title: The Ca2+-binding protein ALG-2 is recruited to endoplasmic reticulum exit sites by Sec31A and stabilizes the localization of Sec31A.
abstract: The formation of transport vesicles that bud from endoplasmic reticulum (ER) exit sites is dependent on the COPII coat made up of three components: the small GTPase Sar1, the Sec23/24 complex, and the Sec13/31 complex. Here, we provide evidence that apoptosis-linked gene 2 (ALG-2), a Ca(2+)-binding protein of unknown function, regulates the COPII function at ER exit sites in mammalian cells. ALG-2 bound to the Pro-rich region of Sec31A, a ubiquitously expressed mammalian orthologue of yeast Sec31, in a Ca(2+)-dependent manner and colocalized with Sec31A at ER exit sites. A Ca(2+) binding-deficient ALG-2 mutant, which did not bind Sec31A, lost the ability to localize to ER exit sites. Overexpression of the Pro-rich region of Sec31A or RNA interference-mediated Sec31A depletion also abolished the ALG-2 localization at these sites. In contrast, depletion of ALG-2 substantially reduced the level of Sec31A associated with the membrane at ER exit sites. Finally, treatment with a cell-permeable Ca(2+) chelator caused the mislocalization of ALG-2, which was accompanied by a reduced level of Sec31A at ER exit sites. We conclude that ALG-2 is recruited to ER exit sites via Ca(2+)-dependent interaction with Sec31A and in turn stabilizes the localization of Sec31A at these sites.
authors.affiliation: Department of Biological Sciences, Tokyo Institute of Technology, Yokohama 226-8501, Japan.
authors.forename: Akinori
authors.initials: A
authors.lastname: Yamasaki
authors.forename: Katsuko
authors.initials: K
authors.lastname: Tani
authors.forename: Akitsugu
authors.initials: A
authors.lastname: Yamamoto
authors.forename: Naomi
authors.initials: N
authors.lastname: Kitamura
authors.forename: Masayuki
authors.initials: M
authors.lastname: Komada
mesh_terms: D051017:Apoptosis Regulatory Proteins / Q000737:chemistry / Q000378:metabolism*; D020126:Brefeldin A / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism; D022083:Cytoplasmic Structures / Q000187:drug effects / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D056827:Endosomal Sorting Complexes Required for Transport; D006367:HeLa Cells; D006801:Humans; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D011392:Proline / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D034741:RNA, Small Interfering; D013816:Thermodynamics; D033921:Vesicular Transport Proteins
chemical_list: D051017:Apoptosis Regulatory Proteins; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D056827:Endosomal Sorting Complexes Required for Transport; C097753:PDCD6 protein, human; C117020:PDCD6IP protein, human; D034741:RNA, Small Interfering; C507455:SEC31A protein, human; D033921:Vesicular Transport Proteins; D020126:Brefeldin A; D011392:Proline; C493083:SAR1A protein, human; D020559:Monomeric GTP-Binding Proteins