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Chimeras of herpes simplex viral VP16 and jun are oncogenic
E R Schuur1, E J Parker, P K Vogt
1Department of Microbiology, University of Southern California School of Medicine, Los Angeles.
Abstract:
The Jun protein binds DNA and regulates transcription as a component of the AP-1 transcription factor complex. In its oncogenic form, Jun can transform cells in culture and cause tumors in animals. Both trans-activation and transformation require several functional domains of Jun, including an amino-terminal trans-activation domain. In this study, properties of Jun required for trans-activation and transformation were explored by replacing the trans-activation domains of c-Jun and its oncogenic counterpart, v-Jun, with the constitutively active trans-activation domain from the herpes simplex virus VP16 protein. The VP16-v-Jun chimera retained similar oncogenic properties to its parent, v-Jun. The VP16-c-Jun chimera, however, was considerably more oncogenic than c-Jun. Substitutions of a phenylalanine in the VP16 domain of the VP16-c-Jun chimera diminished or abolished transformation. Each of the chimeras bound to the AP-1 consensus recognition sequence from the collagenase promoter or from the human T-cell leukemia virus type I long terminal repeat in vitro. None of the VP16-Jun chimeras efficiently stimulated transcription from the collagenase promoter or an artificial promoter containing the human T-cell leukemia virus type I element in vivo. These results demonstrate that the Jun trans-activation domain can be replaced by a heterologous trans-activation domain with retention of oncogenic activity. However, this oncogenic activity is not reflected in the trans-activating properties of the chimeras.
Insights
Replacing the Jun protein's trans-activation domain with VP16 retained oncogenic activity but altered trans-activation properties. This study explores Jun protein's functional domains in cell transformation and transcription regulation.
Area of Science:
- Molecular Biology
- Oncology
- Virology
Background:
- Jun protein, a component of the AP-1 transcription factor complex, regulates DNA binding and transcription.
- Oncogenic forms of Jun, like v-Jun, can induce cell transformation and tumor formation.
- Functional domains, including the amino-terminal trans-activation domain, are crucial for Jun's activity.
Purpose of the Study:
- To investigate the role of Jun's trans-activation domain in its oncogenic and trans-activating functions.
- To explore whether a heterologous trans-activation domain can substitute for Jun's native domain while maintaining oncogenic potential.
Main Methods:
- Constructing chimeric proteins by replacing the trans-activation domains of c-Jun and v-Jun with the VP16 trans-activation domain.
- Assessing the oncogenic properties of these chimeras in cell transformation and animal tumor models.
- Evaluating the DNA-binding and trans-activating capabilities of the chimeras in vitro and in vivo.
Main Results:
- The VP16-v-Jun chimera exhibited oncogenic properties similar to v-Jun.
- The VP16-c-Jun chimera displayed significantly enhanced oncogenicity compared to c-Jun.
- Mutations in the VP16 domain of VP16-c-Jun reduced or abolished transformation.
- All chimeras bound to AP-1 recognition sequences but failed to efficiently stimulate transcription in vivo.
Conclusions:
- The Jun trans-activation domain can be functionally replaced by a heterologous domain (VP16) with retention of oncogenic activity.
- Oncogenic potential does not directly correlate with enhanced trans-activating capacity when the trans-activation domain is altered.
- These findings provide insights into the distinct mechanisms underlying Jun-mediated transformation and transcription regulation.