Cd(II)-binding transcriptional regulator interacts with isoniazid and regulates drug susceptibility in mycobacteria

It is urgent to understand the regulatory mechanism of drug resistance in widespread bacterial pathogens. In Mycobacterium tuberculosis, several transcriptional regulators have been found to play essential roles in regulating its drug resistance. In this study, we found that an ArsR family transcription regulator encoded by Rv2642 (CdiR) responds to isoniazid (INH), a widely used anti-tuberculosis (TB) drug. CdiR negatively regulates self and adjacent genes, including arsC (arsenic-transport integral membrane protein ArsC). CdiR directly interacts with INH and Cd(II). The binding of INH and Cd(II) both reduce its DNA-binding activity. Disrupting cdiR increased the drug susceptibility to INH, whereas overexpressing cdiR decreased the susceptibility. Strikingly, overexpressing arsC increased the drug susceptibility as well as cdiR. Additionally, both changes in cdiR and arsC expression caused sensitivity to other drugs such as rifamycin and ethambutol, where the minimal inhibitory concentrations in the cdiR deletion strain were equal to those of the arsC-overexpressing strain, suggesting that the function of CdiR in regulating drug resistance primarily depends on arsC. Furthermore, we found that Cd(II) enhances bacterial resistance to INH in a CdiR-dependent manner. As a conclusion, CdiR has a critical role in directing the interplay between Cd(II) metal ions and drug susceptibility in mycobacteria.