Role of Arf GTPases in fungal morphogenesis and virulence

Abstract

Virulence of the human fungal pathogen Candida albicans depends on the switch from budding to filamentous growth, which requires sustained membrane traffic and polarized growth. In many organisms, small GTPases of the Arf (ADP-ribosylation factor) family regulate membrane/protein trafficking, yet little is known about their role in fungal filamentous growth. To investigate these GTPases in C. albicans, we generated loss of function mutants in all 3 Arf proteins, Arf1-Arf3, and 2 Arf-like proteins, Arl1 and Arl3. Our results indicate that of these proteins, Arf2 is required for viability and sensitivity to antifungal drugs. Repressible ARF2 expression results in defects in filamentous growth, cell wall integrity and virulence, likely due to alteration of the Golgi. Arl1 is also required for invasive filamentous growth and, although arl1/arl1 cells can initiate hyphal growth, hyphae are substantially shorter than that of the wild-type, due to the inability of this mutant to maintain hyphal growth at a single site. We show that this defect does not result from an alteration of phospholipid distribution and is unlikely to result from the sole Golgin Imh1 mislocalization, as Imh1 is not required for invasive filamentous growth. Rather, our results suggest that the arl1/arl1 hyphal growth defect results from increased secretion in this mutant. Strikingly, the arl1/arl1 mutant is drastically reduced in virulence during oropharyngeal candidiasis. Together, our results highlight the importance of Arl1 and Arf2 as key regulators of hyphal growth and virulence in C. albicans and identify a unique function of Arl1 in secretion.

Arf1 regulates the ER–mitochondria encounter structure (ERMES) in a reactive oxygen species‐dependent manner

“…Labbaoui et al . have reported that deletion of ARF1 in this pathogen had no impact on hyphal development under the serum‐inducing condition. Interestingly, we found that the mutant showed attenuated filamentation on hypha‐inducing plates, including RPMI‐1640, M199, N ‐acetylcysteine (NAG) and Spider (Fig.…”

“…As C. albicans is a dimorphic pathogenic fungus, morphogenetic switching from yeasts to hyphae is critical for its invasion of host tissues [28,29]. Labbaoui et al [21] have reported that deletion of ARF1 in this pathogen had no impact on hyphal development under the serum-inducing condition. Interestingly, we found that the mutant showed attenuated filamentation on hypha-inducing plates, including RPMI-1640, M199, N-acetylcysteine (NAG) and Spider (Fig.…”

Multiple activities of Arl1 GTPase in the trans-Golgi network

“…Interestingly, a novel role of Arl1 in regulation of fungal morphogenesis and virulence has recently been revealed in a Candida-albicans-infected oropharyngeal candidiasis mouse model (Labbaoui et al, 2017). These studies collectively suggest that yeast Arl1 has important physiological roles in the regulation of anterograde transport from the TGN to the cell surface, which in turn impacts upon the first line of cellular defense, and modulates endosomal trafficking required for cell growth and virulence.…”

“…Genetic alterations of Arl1 as well as its effectors were used to characterize developmental and physiological phenotypes (summarized in Fig. 1) (Chang et al, 2015;Cruz-Garcia et al, 2013;Eiseler et al, 2016;Gehart et al, 2012;Hesse et al, 2013;Hsu et al, 2016;Labbaoui et al, 2017;Lieu et al, 2008;Liu et al, 2006;Lock et al, 2005;Marešová and Sychrová, 2010;Marešová et al, 2012;Murray and Stow, 2014;Price et al, 2005;Torres et al, 2014;Yang and Rosenwald, 2016). In mammalian cells, these functions affect a wide range of fundamental cellular processes, including cell polarity (Lock et al, 2005), innate immunity (Bremond et al, 2009;Lieu et al, 2008;Murray and Stow, 2014;Stanley et al, 2012), lipid droplet and chylomicron formation (Hesse et al, 2013;Jaschke et al, 2012), as well as the secretion of insulin (Gehart et al, 2012), chromogranin A (CruzGarcia et al, 2013) and matrix metalloproteinases (MMPs) (Eiseler et al, 2016).…”

“…In mammalian cells, these functions affect a wide range of fundamental cellular processes, including cell polarity (Lock et al, 2005), innate immunity (Bremond et al, 2009;Lieu et al, 2008;Murray and Stow, 2014;Stanley et al, 2012), lipid droplet and chylomicron formation (Hesse et al, 2013;Jaschke et al, 2012), as well as the secretion of insulin (Gehart et al, 2012), chromogranin A (CruzGarcia et al, 2013) and matrix metalloproteinases (MMPs) (Eiseler et al, 2016). In yeast, Arl1 and its effectors are also involved in numerous functions, such as maintenance of cell wall integrity (Liu et al, 2006), ion homeostasis (Marešová and Sychrová, 2010;Munson et al, 2004;Rosenwald et al, 2002), tolerance to stress factors (Jaime et al, 2012;Marešova et al, 2012;Yang and Rosenwald, 2016), regulation of cell proliferation (Benjamin et al, 2011), the unfolded protein response (UPR) (Hsu et al, 2016) and also in the ability of yeast to cause disease (Labbaoui et al, 2017). In addition, these factors regulate the quality control of the endoplasmic reticulum (ER) (Lee et al, 2011), tissue development (Eisman et al, 2006;Torres et al, 2014) and neuronal growth in Drosophila (Chang et al, 2015), and control cell viability in parasites (Price et al, 2005).…”