Bcr1 Functions Downstream of Ssd1 To Mediate Antimicrobial Peptide Resistance in Candida albicans

Abstract

e In order to colonize the host and cause disease, Candida albicans must avoid being killed by host defense peptides. Previously, we determined that the regulatory protein Ssd1 governs antimicrobial peptide resistance in C. albicans. Here, we sought to identify additional genes whose products govern susceptibility to antimicrobial peptides. We discovered that a bcr1⌬/⌬ mutant, like the ssd1⌬/⌬ mutant, had increased susceptibility to the antimicrobial peptides, protamine, RP-1, and human ␤ defensin-2. Homozygous deletion of BCR1 in the ssd1⌬/⌬ mutant did not result in a further increase in antimicrobial peptide susceptibility. Exposure of the bcr1⌬/⌬ and ssd1⌬/⌬ mutants to RP-1 induced greater loss of mitochondrial membrane potential and increased plasma membrane permeability than with the control strains. Therefore, Bcr1 and Ssd1 govern antimicrobial peptide susceptibility and likely function in the same pathway. Furthermore, BCR1 mRNA expression was downregulated in the ssd1⌬/⌬ mutant, and the forced expression of BCR1 in the ssd1⌬/⌬ mutant partially restored antimicrobial peptide resistance. These results suggest that Bcr1 functions downstream of Ssd1. Interestingly, overexpression of 11 known Bcr1 target genes in the bcr1⌬/⌬ mutant failed to restore antimicrobial peptide resistance, suggesting that other Bcr1 target genes are likely responsible for antimicrobial peptide resistance. Collectively, these results demonstrate that Bcr1 functions downstream of Ssd1 to govern antimicrobial peptide resistance by maintaining mitochondrial energetics and reducing membrane permeabilization.T he fungus Candida albicans colonizes the skin and mucosal surfaces of healthy individuals, and colonization is necessary for the organism to cause both superficial and invasive disease. In order to successfully colonize the host and cause disease, C. albicans must resist killing by antimicrobial peptides produced by epithelial cells, leukocytes and platelets. In humans, these antimicrobial peptides include defensins, histatins, cathelicidins, kinocidins, and lactoferrin and transferrin family peptides (1).Several mechanisms that enable C. albicans to resist the injurious effects of antimicrobial peptides have been identified. These mechanisms include inactivation of antimicrobial peptides via either cleavage by secreted aspartyl proteases (2) or binding by secreted fragments of Msb2 (3). In addition, stress response pathways within the fungus are important for resistance to antimicrobial peptides. For example, an intact Hog1 mitogen-activated protein kinase pathway is required for resistance to multiple antimicrobial peptides (4, 5). Previously, we determined that the regulatory factor Ssd1 plays a key role in antimicrobial peptide resistance in C. albicans (6). A strain in which SSD1 was deleted was hypersusceptible to certain antimicrobial peptides, whereas strains that overexpressed SSD1 were resistant to these peptides. In addition, in a murine model of disseminated candidiasis, an ssd1⌬/⌬ null mutant had attenuated virulence, s...

Characterization of Biofilm Formation and the Role of BCR1 in Clinical Isolates of Candida parapsilosis

“…Our observation is consistent with a gene expression study in C. albicans (49), where the bcr1⌬/⌬ mutant showed upregulated mRNA levels of secreted aspartyl proteinase genes (SAP). The function of BCR1 in C. parapsilosis with respect to susceptibility against antimicrobial peptides (protamine, RP-1, and LL-37) is in agreement with a recent study (35) where bcr1⌬/⌬ mutants of C. albicans were shown to display an increased susceptibility to the antimicrobial peptides rational peptide 1 (RP-1), human ␤-defensin 2 (hBD-2), and protamine but not LL-37. The mechanism of action of these antimicrobial peptides in fungi is still unknown.…”

“…Similar to C. albicans, bcr1⌬/⌬ mutants of all strains showed increased susceptibility to protamine and RP-1 compared to wildtype and complemented strains. The resistance to LL-37 was not influenced by BCR1, as reported for C. albicans previously (35).…”

“…The effectiveness of caspofungin against Candida biofilms elevates this drug as a proper candidate for fungal biofilm treatment (43). Recently, it was shown that BCR1 not only affects biofilm formation but also increases susceptibility to antimicrobial peptides in C. albicans (35). We identify here three novel physiological traits of C. parapsilosis regulated by BCR1, namely, colony morphology, asparatyl proteinase secretion, and antimicrobial susceptibility toward antimicrobial peptides.…”

“…The positive control is antimycotic-free biofilm, and its activity was arbitrarily set to 1. bcr1⌬/⌬ mutants show increased susceptibility to protamine and RP-1. Recently, it was reported that the susceptibility of C. albicans to antimicrobial peptides is affected by BCR1 (35). We investigated the effect of BCR1 on susceptibility to the antimicrobial peptides LL-37, protamine, and RP-1 in C. parapsilosis (Fig.…”

Interplay between Candida albicans and the Antimicrobial Peptide Armory

“…Examples include the secretion of AMP-binding proteins that re- direct peptide antimicrobials away from microbial structures (52). As presented below, similar mechanisms were also shown for C. albicans (53)(54)(55)(56)(57)(58).…”