Activation and cellular localization of the cyclosporine A-sensitive transcription factor NF-AT in skeletal muscle cells.
The widely used immunosuppressant cyclosporine A (CSA) blocks nuclear translocation of the transcription factor, NF-AT (nuclear factor of activated T cells), preventing its activity. mRNA for several NF-AT isoforms has been shown to exist in cells outside of the immune system, suggesting a possible mechanism for side effects associated with CSA treatment. In this study, we demonstrate that CSA inhibits biochemical and morphological differentiation of skeletal muscle cells while having a minimal effect on proliferation. Furthermore, in vivo treatment with CSA inhibits muscle regeneration after induced trauma in mice. These results suggest a role for NF-AT-mediated transcription outside of the immune system. In subsequent experiments, we examined the activation and cellular localization of NF-AT in skeletal muscle cells in vitro. Known pharmacological inducers of NF-AT in lymphoid cells also stimulate transcription from an NF-AT-responsive reporter gene in muscle cells. Three isoforms of NF-AT (NF-ATp, c, and 4/x/c3) are present in the cytoplasm of muscle cells at all stages of myogenesis tested. However, each isoform undergoes calcium-induced nuclear translocation from the cytoplasm at specific stages of muscle differentiation, suggesting specificity among NF-AT isoforms in gene regulation. Strikingly, one isoform (NF-ATc) can preferentially translocate to a subset of nuclei within a single multinucleated myotube. These results demonstrate that skeletal muscle cells express functionally active NF-AT proteins and that the nuclear translocation of individual NF-AT isoforms, which is essential for the ability to coordinate gene expression, is influenced markedly by the differentiation state of the muscle cell.
Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
K L
KL
Abbott
B B
BB
Friday
D
D
Thaloor
T J
TJ
Murphy
G K
GK
Pavlath
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D003402:Creatine Kinase / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004622:Embryo, Mammalian; D006801:Humans; D007150:Immunohistochemistry; D008156:Luciferases / Q000032:analysis / Q000096:biosynthesis; D051379:Mice; D008809:Mice, Inbred C3H; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000096:biosynthesis / Q000235:genetics; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012038:Regeneration; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
D004268:DNA-Binding Proteins; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D016572:Cyclosporine; D008156:Luciferases; D003402:Creatine Kinase; D018995:Myosin Heavy Chains; D002118:Calcium