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Two programmed cell death systems in Escherichia coli: an apoptotic-like death is inhibited by the mazEF-mediated death pathway.

Erental A, Sharon I, Engelberg-Kulka H - PLoS Biol. (2012)

Bottom Line: The mazEF-mediated pathway reduces recA mRNA levels.Based on these results, we offer a molecular model for the maintenance of an altruistic characteristic in cell populations.In our model, the ALD pathway is inhibited by the altruistic EDF-mazEF-mediated death pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Molecular Genetics, Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel.

ABSTRACT
In eukaryotes, the classical form of programmed cell death (PCD) is apoptosis, which has as its specific characteristics DNA fragmentation and membrane depolarization. In Escherichia coli a different PCD system has been reported. It is mediated by the toxin-antitoxin system module mazEF. The E. coli mazEF module is one of the most thoroughly studied toxin-antitoxin systems. mazF encodes a stable toxin, MazF, and mazE encodes a labile antitoxin, MazE, which prevents the lethal effect of MazF. mazEF-mediated cell death is a population phenomenon requiring the quorum-sensing pentapeptide NNWNN designated Extracellular Death Factor (EDF). mazEF is triggered by several stressful conditions, including severe damage to the DNA. Here, using confocal microscopy and FACS analysis, we show that under conditions of severe DNA damage, the triggered mazEF-mediated cell death pathway leads to the inhibition of a second cell death pathway. The latter is an apoptotic-like death (ALD); ALD is mediated by recA and lexA. The mazEF-mediated pathway reduces recA mRNA levels. Based on these results, we offer a molecular model for the maintenance of an altruistic characteristic in cell populations. In our model, the ALD pathway is inhibited by the altruistic EDF-mazEF-mediated death pathway.

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The effect of EDF on membrane depolarization.After the various E. coli strains were grown to OD600 0.6, the cells were treated as follows: (A) MG1655+100 µg/ml NA; (B) MG1655+100 µg/ml NA+50 ng/ml EDF; (C) MG1655+100 µg/ml NA+50 ng/ml iEDF (NNGNN); (E) MC4100relA+ΔclpX+100 µg/ml NA; (F) MC4100relA+ΔclpX+100 µg/ml NA+200 ng/ml EDF; (G) MC4100relA+ΔclpX+100 µg/ml NA+200 ng/ml iEDF. The quantitative effect of NA and NA+EDF on the percent of DiBAC4-stained cells is shown in (D) (data from [A–C]) and (H) (data from [E–G]). Error bars in (D) and (H) indicate standard deviation. Staining, FACS analysis, and determining the fraction of the DiBAC4-stained (membrane depolarized) cells were carried out as described in the legend to Figure 1. All data are representative of three independent experiments. FI, fluorescence intensity.
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pbio-1001281-g005: The effect of EDF on membrane depolarization.After the various E. coli strains were grown to OD600 0.6, the cells were treated as follows: (A) MG1655+100 µg/ml NA; (B) MG1655+100 µg/ml NA+50 ng/ml EDF; (C) MG1655+100 µg/ml NA+50 ng/ml iEDF (NNGNN); (E) MC4100relA+ΔclpX+100 µg/ml NA; (F) MC4100relA+ΔclpX+100 µg/ml NA+200 ng/ml EDF; (G) MC4100relA+ΔclpX+100 µg/ml NA+200 ng/ml iEDF. The quantitative effect of NA and NA+EDF on the percent of DiBAC4-stained cells is shown in (D) (data from [A–C]) and (H) (data from [E–G]). Error bars in (D) and (H) indicate standard deviation. Staining, FACS analysis, and determining the fraction of the DiBAC4-stained (membrane depolarized) cells were carried out as described in the legend to Figure 1. All data are representative of three independent experiments. FI, fluorescence intensity.

Mentions: EDF, which is the quorum-sensing pentapeptide NNWNN, is required for mazEF-mediated cell death [28],[29]. Since we have found that mazEF as well as its downstream mediated pathway prevent the recA-mediated ALD pathway, we asked whether EDF is also involved in this inhibitory effect. To this end we used the E. coli MG1655 strain that we previously showed to be defective in EDF production [29]. Using DiBAC4 staining and flow cytometry, we observed membrane depolarization in strain MG1655 treated with NA (Figure 5A). However, in the presence of synthetic EDF (50 ng/ml), DiBAC4 staining was decreased by about 50% (Figure 5B and 5D), whereas addition of the interfering peptide NNGNN (iEDF) (50 ng/ml) did not affect DiBAC4 staining (Figure 5C and 5D). Similar results were obtained using the ΔclpX derivative of strain MC4100relA+ (Figure 5E–5H) that was previously shown to be defective in EDF production [29]. Thus, the EDF-mazEF-mediated cell death pathway is responsible for the inhibition of the ALD pathway.


Two programmed cell death systems in Escherichia coli: an apoptotic-like death is inhibited by the mazEF-mediated death pathway.

Erental A, Sharon I, Engelberg-Kulka H - PLoS Biol. (2012)

The effect of EDF on membrane depolarization.After the various E. coli strains were grown to OD600 0.6, the cells were treated as follows: (A) MG1655+100 µg/ml NA; (B) MG1655+100 µg/ml NA+50 ng/ml EDF; (C) MG1655+100 µg/ml NA+50 ng/ml iEDF (NNGNN); (E) MC4100relA+ΔclpX+100 µg/ml NA; (F) MC4100relA+ΔclpX+100 µg/ml NA+200 ng/ml EDF; (G) MC4100relA+ΔclpX+100 µg/ml NA+200 ng/ml iEDF. The quantitative effect of NA and NA+EDF on the percent of DiBAC4-stained cells is shown in (D) (data from [A–C]) and (H) (data from [E–G]). Error bars in (D) and (H) indicate standard deviation. Staining, FACS analysis, and determining the fraction of the DiBAC4-stained (membrane depolarized) cells were carried out as described in the legend to Figure 1. All data are representative of three independent experiments. FI, fluorescence intensity.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3295820&req=5

pbio-1001281-g005: The effect of EDF on membrane depolarization.After the various E. coli strains were grown to OD600 0.6, the cells were treated as follows: (A) MG1655+100 µg/ml NA; (B) MG1655+100 µg/ml NA+50 ng/ml EDF; (C) MG1655+100 µg/ml NA+50 ng/ml iEDF (NNGNN); (E) MC4100relA+ΔclpX+100 µg/ml NA; (F) MC4100relA+ΔclpX+100 µg/ml NA+200 ng/ml EDF; (G) MC4100relA+ΔclpX+100 µg/ml NA+200 ng/ml iEDF. The quantitative effect of NA and NA+EDF on the percent of DiBAC4-stained cells is shown in (D) (data from [A–C]) and (H) (data from [E–G]). Error bars in (D) and (H) indicate standard deviation. Staining, FACS analysis, and determining the fraction of the DiBAC4-stained (membrane depolarized) cells were carried out as described in the legend to Figure 1. All data are representative of three independent experiments. FI, fluorescence intensity.
Mentions: EDF, which is the quorum-sensing pentapeptide NNWNN, is required for mazEF-mediated cell death [28],[29]. Since we have found that mazEF as well as its downstream mediated pathway prevent the recA-mediated ALD pathway, we asked whether EDF is also involved in this inhibitory effect. To this end we used the E. coli MG1655 strain that we previously showed to be defective in EDF production [29]. Using DiBAC4 staining and flow cytometry, we observed membrane depolarization in strain MG1655 treated with NA (Figure 5A). However, in the presence of synthetic EDF (50 ng/ml), DiBAC4 staining was decreased by about 50% (Figure 5B and 5D), whereas addition of the interfering peptide NNGNN (iEDF) (50 ng/ml) did not affect DiBAC4 staining (Figure 5C and 5D). Similar results were obtained using the ΔclpX derivative of strain MC4100relA+ (Figure 5E–5H) that was previously shown to be defective in EDF production [29]. Thus, the EDF-mazEF-mediated cell death pathway is responsible for the inhibition of the ALD pathway.

Bottom Line: The mazEF-mediated pathway reduces recA mRNA levels.Based on these results, we offer a molecular model for the maintenance of an altruistic characteristic in cell populations.In our model, the ALD pathway is inhibited by the altruistic EDF-mazEF-mediated death pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Molecular Genetics, Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel.

ABSTRACT
In eukaryotes, the classical form of programmed cell death (PCD) is apoptosis, which has as its specific characteristics DNA fragmentation and membrane depolarization. In Escherichia coli a different PCD system has been reported. It is mediated by the toxin-antitoxin system module mazEF. The E. coli mazEF module is one of the most thoroughly studied toxin-antitoxin systems. mazF encodes a stable toxin, MazF, and mazE encodes a labile antitoxin, MazE, which prevents the lethal effect of MazF. mazEF-mediated cell death is a population phenomenon requiring the quorum-sensing pentapeptide NNWNN designated Extracellular Death Factor (EDF). mazEF is triggered by several stressful conditions, including severe damage to the DNA. Here, using confocal microscopy and FACS analysis, we show that under conditions of severe DNA damage, the triggered mazEF-mediated cell death pathway leads to the inhibition of a second cell death pathway. The latter is an apoptotic-like death (ALD); ALD is mediated by recA and lexA. The mazEF-mediated pathway reduces recA mRNA levels. Based on these results, we offer a molecular model for the maintenance of an altruistic characteristic in cell populations. In our model, the ALD pathway is inhibited by the altruistic EDF-mazEF-mediated death pathway.

Show MeSH
Related in: MedlinePlus