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HapX positively and negatively regulates the transcriptional response to iron deprivation in Cryptococcus neoformans.

Jung WH, Saikia S, Hu G, Wang J, Fung CK, D'Souza C, White R, Kronstad JW - PLoS Pathog. (2010)

Bottom Line: However, we also found that HapX plays both positive and negative roles in the regulation of gene expression, including a positive regulatory role in siderophore transporter expression.Although both hapX and hap3 mutants were defective in heme utilization in culture, only HapX made a contribution to virulence, and loss of HapX in a strain lacking the high-affinity iron uptake system did not cause further attenuation of disease.Overall, these results indicated that C. neoformans employs multiple strategies for iron acquisition during infection.

View Article: PubMed Central - PubMed

Affiliation: Department of Biotechnology, Chung-Ang University, Gyeonggi-Do, Republic of Korea.

ABSTRACT
The fungal pathogen Cryptococcus neoformans is a major cause of illness in immunocompromised individuals such as AIDS patients. The ability of the fungus to acquire nutrients during proliferation in host tissue and the ability to elaborate a polysaccharide capsule are critical determinants of disease outcome. We previously showed that the GATA factor, Cir1, is a major regulator both of the iron uptake functions needed for growth in host tissue and the key virulence factors such as capsule, melanin and growth at 37°C. We are interested in further defining the mechanisms of iron acquisition from inorganic and host-derived iron sources with the goal of understanding the nutritional adaptation of C. neoformans to the host environment. In this study, we investigated the roles of the HAP3 and HAPX genes in iron utilization and virulence. As in other fungi, the C. neoformans Hap proteins negatively influence the expression of genes encoding respiratory and TCA cycle functions under low-iron conditions. However, we also found that HapX plays both positive and negative roles in the regulation of gene expression, including a positive regulatory role in siderophore transporter expression. In addition, HapX also positively regulated the expression of the CIR1 transcript. This situation is in contrast to the negative regulation by HapX of genes encoding GATA iron regulatory factors in Aspergillus nidulans and Schizosaccharomyces pombe. Although both hapX and hap3 mutants were defective in heme utilization in culture, only HapX made a contribution to virulence, and loss of HapX in a strain lacking the high-affinity iron uptake system did not cause further attenuation of disease. Therefore, HapX appears to have a minimal role during infection of mammalian hosts and instead may be an important regulator of environmental iron uptake functions. Overall, these results indicated that C. neoformans employs multiple strategies for iron acquisition during infection.

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Overview of differentially-regulated genes in response to different iron sources.A histogram shows the number of genes whose expression changed by at least two-fold with statistical significance (q<0.05). The numbers represent differentially expressed genes in the mutants versus WT in response to different iron sources and also in the WT strain grown under iron-replete versus iron-limited conditions.
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ppat-1001209-g002: Overview of differentially-regulated genes in response to different iron sources.A histogram shows the number of genes whose expression changed by at least two-fold with statistical significance (q<0.05). The numbers represent differentially expressed genes in the mutants versus WT in response to different iron sources and also in the WT strain grown under iron-replete versus iron-limited conditions.

Mentions: Initially, we examined the global changes in transcription for each mutant in comparison with the WT strain in each iron source (Figure 2). This analysis revealed that the hapXΔ mutation had the greatest influence, with 1131 genes down-regulated and 910 up-regulated upon comparison with WT under low-iron conditions. By contrast, Hap3 made a much smaller contribution with 83 genes down-regulated and 230 up-regulated under the same conditions. The cir1Δ mutant had an intermediate influence with 419 and 402 genes down- and up-regulated, respectively. The latter numbers are consistent with our previous analysis of the influence of Cir1 on transcription in a serotype D strain of C. neoformans [15]. Overall, the same global pattern of influence was observed with the cells grown with the three iron sources, although the numbers of genes influenced by the mutations were lower by 30 to 50% compared with the differential expression seen under low-iron conditions. Also, these results indicated that HapX plays a major role in the regulation of gene expression under low-iron conditions. Venn diagrams displaying the overlapping numbers of genes for each mutation and each iron condition are presented in Figure S5. The complete lists of differentially expressed genes that correspond to the numbers in the Venn diagrams are presented in Tables S2, S3, S4, S5.


HapX positively and negatively regulates the transcriptional response to iron deprivation in Cryptococcus neoformans.

Jung WH, Saikia S, Hu G, Wang J, Fung CK, D'Souza C, White R, Kronstad JW - PLoS Pathog. (2010)

Overview of differentially-regulated genes in response to different iron sources.A histogram shows the number of genes whose expression changed by at least two-fold with statistical significance (q<0.05). The numbers represent differentially expressed genes in the mutants versus WT in response to different iron sources and also in the WT strain grown under iron-replete versus iron-limited conditions.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2991262&req=5

ppat-1001209-g002: Overview of differentially-regulated genes in response to different iron sources.A histogram shows the number of genes whose expression changed by at least two-fold with statistical significance (q<0.05). The numbers represent differentially expressed genes in the mutants versus WT in response to different iron sources and also in the WT strain grown under iron-replete versus iron-limited conditions.
Mentions: Initially, we examined the global changes in transcription for each mutant in comparison with the WT strain in each iron source (Figure 2). This analysis revealed that the hapXΔ mutation had the greatest influence, with 1131 genes down-regulated and 910 up-regulated upon comparison with WT under low-iron conditions. By contrast, Hap3 made a much smaller contribution with 83 genes down-regulated and 230 up-regulated under the same conditions. The cir1Δ mutant had an intermediate influence with 419 and 402 genes down- and up-regulated, respectively. The latter numbers are consistent with our previous analysis of the influence of Cir1 on transcription in a serotype D strain of C. neoformans [15]. Overall, the same global pattern of influence was observed with the cells grown with the three iron sources, although the numbers of genes influenced by the mutations were lower by 30 to 50% compared with the differential expression seen under low-iron conditions. Also, these results indicated that HapX plays a major role in the regulation of gene expression under low-iron conditions. Venn diagrams displaying the overlapping numbers of genes for each mutation and each iron condition are presented in Figure S5. The complete lists of differentially expressed genes that correspond to the numbers in the Venn diagrams are presented in Tables S2, S3, S4, S5.

Bottom Line: However, we also found that HapX plays both positive and negative roles in the regulation of gene expression, including a positive regulatory role in siderophore transporter expression.Although both hapX and hap3 mutants were defective in heme utilization in culture, only HapX made a contribution to virulence, and loss of HapX in a strain lacking the high-affinity iron uptake system did not cause further attenuation of disease.Overall, these results indicated that C. neoformans employs multiple strategies for iron acquisition during infection.

View Article: PubMed Central - PubMed

Affiliation: Department of Biotechnology, Chung-Ang University, Gyeonggi-Do, Republic of Korea.

ABSTRACT
The fungal pathogen Cryptococcus neoformans is a major cause of illness in immunocompromised individuals such as AIDS patients. The ability of the fungus to acquire nutrients during proliferation in host tissue and the ability to elaborate a polysaccharide capsule are critical determinants of disease outcome. We previously showed that the GATA factor, Cir1, is a major regulator both of the iron uptake functions needed for growth in host tissue and the key virulence factors such as capsule, melanin and growth at 37°C. We are interested in further defining the mechanisms of iron acquisition from inorganic and host-derived iron sources with the goal of understanding the nutritional adaptation of C. neoformans to the host environment. In this study, we investigated the roles of the HAP3 and HAPX genes in iron utilization and virulence. As in other fungi, the C. neoformans Hap proteins negatively influence the expression of genes encoding respiratory and TCA cycle functions under low-iron conditions. However, we also found that HapX plays both positive and negative roles in the regulation of gene expression, including a positive regulatory role in siderophore transporter expression. In addition, HapX also positively regulated the expression of the CIR1 transcript. This situation is in contrast to the negative regulation by HapX of genes encoding GATA iron regulatory factors in Aspergillus nidulans and Schizosaccharomyces pombe. Although both hapX and hap3 mutants were defective in heme utilization in culture, only HapX made a contribution to virulence, and loss of HapX in a strain lacking the high-affinity iron uptake system did not cause further attenuation of disease. Therefore, HapX appears to have a minimal role during infection of mammalian hosts and instead may be an important regulator of environmental iron uptake functions. Overall, these results indicated that C. neoformans employs multiple strategies for iron acquisition during infection.

Show MeSH
Related in: MedlinePlus