3 / Transcriptomic analysis of non –invasive infections by Aspergillus fumigatus: the case of sino-nasal aspergillosis (SNA) in dogs.

TitleStress-contingent changes in Candida albicans SAPK pathway architecture and regulation. ObjectivesThe Hog1 stress-activated protein kinase (SAPK) in Candida albicans is activated in response to divergent stresses and is essential for virulence. Hog1 activation is dependent on the upstream Pbs2 MAPKK and the Ssk2 MAPKKK, but little is known about how different stress signals are sensed and relayed to the Hog1 module. Based on studies in model yeast, a two-component related signalling pathway (comprising of three stress sensing histidine kinases, the Ypd1 phosphorelay protein, and the Ssk1 response regulator) is predicted to regulate C. albicans Hog1. The objective of this work was to dissect both two-component dependent and independent mechanisms of signal transduction to Hog1 to aid our long term goal in identifying compounds that prevent Hog1 activation and C. albicans virulence. MethodsPanels of gene deletion and tagged C. albicans strains were generated to allow a dissection of protein-protein interactions within the Hog1 module, and an investigation of the impact of different stresses on the activation and cellular localisation of pathway components. ResultstWe find that the Ssk1 response regulator plays a global two-component independent role in Hog1 regulation. Specifically, Ssk1 functions as a scaffolding protein promoting interactions between Pbs2 and Ssk2 within the Hog1 module. Osmotic stress triggers the phosphorylation of Pbs2 which promotes dissociation from the scaffold and the nuclear accumulation of this MAPKK. Strikingly, other stresses such as oxidative stress, fail to induce Pbs2 phosphorylation. Instead we present evidence that oxidative stress-mediated Hog1 activation is due to the inhibition of specific downstream negative regulators of Hog1. ConclusionOur studies have shown for the first time that the architecture of the Hog1 SAPK module is altered in a stress-specific manner, and also challenge the paradigm that SAPK activation is dependent on the activation of upstream regulators. Moreover, our identification of key protein-protein interactions within the Hog1 module involving the Ssk1 response regulator opens up new strategies to identify compounds that inhibit Hog1 signalling in an important fungal pathogen of humans.