Transformation suppressor activity of a Jun transcription factor lacking its activation domain

Area of Science:

• Oncology
• Molecular Biology
• Cellular Transformation

Background:

• The oncoprotein c-Jun is implicated in Ras-mediated cell transformation.
• Both c-Jun synthesis and transcription factor activity are upregulated by Ras.
• c-Jun and Ras cooperate in transformation assays, suggesting distinct but interacting pathways.

Purpose of the Study:

• To investigate the necessity of c-Jun, potentially with interacting factors, for Ras-mediated cell transformation.
• To characterize a dominant-negative Jun mutant's effect on transcription and cell transformation.
• To explore the potential of Jun mutants as anti-oncogenes.

Main Methods:

• Utilized a dominant-negative mutated transcription factor (Jun mutant) lacking an activation domain.
• Assessed the inhibition of transcription stimulation by various oncoproteins and a tumor promoter (TPA).
• Examined the specificity of inhibition for Jun-binding motifs, contrasting with NF-kappa B/Rel motif activation.
• Evaluated the Jun mutant's anti-oncogenic activity in Ras-transformed cells, assessing growth characteristics and tumorigenicity.

Main Results:

• The dominant-negative Jun mutant specifically blocks transcription stimulation mediated by Ras and other oncoproteins.
• Inhibition is specific to Jun-binding motifs, leaving NF-kappa B/Rel activation unaffected.
• The Jun mutant functions as an anti-oncogene in Ras-transformed cells, inducing reversion to non-transformed phenotypes.
• Revertant cells exhibit restored anchorage and density-dependent growth and reduced in vivo tumorigenicity.

Conclusions:

• c-Jun, potentially with interacting partners, is necessary for Ras-mediated cell transformation.
• Dominant-negative Jun mutants can serve as anti-oncogenes, reversing oncogenic phenotypes.
• This approach offers a method to study the role of transcription factors in signal transduction and transformation.