Expression of Candida albicans Sfu1 in fission yeast complements the loss of the iron‐regulatory transcription factor Fep1 and requires Tup co‐repressors

Abstract

The opportunistic pathogenic yeast Candida albicans contains a gene which encodes a putative member of the iron-regulatory GATA factor protein family. This protein, referred to as suppressor of ferric uptake (Sfu1), has two Cys 2 /Cys 2 -type zinc finger domains separated by a conserved Cys-rich region. In Schizosaccharomyces pombe, the GATA-type transcription factor Fe protein 1 (Fep1) represses target gene expression when iron levels exceed those needed by the cell. To ascertain the functional similarity between Sfu1 and Fep1, the C. albicans Sfu1 was expressed in Sz. pombe cells lacking the endogenous fep1 + gene. We determined that Sfu1 is capable of suppressing iron-related phenotypes of fep1 mutant cells. Using a functional SFU1-GFP fusion allele, the Sfu1 protein was localized to the nucleus under both iron-replete and iron-starved conditions. Sfu1 effectively regulated the expression of genes encoding components of the reductive and non-reductive iron transport systems. Furthermore, the iron-responsive regulation mediated by Sfu1 was GATA-dependent. The N-terminal 250 amino acid segment of Sfu1 expressed in and purified from Escherichia coli specifically associated with the hexanucleotide sequence AGATAA in an iron-dependent manner. On the other hand, expression of the full-length C. albicans Sfu1 in Sz. pombe fep1 tup11 tup12 triple mutant cells failed to repress target gene expression under conditions of high iron concentration. Using two-hybrid analysis, we demonstrated that Tup11 and Tup12 physically interacted with Sfu1. Taken together, these results reveal a remarkable functional conservation between Sfu1 from C. albicans and Fep1 from Sz. pombe in their ability to sense excess iron and respond by repressing target gene transcription.

Key Function for the CCAAT-Binding Factor Php4 To Regulate Gene Expression in Response to Iron Deficiency in Fission Yeast

“…Fep1 is a member of the GATA factor family, which is comprised of transcription factors that contain either one or two Cys 2 /Cys 2 -type zinc finger motifs that recognize and bind to GATA-containing DNA sequences (56). Fep1 orthologs are found in many yeast genomes, including Ustilago maydis (Urbs1) (2,3), Neurospora crassa (Sre) (18,66), Aspergillus nidulans (SreA) (17,43,44), Candida albicans (Sfu1) (28,49), and Cryptococcus neoformans (Cir1) (21), but not in Saccharomyces cerevisiae (47). Instead, in S. cerevisiae, the genes required for high-affinity iron uptake are activated by the iron-responsive transcription factors Aft1 and Aft2, for which there are no orthologs in the majority of other fungi, except those that belong to the sensu stricto group of the genus Saccharomyces (9,10,54,64).…”

Both Php4 Function and Subcellular Localization Are Regulated by Iron via a Multistep Mechanism Involving the Glutaredoxin Grx4 and the Exportin Crm1

“…fip1 ϩ , fio1 ϩ , frp1 ϩ , and str1 ϩ /2 ϩ /3 ϩ ) and shuts down their expression to avoid deleterious consequences of iron overload (6,7). When iron levels are low, Fep1 is unable to bind DNA, resulting in the transcriptional induction of genes involved in iron acquisition (6,8,9). Analogous to S. pombe, other fungi use Fep1 orthologs to repress transcription of target genes in response to high iron.…”

“…S. pombe grx4⌬ and php4⌬ grx4⌬ disruption strains, as well as control strains, were cultivated in culture jars under microaerobic conditions using the GazPack EZ system (BD Biosciences). For two-hybrid experiments, S. cerevisiae strain L40 (Mata his3⌬200 trp1-901 leu2-3, 112 ade2 LYS2::(lexAop) 4 -HIS3 URA3::(lexAop) 8 -lacZ) (35) was grown in synthetic minimal medium containing 83 mg/liter histidine, adenine, uracil, and lysine, 2% dextrose, 50 mM MES buffer (pH 6.1), and 0.67% yeast nitrogen base minus copper and iron (MP Biomedicals, Solon, OH).…”

Depletion of the Cullin Cdc53p Induces Morphogenetic Changes in Candida albicans

“…Known regulators include Sfu1p, the homologue of the transcriptional repressor Fep1p in the filamentous fungi Schizosaccharomyces pombe (34,53) and the pH-responsive transcriptional activator Rim101p (10,17,18). However, no general Sfu1p or Rim101p transcriptional response could be observed in the transcriptional profile of Cdc53p-depleted cells, rendering both factors unlikely to elicit the observed Cdc53p-dependent upregulation of the high-affinity iron transport genes.…”