Regulation of Copper Toxicity by Candida albicans GPA2

Abstract

Copper is an essential nutrient that is toxic to cells when present in excess. The fungal pathogen Candida albicans employs several mechanisms to survive in the presence of excess copper, but the molecular pathways that govern these responses are not completely understood. We report that deletion of GPA2, which specifies a G-protein ␣ subunit, confers increased resistance to excess copper and propose that the increased resistance is due to a combination of decreased copper uptake and an increase in copper chelation by metallothioneins. This is supported by our observations that a gpa2⌬/⌬ mutant has reduced expression of the copper uptake genes, CTR1 and FRE7, and a marked decrease in copper accumulation following exposure to high copper levels. Furthermore, deletion of GPA2 results in an increased expression of the copper metallothionein gene, CRD2. Gpa2p functions upstream in the cyclic AMP (cAMP)-protein kinase A (PKA) pathway to govern hyphal morphogenesis. The copper resistance phenotype of the gpa2⌬/⌬ mutant can be reversed by artificially increasing the intracellular concentration of cAMP. These results provide evidence for a novel role of the PKA pathway in regulation of copper homeostasis. Furthermore, the connection between the PKA pathway and copper homeostasis appears to be conserved in the pathogen Cryptococcus neoformans but not in the nonpathogenic Saccharomyces cerevisiae.

Candida albicans adapts to host copper during infection by swapping metal cofactors for superoxide dismutase

“…However, Cu was not elevated in mac1Δ/Δ cells and if anything Cu was low (Fig. 4C, Lower), presumably reflecting loss of Ctr1 Cu transport as has been previously reported for mac1Δ/Δ strains (43). Cu starvation therefore works through Mac1 to induce SOD3 and repress SOD1.…”

Aspergillus fumigatus Copper Export Machinery and Reactive Oxygen Intermediate Defense Counter Host Copper-Mediated Oxidative Antimicrobial Offense

“…Physiological studies of the pathogenic ascomycete C. albicans identified a putative homolog of the human ATP7A P-type copper ATPase and S. cerevisiae Ccc2p (Lowe et al, 2004), Crp1p, as critical for copper detoxification with the metallothionein Cup1p responsible for residual copper resistance when CRP1 was deleted and both proteins essential for establishing full virulence (Douglas et al, 2012; Mackie et al, 2016; Schwartz et al, 2013; Weissman et al, 2000) (Table 1). Both CRP1 and CUP1 are induced by elevated copper concentrations through the homolog of Ace1p (Schwartz et al, 2013; Weissman et al, 2000). In the pathogenic basidiomycete C. neoformans , one copper-binding transcription factor, Cuf1, regulates expression of both copper importers Ctr1 and Ctr4 as well as the two metallothioneins Cmt1 and Cmt2 involved in copper detoxification (Ding et al, 2011; Waterman et al, 2007).…”

The Yin and Yang of copper during infection

“…With high Cu, C. albicans Cup2 not only induces MTs but also a cell surface copper exporting ATPase (Crp1) to extrude copper from the cell, analogous to the copper elimination response of bacteria [74, 75]. Additionally, the C. albicans Mac1 sensor for low copper induces copper uptake as well as genes that control iron metabolism and modulate utilization of copper as an enzymatic cofactor [76, 77].…”

“…Variations on this theme are seen in pathogenic fungi, presumably to accommodate challenges in copper at the host-pathogen interface. The Cup2 and Mac1 regulons in C. albicans have been expanded to include a copper exporting ATPase Crp1 induced with high copper [74, 75] and the induction of non-copper alternatives for enzymes involved in mitochondrial respiration ( AOX2 ) and cytosolic anti-oxidant protection ( SOD3) during times of low copper [76, 77, 79] . C. albicans Mac1 can also repress the gene encoding Cu/Zn Sod1, helping to spare copper under cases of copper limitation [45].…”