Eukaryotic cells employ a variety of mechanisms to maintain protein quality control and homeostasis. Here we provide evidence that one such mechanism in S. cerevisiae involves the regulated release of excess or misfolded proteins to the extracellular space. Overexpression of an epitope tagged allele of the GPI-linked cell wall protein Utr2/Crh2p (Utr2/Crh2-GFP, HA) causes endoplasmic reticulum (ER) stress and secretion of Crh2-GFP/HA into the extracellular space. Secretion is dependent on two GPI-linked aspartyl proteases (Yps1p/2p) and components of the unfolded protein response (Ire1p and Hac1p), but is independent of ERAD components such as Hrd1p and Doa10p. Supporting the idea that this process represents a mechanism for protein quality control, Crh2-HA is increased in strains lacking Bst1p, a protein required for the proteasomal degradation of GPI-linked proteins. Furthermore, secretion is dependent on Sec18p, indicating that it requires ER-to-Golgi trafficking and, accordingly, Crh2-HA accumulates in the ER in ire1Delta and bst1Delta mutants by cycloheximide chase experiments. Since a fraction of Utr2/Crh2-GFP properly localizes to the cell wall in ire1Delta, extracellular secretion appears to occur through a pathway that is distinct from the normal GPI-protein trafficking pathway. Taken together, these data support a model in which UPR/yapsin-mediated extracellular release of overexpressed Utr2/Crh2-HA/GFP is an alternative pathway for the removal of excess or misfolded secretory proteins functioning in parallel with proteasome-mediated degradation in S. cerevisiae. This model provides an explanation for the deleterious effects of Yps1/2p on industrial production of some recombinant proteins in S. cerevisiae.
|Evidence ID||Analyze ID||Interactor||Interactor Systematic Name||Interactor||Interactor Systematic Name||Type||Assay||Annotation||Action||Modification||Phenotype||Source||Reference||Note|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Gene Ontology Term||Gene Ontology Term ID||Qualifier||Aspect||Method||Evidence||Source||Assigned On||Annotation Extension||Reference|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
|Evidence ID||Analyze ID||Regulator||Regulator Systematic Name||Target||Target Systematic Name||Experiment||Assay||Construct||Conditions||Strain Background||Reference|