Upon infection of host cells, Salmonella enterica serovar Typhimurium resides in a modified-endosomal compartment referred to as the Salmonella-containing vacuole (SCV). SCV biogenesis is driven by multiple effector proteins translocated through two type III secretion systems (T3SS-1 and T3SS-2). While many host proteins targeted by these effector proteins have been characterised, the role of host lipids in SCV dynamics remains poorly understood. Previous studies have shown that S. Typhimurium infection in macrophages leads to accumulation of intracellular cholesterol, some of which concentrates in and around SCVs; however, the underlying mechanisms remain unknown. Here, we show that S. Typhimurium utilises the T3SS-2 effector SseJ to downregulate expression of the host cholesterol transporter ABCA1 in macrophages, leading to a ~45% increase in cellular cholesterol. Mechanistically, SseJ activates a signalling cascade involving the host kinases FAK and Akt to suppress Abca1 expression. Mutational inactivation of SseJ acyltransferase activity, silencing FAK, or inhibiting Akt prevents Abca1 downregulation and the corresponding accumulation of cholesterol during infection. Importantly, RNAi-mediated silencing of ABCA1 rescued bacterial survival in FAK-deficient macrophages, suggesting that Abca1 downregulation and cholesterol accumulation are important for intracellular survival.

中文翻译：

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鼠伤寒沙门氏菌通过 SseJ 介导的宿主胆固醇转运蛋白 ABCA1 抑制来操纵巨噬细胞胆固醇稳态

在感染宿主细胞后，肠沙门氏菌鼠伤寒血清型存在于称为含沙门氏菌液泡 (SCV) 的修饰内体隔室中。SCV 生物发生由通过两种 III 型分泌系统（T3SS-1 和 T3SS-2）易位的多种效应蛋白驱动。虽然这些效应蛋白靶向的许多宿主蛋白已被表征，但宿主脂质在 SCV 动力学中的作用仍然知之甚少。以前的研究表明，S。巨噬细胞中的鼠伤寒感染导致细胞内胆固醇的积累，其中一些集中在 SCV 内部和周围；然而，潜在的机制仍然未知。在这里，我们证明S. Typhimurium 利用 T3SS-2 效应器 SseJ 下调巨噬细胞中宿主胆固醇转运蛋白 ABCA1 的表达，导致细胞胆固醇增加约 45%。从机制上讲，SseJ 激活涉及宿主激酶 FAK 和 Akt 的信号级联以抑制Abca1表达。SseJ 酰基转移酶活性的突变失活、沉默 FAK 或抑制 Akt 可防止Abca1下调和感染期间相应的胆固醇积累。重要的是，RNAi 介导的 ABCA1 沉默挽救了 FAK 缺陷巨噬细胞中的细菌存活，这表明Abca1下调和胆固醇积累对细胞内存活很重要。