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

J Cell Physiol. 2005 Mar;202(3):787-95. doi: 10.1002/jcp.20174.

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 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcineurin / metabolism
  • Calcium / metabolism*
  • Cell Differentiation / physiology
  • Cell Line
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • GATA2 Transcription Factor
  • Gene Expression Regulation*
  • Hypertrophy
  • Muscle Development
  • Muscle Fibers, Skeletal / cytology*
  • Muscle Fibers, Skeletal / metabolism
  • Muscle Fibers, Slow-Twitch / physiology
  • Myosins / genetics
  • Myosins / metabolism
  • Promoter Regions, Genetic
  • Rats
  • Signal Transduction / physiology
  • Transcription Factors / genetics
  • Transcription Factors / metabolism
  • Transcription, Genetic*

Substances

  • DNA-Binding Proteins
  • GATA2 Transcription Factor
  • Gata2 protein, rat
  • Transcription Factors
  • Calcineurin
  • Myosins
  • Calcium