Role of the Cryptococcus neoformans Copper Acquisition Machinery in lethal meningitis
Biochemistry
Cell Biology
Final Report Abstract
The fungus Cryptococcus neoformans (C. neoformans) is a life threatening fungal pathogen, responsible for ~200,000 deaths per year worldwide. C. neoformans preferentially infects individuals who are immunocompromised or suppressed due to HIVAIDS, diabetes, cancer chemotherapy or organ transplant recipients. C. neoformans is acquired through the respiratory route and survival from alveolar macrophage phagocytosis in the lung allows it to disseminate to the brain, where it causes lethal meningitis. Recent advances in the Thiele lab have demonstrated Cu homeostasis mechanisms to be important for C. neoformans virulence and survival during host infection and identified the transcription factor Cuf1 as central switch regulating both-high Cu and low Curesponsive genes. A genome wide analysis using a combinatorial approach of RNA-seq and ChIP-seq identified dozens of new and novel Cuf1-regulated genes, among those, genes previously shown to be involved in cell wall remodeling, connecting Cu homeostasis mechanisms with cell wall remodeling. Strikingly, depletion of Cuf1 and components of the Cu acquisition machinery leads to an impaired growth in presence of cell wall stressors when grown on Cu limiting media. Most excitingly a susceptibility towards cell wall stress was also observed in cells exclusively lacking Bim1, the second highest induced transcript during Cu deficiency, which was recently shown to be involved in Ctr1 mediated Cu uptake. Bim1 is a GPI anchored protein and localizes to the plasma membrane, attached to ß-glucans in the cell wall, but is also partially secreted to the extracellular media. Protein sequence analysis showed that Bim1 possess a homology towards members of the Lytic Polysaccharide Monooxygenase (LPMO) family, which comprises Cu-binding enzymes involved in oxidative degradation of polysaccharides found in the cell wall of plants, fungi and bacteria, suggesting a potential role for Bim1 in cell wall remodeling mechanism during Cu deficiency. In fact, recent experimental data showed that Bim1 deletion effects cell wall chitosan levels, a CW component essential for maintaining cell wall integrity, cell morphology, melanin attachment and more importantly virulence. However, the mechanism of action of how Bim1 deletion effects the cryptococcal cell wall is yet not understood and will need further investigations. Given that depletion of Cuf1 or Bim1 effects cell wall integrity during Cu deficiency, I was able to show that the latter sensitizes C. neoformans to the cell wall targeting drug Caspofungin. Thus creating a novel link between Cu homeostasis mechanism and Caspofungin resistance, which could result in a new avenue of treatment of cryptococcal meningitis, a host niche where C. neoformans senses a low Cu environment.
Publications
- (2018) Genome-wide analysis of the regulation of Cu metabolism in Cryptococcus neoformans. Mol Micro. 108(5): 473-494
Garcia-Santamarina S, Festa RA, Smith AD, Yu CH, Probst C, Ding C, Homer CM, Madhani H, Perfect JR, Thiele DJ
(See online at https://doi.org/10.1111/mmi.13960)
