title: Regulation of the nuclear export of the transcription factor NFATc1 by protein kinases after slow fibre type electrical stimulation of adult mouse skeletal muscle fibres.
abstract: The transcription factor nuclear factor of activated T cells (NFAT)c1 has been shown to be involved in turning on slow skeletal muscle fibre gene expression. Previous studies from our laboratory have characterized the stimulation pattern-dependent nuclear import and resting shuttling of NFATc1-green fluorescent protein (GFP) in flexor digitorum brevis (FDB) muscle fibres from adult mouse. In this study, we use viral expression of the transcription factor NFATc1-GFP fusion protein to investigate the mechanisms underlying the nuclear export of the NFATc1-GFP that accumulated in the nuclei of cultured dissociated adult mouse FDB muscle fibres during slow-twitch fibre type electrical stimulation. In these studies, we found that inhibition of either glycogen synthase kinase 3beta (GSK3beta) or casein kinase 1 or 2 (CK1/2) markedly slowed the decay of nuclear NFATc1-GFP after cessation of muscle fibre electrical stimulation, whereas inhibition of casein kinase 1delta, p38 mitogen-activated protein kinase, c-Jun N-terminal kinase and protein kinase A had little effect. Simultaneous inhibition of GSK3beta and CK1/2 completely blocked the nuclear export of NFATc1-GFP after muscle activity. We also developed a simplified model of NFATc1 phosphorylation/dephosphorylation and nuclear fluxes, and used this model to simulate the observed time courses of nuclear NFATc1-GFP with and without NFATc1 kinase inhibition. Our results suggest that GSK3beta and CK1/2 are the major protein kinases that contribute to the removal of NFATc1 that accumulates in muscle fibre nuclei during muscle activity, and that GSK3beta and CK1/2 are responsible for phosphorylating NFATc1 in muscle nuclei in a complementary or synergistic fashion.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 108 North Greene Street, Baltimore, MD 21201-1503, USA.
authors.forename: Tiansheng
authors.initials: T
authors.lastname: Shen
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Cseresnyés
authors.forename: Yewei
authors.initials: Y
authors.lastname: Liu
authors.forename: William R
authors.initials: WR
authors.lastname: Randall
authors.forename: Martin F
authors.initials: MF
authors.lastname: Schneider
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D047389:Casein Kinase I / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D047390:Casein Kinase II / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D004558:Electric Stimulation; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D049452:Green Fluorescent Proteins; D051379:Mice; D008815:Mice, Inbred Strains; D008962:Models, Theoretical; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000502:physiology*; D050778:NFATC Transcription Factors / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors
chemical_list: D050778:NFATC Transcription Factors; C494005:Nfatc1 protein, mouse; D049452:Green Fluorescent Proteins; D047389:Casein Kinase I; D047390:Casein Kinase II; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3