The mitochondrial antiviral signaling (MAVS) protein on the mitochondrial outer membrane acts as a central signaling molecule in the RIG-I-like receptor (RLR) signaling pathway by linking upstream viral RNA recognition to downstream signal activation. We previously reported that mitochondrial E3 ubiquitin ligase, MARCH5, degrades the MAVS protein aggregate and prevents persistent downstream signaling. Since the activated RIG-I oligomer interacts and nucleates the MAVS aggregate, MARCH5 might also target this oligomer. Here, we report that MARCH5 targets and degrades RIG-I, but not its inactive phosphomimetic form (RIG-IS8E). The MARCH5-mediated reduction of RIG-I is restored in the presence of MG132, a proteasome inhibitor. Upon poly(I:C) stimulation, RIG-I forms an oligomer and co-expression of MARCH5 reduces the expression of this oligomer. The RING domain of MARCH5 is necessary for binding to the CARD domain of RIG-I. In an in vivo ubiquitination assay, MARCH5 transfers the Lys 48-linked polyubiquitin to Lys 193 and 203 residues of RIG-I. Thus, dual targeting of active RIG-I and MAVS protein oligomers by MARCH5 is an efficient way to switch-off RLR signaling. We propose that modulation of MARCH5 activity might be beneficial for the treatment of chronic immune diseases.

中文翻译：

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先天免疫中 MARCH5 线粒体泛素连接酶双重靶向 RIG-I 和 MAVS。


线粒体外膜上的线粒体抗病毒信号 (MAVS) 蛋白通过将上游病毒 RNA 识别与下游信号激活联系起来，充当 RIG-I 样受体 (RLR) 信号通路中的中央信号分子。我们之前报道过线粒体 E3 泛素连接酶 MARCH5 会降解 MAVS 蛋白聚集体并阻止持续的下游信号传导。由于激活的 RIG-I 寡聚物与 MAVS 聚集体相互作用并使 MAVS 聚集体成核，因此 MARCH5 也可能以该寡聚物为目标。在此，我们报告 MARCH5 靶向并降解 RIG-I，但不靶向其非活性磷酸模拟形式 (RIG-IS8E)。当蛋白酶体抑制剂 MG132 存在时，MARCH5 介导的 RIG-I 减少得以恢复。在 Poly(I:C) 刺激下，RIG-I 形成寡聚体，MARCH5 的共表达会减少该寡聚体的表达。 MARCH5 的 RING 结构域对于结合 RIG-I 的 CARD 结构域是必需的。在体内泛素化测定中，MARCH5 将 Lys 48 连接的多聚泛素转移至 RIG-I 的 Lys 193 和 203 残基。因此，MARCH5 对活性 RIG-I 和 MAVS 蛋白寡聚体的双重靶向是关闭 RLR 信号传导的有效方法。我们认为调节 MARCH5 活性可能有利于慢性免疫疾病的治疗。