Connecting virulence pathways to cell-cycle progression in the fungal pathogen Cryptococcus neoformans

Abstract

Proliferation and host evasion are critical processes to understand at a basic biological level for improving infectious disease treatment options. The human fungal pathogen Cryptococcus neoformans causes fungal meningitis in immunocompromised individuals by proliferating in cerebrospinal fluid. Current antifungal drugs target “virulence factors” for disease, such as components of the cell wall and polysaccharide capsule in C. neoformans. However, mechanistic links between virulence pathways and the cell cycle are not as well studied. Recently, cell-cycle synchronized C. neoformans cells were profiled over time to identify gene expression dynamics (Kelliher et al., PLoS Genet 12(12):e1006453, 2016). Almost 20% of all genes in the C. neoformans genome were periodically activated during the cell cycle in rich media, including 40 genes that have previously been implicated in virulence pathways. Here, we review important findings about cell-cycle-regulated genes in C. neoformans and provide two examples of virulence pathways—chitin synthesis and G-protein coupled receptor signaling—with their putative connections to cell division. We propose that a “comparative functional genomics” approach, leveraging gene expression timing during the cell cycle, orthology to genes in other fungal species, and previous experimental findings, can lead to mechanistic hypotheses connecting the cell cycle to fungal virulence.

Calcium Binding Protein Ncs1 Is Calcineurin Regulated in Cryptococcus neoformans and Essential for Cell Division and Virulence

“…As cell division is linked to the cell cycle, we evaluated whether cells lacking NCS1 displayed defects in cell cycle regulation by measuring the levels of two transcripts associated with different stages of the cell cycle: the G 1 cyclin encoded by CNL1 ( 52 ) and the S phase DNA replication licensing factor encoded by MCM2 ( 53 , 54 ). We also measured the transcript levels of the G protein-coupled receptor encoded by GPA2 , which displays oscillatory expression during the cell cycle ( 53 , 54 ). All three genes were upregulated in the ncs1Δ strain compared to the WT after 4 h of growth in YPD ( Fig.…”

“…Given that expression of ∼40 virulence-associated genes is linked to the cell cycle in C. neoformans , the control of this process is fundamental to disease progression ( 53 ). In S. cerevisiae , Ca 2+ homeostasis is linked to cell cycle regulation, as a decrease in intracellular Ca 2+ leads to transient arrest in the G 1 phase, followed by interruption in the G 2 /M phase ( 27 , 56 – 58 ).…”

A Unique Dual-Readout High-Throughput Screening Assay To Identify Antifungal Compounds with Aspergillus fumigatus

“…The site of bud formation requires extensive cell wall remodeling and synthesis for the emergence and generation of the daughter cell, and chitin synthesis is required for primary septum formation between mother and daughter cells. Thus, the cell wall synthesis genes are expressed differentially throughout the cell cycle ( 39 , 40 ) and the cell wall integrity pathway is activated at a distinct point during the cell cycle ( 41 , 42 ). The mammalian kinome studies of PIK-75 identified CDK7, CDK9, and CDK14 as targets of PIK-75 ( 43 ).…”

Calcium binding protein Ncs1 is calcineurin-regulated inCryptococcus neoformansand essential for cell division and virulence

“…Given that expression of ~40 virulence-associated genes is linked to the cell cycle in C. neoformans, the control of this process is fundamental to disease progression (51). In S. cerevisiae, Ca 2+ homeostasis is linked to cell cycle regulation as a decrease in intracellular Ca 2+ leads to transient arrest in the G1 phase, followed by interruption in the G2/M phase (27,(54)(55)(56).…”

“…As cell division is linked to the cell cycle, we evaluated whether cells lacking NCS1 displayed defects in cell cycle regulation by measuring the levels of two transcripts associated with different stages of the cell cycle: the G1 cyclin encoded by CNL1 (50) and the S phase DNA replication licensing factor encoded by MCM2 (51,52).…”