Section of Bacterial Pathogenesis, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8510, Japan.
Cell Microbiol. 2012 Aug;14(8):1149-65. doi: 10.1111/j.1462-5822.2012.01792.x. Epub 2012 Apr 17.
Autophagy mediates the degradation of cytoplasmic contents in the lysosome and plays a significant role in immunity. Here we identified the small GTPases Rab9A and Rab23 as novel autophagy regulators during Group A streptococcus (GAS) infection. Rab9A was recruited to GAS-containing autophagosome-like vacuoles (GcAVs) after autophagosomal maturation and its activity was required for GcAV enlargement and eventual lysosomal fusion. GcAV enlargement appeared to be related to homotypic fusion of GcAVs with Rab9A. Rab23 was recruited to GAS-capturing forming autophagosomes. Knockdown of Rab23 expression decreased both LC3- and Atg5-positive GAS formation and caused the accumulation of LC3-positive structures that did not associate with intracellular GAS. It was suggested, therefore, that Rab23 is required for GcAV formation and is involved in GAS targeting of autophagic vacuoles. Furthermore, knockdown of Rab9A or Rab23 expression impaired the degradation of intracellular GAS. Therefore, our data reveal that the Rab9A and Rab23 GTPases play crucial roles in autophagy of GAS. However, neither Rab9A nor Rab23 were localized to starvation-induced autophagosomes. Not only Rab9A but also Rab23 was dispensable for starvation-induced autophagosome formation. These findings demonstrate that specific Rab proteins function at distinct steps during autophagy in response to GAS infection.
自噬介导溶酶体中细胞质内容物的降解，在免疫中发挥重要作用。在这里，我们鉴定了小 GTPases Rab9A 和 Rab23，它们是 A 组链球菌（GAS）感染过程中新型的自噬调节剂。Rab9A 在自噬体成熟后被募集到含有 GAS 的自噬体样空泡（GcAV）中，其活性对于 GcAV 扩大和最终溶酶体融合是必需的。GcAV 的扩大似乎与 GcAV 与 Rab9A 的同源融合有关。Rab23 被募集到捕获 GAS 的形成自噬体中。Rab23 表达的敲低减少了 LC3-和 Atg5 阳性 GAS 的形成，并导致 LC3 阳性结构的积累，这些结构与细胞内 GAS 无关。因此，Rab23 被认为是 GcAV 形成所必需的，并且参与 GAS 靶向自噬小泡。此外，Rab9A 或 Rab23 表达的敲低会损害细胞内 GAS 的降解。因此，我们的数据表明，Rab9A 和 Rab23 GTPases 在 GAS 的自噬中发挥关键作用。然而，Rab9A 和 Rab23 都没有定位于饥饿诱导的自噬体中。不仅 Rab9A，而且 Rab23 对于饥饿诱导的自噬体形成都是可有可无的。这些发现表明，特定的 Rab 蛋白在 GAS 感染诱导的自噬中特定步骤中发挥作用。
