Abstract
Cryptococcus neoformans is one of the few environmental fungi that can survive within a mammalian host and cause disease. Although many of the factors responsible for establishing virulence have been recognized, how they are expressed in response to certain host-derived cellular stresses is rarely addressed. Here, we characterize the temporal translational response of C. neoformans to oxidative stress. We find that translation is largely inhibited through the phosphorylation of the critical initiation factor eIF2α (α subunit of eukaryotic initiation factor 2) by a sole kinase. Preventing eIF2α-mediated translational suppression resulted in growth sensitivity to hydrogen peroxide (H2O2). Our work suggests that translational repression in response to H2O2 partly facilitates oxidative stress adaptation by accelerating the decay of abundant non-stress-related transcripts while facilitating the proper expression levels of select oxidative stress response factors. Our results illustrate translational suppression as a critical determinant of select mRNA decay, gene expression, and subsequent survival in response to oxidative stress.IMPORTANCE Fungal survival in a mammalian host requires the coordinated expression and downregulation of a large cohort of genes in response to cellular stresses. Initial infection with C. neoformans occurs in the lungs, where it interacts with host macrophages. Surviving macrophage-derived cellular stresses, such as the production of reactive oxygen and nitrogen species, is believed to promote dissemination into the central nervous system. Therefore, investigating how an oxidative stress-resistant phenotype is brought about in C. neoformans not only furthers our understanding of fungal pathogenesis but also unveils mechanisms of stress-induced gene reprogramming. We discovered that H2O2-derived oxidative stress resulted in severe translational suppression and that this suppression was necessary for the accelerated decay and expression of tested transcripts.
Highlights
Cryptococcus neoformans is one of the few environmental fungi that can survive within a mammalian host and cause disease
We used puromycin incorporation and polysome profiling to show that oxidative stress does not result in complete translational inhibition and that many oxidative stress response mRNAs are able to associate with ribosomes
Polysome profiling, which examines the extent of ribosome association with mRNA in lysate by separating out large macromolecular complexes based on density in a sucrose gradient subjected to ultracentrifugation, suggests that the majority of the C. neoformans 40S and 60S subunits are engaged with mRNAs at exponential phase (Fig. 1A)
Summary
Cryptococcus neoformans is one of the few environmental fungi that can survive within a mammalian host and cause disease. Our results illustrate translational suppression as a critical determinant of select mRNA decay, gene expression, and subsequent survival in response to oxidative stress. IMPORTANCE Fungal survival in a mammalian host requires the coordinated expression and downregulation of a large cohort of genes in response to cellular stresses. We discovered that H2O2-derived oxidative stress resulted in severe translational suppression and that this suppression was necessary for the accelerated decay and expression of tested transcripts. We find that translation is severely inhibited in response to H2O2 in an eIF2␣ (␣ subunit of eukaryotic initiation factor 2)-dependent manner. Our work supports translational inhibition as the driving force of initial oxidative stress-induced decay of transcripts abundant under unstressed conditions, with eIF2␣ phosphorylation triggering the decay. This work characterizes the interplay between mRNA translation and decay as it pertains to oxidative stress resistance in a human fungal pathogen
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