A large-body of experimental data suggests that activated cellular oncogenes may be responsible for at least some human neoplasias. The c-oncs whose proteins have tyrosine kinase activity comprise a subclass whose mechanisms of transformation are probably closely related. src is the best studied representative of this class. We have shown that the kinase and transforming activities of its normal protein product, pp60c-src, can be controlled by phosphorylation at tyrosines 416 and 527 and have found evidence suggesting that these phosphorylations are transiently altered in overexpressed pp60c-src in vivo. In addition, we have shown that pp60c-src has enhanced specific kinase activity and is specifically phosphorylated at an amino region threonine and (possibly) at additional serine residues during mitosis. Using recombinant DNA, gene transfer and cell synchronization techniques with established cell lines, we will explore the implication that pp60c-src plays a role in progression through mitosis and the possibility that it is regulated in a cell cycle dependent manner in other phases of the cycle as well. In related experiments, we will extend our studies of the regulatory roles of tyrosine 416 and 527 phosphorylation and amino region modifications. In collaboration with other laboratories we will use antibody microinjection and antisense techniques to see if c- src activities are required for progression through the cell cycle and/or response to growth factors and will study the effects of expression of pp60c-src and pp60c-src phosphorylation site mutants in transgenic mice. These studies are part of our long term goal to trace the molecular pathways of transformation by an oncogene as a model for carcinogenesis.
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