Activation and cellular localization of the cyclosporine A-sensitive transcription factor NF-AT in skeletal muscle cells

• Published in: Molecular biology of the cell 1998-10, Vol.9 (10), p.2905-2916
• Main Authors: Abbott, K L, Friday, B B, Thaloor, D, Murphy, T J, Pavlath, G K
• Format: Article
• Language: English
• Subjects: Animals; Calcium - metabolism; Cell Differentiation - drug effects; Cell Nucleus - drug effects; Cell Nucleus - metabolism; Cell Nucleus - ultrastructure; Cells, Cultured; Creatine Kinase - metabolism; Cyclosporine - pharmacology; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Embryo, Mammalian; Humans; Immunohistochemistry; Luciferases - analysis; Luciferases - biosynthesis; Mice; Mice, Inbred C3H; Mice, Inbred Strains; Mice, Knockout; Muscle, Skeletal - cytology; Muscle, Skeletal - drug effects; Muscle, Skeletal - metabolism; Myosin Heavy Chains - biosynthesis; Myosin Heavy Chains - genetics; NFATC Transcription Factors; Nuclear Proteins - metabolism; Recombinant Fusion Proteins - biosynthesis; Regeneration; Transcription Factors - deficiency; Transcription Factors - genetics; Transcription Factors - metabolism
• ISSN: 1059-1524; 1939-4586
• DOI: 10.1091/mbc.9.10.2905

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.