The Mycobacterium tuberculosis iniA gene is essential for activity of an efflux pump that confers drug tolerance to both isoniazid and ethambutol

Authors

  • Roberto Colangeli,

    1. Division of Infectious Disease and the Center for Emerging Pathogens, Department of Medicine, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA.
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  • Danica Helb,

    1. Division of Infectious Disease and the Center for Emerging Pathogens, Department of Medicine, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA.
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  • Sudharsan Sridharan,

    1. Department of Biochemistry and Biophysics,
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  • Jingchuan Sun,

    1. Microscopy and Imaging Center and Department of Biology, Texas A and M University, College Station, TX 77843, USA.
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  • Mandira Varma-Basil,

    1. Division of Infectious Disease and the Center for Emerging Pathogens, Department of Medicine, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA.
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  • Manzour Hernando Hazbón,

    1. Division of Infectious Disease and the Center for Emerging Pathogens, Department of Medicine, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA.
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  • Ryhor Harbacheuski,

    1. Public Health Research Institute, Newark NJ 07103, USA.
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  • Nicholas J. Megjugorac,

    1. Division of Infectious Disease and the Center for Emerging Pathogens, Department of Medicine, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA.
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  • William R. Jacobs Jr,

    1. Howard Hughes Medical Institute, Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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  • Andreas Holzenburg,

    1. Department of Biochemistry and Biophysics,
    2. Microscopy and Imaging Center and Department of Biology, Texas A and M University, College Station, TX 77843, USA.
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  • James C. Sacchettini,

    1. Department of Biochemistry and Biophysics,
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  • David Alland

    Corresponding author
    1. Division of Infectious Disease and the Center for Emerging Pathogens, Department of Medicine, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA.
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E-mail allandda@umdnj.edu; Tel. (+1) 973 972 2179; Fax (+1) 973 972 1141.

Summary

Little is known about the intracellular events that occur following the initial inhibition of Mycobacterium tuberculosis by the first-line antituberculosis drugs isoniazid (INH) and ethambutol (EMB). Understanding these pathways should provide significant insights into the adaptive strategies M. tuberculosis undertakes to survive antibiotics. We have discovered that the M. tuberculosis iniA gene (Rv 0342) participates in the development of tolerance to both INH and EMB. This gene is strongly induced along with iniB and iniC (Rv 0341 and Rv 0343) by treatment of Mycobacterium bovis BCG or M. tuberculosis with INH or EMB. BCG strains overexpressing M. tuberculosis iniA grew and survived longer than control strains upon exposure to inhibitory concentrations of either INH or EMB. An M. tuberculosis strain containing an iniA deletion showed increased susceptibility to INH. Additional studies showed that overexpression of M. tuberculosis iniA in BCG conferred resistance to ethidium bromide, and the deletion of iniA in M. tuberculosis resulted in increased accumulation of intracellular ethidium bromide. The pump inhibitor reserpine reversed both tolerance to INH and resistance to ethidium bromide in BCG. These results suggest that iniA functions through an MDR-pump like mechanism, although IniA does not appear to directly transport INH from the cell. Analysis of two-dimensional crystals of the IniA protein revealed that this predicted transmembrane protein forms multimeric structures containing a central pore, providing further evidence that iniA is a pump component. Our studies elucidate a potentially unique adaptive pathway in mycobacteria. Drugs designed to inhibit the iniA gene product may shorten the time required to treat tuberculosis and may help prevent the clinical emergence of drug resistance.

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