(JOINT PROPOSAL WITH NEWCASTLE UNIVERSITY) MECHANISMS LINKING PHOSPHATE ACQUISITION, STRESS RESISTANCE, AND VIRULENCE IN THE FUNGAL PATHOGEN CANDIDA ALBICANS.

Mechanisms linking phosphate acquisition, stress resistance, and virulence in the fungal pathogen Candida albicans

"Pathogenic microbes must be able to mount robust stress responses to allow them to survive the barrage of chemical weapons released by the host's immune system to kill invading pathogens. The importance of such immune-based defences is highlighted by the fact that patients with weakened immune systems are particularly prone to both bacterial and fungal infections. We recently made the unexpected finding that intracellular phosphate levels, which are controlled by the regulatory factor Pho4, are essential for the human fungal pathogen Candida albicans to survive many stresses encountered during infection such as superoxide stress. Because of this, engineered C. albicans cells lacking Pho4 are very sensitive to killing by macrophages, and are much less virulent than wild-type Candida cells in various infection models. Our pilot studies have shown that the superoxide stress-sensitivity, exhibited by cells lacking Pho4, is due to a previously uncharacterised role for phosphate in regulating copper homeostasis. Copper is an essential metal co-factor for the C. albicans Sod1 superoxide dismutase enzyme, and we find that Sod1 activity is impaired in cells lacking Pho4 resulting in reduced resistance to superoxide stress.

In this proposal we aim to build on these novel connections linking phosphate acquisition and metal homeostasis to the stress resistance and virulence of a major human pathogen, to ask two key questions: (a) how does reduced intracellular phosphate levels de-regulate copper homeostasis resulting in acute sensitivity to superoxide stress, and (b) can the prevention of phosphate acquisition in C. albicans be exploited as a novel therapeutic strategy to help prevent life-threatening infections? This project benefits from our complementary areas of expertise in C. albicans stress responses, infection modelling and the study of metal homeostasis mechanisms. Specifically, we will utilise a powerful combination of precision molecular tools to characterise the pathways that regulate Pho4 in C. albicans, and state-of-the-art technologies to study metal-protein interactions to determine how phosphate impairs copper homeostasis. In addition, we will translate our knowledge of Pho4 regulation in C. albicans and perform a high-throughput screen to identify drugs that inhibit phosphate acquisition. This, in combination with the subsequent testing of such compounds in infection models, has the exciting potential to identify new drugs that inhibit C. albicans pathogenicity.

This project is important for several reasons. First of all it will increase our fundamental understanding of how phosphate acquisition is vital for stress resistance and virulence of a major fungal pathogen of humans. Secondly, as intracellular phosphate homeostasis is emerging as a key virulence determinant in a number of other human and plant fungal pathogens, our findings in C. albicans may have wide reaching consequences for other host-fungus interactions. Finally, it has the potential to identify new drugs that block phosphate acquisition and attenuate fungal virulence. This is important because there is a limited repertoire of antifungal drugs available to treat systemic infections and resistance to such drugs is now a major problem. Indeed, despite the availability of such drugs, C. albicans causes over 400,000 life-threatening systemic infections each year, thus highlighting the urgent need for new effective therapies"