Department of Molecular Genetics and Microbiology, Duke University, Medical Center, Durham, North Carolina 27710.
Geriatric Research, Education, and Clinical Center, VA Medical Center, Durham, North Carolina 27705.
J Biol Chem. 2011 Sep 2;286(35):30471-30480. doi: 10.1074/jbc.M111.251967. Epub 2011 Jul 12.
The immunity-related GTPases (IRGs) are a family of proteins induced by interferon-γ that play a crucial role in innate resistance to intracellular pathogens. The M subfamily of IRG proteins (IRGM) plays a profound role in this context, in part because of the ability of its members to regulate the localization and expression of other IRG proteins. We present here evidence that IRGM proteins affect the localization of the guanylate-binding proteins (GBPs), a second family of interferon-induced GTP-binding proteins that also function in innate immunity. Absence of Irgm1 or Irgm3 led to accumulation of Gbp2 in intracellular compartments that were positive for both the macroautophagy (hereafter referred to as autophagy) marker LC3 and the autophagic adapter molecule p62/Sqstm1. Gbp2 was similarly relocalized in cells in which autophagy was impaired because of the absence of Atg5. Both in Atg5- and IRGM-deficient cells, the IRG protein Irga6 relocalized to the same compartments as Gbp2, raising the possibility of a common regulatory mechanism. However, other data indicated that Irga6, but not Gbp2, was ubiquitinated in IRGM-deficient cells. Similarly, coimmunoprecipitation studies indicated that although Irgm3 did interact directly with Irgb6, it did not interact with Gbp2. Collectively, these data suggest that IRGM proteins indirectly modulate the localization of GBPs through a distinct mechanism from that through which they regulate IRG protein localization. Further, these results suggest that a core function of IRGM proteins is to regulate autophagic flux, which influences the localization of GBPs and possibly other factors that instruct cell-autonomous immune resistance.
免疫相关 GTPases（IRGs）是一类干扰素-γ诱导的蛋白质家族，在固有抵抗细胞内病原体方面发挥着关键作用。IRG 蛋白的 M 亚家族（IRGM）在这方面发挥了深远的作用，部分原因是其成员能够调节其他 IRG 蛋白的定位和表达。我们在此提出证据表明，IRGM 蛋白影响鸟苷酸结合蛋白（GBPs）的定位，GBPs 是干扰素诱导的 GTP 结合蛋白的第二个家族，也在固有免疫中发挥作用。Irgm1 或 Irgm3 的缺失导致 Gbp2 在 LC3 阳性的细胞内隔室中积累，LC3 是巨自噬（以下简称自噬）的标记物，而自噬衔接分子 p62/Sqstm1。由于 Atg5 的缺失导致自噬受损，Gbp2 也同样在细胞中重新定位。在 Atg5 和 IRGM 缺陷细胞中，IRG 蛋白 Irga6 与 Gbp2 重新定位到相同的隔室，这表明存在共同的调节机制。然而，其他数据表明，Irgm3 缺陷细胞中，只有 Irga6 而不是 Gbp2 发生泛素化。同样，共免疫沉淀研究表明，尽管 Irgm3 与 Irgb6 直接相互作用，但它与 Gbp2 不相互作用。总的来说，这些数据表明，IRGM 蛋白通过与调节 IRG 蛋白定位不同的机制间接调节 GBPs 的定位。此外，这些结果表明，IRGM 蛋白的核心功能是调节自噬流，这影响了 GBPs 和可能其他指导细胞自主免疫抵抗的因素的定位。
