Distinct roles of the 7-transmembrane receptor protein Rta3 in regulating the asymmetric distribution of phosphatidylcholine across the plasma membrane and biofilm formation inCandida albicans

Abstract

Fungal pathogens like Candida albicans exhibit several survival mechanisms to evade attack by antifungals and colonize host tissues. Rta3, a member of the Rta1-like family of lipid-translocating exporters has a 7-transmembrane domain (7TMD) topology, similar to the G-protein-coupled receptors (GPCR) and is unique to the fungal kingdom. Our findings point towards a role for the plasma membrane localized Rta3 in providing tolerance to miltefosine, an analog of alkylphosphocholine, by maintaining mitochondrial energetics. Concurrent with miltefosine susceptibility, the rta3Δ/Δ strain displays increased inward translocation (flip) of fluorophore-labelled phosphatidylcholine (PC) across the plasma membrane attributed to enhanced PC-specific flippase activity. We also assign a novel role to Rta3 in the Bcr1-regulated pathway for in vivo biofilm development. Transcriptome analysis reveals that Rta3 regulates expression of Bcr1 target genes involved in cell surface properties, adhesion, and hyphal growth. We show that rta3Δ/Δ mutant is biofilm-defective in a rat venous catheter model of infection and that BCR1 overexpression rescues this defect, indicating that Bcr1 functions downstream of Rta3 to mediate biofilm formation in C. albicans. The identification of this novel Rta3-dependent regulatory network that governs biofilm formation and PC asymmetry across the plasma membrane will provide important insights into C. albicans pathogenesis.

High-resolution mycobiota analysis reveals dynamic intestinal translocation preceding invasive candidiasis

“…6). The RTA3 homolog in C. albicans encodes a putative lipid flippase and contributes to antifungal resistance and biofilm development 36,37 . The functional relevance of RTA3 amplification in C. parapsilosis pathogenesis will require further investigation.…”

Disruption of Membrane Integrity by the Bacterium-Derived Antifungal Jagaricin

“…This could provide an additional explanation for the resistance phenotype of the inositol polyphosphate phosphatases, since an elevated level of highly phosphorylated inositol phosphates would have the same effect. Interestingly, of the three most strongly upregulated jagaricin phospholipid translocases, Rta2 and Rta4 are targets of calcineurin regulation and upregulated under extracellular Ca 2ϩ stress (53,54), and Rta3 has been shown to regulate membrane asymmetry in C. albicans (55). Therefore, membrane asymmetry regulation in response to elevated cytosolic Ca 2ϩ levels might (partially) restore cell homeostasis under the severe stress induced by jagaricin.…”

The Significance of Lipids to Biofilm Formation in Candida albicans: An Emerging Perspective

“…Such data wherein a connection between phospholipid flippase activity and cell adhesion has been established is not available in C. albicans . In this context, it is pertinent to mention the recent identification of Rta3, a 7-transmembrane receptor protein and its roles in regulating the activity of an unidentified PC-specific flippase, adhesion, and biofilm formation in C. albicans [118]. Absence of Rta3 causes an increase in the flip movement of PC plausibly by regulating an unidentified PC-specific flippase; thus perturbing the asymmetric distribution of PC across the plasma membrane [118].…”