The broad objective of this project is to identify specific alterations in growth control mechanisms that are causally related to the neoplastic growth potential of rat mammary carcinoma (RMT) cells. To accomplish this, experiments have focused on understanding growth control mechanisms operative for normal rat mammary epithelial (RME) cells and from that perspective examining for normal rat mammary epithelial (RME) cells and from that perspective examining growth control in corresponding tumor derived cells. We have found that, whereas RME cells have a finite and reproducible proliferative lifespan in culture, every primary tumor examined has cells that are immortal with respect to their proliferative potential in culture. Despite this difference, no all immortal RMT cells express neoplastic potential when transplanted into syngeneic hosts. However, immortal RMT cells that also have become independent of growth factors strictly required by RME cells for growth in serum-free culture express high neoplastic potential upon transplantation to syngeneic recipients. Therefore, this project is aimed at determining the cellular and molecular basis for the acquisition of growth factor independence by neoplastic cells and to test directly the hypothesis that growth factor independence is causally related to neoplastic potential.
The specific aims are: 1) To determine if the loss of specific growth factor requirements by growth factor independent RMT cells results from growth factor synthesis by these cells and if so, to identify and characterize the autocrine factors responsible for this altered phenotype. 2) To determine if induction of growth factor independence in normal RME cells or in immortalized growth factor dependent RMT cells by chemical carcinogen treatment in vitro results in concomitant acquisition of neoplastic potential in vivo; and 3) To test the hypothesis that some (or all) growth factor independent RMT cells became so by mechanism not directly involving growth factor synthesis, but via activation of proto- oncogenes that are homologous to growth factor receptors, (e.g. c- erbB or e.g. c-erbB-2) or that act in growth factor mediated signal transduction (e.g. c-ras).
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