Mechanisms directing stress-specific outputs from a regulatory hub - Hog1 in Candida albicans

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

Stress-activated protein kinase (SAPK) pathways are important stress signalling modules found in all eukaryotic cells. These pathways comprise of a protein kinase cascade that activates the SAPK by phosphorylation at a conserved TGY motif. However, TGY phosphorylation alone is not sufficient to explain how SAPKs programme stress-specific outputs in response to diverse stress inputs. The Hog1 SAPK is critical for the adaptation of the pathogenic fungus Candida albicans to a diverse range of stresses, and is essential for its virulence. Notably, in addition to TGY phosphorylation, we have found that C. albicans Hog1 is subjected to three further posttranslational modifications in a stress-specific fashion: (a) phosphorylation at T179, (b) oxidation, and (c) S-nitrosylation. Our working hypothesis is that these stress-specific SAPK modifications modulate the stress-specific outputs of Hog1. In this project we will test this, firstly by establishing the impact of blocking these modifications upon the ability of Hog1 to drive stress-specific adaptation in C. albicans. We will then perform complementary interaction, expression and chemogenetic screens to define the Hog1 interactome under different stress conditions. This will allow us to test our prediction that Hog1 phosphorylation, oxidation and S-nitrosylation programme stress-dependent interactions. In addition, the global characterisation of environmentally contingent outputs of the Hog1 interactome will facilitate the identification of those components vital in mediating stress-specific downstream responses. Finally we will establish the impact of the novel posttranslational modifications of Hog1, and the Hog1-dependent stress-specific responses identified in this study, on C. albicans-host interactions and disease progression using well established tools and infection models.

To achieve the maximum impact for our project we will:
1. Ensure that our scientific observations and datasets are disseminated effectively across the academic community
2. Protect and exploit commercially valuable intellectual property that arises during the course of the project.
3. Contribute to public outreach programmes with a view to enhancing the public understanding of science
4. Further enhance our collaborations in the UK and abroad.
5. Provide an excellent training for our PDRAs in medical mycology, molecular biology, genomics and infection biology.

ACADEMIC DISSEMINATION: We will ensure that our work is disseminated broadly across the academic community through publication in leading journals, presentations at the top international conferences in our field, collaboration with international colleagues, the release of datasets through recognised public repositories and our personal websites, and through the activities of the Wellcome Trust Strategic Award in Medical Mycology and Fungal Immunology.

RELEVANCE TO HUMAN HEALTH AND COMMERCIAL EXPLOITATION: This project addresses an important biological question of relevance to human health and we will protect and exploit potentially valuable findings. The relevance to human health lies at two levels.
A. We will establish how the Hog1 SAPK regulates key fitness attributes in a major pathogen of humans. Fungal infections represent a significant and understudied medical problem (Science vol 336, 647). C. albicans is widespread in humans, a frequent cause of oral thrush and vaginitis, and the most prevalent cause of life-threatening systemic fungal infections in immunocompromised patients. Candida is the fourth leading cause of hospital-acquired bloodstream infections with a mortality rate above 40%, exceeding that of all Gram-negative bacterial septicaemias. Furthermore, systemic fungal infections significantly extend the average length of stay of intensive care patients, having a major impact upon medical care budgets (~1000 Euros per day per infected patient). Efforts to extend and improve the efficacy of antifungal therapies depend on a better understanding of fungal pathobiology. This project directly addresses this need because stress adaptation is critical for fungal virulence and disease progression, and our project is likely to provide information that leads to improvements in antifungal therapies. This view is reinforced by the support from NovoBiotics, an SME developing novel antimicrobial peptides. Our work will reveal mechanisms by which Hog1-related mechanisms promote the resistance of Candida to these peptides, thereby allowing Novabiotics to develop approaches that circumvent these resistance mechanisms. This principle can be extended to other antifungal therapies because Hog1 also promotes resistance to other types of antifungal drug.
B. SAPKs are highly conserved and the mechanisms we are examining in C. albicans are conserved in human cells. Hence, our findings will be translatable to human systems where the SAPKs p38 and JNK1 regulate cytokine responses, T cell proliferation, apoptosis and differentiation as well as stress adaptation. All of these processes underpin human health and represent attractive therapeutic targets.

PUBLIC OUTREACH: We will continue our contributions to local and national public outreach programmes as detailed in the Pathways to Impact.

COLLABORATIONS: This project involves the establishment of a new international collaboration (with Morten Grotli, University of Gothenburg) which provides access to novel molecules that facilitate a chemogenomic screen for Hog1 interactors. This new collaboration strengthens our network of eminent international collaborators.

TRAINING: We will provide an excellent research training in fungal genomics, molecular and cell biology and infection biology for our PDRAs. Also, we will enhance their career prospects by providing training in transferable skills and networking.