Proteomic profiling of Cryptococcus neoformans

The opportunistic fungal pathogen Cryptococcus neoformans causes life-threatening meningitis in immunocompromised individuals. The expression of virulence factors including capsule and melanin is in part regulated by the cyclic-AMP/Protein Kinase A (PKA) signal transduction pathway. In this study, we investogated the influence of PKA on the composition of the intracellular proteome to obatin a comprehensive understanding of the regulation that underpins virulence. Through quantitative proteomics, enrichment and bioinformatic analyses, and an interactome study, we discovered a conserved pattern of PKA regulation for proteins associated with translation, the proteasome, metabolism, amino acid biosynthesis, and virulence-related functions. PKA regulation of the ubiquitin-proteasome pathway in C. neoformans showed a striking parallel with connections between PKA and protein degradation in chronic neurodegenerative disorders and other human diseases. Further investigation using the proteasome inhibitor bortezomib revealed an impact on capsule production and fungal growth. These results prompted additional studies of the antifungal activity of bortezomib in the context of cAMP signlaing and in combination with fluconazole. Taken together, the data suggest a model whereby PKA activation causes a shift in proteostasis and the function of the endoplasmic reticulum to support the synthesis and export of capsule polysaccharide. Overall, this study revealed a remarkably broad and conserved influence of the cAMP/PKA pathway on the proteome, and identified proteostasis as a potential therapeutic target for the treatment of cryptococcosis.