title: A calmodulin-binding site on cyclin E mediates Ca2+-sensitive G1/s transitions in vascular smooth muscle cells.
abstract: Calcium transients are known to control several transition points in the eukaryotic cell cycle. For example, we have previously shown that a coordinate elevation in the intracellular free calcium ion concentration is required for G1- to S-phase cell cycle progression in vascular smooth muscle cells (VSMC). However, the molecular basis for this Ca2+ sensitivity was not known. Using buffers with differing [Ca2+], we found that the kinase activity of mouse and human cyclin E/CDK2, but not other G1/S-associated cell cycle complexes, was responsive to physiological changes in [Ca2+]. We next determined that this Ca2+-responsive kinase activity was dependent on a direct interaction between calmodulin (CaM), one of the major Ca2+-signal transducers of eukaryotic cells, and cyclin E. Pharmacological inhibition of CaM abrogated the Ca2+ sensitivity of cyclin E/CDK2 and retarded mouse VSMC proliferation by causing G1 arrest. We next defined the presence of a highly conserved 22 amino acid N-terminal CaM-binding motif in mammalian cyclin E genes (dissociation constant, 1.5+/-0.1 micromol/L) and showed its essential role in mediating Ca2+-sensitive kinase activity of cyclin E/CDK2. Mutant human cyclin E protein, lacking this CaM-binding motif, was incapable of binding CaM or responding to [Ca2+]. Taken together, these findings reveal CaM-dependent cyclin E/CDK2 activity as a mediator of the known Ca2+ sensitivity of the G1/S transition of VSMC.
authors.affiliation: Heart & Stroke Richard Lewar Centre of Excellence in Cardiovascular Research, Faculty of Medicine, Department of Medicine, University of Toronto, Ontario, Canada.
authors.forename: Jaehyun
authors.initials: J
authors.lastname: Choi
authors.forename: Andrew
authors.initials: A
authors.lastname: Chiang
authors.forename: Nicolas
authors.initials: N
authors.lastname: Taulier
authors.forename: Robert
authors.initials: R
authors.lastname: Gros
authors.forename: Asif
authors.initials: A
authors.lastname: Pirani
authors.forename: Mansoor
authors.initials: M
authors.lastname: Husain
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D019703:Calcineurin / Q000502:physiology; D002118:Calcium / Q000502:physiology*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D019927:Cyclin E / Q000235:genetics / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D016193:G1 Phase / Q000502:physiology*; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D051379:Mice; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000378:metabolism; D009154:Mutation; D032389:Myocytes, Smooth Muscle / Q000166:cytology* / Q000378:metabolism; D016196:S Phase / Q000502:physiology*
chemical_list: D002147:Calmodulin; D019927:Cyclin E; D007093:Imidazoles; C031938:calmidazolium; D051357:Cyclin-Dependent Kinase 2; D019703:Calcineurin; D002118:Calcium