Data_Sheet_1_Interaction of the Factor H Family Proteins FHR-1 and FHR-5 With DNA and Dead Cells: Implications for the Regulation of Complement Activation and Opsonization.PDF

Complement plays an essential role in the opsonophagocytic clearance of apoptotic/necrotic cells. Dysregulation of this process may lead to inflammatory and autoimmune diseases. Factor H (FH), a major soluble complement inhibitor, binds to dead cells and inhibits excessive complement activation on their surface, preventing lysis, and the release of intracellular material, including DNA. The FH-related (FHR) proteins share common ligands with FH, due to their homology with this complement regulator, but they lack the domains that mediate the complement inhibitory activity of FH. Because their roles in complement regulation is controversial and incompletely understood, we studied the interaction of FHR-1 and FHR-5 with DNA and dead cells and investigated whether they influence the regulatory role of FH and the complement activation on DNA and dead cells. FH, FHR-1, and FHR-5 bound to both plasmid DNA and human genomic DNA, where both FHR proteins inhibited FH–DNA interaction. The FH cofactor activity was inhibited by FHR-1 and FHR-5 due to the reduced binding of FH to DNA in the presence of the FHRs. Both FHRs caused increased complement activation on DNA. FHR-1 and FHR-5 bound to late apoptotic and necrotic cells and recruited monomeric C-reactive protein and pentraxin 3, and vice versa. Interactions of the FHRs with pentraxins resulted in enhanced activation of both the classical and the alternative complement pathways on dead cells when exposed to human serum. Altogether, our results demonstrate that FHR-1 and FHR-5 are competitive inhibitors of FH on DNA; moreover, FHR–pentraxin interactions promote opsonization of dead cells.

补体（Complement）在凋亡细胞与坏死细胞的调理吞噬清除过程中发挥核心作用。该过程的失调可引发炎症性疾病与自身免疫性疾病。补体因子H（Factor H，FH）作为主要的可溶性补体调节抑制因子，可结合死亡细胞并抑制其表面的过度补体激活，从而阻止细胞裂解以及包括DNA在内的胞内物质释放。FH相关蛋白（FH-related，FHR）因与该补体调节因子具有序列同源性，可与FH共享配体，但缺失介导FH补体抑制活性的结构域。由于FHR蛋白在补体调控中的作用尚存争议且尚未完全阐明，本研究探究了FHR-1与FHR-5分别与DNA及死亡细胞的相互作用，并考察了它们是否会影响FH的调控功能以及DNA和死亡细胞表面的补体激活。FH、FHR-1及FHR-5均可结合质粒DNA与人类基因组DNA，且两种FHR蛋白均能抑制FH与DNA的结合。由于FHR蛋白存在时FH与DNA的结合能力下降，FHR-1与FHR-5可抑制FH的辅因子活性。两种FHR蛋白均可增强DNA表面的补体激活水平。FHR-1与FHR-5可结合晚期凋亡细胞与坏死细胞，并募集单体C反应蛋白（C-reactive protein）与五聚蛋白3（pentraxin 3），反之亦然。FHR蛋白与五聚蛋白的相互作用，可使得暴露于人血清的死亡细胞的经典补体通路与替代补体通路激活水平均得到增强。综上，本研究结果表明，FHR-1与FHR-5是FH在DNA结合层面的竞争性抑制剂；此外，FHR-五聚蛋白相互作用可促进死亡细胞的调理作用。