Post-Transcriptional Regulation of the Sef1 Transcription Factor Controls the Virulence of Candida albicans in Its Mammalian Host
Figure 4
Sfu1 and Ssn3 mediate opposing effects on Sef1 stability and virulence.
a) Sef1 protein is stabilized in an sfu1ΔΔ mutant. Wild-type or sfu1ΔΔ strains containing Sef1-Myc were propagated in iron-replete medium containing 2 mg/ml cycloheximide. Samples were recovered at the indicated time points, and Sef1-Myc was visualized using monoclonal antibodies against the Myc epitope, followed by incubation with secondary antibodies that were coupled to infrared dyes and quantified using a Li-Cor instrument. Note that a single band corresponding to higher mobility (unphosphorylated) Sef1 is present in both strains. b) Sef1 protein is destabilized in the ssn3ΔΔ mutant. The experiment was performed as above, except that cells were propagated in iron-depleted medium containing cycloheximide. Note that phosphorylated Sef1 recovered from wild-type cells runs with slower mobility. c) Model for Sef1 regulation by Sfu1 and Ssn3 under iron-replete vs. iron-depleted conditions. Note that, even under iron-replete conditions when nuclear Sfu1 functions as a transcriptional repressor, a cytoplasmic pool of Sfu1 is available (Figure S4) that could participate in Sef1 sequestration. d) Overexpression of SFU1 leads to attenuated C. albicans virulence in a murine bloodstream infections model. * signifies p<0.02, log-rank test. E) Deletion of SSN3 leads to attenuated C. albicans virulence, and restoration of one copy of wild-type SSN3 complements the defect. * signifies p<0.0001.