Baulard A R, Betts J C, Engohang-Ndong J, Quan S, McAdam R A, Brennan P J, Locht C, Besra G S
INSERM U447, Institut de Biologie de Lille, Institut Pasteur de Lille, 59019 Lille, France.
J Biol Chem. 2000 Sep 8;275(36):28326-31. doi: 10.1074/jbc.M003744200.
The anti-tuberculosis drug ethionamide (ETH), which is a structural analog of isoniazid (INH), is known to strongly inhibit mycolic acid synthesis in Mycobacterium tuberculosis. Although several targets have been identified for INH, only speculative information is available concerning ETH. Mutations within the promoter and the coding region of enoyl-acyl carrier protein reductase (InhA) were found to confer resistance to both drugs, thus leading to the impression that INH and ETH may share a common mode of action. However, a notable distinction between the two drugs lies in the lack of cross-resistance in clinical isolates. This may be attributed in part to the fact that the pro-drug INH must be activated via KatG, and no activation step for ETH has yet been described. Here we report the identification of an activator for ETH. The ETH activator (Rv3854c), which we have termed EthA, was found to be homologous to various monooxygenases and induced ETH sensitivity when overexpressed in mycobacteria. Interestingly, the neighboring open reading frame (Rv3855), which was found homologous to transcriptional repressors of the tetR family, led to ETH resistance when overexpressed. In addition, chromosomal inactivation of this gene by transposition led to ETH hypersensitivity. These data strongly suggest that Rv3855, which we have termed EthR, regulates the production of EthA, which subsequently activates the pro-drug ETH. This study opens up new avenues of research relating to ETH activation in mycobacteria, possibly leading to an improved efficacy of ETH and to the generation of new anti-mycobacterial agents.
抗结核药物乙硫异烟胺（ETH）是异烟肼（INH）的结构类似物，已知其能强烈抑制结核分枝杆菌中分枝菌酸的合成。尽管已确定INH有几个作用靶点，但关于ETH只有一些推测性信息。烯酰 - 酰基载体蛋白还原酶（InhA）的启动子和编码区域内的突变被发现会使细菌对这两种药物都产生耐药性，因此给人一种印象，即INH和ETH可能有共同的作用方式。然而，这两种药物之间一个显著的区别在于临床分离株中不存在交叉耐药性。这可能部分归因于前体药物INH必须通过KatG激活，而尚未描述ETH的激活步骤。在此我们报告了一种ETH激活剂的鉴定。我们将ETH激活剂（Rv3854c）命名为EthA，发现它与各种单加氧酶同源，并且在分枝杆菌中过表达时会诱导ETH敏感性。有趣的是，发现与tetR家族转录阻遏物同源的相邻开放阅读框（Rv3855）在过表达时会导致ETH耐药性。此外，通过转座使该基因发生染色体失活会导致ETH超敏反应。这些数据有力地表明，我们命名为EthR的Rv3855调节EthA的产生，随后EthA激活前体药物ETH。这项研究开辟了与分枝杆菌中ETH激活相关的新研究途径，可能会提高ETH的疗效并产生新的抗分枝杆菌药物。
