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Role of the heat shock transcription factor, Hsf1, in a major fungal pathogen that is obligately associated with warm-blooded animals.

Nicholls S, Leach MD, Priest CL, Brown AJ - Mol. Microbiol. (2009)

Bottom Line: However, this is not the case, as an Hsf1-specific HSE-lacZ reporter is not activated by oxidative, osmotic, weak acid or pH stress.Furthermore, Hsf1 regulates the expression of HSE-containing genes in response to growth temperature in C. albicans.Therefore, the main role of Hsf1 in this pathogen might be the homeostatic modulation of chaperone levels in response to growth temperature, rather than the activation of acute responses to sudden thermal transitions.

View Article: PubMed Central - PubMed

Affiliation: Aberdeen Fungal Group, School of Medical Sciences, University of Aberdeen, Institute of Medical Sciences, Aberdeen AB25 2ZD, UK.

ABSTRACT
All organisms have evolved mechanisms that protect them against environmental stress. The major fungal pathogen of humans, Candida albicans, has evolved robust stress responses that protect it against human immune defences and promote its pathogenicity. However, C. albicans is unlikely to be exposed to heat shock as it is obligatorily associated with warm-blooded animals. Therefore, we examined the role of the heat shock transcription factor (Hsf1) in this pathogen. We show that C. albicans expresses an evolutionarily conserved Hsf1 (orf19.4775) that is phosphorylated in response to heat shock, induces transcription via the heat shock element (HSE), contributes to the global transcriptional response to heat shock, and is essential for viability. Why has Hsf1 been conserved in this obligate animal saprophyte? We reasoned that Hsf1 might contribute to medically relevant stress responses. However, this is not the case, as an Hsf1-specific HSE-lacZ reporter is not activated by oxidative, osmotic, weak acid or pH stress. Rather, Hsf1 is required for the expression of essential chaperones in the absence of heat shock (e.g. Hsp104, Hsp90, Hsp70). Furthermore, Hsf1 regulates the expression of HSE-containing genes in response to growth temperature in C. albicans. Therefore, the main role of Hsf1 in this pathogen might be the homeostatic modulation of chaperone levels in response to growth temperature, rather than the activation of acute responses to sudden thermal transitions.

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HSF1 is required for basal expression and heat shock induction of HSP genes in C. albicans. C. albicans strains were grown at 30°C in YPD containing or lacking 20 μg ml−1 doxycycline for 6 h. Cells were subjected to a 30–45°C heat shock for 30 min, or maintained at 30°C: wild type, +/+ (THE1); heterozygous hsf1/HSF1 mutant, Δ/+ (CLM60-1); conditional hsf1/tetp-HSF1 mutant, Δ/tet (CLM62-1) (Table 1). RNA was isolated from these cells and subjected to Northern blotting. Filters were probed for the HSP70, HSP90, HSP140 and ACT1 mRNAs. The HSP70 probe cross-reacted with transcripts from several HSP70 family members: HSP70, SSA2, SSB1, KAR2 and SSCI (not shown).
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fig03: HSF1 is required for basal expression and heat shock induction of HSP genes in C. albicans. C. albicans strains were grown at 30°C in YPD containing or lacking 20 μg ml−1 doxycycline for 6 h. Cells were subjected to a 30–45°C heat shock for 30 min, or maintained at 30°C: wild type, +/+ (THE1); heterozygous hsf1/HSF1 mutant, Δ/+ (CLM60-1); conditional hsf1/tetp-HSF1 mutant, Δ/tet (CLM62-1) (Table 1). RNA was isolated from these cells and subjected to Northern blotting. Filters were probed for the HSP70, HSP90, HSP140 and ACT1 mRNAs. The HSP70 probe cross-reacted with transcripts from several HSP70 family members: HSP70, SSA2, SSB1, KAR2 and SSCI (not shown).

Mentions: RNA was extracted from wild-type cells (THE1), the heterozygote (CLM61-1) and the conditional mutant (CLM62-1) grown at 30°C or subjected to a 45°C heat shock for 30 min (Fig. 3). The HSP90 and HSP70 mRNAs were expressed at significant levels in all three strains even under basal conditions (at 30°C), but their expression increased further in response to the heat shock. Minimal HSP104 expression was observed under basal conditions, but this mRNA was strongly upregulated by the heat shock (Fig. 3). No induction of these HSP mRNAs was observed in hsf1/tetp-HSF1 cells treated with doxycycline for 6 h. At this stage most hsf1/tetp-HSF1 cells remain viable (Fig. 1B). Furthermore these cells remain transcriptionally responsive to other stimuli. For example, doxycycline-treated hsf1/tetp-HSF1 cells still respond to oxidative and osmotic stress by upregulating the CTA1 and PGA23 transcripts respectively (Fig. 4). Therefore, Hsf1 is required for the induction of the HSP70, HSP90 and HSP104 mRNAs in response to heat shock.


Role of the heat shock transcription factor, Hsf1, in a major fungal pathogen that is obligately associated with warm-blooded animals.

Nicholls S, Leach MD, Priest CL, Brown AJ - Mol. Microbiol. (2009)

HSF1 is required for basal expression and heat shock induction of HSP genes in C. albicans. C. albicans strains were grown at 30°C in YPD containing or lacking 20 μg ml−1 doxycycline for 6 h. Cells were subjected to a 30–45°C heat shock for 30 min, or maintained at 30°C: wild type, +/+ (THE1); heterozygous hsf1/HSF1 mutant, Δ/+ (CLM60-1); conditional hsf1/tetp-HSF1 mutant, Δ/tet (CLM62-1) (Table 1). RNA was isolated from these cells and subjected to Northern blotting. Filters were probed for the HSP70, HSP90, HSP140 and ACT1 mRNAs. The HSP70 probe cross-reacted with transcripts from several HSP70 family members: HSP70, SSA2, SSB1, KAR2 and SSCI (not shown).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3675641&req=5

fig03: HSF1 is required for basal expression and heat shock induction of HSP genes in C. albicans. C. albicans strains were grown at 30°C in YPD containing or lacking 20 μg ml−1 doxycycline for 6 h. Cells were subjected to a 30–45°C heat shock for 30 min, or maintained at 30°C: wild type, +/+ (THE1); heterozygous hsf1/HSF1 mutant, Δ/+ (CLM60-1); conditional hsf1/tetp-HSF1 mutant, Δ/tet (CLM62-1) (Table 1). RNA was isolated from these cells and subjected to Northern blotting. Filters were probed for the HSP70, HSP90, HSP140 and ACT1 mRNAs. The HSP70 probe cross-reacted with transcripts from several HSP70 family members: HSP70, SSA2, SSB1, KAR2 and SSCI (not shown).
Mentions: RNA was extracted from wild-type cells (THE1), the heterozygote (CLM61-1) and the conditional mutant (CLM62-1) grown at 30°C or subjected to a 45°C heat shock for 30 min (Fig. 3). The HSP90 and HSP70 mRNAs were expressed at significant levels in all three strains even under basal conditions (at 30°C), but their expression increased further in response to the heat shock. Minimal HSP104 expression was observed under basal conditions, but this mRNA was strongly upregulated by the heat shock (Fig. 3). No induction of these HSP mRNAs was observed in hsf1/tetp-HSF1 cells treated with doxycycline for 6 h. At this stage most hsf1/tetp-HSF1 cells remain viable (Fig. 1B). Furthermore these cells remain transcriptionally responsive to other stimuli. For example, doxycycline-treated hsf1/tetp-HSF1 cells still respond to oxidative and osmotic stress by upregulating the CTA1 and PGA23 transcripts respectively (Fig. 4). Therefore, Hsf1 is required for the induction of the HSP70, HSP90 and HSP104 mRNAs in response to heat shock.

Bottom Line: However, this is not the case, as an Hsf1-specific HSE-lacZ reporter is not activated by oxidative, osmotic, weak acid or pH stress.Furthermore, Hsf1 regulates the expression of HSE-containing genes in response to growth temperature in C. albicans.Therefore, the main role of Hsf1 in this pathogen might be the homeostatic modulation of chaperone levels in response to growth temperature, rather than the activation of acute responses to sudden thermal transitions.

View Article: PubMed Central - PubMed

Affiliation: Aberdeen Fungal Group, School of Medical Sciences, University of Aberdeen, Institute of Medical Sciences, Aberdeen AB25 2ZD, UK.

ABSTRACT
All organisms have evolved mechanisms that protect them against environmental stress. The major fungal pathogen of humans, Candida albicans, has evolved robust stress responses that protect it against human immune defences and promote its pathogenicity. However, C. albicans is unlikely to be exposed to heat shock as it is obligatorily associated with warm-blooded animals. Therefore, we examined the role of the heat shock transcription factor (Hsf1) in this pathogen. We show that C. albicans expresses an evolutionarily conserved Hsf1 (orf19.4775) that is phosphorylated in response to heat shock, induces transcription via the heat shock element (HSE), contributes to the global transcriptional response to heat shock, and is essential for viability. Why has Hsf1 been conserved in this obligate animal saprophyte? We reasoned that Hsf1 might contribute to medically relevant stress responses. However, this is not the case, as an Hsf1-specific HSE-lacZ reporter is not activated by oxidative, osmotic, weak acid or pH stress. Rather, Hsf1 is required for the expression of essential chaperones in the absence of heat shock (e.g. Hsp104, Hsp90, Hsp70). Furthermore, Hsf1 regulates the expression of HSE-containing genes in response to growth temperature in C. albicans. Therefore, the main role of Hsf1 in this pathogen might be the homeostatic modulation of chaperone levels in response to growth temperature, rather than the activation of acute responses to sudden thermal transitions.

Show MeSH
Related in: MedlinePlus