Taking in account that exposure of Δhog1 cells PRIMA-1MET cell line to high iron concentrations further increased the comparably high basal intracellular ROS levels in the mutant, the decreased viability of the Δhog1

mutant under such conditions could be due to elevated oxidative stress. However, other EX 527 purchase mechanisms independent from Hog1p were also described for the initiation of oxidative stress responses [52]. These mechanisms could allow also the mutant strains to adapt to the stress conditions so that the reduced viability was observed only as immediate response and did not lead to significant growth defects. It has yet to be elucidated which elements downstream of Hog1p provide the link between the HOG pathway and factors which regulate reductive iron uptake. As many Hog1p repressed genes, including those involved in iron uptake (FET34, FRE10, FTR1 and RBT5), were also found to be repressed by Tup1p [27], a role for this global co-repressor downstream of Hog1p could be assumed. NVP-BGJ398 price Indeed, a role of Tup1p in regulating iron uptake has been reported [17]. However, the details remain to be elucidated. In this study, we used several single gene deletion mutants which were generated by different approaches

[31, 44, 53, 54]. All mutant strains were descendants of the strain CAI-4 [55], in which both copies of IRO1 are deleted. Additionally, all strains ectopically express URA3. IRO1 is a gene that encodes a transcription factor with a potential role in iron utilization. Expression of IRO1 in a Δaft1 S. cerevisiae strain restored growth in iron depleted media. However, a role of IRO1 in C. albicans iron metabolism is not confirmed [56].

On the other hand, ectopic expression of URA3 has been shown to affect several features of C. albicans, such as hyphal morphology, adhesion, virulence and cellular proteome in addition to Ura3p activity [57, 58]. In all of our experiments, the DAY286 reference strain behaved similar to the WT SC5314. Additionally, CNC13 and JMR114 (Δhog1) as well as BRD3 and JJH31 (Δpbs2) showed similar features. Thus, no effects of the ectopic expression of URA3 or the absence of IRO1 were observed. Conclusions We report here for the first time in fungi, that the conserved stress activated MAP kinase Hog1p Phosphatidylinositol diacylglycerol-lyase of C. albicans is involved in the response to changes in extracellular iron levels. Previous studies had only shown that deletion of HOG1 led to the de-repression of HAIU components in this fungus under otherwise repressive conditions. We found that repression of HAIU components of the reductive pathway by Hog1p occurs independently of environmental iron availability. Exposure of C. albicans to high iron concentrations renders Hog1p hyper-phosphorylated. Thus, our results suggest that Hog1p has a dual role in C. albicans iron homeostasis.