Signaling in Tumor Cells

The family of adaptor proteins Grb7 (growth factor receptor bound protein 7) are formed by Grb7, Grb10 and Grb14. These proteins have a conserved modular structure made up of the following domains: a proline-rich (PR) domain at the N-terminus followed by a Ras-associating (RA) domain, a pleckstrin homology (PH) domain, a domain denoted BPS (between PH and SH2) and a Src homology 2 (SH2) domain in the C-terminus. Our research group has shown that calmodulin (CaM) interacts with Grb7/Grb10/Grb14 in a Ca2+-dependent manner and has identified the CaM-binding site(s) (CaM-BD) located in the proximal region of the PH domain. While Grb7 has a single CaM interaction site, Grb10 has auxiliary CaM-binding sites that we have also identified, and Grb14 appears to harbor some additional CaM binding site(s). Grb7 is involved among other functions in cell migration, cell proliferation and angiogenesis and plays a key role in the invasiveness and metastatic capacity of tumor cells. Grb10 is involved in the control of the insulin and insulin-like growth factor type I (IGF-I) receptors, cell proliferation and embryonic development. Grb14 is also involved in the control of the insulin and IGF-I receptors and in cell proliferation. Grb10 and Grb14 also play an important role in tumorogenesis. We have also determined that the CaB-BD of Grb7 plays an essential role in the migration and proliferation of tumor cells, tumor growth and tumor-associated angiogenesis in vivo. Our working hypothesis is that the respective CaM-BDs of Grb7/Grb10/Grb14 are regulatory regions implicated in the Ca2+/CaM-mediated functions of these proteins and play a key role in various types of cancer. Therefore, the general objectives of this project are as follows: 1) Since during cellular migration a gradient of cytosolic Ca2+ concentration is established, high in the posterior region of the cell and low in the leading advancing edge, where transient peaks of increasing Ca2+ concentration are generated, we propose to determine whether CaM, as a Ca2+ sensor, after binding to Grb7 controls the migration and directionality of invasive tumor cells, and the role played by its CaB-BD in this process; 2) Since tumor cells present high glucose consumption and lactic acid production due to the known Warburg effect (high glycolysis even in the presence of oxygen) and the insulin receptor is essential for the transport and metabolism of glucose by tumor cells, we intend to determine whether the Ca2+/CaM complex plays a regulatory role in this process after binding to the corresponding CaM-BDs of Grb10 and Grb14, since it is known that both Grb10 and Grb14 are physiological inhibitors of the tyrosine kinase activity of the insulin and IGF-I receptors and its intracellular signaling pathways, particularly by acting on IRS1/2 (insulin receptor substrates 1/2). This project could facilitate the development of drugs acting on the CaM-BD of Grb7 to inhibit the invasiveness of metastatic tumor cells; and on the CaM-BDs of Grb10/Grb14 to enhance their inhibitory activity on insulin and IGF-I receptors to disrupt the glycolytic metabolism of tumor cells under hypoxic conditions prevalent in tumors.