Deletion of the copper transporter CaCCC2 reveals two distinct pathways for iron acquisition in Candida albicans

Abstract

Summary Efficient iron acquisition is an essential requirement for growth of pathogenic organisms in the iron‐poor host environment. In Saccharomyces cerevisiae, high‐affinity iron import depends on the multicopper ferroxidase ScFet3. ScFet3 biogenesis in the trans‐Golgi compartment requires a copper‐transporting P‐type ATPase, ScCcc2. Here, we describe the isolation by functional complementation of a Ccc2 homologue from the pathogenic yeast Candida albicans. CaCcc2 is functionally distinct from a previously described C. albicans copper‐transporting P‐type ATPase, CaCrp1, which appears to be specifically involved in copper detoxification. Regulation of CaCCC2 and the phenotype of the homozygous CaCCC2 deletion indicate that it is required for high‐affinity iron import, making it the bona fide CCC2 homologue of C. albicans. Remarkably, in a mouse model of systemic infection, the Caccc2Δ strain displayed robust proliferation and no significant reduction in pathogenicity, suggesting the existence of alternative mechanisms of iron uptake from host tissues. We identify haemin and haemoglobin as potential iron sources that can be used by C. albicans in a CaCcc2‐independent manner.

The CaCTR1 gene is required for high-affinity iron uptake and is transcriptionally controlled by a copper-sensing transactivator encoded by CaMAC1

“…In S. cerevisiae, it has been observed that deletions in genes that facilitate high-affinity copper uptake or delivery of copper ions to the multicopper oxidase ScFet3p result in strains that also display defective high-affinity iron uptake (Knight et al, 1996;Lin et al, 1997;Yuan et al, 1995). Furthermore, growing evidence suggests that reductive iron uptake in C. albicans may also be dependent on copper uptake (Eck et al, 1999;Knight et al, 2002;Weissman et al, 2002).…”

“…In the same report, PPD oxidase activity was also shown to be dependent upon copper and this dependency was proposed to be due to the requirement of CaFet3p. However, although a Caftr1-null mutant was unable to establish an infection in a systemic mouse model, virulence of a Cafet3-null mutant and a Caccc2-null mutant has been shown to be essentially the same as that of a wild-type strain (Eck et al, 1999;Ramanan & Wang, 2000;Weissman et al, 2002). Therefore, it appears that there is a paradox with the requirement of multicopper oxidase activity for reductive iron uptake in C. albicans, as deletions in CaFET3 and CaCCC2 would be expected to result in reduced virulence.…”

“…Therefore, it appears that there is a paradox with the requirement of multicopper oxidase activity for reductive iron uptake in C. albicans, as deletions in CaFET3 and CaCCC2 would be expected to result in reduced virulence. However, CaCCC2 was isolated and characterized by functional rescue of a corresponding S. cerevisiae mutant and its complete biochemical properties have not been fully elucidated (Weissman et al, 2002). There are also four additional ORFs that are present on the C. albicans genome database with predicted protein products that display significant sequence identity to CaFet3p.…”

“…There are also four additional ORFs that may encode multi-copper oxidases present on the C. albicans genomic database (Knight et al, 2002). Evidence for the requirement of copper for reductive iron uptake in C. albicans is further strengthened by the characterization of a gene homologous to ScCCC2 (Weissman et al, 2002). A homozygous deletion of CaCCC2 results in strains with defective high-affinity iron uptake, presumably as a result of incorrect delivery and incorporation of copper into CaFet3p (Weissman et al, 2002).…”

“…Evidence for the requirement of copper for reductive iron uptake in C. albicans is further strengthened by the characterization of a gene homologous to ScCCC2 (Weissman et al, 2002). A homozygous deletion of CaCCC2 results in strains with defective high-affinity iron uptake, presumably as a result of incorrect delivery and incorporation of copper into CaFet3p (Weissman et al, 2002). However, although reductive iron uptake has been shown to be reliant on copper in C. albicans, Cafet3 and Caccc2-null mutants were still able to set up a systemic infection in mice (Eck et al, 1999).…”