Croker Daniel E, Monk Peter N, Halai Reena, Kaeslin Geraldine, Schofield Zoe, Wu Mike Cl, Clark Richard J, Blaskovich Mark At, Morikis Dimitrios, Floudas Christodoulos A, Cooper Matthew A, Woodruff Trent M
School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia.
Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia.
Immunol Cell Biol. 2016 Sep;94(8):787-95. doi: 10.1038/icb.2016.43. Epub 2016 Apr 25.
The complement cascade is comprised of a highly sophisticated network of innate immune proteins that are activated in response to invading pathogens or tissue injury. The complement activation peptide, C5a, binds two seven transmembrane receptors, namely the C5a receptor 1 (C5aR1) and C5a receptor 2 (C5aR2, or C5L2). C5aR2 is a non-G-protein-signalling receptor whose biological role remains controversial. Some of this controversy arises owing to the lack of selective ligands for C5aR2. In this study, a library of 61 peptides based on the C-terminus of C5a was assayed for the ability to selectively modulate C5aR2 function. Two ligands (P32 and P59) were identified as functionally selective C5aR2 ligands, exhibiting selective recruitment of β-arrestin 2 via C5aR2, partial inhibition of C5a-induced ERK1/2 activation and lipopolysaccharide-stimulated interleukin-6 release from human monocyte-derived macrophages. Importantly, neither ligand could induce ERK1/2 activation or inhibit C5a-induced ERK1/2 activation via C5aR1 directly. Finally, P32 inhibited C5a-mediated neutrophil mobilisation in wild-type, but not C5aR2(-/-) mice. These functionally selective ligands for C5aR2 are novel tools that can selectively modulate C5a activity in vitro and in vivo, and thus will be valuable tools to interrogate C5aR2 function.
补体级联反应由一个高度复杂的固有免疫蛋白网络组成，这些蛋白在病原体入侵或组织损伤时被激活。补体激活肽C5a与两种七跨膜受体结合，即C5a受体1（C5aR1）和C5a受体2（C5aR2，或C5L2）。C5aR2是一种非G蛋白信号受体，其生物学作用仍存在争议。部分争议源于缺乏针对C5aR2的选择性配体。在本研究中，对基于C5a C末端的61种肽库进行了选择性调节C5aR2功能能力的检测。鉴定出两种配体（P32和P59）为功能选择性C5aR2配体，它们通过C5aR2选择性募集β-抑制蛋白2，部分抑制C5a诱导的ERK1/2激活以及脂多糖刺激的人单核细胞衍生巨噬细胞释放白细胞介素-6。重要的是，两种配体均不能直接通过C5aR1诱导ERK1/2激活或抑制C5a诱导的ERK1/2激活。最后，P32抑制野生型小鼠中C5a介导的中性粒细胞动员，但对C5aR2基因敲除小鼠无效。这些针对C5aR2的功能选择性配体是新型工具，可在体外和体内选择性调节C5a活性，因此将成为研究C5aR2功能的宝贵工具。
