Golgi enzymes do not cycle through the endoplasmic reticulum during protein secretion or mitosis.
Golgi-specific sialyltransferase (ST) expressed as a chimera with the rapamycin-binding domain of mTOR, FRB, relocates to the endoplasmic reticulum (ER) in cells exposed to rapamycin that also express invariant chain (Ii)-FKBP in the ER. This result has been taken to indicate that Golgi-resident enzymes cycle to the ER constitutively. We show that ST-FRB is trapped in the ER even without Ii-FKBP upon rapamycin addition. This is because ER-Golgi-cycling FKBP proteins contain a C-terminal KDEL-like sequence, bind ST-FRB in the Golgi, and are transported together back to the ER by KDEL receptor-mediated retrograde transport. Moreover, depletion of KDEL receptor prevents trapping of ST-FRB in the ER by rapamycin. Thus ST-FRB cycles artificially by binding to FKBP domain-containing proteins. In addition, Golgi-specific O-linked glycosylation of a resident ER protein occurs only upon artificial fusion of Golgi membranes with ER. Together these findings support the consensus view that there is no appreciable mixing of Golgi-resident enzymes with ER under normal conditions.
Cell and Developmental Biology Department, Centre for Genomic Regulation, Barcelona Institute for Science and Technology, 08003 Barcelona, Spain.|Department of Molecular and Cell Biology and Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720.
Julien
J
Villeneuve
Cell and Developmental Biology Department, Centre for Genomic Regulation, Barcelona Institute for Science and Technology, 08003 Barcelona, Spain.|Universitat Pompeu Fabra, 08002 Barcelona, Spain.
Juan
J
Duran
Cell and Developmental Biology Department, Centre for Genomic Regulation, Barcelona Institute for Science and Technology, 08003 Barcelona, Spain.
Margherita
M
Scarpa
Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA 94143.|Institute for Human Genetics, University of California, San Francisco, San Francisco, CA 94143.
Laia
L
Bassaganyas
Cell and Developmental Biology Department, Centre for Genomic Regulation, Barcelona Institute for Science and Technology, 08003 Barcelona, Spain.
Josse
J
Van Galen
Cell and Developmental Biology Department, Centre for Genomic Regulation, Barcelona Institute for Science and Technology, 08003 Barcelona, Spain Vivek.Malhotra@crg.eu.|Universitat Pompeu Fabra, 08002 Barcelona, Spain.|Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain.
Vivek
V
Malhotra
D000818:Animals; D001692:Biological Transport; D019556:COS Cells; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism* / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008938:Mitosis / Q000502:physiology; D000072417:Protein Domains; D000069284:Protein Translocation Systems; D021381:Protein Transport / Q000502:physiology*; D018000:Receptors, Peptide / Q000378:metabolism; D012799:Sialyltransferases / Q000378:metabolism; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases
C064459:KDEL receptor; D000069284:Protein Translocation Systems; D018000:Receptors, Peptide; D012799:Sialyltransferases; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus