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Critical proliferation-independent window for basic fibroblast growth factor repression of myogenesis via the p42/p44
L L Tortorella1, D J Milasincic, P F Pilch
1Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
Abstract:
In many cell types including myoblasts, growth factors control proliferation and differentiation, in part, via the mitogen-activated protein kinase (MAPK) pathway (also known as the extracellular regulated kinase (Erk) pathway). In C2C12 myoblast cells, insulin-like growth factor-1 and basic fibroblast growth factor (bFGF) activate MAPK/Erk, and both growth factors promote myoblast proliferation. However, these factors have opposing roles with respect to differentiation; insulin-like growth factor-1 enhances muscle cell differentiation, whereas bFGF inhibits the expression of the muscle-specific transcription factors MyoD and myogenin. Cells treated with bFGF and PD98059, a specific inhibitor of the MAPK pathway, show enhanced expression of the muscle-specific transcription factors MyoD and myogenin as compared with cells not exposed to this inhibitor. Inhibiting MAPK activity also enhances myoblast fusion and the expression of the late differentiation marker myosin heavy chain. Basic FGF mediated repression of muscle-specific genes does not result from continued cell proliferation, since bFGF-treated cells progress through only one round of cell division. We have identified a critical boundary 16 to 20 h after plating during which bFGF induced MAPK activity is able to repress myogenic gene expression and differentiation. Thus, the targets of MAPK that regulate myogenesis are functional at this time and their identification is in progress.
Insights
Basic fibroblast growth factor (bFGF) inhibits muscle cell differentiation by activating the mitogen-activated protein kinase (MAPK) pathway. Inhibiting MAPK enhances myogenic gene expression and differentiation in myoblasts.
Area of Science:
- Cell Biology
- Molecular Biology
- Developmental Biology
Background:
- Growth factors regulate cell proliferation and differentiation in myoblasts.
- The mitogen-activated protein kinase (MAPK) pathway, also known as extracellular regulated kinase (Erk) pathway, is a key signaling cascade involved in these processes.
- Differentiation of muscle cells (myogenesis) involves specific transcription factors like MyoD and myogenin.
Purpose of the Study:
- To investigate the role of MAPK/Erk pathway in mediating the opposing effects of growth factors on myoblast differentiation.
- To determine how basic fibroblast growth factor (bFGF) inhibits muscle-specific gene expression and differentiation.
- To identify the critical time window during which MAPK activity influences myogenesis.
Main Methods:
- Utilized C2C12 myoblast cell line.
- Administered growth factors (insulin-like growth factor-1, bFGF) and a MAPK inhibitor (PD98059).
- Assessed cell proliferation, differentiation markers (MyoD, myogenin, myosin heavy chain), and MAPK/Erk pathway activation.
Main Results:
- Both insulin-like growth factor-1 and bFGF promote myoblast proliferation via MAPK/Erk activation.
- Insulin-like growth factor-1 enhances differentiation, while bFGF inhibits it by repressing myogenic gene expression.
- Inhibition of MAPK activity with PD98059 reversed bFGF-mediated repression, enhancing MyoD, myogenin, and myosin heavy chain expression.
- bFGF-induced MAPK activity represses myogenic gene expression and differentiation within a critical 16-20 hour window after plating.
Conclusions:
- MAPK pathway plays a critical role in regulating myoblast differentiation.
- bFGF inhibits myogenesis through MAPK activation, independent of sustained proliferation.
- Specific MAPK targets regulating myogenesis are active during a defined temporal window, warranting further investigation.