Stress-responsive roles of the C. neoformans human-like eIF3 complex

Abstract

Eukaryotic translation initiation factor 3 (eIF3) is a complex of proteins that plays a pleiotropic role in translation regulation across eukaryotes, but the composition of eIF3 complexes varies with retention and loss of subunit genes across evolution. The model yeast Saccharomyces cerevisiae encodes six eIF3 subunits whereas mammals encode thirteen subunits. The basidiomycete fungus and opportunistic fungal pathogen, Cryptococcus neoformans, encodes a mammalian complement of eIF3 subunits. In this report, we investigated the contribution of the non-essential eIF3 subunit genes to cryptococcal stress tolerance. We found that mutants in the four nonessential subunits, eIF3d, eIF3e, eIF3k and eIF3l all exhibit sensitivity to mitochondrial perturbation, and that mutants in eIF3d and eIF3e exhibit opposite susceptibilities to the antifungal drug fluconazole and the hypoxia mimetic cobalt chloride. Loss of eIF3d resulted in reduced eIF2 phosphorylation in response to stress, but the mutant was still able to repress translation to the same extent as the wild type and was defective in induction of integrated stress response regulon. Despite producing higher levels of urease and melanin, the eIF3d deletion mutant was avirulent in Galleria mellonella larvae. Together our data demonstrates the importance of C. neoformans eIF3 in stress adaptation and pathogenesis. ImportanceCryptococcus neoformans is an opportunistic fungal pathogen that causes cryptococcal meningoencephalitis in immunocompromised individuals leading to [~]120,000 deaths worldwide annually. When C. neoformans is exposed to host-relevant stressors, such as oxidative stress and thermal stress, it reprograms the translating pool of mRNAs to favor stress adaptation. Eukaryotic translation initiation factor 3 is a multi-subunit complex with roles in stress-responsive translation across eukaryotes yet is unexplored in C. neoformans. We found that C. neoformans encodes orthologues of all thirteen mammalian eIF3 subunits. Mutational analysis of non-essential subunits implicated eIF3 in responses to mitochondrial stress and antifungal susceptibility in C. neoformans, and demonstrates a role for eIF3d in the induction of the integrated stress response as well as in Cryptococcal pathogenesis. Further work will investigate the specific mRNAs that are regulated by eIF3 in response to host-relevant stressors in C. neoformans.