Altered pp60src kinase activity in regressing tumors induced by Rous sarcoma virus

Tumors which are induced in chickens by Rous sarcoma virus (RSV) usually grow progressively for several weeks and then regress. pp60src kinase activity was found to be reduced in cultured tumor cells which derived from regressing sarcomas by 60-75% as compared to progressively growing neoplasms. We further found that a cellular pp89 which co-precipitated with pp60src was largely diminished in tumor cells derived from regressing as compared with progressively growing sarcomas. In contrast, immunoprecipitation analyses from membrane or cytosol fractions did not reveal any significant differences between these 2 types of tumor cells in distribution of pp60src. Moreover, partial proteolysis or isoelectric focussing of labelled immunoprecipitated pp60src did not reveal major differences between the 2 tumor cell types. These data indicate that the lack of pp89 cell binding to pp60src in regressing sarcoma cells correlates well with the diminution of the pp60src kinase activity in these cells, but does not affect the transport of pp60src to the plasma membrane.