Hypertrophy and transcriptional regulation induced in myogenic cell line L6-C5 by an increase of extracellular calcium.
Calcium plays a pivotal role in the establishment of the differentiated phenotype in myogenic cells but the involved molecular mechanisms are still matter of debate. Here we studied the effects of exposing L6-C5 myogenic cells to high extracellular Ca2+ concentration ([Ca2+]o), which induces an increase of intracellular calcium ([Ca2+]i) without involving Ca2+ release from the intracellular stores but exclusively due to plasma membrane influx (Naro et al., 2003). Exposure of L6-C5 cells to [Ca2+]o up to 20 mM for 30 min, before shifting them into a differentiative medium, induced the appearance of multinucleated, myosin-positive myotubes, much larger than in control cells with an increased protein/DNA ratio. These large myotubes showed nuclear accumulation of the hypertrophy marker GATA-2. The hypertrophic growth of these cells was blocked by cyclosporin A (CsA), FK506, or overexpression of a calcineurin-dominant negative protein, suggesting the involvement in this process of the Ca2+ responsive phosphatase calcineurin. Furthermore, transient exposure of L6-C5 cells to high [Ca2+]o increased the expression of luciferase reporter driven by myoglobin (Mb) and beta-MHC promoters but not IIB-MHC and MCK promoters. Luciferase transcription driven by CK promoter was, instead, enhanced by mobilizing Ca2+ from the intracellular stores. These data indicate that a transient increase of [Ca2+]i due to plasma-membrane influx is sufficient to induce a hypertrophic phenotype and an increased expression of slow-fiber genes but not fast-fiber genes.
De Arcangelis
V
V
Dipartimento di Istologia ed Embriologia Medica, Università di Roma La Sapienza, Italy.
Coletti
D
D
Canato
M
M
Molinaro
M
M
Adamo
S
S
Reggiani
C
C
Naro
F
F
D000818:Animals; D019703:Calcineurin / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D050989:GATA2 Transcription Factor; D005786:Gene Expression Regulation; D006984:Hypertrophy; D024510:Muscle Development; D018485:Muscle Fibers, Skeletal / Q000166:cytology* / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology; D009218:Myosins / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D051381:Rats; D015398:Signal Transduction / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; D050989:GATA2 Transcription Factor; C494713:Gata2 protein, rat; D014157:Transcription Factors; D019703:Calcineurin; D009218:Myosins; D002118:Calcium