Hypertrophy and transcriptional regulation induced in myogenic cell line L6-C5 by an increase of extracellular calcium

✍ Scribed by V. De Arcangelis; D. Coletti; M. Canato; M. Molinaro; S. Adamo; C. Reggiani; F. Naro

• Book ID: 102312976
• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 430 KB
• Volume: 202
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.20174

✦ Synopsis

Abstract

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 Ca^2+^ concentration ([Ca^2+^]~o~), which induces an increase of intracellular calcium ([Ca^2+^]~i~) without involving Ca^2+^ release from the intracellular stores but exclusively due to plasma membrane influx (Naro et al., 2003). Exposure of L6‐C5 cells to [Ca^2+^]~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 Ca^2+^ responsive phosphatase calcineurin. Furthermore, transient exposure of L6‐C5 cells to high [Ca^2+^]~o~ increased the expression of luciferase reporter driven by myoglobin (Mb) and β‐MHC promoters but not IIB‐MHC and MCK promoters. Luciferase transcription driven by CK promoter was, instead, enhanced by mobilizing Ca^2+^ from the intracellular stores. These data indicate that a transient increase of [Ca^2+^]~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. © 2004 Wiley‐Liss, Inc.