Biology subjects

Ajay Kumar, R.

Publications and source records attributed to Ajay Kumar, R..

3 recordsLinked to original sources

bioRxiv2022

Mycobacterium tuberculosis transcriptional regulator Rv1019 is upregulated in hypoxia and negatively regulates Rv3230c-Rv3229c operon encoding enzymes in the oleic acid biosynthetic pathway

The main obstacle in eradicating tuberculosis is the ability of Mycobacterium tuberculosis to remain dormant in the host, and then to get reactivated even years later under immuno-compromised conditions. Transcriptional regulation in intracellular pathogens plays an important role in adapting to the challenging environment inside the host cells. Previously, we demonstrated that Rv1019, a putative transcriptional regulator of M. tuberculosis H37Rv, is an autorepressor. We showed that, Rv1019 is cotranscribed with Rv1020 (mfd) and Rv1021 (mazG) encoding DNA repair proteins and negatively regulates the expression of these genes. In the present study, we show that Rv1019 also regulates the expression of the genes Rv3230c and Rv3229c (desA3) which form a two-gene operon in M. tuberculosis. Constitutive expression of Rv1019 in M. tuberculosis significantly downregulated the expression of these genes. Employing Waynes hypoxia-induced dormancy model of M. tuberculosis, we show that Rv1019 is upregulated (3-fold) under hypoxia. Finally, by reporter assay, using M. smegmatis as a model, we validate that Rv1019 is recruited to the promoter of Rv3230c-Rv3229c during hypoxia and negatively regulates this operon which is involved in the biosynthesis of oleic acid.

molecular biology↗

bioRxiv2021

Chrysomycin A inhibits the topoisomerase I of Mycobacterium tuberculosis.

Novel anti-tuberculosis drugs are essential to manage drug resistant tuberculosis, caused by the notorious pathogen Mycobacterium tuberculosis. We recently reported the antimycobacterial activity of chrysomycin A in vitro and in infected macrophages. In this study, we report that the molecule inhibits the growth of drug resistant clinical strains of Mycobacterium tuberculosis and acts in synergy with anti-TB drugs such as ethambutol, ciprofloxacin and novobiocin. In pursuit of its mechanism of action, it was found that chrysomycin A renders bactericidal activity by interacting with DNA at specific sequences and by inhibiting topoisomerase I activity of Mycobacterium tuberculosis. It also exhibits weak inhibition of gyrase enzyme of the pathogen.

biochemistry↗

bioRxiv2020

Transcription repressor protein ZBTB25 interacts with HDAC1 in macrophages infected with Mycobacterium tuberculosis, and its inhibition leads to autophagy and killing of the intracellular pathogen

Downregulation of host gene expression is one of the key strategies adopted by intracellular pathogens such as Mycobacterium tuberculosis (MTB) for their survival and subsequent pathogenesis. In a previous study, we have shown that HDAC1 levels go up in macrophages infected with MTB and it hypoacetylates histone H3 at the promoter of IL-12B gene leading to its downregulation. Here we show that after infection with MTB, the levels of the phosphorylated form of HDAC1 increase significantly in macrophages. Employing immunoprecipitation and LC-MS/MS, we found transcriptional repressor protein ZBTB25 associates with HDAC1 silencing complex along with transcriptional corepressor Sin3a. By chromatin immunoprecipitation and PCR analyses, we found that phosphorylated HDAC1, Sin3a, and ZBTB25 are recruited to the promoter of IL-12B to downregulate its expression in infected macrophages. Knocking down of ZBTB25 enhanced release of IL-12p40 from infected macrophages. Interestingly, the treatment of infected macrophages with CI994 (inhibitor of HDAC1) or dithiopyridine (inhibitor of ZBTB25) promoted the colocalization of LC3 (microtubule-associated protein 1A/1B-light chain 3, a marker for autophagy) and MTB in autophagosomes. Induction of autophagy resulted in the killing of intracellular MTB. Enhanced phosphorylation of JAK2 and STAT4 was observed in macrophages upon CI994 and dithiopyridine treatment, and inhibition of JAK2/STAT4 negated the killing of intracellular mycobacteria suggesting a possible role of these proteins in the autophagy-mediated killing of intracellular MTB.

microbiology↗