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Ras/MAP kinase pathway is associated with the control of myotube formation but not myofibril assembly in quail
E Hirayama1, A Isobe, Y Kajihara
1Institute of Molecular and Cellular Biology for Pharmaceutical Sciences, Kyoto Pharmaceutical University, Japan.
Abstract:
Tyrosine kinase activity of v-Src from Rous sarcoma virus (RSV) inhibits the differentiation of quail myoblasts. To clarify the inhibitory mechanism, we focused on the signaling pathways from v-Src. When the activation of the Ras/MAP (mitogen-activated protein) kinase pathway was inhibited by a dominant-negative mutant of Ras or PD98059, a specific inhibitor of p42 MAP kinase kinase, differentiation was restored; muscle specific proteins were expressed and myotubes formed even under active conditions of v-Src. Wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase (P13-kinase), showed no effects on the inhibition by v-Src. These findings suggest that v-Src activates the Ras/MAP kinase signaling pathway, but not the P13-kinase pathway, and inhibits the differentiation. However, the myotubes derived from the dominant-negative Ras did not form actin fibers, suggesting that myofibril assembly is regulated by other pathway(s) from v-Src.
Insights
Rous sarcoma virus (RSV) v-Src tyrosine kinase inhibits quail myoblast differentiation by activating the Ras/MAP kinase pathway. Inhibiting this pathway restores differentiation, but myofibril assembly requires additional signaling.
Area of Science:
- Cell Biology
- Molecular Biology
- Virology
Background:
- Rous sarcoma virus (RSV) encodes v-Src, a tyrosine kinase.
- v-Src activity is known to interfere with cellular differentiation processes.
- Understanding the specific signaling pathways modulated by v-Src is crucial for elucidating its inhibitory mechanisms.
Purpose of the Study:
- To investigate the molecular mechanisms by which v-Src tyrosine kinase inhibits quail myoblast differentiation.
- To identify the specific signaling pathways activated by v-Src that mediate this inhibition.
- To differentiate the roles of Ras/MAP kinase and phosphatidylinositol 3-kinase (P13-kinase) pathways in v-Src-induced inhibition.
Main Methods:
- Utilized dominant-negative Ras mutants and PD98059 (p42 MAP kinase kinase inhibitor) to block Ras/MAP kinase signaling.
- Employed wortmannin, a specific inhibitor of P13-kinase, to assess its role.
- Monitored quail myoblast differentiation, including muscle-specific protein expression and myotube formation.
- Observed actin fiber formation in differentiated myotubes.
Main Results:
- Inhibition of the Ras/MAP kinase pathway, using dominant-negative Ras or PD98059, restored myoblast differentiation despite active v-Src.
- Muscle-specific proteins were expressed, and myotubes formed when Ras/MAP kinase signaling was blocked.
- Wortmannin treatment showed no effect on v-Src-mediated inhibition of differentiation.
- Myotubes derived from cells with inhibited Ras/MAP kinase signaling failed to form actin fibers.
Conclusions:
- v-Src inhibits quail myoblast differentiation primarily through the activation of the Ras/MAP kinase signaling pathway.
- The P13-kinase pathway is not involved in v-Src's inhibition of myoblast differentiation.
- While Ras/MAP kinase signaling is essential for differentiation, other v-Src-regulated pathways are involved in myofibril assembly.