Abstract
Ecm33 is a glycosylphosphatidylinositol-anchored protein in the human pathogen Candida albicans. This protein is known to be involved in fungal cell wall integrity (CWI) and is also critical for normal virulence in the mouse model of hematogenously disseminated candidiasis, but its function remains unknown. In this work, several phenotypic analyses of the C. albicans ecm33/ecm33 mutant (RML2U) were performed. We observed that RML2U displays the inability of protoplast to regenerate the cell wall, activation of the CWI pathway, hypersensitivity to temperature, osmotic and oxidative stresses and a shortened chronological lifespan. During the exponential and stationary culture phases, nuclear and actin staining revealed the possible arrest of the cell cycle in RML2U cells. Interestingly, a “veil growth,” never previously described in C. albicans, was serendipitously observed under static stationary cells. The cells that formed this structure were also observed in cornmeal liquid cultures. These cells are giant, round cells, without DNA, and contain large vacuoles, similar to autophagic cells observed in other fungi. Furthermore, RML2U was phagocytozed more than the wild-type strain by macrophages at earlier time points, but the damage caused to the mouse cells was less than with the wild-type strain. Additionally, the percentage of RML2U apoptotic cells after interaction with macrophages was fewer than in the wild-type strain.
Highlights
The fungal cell wall is an essential organelle that is required for the maintainance of cell integrity and plays an important role in primary interactions between pathogenic fungi and their hosts
Cells were treated with glusulase to obtain more than 90% protoplasts and these were incubated in regeneration conditions for 0, 3, or 24 h
We propose a model of C. albicans-macrophage interaction in which more than 30% of SC5314 C. albicans cells ingested by RAW 264.7 died through apoptosis after 12 h of interaction (Cabezón et al, under revision)
Summary
The fungal cell wall is an essential organelle that is required for the maintainance of cell integrity and plays an important role in primary interactions between pathogenic fungi and their hosts. The composition of the Candida albicans cell wall consists of β-1,6-glucan, β-1,3-glucan and chitin, as well as different attached proteins, including glycosylphosphatidylinositol (GPI) proteins (Chaffin, 2008; Free, 2013). These GPI proteins contain a C-terminal domain that allows for linkage to a GPI anchor and might target proteins to the membrane or the cell wall. Recent proteomic analysis of the extracellular medium of RML2U relates Ecm to the proper functioning of the classical secretion pathway and to the composition, shape, and quantity of extracellular vesicles (Gil-Bona et al, 2015b). There is evidence of crosstalk between the TOR and cell wall integrity (CWI) pathways (Fuchs and Mylonakis, 2009)
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