of Work: The focus of this project is to examine the mechanism(s) by which prostaglandins 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 the EGFR pathway. The linoleate metabolite, 13 (S)-HpODE stimulated EGF-dependenat DNA synthesis while prostaglandins inhibited growth. The enhancement fo the mitogenic response by 13 (S)-HODE was observed in variant SHE cells that had tumor suppressor gene function (supB+) and the response is lost on progression to the tumor suppressor (-) cell line (supB-). 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 Ras and Raf-1 to cause a down regulation of the MAP kinase pathway and thus inhibition of MAP kinase. 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. We have recently studied the interaction of EFGR with other signaling proteins. EGFR appears to be associated with the tyrosine phosphotase SHP-2 and its linker protein GAB-1. We also observed that SHP-2 activity is greater in supB+ cells compared to supB- cells. Sequence analyses revealed no difference between SHP-2 from supB+ and supB- cells. The addition of 13-HODE however, did not alter its activity but increased its association of SHP-2 with other phosphorylated protein. The mechanism for this response is currently under study.
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