AUTHOR=Gupta Shailesh Kumar , Angara Rajendra Kumar , Yousuf Suhail , Reddy Chilakala Gangi , Ranjan Akash 

TITLE=Ectopic Expression of Rv0023 Mediates Isoniazid/Ethionamide Tolerance via Altering NADH/NAD+ Levels in Mycobacterium smegmatis

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.00003

DOI=10.3389/fmicb.2020.00003

ISSN=1664-302X

ABSTRACT=<p>Tuberculosis (TB) caused by <italic>Mycobacterium tuberculosis</italic> (<italic>Mtb</italic>) accounts for nearly 1.2 million deaths per annum worldwide. Due to the emergence of multidrug-resistant (MDR) <italic>Mtb</italic> strains, TB, a curable and avertable disease, remains one of the leading causes of morbidity and mortality. Isoniazid (INH) is a first-line anti-TB drug while ethionamide (ETH) is used as a second-line anti-TB drug. INH and ETH resistance develop through a network of genes involved in various biosynthetic pathways. In this study, we identified Rv0023, an <italic>Mtb</italic> protein belonging to the xenobiotic response element (XRE) family of transcription regulators, which has a role in generating higher tolerance toward INH and ETH in <italic>Mycobacterium smegmatis</italic> (<italic>Msmeg</italic>). Overexpression of Rv0023 in <italic>Msmeg</italic> leads to the development of INH- and ETH-tolerant strains. The strains expressing Rv0023 have a higher ratio of NADH/NAD<sup>+</sup>, and this physiological event is known to play a crucial role in the development of INH/ETH co-resistance in <italic>Msmeg</italic>. Gene expression analysis of some target genes revealed reduction in the expression of the <italic>ndh</italic> gene, but no direct interaction was observed between Rv0023 and the <italic>ndh</italic> promoter region. <italic>Rv0023</italic> is divergently expressed to <italic>Rv0022c</italic> (<italic>whiB5</italic>) and we observed a direct interaction between the recombinant Rv0023 protein with the upstream region of <italic>Rv0022c</italic>, confirmed using reporter constructs of <italic>Msmeg</italic>. However, we found no indication that this interaction might play a role in the development of INH/ETH drug tolerance.</p>