NEOPLASTIC TRANSFORMATION OF HUMAN EPITHELIAL CELLS BY ONCOGENES

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Five families of activated protooncogenes, ras, raf, jun, erbB-2 (neu) and myc have so far been associated with human bronchogenic carcinoma. Human bronchial epithelial cells in vitro are being used to investigate the functional role of these specific oncogenes and growth regulatory genes in carcinogenesis and tumor progression. Overexpression of erbB-2 causes neoplastic transformation of human bronchial epithelial cells. The molecular mechanisms of ras and raf myc induction of neoplastic transformation is the major focus of current and future studies. We are investigating the role of ras and raf in the transduction of signals from ligand activated cellular membrane receptors to the nucleus and subsequent altered expression of growth and terminal differentiation genes. We hypothesize that receptor-mediated phosphorylation of the raf kinase causes both an increase in its activity and a translocation to the nucleus. Possible substrates of the activated raf kinase include PI kinase and nuclear regulatory proteins, myc and p53. The effects of mutant p53 gene on cell growth and terminal squamous differentiation will be assessed. The cooperativity of mutant p53 and ras genes in the "immortalization" and neoplastic transformation of normal human bronchial epithelial cells is being studied. Human papillomaviruses 16 and 18 have been shown to "immortalize" normal bronchial epithelial cells. Since the Ha-ras or myc/raf transformed bronchial epithelial cells are highly invasive and metastatic in athymic nude mice, we plan to investigate the regulation and expression of genes considered to be involved in tumor metastasis including Nm23, collagenase IV and TIMP-2.