Limits...
Streptolysin O and its co-toxin NAD-glycohydrolase protect group A Streptococcus from Xenophagic killing.

O'Seaghdha M, Wessels MR - PLoS Pathog. (2013)

Bottom Line: Whereas this process was associated with killing of GAS in HeLa cells, studies in human keratinocytes found SLO production enhanced intracellular survival.We found that SLO expression was associated with prolonged intracellular survival; unexpectedly, expression of the co-toxin NADase was required for this effect.We conclude that SLO stimulates xenophagy in pharyngeal keratinocytes, but the coordinated action of SLO and NADase prevent maturation of GAS-containing autophagosomes, thereby prolonging GAS intracellular survival.

View Article: PubMed Central - PubMed

Affiliation: Division of Infectious Diseases, Boston Children's Hospital and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, United States of America.

ABSTRACT
Group A Streptococcus (Streptococcus pyogenes or GAS) causes pharyngitis, severe invasive infections, and the post-infectious syndromes of glomerulonephritis and rheumatic fever. GAS can be internalized and killed by epithelial cells in vitro, a process that may contribute to local innate defense against pharyngeal infection. Secretion of the pore-forming toxin streptolysin O (SLO) by GAS has been reported to stimulate targeted autophagy (xenophagy) upon internalization of the bacteria by epithelial cells. Whereas this process was associated with killing of GAS in HeLa cells, studies in human keratinocytes found SLO production enhanced intracellular survival. To reconcile these conflicting observations, we now report in-depth investigation of xenophagy in response to GAS infection of human oropharyngeal keratinocytes, the predominant cell type of the pharyngeal epithelium. We found that SLO expression was associated with prolonged intracellular survival; unexpectedly, expression of the co-toxin NADase was required for this effect. Enhanced intracellular survival was lost upon deletion of NADase or inactivation of its enzymatic activity. Shortly after internalization of GAS by keratinocytes, SLO-mediated damage to the bacteria-containing vacuole resulted in exposure to the cytosol, ubiquitination of GAS and/or associated vacuolar membrane remnants, and engulfment of GAS in LC3-positive vacuoles. We also found that production of streptolysin S could mediate targeting of GAS to autophagosomes in the absence of SLO, a process accompanied by galectin 8 binding to damaged GAS-containing endosomes. Maturation of GAS-containing autophagosome-like vacuoles to degradative autolysosomes was prevented by SLO pore-formation and by SLO-mediated translocation of enzymatically active NADase into the keratinocyte cytosol. We conclude that SLO stimulates xenophagy in pharyngeal keratinocytes, but the coordinated action of SLO and NADase prevent maturation of GAS-containing autophagosomes, thereby prolonging GAS intracellular survival. This novel activity of NADase to block autophagic killing of GAS in pharyngeal cells may contribute to pharyngitis treatment failure, relapse, and chronic carriage.

Show MeSH

Related in: MedlinePlus

SLO, SLS, and NADase affect xenophagy and GAS intracellular survival.A. Confocal microscopy demonstrating the association between ubiquitin (green) and intracellular GAS (red) at 30 min post-infection in keratinocytes infected with GAS strain 188, 188SLO-, 188NADase-, or 188SLO(Y255A). Extracellular GAS were stained blue and red for identification as described in Figure 2. Scale bar = 10 µm. The percentage of intracellular GAS that were associated with ubiquitin is indicated for each strain, based on quantification of at least 100 bacteria in three independent experiments. B. Hemolytic activity of culture supernatants of GAS strain 188, 188SLO-, and 188SLO(Y255A). The amino acid substitution Y255A in SLO abrogates the ability of SLO to porate the host cell membrane, demonstrated by the failure of culture supernatants from 188SLO(Y255A) to lyse erythrocytes despite producing wild-type amounts of the variant SLO protein. Inset, corresponding Western blot for SLO in culture supernatants from these strains. C. NADase activity in cell culture supernatants and in the cytosol of keratinocytes infected with GAS strain 771, 771SLO-, 771SLO(Y255A), or 771NADase-. Intracellular NADase activity due to translocation by extracellular GAS was identical between 771 and 771SLO(Y255A), but reduced in 771SLO-. D. The intracellular survival of 188SLO(Y255A) was significantly lower than that of its parental strain, 188, and similar to that of 188SLO-. *, P<0.01. E. Confocal microscopy demonstrating the association between galectin 8 (green) and intracellular GAS (red) in keratinocytes infected for 30 min with GAS strain 188, 188SLO-, or 188 SLO-SLS-. Extracellular GAS (GAS(out)) were stained blue and red for identification as described in Figure 2. Scale bar = 10 µm. The percentage of intracellular GAS that were associated with galectin 8 is indicated for each strain, based on quantification of at least 100 bacteria in three independent experiments. 188SLO-SLS- was never associated with galectin 8 (0%).
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3675196&req=5

ppat-1003394-g004: SLO, SLS, and NADase affect xenophagy and GAS intracellular survival.A. Confocal microscopy demonstrating the association between ubiquitin (green) and intracellular GAS (red) at 30 min post-infection in keratinocytes infected with GAS strain 188, 188SLO-, 188NADase-, or 188SLO(Y255A). Extracellular GAS were stained blue and red for identification as described in Figure 2. Scale bar = 10 µm. The percentage of intracellular GAS that were associated with ubiquitin is indicated for each strain, based on quantification of at least 100 bacteria in three independent experiments. B. Hemolytic activity of culture supernatants of GAS strain 188, 188SLO-, and 188SLO(Y255A). The amino acid substitution Y255A in SLO abrogates the ability of SLO to porate the host cell membrane, demonstrated by the failure of culture supernatants from 188SLO(Y255A) to lyse erythrocytes despite producing wild-type amounts of the variant SLO protein. Inset, corresponding Western blot for SLO in culture supernatants from these strains. C. NADase activity in cell culture supernatants and in the cytosol of keratinocytes infected with GAS strain 771, 771SLO-, 771SLO(Y255A), or 771NADase-. Intracellular NADase activity due to translocation by extracellular GAS was identical between 771 and 771SLO(Y255A), but reduced in 771SLO-. D. The intracellular survival of 188SLO(Y255A) was significantly lower than that of its parental strain, 188, and similar to that of 188SLO-. *, P<0.01. E. Confocal microscopy demonstrating the association between galectin 8 (green) and intracellular GAS (red) in keratinocytes infected for 30 min with GAS strain 188, 188SLO-, or 188 SLO-SLS-. Extracellular GAS (GAS(out)) were stained blue and red for identification as described in Figure 2. Scale bar = 10 µm. The percentage of intracellular GAS that were associated with galectin 8 is indicated for each strain, based on quantification of at least 100 bacteria in three independent experiments. 188SLO-SLS- was never associated with galectin 8 (0%).

Mentions: The finding that NADase plays a major role in GAS intracellular survival raised the possibility that the importance of SLO in GAS survival might be limited to its ability to translocate NADase into the host cell. In order to test whether the pore-forming activity of SLO also contributes to GAS intracellular survival independently of NADase translocation, we took advantage of the observation of Magassa et al. that the pore-forming and NADase-translocating activities of SLO are separable: these authors described an amino acid substitution in SLO, Y255A, that prevented pore-formation and cytolytic activity, but preserved NADase translocation [32]. We introduced this substitution into the chromosomal slo locus in strain 188 to generate 188SLO(Y255A). Measurement of the hemolytic titer and SLO production from the culture supernatant of 188SLO(Y255A) confirmed that the mutant strain had lost the capacity to lyse erythrocytes but still produced a similar amount of SLO protein as the parent strain (Figure 4B).


Streptolysin O and its co-toxin NAD-glycohydrolase protect group A Streptococcus from Xenophagic killing.

O'Seaghdha M, Wessels MR - PLoS Pathog. (2013)

SLO, SLS, and NADase affect xenophagy and GAS intracellular survival.A. Confocal microscopy demonstrating the association between ubiquitin (green) and intracellular GAS (red) at 30 min post-infection in keratinocytes infected with GAS strain 188, 188SLO-, 188NADase-, or 188SLO(Y255A). Extracellular GAS were stained blue and red for identification as described in Figure 2. Scale bar = 10 µm. The percentage of intracellular GAS that were associated with ubiquitin is indicated for each strain, based on quantification of at least 100 bacteria in three independent experiments. B. Hemolytic activity of culture supernatants of GAS strain 188, 188SLO-, and 188SLO(Y255A). The amino acid substitution Y255A in SLO abrogates the ability of SLO to porate the host cell membrane, demonstrated by the failure of culture supernatants from 188SLO(Y255A) to lyse erythrocytes despite producing wild-type amounts of the variant SLO protein. Inset, corresponding Western blot for SLO in culture supernatants from these strains. C. NADase activity in cell culture supernatants and in the cytosol of keratinocytes infected with GAS strain 771, 771SLO-, 771SLO(Y255A), or 771NADase-. Intracellular NADase activity due to translocation by extracellular GAS was identical between 771 and 771SLO(Y255A), but reduced in 771SLO-. D. The intracellular survival of 188SLO(Y255A) was significantly lower than that of its parental strain, 188, and similar to that of 188SLO-. *, P<0.01. E. Confocal microscopy demonstrating the association between galectin 8 (green) and intracellular GAS (red) in keratinocytes infected for 30 min with GAS strain 188, 188SLO-, or 188 SLO-SLS-. Extracellular GAS (GAS(out)) were stained blue and red for identification as described in Figure 2. Scale bar = 10 µm. The percentage of intracellular GAS that were associated with galectin 8 is indicated for each strain, based on quantification of at least 100 bacteria in three independent experiments. 188SLO-SLS- was never associated with galectin 8 (0%).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3675196&req=5

ppat-1003394-g004: SLO, SLS, and NADase affect xenophagy and GAS intracellular survival.A. Confocal microscopy demonstrating the association between ubiquitin (green) and intracellular GAS (red) at 30 min post-infection in keratinocytes infected with GAS strain 188, 188SLO-, 188NADase-, or 188SLO(Y255A). Extracellular GAS were stained blue and red for identification as described in Figure 2. Scale bar = 10 µm. The percentage of intracellular GAS that were associated with ubiquitin is indicated for each strain, based on quantification of at least 100 bacteria in three independent experiments. B. Hemolytic activity of culture supernatants of GAS strain 188, 188SLO-, and 188SLO(Y255A). The amino acid substitution Y255A in SLO abrogates the ability of SLO to porate the host cell membrane, demonstrated by the failure of culture supernatants from 188SLO(Y255A) to lyse erythrocytes despite producing wild-type amounts of the variant SLO protein. Inset, corresponding Western blot for SLO in culture supernatants from these strains. C. NADase activity in cell culture supernatants and in the cytosol of keratinocytes infected with GAS strain 771, 771SLO-, 771SLO(Y255A), or 771NADase-. Intracellular NADase activity due to translocation by extracellular GAS was identical between 771 and 771SLO(Y255A), but reduced in 771SLO-. D. The intracellular survival of 188SLO(Y255A) was significantly lower than that of its parental strain, 188, and similar to that of 188SLO-. *, P<0.01. E. Confocal microscopy demonstrating the association between galectin 8 (green) and intracellular GAS (red) in keratinocytes infected for 30 min with GAS strain 188, 188SLO-, or 188 SLO-SLS-. Extracellular GAS (GAS(out)) were stained blue and red for identification as described in Figure 2. Scale bar = 10 µm. The percentage of intracellular GAS that were associated with galectin 8 is indicated for each strain, based on quantification of at least 100 bacteria in three independent experiments. 188SLO-SLS- was never associated with galectin 8 (0%).
Mentions: The finding that NADase plays a major role in GAS intracellular survival raised the possibility that the importance of SLO in GAS survival might be limited to its ability to translocate NADase into the host cell. In order to test whether the pore-forming activity of SLO also contributes to GAS intracellular survival independently of NADase translocation, we took advantage of the observation of Magassa et al. that the pore-forming and NADase-translocating activities of SLO are separable: these authors described an amino acid substitution in SLO, Y255A, that prevented pore-formation and cytolytic activity, but preserved NADase translocation [32]. We introduced this substitution into the chromosomal slo locus in strain 188 to generate 188SLO(Y255A). Measurement of the hemolytic titer and SLO production from the culture supernatant of 188SLO(Y255A) confirmed that the mutant strain had lost the capacity to lyse erythrocytes but still produced a similar amount of SLO protein as the parent strain (Figure 4B).

Bottom Line: Whereas this process was associated with killing of GAS in HeLa cells, studies in human keratinocytes found SLO production enhanced intracellular survival.We found that SLO expression was associated with prolonged intracellular survival; unexpectedly, expression of the co-toxin NADase was required for this effect.We conclude that SLO stimulates xenophagy in pharyngeal keratinocytes, but the coordinated action of SLO and NADase prevent maturation of GAS-containing autophagosomes, thereby prolonging GAS intracellular survival.

View Article: PubMed Central - PubMed

Affiliation: Division of Infectious Diseases, Boston Children's Hospital and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, United States of America.

ABSTRACT
Group A Streptococcus (Streptococcus pyogenes or GAS) causes pharyngitis, severe invasive infections, and the post-infectious syndromes of glomerulonephritis and rheumatic fever. GAS can be internalized and killed by epithelial cells in vitro, a process that may contribute to local innate defense against pharyngeal infection. Secretion of the pore-forming toxin streptolysin O (SLO) by GAS has been reported to stimulate targeted autophagy (xenophagy) upon internalization of the bacteria by epithelial cells. Whereas this process was associated with killing of GAS in HeLa cells, studies in human keratinocytes found SLO production enhanced intracellular survival. To reconcile these conflicting observations, we now report in-depth investigation of xenophagy in response to GAS infection of human oropharyngeal keratinocytes, the predominant cell type of the pharyngeal epithelium. We found that SLO expression was associated with prolonged intracellular survival; unexpectedly, expression of the co-toxin NADase was required for this effect. Enhanced intracellular survival was lost upon deletion of NADase or inactivation of its enzymatic activity. Shortly after internalization of GAS by keratinocytes, SLO-mediated damage to the bacteria-containing vacuole resulted in exposure to the cytosol, ubiquitination of GAS and/or associated vacuolar membrane remnants, and engulfment of GAS in LC3-positive vacuoles. We also found that production of streptolysin S could mediate targeting of GAS to autophagosomes in the absence of SLO, a process accompanied by galectin 8 binding to damaged GAS-containing endosomes. Maturation of GAS-containing autophagosome-like vacuoles to degradative autolysosomes was prevented by SLO pore-formation and by SLO-mediated translocation of enzymatically active NADase into the keratinocyte cytosol. We conclude that SLO stimulates xenophagy in pharyngeal keratinocytes, but the coordinated action of SLO and NADase prevent maturation of GAS-containing autophagosomes, thereby prolonging GAS intracellular survival. This novel activity of NADase to block autophagic killing of GAS in pharyngeal cells may contribute to pharyngitis treatment failure, relapse, and chronic carriage.

Show MeSH
Related in: MedlinePlus