The Role of TIMPs in Cell Growth and Differentiation: Tumor Angiogenesis

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Summary: EGF-stimulation of the A549 human lung carcinoma cell line demonstrated that the suppression of cell growth response was mediated by the activation of protein tyrosine phosphatase activity and resulted in reduced EGF receptor phosphorylation. Competition binding experiments using anti-integrin antibodies identified integrin α3β1 as a putative cell surface receptor for TIMP-2 on human microvascular endothelial cells (hMVECs). Ala+TIMP-2 also inhibited VEGF-A or FGF-2 stimulated mitogenesis in vitro and angiogenesis in vivo a, thus demonstrating that the angio-inhibitory activity of TIMP-2 is dissociable from MMP-inhibition. The mechanism of this effect involves an integrin receptor inactivation of growth factor receptor signaling, known as heterologous receptor inactivation. This was the first demonstration that integrins could negatively regulate activation of a receptor tyrosine kinase This work has defined a new paradigm for TIMP biology by demonstrating that TIMPs are multifunctional proteins, with cell surface receptors and through interaction with these receptors they can directly influence cellular behavior. Using both in vitro and in vivo models our current and future work is focused on identifying the α3β1 integrin binding domain(s) in TIMP-2 and furthering our understanding of the cellular effects following TIMP-2 interaction with α3β1 in both normal and neoplastic cells, as well as the subsequent alterations in the tumor microenvironment. It is our goal to further characterize the MMP-independent and MMP-dependent effects of TIMPs in the tumor microenvironment and their relative contribution to tumor suppression and/or progression. These studies should identify crucial mechanisms in the regulation of cell behavior by the extracellular matrix in normal tissues and the tumor microenvironment, and possibly lead to new therapeutic strategies for cancer treatment. These findings suggest that defining the domain(s) responsible for TIMP-2-binding to α3β1 will be critical to further dissecting the multiple biological activities of this complex molecule, as well as defining the functional contributions of this activity to the microenvironment in both normal and malignant tissues. The focus of this project is to determine the mechanisms of the anti-angiogenic and anti-tumorigenic effects of Ala+TIMP-2. Preliminary work with human microvascular endothelial cells has demonstrated a mechanism known as heterologous receptor inactivation. In this effect the TIMP-2 receptor α3β1 decreases phosphorylation and activation of receptor tyrosine kinases such as the vascular endothelial growth factor receptor (VEGFR)-2, fibroblast growth factor recetpor (FGFR)-1 and epidermal growth factor receptor (EGFR) by activation a phosphotyrosine phosphatase known as Shp-1. However, recent experiments in tumor cells and endothelial cells have revealed that the growth suppressor activity of Ala+TIMP-2 is more complex and appears to involve apoptotic pathways and changes in gene expression of the epithelial to mesenchymal transition that is essential to tumor invasion and metastasis. It is the purpose of this project to identify and delineate these pathways with the aim of developing Ala+TIMP-2 as a novel cancer therapeutic and identifying potential new therapeutic targets.