title: Calcium-calmodulin kinase I cooperatively regulates nucleocytoplasmic shuttling of CCTα by accessing a nuclear export signal.
abstract: We identified a new calmodulin kinase I (CaMKI) substrate, cytidyltransferase (CCTα), a crucial enzyme required for maintenance of cell membranes. CCTα becomes activated with translocation from the cytoplasm to the nuclear membrane, resulting in increased membrane phospholipids. Calcium-activated CCTα nuclear import is mediated by binding of its C-terminus to 14-3-3 ζ, a regulator of nuclear trafficking. Here CaMK1 phosphorylates residues within this C-terminus that signals association of CCTα with 14-3-3 ζ to initiate calcium-induced nuclear entry. CaMKI docks within the CCTα membrane-binding domain (residues 290-299), a sequence that displays similarities to a canonical nuclear export signal (NES) that also binds CRM1/exportin 1. Expression of a CFP-CCTα mutant lacking residues 290-299 in cells results in cytosolically retained enzyme. CRM1/exportin 1 was required for CCTα nuclear export, and its overexpression in cells was partially sufficient to trigger CCTα nuclear export despite calcium stimulation. An isolated CFP-290-299 peptide remained in the nucleus in the presence of leptomycin B but was able to target to the cytoplasm with farnesol. Thus CaMKI vies with CRM1/exportin 1 for access to a NES, and assembly of a CaMKI-14-3-3 ζ-CCTα complex is a key effector mechanism that drives nuclear CCTα translocation.
authors.affiliation: Acute Lung Injury Center of Excellence, Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA.
authors.forename: Marianna
authors.initials: M
authors.lastname: Agassandian
authors.forename: Bill B
authors.initials: BB
authors.lastname: Chen
authors.forename: Roopa
authors.initials: R
authors.lastname: Pulijala
authors.forename: Leah
authors.initials: L
authors.lastname: Kaercher
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Glasser
authors.forename: Rama K
authors.initials: RK
authors.lastname: Mallampalli
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism; D021581:Active Transport, Cell Nucleus; D000818:Animals; D002118:Calcium / Q000378:metabolism; D054729:Calcium-Calmodulin-Dependent Protein Kinase Type 1 / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D056404:Chaperonin Containing TCP-1 / Q000378:metabolism*; D005204:Farnesol; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins / Q000378:metabolism*; D051379:Mice; D009685:Nuclear Envelope / Q000378:metabolism; D049790:Nuclear Export Signals / Q000502:physiology*; D019913:Nuclear Localization Signals / Q000378:metabolism; D010743:Phospholipids / Q000096:biosynthesis; D021381:Protein Transport; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D015398:Signal Transduction; D000097606:Exportin 1 Protein
chemical_list: D048948:14-3-3 Proteins; D002118:Calcium; D054729:Calcium-Calmodulin-Dependent Protein Kinase Type 1; D056404:Chaperonin Containing TCP-1; D005204:Farnesol; D005231:Fatty Acids, Unsaturated; D028884:Karyopherins; D049790:Nuclear Export Signals; D019913:Nuclear Localization Signals; D010743:Phospholipids; D018160:Receptors, Cytoplasmic and Nuclear; D000097606:Exportin 1 Protein; C517598:Camk1 protein, mouse; C038753:leptomycin B