title: Apoptosis-linked gene-2 (ALG-2)/Sec31 interactions regulate endoplasmic reticulum (ER)-to-Golgi transport: a potential effector pathway for luminal calcium.
abstract: Luminal calcium released from secretory organelles has been suggested to play a regulatory role in vesicle transport at several steps in the secretory pathway; however, its functional roles and effector pathways have not been elucidated. Here we demonstrate for the first time that specific luminal calcium depletion leads to a significant decrease in endoplasmic reticulum (ER)-to-Golgi transport rates in intact cells. Ultrastructural analysis revealed that luminal calcium depletion is accompanied by increased accumulation of intermediate compartment proteins in COPII buds and clusters of unfused COPII vesicles at ER exit sites. Furthermore, we present several lines of evidence suggesting that luminal calcium affected transport at least in part through calcium-dependent interactions between apoptosis-linked gene-2 (ALG-2) and the Sec31A proline-rich region: 1) targeted disruption of ALG-2/Sec31A interactions caused severe defects in ER-to-Golgi transport in intact cells; 2) effects of luminal calcium and ALG-2/Sec31A interactions on transport mutually required each other; and 3) Sec31A function in transport required luminal calcium. Morphological phenotypes of disrupted ALG-2/Sec31A interactions were characterized. We found that ALG-2/Sec31A interactions were not required for the localization of Sec31A to ER exit sites per se but appeared to acutely regulate the stability and trafficking of the cargo receptor p24 and the distribution of the vesicle tether protein p115. These results represent the first outline of a mechanism that connects luminal calcium to specific protein interactions regulating vesicle trafficking machinery.
authors.affiliation: From the Division of Biological Sciences and Center for Structural and Functional Neuroscience, University of Montana, Missoula, Montana 59812-4824 and.
authors.forename: Jared R
authors.initials: JR
authors.lastname: Helm
authors.affiliation: From the Division of Biological Sciences and Center for Structural and Functional Neuroscience, University of Montana, Missoula, Montana 59812-4824 and.
authors.forename: Marvin
authors.initials: M
authors.lastname: Bentley
authors.affiliation: From the Division of Biological Sciences and Center for Structural and Functional Neuroscience, University of Montana, Missoula, Montana 59812-4824 and.
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Thorsen
authors.affiliation: From the Division of Biological Sciences and Center for Structural and Functional Neuroscience, University of Montana, Missoula, Montana 59812-4824 and.
authors.forename: Ting
authors.initials: T
authors.lastname: Wang
authors.affiliation: From the Division of Biological Sciences and Center for Structural and Functional Neuroscience, University of Montana, Missoula, Montana 59812-4824 and.
authors.forename: Lauren
authors.initials: L
authors.lastname: Foltz
authors.affiliation: the Cell Microscopy Center, Department of Cell Biology, University Medical Center Utrecht, AZU Room H02.313, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands.
authors.forename: Viola
authors.initials: V
authors.lastname: Oorschot
authors.affiliation: the Cell Microscopy Center, Department of Cell Biology, University Medical Center Utrecht, AZU Room H02.313, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands.
authors.forename: Judith
authors.initials: J
authors.lastname: Klumperman
authors.affiliation: From the Division of Biological Sciences and Center for Structural and Functional Neuroscience, University of Montana, Missoula, Montana 59812-4824 and jesse.hay@umontana.edu.
authors.forename: Jesse C
authors.initials: JC
authors.lastname: Hay
mesh_terms: D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D008856:Microscopy, Fluorescence; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000235:genetics; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; D002135:Calcium-Binding Proteins; C097753:PDCD6 protein, human; D034741:RNA, Small Interfering; C507455:SEC31A protein, human; D033921:Vesicular Transport Proteins; D002118:Calcium
keywords: Calcium-binding Protein; Endoplasmic Reticulum (ER); Endoplasmic Reticulum to Golgi Transport; Golgi; Membrane Trafficking; Secretion; Vesicles