A substantial body of evidence indicates that ras signaling pathways play a role in multi-stage progression of human breast cancer, even though the mechanisms of activation of these pathways does not usually include activating mutations in the ras genes. We have identified ets-2 as a nuclear target of ras pathways that can persistently activate gene expression, and more recently have demonstrated that ets-2 can also repress gene expression in a signaling-dependent fashion. Gene targets include members of the EGF ligand family, such as HB-EGF, as well as a group of extracellular proteases including urokinase plasminogen activator, stromelysin 1/MMP3, MMP9 and MMP-MT1. The identity of these target genes suggests that the ras/ets-2 pathway may be activated during the epithelial-mesenchymal transition that occurs in the tumor cell and coincides with a more metastatic phenotype. However, these target genes are also expressed in other types of cells in the tumor microenvironment during tumor progression, particularly in macrophages and stromal fibroblasts. This leads to the proposition that the ras/ets-2 pathway may be activated in several cell types in the tumor microenvironment and may play distinct roles in different stages of tumor progression. We propose to use conditional gene knockout approaches to remove ets-2 in macrophages and stromal fibroblasts in the mammary tumor microenvironment. We also propose to develop orthotopic mouse models that will allow us to study the role of ets-2 stromal fibroblasts during tumor metastasis. In combination with the other two Projects in this Program Project Grant, we will also study interactions between the ras/ets-2, Pten and Rb/E2F pathways. These experiments will give us a better understanding of the role of the ras/ets-2 pathway in coordinating expression of genes in a temporal and spatial specific pattern during mammary tumor progression.