Department of Medical Research, Veterans Administration Medical Center, Long Beach, California 90822, USA.
Am J Physiol Gastrointest Liver Physiol. 2009 Oct;297(4):G825-33. doi: 10.1152/ajpgi.00250.2009. Epub 2009 Jul 23.
Infection with the gram-negative enteropathogenic Escherichia coli (EPEC), a food-borne pathogen, represents a significant risk to human health. Whereas diarrhea is a major consequence of this infection, malnutrition also occurs especially in severe and prolonged cases, which may aggravate the health status of the infected hosts. Here we examined the effect of EPEC infection on the intestinal uptake of the water-soluble vitamin B1 (thiamin) using an established human intestinal epithelial Caco-2 cell model. The results showed that infecting Caco-2 cells with wild-type EPEC (but not with nonpathogenic E. coli, killed EPEC, or filtered supernatant) leads to a significant (P < 0.01) inhibition in thiamin uptake. Kinetic parameters of both the nanomolar (mediated by THTR-2) and the micromolar (mediated by THTR-1) saturable thiamin uptake processes were affected by EPEC infection. Cell surface expression of hTHTR-1 and -2 proteins, (determined by the biotinylation method) showed a significantly (P < 0.01) lower expression in EPEC-treated cells compared with controls. EPEC infection also affected the steady-state mRNA levels as well as promoter activity of the SLC19A2 and SLC19A3 genes. Infecting Caco-2 cells with EPEC mutants that harbor mutations in the escN gene (which encodes a putative ATPase for the EPEC type III secretion system, TTSS) or the espA, espB, or espD genes (which encode structural components of the TTSS) did not affect thiamin uptake. On the other hand, mutations in espF and espH genes (which encode effector proteins) exhibited partial inhibition in thiamin uptake. These results demonstrate for the first time that EPEC infection of human intestinal epithelial cells leads to inhibition in thiamin uptake via effects on physiological and molecular parameters of hTHTR-1 and -2. Furthermore, the inhibition appears to be dependent on a functional TTSS of EPEC.
肠致病性大肠杆菌（EPEC）是一种食源性病原体，感染该病原体对人类健康构成重大威胁。虽然腹泻是这种感染的主要后果，但营养不良也会发生，尤其是在严重和长期的情况下，这可能会使感染宿主的健康状况恶化。在这里，我们使用已建立的人肠上皮 Caco-2 细胞模型研究了 EPEC 感染对水溶性维生素 B1（硫胺素）肠内摄取的影响。结果表明，用野生型 EPEC 感染 Caco-2 细胞（而非无致病性大肠杆菌、失活的 EPEC 或过滤上清液）会导致硫胺素摄取显著（P < 0.01）抑制。EPEC 感染还影响了纳米摩尔（由 THTR-2 介导）和微摩尔（由 THTR-1 介导）硫胺素摄取过程的动力学参数。通过生物素化法测定的 hTHTR-1 和 -2 蛋白的细胞表面表达在 EPEC 处理的细胞中明显（P < 0.01）低于对照。EPEC 感染还影响了 SLC19A2 和 SLC19A3 基因的稳态 mRNA 水平和启动子活性。感染带有 escN 基因突变（该基因编码 EPEC 型 III 型分泌系统（TTSS）的假定 ATP 酶）或 espA、espB 或 espD 基因突变（编码 TTSS 结构成分）的 EPEC 突变体的 Caco-2 细胞不会影响硫胺素摄取。另一方面，espF 和 espH 基因突变（编码效应蛋白）表现出硫胺素摄取的部分抑制。这些结果首次证明，EPEC 感染人肠上皮细胞会通过对 hTHTR-1 和 -2 的生理和分子参数产生影响，导致硫胺素摄取抑制。此外，这种抑制似乎依赖于 EPEC 的功能性 TTSS。
