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v-Myc, but not Max, possesses domains that function in both transcription activation and cellular transformation
1Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907.
Abstract:
Deregulated expression of myc gene family members is associated with the development of malignant neoplasms in several species. Despite the evidence linking expression of this family of nuclear proteins with the proper control of cellular growth and development, the function of the myc protein remains unknown. Intrigued by the observed structural similarity between the myc protein and several eukaryotic transcription factors, we have investigated the ability of the MC29 viral myc protein to activate transcription of a heterologous promoter in C3H10T1/2 cells. Overlapping portions of v-myc coding sequences were inserted 3' to the yeast GAL4 DNA-binding domain and tested for their ability to activate transcription of a chloramphenicol acetyl transferase reporter gene containing GAL4 binding sites. Two transcription activation domains were identified within the amino terminus of v-Myc. The importance of these regions for cellular transformation was examined using ras/myc co-transformation assays. Our results demonstrate that deletion of either of the transcription activation domains, or the DNA-binding and protein oligomerization domains, abolishes the ability of v-Myc to cooperate with Ras to transform C3H10T1/2 cells. Similarly, we investigated whether Max, the protein-binding partner of Myc, also possesses the potential to activate transcription. Interestingly, chimeric GAL4/Max proteins were not functional in our assays, suggesting that the potential of the Myc-Max complex to influence gene expression and function in cellular transformation relies primarily on sequences found within the amino terminus of Myc.
Insights
The myc gene family is linked to cancer. Researchers found two key transcription activation domains in the v-Myc protein, essential for its role in cellular transformation alongside Ras.
Area of Science:
- Molecular Biology
- Oncology
- Cellular Biology
Background:
- The myc gene family plays a role in cell growth and development.
- Deregulated myc gene expression is linked to various cancers.
- The precise function of myc proteins in transcription and cellular transformation is not fully understood.
Purpose of the Study:
- To investigate the transcriptional activation potential of the v-Myc protein.
- To identify functional domains within v-Myc responsible for transcriptional activation and cellular transformation.
- To explore the transcriptional role of the Myc-Max complex.
Main Methods:
- Utilized a yeast GAL4 DNA-binding domain fusion system to test v-Myc domains for transcriptional activation.
- Employed a chloramphenicol acetyl transferase reporter gene assay.
- Conducted ras/myc co-transformation assays to assess the role of v-Myc domains in cellular transformation.
Main Results:
- Identified two transcription activation domains within the amino terminus of v-Myc.
- Demonstrated that deletion of these activation domains, or DNA-binding/oligomerization domains, abrogates v-Myc's ability to cooperate with Ras in cell transformation.
- Found that chimeric GAL4/Max proteins were not transcriptionally active, suggesting Myc's amino terminus is critical for the Myc-Max complex's function.
Conclusions:
- The amino terminus of v-Myc contains critical transcription activation domains necessary for cellular transformation.
- The Myc-Max complex's function in gene expression and cellular transformation relies heavily on sequences within the v-Myc amino terminus.
- These findings provide insight into the molecular mechanisms underlying myc-driven oncogenesis.