLR7/9 trafficking, little is known about a mechanism underlying NA transportation. We here show that Mucolipin 1 (Mcoln1), a member of the transient receptor potential (TRP) cation channel gene family, has an important role in ssRNA trafficking into lysosomes. Mcoln1(-/-) dendritic cells (DCs) showed impaired TLR7 responses to ssRNA. A mucolipin agonist specifically enhanced TLR7 responses to ssRNAs. The channel activity of Mcoln1 is activated by a phospholipid phosphatidylinositol (3,5) bisphosphate (PtdIns(3,5)P2), which is generated by a class III lipid kinase PIKfyve. A PIKfyve inhibitor completely inhibited TLR7 responses to ssRNA in DCs. Confocal analyses showed that ssRNA transportation to lysosomes in DCs was impaired by PIKfyve inhibitor as well as by the lack of Mcoln1. Transportation of TLR9 ligands was also impaired by the PIKfyve inhibitor. These results demonstrate that the PtdIns(3,5)P2-Mcoln1 axis has an important role in ssRNA transportation into lysosomes in DCs.
Toll样受体7（TLR7）和TLR9在内溶酶体中识别微生物单链RNA（ssRNA）和单链DNA。内溶酶体中的核酸（NA）识别被认为对于避免TLR7/9对自身来源的NA产生反应很重要。自身来源的NA异常转运至内溶酶体易引发自身免疫性疾病。为了限制内溶酶体中的NA识别，TLR7/9的运输受到多跨膜蛋白Unc93B1的严格控制。与TLR7/9的运输不同，关于NA运输的潜在机制知之甚少。我们在此表明，瞬时受体电位（TRP）阳离子通道基因家族成员黏脂蛋白1（Mcoln1）在ssRNA转运至溶酶体中起重要作用。Mcoln1基因敲除的树突状细胞（DC）对ssRNA的TLR7反应受损。一种黏脂蛋白激动剂特异性增强了TLR7对ssRNA的反应。Mcoln1的通道活性由磷脂酰肌醇（3,5）二磷酸（PtdIns(3,5)P2）激活，PtdIns(3,5)P2由III类脂质激酶PIKfyve产生。PIKfyve抑制剂完全抑制了DC中TLR7对ssRNA的反应。共聚焦分析表明，PIKfyve抑制剂以及Mcoln1的缺失均损害了DC中ssRNA向溶酶体的转运。TLR9配体的转运也受到PIKfyve抑制剂的损害。这些结果表明，PtdIns(3,5)P2-Mcoln1轴在DC中ssRNA转运至溶酶体中起重要作用。
