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The Candida albicans Histone Acetyltransferase Hat1 Regulates Stress Resistance and Virulence via Distinct Chromatin Assembly Pathways.

Tscherner M, Zwolanek F, Je S, Sedlazeck FJ, Petryshyn A, Frohner IE, Mavrianos J, Chauhan N, von Haeseler A, Kuchler K - PLoS Pathog. (2015)

Bottom Line: Hydrogen peroxide resistance in cells lacking Hat1 results from higher induction rates of oxidative stress gene expression, accompanied by reduced histone density as well as subsequent increased RNA polymerase recruitment.Remarkably, the oxidative stress phenotype of hat1Δ/Δ cells is a species-specific trait only found in C. albicans and members of the CTG clade.The reduced azole susceptibility appears to be conserved in a wider range of fungi.

View Article: PubMed Central - PubMed

Affiliation: Department for Medical Biochemistry, Medical University of Vienna, Max F. Perutz Laboratories, Campus Vienna Biocenter, Vienna, Austria.

ABSTRACT
Human fungal pathogens like Candida albicans respond to host immune surveillance by rapidly adapting their transcriptional programs. Chromatin assembly factors are involved in the regulation of stress genes by modulating the histone density at these loci. Here, we report a novel role for the chromatin assembly-associated histone acetyltransferase complex NuB4 in regulating oxidative stress resistance, antifungal drug tolerance and virulence in C. albicans. Strikingly, depletion of the NuB4 catalytic subunit, the histone acetyltransferase Hat1, markedly increases resistance to oxidative stress and tolerance to azole antifungals. Hydrogen peroxide resistance in cells lacking Hat1 results from higher induction rates of oxidative stress gene expression, accompanied by reduced histone density as well as subsequent increased RNA polymerase recruitment. Furthermore, hat1Δ/Δ cells, despite showing growth defects in vitro, display reduced susceptibility to reactive oxygen-mediated killing by innate immune cells. Thus, clearance from infected mice is delayed although cells lacking Hat1 are severely compromised in killing the host. Interestingly, increased oxidative stress resistance and azole tolerance are phenocopied by the loss of histone chaperone complexes CAF-1 and HIR, respectively, suggesting a central role for NuB4 in the delivery of histones destined for chromatin assembly via distinct pathways. Remarkably, the oxidative stress phenotype of hat1Δ/Δ cells is a species-specific trait only found in C. albicans and members of the CTG clade. The reduced azole susceptibility appears to be conserved in a wider range of fungi. Thus, our work demonstrates how highly conserved chromatin assembly pathways can acquire new functions in pathogenic fungi during coevolution with the host.

No MeSH data available.


Related in: MedlinePlus

Cells lacking Hat1 show reduced virulence but persist in mouse kidneys.(A) Reduced growth rate of the hat1Δ/Δ strain was determined by measuring the OD600 of cells growing in YPD at 30°C. (B) Cells lacking Hat1 are not cleared efficiently from kidneys. At the indicated time points, fungal burdens in kidneys of mice infected with C. albicans strains were determined and expressed as CFUs per gram kidney. Groups of 5–10 mice were analyzed at each time point and statistical significance was determined using the non-parametric Mann-Whitney-test. n.s.: not significant, *P<0.05 and **P<0.01 relative to the corresponding wild-type. (C) hat1Δ/Δ cells are defective in killing the host. Survival of mice infected with the indicated strains was monitored over 32 days post infection (p.i.). The data are presented as Kaplan-Meier survival curves. Groups of 6 mice were infected per C. albicans strain. Statistical significance was determined using the Log-rank test. ns: not significant; (D) Fungal burdens in kidneys of surviving mice from panel C were determined and expressed as CFUs per gram organ. One mouse infected with the hat1Δ/Δ strain was able to clear Candida. (E) The cac2Δ/Δ strain is not cleared efficiently from kidneys. Experiment was performed as described in (B). Groups of 4–5 mice were analyzed at each time point. (F) Infection with hat1Δ/Δ cells causes reduced kidney damage. Urea levels were determined in sera of infected mice at day 3 and 7 post infection. n.s.: not significant, *P<0.05, **P<0.01 relative to the wild-type (Student's t-test).
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ppat.1005218.g009: Cells lacking Hat1 show reduced virulence but persist in mouse kidneys.(A) Reduced growth rate of the hat1Δ/Δ strain was determined by measuring the OD600 of cells growing in YPD at 30°C. (B) Cells lacking Hat1 are not cleared efficiently from kidneys. At the indicated time points, fungal burdens in kidneys of mice infected with C. albicans strains were determined and expressed as CFUs per gram kidney. Groups of 5–10 mice were analyzed at each time point and statistical significance was determined using the non-parametric Mann-Whitney-test. n.s.: not significant, *P<0.05 and **P<0.01 relative to the corresponding wild-type. (C) hat1Δ/Δ cells are defective in killing the host. Survival of mice infected with the indicated strains was monitored over 32 days post infection (p.i.). The data are presented as Kaplan-Meier survival curves. Groups of 6 mice were infected per C. albicans strain. Statistical significance was determined using the Log-rank test. ns: not significant; (D) Fungal burdens in kidneys of surviving mice from panel C were determined and expressed as CFUs per gram organ. One mouse infected with the hat1Δ/Δ strain was able to clear Candida. (E) The cac2Δ/Δ strain is not cleared efficiently from kidneys. Experiment was performed as described in (B). Groups of 4–5 mice were analyzed at each time point. (F) Infection with hat1Δ/Δ cells causes reduced kidney damage. Urea levels were determined in sera of infected mice at day 3 and 7 post infection. n.s.: not significant, *P<0.05, **P<0.01 relative to the wild-type (Student's t-test).

Mentions: Deletion of HAT1 causes reduced growth rate in vitro with morphological defects even in complete media (Fig 9A) [10], which has been shown to reduce virulence of several C. albicans mutants [28,30,60–63]. However, cells lacking Hat1 are also more resistant to killing by immune cells (Fig 8D). Therefore, we wanted to test how these seemingly opposing phenotypes caused by the deletion of HAT1 affect virulence of C. albicans. We used a mouse model of systemic candidiasis. Infection was performed via the tail vein and fungal burdens in kidneys were followed at day 1, 3 and 7. Interestingly, after 24 hours mice infected with the hat1Δ/Δ mutant showed significantly reduced CFUs in the kidneys when compared to the wild-type or the restored strain (Fig 9B). However, the fungal burden of the mutant increased until day 7 after infection reaching the levels of the wild-type and the reintegrant (Fig 9B). Thus, cells lacking Hat1 are not efficiently cleared from infected mice as they are able to compensate the in vitro growth defect in vivo. To further investigate the virulence properties of the hat1Δ/Δ strain, we determined the survival rate of infected mice. Interestingly, 15 days post infection the majority of wild-type infected mice had died, whereas all of the mice infected with the hat1Δ/Δ strain were still alive (Fig 9C). Even after 32 days, only one mouse infected with the hat1Δ/Δ mutant had died. Of note, mice infected with the reintegrant showed an intermediate survival rate, which was however not significant when compared to the wild-type strain (Fig 9C). Although the majority of mice survived the infection with cells lacking Hat1, mutant cells were not cleared from the kidneys in 4 out of 5 individuals (Fig 9D). Instead, the fungal burden stayed high until the end of the experiment. Furthermore, two mice survived infection with the restored strain and for both Candida was not cleared (Fig 9D). Thus, again the revertant strain showed an intermediate phenotype most likely due to haploinsufficiency.


The Candida albicans Histone Acetyltransferase Hat1 Regulates Stress Resistance and Virulence via Distinct Chromatin Assembly Pathways.

Tscherner M, Zwolanek F, Je S, Sedlazeck FJ, Petryshyn A, Frohner IE, Mavrianos J, Chauhan N, von Haeseler A, Kuchler K - PLoS Pathog. (2015)

Cells lacking Hat1 show reduced virulence but persist in mouse kidneys.(A) Reduced growth rate of the hat1Δ/Δ strain was determined by measuring the OD600 of cells growing in YPD at 30°C. (B) Cells lacking Hat1 are not cleared efficiently from kidneys. At the indicated time points, fungal burdens in kidneys of mice infected with C. albicans strains were determined and expressed as CFUs per gram kidney. Groups of 5–10 mice were analyzed at each time point and statistical significance was determined using the non-parametric Mann-Whitney-test. n.s.: not significant, *P<0.05 and **P<0.01 relative to the corresponding wild-type. (C) hat1Δ/Δ cells are defective in killing the host. Survival of mice infected with the indicated strains was monitored over 32 days post infection (p.i.). The data are presented as Kaplan-Meier survival curves. Groups of 6 mice were infected per C. albicans strain. Statistical significance was determined using the Log-rank test. ns: not significant; (D) Fungal burdens in kidneys of surviving mice from panel C were determined and expressed as CFUs per gram organ. One mouse infected with the hat1Δ/Δ strain was able to clear Candida. (E) The cac2Δ/Δ strain is not cleared efficiently from kidneys. Experiment was performed as described in (B). Groups of 4–5 mice were analyzed at each time point. (F) Infection with hat1Δ/Δ cells causes reduced kidney damage. Urea levels were determined in sera of infected mice at day 3 and 7 post infection. n.s.: not significant, *P<0.05, **P<0.01 relative to the wild-type (Student's t-test).
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ppat.1005218.g009: Cells lacking Hat1 show reduced virulence but persist in mouse kidneys.(A) Reduced growth rate of the hat1Δ/Δ strain was determined by measuring the OD600 of cells growing in YPD at 30°C. (B) Cells lacking Hat1 are not cleared efficiently from kidneys. At the indicated time points, fungal burdens in kidneys of mice infected with C. albicans strains were determined and expressed as CFUs per gram kidney. Groups of 5–10 mice were analyzed at each time point and statistical significance was determined using the non-parametric Mann-Whitney-test. n.s.: not significant, *P<0.05 and **P<0.01 relative to the corresponding wild-type. (C) hat1Δ/Δ cells are defective in killing the host. Survival of mice infected with the indicated strains was monitored over 32 days post infection (p.i.). The data are presented as Kaplan-Meier survival curves. Groups of 6 mice were infected per C. albicans strain. Statistical significance was determined using the Log-rank test. ns: not significant; (D) Fungal burdens in kidneys of surviving mice from panel C were determined and expressed as CFUs per gram organ. One mouse infected with the hat1Δ/Δ strain was able to clear Candida. (E) The cac2Δ/Δ strain is not cleared efficiently from kidneys. Experiment was performed as described in (B). Groups of 4–5 mice were analyzed at each time point. (F) Infection with hat1Δ/Δ cells causes reduced kidney damage. Urea levels were determined in sera of infected mice at day 3 and 7 post infection. n.s.: not significant, *P<0.05, **P<0.01 relative to the wild-type (Student's t-test).
Mentions: Deletion of HAT1 causes reduced growth rate in vitro with morphological defects even in complete media (Fig 9A) [10], which has been shown to reduce virulence of several C. albicans mutants [28,30,60–63]. However, cells lacking Hat1 are also more resistant to killing by immune cells (Fig 8D). Therefore, we wanted to test how these seemingly opposing phenotypes caused by the deletion of HAT1 affect virulence of C. albicans. We used a mouse model of systemic candidiasis. Infection was performed via the tail vein and fungal burdens in kidneys were followed at day 1, 3 and 7. Interestingly, after 24 hours mice infected with the hat1Δ/Δ mutant showed significantly reduced CFUs in the kidneys when compared to the wild-type or the restored strain (Fig 9B). However, the fungal burden of the mutant increased until day 7 after infection reaching the levels of the wild-type and the reintegrant (Fig 9B). Thus, cells lacking Hat1 are not efficiently cleared from infected mice as they are able to compensate the in vitro growth defect in vivo. To further investigate the virulence properties of the hat1Δ/Δ strain, we determined the survival rate of infected mice. Interestingly, 15 days post infection the majority of wild-type infected mice had died, whereas all of the mice infected with the hat1Δ/Δ strain were still alive (Fig 9C). Even after 32 days, only one mouse infected with the hat1Δ/Δ mutant had died. Of note, mice infected with the reintegrant showed an intermediate survival rate, which was however not significant when compared to the wild-type strain (Fig 9C). Although the majority of mice survived the infection with cells lacking Hat1, mutant cells were not cleared from the kidneys in 4 out of 5 individuals (Fig 9D). Instead, the fungal burden stayed high until the end of the experiment. Furthermore, two mice survived infection with the restored strain and for both Candida was not cleared (Fig 9D). Thus, again the revertant strain showed an intermediate phenotype most likely due to haploinsufficiency.

Bottom Line: Hydrogen peroxide resistance in cells lacking Hat1 results from higher induction rates of oxidative stress gene expression, accompanied by reduced histone density as well as subsequent increased RNA polymerase recruitment.Remarkably, the oxidative stress phenotype of hat1Δ/Δ cells is a species-specific trait only found in C. albicans and members of the CTG clade.The reduced azole susceptibility appears to be conserved in a wider range of fungi.

View Article: PubMed Central - PubMed

Affiliation: Department for Medical Biochemistry, Medical University of Vienna, Max F. Perutz Laboratories, Campus Vienna Biocenter, Vienna, Austria.

ABSTRACT
Human fungal pathogens like Candida albicans respond to host immune surveillance by rapidly adapting their transcriptional programs. Chromatin assembly factors are involved in the regulation of stress genes by modulating the histone density at these loci. Here, we report a novel role for the chromatin assembly-associated histone acetyltransferase complex NuB4 in regulating oxidative stress resistance, antifungal drug tolerance and virulence in C. albicans. Strikingly, depletion of the NuB4 catalytic subunit, the histone acetyltransferase Hat1, markedly increases resistance to oxidative stress and tolerance to azole antifungals. Hydrogen peroxide resistance in cells lacking Hat1 results from higher induction rates of oxidative stress gene expression, accompanied by reduced histone density as well as subsequent increased RNA polymerase recruitment. Furthermore, hat1Δ/Δ cells, despite showing growth defects in vitro, display reduced susceptibility to reactive oxygen-mediated killing by innate immune cells. Thus, clearance from infected mice is delayed although cells lacking Hat1 are severely compromised in killing the host. Interestingly, increased oxidative stress resistance and azole tolerance are phenocopied by the loss of histone chaperone complexes CAF-1 and HIR, respectively, suggesting a central role for NuB4 in the delivery of histones destined for chromatin assembly via distinct pathways. Remarkably, the oxidative stress phenotype of hat1Δ/Δ cells is a species-specific trait only found in C. albicans and members of the CTG clade. The reduced azole susceptibility appears to be conserved in a wider range of fungi. Thus, our work demonstrates how highly conserved chromatin assembly pathways can acquire new functions in pathogenic fungi during coevolution with the host.

No MeSH data available.


Related in: MedlinePlus