The vacuole import and degradation pathway utilizes early steps of endocytosis and actin polymerization to deliver cargo proteins to the vacuole for degradation.
When glucose is added to yeast cells that are starved for 3 days, fructose-1,6-bisphosphatase (FBPase) and malate dehydrogenase 2 are degraded in the vacuole via the vacuole import and degradation (Vid) pathway. In this study, we examined the distribution of FBPase at the ultrastructural level. FBPase was observed in areas close to the plasma membrane and in cytoplasmic structures that are heterogeneous in size and density. We have isolated these intracellular structures that contain FBPase, the Vid vesicle marker Vid24p, and the endosomal marker Pep12p. They appeared irregular in size and shape. In yeast, actin polymerization plays an important role in early steps of endocytosis. Mutants that affect actin polymerization inhibited FBPase degradation, suggesting that actin polymerization is important for FBPase degradation. Both FBPase and malate dehydrogenase 2 were associated with actin patches. Vid vesicle proteins such as Vid24p or Sec28p were also at actin patches, although they dissociated from these structures at later time points. We propose that Vid24p and Sec28p are present at actin patches during glucose starvation. Cargo proteins arrive at these sites following the addition of glucose, and the endocytic vesicles then pinch off from the plasma membrane. Following the fusion of endosomes with the vacuole, cargo proteins are then degraded in the vacuole.
Brown
C Randell
CR
Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
Dunton
Danielle
D
Chiang
Hui-Ling
HL
D000199:Actins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D020756:Coatomer Protein / Q000235:genetics / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D006597:Fructose-Bisphosphatase / Q000235:genetics / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology; D008291:Malate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D050765:Qa-SNARE Proteins; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D013549:Sweetening Agents / Q000494:pharmacology; D014617:Vacuoles / Q000235:genetics / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism
D000199:Actins; D020756:Coatomer Protein; C081224:PEP12 protein, S cerevisiae; D050765:Qa-SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; C532448:Sec28 protein, S cerevisiae; D013549:Sweetening Agents; C111452:VID24 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D008291:Malate Dehydrogenase; D006597:Fructose-Bisphosphatase; D005947:Glucose