Transforming growth factor-? (TGF-?) plays a critical role in cancer initiation and progression. Carcinoma cells often have shown enhanced TGF-? production and activation, resulting in autocrine effects on cell physiology and behavior. Among these, a lot of attention has focused on TGF-?'s ability to induce an epithelial to mesenchymal transition (EMT) that results in de-adhesion, increased motility and invasion. The roles of TGF-? in cancer cell behavior, tumor microenvironment and cancer progression are subject of extensive investigation, but the respective roles of the underlying TGF-?-activated signaling pathways in cancer cell behavior are less understood. Most studies in this context address the roles of TGF-?-activated Smads, which serve as transcription (co)factors to regulate gene expression. Recent studies, including some from this lab, have characterized non-Smad signaling pathways that are directly activated in response to TGF-?. These may explain non-transcription responses to TGF-? such as migration, changes in cell shape and protein translation, yet may also affect the activities of the Smads. The functions of the non-Smad signaling events in the TGF-?-directed effects on cancer cell behavior and cancer progression are essentially unknown. We recently reported that, in TGF-?-induced epithelia EMT, TGF-? activates the PI3-kinase-Akt-TOR pathway, resulting in increased protein synthesis and cell size, and that this pathway mediates the increased motility and invasion of cells that undergo TGF-?-induced EMT. We also reported that, in response to TGF-?, ShcA is recruited to the type I TGF-? receptor T?RI and phosphorylated on Ser and Tyr, in turn resulting in activation of Erk MAP kinase. Our observation that T?RI is a dual specificity kinase explains ShcA phosphorylation on Ser and Tyr, whereas T?RI phosphorylation on Tyr in response to TGF-? may provide the biochemical basis for activation of both the PI3K-Akt-TOR and the Shc-Erk MAPK pathways by TGF-?. Finally, we discovered that phosphorylation of T?RI in response to TGF-? induces T?RI sumoylation. T?RI sumoylation in turn regulates TGF-?-signaling dependent invasion of cancer cells. We propose to further characterize the mechanisms of these signaling events at the molecular level and to use this knowledge to address their roles in cancer cell behavior and cancer progression.
Aim 1 will focus on how TGF-? activates the PI3K-Akt-TOR pathway and on the role of this component of TGF-? signaling in cell invasion and cancer progression.
Aim 2 will study the role of TGF-?-activated ShcA-Erk MAP kinase signaling in EMT, invasion and cancer progression.
Aim 3 proposes to better characterize the sumoylation of T?RI and to understand its role in the TGF-? response and cancer progression. Our enthusiasm for this program is driven not only by its inherent scientific importance, but also by its translational potential.
The progression of cancer leading to death is in most cases not the result of the first tumor growing, but rather because that tumor starts invading other tissues and disseminating throughout the body to give rise to additional tumors, a process called metastasis. Cancer invasion and metastasis are driven by a protein called TGF-?, which is made by the tumor cells themselves and instructs them to undergo the changes that lead to invasion and metastasis. Recently, novel signaling pathways were found that are activated by TGF-? and complement the previously studied one that received all attention. The proposed research aims at better understanding the molecular basis of these additional pathways and their roles in cancer cell behavior, cancer progression and metastasis. This knowledge is likely to provide new and more selective avenues than hitherto possible to block the invasive and metastatic behavior of cancers.
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