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Mitogen-activated protein kinase pathway is involved in the differentiation of muscle cells
E Gredinger1, A N Gerber, Y Tamir
1Department of Biochemistry, Rappaport Institute for Research in the Medical Sciences, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa 31096, Israel.
Abstract:
The differentiation of muscle cells is controlled by the MyoD family of transcription factors. This family is regulated by extracellular growth factors that transmit largely unknown signals into the cells. Here we show that the activity of extracellular signal-regulated protein kinase (ERK), a kinase that is part of the mitogen-activated protein kinase (MAPK) cascade, is low in myoblasts and is induced with the onset of terminal differentiation of C2 cells. ERK activity is also induced in fibroblasts that were modified to express MyoD, but not in the parental fibroblast cells. Thus, ERK induction is an intrinsic property of muscle cells. A specific MAPK kinase inhibitor (PD098059) that was added to C2 cells partially inhibited the fusion of myoblasts to multinucleated myotubes without affecting the expression of muscle-specific markers. This inhibitor blocked the induction of MyoD expression that normally takes place during terminal differentiation. Two lines of evidence suggest that the MAPK cascade induces the activity of MyoD: 1) the expression of constitutively activated forms of MEK1 or Raf1 enhanced the transcriptional activity of MyoD in 10T1/2 fibroblasts; and 2) the addition of PD098059 to fibroblast cells expressing a conditional MyoD-estrogen fusion protein significantly inhibited the expression of MyoD-responsive genes. Our results indicate that the MAPK pathway is activated in differentiating muscle cells and that it positively regulates the expression and activity of MyoD protein.
Insights
The mitogen-activated protein kinase (MAPK) pathway, specifically extracellular signal-regulated kinase (ERK), is activated during muscle cell differentiation. This pathway positively regulates the MyoD transcription factor, crucial for muscle development.
Area of Science:
- Cell Biology
- Molecular Biology
- Developmental Biology
Background:
- Muscle cell differentiation is orchestrated by MyoD transcription factors.
- Extracellular growth factors regulate MyoD, but intracellular signaling pathways remain largely uncharacterized.
Purpose of the Study:
- To investigate the role of the mitogen-activated protein kinase (MAPK) cascade, particularly extracellular signal-regulated kinase (ERK), in muscle cell differentiation.
- To determine if ERK activation is an intrinsic property of muscle cells and its relationship with MyoD.
Main Methods:
- Assessed ERK activity in differentiating C2 myoblasts and MyoD-expressing fibroblasts.
- Utilized a specific MAPK kinase inhibitor (PD098059) to examine its effects on myoblast fusion and MyoD expression.
- Investigated MyoD transcriptional activity using constitutively active MEK1/Raf1 and MyoD-estrogen fusion proteins in fibroblasts.
Main Results:
- ERK activity was low in myoblasts and induced upon terminal differentiation in C2 cells and MyoD-expressing fibroblasts.
- PD098059 partially inhibited myoblast fusion and blocked MyoD induction.
- Activating MAPK pathway components enhanced MyoD transcriptional activity, while inhibition reduced MyoD-responsive gene expression.
Conclusions:
- The MAPK pathway is activated during muscle cell differentiation.
- MAPK signaling positively regulates MyoD expression and activity, playing a key role in the differentiation process.