The interactome of Cryptococcus neoformans Rmt5 reveals multiple regulatory points in fungal cell biology and pathogenesis

Abstract

Protein arginine methylation is a key post-translational modification in eukaryotes that modulates core cellular processes, including translation, morphology, transcription, and RNA fate. However, this has not been explored in Cryptococcus neoformans, a human-pathogenic basidiomycetous encapsulated fungus. We characterized the five protein arginine methyltransferases in C. neoformans and highlight Rmt5 as critical regulator of cryptococcal morphology and virulence. An rmt5{Delta} mutant was defective in thermotolerance, had a remodeled cell wall, and exhibited enhanced growth in an elevated carbon dioxide atmosphere and in chemically induced hypoxia. We revealed that Rmt5 interacts with post-transcriptional gene regulators, such as RNA-binding proteins and translation factors. Further investigation of the rmt5{Delta} mutant showed that Rmt5 is critical for the homeostasis of eIF2 and its phosphorylation state following 3-amino-1,2,4-triazole-induced ribosome stalling. RNA sequencing of one rmt5{Delta} clone revealed stable chromosome 9 aneuploidy that was ameliorated by complementation but did not impact the rmt5{Delta} phenotype. As a result of these diverse interactions and functions, loss of RMT5 enhanced phagocytosis by murine macrophages and attenuated disease progression in mice. Taken together, our findings link arginine methylation to critical cryptococcal cellular processes that impact pathogenesis, including post-transcriptional gene regulation by RNA-binding proteins. SignificanceThe fungal pathogen Cryptococcus neoformans is a huge threat for people living with immune deficits, especially HIV/AIDS. Its virulence potential is dependent on virulence factors, stress adaptation, and thermotolerance. Post-transcriptional gene regulation is important for these pathogenic processes, but the mechanisms that govern post-transcriptional regulator function are unexplored. Protein arginine methylation is a major modification of post-transcriptional regulators that has not been investigated in pathogenic fungi. Here we investigated the role of arginine methylation by arginine methyltransferases on the biology and virulence of C. neoformans. Phenotypic characterization of deletion mutants revealed pleiotropic functions for RMTs in this pathogen. Further investigation of the Rmt5 interactome using proximity-dependent biotinylation revealed interactions with RNA binding proteins and translation factors, thereby impacting virulence-associated processes.