NFAT activation by membrane potential follows a calcium pathway distinct from other activity-related transcription factors in skeletal muscle cells.
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.
Valdés
Juan Antonio
JA
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.
Gaggero
Eduardo
E
Hidalgo
Jorge
J
Leal
Nancy
N
Jaimovich
Enrique
E
Carrasco
M Angélica
MA
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
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