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Nicola Casali

Publications and source records attributed to Nicola Casali.

7 recordsLinked to original sources
PubMed2007

Accelerated immunopathological response of mice infected with Mycobacterium tuberculosis disrupted in the mce1 operon negative transcriptional regulator.

Mycobacterium tuberculosis causes a variety of clinical outcomes determined by host as well as bacterial factors. M. tuberculosis disrupted in the mce1 operon causes increased mortality in immunocompetent mice. This operon is negatively regulated by mce1R (Rv0165c). We studied the role of mce1R in infection outcome in mice. At 5 x 10(4) tail vein infectious dose, the median survival time (MST) of mice infected with the mce1R mutant M. tuberculosis H37Rv was 293 days, while mice infected with the wild-type H37Rv survived more than 350 days (P < 0.0001). At a higher dose (5 x 10(6)), the MST of mutant-infected mice was 32 days, compared with 127 days for wild type-infected mice (P < 0.0001). With either tail vein or aerosol infection, mutant-infected mice developed larger granulomatous lesions in their lungs than mice infected with the wild type. Mutant-infected mice were unable to control the bacterial burden in the first 4 weeks of infection, but even after achieving control later, these mice succumbed to granulomatous pneumonia. These observations suggest that the early deregulated expression of the mce1 operon products determines later granulomatous tissue response. mce1 operon may homeostatically regulate the cell wall architecture in vivo that elicits a steady-state granuloma tissue response permitting M. tuberculosis to establish a long-term infection.

Animals↗
PubMed2006

Regulation of the Mycobacterium tuberculosis mce1 operon.

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 Deltamce1R 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 Deltamce1R. 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.

Amino Acid Sequence↗
PubMed2003

Hypervirulent mutant of Mycobacterium tuberculosis resulting from disruption of the mce1 operon.

An estimated one-third of the world's population is latently infected with Mycobacterium tuberculosis, the etiologic agent of tuberculosis. Here, we demonstrate that, unlike wild-type M. tuberculosis, a strain of M. tuberculosis disrupted in the mce1 operon was unable to enter a stable persistent state of infection in mouse lungs. Instead, the mutant continued to replicate and killed the mice more rapidly than did the wild-type strain. Histological examination of mouse lungs infected with the mutant strain revealed diffusely organized granulomas with aberrant inflammatory cell migration. Murine macrophages infected ex vivo with the mutant strain were reduced in their ability to produce tumor necrosis factor alpha, IL-6, monocyte chemoattractant protein 1, and nitric oxide (NO), but not IL-4. The mce1 mutant strain complemented with the mce1 genes stimulated tumor necrosis factor alpha and NO production by murine macrophages at levels stimulated by the wild-type strain. These observations indicate that the mce1 operon mutant is unable to stimulate T helper 1-type immunity in mice. The hypervirulence of the mutant strain may have resulted from its inability to stimulate a proinflammatory response that would otherwise induce organized granuloma formation and control the infection without killing the organism. The mce1 operon of M. tuberculosis may be involved in modulating the host inflammatory response in such a way that the bacterium can enter a persistent state without being eliminated or causing disease in the host.

Animals↗
PubMed2003

Deletion of two-component regulatory systems increases the virulence of Mycobacterium tuberculosis.

Two-component regulatory signal transduction systems are widely distributed among bacteria and enable the organisms to make coordinated changes in gene expression in response to a variety of environmental stimuli. The genome sequence of Mycobacterium tuberculosis contains 11 complete two-component systems, four isolated homologous regulators, and three isolated homologous sensors. We have constructed defined mutations in six of these genes and measured virulence in a SCID mouse model. Mice infected with four of the mutants (deletions of devR, tcrXY, trcS, and kdpDE) died more rapidly than those infected with wild-type bacteria. The other two mutants (narL and Rv3220c) showed no change compared to the wild-type H37Rv strain. The most hypervirulent mutant (devRdelta) also grew more rapidly in the acute stage of infection in immunocompetent mice and in gamma interferon-activated macrophages. These results define a novel class of genes in this pathogen whose presence slows down its multiplication in vivo or increases its susceptibility to host killing mechanisms. Thus, M. tuberculosis actively maintains a balance between its own survival and that of the host.

Animals↗
PubMed2002

Invasion activity of a Mycobacterium tuberculosis peptide presented by the Escherichia coli AIDA autotransporter.

The mce1A gene of Mycobacterium tuberculosis was initially identified by its ability to promote uptake of Escherichia coli into HeLa cells. It was subsequently shown that this activity was confined to a 58-amino-acid region of the protein. A 72-amino-acid fragment (InvX) incorporating this active peptide was expressed in E. coli as a fusion to the AIDA (adhesin involved in diffuse adherence) autotransporter translocator, and its stable expression on the surface of the bacterium was demonstrated. Recombinant E. coli expressing InvX-AIDA showed extensive association with HeLa cells, and InvX was shown to be sufficient for internalization. Uptake was found to be both microtubule and microfilament dependent and required the Rho family of GTPases. Thus, the E. coli AIDA system facilitated both the qualitative and quantitative analysis of the functional domain of a heterologous protein.

Adhesins, Escherichia coli↗
PubMed1998

Characterization of a haemolysin from Mycobacterium tuberculosis with homology to a virulence factor of Serpulina hyodysenteriae.

Scrutiny of sequence data from the Mycobacterium leprae genome sequencing project identified the presence of a gene encoding a 268-amino-acid polypeptide which is highly similar to a pore-forming haemolysin/cytotoxin virulence determinant, TlyA, from the swine pathogen Serpulina hyodysenteriae. Using degenerate oligonucleotide primers based on the TlyA sequences, the Mycobacterium tuberculosis homologue was amplified and this product was used to obtain the clone and sequence a 2.5 kb fragment containing the whole M. tuberculosis tlyA gene. tlyA encodes a 267-amino-acid protein with a predicted molecular mass of 28 kDa. TlyA homologues were identified by PCR in M. leprae, Mycobacterium avium and Mycobacterium bovis BCG, but appeared absent in Mycobacterium smegmatis, Mycobacterium vaccae, Mycobacterium kansasii, Mycobacterium chelonae and Mycobacterium phlei. The M. tuberculosis gene appeared to be the first gene in an operon containing at least two other genes. Introduction of the M. tuberculosis tlyA gene into M. smegmatis using a mycobacterial shuttle expression plasmid converted non-haemolytic cells into those exhibiting significant haemolytic activity. Similarly, inducible haemolytic activity was observed in sonicated bacteria when tlyA was expressed as a His6-tagged fusion protein in Escherichia coli. tlyA mRNA was detected in both M. tuberculosis and M. bovis BCG using RT-PCR, confirming that this gene is expressed in organisms cultured in vitro.

Amino Acid Sequence↗