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      Regulation of gene expression by NFAT transcription factors in hibernating ground squirrels is dependent on the cellular environment

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          Calcineurin is a calmodulin-stimulated phosphatase that regulates the nuclear translocation of nuclear factor of activated T cell (NFAT) c1-4 through dephosphorylation. We believe that this mechanism plays various roles in the remodeling and maintenance of Ictidomys tridecemlineatus skeletal muscle. During hibernation, bouts of torpor and arousal take place, and squirrels do not lose muscle mass despite being inactive. Protein expression of Ca 2+ signaling proteins were studied using immunoblotting. A DNA-protein interaction ELISA technique was created to test the binding of NFATs in the nucleus to DNA probes containing the NFAT response element under environmental conditions reflective of those during hibernation. Calcineurin protein levels increased by 3.08-fold during torpor (compared to euthermic control), whereas calpain1 levels also rose by 3.66-fold during torpor. Calmodulin levels were elevated upon entering torpor. NFATc4 binding to DNA showed a 1.4-fold increase during torpor, and we found that this binding was further enhanced when 600 nM of Ca 2+ was supplemented. We also found that decreasing the temperature of ELISAs resulted in progressive decreases in the binding of NFATs c1, c3, and c4 to DNA. In summary, calmodulin and calpain1 appear to activate calcineurin and NFATc4 during torpor. NFAT binding to target promoters is affected by intranuclear [Ca 2+] and environmental temperatures. Therefore, Ca 2+ signaling and temperature changes play key roles in regulation of the NFAT-calcineurin pathway in skeletal muscle of hibernating 13-lined ground squirrels over the torpor-arousal cycle, and they may contribute to the avoidance of disuse-induced muscle atrophy that occurs naturally in these animals.

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          Author and article information

          613-520-3678 , kenneth.storey@carleton.ca
          Cell Stress Chaperones
          Cell Stress Chaperones
          Cell Stress & Chaperones
          Springer Netherlands (Dordrecht )
          25 June 2016
          September 2016
          : 21
          : 5
          : 883-894
          Institute of Biochemistry and Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6 Canada
          PMC5003805 PMC5003805 5003805 713
          © Cell Stress Society International 2016
          Funded by: Natural Sciences and Engineering Research Council of Canada (CA)
          Award ID: 6793
          Award Recipient :
          Original Paper
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          © Cell Stress Society International 2016


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