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Transformation by Raf and other oncogenes renders cells differentially sensitive to growth inhibition by a dominant
U R Rapp1, J Troppmair, T Beck
1Laboratory of Viral Carcinogenesis, National Cancer Institute, Frederick Cancer Research and Development Center, Maryland 21702-1201.
Abstract:
In NIH3T3 cells expressing active Raf-1 protein serine/threonine kinase (PSK) c-jun expression is constitutive while c-fos expression is attenuated. This alteration prompted us to determine whether oncogene transformation would render cells differentially sensitive to growth inhibition by a dominant negative mutant of c-jun, TAM 67. Growth inhibition was observed in three types of assays: (1) transfection of TAM 67 into cells stably transformed by a variety of oncogenes, (2) cotransfection of TAM 67 with oncogene expression plasmids into NIH3T3 cells and (3) titration of oncogene-expressing retroviruses on cells stably expressing TAM 67. The results clearly demonstrate that Raf-1 dependent oncogenes, which include receptor protein tyrosine kinases (PTKs)-, intracellular PTKs- and Ras-derived genes share the Raf phenotype of constitutive c-jun expression, attenuated c-fos induction, and high sensitivity to growth suppression by TAM 67. Additionally, the intracellular PSK oncogene, mos and the nuclear oncogenes c-myc, c-fos, and SV40 T antigen were TAM 67-sensitive for transformation. This universal pattern of altered growth regulation in oncogene transformed fibroblast cell lines highlights the potential usefulness of c-jun based inhibitors for control of tumor cell growth.
Insights
Oncogene transformation alters gene expression, making cells sensitive to growth inhibition by c-jun inhibitors like TAM 67. This suggests potential for c-jun based therapies in controlling tumor cell growth.
Area of Science:
- Molecular Biology
- Oncology
- Cell Biology
Background:
- Active Raf-1 protein serine/threonine kinase (PSK) influences c-jun and c-fos expression in NIH3T3 cells.
- Oncogene transformation can alter cellular growth regulation pathways.
Purpose of the Study:
- To investigate if oncogene transformation confers differential sensitivity to growth inhibition by a dominant-negative c-jun mutant (TAM 67).
- To identify oncogenes that induce sensitivity to TAM 67 mediated growth suppression.
Main Methods:
- Transfection of TAM 67 into oncogene-transformed cells.
- Cotransfection of TAM 67 with oncogene plasmids into NIH3T3 cells.
- Retroviral titration of oncogenes on TAM 67 expressing cells.
Main Results:
- Raf-1 dependent oncogenes (receptor and intracellular PTKs, Ras-derived) induce constitutive c-jun expression, attenuated c-fos induction, and TAM 67 sensitivity.
- Intracellular PSK (mos) and nuclear oncogenes (c-myc, c-fos, SV40 T antigen) also exhibited TAM 67 sensitivity.
Conclusions:
- A common pattern of altered growth regulation exists in oncogene-transformed fibroblasts.
- c-jun based inhibitors demonstrate potential for controlling tumor cell proliferation.