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Analysis of AP-1 function in cellular transformation pathways
1Department of Tumor Virus Research, University of Tokyo, Japan.
Abstract:
To understand the role of endogenous AP-1 activity in cellular transformation induced by oncogenes, we have made use of a fos mutant (supfos-1) and a jun mutant (supjun-1), either of which can function as a transdominant inhibitor of AP-1-mediated transcriptional regulation. Chicken embryo fibroblasts (CEF) infected with a series of transforming retroviruses were doubly infected with retrovirus carrying supfos-1 or supjun-1, and suppression of cellular transformation was monitored in terms of reversion to normal cellular morphology or acquisition of anchorage-dependent growth. Cellular transformation induced by several exogenously expressed transforming genes of the fos or jun family was efficiently suppressed, as expected. CEF transformed by v-src, v-yes, v-fps, c-Ha-ras, and N-terminally truncated c-raf were also induced to revert to the normal phenotype by these transdominant mutants, suggesting that functional transcription factor AP-1 activity is essential for the cellular transformation induced by these oncogenes. The suppression is not attributable to nonspecific inhibition of cellular proliferation, because CEF transformed by v-ros or v-myc were not induced to revert to the normal phenotype. We next analyzed changes in all known components of chicken AP-1 induced by v-src, c-Ha-ras, or activated c-raf transformation. The levels of both Fra-2 and c-Jun expression were elevated two- to fourfold, and hyperphosphorylation of Fra-2 was also observed. We further showed that Fra-2-c-Jun heterodimer is mainly responsible for the elevated AP-1 DNA-binding activity in these transformed cells, and we propose that this heterodimer play a crucial role in the transformation induced by these oncogenes.
Insights
Inhibiting AP-1 (activator protein-1) transcription factor activity suppressed oncogene-induced cellular transformation. The Fra-2/c-Jun heterodimer is crucial for this transformation, highlighting AP-1
Area of Science:
- Molecular Biology
- Oncology
- Cellular Biology
Background:
- Activating protein-1 (AP-1) is a transcription factor implicated in cellular processes.
- Understanding AP-1's role in oncogene-induced cellular transformation is crucial for cancer research.
Purpose of the Study:
- To investigate the necessity of endogenous AP-1 activity for cellular transformation mediated by various oncogenes.
- To identify specific AP-1 components involved in oncogenic transformation.
Main Methods:
- Utilized transdominant inhibitory fos (supfos-1) and jun (supjun-1) mutants in chicken embryo fibroblasts (CEF).
- Assessed suppression of cellular transformation by monitoring reversion to normal morphology and anchorage-dependent growth.
- Analyzed expression and activity of AP-1 components in oncogene-transformed CEF.
Main Results:
- supfos-1 and supjun-1 efficiently suppressed transformation induced by fos/jun family oncogenes, v-src, v-yes, v-fps, c-Ha-ras, and c-raf.
- Suppression was specific, as CEF transformed by v-ros or v-myc did not revert.
- v-src, c-Ha-ras, and c-raf transformation elevated Fra-2 and c-Jun expression, with Fra-2 hyperphosphorylation observed.
- The Fra-2/c-Jun heterodimer was identified as the primary driver of elevated AP-1 DNA-binding activity in transformed cells.
Conclusions:
- Endogenous AP-1 activity is essential for cellular transformation induced by a range of oncogenes.
- The Fra-2/c-Jun heterodimer plays a critical role in oncogene-induced cellular transformation.