Related Experiment Videos
An activated c-Ha-ras allele blocks the induction of muscle-specific genes whose expression is contingent on mitogen
Abstract:
During myogenesis, induction of muscle-specific genes is subject to negative control by polypeptide mitogens and type-beta transforming growth factor. Since transduction of growth factor signals may require proteins encoded by cellular ras oncogenes, we have tested whether a mutationally altered Harvey ras expression vector, by itself, can prevent establishment of a differentiated phenotype in BC3H1 mouse myoblasts. Transfection with the valine-12 allele of the human Harvey ras gene, under the control of its own promoter, was sufficient to prevent the induction of both muscle creatine kinase activity and the nicotinic acetylcholine receptor following mitogen withdrawal but did not inhibit withdrawal from the cell cycle. The loss of creatine kinase activity resulted from a corresponding block to induction of muscle creatine kinase mRNA. Similarly, mitogen withdrawal elicited little or no alpha-actin mRNA in ras-transfected cells. These results suggest that an activated ras allele can inhibit myogenesis through a mechanism independent of cell proliferation and can preclude activation of genes whose up-regulation normally accompanies mitogen withdrawal.
Insights
An activated ras oncogene can block muscle cell differentiation by preventing the activation of muscle-specific genes, independent of cell proliferation. This finding impacts understanding of myogenesis and cancer development.
Area of Science:
- Molecular Biology
- Cell Biology
- Developmental Biology
Background:
- Muscle-specific gene induction during myogenesis is negatively regulated by growth factors.
- Growth factor signaling pathways often involve proteins encoded by cellular ras oncogenes.
Purpose of the Study:
- To investigate if a mutated Harvey ras oncogene can inhibit the differentiation of BC3H1 mouse myoblasts.
- To determine if ras oncogene activation affects muscle-specific gene expression independently of cell cycle withdrawal.
Main Methods:
- Transfection of BC3H1 myoblasts with a valine-12 allele of the human Harvey ras gene.
- Assessment of muscle creatine kinase activity and nicotinic acetylcholine receptor expression.
- Quantification of muscle creatine kinase and alpha-actin mRNA levels following mitogen withdrawal.
Main Results:
- Transfection with activated Harvey ras prevented the induction of muscle creatine kinase activity and nicotinic acetylcholine receptor.
- The block in creatine kinase activity correlated with a failure to induce muscle creatine kinase mRNA.
- Activated ras also inhibited the induction of alpha-actin mRNA, indicating a broader effect on muscle-specific gene activation.
- Ras-induced inhibition of differentiation occurred without affecting withdrawal from the cell cycle.
Conclusions:
- An activated ras oncogene can inhibit myogenesis independently of cell proliferation.
- Ras signaling can block the activation of key muscle-specific genes required for differentiation.
- These findings suggest a role for ras in regulating developmental processes beyond cell cycle control.