THR1 mediates GCN4 and CDC4 to link morphogenesis with nutrient sensing and the stress response in Candida�albicans

Abstract

Candida albicans (C. albicans) CDC4 (CaCDC4), encoding the F-box protein for the substrate specificity of the Skp1-cullin-F-box E3 ubiquitin ligase complex, suppresses the yeast-to-filament transition in C. albicans. In our previous study, Thr1 was identified as a CaCdc4-associated protein using affinity purification. THR1 encodes a homoserine kinase, which is involved in the threonine biosynthesis pathway. The present study generated a strain with repressible CaCDC4 expression and continuous THR1 expression. Colony and cell morphology analyses, as well as immunoblotting, revealed that the Thr1 protein was detectable under conditions in which the expression of CaCDC4 was repressed and that the filaments resulting from the repressed expression of CaCDC4 were suppressed by the constitutive expression of THR1 in C. albicans. Additionally, by using the CaSAT1-flipper method, the present study produced null mutants of THR1, GCN4, and CaCDC4. The phenotypic consequences were evaluated by growth curves, spotting assays, microscopic analysis, reverse transcription-polymerase chain reaction and XTT-based biofilm formation ability. The results revealed that fewer cells lacking THR1 entered the stationary phase but had no apparent morphological alteration. It was observed that the expression of THR1 was upregulated concurrently with GCN4 during nutrient depletion and that cells lacking GCN4 rescued the lethality of cells in the absence of THR1 in conditions accumulating homoserine in the threonine biosynthesis pathway. Of note, it was found that cells with either CaCDC4 or THR1 loss were sensitive to oxidative stress and osmotic stress, with those with THR1 loss being more sensitive. In addition, it was observed that cells with loss of either CaCDC4 or THR1 exhibited the ability to increase biofilm formation, with those lacking CaCDC4 exhibiting a greater extent of enhancement. It was concluded that CaCDC4 is important in the coordination of morphogenesis, nutrient sensing, and the stress response through THR1 in C. albicans.

Molecular Characterization of Candida auris Isolates at a Major Tertiary Care Center in Lebanon

“…C. albicans cells lacking THR1 accumulate the toxic biosynthetic intermediate homoserine and are attenuated in terms of virulence and die rapidly upon threonine starvation and serum incubation ( Kingsbury and McCusker, 2010a , b ). Moreover, C. albicans THR1-depleted mutants exhibited increased sensitivity to oxidative and osmotic stress ( Lee et al, 2018 ). Regarding the phylogenetic analysis, different findings have been reported globally.…”

Systematic Identification and Characterization of Five Transcription Factors Mediating the Oxidative Stress Response in Candida Albicans

“…Altogether, these ndings suggest that other signaling pathways are likely involved in the C. albicans oxidative stress response to H 2 O 2 . The transcription factor Stp2 is reported to contribute to nutrient adaption/sensing and bio lm formation in C. albicans via targeting the rapamycin (TOR) signaling pathway [40][41][42][43]. Therefore, investigating whether our ve identi ed transcription factors participate in the TOR signaling pathway in the presence of ROS is an intriguing area of future interest.…”

A putative F‐box‐domain‐encoding gene AOL_s00076g207 regulates the development and pathogenicity of Arthrobotrys oligospora

“…F-box protein plays crucial roles in plant growth and development as well as plant responses to environmental stimuli by tagging the substrate to proteasomal degradation [29]. In the Candida albicans CDC4 (CaCDC4) that encodes the F-box protein, it was found that the cells with loss of CaCDC4 were sensitive to oxidative stress and osmotic stress [30]. The F-box protein Fbx15 has been shown to regulate stress responses, gliotoxin production, environmental adaptation and virulence in Aspergillus fumigatus [31].…”