A Novel Mechanism of Growth Phase-dependent Tolerance to Isoniazid in Mycobacteria

Makoto Niki,Mamiko Niki,Yoshitaka Tateishi,Yuriko Ozeki,Teruo Kirikae,Astrid Lewin,Yusuke Inoue,Makoto Matsumoto,John L Dahl,Hisashi Ogura,Kazuo Kobayashi,Sohkichi Matsumoto

doi:10.1074/jbc.m111.333385

Abstract

Tuberculosis remains one of the most deadly infectious diseases worldwide and is a leading public health problem. Although isoniazid (INH) is a key drug for the treatment of tuberculosis, tolerance to INH necessitates prolonged treatment, which is a concern for effective tuberculosis chemotherapy. INH is a prodrug that is activated by the mycobacterial enzyme, KatG. Here, we show that mycobacterial DNA-binding protein 1 (MDP1), which is a histone-like protein conserved in mycobacteria, negatively regulates katG transcription and leads to phenotypic tolerance to INH in mycobacteria. Mycobacterium smegmatis deficient for MDP1 exhibited increased expression of KatG and showed enhanced INH activation compared with the wild-type strain. Expression of MDP1 was increased in the stationary phase and conferred growth phase-dependent tolerance to INH in M. smegmatis. Regulation of KatG expression is conserved between M. smegmatis and Mycobacterium tuberculosis complex. Artificial reduction of MDP1 in Mycobacterium bovis BCG was shown to lead to increased KatG expression and susceptibility to INH. These data suggest a mechanism by which phenotypic tolerance to INH is acquired in mycobacteria.

Highlights

The mechanism underlying mycobacterial phenotypic tolerance to isoniazid is unknown
mycobacterial DNA-binding protein 1 (MDP1)-deficient M. smegmatis Showed Increased Susceptibility to INH—To determine whether MDP1 is involved in the acquisition of drug sensitivity in mycobacteria, we analyzed the susceptibility of M. smegmatis WT, MDP1-KO, and MDP1Comp cells to antibiotics
These results suggested that susceptibility to INH is affected by the presence of MDP1 in M. smegmatis cells

Summary

Background

Results: MDP1, a mycobacterial histone-like protein, down-regulates KatG expression. Conclusion: Down-regulation of KatG by MDP1 causes growth phase-dependent phenotypic tolerance to isoniazid in mycobacteria. We show that mycobacterial DNA-binding protein 1 (MDP1), which is a histone-like protein conserved in mycobacteria, negatively regulates katG transcription and leads to phenotypic tolerance to INH in mycobacteria. Artificial reduction of MDP1 in Mycobacterium bovis BCG was shown to lead to increased KatG expression and susceptibility to INH These data suggest a mechanism by which phenotypic tolerance to INH is acquired in mycobacteria. The reason why mycobacteria in the stationary phase acquire INH tolerance has not been fully elucidated, it is likely that the regulated expression of genes involved in the action of this drug is responsible for INH tolerance. This mechanism may strongly impact our understanding of phenotypic tolerance to INH in M. tuberculosis

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION