The Role Of Mycobacterium Tuberculosis Regions Of Difference (RD6) Gene Rv1515c In Intracellular Survival And Underlying Molecular Mechanisms

Tuberculosis (TB), caused by pathogenic Mycobacterium tuberculosis (M. tuberculosis), remains an immense global health concern. According to Global Tuberculosis Report 2014(World Health Organization Tuberculosis Dataand Statistics, 2014), there are 9.0 million new cases and 1.5 million people died from TB, which contains 360,000 deaths are HIV-positive. Despite of the vaccines and anti-tuberculosis drugs, the emergence of multi-drug-resistant (MDR) strains and co-infection with HIV lead to the situation of TB treatment is still more serious.The process that intracellular survival of M. tuberculosis depends on an series of specific virulence factors or operon to colonize, replicate and persist in the host. Bioinformatics analysis identified 16 RDs (Mtb-specific regions of difference, RD1 to RD16) that were deleted/absent in some or all strains ofM bovis and/or BCG. RDs have emerged as important for typing systems for epidemiological and evolutionary studies of M. tuberculosis. As far as we known, ESAT-6 and CFP10, which the major virulence factor of M.tuberculosis H37Rv and induced strong responses in TB patients, was located at RD1 containing nine genes that is critical for the ESX-1 secretion system. The specific RDs were immunodominant and could be useful for diagnostic applications using antibody and cell-mediated immunity-based assays.Mtb region of difference 6 (RD6) contains 11 genes:Rv1506c-Rv1516c, which including three proteins associated with glycometabolism (GmdA, EpiA, Rv1516c) and two cytomembrane proteins (Rv1508c and Rv1510). RD6 gene rv1515c encodes a conserved hypothetical protein. There is no idea about the functional of rv1515c for Mtb. To research it, we heterologously express rv1515c in the non-pathogenic fast-growing M. smegmatis strain to construct the recombinant MS_Rv1515c.In this study, we firstly addressed the role of RD6 gene rv1515c involved in the pathogen-host interaction. Our data demonstrated that rv1515c gene can enhance the viability of M. smegmatis in vitro. rv1515c gene altered the phenotypic of M. smegmatis including sliding motility, morphology and bio film formation, which might be associated with the synthesis of fatty acid (FA). MS_Rv1515c showed growth advantage over the control under different stresses such as H2O2, hydrazine, SDS and low pH. To gain further insight as to whether Rvl515c modulates the gene expression profile of macrophages including RAW264.7 and THP-1 cell, we infected macrophages by the MS_Rv1515c as well as the control strains, followed by real-time PCR (RT-PCR) assay for the mRNA expression level of cytokines. The data showed that the mRNA expression of IL-6 and IL-10 in RAW264.7 cells were down-regulated by stimulation with the MS_Rv1515c compared to the control strains (p<0.05). In addition to IL-6 and IL-10, we got the same results that the mRNA expression of TNF-a and caspase-1 were significantly down-regulated in THP-1 cells.Taken together, our results indicated that Rv1515c protein is an immune microenvironment modulator associated with M. tuberculosis pathogenesis. We speculate that inhibitors of Rv1515c might be promising novel antibiotics or leads for new antibiotics against tuberculosis.