Studies on pp60src and associated kinase activity in regressing tumors induced by Rous sarcoma virus
Poulin, L.; Spira, B.; Wainberg, M.A.
In Vivo 1(2): 125-130
1987
ISSN/ISBN: 0258-851X PMID: 2856518 Document Number: 293014
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.