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Studies on pp60src and associated kinase activity in regressing tumors induced by Rous sarcoma virus
L Poulin1, B Spira, M A Wainberg
1Lady Davis Institute for Medical Research, Sir Mortimer B. Davis, Jewish General Hospital, Montreal, Quebec, Canada.
Abstract:
Rous sarcoma virus induced chicken tumors usually grow progressively for several weeks and then regress. pp60src kinase activity was reduced in cultured tumor cells which derived from regressing sarcomas by 60-75% as compared to progressively-growing neoplasms. We have demonstrated the presence of inhibitory activity to pp60src kinase activity in extracts of regressing tumor cells. Such extracts were able to reduced by 60% the level of kinase activity found in progressively-growing tumors, as measured in a IgG phosphorylation assay. Immunoprecipitation analyses of membrane or cytosol fractions did not reveal any significant differences between these two types of tumor cells in distribution of pp60src. The pp60src kinase of progressively-growing tumor cells was more sensitive than that of "regressor" cells to inhibition by P1, P4 di-(adenosine-5') tetraphosphate (Ap4 A) and to heat inactivation. These results suggest that the reduction of pp60src kinase activity in regressing neoplasms might be due to the presence of inhibitors in such cells, but that the basal levels of activity which remain are relatively resistant to further perturbation by heat and/or chemical antagonists.
Insights
Tumor cells from regressing Rous sarcoma virus-induced chicken sarcomas show reduced pp60src kinase activity. Inhibitory factors in these regressing tumors may contribute to decreased kinase activity, with remaining activity being more resistant to inhibition.
Area of Science:
- Oncology
- Virology
- Molecular Biology
Background:
- Rous sarcoma virus (RSV)-induced chicken tumors exhibit a growth-regression pattern.
- pp60src kinase activity is a key factor in RSV-induced tumorigenesis.
- Understanding the regulation of pp60src kinase activity during tumor regression is crucial.
Purpose of the Study:
- To investigate the mechanisms underlying the reduction of pp60src kinase activity in regressing chicken sarcomas.
- To identify potential inhibitory factors present in regressing tumor cells.
- To compare the properties of pp60src kinase in progressively growing versus regressing tumors.
Main Methods:
- Culturing of Rous sarcoma virus-induced chicken tumor cells.
- Measurement of pp60src kinase activity using IgG phosphorylation assays.
- Immunoprecipitation analysis of cellular fractions.
- Assays for inhibition by di-(adenosine-5 oun) tetraphosphate (Ap4A) and heat inactivation.
Main Results:
- pp60src kinase activity was significantly reduced (60-75%) in cultured cells from regressing sarcomas compared to progressively growing tumors.
- Extracts from regressing tumor cells demonstrated inhibitory activity against pp60src kinase (60% reduction).
- pp60src kinase from progressively growing tumors was more sensitive to inhibition by Ap4A and heat inactivation than that from regressing tumors.
Conclusions:
- Reduced pp60src kinase activity in regressing chicken sarcomas is likely due to the presence of inhibitory substances within the tumor cells.
- The remaining pp60src kinase activity in regressing tumors exhibits increased resistance to heat and chemical inhibition.