Role of the 14–3–3 protein in carbon metabolism of the pathogenic yeast Candida albicans

Abstract

We previously demonstrated that the pathogenic yeast Candida albicans effectively adapts to utilize L-sorbose (Sou + ) by a novel mechanism based on the loss of one copy of chromosome 5, probably due to the reduction of copy number of a negative regulator located on this chromosome. We report here another negative regulator of Lsorbose utilization, an orthologue of the Saccharomyces cerevisiae BMH1 gene, which encodes the evolutionarily conserved protein 14-3-3. This essential gene is located on chromosome 1, does not have paralogues, and is supposedly a component of the regulatory network. Experiments involving disruption of one allele of BMH1 and overexpression of BMH1 revealed that BMH1 represses the transcription of SOU1, which is responsible for the utilization of L-sorbose. Although the exact mechanism of the interaction between BMH1 and SOU1 is not known, it is clear that the control is based on the ratio of gene copy number, and that BMH1 does not control the loss of chromosome 5, the major mechanism producing Sou + mutants. We propose that function of BMH1 as a negative regulator of SOU1 contributes to a general cellular homeostasis. This is a first report on the role of the C. albicans essential gene BMH1 as a negative regulator of the utilization of secondary carbon source in yeast, which further substantiates the involvement of 14-3-3 proteins in diverse functions.

Loss and gain of chromosome 5 controls growth of Candida albicans on sorbose due to dispersed redundant negative regulators

“…However, Sou Ϫ strains became Sou ϩ because of hemizygous deletion of all five regions or hemizygous deletions that combined the regions from two putative pathways: A, B, and 135; A, 135, C, and 139; and A, C, and 139. We have previously reported a weak CSU on chromosome 1, an essential gene BMH1, deletion of one copy of which increased SOU1 transcript by twofold (10). In addition, three other potential weak regulators, CSU2, CSU5, and CSU6, from different chromosomes, were partially characterized (G. Janbon, Y.-K.W., and E.R., unpublished data).…”

“…In this plasmid, a chromosome fragment was coexpressed with SOU1, which confers a Sou ϩ phenotype (ref. 10; and see Supporting Materials and Methods, which is published as supporting information on the PNAS web site). When a plasmid insert carried a putative CSU gene for a negative regulator, SOU1 was repressed, and the Sou Ϫ phenotype of the strain CAF4-2 was restored.…”

“…During Sou Ϫ -to-Sou ϩ transition, the SOU1 transcript increases several-fold, although both SOU1 copies and its upstream sequences remain intact, suggesting that the copy number of chromosome 5 controls the copy number of a (CSU) gene, encoding a negative regulator residing on this chromosome. The ratio between CSU and SOU1, thus, determines the Sou phenotype (3,(8)(9)(10)(11).…”

Transcriptional Regulatory Circuitries in the Human Pathogen Candida albicans Involving Sense–Antisense Interactions

“…Uridine (50 mg/ml) was added when needed. The proper growth and handling of cells preventing chromosomal instability was previously reported (Rustchenko-Bulgac 1991;Perepnikhatka et al 1999;Wang et al 2004;Ahmad et al 2008).…”

“…We used an important tool, a low copy number replicative plasmid pCA88 overexpressing the metabolic gene SOU1, thus causing the Sou 2 recipient strain to utilize sorbose, Sou 2 / Sou + (Wang et al 2004). This plasmid was previously used for preparing a Ch5 DNA library and subsequently cloning a negative regulatory gene CSU51, as well as unique regions carrying other putative CSUs on Ch5, as based on the reversal of sorbose utilization, Sou + / Sou 2 .…”