The Candida albicans Vacuole Is Required for Differentiation and Efficient Macrophage Killing

Abstract

Yeast-hypha differentiation is believed to be necessary for the normal progression of Candida albicans infections. The emergence and extension of a germ tube from a parental yeast cell are accompanied by dynamic changes in vacuole size and morphology. Although vacuolar function is required during this process, it is unclear if it is vacuolar expansion or some other vacuolar function that is important. We previously described a C. albicans vps11Delta mutant which lacked a recognizable vacuole compartment and with defects in multiple vacuolar functions. These include sensitivities to stress, reduced proteolytic activities, and severe defects in filamentation. Herein we utilize a partially functional VPS11 allele (vps11hr) to help define which vacuolar functions are required for differentiation and which influence interaction with macrophages. Mutant strains harboring this allele are not osmotically or temperature sensitive and have normal levels of secreted aspartyl protease and carboxypeptidase Y activity but have a fragmented vacuole morphology. Moreover, this mutant is defective in filamentation, suggesting that the major role the vacuole plays in yeast-hypha differentiation may relate directly to its morphology. The results of this study support the hypothesis that vacuole expansion is required during germ tube emergence. Both vps11 mutants were severely attenuated in their ability to kill a macrophage cell line. The viability of the vps11delta mutant was significantly reduced during macrophage interaction compared to that in the control strains, while the vps11hr mutant was unaffected. This implies some vacuolar functions are required for Candida survival within the macrophage, while additional vacuolar functions are required to inflict injury on the macrophage.

Mutational Analysis of Candida albicans SNF7 Reveals Genetically Separable Rim101 and ESCRT Functions and Demonstrates Divergence in bro1-Domain Protein Interactions

“…Defects in both vesicle trafficking and pH sensing have been shown to affect hyphal formation (Davis et al 2000b;Gunther et al 2005;Palmer et al 2005;Bernardo et al 2008). Few of our alaninescanning snf7 alleles conferred strong defects in filamentation, which reinforces that few snf7 alleles completely abolished Snf7 function.…”

“…Filamentation-related snf7 phenotypes: Vesicle trafficking and Rim101 activation are both required for filamentation, a critical virulence trait of C. albicans (Bruckmann et al 2000;Kullas et al 2004;Palmer et al 2005;Bernardo et al 2008). We wished to further investigate the role of these processes and their relative contributions to filamentation.…”

Deletion of Vacuolar Proton-translocating ATPase Voa Isoforms Clarifies the Role of Vacuolar pH as a Determinant of Virulence-associated Traits in Candida albicans*

“…Our conclusion that an acidic vacuolar lumen is not essential for C. albicans biofilm formation and macrophage killing in vitro supports that concept. However, it should not diminish the importance of vacuolar functions in pathogenesis, including vacuolar expansion (40,53), trafficking (45,54), and heavy metal sequestration (9,26).…”

“…albicans biofilms were formed and analyzed for metabolic activity using the 2Ј,3Ј-bis-(2-methoxy-4-nitro-5-sulfophenyl)-5-(phenylaminocarbonyl)-2H-tetrazolium hydroxide (XTT) reduction method as previously described (39). Macrophage killing assays were performed as described previously (40). J774A.1 murine macrophage cells (ATCC) and C. albicans strains were co-incubated at a multiplicity of infection of 2 for 24 h. Macrophage viability was assessed using 0.2 M calcein AM and 4 M ethidium bromide homodimer (LIVE/DEAD Viability/Cytotoxicity kit, Invitrogen).…”

Effects of hemin, CO2, and pH on the branching of Candida albicans filamentous forms

“…It is well documented that the proper timing and the rate of Y → H and H → Y morphological transitions are the prerequisites of a successful invasion of the host by C. albicans [35,36,39,47]. Any disturbance in the formation of the hypha may result in the failure of invasive growth and reduced virulence [48,49]. Very importantly, yeast cells and true hyphae are always observed during C. albicans infections, such as oral candidiasis [50] or invasive candidiasis in the spleen, kidney, and liver [51,52].…”