Institute of Immunology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
Institute of Experimental Medicine, AG Systematic Proteome Research and Bioanalytics, Christian-Albrechts-Universität, Kiel, Germany.
Front Immunol. 2021 Mar 8;12:642545. doi: 10.3389/fimmu.2021.642545. eCollection 2021.
Murine T cells express the GPI-anchored ADP-ribosyltransferase 2.2 (ARTC2.2) on the cell surface. In response to T cell activation or extracellular NAD or ATP-mediated gating of the P2X7 ion channel ARTC2.2 is shed from the cell surface as a soluble enzyme. Shedding alters the target specificity of ARTC2.2 from cell surface proteins to secreted proteins. Here we demonstrate that shed ARTC2.2 potently ADP-ribosylates IFN-γ in addition to other cytokines. Using mass spectrometry, we identify arginine 128 as the target site of ADP-ribosylation. This residue has been implicated to play a key role in binding of IFN-γ to the interferon receptor 1 (IFNR1). Indeed, binding of IFN-γ to IFNR1 blocks ADP-ribosylation of IFN-γ. Moreover, ADP-ribosylation of IFN-γ inhibits the capacity of IFN-γ to induce STAT1 phosphorylation in macrophages and upregulation of the proteasomal subunit ß5i and the proteasomal activator PA28-α in podocytes. Our results show that ADP-ribosylation inhibits the signaling functions of IFN-γ and point to a new regulatory mechanism for controlling signaling by IFN-γ.
鼠源 T 细胞在细胞表面表达糖基磷脂酰肌醇锚定的 ADP-核糖基转移酶 2.2（ARTC2.2）。在 T 细胞激活或细胞外 NAD 或 ATP 门控 P2X7 离子通道的情况下，ARTC2.2 作为可溶性酶从细胞表面脱落。脱落改变了 ARTC2.2 的靶标特异性，从细胞表面蛋白到分泌蛋白。在这里，我们证明脱落的 ARTC2.2 除了其他细胞因子外，还能强烈 ADP-核糖基化 IFN-γ。使用质谱法，我们确定精氨酸 128 是 ADP-核糖基化的靶位。该残基已被证明在 IFN-γ与干扰素受体 1（IFNR1）结合中发挥关键作用。事实上，IFN-γ与 IFNR1 的结合阻止了 IFN-γ的 ADP-核糖基化。此外，IFN-γ的 ADP-核糖基化抑制了 IFN-γ在巨噬细胞中诱导 STAT1 磷酸化以及在足细胞中上调蛋白酶体亚基 ß5i 和蛋白酶体激活剂 PA28-α 的能力。我们的结果表明，ADP-核糖基化抑制了 IFN-γ的信号转导功能，并指出了控制 IFN-γ信号转导的新调节机制。
