Depletion of the Cullin Cdc53p Induces Morphogenetic Changes in Candida albicans

Abstract

Candida albicans is an important opportunistic human fungal pathogen that can cause both mucosal and systemic infections in immunocompromised patients. Critical for the virulence of C. albicans is its ability to undergo a morphological transition from yeast to hyphal growth mode. Proper induction of filamentation is dependent on the ubiquitination pathway, which targets proteins for proteasome-mediated protein degradation or activates them for signaling events. In the present study, we evaluated the role of ubiquitination in C. albicans by impairing the function of the major ubiquitin-ligase complex SCF. This was done by depleting its backbone, the cullin Cdc53p (orf19.1674), using a tetracycline downregulatable promoter system. Cdc53p-depleted cells displayed an invasive phenotype and constitutive filamentation under conditions favoring yeast growth mode, both on solid and in liquid media. In addition, these cells exhibited an early onset of cell death, as judged from propidium iodide staining, suggesting that CDC53 is an essential gene in C. albicans. To identify Cdc53p-dependent pathways in C. albicans, a genome-wide expression analysis was carried out that revealed a total of 425 differentially expressed genes (fold change, >2; P < 0.05) with 192 up-and 233 downregulated genes in the CDC53-repressed mutant compared to the control strain. GO term analysis identified biological processes significantly affected by Cdc53p depletion, including amino acid starvation response, with 14 genes being targets of the transcriptional regulator Gcn4p, and reductive iron transport. These results indicate that Cdc53p enables C. albicans to adequately respond to environmental signals.Candida albicans is an important human fungal pathogen that can cause both superficial and systemic infections in immunocompromised patients (57). The ability of this fungus to grow in and change between different morphological forms such as budding yeast (round or oval cells), true hyphae (filamentous cells without constrictions at the sites of septation), and pseudohyphae (chains of elongated cells with constrictions at the sites of septation) (66) is considered critical for its virulence (12, 41). Several environmental conditions are known to trigger a switch from yeast to filamentous growth mode, such as neutral pH, nutrient starvation, contact to solid surfaces, and growth in the presence of serum at 37°C, the latter mimicking the bloodstream and other environments in the host (reviewed in reference 21).Various signal transduction pathways contribute to the regulation of the yeast-filament growth switch, forming a complex network that converges on a common set of hypha-specific genes (35). As in Saccharomyces cerevisiae, a mitogen-activated protein kinase (MAPK) pathway is involved in filamentation in C. albicans, consisting of the kinases Cst20p, probably Ste11p, Hst7p, Cek1p, and the executing transcription factor Cph1p (reviewed in references 11 and 47). Further filamentationinducing pathways include the cyclic AMP-dependent protein kinas...

Regulatory Circuitry Governing Fungal Development, Drug Resistance, and Disease

“…It was recently proposed that Cdc53, a component of a ubiquitin-ligase complex, directly regulates Gcn4 and, therefore, amino-acid-induced morphogenesis (584). The depletion of CDC53 promotes pseudohyphal growth as well as an amino acid starvation-like transcriptional response (584).…”

G 1 /S Transcription Factor Orthologues Swi4p and Swi6p Are Important but Not Essential for Cell Proliferation and Influence Hyphal Development in the Fungal Pathogen Candida albicans

“…Depletion of the G 1 cyclin Cln3p, on the other hand, resulted in a G 1 phase arrest in yeast cells and subsequent development of hyphae and pseudohyphae (7,22), supporting a link between G 1 phase and hyphal development. Depletion of Cln3p in S. cerevisiae, on the other hand, did not activate development (27,59), and blocking/delaying other cell cycle stages in C. albicans did not result in true hyphae (1,5,6,10,13,14,18,47,68,75,80,83).…”

Orthologues of the Anaphase-Promoting Complex/Cyclosome Coactivators Cdc20p and Cdh1p Are Important for Mitotic Progression and Morphogenesis in Candida albicans

“…The Skp/Cullin/F-box (SCF) E3 ubiquitin ligase complex targets degradation of proteins during G 1 /S to G 2 /M phases of the cell cycle in most systems, and orthologues of some components have been characterized in C. albicans, including Cdc4p, Grr1p, and Cdc53p (4,14,40,74). Absence of these factors resulted in pseudohyphal and/or hyphal growth.…”