Abstract
Iron is essential for the growth of almost every organism. Importantly, iron-withholding is also a mechanism for the host to against microbial infection. Microbial pathogens have developed different systems to acquire iron from the host and their surrounding environments. In addition, iron availability is shown to serve as a signal to induce the expression of virulence traits of pathogens. Candida albicans, an opportunistic fungal pathogen, usually presents as a commensal in the host. However, when the host becomes immunocompromised, it can cause life-threatening system infections. C. albicans harbors at least three different iron-uptake systems, including a siderophore uptake system mediated by a ferrichrome siderophore transporter Sit1. CaSit1 not only does uptake siderophore, but is also involved in C. albicans invasion to the host tissues. Transcription of the CaSIT1 gene is highly expressed at the low iron condition, while is repressed in high iron environment. The main focus of this study is to examine transcriptional regulation of CaSIT1 by analyzing the 5’UTR of CaSIT1 fused with a lacZ reporter gene. Serial deletion of the promoter region of CaSIT1 revealed a 22-bp cis-regulatory element that is responsible for gene repression at high-iron condition, while a 27-bp region and a 23-bp region are involved in gene activation under a low-iron condition. In addition, electrophoretic mobility shift assays were performed to examine proteins possibly interacting with these elements. The results suggest that there is a DNA binding protein represses CaSIT1 in high iron condition. Then, DNA affinity precipitation assay and LC-MS/MS were carried out to identify the protein which interacts with this cis-element. Together, this study provides an important insight for our understanding how C. albicans regulates its virulence-related gene in response to the host environments, such as iron availability.