title: Activity- and calcineurin-independent nuclear shuttling of NFATc1, but not NFATc3, in adult skeletal muscle fibers.
abstract: The transcription factor NFATc1 may be involved in slow skeletal muscle gene expression. NFATc1 translocates from cytoplasm to nuclei during slow fiber type electrical stimulation of skeletal muscle fibers because of activation of the Ca(2+)-dependent phosphatase calcineurin, resulting in nuclear factor of activated T-cells (NFAT) dephosphorylation and consequent exposure of its nuclear localization signal. Here, we find that unstimulated adult skeletal muscle fibers exhibit a previously unanticipated nucleocytoplasmic shuttling of NFATc1 without appreciable nuclear accumulation. In resting fibers, the nuclear export inhibitor leptomycin B caused nuclear accumulation of NFATc1 (but not of isoform NFATc3) and formation of NFATc1 intranuclear bodies independent of calcineurin. The rate of nuclear uptake of NFATc1 was 4.6 times lower in resting fibers exposed to leptomycin B than during electrical stimulation. Inhibitors of glycogen synthase kinase and protein kinase A or of casein kinase 1 slowed the decay of nuclear NFATc1 after electrical stimulation, but they did not cause NFATc1 nuclear uptake in unstimulated fibers. We propose that two nuclear translocation pathways, one pathway mediated by calcineurin activation and NFAT dephosphorylation and the other pathway independent of calcineurin and possibly independent of NFAT dephosphorylation, determine the distribution of NFATc1 between cytoplasm and nuclei in adult skeletal muscle.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Tiansheng
authors.initials: T
authors.lastname: Shen
authors.forename: Yewei
authors.initials: Y
authors.lastname: Liu
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Cseresnyés
authors.forename: Arie
authors.initials: A
authors.lastname: Hawkins
authors.forename: William R
authors.initials: WR
authors.lastname: Randall
authors.forename: Martin F
authors.initials: MF
authors.lastname: Schneider
mesh_terms: D000818:Animals; D019703:Calcineurin / Q000378:metabolism; D065095:Calcineurin Inhibitors; D047389:Casein Kinase I / Q000037:antagonists & inhibitors / Q000378:metabolism; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism*; D004558:Electric Stimulation; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006801:Humans; D045586:Intranuclear Inclusion Bodies / Q000737:chemistry; D051379:Mice; D008815:Mice, Inbred Strains; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology; D050778:NFATC Transcription Factors / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects
chemical_list: D065095:Calcineurin Inhibitors; D005231:Fatty Acids, Unsaturated; D050778:NFATC Transcription Factors; C494003:NFATC1 protein, human; C494008:NFATC3 protein, human; D047428:Protein Kinase Inhibitors; D047389:Casein Kinase I; D017868:Cyclic AMP-Dependent Protein Kinases; D019703:Calcineurin; C038753:leptomycin B