Regulation of the Mycobacterium tuberculosis mce1 Operon

Abstract

In the murine model of infection, a Mycobacterium tuberculosis mce1 operon mutant elicits an aberrant granulomatous response, resulting in uncontrolled replication and failure to enter a persistent state. In this study, we demonstrate that the mce1 genes can be transcribed as a 13-gene polycistronic message encompassing Rv0166 to Rv0178. Quantitative reverse transcriptase PCR and immunoblot analyses revealed that the mce1 genes and proteins are expressed during in vitro growth but are significantly down-regulated in intracellular bacilli isolated from murine macrophages. A homologue of the FadR subfamily of GntR transcriptional regulators, Rv0165c (designated Mce1R), lies upstream and is divergently transcribed from the operon. To investigate whether this gene plays a role in regulation of mce1 expression, we created an M. tuberculosis mce1R deletion mutant. There was no difference in expression of mce1 operon genes in ⌬mce1R compared to expression in the wild type during logarithmic growth in vitro. However, in bacilli isolated from murine macrophages, expression of mce1 genes was significantly higher in ⌬mce1R. In addition, overexpression of mce1R resulted in repression of the mce1 genes. These data demonstrate that Mce1R is a negative regulator that acts intracellularly to repress expression of the mce1 operon. We propose that Mce1R facilitates balanced temporal expression of the mce1 products required for organized granuloma formation, which is both protective to the host and necessary for the persistence of M. tuberculosis.Tuberculosis causes approximately two million deaths annually, and it has been estimated that two billion people are currently infected with the causative agent, Mycobacterium tuberculosis (10). Infection is initiated by inhalation of the bacilli into the lung, where they are ultimately ingested by alveolar macrophages. In the typical immunocompetent host, the cellmediated immune response results in the formation of a granuloma, the pathological hallmark of tuberculosis. In the majority of cases, this response is sufficient to contain the infection and prevent disease; however, viable bacilli remain within granulomas and can cause active disease years later.In the past decade, dramatic advances facilitating the molecular biological manipulation of mycobacteria have increased our knowledge of the mechanisms that tubercle bacilli use to survive within macrophages (33); however, little remains known about the bacterial determinants of infection outcome. Previous studies suggest that the M. tuberculosis mce1 operon is important in establishing a persistent infection in mice (32). It was shown that M. tuberculosis mce1 mutants failed to induce a characteristic proinflammatory response in ex vivo-infected murine macrophages. This phenotype was manifested in vivo by aberrant inflammatory cell migration and poor granuloma formation, leading to uncontrolled bacterial growth and rapid death of mutant-infected mice.The six Mce1 proteins (Mce1A to Mce1F) contain putative signal sequences indicative o...

Mce3R, a TetR-type transcriptional repressor, controls the expression of a regulon involved in lipid metabolism in Mycobacterium tuberculosis

“…KstR, a TetR-type regulator, has been previously shown to control the expression of the mce4 operon and that of other genes involved in fatty acid metabolism (Kendall et al, 2007). Moreover, the first gene in the mce1 operon is fadE5 (Casali et al, 2006). Therefore, all of these findings are clearly consistent with the proposed role of Mce proteins as components of ABC-like transport systems whose substrates may be lipids.…”

The pleiotropic transcriptional response of Mycobacterium tuberculosis to vitamin C is robust and overlaps with the bacterial response to multiple intracellular stresses

“…The 13-gene mce1 operon, Rv0166 to Rv0178, was downregulated. This operon is downregulated under multiple stresses, including hypoxia, nutrient starvation and detergent exposure (Manganelli et al, 2001;Sherman et al, 2001;Betts et al, 2002), and also in infected bone marrow-derived murine macrophages and RAW murine macrophages (Casali et al, 2006), suggesting that vit C may in some way mimic the intracellular environment.…”

Mycobacterium tuberculosis Mce1 protein complex initiates rapid induction of transcription of genes involved in substrate trafficking

“…In a previous study, it was shown that mRNA synthesis of mce1A was repressed by 4 h post H37Rv infection. 16 The decreased transcription of Abca1 by 4 and 10 h in comparison with 60 min post H37Rv infection support a role for the Mce1 protein complex on transcription of Abca1. However, a steady increase in the transcription of the Abca1 gene was also observed from the 30 min time point to 10 h post D-mce1 H37Rv, suggesting a time-dependent role for the Mce1 protein complex on the Abca1 gene transcription (Table 1b).…”