Global Role of the Protein Kinase Gcn2 in the Human Pathogen Candida albicans

Abstract

The pathogen Candida albicans responds to amino acid starvation by activating pseudohyphal development and the expression of amino acid biosynthetic genes (GCN response). In Saccharomyces cerevisiae, the GCN response is dependent on Gcn2, which regulates the translation of the transcription factor Gcn4. Therefore, we examined the role of Gcn2 in C. albicans by using molecular, cellular, and genomic approaches. We show that C. albicans GCN2 encodes an eIF2␣ kinase, like its S. cerevisiae homologue. However, GCN4 appears to be regulated mainly at the transcriptional level in C. albicans. Furthermore, the inactivation of C. albicans Gcn2 only partially attenuates growth under amino acid starvation conditions and resistance to the histidine analogue 3-aminotriazole. Our comparison of the Gcn4 and Gcn2 regulons by transcript profiling reinforces the view that Gcn2 contributes to, but is not essential for, the activation of general amino acid control in C. albicans.

A single inhibitory upstream open reading frame (uORF) is sufficient to regulateCandida albicans GCN4translation in response to amino acid starvation conditions

“…To further examine this finding, we compared the sensitivity of gcn2 and gcn4 mutants to a range of 3AT concentrations. In agreement with previous observations (Tripathi et al 2002;Tournu et al 2005), gcn4 mutants are hypersensitive to amino acid starvation conditions and were unable to grow on plates containing 1 mM 3AT (Fig. 1D).…”

“…Loss of GCN2 was reported to cause only a minor decrease in the resistance of C. albicans to 3AT, suggesting that the C. albicans GCN response is not Gcn2 dependent (Tournu et al 2005). To further examine this finding, we compared the sensitivity of gcn2 and gcn4 mutants to a range of 3AT concentrations.…”

“…C. albicans can mount a GCN (general amino acid control) response, where it induces the expression of most amino acid biosynthetic pathways in response to amino acid starvation, dependent on the Gcn4 transcription factor (Tripathi et al 2002). Surprisingly, however, GCN4 expression was thought to mainly be regulated at the transcriptional level in C. albicans, and Gcn2 has been proposed to play only a minor role in the activation of general amino acid control (Tournu et al 2005). We show here that C. albicans Gcn4 expression is subject to both transcriptional and translational controls, but the induction of GCN4 expression is predominantly regulated at the translational level in response to amino acid starvation conditions.…”

Rearrangements of the transcriptional regulatory networks of metabolic pathways in fungi

“…In fact, the C. albicans ortholog of the eIF2a kinase Gcn2 has limited involvement in the AA starvation response since its inactivation only partially attenuates growth under starvation conditions [46] (Figure 2b). This suggests that Gcn4 is a conserved amino-acid biosynthesis regulatory protein in ascomycetes, that it coordinates the AA and tRNA-amycoacyltransferase regulons in a subset of ascomycetes species including C. albicans and N. crassa and that direct posttranscriptional regulation of GCN4 mRNA translation by the Gcn2 kinase is lost or less stringent in some fungal species like C. albicans.…”

Differential virulence of Candida albicansandC. dubliniensis: A role for Tor1 kinase?

“…2). 27 Due to the inability of C. dubliniensis to filament at alkaline pH in nutrient rich conditions and the ability to rescue this phenotype with rapamycin (similar to mds3D) it is our hypothesis that signaling of alkaline pH signals via the Mds3/Sit4 complex is somehow defective. Alternatively, Tor1 may simply have greater kinase activity or perhaps a lower activation threshold in C. dubliniensis relative to C. albicans, which acts to repress downstream activities like filamentation.…”