title: KDEL and KKXX retrieval signals appended to the same reporter protein determine different trafficking between endoplasmic reticulum, intermediate compartment, and Golgi complex.
abstract: Many endoplasmic reticulum (ER) proteins maintain their residence by dynamic retrieval from downstream compartments of the secretory pathway. In previous work we compared the retrieval process mediated by the two signals, KKMP and KDEL, by appending them to the same neutral reporter protein, CD8, and found that the two signals determine a different steady-state localization of the reporter. CD8-K (the KDEL-bearing form) was restricted mainly to the ER, whereas CD8-E19 (the KKMP-bearing form) was distributed also to the intermediate compartment and Golgi complex. To investigate whether this different steady-state distribution reflects a difference in exit rates from the ER and/or in retrieval, we have now followed the first steps of export of the two constructs from the ER and their trafficking between ER and Golgi complex. Contrary to expectation, we find that CD8-K is efficiently recruited into transport vesicles, whereas CD8-E19 is not. Thus, the more restricted ER localization of CD8-K must be explained by a more efficient retrieval to the ER. Moreover, because most of ER resident CD8-K is not O-glycosylated but almost all CD8-E19 is, the results suggest that CD8-K is retrieved from the intermediate compartment, before reaching the Golgi, where O-glycosylation begins. These results illustrate how different retrieval signals determine different trafficking patterns and pose novel questions on the underlying molecular mechanisms.
authors.affiliation: Department of Biochemistry and Medical Biotechnology, University of Naples Federico II, Italy.
authors.forename: Mariano
authors.initials: M
authors.lastname: Stornaiuolo
authors.forename: Lavinia V
authors.initials: LV
authors.lastname: Lotti
authors.forename: Nica
authors.initials: N
authors.lastname: Borgese
authors.forename: Maria-Rosaria
authors.initials: MR
authors.lastname: Torrisi
authors.forename: Giovanna
authors.initials: G
authors.lastname: Mottola
authors.forename: Gianluca
authors.initials: G
authors.lastname: Martire
authors.forename: Stefano
authors.initials: S
authors.lastname: Bonatti
mesh_terms: D000818:Animals; D016827:CD8 Antigens / Q000235:genetics / Q000378:metabolism*; D002458:Cell Fractionation; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D017930:Genes, Reporter; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D008855:Microscopy, Electron, Scanning; D009842:Oligopeptides / Q000378:metabolism*; D021382:Protein Sorting Signals; D021381:Protein Transport / Q000502:physiology; D022161:Transport Vesicles / Q000378:metabolism
chemical_list: D016827:CD8 Antigens; D009842:Oligopeptides; D021382:Protein Sorting Signals; C073762:lysyl-aspartyl-glutamyl-leucine