INTERACTION OF LIPIDS WITH EGFR SIGNALING PATHWAY

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Summary of Work: The focus of this project is to examine the mechanism(s) by which prosta-glandins and linoleic acid metabolites potentiate the EGF mitogenic signal. We have used Syrian hamster embryo (SHE) cells as a model to study the interaction of lipids with EGFR pathway. The linoleate metabolite, 13(S)-HODE stimulated EGF-dependent DNA synthesis while prostaglandins inhibited growth. The enhancement of the mitogenic response by 13(S)-HODE was observed in variant SHE cells that has tumor suppressor gene function (supB+) and the response is lost on progression to the tumor suppressor (-) cell line (supB-). These results suggest that linoleate products may act at control points where tumor suppressor genes interact with EGF-mitogenic signals, in particular, the protein tyrosine phosphorylation pathway. We have recently examined in more detail the expression of signaling proteins and the extent of their tyrosine phosphorylation of the EGF signaling pathway in the two SHE cell variants. The addition of PGE2 did not alter tyrosine phosphorylation of EGFR and GAP protein but did down regulate the MAP kinase pathway. PGE2 inhibited the activity of Raf-1 which attenuated the interaction between the Ras and Raf-1 to cause a down regulation of the MAP kinase pathway and thus inhibition MAP kinase. Our results indicate that PGE2 inhibition of mitogenesis is mediated by inhibition of MAP kinase rather than an inhibition of cell cyclic kinetics as others have proposed. The addition of 13(S)-HpODE up- regulated the EGFR phosphorylation events including a stimulation of MAP kinase activity in the supB+ cells but not the supB- cells. The lipid metabolite attenuated the dephosphorylation of the EGFR in the supB+ cells thereby up-regulating the entire EGFR pathway. The mechanism for this response is currently under study.