Borthakur Alip, Gill Ravinder K, Hodges Kim, Ramaswamy Krishnamurthy, Hecht Gail, Dudeja Pradeep K
Department of Medicine, University of Illinois at Chicago and Jesse Brown Veteran Affairs Medical Center, 820 South Damen Ave., Chicago, IL 60612, USA.
Am J Physiol Gastrointest Liver Physiol. 2006 Jan;290(1):G30-5. doi: 10.1152/ajpgi.00302.2005. Epub 2005 Sep 8.
Enteropathogenic Escherichia coli (EPEC), a food-borne human pathogen, is responsible for infantile diarrhea, especially in developing countries. The pathophysiology of EPEC-induced diarrhea, however, is not completely understood. Our recent studies showed modulation of Na+/H+ and Cl-/HCO3- exchange activities in Caco-2 cells in response to EPEC infection. We hypothesized that intestinal short-chain fatty acid absorption mediated by monocarboxylate transporter 1 (MCT1) might also be altered by EPEC infection. The aim of the current studies was to examine the effect of EPEC infection on butyrate uptake. Caco-2 cells were infected with wild-type EPEC, various mutant strains, or nonpathogenic E. coli HS4, and [14C]butyrate uptake was determined. EPEC, but not nonpathogenic E. coli, significantly decreased butyrate uptake. Infection of cells with strains harboring mutations in escN, which encodes a putative ATPase for the EPEC type III secretion system (TTSS), or in the espA, espB, or espD genes encoding structural components of the TTSS, had no effect on butyrate uptake, indicating the TTSS dependence. On the other hand, strains with mutations in the effector protein genes espF, espG, espH, and map inhibited butyrate uptake, similar to the wild-type EPEC. Surface expression of MCT1 decreased considerably after EPEC but not after nonpathogenic E. coli infection. In conclusion, our studies demonstrate inhibition of MCT1-mediated butyrate uptake in Caco-2 cells in response to EPEC infection. This inhibition was dependent on a functional TTSS and the structural proteins EspA, -B, and -D of the translocation apparatus.
肠致病性大肠杆菌（EPEC）是一种食源性人类病原体，可导致婴儿腹泻，在发展中国家尤为常见。然而，EPEC引起腹泻的病理生理学尚未完全明确。我们最近的研究表明，EPEC感染会调节Caco-2细胞中的Na+/H+和Cl-/HCO3-交换活性。我们推测，由单羧酸转运蛋白1（MCT1）介导的肠道短链脂肪酸吸收也可能因EPEC感染而改变。本研究的目的是检测EPEC感染对丁酸盐摄取的影响。用野生型EPEC、各种突变菌株或非致病性大肠杆菌HS4感染Caco-2细胞，并测定[14C]丁酸盐摄取量。EPEC而非非致病性大肠杆菌显著降低了丁酸盐摄取。用编码EPEC III型分泌系统（TTSS）假定ATP酶的escN或编码TTSS结构成分的espA、espB或espD基因发生突变的菌株感染细胞，对丁酸盐摄取没有影响，表明其对TTSS的依赖性。另一方面，效应蛋白基因espF、espG、espH和map发生突变的菌株抑制丁酸盐摄取，与野生型EPEC相似。EPEC感染后MCT1的表面表达显著降低，而非致病性大肠杆菌感染后则无此现象。总之，我们的研究表明，EPEC感染会抑制Caco-2细胞中MCT1介导的丁酸盐摄取。这种抑制依赖于功能性TTSS以及转运装置的结构蛋白EspA、-B和-D。
