Translational and morphological effects of signalling alcohols on C. albicans

Abstract

Candida albicans is a polymorphic yeast that can cause life threatening systemicinfections in immunocompromised individuals. One key attribute of C. albicans thatenhances its pathogenicity is the ability to switch morphologies between filamentousand vegetative modes in response to specific environmental conditions. Stressfulchanges in such cellular conditions commonly cause a rapid inhibition of global proteinsynthesis leading to altered programmes of gene expression. In Saccharomycescerevisiae, fusel alcohols signal nitrogen scarcity and induce pseudohyphal growthenabling yeast colonies to spread towards nutrient replete areas. These alcohols alsoinhibit protein synthesis by targeting the translation initiation factor, eIF2B. eIF2B isthe guanine nucleotide exchange factor for eIF2, which supports eIF2-GTP productionand represents a key regulated step in translation initiation. eIF2-GTP interacts withMet-tRNAiMet to form the ternary complex which is essential for translation initiation.Fusel alcohols target eIF2B leading to reduced levels of ternary complex and reducedprotein synthesis.In Candida albicans, a variety of cell biological and genetic assays suggest that fuselalcohols and ethanol inhibit protein synthesis by targeting the translation initiationfactor, eIF2B, and they also induce hyphal/pseudohyphal growth, a process that isassociated with pathogenesis in C. albicans. In contrast to fusel alcohols, farnesol, aquorum sensing alcohol, does not appear to impact upon eIF2B activity. Rather,biochemical and mass spectrometric analysis suggest farnesol affects the interaction ofthe mRNA with the small ribosomal subunit during translation initiation. Furtherelucidation of the effect of farnesol on C. albicans transcript levels and ribosomeassociation by next generation sequencing gave insight into the genes that aredifferentially expressed following farnesol treatment. While genes involved inmorphological differentiation were generally repressed, those involved in proteinsynthesis were upregulated, possibly as an adaptive response to inhibition of proteinsynthesis by farnesol. Intriguingly, the regulation of these functional categories of genesoccurred in a co-ordinated manner at either the transcript level or at the level ofribosome association, but rarely was gene expression regulated at both transcriptionaland post-transcriptional levels for the same gene.

Date of Award	1 Aug 2015
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Mark Ashe (Supervisor) & Christopher Grant (Supervisor)