AUTHOR=Rani Anshu , Alam Anwar , Ahmad Faraz , P. Manjunath , Saurabh Abhinav , Zarin Sheeba , Mitra Dipendra Kumar , Hasnain Seyed E. , Ehtesham Nasreen Z. 

TITLE=Mycobacterium tuberculosis Methyltransferase Rv1515c Can Suppress Host Defense Mechanisms by Modulating Immune Functions Utilizing a Multipronged Mechanism

JOURNAL=Frontiers in Molecular Biosciences

VOLUME=9

YEAR=2022

URL=https://www.frontiersin.org/journals/molecular-biosciences/articles/10.3389/fmolb.2022.906387

DOI=10.3389/fmolb.2022.906387

ISSN=2296-889X

ABSTRACT=<p><italic>Mycobacterium tuberculosis</italic> (<italic>M. tb</italic>) gene <italic>Rv1515c</italic> encodes a conserved hypothetical protein exclusively present within organisms of MTB complex and absent in non-pathogenic mycobacteria. <italic>In silico</italic> analysis revealed that Rv1515c contain S-adenosylmethionine binding site and methyltransferase domain. The DNA binding and DNA methyltransferase activity of Rv1515c was confirmed <italic>in vitro</italic>. Knock-in of Rv1515c in a model mycobacteria <italic>M. smegmatis</italic> (<italic>M. s</italic>_Rv1515c) resulted in remarkable physiological and morphological changes and conferred the recombinant strain with an ability to adapt to various stress conditions, including resistance to TB drugs. <italic>M. s</italic>_Rv1515c was phagocytosed at a greater rate and displayed extended intra-macrophage survival <italic>in vitro</italic>. Recombinant <italic>M. s</italic>_Rv1515c contributed to enhanced virulence by suppressing the host defense mechanisms including RNS and ROS production, and apoptotic clearance. <italic>M. s</italic>_Rv1515c, while suppressing the phagolysosomal maturation, modulated pro-inflammatory cytokine production and also inhibited antigen presentation by downregulating the expression of MHC-I/MHC-II and co-stimulatory signals CD80 and CD86. Mice infected with <italic>M. s</italic>_Rv1515c produced more Treg cells than vector control (<italic>M. s</italic>_Vc) and exhibited reduced effector T cell responses, along-with reduced expression of macrophage activation markers in the chronic phase of infection. <italic>M. s</italic>_Rv1515c was able to survive in the major organs of mice up to 7 weeks post-infection. These results indicate a crucial role of Rv1515c in <italic>M. tb</italic> pathogenesis.</p>