A novel growth inhibitor of the TGF-beta-family has been cloned and sequenced from human placental cDNA; the new form is designated TGF-beta-3. TGF-betas are secreted as inactive precursor molecules, that are subsequently proteolytically cleaved to yield biologically active mature dimers of 25 KDa. The precursor regions of TGF-beta-1 and TGF-beta-3 contain an RGD sequence. TGF-betas influence the proliferation and differentiation processes of cells, and specifically demonstrate potent growth inhibitory activity on many cell types, especially carcinomas. Preliminary experiments showed that TGF-beta-3 exhibited at least 10 fold greater growth inhibitory activity on cells, including a human lung carcinoma. Recently, different functions, partially mediated through specific receptors have been demonstrated for TGF-beta-1 and TGF-beta-2. Since TGF-beta-3 is a newly discovered protein its distribution, functions, and receptor binding characteristics are unknown. Anti- sera will be raised to synthetic peptides of both the precursor and mature forms of TGF-beta-3. Non-cross-reacting anti-peptide IgG will be used analytically to screen normal and neoplastic cells and tissues for TGF-beta-3 by immunofluorescence. Immunoprecipitation and immunoaffinity chromatographic techniques will be employed to quantitate and purify mature TGF-beta-3 and the precursor form of TGF-beta-1 and TGF-beta-3 from cells and tissues. Purified TGF- beta-3 will be used to quantitate its specific activity in various TGF-beta specific functions and to identify and characterize its receptor binding entities on the cell surface. By stimulating the production of certain components of the extracellular matrix (ECM) such as fibronectin (Fn) and collagen, and by preventing ECM breakdown through the synthesis of anticatalytic proteins such as plasminogen activator inhibitor (PAI), TGF-beta appears to have an important effect on maintaining the integrity of the ECM. The influence of TGF-beta-3 on Fn, collagen, and PAI production will be assessed. The possibility that the inactive TGF-beta-3 precursor molecule binds to the Fn receptor through its RGD sequence, creating a negative feedback mechanism, will be examined. Blocking the binding of fibronectin to its receptor would cause decreased adherence of cells to the ECM. The Fn receptor is phosphorylated on tyrosines in transformed but not normal cells. The ability of TGF-beta-3 to ameliorate transformation related properties by preventing tyrosine phosphorylation of the Fn receptor will be evaluated. The significance of these studies in understanding control mechanisms of tumor cell proliferation and metastasis may elucidate concepts for future therapeutics in two important areas of cancer research.
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