Toxic Metals and Proteostasis – Molecular mechanisms of arsenite and cadmium-induced protein aggregation in Saccharomyces cerevisiae

Abstract

Cadmium and arsenite are common environmental pollutants; considered highly toxic and pose a substantial threat to human health with millions of people worldwide being at risk of exposure. Cadmium and arsenite are carcinogenic and associated with age-related and neurodegenerative diseases that are characterized by the accumulation of protein aggregates. Arsenite induces protein misfolding of newly synthesized proteins leading to widespread protein aggregation. Additionally, cadmium is known to interfere with proteins in vitro, but little is known about how it affects proteins in vivo. This thesis focuses on arsenite- and cadmium-induced protein aggregation and toxicity and aims to provide novel insights into the regulation of how these aggregates are formed and how the cells protein quality control mechanisms contribute to prevent the accumulation of protein aggregates and hence avoid arsenite and cadmium toxicity, using Saccharomyces cerevisiae as model organism. Here, we demonstrate that cadmium induces aggregation of cytosolic proteins in living yeast cells by primarily targeting proteins in the process of synthesis or folding. We show that protein aggregation contributes to cadmium toxicity. Furthermore, by using a genome-wide imaging approach, we identified cellular processes and functions that affect arsenite-induced protein aggregation and toxicity. Our study revealed that appropriate transcriptional and translational control is crucial to avoid arsenite-induced proteotoxicity. Additionally, we investigated the spatial localization of arsenite-induced protein aggregates on a single cell level. We showed that initially, many small aggregates form during arsenite stress, which later coalesce into fewer bigger foci and are distinctly localized inside the cell where the majority is cytosolic, associated to organelles such as mitochondria, nucleus and endoplasmic reticulum or found inside the nucleus and mitochondria. Taken together, our findings provide novel insights into the regulation of how protein aggregates are formed during cadmium and arsenite stress and highlights the importance of the protein quality control systems that protect cells from arsenite and cadmium toxicity.