Anaerobic regulation of Actinobacillus actinomycetemcomitans leukotoxin transcription is ArcA/FnrA-independent and requires a novel promoter element

Kolodrubetz, David J; Phillips, Linda; Jacobs, Chris; Burgum, Alex; Kraig, Ellen

doi:10.1016/j.resmic.2003.09.001

Cited by 19 publications

(27 citation statements)

References 36 publications

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“…Previous studies of leukotoxin promoter mutations from two labs reached somewhat different conclusions about the regulatory elements involved in controlling transcription of the leukotoxin operon (24,48). This disparity could be due to the use, in both cases, of reporter genes on plasmids, which might not accurately reflect the chromosomal environment of the leukotoxin operon.…”

Section: Resultsmentioning

confidence: 98%

“…Instead, either a third unidentified transcription factor or a DNA topology change must be involved in the aerobic/anaerobic modulation of leukotoxin transcription. The former possibility seems unlikely since we have demonstrated that the classical oxygen-regulatory proteins FNR and ArcA/B do not regulate ltxA transcription (24) and since all of the BamHI mutants are still oxygen regulated; if a third transcription factor were the oxygen response regulator, we would have expected at least one of the base substitution mutants to have mutated the binding site for a putative third transcription factor resulting in nonregulated ltxA transcription. This was not observed (Fig.…”

Section: Discussionmentioning

confidence: 95%

“…DNAs from plasmids pDK759 to pDK766, which contain BamHI linker mutations at sequential positions in the leukotoxin promoter (24), were used as DNA templates in PCRs with primers LKT467 and LKT768. Each of the 205-bp PCR products, which extend from Ϫ163 to ϩ44 in the leukotoxin promoter region, was cloned into the SacI/PstI sites of pDK810.…”

Section: Methodsmentioning

confidence: 99%

“…We, along with others, have shown that leukotoxin levels increase when A. actinomycetemcomitans is grown anaerobically (17,22,23). Interestingly, leukotoxin synthesis in A. actinomycetemcomitans mutants in fnr and arcA is still induced anaerobically (24). This indicates that leukotoxin expression is not modulated by FNR or ArcA/ArcB, which control the synthesis of most of the oxygen-regulated genes in Escherichia coli and other Gram-negative bacteria (25,26,27,28,29).…”

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confidence: 99%

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Mlc Is a Transcriptional Activator with a Key Role in Integrating Cyclic AMP Receptor Protein and Integration Host Factor Regulation of Leukotoxin RNA Synthesis in Aggregatibacter actinomycetemcomitans

et al. 2013

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Aggregatibacter actinomycetemcomitans, a periodontal pathogen, synthesizes leukotoxin (LtxA), a protein that helps the bacterium evade the host immune response. Transcription of the ltxA operon is induced during anaerobic growth. The cyclic AMP (cAMP) receptor protein (CRP) indirectly increases ltxA expression, but the intermediary regulator is unknown. Integration host factor (IHF) binds to and represses the leukotoxin promoter, but neither CRP nor IHF is responsible for the anaerobic induction of ltxA RNA synthesis. Thus, we have undertaken studies to identify other regulators of leukotoxin transcription and to demonstrate how these proteins work together to modulate leukotoxin synthesis. First, analyses of ltxA RNA expression from defined leukotoxin promoter mutations in the chromosome identify positions ؊69 to ؊35 as the key control region and indicate that an activator protein modulates leukotoxin transcription. We show that Mlc, which is a repressor in Escherichia coli, functions as a direct transcriptional activator in A. actinomycetemcomitans; an mlc deletion mutant reduces leukotoxin RNA synthesis, and recombinant Mlc protein binds specifically at the ؊68 to ؊40 region of the leukotoxin promoter. Furthermore, we show that CRP activates ltxA expression indirectly by increasing the levels of Mlc. Analyses of ⌬mlc, ⌬ihf, and ⌬ihf ⌬mlc strains demonstrate that Mlc can increase RNA polymerase (RNAP) activity directly and that IHF represses ltxA RNA synthesis mainly by blocking Mlc binding. Finally, a ⌬ihf ⌬mlc mutant still induces ltxA during anaerobic growth, indicating that there are additional factors involved in leukotoxin transcriptional regulation. A model for the coordinated regulation of leukotoxin transcription is presented.

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Section: Resultsmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 95%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Mlc Is a Transcriptional Activator with a Key Role in Integrating Cyclic AMP Receptor Protein and Integration Host Factor Regulation of Leukotoxin RNA Synthesis in Aggregatibacter actinomycetemcomitans

et al. 2013

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“…The role of O 2 in the expression of LKT was studied by Uhlich et al and it was demonstrated that FnrP, homologous to Fnr, the global transcriptional regulator of anaerobic respiration in Escherichia coli, suppresses and increases LKT transcription respectively under aerobic and anaerobic conditions [171,172]. Furthermore, similar results of anaerobic regulation of toxin production have been obtained with Actinobacillus actinomycetemcomitans [97]. At first sight, an increase in toxin production under anaerobic conditions seems astonishing for a respiratory pathogen.…”

Section: Gene Organisation and Transcriptional Regulationmentioning

confidence: 87%

How Mannheimia haemolytica defeats host defence through a kiss of death mechanism

2005

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-Mannheimia haemolytica induced pneumonias are only observed in goats, sheep and cattle. The bacterium produces several virulence factors,whose principal ones are lipopolysaccharide and leukotoxin. The latter is cytotoxic only for ruminant leukocytes, a phenomenon that is correlated with its ability to bind and interact with the ruminant β2-integrin Lymphocyte Function-associated Antigen 1. This paper globally reviews all the information available on host-pathogen interactions underlying respiratory mannheimiosis (formerly pasteurellosis), from the stable and the Petri dish to the biochemical cascade of events triggered by the leukotoxin inside ruminant leukocytes. One conclusion can be made: the most widespread cattle respiratory disease with the most important impact on beef production worldwide, is probably due to a tiny ruminant-specific focal variation in the CD18-and/or CD11a-expressing genes.

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The cyclic-AMP receptor protein (CRP) regulon in Aggregatibacter actinomycetemcomitans includes leukotoxin

Feuerbacher

Burgum

Kolodrubetz

2011

Microbial Pathogenesis

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The cyclic-AMP receptor protein (CRP) acts as a global regulatory protein among bacteria. Here, the CRP regulon has been defined in Aggregatibacter actinomycetemcomitans using microarray analysis of A. actinomycetemcomitans strain JP2 wild type cells compared to an isogenic crp deletion mutant. Genes whose expression levels changed at least 2-fold with p ≤ 0.05 were considered significant. Of the 300 genes identified as being CRP-regulated, 139 were CRP-activated, including leukotoxin, with the remaining being CRP-repressed. The 300 genes represent 14.2% of ORFs probed which is significantly higher than what has been reported for CRP regulons in other bacteria. If the CRP-regulated genes are put into 17 functional classes, all 17 categories had at least 1 CRP-regulated gene. Several functional categories, mainly transport and binding proteins and energy metabolism proteins, were disproportionately represented in the CRP-regulated subset of genes relative to their overall representation in the genome. This is similar to the patterns seen in other bacteria. Finally, quantitative RT-PCR was used to show that the leukotoxin RNA levels were repressed 16-fold in the CRP mutant indicating that CRP activates leukotoxin transcription. However, this regulation appears to be acting through another regulatory protein since the leukotoxin promoter, unlike ~129 other promoters of CRP-regulated genes, does not have a match to the consensus CRP binding site. Several candidate genes for this intermediary transcription factor have been identified in the CRP-regulon.

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Anaerobic regulation of Actinobacillus actinomycetemcomitans leukotoxin transcription is ArcA/FnrA-independent and requires a novel promoter element

Cited by 19 publications

References 36 publications

Mlc Is a Transcriptional Activator with a Key Role in Integrating Cyclic AMP Receptor Protein and Integration Host Factor Regulation of Leukotoxin RNA Synthesis in Aggregatibacter actinomycetemcomitans

Mlc Is a Transcriptional Activator with a Key Role in Integrating Cyclic AMP Receptor Protein and Integration Host Factor Regulation of Leukotoxin RNA Synthesis in Aggregatibacter actinomycetemcomitans

How Mannheimia haemolytica defeats host defence through a kiss of death mechanism

The cyclic-AMP receptor protein (CRP) regulon in Aggregatibacter actinomycetemcomitans includes leukotoxin

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