Fab1p and AP-1 are required for trafficking of endogenously ubiquitylated cargoes to the vacuole lumen in S. cerevisiae.
In S. cerevisiae synthesis of phosphatidylinositol (3,5)-bisphosphate [PtdIns(3,5)P2] by Fab1p is required for several cellular events, including an as yet undefined step in the ubiquitin-dependent trafficking of some integral membrane proteins from the trans-Golgi network to the vacuole lumen. AP-1 is a heterotetrameric clathrin adaptor protein complex that binds cargo proteins and clathrin coats, and regulates bi-directional protein trafficking between the trans-Golgi network and the endocytic/secretory pathway. Like fab1Delta cells, AP-1 complex component mutants have lost the ability to traffic ubiquitylated cargoes to the vacuole lumen - the first demonstration that AP-1 is required for this process. Deletion mutants of AP-1 complex components are compromised in their ability to synthesize PtdIns(3,5)P2, indicating that AP-1 is required for correct in vivo activation of Fab1p. Furthermore, wild-type protein sorting can be restored in AP-1 mutants by overexpression of Fab1p, implying that the protein-sorting defect in these cells is as a result of disruption of PtdIns(3,5)P2 synthesis. Finally, we show that Fab1p and Vac14p, an activator of Fab1p, are also required for another AP-1-dependent process: chitin-ring deposition in chs6Delta cells. Our data imply that AP-1 is required for some Fab1p and PtdIns(3,5)P2-dependent processes.
Phelan
John P
JP
Department of Biochemistry and Molecular Biology, University College London, Darwin Building, Gower Street, London, WC1E 6BT, UK.
Millson
Stefan H
SH
Parker
Peter J
PJ
Piper
Peter W
PW
Cooke
Frank T
FT
D000595:Amino Acid Sequence; D002966:Clathrin / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed / Q000379:methods; D010716:Phosphatidylinositols / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D025801:Ubiquitin / Q000378:metabolism; D014617:Vacuoles / Q000378:metabolism*; D021601:trans-Golgi Network / Q000378:metabolism
D002966:Clathrin; D010716:Phosphatidylinositols; D029701:Saccharomyces cerevisiae Proteins; D018808:Transcription Factor AP-1; D025801:Ubiquitin; C095504:FAB1 protein, S cerevisiae; D017853:Phosphotransferases (Alcohol Group Acceptor)