title: NFAT activation by membrane potential follows a calcium pathway distinct from other activity-related transcription factors in skeletal muscle cells.
abstract: Depolarization of skeletal muscle cells triggers intracellular Ca2+ signals mediated by ryanodine and inositol 1,4,5-trisphosphate (IP3) receptors. Previously, we have reported that K+-induced depolarization activates transcriptional regulators ERK, cAMP response element-binding protein, c-fos, c-jun, and egr-1 through IP3-dependent Ca2+ release, whereas NF-kappa B activation is elicited by both ryanodine and IP3 receptor-mediated Ca2+ signals. We have further shown that field stimulation with electrical pulses results in an NF-kappa B activation increase dependent of the amount of pulses and independent of their frequency. In this work, we report the results obtained for nuclear factor of activated T cells (NFAT)-mediated transcription and translocation generated by both K+ and electrical stimulation protocols in primary skeletal muscle cells and C2C12 cells. The Ca2+ source for NFAT activation is through release by ryanodine receptors and extracellular Ca2+ entry. We found this activation to be independent of the number of pulses within a physiological range of stimulus frequency and enhanced by long-lasting low-frequency stimulation. Therefore, activation of the NFAT signaling pathway differs from that of NF-kappa B and other transcription factors. Calcineurin enzyme activity correlated well with the relative activation of NFAT translocation and transcription using different stimulation protocols. Furthermore, both K+-induced depolarization and electrical stimulation increased mRNA levels of the type 1 IP3 receptor mediated by calcineurin activity, which suggests that depolarization may regulate IP3 receptor transcription. These results confirm the presence of at least two independent pathways for excitation-transcription coupling in skeletal muscle cells, both dependent on Ca2+ release and triggered by the same voltage sensor but activating different intracellular release channels.
authors.affiliation: Centro Fondo de Investigación Avanzado en Areas Prioritarias de Estudios Moleculares de la Célula, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile.
authors.forename: Juan Antonio
authors.initials: JA
authors.lastname: Valdés
authors.forename: Eduardo
authors.initials: E
authors.lastname: Gaggero
authors.forename: Jorge
authors.initials: J
authors.lastname: Hidalgo
authors.forename: Nancy
authors.initials: N
authors.lastname: Leal
authors.forename: Enrique
authors.initials: E
authors.lastname: Jaimovich
authors.forename: M Angélica
authors.initials: MA
authors.lastname: Carrasco
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D000831:Animals, Newborn; D019703:Calcineurin / Q000378:metabolism; D065095:Calcineurin Inhibitors; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002460:Cell Line; D016572:Cyclosporine / Q000494:pharmacology; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000235:genetics / Q000378:metabolism; D008564:Membrane Potentials; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D050778:NFATC Transcription Factors / Q000378:metabolism*; D010766:Phosphorylation; D011188:Potassium / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D065095:Calcineurin Inhibitors; D004791:Enzyme Inhibitors; D053496:Inositol 1,4,5-Trisphosphate Receptors; D050778:NFATC Transcription Factors; D012333:RNA, Messenger; D019837:Ryanodine Receptor Calcium Release Channel; D016572:Cyclosporine; D019703:Calcineurin; D011188:Potassium; D002118:Calcium