Abstract
In the yeast Saccharomyces cerevisiae, components of the High Osmolarity Glycerol (HOG) pathway are important for the response to diverse stresses including response to endoplasmic reticulum stress (ER stress), which is produced by the accumulation of unfolded proteins in the lumen of this organelle. Accumulation of unfolded proteins may be due to the inhibition of protein N-glycosylation, which can be achieved by treatment with the antibiotic tunicamycin (Tn). In this work we were interested in finding proteins involved in the ER stress response regulated by Hog1, the mitogen activated protein kinase (MAPK) of the HOG pathway. A high gene dosage suppression screening allowed us to identify genes that suppressed the sensitivity to Tn shown by a hog1Δ mutant. The suppressors participate in a limited number of cellular processes, including lipid/carbohydrate biosynthesis and protein glycosylation, vesicle-mediated transport and exocytosis, cell wall organization and biogenesis, and cell detoxification processes. The finding of suppressors Rer2 and Srt1, which participate in the dolichol biosynthesis pathway revealed that the hog1Δ strain has a defective polyprenol metabolism. This work uncovers new genetic and functional interactors of Hog1 and contributes to a better understanding of the participation of this MAPK in the ER stress response.
Highlights
The synthesis of transmembrane and secreted proteins occurs in ribosomes attached to the endoplasmic reticulum (ER) membrane
In order to shed light onto the way in which Hog1 participates in the response to ER stress inducers, we designed a dosage-suppression screening to identify genes required for the Hog1-Tn response
Yeast transformants were plated in medium containing Tn to isolate cells resistant to the antibiotic; the transformants were dropped on plates containing KCl in order to identify the clones that were sensitive to hyperosmotic stress (Figure 1)
Summary
The synthesis of transmembrane and secreted proteins occurs in ribosomes attached to the endoplasmic reticulum (ER) membrane. Processed proteins continue through the secretion pathway in order to be transported to their final location. ER stress triggers a cellular response that includes the unfolded protein response (UPR), which is a conserved signaling pathway present in all eukaryotic cells, including yeast [1], Dictyostelium discoideum [2], plants [3], and mammals [4]. In the yeast Saccharomyces cerevisiae the UPR consists of an endoplasmic reticulum membrane sensor named Ire1 [5], which in the presence of misfolded proteins oligomerises and autophosphorylates [6,7]; this in turn triggers its cytoplasmic endonuclease activity, which processes the HAC1 pre-mRNA [8]
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