Mechanisms of TGFbeta-mediated fibroblastic transition

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The transforming growth factor beta (TGFbeta) family of secreted factors play important role(s) in development, homeostasis and functioning of biological systems. A number of human diseases are associated with abnormal operation of the TGFbeta signaling network. TGFbeta exhibits a tumor suppressor activity and components of its signaling pathway are frequently mutated or silenced in cancers. However, TGFbeta contributes to the progression and invasiveness of tumors by stimulating an epithelial to mesenchymal transition (EMT) and cell migration. EMT is a complex process associated with alterations in epithelial cell contacts, changes in cell morphology, reorganization of the cell cytoskeleton, expression of fibroblastic markers (fibronectin, vimentin) and enhancement of cell migration. These effects of TGFbeta are also involved in wound repair and fibrosis of various tissues. The mechanism(s) of TGFbeta-induced EMT and cell migration are not well understood. We made the important observation that TGFbeta- mediated EMT and cell migration are impaired by inhibitors of p38 mitogen activated protein kinase (p38Mapk), without inhibition of the antiproliferative activity of TGFbeta. Thus, the p38Mapk pathway may play a critical role in TGFbeta's tumor promoting activity. We also observed that p38Mapk activation is mediated by Rho-family GTPases. The mechanism by which TGFbeta signals to Rho-like GTPases and p38Mapk has not yet been defined. We hypothesize that activation of the p38Mapk pathway by kinase- active TGFbeta receptors mediated by Rho-family GTPases is required for setting up a program of changes in the cell phenotype leading to TGFbeta-induced fibroblastic transition and cell migration. This hypothesis will be tested by the following specific aims. Aim 1: To examine the role of kinase function of TGFbeta receptors in activation of Rho-like GTPases and the p38Mapk pathway. Aim 2: To examine in vitro the effect of dominant negative and constitutively active mutants of MKK3 and MKK6, p38Mapk activating kinases, on the TGFbeta-induced EMT and cell migration. Aim 3: To evaluate the role of the p38Mapk pathway in tumor cell motility, invasiveness and metastasis in mouse models. The proposed research will help to define the TGFbeta signaling network and will facilitate the design of novel selective inhibition of TGFbeta's tumor promoting activity.