The molecular mechanisms that lead to malignant transformation of pancreatic exocrine cells and their subsequent growth advantage are not known. However, it is established that cultured human pancreatic cancer cells overexpress the epidermal growth factor receptor (EGFR). In contrast, the receptors for insulin, insulin-like growth factor 1 (IGF- 1), tumor necrosis factor (TNF), interferon-gamma (IFN), and acetylcholine are not overexpressed in these cells. In addition to having increased EGFR mRNA levels, these cells produce transforming growth factor-alpha (TFG-alpha) and avidly bind and internalize EGF and TFG-alpha. However, in human pancreatic cancer cells. EGF is recycled and is not readily processed into low molecular weight moieties while TGF-alpha is rapidly degraded. Although both ligands induce EGFR tyrosine phosphorylation and enhance phosphatidylinositol hydrolysis in these cells, their actions on these important biological processes exhibit quantitative and qualitative differences. Further, TGF-alpha is more potent that EGF at stimulating their anchorage-independent growth, and is less efficient than EGF at down regulating EGFR. These observations raise the possibility that EGF and TGF-alpha may exert complementary effects that together may combine to provide pancreatic cancer cells with a unique growth advantage. Indeed, we recently found that EGFR, EGF, and TGF-alpha are overexpressed in human pancreatic cancer tissues. Therefore, in the present proposal we will test the hypothesis that excessive activation of EGFR by EGF and TGF-alpha may be of fundamental importance for the growth of human pancreatic cancer cells. To test our hypothesis, we will elucidate the mechanisms that allow EGF and TGF-alpha to exhibit biological differences in pancreatic cancer cells, study the signal transduction pathways that are activated by EGF and TGF-alpha in these cells by comparison with normal rat and human pancreatic duct cells, use specific antisense expression constructs and/or antisense oligodeoxynucleotides to inhibit TGF-alpha expression in cultured human pancreatic cancer cells, use similar techniques as well as dominant EGFR mutations to inhibit EGFR expression and EGFR-mediated mitogenesis in these cells, and assess the regulation of TGF-alpha gene expression in relation to the pancreatic microenvironment. We will also determine the potential role of EGFR overactivation in a nude mouse model of pancreatic cancer, and determine whether TGF-alpha coupled to pseudomonas toxin can inhibit the growth of pancreatic cancers. Finally, we will use the knowledge gained from our studies to develop a non-invasive diagnostic test for pancreatic cancer.
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