Intestinal Long-Chain Fatty Acids Act as a Direct Signal To Modulate Expression of the Salmonella Pathogenicity Island 1 Type III Secretion System.
Intestinal Long-Chain Fatty Acids Act as a Direct Signal To Modulate Expression of the Salmonella Pathogenicity Island 1 Type III Secretion System.
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DOI：
10.1128/mbio.02170-15
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发表时间：
2016-02-16
期刊：
影响因子：
6.4
通讯作者：
Slauch JM
中科院分区：
文献类型：
--
作者：
Golubeva YA;Ellermeier JR;Cott Chubiz JE;Slauch JM
沙门氏菌肠道血清型鼠伤寒沙门氏菌使用沙门氏菌致病岛1（SPI 1）III型分泌系统（T3 SS）诱导炎性腹泻和细菌摄取到肠上皮细胞中。hilA是T3 SS结构基因的转录激活因子，其表达直接受三个AraC样调节因子HilD、HilC和RtsA的调控，每一个AraC样调节因子都能激活hilD、hilC、rtsA和hilA基因，形成一个复杂的前馈调控环。SPI 1基因的表达受到许多调控输入的严格控制，以确保T3 SS装置产生的适当时机。已知FadD（降解长链脂肪酸（LCFA）所需的酰基辅酶A（酰基-CoA）合成酶）的缺失会降低hilA表达。我们发现，自由外部LCFA抑制表达的hilA独立的FadD和LCFA降解途径。遗传和生物化学证据表明，LCFA直接作用于主要阻断HilD活性。进一步的分析显示，在不存在FadD的情况下，由于游离LCFA的内源性产生，hilA表达下调，游离LCFA经由TolC分泌到培养基中，然后经由FadL转运回细菌细胞中。在小鼠口服竞争试验中，fadL突变体的毒性比野生型菌株更强，与LCFA降解无关，这表明在宿主中，饮食LCFA作为适当调节SPI 1表达的信号，而不是能量来源。沙门氏菌必须对不同的环境信号做出反应，才能在宿主肠道的适当位置表达其入侵机制，从而引起疾病。我们发现，宿主肠道游离长链脂肪酸（LCFA）影响沙门氏菌的入侵，通过减少SPI 1 III型分泌系统的表达，主要通过AraC样激活剂HilD。这种调节不需要LCFA的降解，表明游离LCFA作为适当肠定位的线索以侵入宿主上皮细胞，而不是作为营养源。
Salmonella enterica serovar Typhimurium uses the Salmonella pathogenicity island 1 (SPI1) type III secretion system (T3SS) to induce inflammatory diarrhea and bacterial uptake into intestinal epithelial cells. The expression of hilA, encoding the transcriptional activator of the T3SS structural genes, is directly controlled by three AraC-like regulators, HilD, HilC, and RtsA, each of which can activate hilD, hilC, rtsA, and hilA genes, forming a complex feed-forward regulatory loop. Expression of the SPI1 genes is tightly controlled by numerous regulatory inputs to ensure proper timing in production of the T3SS apparatus. Loss of FadD, an acyl coenzyme A (acyl-CoA) synthetase required for degradation of long-chain fatty acids (LCFAs), was known to decrease hilA expression. We show that free external LCFAs repress expression of hilA independently of FadD and the LCFA degradation pathway. Genetic and biochemical evidence suggests that LCFAs act directly to block primarily HilD activity. Further analyses show that in the absence of FadD, hilA expression is downregulated due to endogenous production of free LCFAs, which are excreted into the culture medium via TolC and then transported back into the bacterial cell via FadL. A fadL mutant is more virulent than the wild-type strain in mouse oral competition assays independently of LCFA degradation, showing that, in the host, dietary LCFAs serve as a signal for proper regulation of SPI1 expression, rather than an energy source. To cause disease, Salmonella must respond to diverse environmental cues to express its invasion machinery at the appropriate location in the host intestine. We show that host intestinal free long-chain fatty acids (LCFAs) affect Salmonella invasion by reducing expression of the SPI1 type III secretion system, acting primarily via the AraC-like activator HilD. Degradation of LCFAs is not required for this regulation, showing that free LCFAs serve as a cue to proper intestinal localization to invade host epithelial cells and not as a nutrient source.