PI3K signaling of autophagy is required for starvation tolerance and virulenceof Cryptococcus neoformans

Abstract

Autophagy is a process by which cells recycle cytoplasm and defective organelles during stress situations such as nutrient starvation. It can also be used by host cells as an immune defense mechanism to eliminate infectious pathogens. Here we describe the use of autophagy as a survival mechanism and virulence-associated trait by the human fungal pathogen Cryptococcus neoformans. We report that a mutant form of C. neoformans lacking the Vps34 PI3K (vps34Δ), which is known to be involved in autophagy in ascomycete yeast, was defective in the formation of autophagy-related 8-labeled (Atg8-labeled) vesicles and showed a dramatic attenuation in virulence in mouse models of infection. In addition, autophagic vesicles were observed in WT but not vps34Δ cells after phagocytosis by a murine macrophage cell line, and Atg8 expression was exhibited in WT C. neoformans during human infection of brain. To dissect the contribution of defective autophagy in vps34Δ C. neoformans during pathogenesis, a strain of C. neoformans in which Atg8 expression was knocked down by RNA interference was constructed and these fungi also demonstrated markedly attenuated virulence in a mouse model of infection. These results demonstrated PI3K signaling and autophagy as a virulence-associated trait and survival mechanism during infection with a fungal pathogen. Moreover, the data show that molecular dissection of such pathogen stress-response pathways may identify new approaches for chemotherapeutic interventions.

Sensing of mammalian IL-17A regulates fungal adaptation and virulence

“…6c), were not similarly affected by IL-17A. Thus, much like in Cryptococcus neoformans 18 , the TOR-dependent autophagy pathway might be involved in virulence in vivo. To clarify this issue, we evaluated whether autophagy could be demonstrated at sites of infection, and the impact on fungal adaptation and virulence.…”

“…S1e-h), a finding highlighting the complex cross-regulation between Th1 and Th17 responses that would also include an action on fungal cells. Host IL-17A sensing occurs via the TOR nutrient sensing pathway, a conserved mechanism among yeasts and filamentous fungi 33 that regulates autophagy 34 , cell growth and virulence 4,18,35 . Autophagy is an evolutionary conserved response to stress that has been linked to important protective roles in mammalian cells 36 .…”

“…19.130) of the serine/threonine protein kinase Vps15. Vps15 has a role in yeast autophagy in response to nutrient starvation 17 , and functions as a membrane-associated complex with class III phosphoinositide 3-kinase 17,18 . Overall, the IL-17A-modulated transcriptional profile mirrored that induced in C. albicans by rapamycin 4 , suggesting a role for inhibition of the target of rapamycin (TOR) signalling pathway in the activation of autophagy by IL-17A.…”

Mating Pheromone in Cryptococcus neoformans Is Regulated by a Transcriptional/Degradative “Futile” Cycle

“…Episomal expression of plasmids in C. neoformans have statistically insignificant differences in virulence from wild-type parental strains (35). Fungal viability was confirmed by growth of inocula on YPD agar.…”

Survival Defects of Cryptococcus neoformans Mutants Exposed to Human Cerebrospinal Fluid Result in Attenuated Virulence in an Experimental Model of Meningitis

“…Because of their multifaceted nature, it is unclear which aspect is responsible for the CSF survival defect of this mutant. Recently, 1-phosphatidylinositol-3-kinase (PI3K) was found to be required for the formation of autophagic vesicles under nutrient starvation and linked to the virulence of C. neoformans (23). Nutrient starvation, however, is not likely responsible for the severe CSF phenotype because the pik1⌬ mutant survived like the WT in minimal media such as PBS and CSF itself contains readily available carbon sources (55).…”