Crane John K, Naeher Tonniele M, Shulgina Irina, Zhu Chengru, Boedeker Edgar C
Department of Medicine, Division of Infectious Diseases, University at Buffalo, Buffalo, New York 14214, USA.
Infect Immun. 2007 Dec;75(12):5974-84. doi: 10.1128/IAI.00750-07. Epub 2007 Sep 17.
Enteropathogenic Escherichia coli (EPEC) infection triggers the release of ATP from host intestinal cells, and the ATP is broken down to ADP, AMP, and adenosine in the lumen of the intestine. Ecto-5'-nucleotidase (CD73) is the main enzyme responsible for the conversion of 5'-AMP to adenosine, which triggers fluid secretion from host intestinal cells and also has growth-promoting effects on EPEC bacteria. In a recent study, we examined the role of the host enzyme CD73 in EPEC infection by testing the effect of ecto-5'-nucleotidase inhibitors. Zinc was a less potent inhibitor of ecto-5'-nucleotidase in vitro than the nucleotide analog alpha,beta-methylene-ADP, but in vivo, zinc was much more efficacious in preventing EPEC-induced fluid secretion in rabbit ileal loops than alpha,beta-methylene-ADP. This discrepancy between the in vitro and in vivo potencies of the two inhibitors prompted us to search for potential targets of zinc other than ecto-5'-nucleotidase. Zinc, at concentrations that produced little or no inhibition of EPEC growth, caused a decrease in the expression of EPEC protein virulence factors, such as bundle-forming pilus (BFP), EPEC secreted protein A, and other EPEC secreted proteins, and reduced EPEC adherence to cells in tissue culture. The effects of zinc were not mimicked by other transition metals, such as manganese, iron, copper, or nickel, and the effects were not reversed by an excess of iron. Quantitative real-time PCR showed that zinc reduced the abundance of the RNAs encoded by the bfp gene, by the plasmid-encoded regulator (per) gene, by the locus for the enterocyte effacement (LEE)-encoded regulator (ler) gene, and by several of the esp genes. In vivo, zinc reduced EPEC-induced fluid secretion into ligated rabbit ileal loops, decreased the adherence of EPEC to rabbit ileum, and reduced histopathological damage such as villus blunting. Some of the beneficial effects of zinc on EPEC infection appear to be due to the action of the metal on EPEC bacteria as well as on the host.
肠致病性大肠杆菌（EPEC）感染会引发宿主肠道细胞释放ATP，且ATP在肠腔内会分解为ADP、AMP和腺苷。ecto-5'-核苷酸酶（CD73）是负责将5'-AMP转化为腺苷的主要酶，这会引发宿主肠道细胞的液体分泌，并且对EPEC细菌具有促生长作用。在最近的一项研究中，我们通过测试ecto-5'-核苷酸酶抑制剂的作用来研究宿主酶CD73在EPEC感染中的作用。在体外，锌作为ecto-5'-核苷酸酶的抑制剂，其效力低于核苷酸类似物α,β-亚甲基-ADP，但在体内，锌在预防兔回肠袢中EPEC诱导的液体分泌方面比α,β-亚甲基-ADP更有效。这两种抑制剂在体外和体内效力之间的差异促使我们寻找除ecto-5'-核苷酸酶之外锌的潜在靶点。锌在对EPEC生长几乎没有抑制或完全没有抑制的浓度下，会导致EPEC蛋白毒力因子的表达下降，如束状菌毛（BFP）、EPEC分泌蛋白A和其他EPEC分泌蛋白，并减少EPEC在组织培养中对细胞的黏附。锌的这些作用不能被其他过渡金属（如锰、铁、铜或镍）模拟，并且过量的铁也不能逆转这些作用。定量实时PCR表明，锌降低了bfp基因、质粒编码调节因子（per）基因、肠上皮细胞脱落位点（LEE）编码调节因子（ler）基因以及几个esp基因所编码RNA的丰度。在体内，锌减少了EPEC诱导的液体分泌进入结扎的兔回肠袢，降低了EPEC对兔回肠的黏附，并减少了诸如绒毛变钝等组织病理学损伤。锌对EPEC感染的一些有益作用似乎是由于该金属对EPEC细菌以及宿主的作用。
