The long-term goal is to determine the mechanism of neoplastic transformation by tryosine-specific protein kinases. We have demonstrated that tyrosine kinase activity is amplified in the plasma membrane of baby hamster kidney (BHK) cells grown in suspension but not monolayer cultures; a similar elevation was observed in two other cell lines that were selected for anchorage-independent growth in suspension cultures. Thus, our working hypothesis is that tyrosine kinase activity may directly promote anchorage independence of cells. To test our hypothesis for function of tyrosine kinases, BHK cells that are temperature sensitive for anchorage-independent growth will be examined for temperature dependence of tyrosine kinase expression. We will also ask whether amplified tyrosine kinase expression is commonly coupled to capability of anchorage-independent growth of other cells including cells that grow in soft agar and cells transformed by retroviruses whose oncogenes do not encode tyrosine kinases. Tyrosine kinase expression in each case will be assessed by comparing the levels of tyrosine kinase activity in isolated plasma membranes and by comparing phosphotyrosine content in cellular proteins. To shed light on how tyrosine kinases influence anchorage independence, we will characterize the tyrosine kinase and substrates for the kinase in BHK cells that are not transformed by chemicals or viruses, but are selected for anchorage-independent growth in suspension cultures. To facilitate purification, the tyrosine kinase will be purified from isolated plasma membranes that were captured in the membrane envelope of vesicular stomatitis virus (VSV) that are grown in these same cells. Antiserum will be made to the purified tyrosine kinase and will be used to compare immunological relatedness to other tyrosine kinases and to quantitate levels of suspension culture tyrosine kinases in cells. Expression of the tyrosine kinase in suspension cultures will be compared to expression in retroviral transformed cells by examining the phosphotyrosine-containing proteins in both cell types. Possible identity of suspension culture tyrosine kinase to those encoded by retroviral oncogenes will be assessed by biochemical and immunological comparisons. In future studies we will test tumorigenicity of cells selected for both anchorage independence and elevated tyrosine kinase activity.