Cryptococcus gattii urease as a virulence factor and the relevance of enzymatic activity in cryptococcosis pathogenesis

Abstract

Ureases (EC 3.5.1.5) are Ni(2+) -dependent metalloenzymes produced by plants, fungi and bacteria that hydrolyze urea to produce ammonia and CO2 . The insertion of nickel atoms into the apo-urease is better characterized in bacteria, and requires at least three accessory proteins: UreD, UreF, and UreG. Our group has demonstrated that ureases possess ureolytic activity-independent biological properties that could contribute to the pathogenicity of urease-producing microorganisms. The presence of urease in pathogenic bacteria strongly correlates with pathogenesis in some human diseases. Some medically important fungi also produce urease, including Cryptococcus neoformans and Cryptococcus gattii. C. gattii is an etiological agent of cryptococcosis, most often affecting immunocompetent individuals. The cryptococcal urease might play an important role in pathogenesis. It has been proposed that ammonia produced via urease action might damage the host endothelium, which would enable yeast transmigration towards the central nervous system. To analyze the role of urease as a virulence factor in C. gattii, we constructed knockout mutants for the structural urease-coding gene URE1 and for genes that code the accessory proteins Ure4 and Ure6. All knockout mutants showed reduced multiplication within macrophages. In intranasally infected mice, the ure1Δ (lacking urease protein) and ure4Δ (enzymatically inactive apo-urease) mutants caused reduced blood burdens and a delayed time of death, whereas the ure6Δ (enzymatically inactive apo-urease) mutant showed time and dose dependency with regard to fungal burden. Our results suggest that C. gattii urease plays an important role in virulence, in part possibly through enzyme activity-independent mechanism(s).

Global Reprogramming of Host Kinase Signaling in Response to Fungal Infection

“…For CFU assays, the treated cells were washed with fresh drug-free medium 3 times, and then infected with C. neoformans as described above. To test the effects of the examined chemicals on the activity or expression of fungal virulence determinants, we measured urease activity and capsule as described (Feder et al, 2015; Kwon-Chung et al, 1987). …”

Continental Drift and Speciation of the Cryptococcus neoformans and Cryptococcus gattii Species Complexes

“…For example, the two cryptococcal complex species complexes share such virulence-associated phenotypes as polysaccharide capsules (18), thermotolerance of mammalian temperatures (18), melanin production (18), urease (19, 20) and phospholipase (21, 22) activities, intracellular replication (23, 24), nonlytic exocytosis (25, 26), and inositol production (27). Although it is possible that these phenotypes evolved independently, the fact that they are not shared, or rarely shared, by other closely related species supports the view that they evolved in the common ancestor of both the C. neoformans and C. gattii species complexes.…”

Fungal Dimorphism and Virulence: Molecular Mechanisms for Temperature Adaptation, Immune Evasion, and In Vivo Survival

“…Deletion of either gene results in decreased ability for NIC1 Δ and URE1 Δ yeast cells to penetrate the central nervous system [82]. URE1 also contributes to the pathogenesis of Cryptococcus gattii , which primarily causes pulmonary infection without an increased predilection for CNS invasion in animal models [83, 84]. C. gattii URE1 Δ have attenuated virulence during pulmonary infection, reduced capacity to disseminate to the bloodstream, and impaired intracellular replication within macrophages [83].…”