The exocyst subunit Sec3 is regulated by a protein quality control pathway

• Published in: The Journal of biological chemistry Vol. 292; no. 37; pp. 15240 - 15253
• Main Authors: Kampmeyer, Caroline, Karakostova, Antonina, Schenstrøm, Signe M., Abildgaard, Amanda B., Lauridsen, Anne-Marie, Jourdain, Isabelle, Hartmann-Petersen, Rasmus
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.09.2017; American Society for Biochemistry and Molecular Biology
• Subjects: chaperone; Deubiquitinating Enzymes - antagonists & inhibitors; Deubiquitinating Enzymes - genetics; Deubiquitinating Enzymes - metabolism; Endocytosis - drug effects; Endopeptidases - genetics; Endopeptidases - metabolism; Enzyme Inhibitors - pharmacology; exocytosis; Exocytosis - drug effects; Gene Deletion; HSP70 Heat-Shock Proteins - antagonists & inhibitors; HSP70 Heat-Shock Proteins - genetics; HSP70 Heat-Shock Proteins - metabolism; Microscopy, Electron, Transmission; Models, Biological; Mutation; proteasome; Proteasome Endopeptidase Complex - drug effects; Proteasome Endopeptidase Complex - genetics; Proteasome Endopeptidase Complex - metabolism; Proteasome Endopeptidase Complex - ultrastructure; protein folding; Protein Stability - drug effects; Protein Synthesis and Degradation; Proteolysis - drug effects; Recombinant Fusion Proteins - chemistry; Recombinant Fusion Proteins - metabolism; Schizosaccharomyces - drug effects; Schizosaccharomyces - growth & development; Schizosaccharomyces - physiology; Schizosaccharomyces - ultrastructure; Schizosaccharomyces pombe Proteins - antagonists & inhibitors; Schizosaccharomyces pombe Proteins - genetics; Schizosaccharomyces pombe Proteins - metabolism; Secretory Vesicles - drug effects; Secretory Vesicles - physiology; Secretory Vesicles - ultrastructure; Stress, Physiological - drug effects; Temperature; ubiquitin; Ubiquitin-Protein Ligases - antagonists & inhibitors; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - metabolism; Ubiquitination - drug effects; Vesicular Transport Proteins - antagonists & inhibitors; Vesicular Transport Proteins - genetics; Vesicular Transport Proteins - metabolism; proteasome; exocytosis; protein folding; chaperone; ubiquitin
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M117.789867

Exocytosis involves fusion of secretory vesicles with the plasma membrane, thereby delivering membrane proteins to the cell surface and releasing material into the extracellular space. The tethering of the secretory vesicles before membrane fusion is mediated by the exocyst, an essential phylogenetically conserved octameric protein complex. Exocyst biogenesis is regulated by several processes, but the mechanisms by which the exocyst is degraded are unknown. Here, to unravel the components of the exocyst degradation pathway, we screened for extragenic suppressors of a temperature-sensitive fission yeast strain mutated in the exocyst subunit Sec3 (sec3-913). One of the suppressing DNAs encoded a truncated dominant-negative variant of the 26S proteasome subunit, Rpt2, indicating that exocyst degradation is controlled by the ubiquitin-proteasome system. The temperature-dependent growth defect of the sec3-913 strain was gene dosage-dependent and suppressed by blocking the proteasome, Hsp70-type molecular chaperones, the Pib1 E3 ubiquitin-protein ligase, and the deubiquitylating enzyme Ubp3. Moreover, defects in cell septation, exocytosis, and endocytosis in sec3 mutant strains were similarly alleviated by mutation of components in this pathway. We also found that, particularly under stress conditions, wild-type Sec3 degradation is regulated by Pib1 and the 26S proteasome. In conclusion, our results suggest that a cytosolic protein quality control pathway monitors folding and proteasome-dependent turnover of an exocyst subunit and, thereby, controls exocytosis in fission yeast.