title: p125 is localized in endoplasmic reticulum exit sites and involved in their organization.
abstract: Transport vesicles coated with the COPII complex, which is assembled from Sar1p, Sec23p-Sec24p, and Sec13p-Sec31p, are involved in protein export from the endoplasmic reticulum (ER). We previously identified and characterized a novel Sec23p-interacting protein, p125, that is only expressed in mammals and exhibits sequence homology with phosphatidic acid-preferring phospholipase A(1) (PA-PLA(1)). In this study, we examined the localization and function of p125 in detail. By using immunofluorescence and electron microscopy, we found that p125 is principally localized in ER exit sites where COPII-coated vesicles are produced. Analyses of chimeric proteins comprising p125 and two other members of the mammalian PA-PLA(1) family (PA-PLA(1) and KIAA0725p) showed that, for localization to ER exit sites, the p125-specific N-terminal region is critical, and the putative lipase domain is interchangeable with KIAA0725p but not with PA-PLA(1). RNA interference-mediated depletion of p125 affected the organization of ER exit sites. The structure of the cis-Golgi compartment was also substantially disturbed, whereas the medial-Golgi was not. Protein export from the ER occurred without a significant delay in p125-depleted cells. Our study suggests that p125 is a mammalian-specific component of ER exit sites and participates in the organization of this compartment.
authors.affiliation: School of Life Science, Tokyo University of Pharmacy and Life Science, Hachioji, Tokyo 192-0392, Japan.
authors.forename: Wakako
authors.initials: W
authors.lastname: Shimoi
authors.forename: Ichiko
authors.initials: I
authors.lastname: Ezawa
authors.forename: Koji
authors.initials: K
authors.lastname: Nakamoto
authors.forename: Shihoko
authors.initials: S
authors.lastname: Uesaki
authors.forename: Gavin
authors.initials: G
authors.lastname: Gabreski
authors.forename: Meir
authors.initials: M
authors.lastname: Aridor
authors.forename: Akitsugu
authors.initials: A
authors.lastname: Yamamoto
authors.forename: Masami
authors.initials: M
authors.lastname: Nagahama
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Tagaya
authors.forename: Katsuko
authors.initials: K
authors.lastname: Tani
mesh_terms: D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000378:metabolism / Q000648:ultrastructure; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D007425:Intracellular Membranes / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D028861:Nuclear Pore Complex Proteins; D010750:Phosphoproteins / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism; D016601:RNA-Binding Proteins; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D033921:Vesicular Transport Proteins / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D018076:DNA, Complementary; D008565:Membrane Proteins; D028861:Nuclear Pore Complex Proteins; D010750:Phosphoproteins; D011506:Proteins; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; C079620:SEC13 protein, S cerevisiae; C512739:SEC23A protein, human; C120603:SEC23IP protein, human; C118289:SEC24 protein, S cerevisiae; C106113:SEC31 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C512740:Sec23a protein, rat; D033921:Vesicular Transport Proteins; C493083:SAR1A protein, human; C513282:SAR1B protein, human; D020559:Monomeric GTP-Binding Proteins