Tumor-derived Syrian hamster embryo (SHE) cell lines, induced in vitro by treatment with chemical carcinogens, contained increased levels of pp60c-src kinase activity compared to preneoplastic parental cell lines and normal SHE cells. The increased kinase activity di not result from an increase in the pp60c-src content of the SHE cell lines, but represented a 4-11 fold increase in the pp60c-src kinase specificity activity. Both the extent of phosphorylation and the velocity of pp66c- src phosphotransferase activity ere increased in the tumor-derived cell lines. SHE cell lines producing chicken pp60c-src were isolated following co-transfection with plasmids bearing the chicken c-src and neor genes. Chicken pp60c-src expressed in an asbestos-transformed tumor-derived cell line showed an approximate 3-fold activation of tyrosine kinase activity compared to chicken pp60c-src expressed in the preneoplastic cell line. We suggest that these results indicate that activation of pp60c-src is mediated by trans-acting cellular factors present in the tumor-derived cells. Analysis of pp60c-src in normal SHE cells, preneoplastic cell lines and tumor-derived cell lines showed no alteration in the phosphorylation of tyr-527 or tyr-416, two tyrosine residues whose phosphorylation states have been associated with modulation of kinase activity. In addition, a strong correlation was observed between the activation of endogenous pp60c-src tyrosine kinase specific activity and the presence of additional phosphotyrosine- containing proteins. These studies indicate that the neoplastic progression of cells may be accompanied by the activation of proto- oncogene products, such as the pp60c-src tyrosine kinase, by mechanisms that may not directly involve genetic alteration of the proto-oncogene DNA sequence and that novel tyrosine phosphorylations may result from this activation.

Agency
National Institute of Health (NIH)
Institute
National Institute of Environmental Health Sciences (NIEHS)
Type
Intramural Research (Z01)
Project #
1Z01ES025029-06
Application #
3898102
Study Section
Project Start
Project End
Budget Start
Budget End
Support Year
6
Fiscal Year
1989
Total Cost
Indirect Cost
Name
U.S. National Inst of Environ Hlth Scis
Department
Type
DUNS #
City
State
Country
United States
Zip Code