Kato Jiro, Zhu Jianfeng, Liu Chengyu, Moss Joel
Pulmonary-Critical Care Medicine Branch, National Heart, Lung and Blood Institute, National Institutes of Health, Building 10, Room 6D05, MSC 1590, Bethesda, MD 20892-1590, USA.
Mol Cell Biol. 2007 Aug;27(15):5534-43. doi: 10.1128/MCB.00302-07. Epub 2007 May 25.
Cholera toxin (CT) produced by Vibrio cholerae causes the devastating diarrhea of cholera by catalyzing the ADP-ribosylation of the alpha subunit of the intestinal Gs protein (Gsalpha), leading to characteristic water and electrolyte losses. Mammalian cells contain ADP-ribosyltransferases similar to CT and an ADP-ribosyl(arginine)protein hydrolase (ADPRH), which cleaves the ADP-ribose-(arginine)protein bond, regenerating native protein and completing an ADP-ribosylation cycle. We hypothesized that ADPRH might counteract intoxication by reversing the ADP-ribosylation of Gsalpha. Effects of intoxication on murine ADPRH-/- cells were greater than those on wild-type cells and were significantly reduced by overexpression of wild-type ADPRH in ADPRH-/- cells, as evidenced by both ADP-ribose-arginine content and Gsalpha modification. Similarly, intestinal loops in the ADPRH-/- mouse were more sensitive than their wild-type counterparts to toxin effects on fluid accumulation, Gsalpha modification, and ADP-ribosylarginine content. Thus, CT-catalyzed ADP-ribosylation of cell proteins can be counteracted by ADPRH, which could function as a modifier gene in disease. Further, our study demonstrates that enzymatic cross talk exists between bacterial toxin ADP-ribosyltransferases and host ADP-ribosylation cycles. In disease, toxin-catalyzed ADP-ribosylation overwhelms this potential host defense system, resulting in persistence of ADP-ribosylation and intoxication of the cell.
霍乱弧菌产生的霍乱毒素（CT）通过催化肠道Gs蛋白（Gsα）的α亚基的ADP核糖基化，导致霍乱严重腹泻，进而引起典型的水和电解质流失。哺乳动物细胞含有与CT相似的ADP核糖基转移酶和一种ADP核糖基（精氨酸）蛋白水解酶（ADPRH），该酶可切割ADP核糖-（精氨酸）蛋白键，使天然蛋白再生并完成ADP核糖基化循环。我们推测ADPRH可能通过逆转Gsα的ADP核糖基化来对抗中毒。中毒对小鼠ADPRH-/-细胞的影响大于对野生型细胞的影响，并且在ADPRH-/-细胞中过表达野生型ADPRH可显著降低这种影响，ADP核糖-精氨酸含量和Gsα修饰均证明了这一点。同样，ADPRH-/-小鼠的肠袢比野生型小鼠的肠袢对毒素在液体蓄积、Gsα修饰和ADP核糖基精氨酸含量方面的影响更敏感。因此，ADPRH可以对抗CT催化的细胞蛋白ADP核糖基化，其可能作为疾病中的修饰基因发挥作用。此外，我们的研究表明细菌毒素ADP核糖基转移酶与宿主ADP核糖基化循环之间存在酶促相互作用。在疾病中，毒素催化的ADP核糖基化使这种潜在的宿主防御系统不堪重负，导致ADP核糖基化持续存在并使细胞中毒。
