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Cooperating oncogenes converge to regulate cyclin/cdk complexes
A C Lloyd1, F Obermüller, S Staddon
1Imperial Cancer Research Fund (ICRF), London, UK.
Abstract:
The cooperation of oncogenes in the transformation of primary rat Schwann cells is a strikingly synergistic process. We have explored the molecular mechanisms involved. Activation of an inducible Raf kinase results in morphologically transformed cells that are arrested in G1 via the induction of p21(CiP1) and subsequent inhibition of cyclin/cdk activity. In contrast, coexpression of SV40 large T (LT) or a dominant-negative mutant of p53 abolishes p21(CiP1) induction and alleviates the growth arrest. Moreover in this scenario, Raf activation results in an increase in the specific activity of cyclin/cdk complexes with Raf and LT cooperating to superinduce cyclin A/cdk2 activity and stimulate proliferation in the absence of mitogens. Thus, signaling by Raf and its cooperating partners converges at the regulation of cyclin/cdk complexes, with the cellular responses to Raf modulated by p53.
Insights
Oncogene cooperation drives synergistic cell transformation. Raf kinase activation halts cell cycle via p21(CiP1), but SV40 large T antigen or mutant p53 overrides this arrest, promoting proliferation by modulating cyclin/cdk activity.
Area of Science:
- Cellular biology
- Molecular oncology
- Cancer research
Background:
- Oncogene cooperation is crucial for synergistic cell transformation.
- Understanding the molecular mechanisms of oncogene cooperation is key to cancer research.
Purpose of the Study:
- To investigate the molecular mechanisms underlying synergistic transformation of primary rat Schwann cells by cooperating oncogenes.
- To elucidate the roles of Raf kinase, SV40 large T antigen (LT), and p53 in cell cycle regulation during transformation.
Main Methods:
- Activation of an inducible Raf kinase in primary rat Schwann cells.
- Coexpression of SV40 large T (LT) or a dominant-negative p53 mutant.
- Analysis of cell cycle arrest, p21(CiP1) induction, and cyclin/cdk activity.
Main Results:
- Raf kinase activation induced cell cycle arrest at G1 by upregulating p21(CiP1), inhibiting cyclin/cdk activity.
- SV40 LT or dominant-negative p53 abolished p21(CiP1) induction and growth arrest.
- Raf and LT cooperated to increase cyclin A/cdk2 activity, stimulating proliferation independently of mitogens.
Conclusions:
- Raf signaling converges with cooperating partners (LT, p53) at the regulation of cyclin/cdk complexes.
- Cellular responses to Raf activation are modulated by p53 status.
- This study reveals a critical interplay between oncogenes and cell cycle regulators in cancer development.