title: Nuclear sequestration of beta-subunits by Rad and Rem is controlled by 14-3-3 and calmodulin and reveals a novel mechanism for Ca2+ channel regulation.
abstract: Voltage-gated Ca2+ channels (VDCCs) are heteromultimeric proteins that mediate Ca2+ influx into cells upon membrane depolarization. These channels are involved in various cellular events, including gene expression, regulation of hormone secretion and synaptic transmission. Kir/Gem, Rad, Rem, and Rem2 belong to the RGK family of Ras-related small G proteins. RGK proteins interact with the beta-subunits and downregulate VDCC activity. Kir/Gem was proposed to prevent surface expression of functional Ca2+ channels, while for Rem2 the mechanism remains controversial. Here, we have analyzed the mechanism by which Rad and Rem regulate VDCC activity. We show that, similar to Kir/Gem and Rem2, 14-3-3 and CaM binding regulate the subcellular distribution of Rad and Rem, which both inhibit Ca2+ channel activity by preventing its expression on the cell surface. This function is regulated by calmodulin and 14-3-3 binding only for Rad and not for Rem. Interestingly, nuclear targeting of Rad and Rem can relocalize and sequester the beta-subunit to the nucleus, thus providing a novel mechanism for Ca2+ channel downregulation.
authors.affiliation: Epithelial Cell Biology Laboratory, Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore, Singapore 138673. beguinp@imcb.a-star.edu.sg
authors.forename: Pascal
authors.initials: P
authors.lastname: Béguin
authors.forename: Ramasubbu Narayanan
authors.initials: RN
authors.lastname: Mahalakshmi
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Nagashima
authors.forename: Damian Hwee Kiat
authors.initials: DH
authors.lastname: Cher
authors.forename: Hiroki
authors.initials: H
authors.lastname: Ikeda
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Yamada
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Seino
authors.forename: Walter
authors.initials: W
authors.lastname: Hunziker
mesh_terms: D048948:14-3-3 Proteins / Q000502:physiology*; D021581:Active Transport, Cell Nucleus; D000818:Animals; D015220:Calcium Channels / Q000378:metabolism*; D002147:Calmodulin / Q000502:physiology*; D002460:Cell Line; D015536:Down-Regulation; D006801:Humans; D017874:Immediate-Early Proteins; D051379:Mice; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D021122:Protein Subunits / Q000378:metabolism; D014162:Transfection; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D048948:14-3-3 Proteins; D015220:Calcium Channels; D002147:Calmodulin; D017874:Immediate-Early Proteins; D021122:Protein Subunits; C084355:RRAD protein, human; C108135:Rem protein, mouse; C490030:Rrad protein, mouse; C490245:GEM protein, human; C088119:Gem protein, mouse; D020559:Monomeric GTP-Binding Proteins; D018631:ras Proteins