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Serum-independent phosphorylation of c-Jun and alterations in AP-1 components by transformation with various
S Kamada1, K Toyoshima, T Akiyama
1Department of Oncogene Research, Osaka University, Japan.
Abstract:
To understand the mechanisms regulating the transactivating activity of Jun/AP-1, we analyzed alterations in c-Jun induced by growth stimulation and cell transformation. Serum stimulation of quiescent NIH3T3 cells induced a marked increase in phosphorylation of c-Jun in its amino-terminal activation domain. On the other hand, this domain was highly phosphorylated, in a serum-independent manner, in cells transformed with various oncogenes, including active c-raf-1, v-src, active Ha-ras, and active erbB-2. There were no obvious differences in the phosphorylation states of c-Jun in exponentially growing normal and transformed cells. However, in the exponentially growing state, the TRECAT activity in transformed cells was markedly higher than that in normal cells. Gel retardation analysis indicated that the AP-1 components in transformed cells were significantly different from those in normal cells. These results suggest that some other alterations besides phosphorylation of c-Jun are involved in enhancement of AP-1 activity in exponentially growing transformed cells.
Insights
Cell transformation and growth stimulation alter c-Jun phosphorylation, impacting Jun/AP-1 activity. Transformed cells show enhanced AP-1 activity due to factors beyond c-Jun phosphorylation.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncogenesis
Background:
- Jun/AP-1 transcription factors regulate gene expression critical for cell growth and differentiation.
- Dysregulation of Jun/AP-1 activity is implicated in various cancers.
- Understanding c-Jun regulation is key to deciphering oncogenic transformation.
Purpose of the Study:
- To investigate the regulatory mechanisms of Jun/AP-1 transactivating activity.
- To analyze alterations in c-Jun phosphorylation during growth stimulation and oncogenic transformation.
- To identify factors contributing to enhanced AP-1 activity in transformed cells.
Main Methods:
- Serum stimulation of quiescent NIH3T3 cells.
- Analysis of c-Jun phosphorylation in normal and oncogene-transformed cells.
- TRECAT assay to measure AP-1 activity.
- Gel retardation analysis to assess AP-1 components.
Main Results:
- Serum stimulation increased c-Jun phosphorylation in normal cells.
- Transformed cells exhibited serum-independent, high c-Jun phosphorylation.
- No significant differences in c-Jun phosphorylation between exponentially growing normal and transformed cells.
- Markedly higher TRECAT activity in exponentially growing transformed cells compared to normal cells.
- Distinct AP-1 components in transformed versus normal cells.
Conclusions:
- c-Jun phosphorylation is modulated by growth stimulation and oncogenic transformation.
- Enhanced AP-1 activity in transformed cells involves alterations beyond c-Jun phosphorylation.
- Further investigation into AP-1 component changes is necessary to understand oncogenic transformation.