Remodeling of secretory compartments creates CUPS during nutrient starvation

• Published in: The Journal of cell biology Vol. 207; no. 6; pp. 695 - 703
• Main Authors: Cruz-Garcia, David, Curwin, Amy J, Popoff, Jean-François, Bruns, Caroline, Duran, Juan M, Malhotra, Vivek
• Format: Journal Article
• Language: English
• Published: United States Rockefeller University Press 22-12-2014; The Rockefeller University Press
• Subjects: 1-Phosphatidylinositol 4-Kinase - metabolism; Biosynthesis; Class III Phosphatidylinositol 3-Kinases - metabolism; COP-Coated Vesicles - metabolism; Culture Media; Endoplasmic reticulum; Endoplasmic Reticulum - metabolism; Enzymes; Glucose - metabolism; Guanine Nucleotide Exchange Factors - metabolism; Membranes; Protein Transport; Proteins; Qa-SNARE Proteins - metabolism; Saccharomyces cerevisiae - cytology; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - metabolism; Secretory Vesicles - metabolism; Vesicular Transport Proteins - metabolism; Yeast
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.201407119

Upon starvation, Grh1, a peripheral membrane protein located at endoplasmic reticulum (ER) exit sites and early Golgi in Saccharomyces cerevisiae under growth conditions, relocates to a compartment called compartment for unconventional protein secretion (CUPS). Here we report that CUPS lack Golgi enzymes, but contain the coat protein complex II (COPII) vesicle tethering protein Uso1 and the Golgi t-SNARE Sed5. Interestingly, CUPS biogenesis is independent of COPII- and COPI-mediated membrane transport. Pik1- and Sec7-mediated membrane export from the late Golgi is required for complete assembly of CUPS, and Vps34 is needed for their maintenance. CUPS formation is triggered by glucose, but not nitrogen starvation. Moreover, upon return to growth conditions, CUPS are absorbed into the ER, and not the vacuole. Altogether our findings indicate that CUPS are not specialized autophagosomes as suggested previously. We suggest that starvation triggers relocation of secretory and endosomal membranes, but not their enzymes, to generate CUPS to sort and secrete proteins that do not enter, or are not processed by enzymes of the ER-Golgi pathway of secretion.