Growth factors play key roles in the process of malignant transformation, in normal cell physiology and in embryonic development. One of these factors, transforming growth factor-alpha (TGF-alpha), is structurally related to epidermal growth factor (EGF) and binds to the same receptor as EGF. The recently established widespread synthesis of TGF-alpha in normal cells of epithelial origin, such as keratinocytes, and in many tumor cells, such as carcinomas, has made it increasingly clear that TGF-alpha represents a major physiological ligand of the EGF/TGF-alpha receptor. Whereas considerable knowledge on the sites of synthesis has been obtained, little is as yet known about the function of this growth factor and its role in the cell physiology. The physiological function of TGF-alpha is the focus of this grant application, which proposes two studies aimed at gaining insight into the role of this factor in normal and tumor cells. Previous work has shown that TGF-alpha is synthesized as a transmembrane precursor, which may undergo proteolytic cleavage of the ectodomain, but very often remains uncleaved at the cell surface. Our first major objective focuses on the role of the highly conserved cytoplasmic domain of the TGF-alpha precursor. Specifically, we will explore at the cellular level whether the intact transmembrane TGF-alpha precursor itself is able to transduce any signals, and thus may serve as a signal transducing receptor. In the same context, we will attempt to determine whether there are any cytoplasmic proteins that interact with the cytoplasmic domain of the TGF-alpha precursor. The second major objective is to define the role of TGF-alpha in malignancy and in normal development of the mouse by inactivating the TGF-alpha functional synthesis in tumor cells and in mice. The expression of TGF-alpha in select carcinoma cell lines will be abolished by using antisense sequences. In parallel, the role of TGF-alpha in murine development will be evaluated following inactivation of the genes for TGF-alpha and the EGF/TGF-alpha receptor using established gene targeting methods. These studies should lead to a better understanding of the role of TGF- alpha in pre- and postnatal development and especially in the physiology of normal epithelia and ectodermally derived tumor cells. In addition, since abnormal expression of TGF-alpha may contribute to the derivation of ectodermal tumors and the overproliferation of epithelia, e.g., in psoriasis, it is also our hope that this knowledge will provide a rational basis for the prevention, diagnosis and treatment of some epithelial disorders, including epithelial tumors.
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