The transcriptional response of saccharomyces cerevisiae to proapoptotic concentrations of pichia membranifaciens killer toxin

Abstract

PMKT (Pichia membranifaciens killer toxin) reportedly has antimicrobial activity against yeasts and filamentous fungi. In previous research we posited that high PMKT concentrations pose a serious challenge for cell survival by disrupting plasma membrane electrochemical gradients, inducing a transcriptional response similar to that of certain stimuli such as hyperosmotic shock. This response was related to the HOG-pathway with Hog1p phosphorylation and a transitional increase in intracellular glycerol accumulation. Such a response was consistent with the notion that the effect induced by high PMKT concentrations lies in an alteration to the ionic homeostasis of the sensitive cell.

By contrast, the evidence presented here shows that low PMKT doses lead to a cell death process in Saccharomyces cerevisiae accompanied by cytological and biochemical indicators of apoptotic programmed cell death, namely, the production of reactive oxygen species, DNA strand breaks, metacaspase activation and cytochrome c release. Furthermore, dying cells progressed from an apoptotic state to a secondary necrotic state, and the rate at which this change occurred was proportional to the intensity of the stimulus. We have explored the global gene expression response of S. cerevisiae during that stimulus. The results obtained from DNA microarrays indicate that genes related with an oxidative stress response were induced in response to proapoptotic concentrations of PMKT, showing that the coordinated transcriptional response is not coincident with that obtained when ionophoric concentrations of PMKT are used. By contrast, cwp2Δ mutants showed no signs of apoptosis, indicating that the initial steps of the killer mechanism coincide when proapoptotic (low) or ionophoric (high) PMKT concentrations are used. Additionally, low dosages of PMKT promoted Hog1p phosphorylation and glycerol accumulation.