The focus of this project is to examine the mechanism(s) by which prostaglandins and linoleic acid metabolites potentiate the EGF mitogenic signal in fibroblast cell lines. In our previous work with Syrian hamster embryo (SHE) cells, we found that linoleate products stimulate EGF- dependent DNA synthesis in normal cells, but do not enhance the mitogenic response in variant SHE cells that had lost tumor suppressor gene function. One plausible interpretation of these results is that the tumor suppressor (-) cell line lacks the responsive element in the EGF signal transduction pathway which interacts with linoleate compounds. 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. One minor differences in protein levels was observed with the exception that higher level of eps8 was observed in the supB' variant. The SH-2 containing tyrosine phosphatase PTP-1-D binds to the phosphorylated EGFR in the supB+ as expected but does not bind to the phosphorylated EGFR in the supB' cells. Incubation of human purified PTP-1-D with SHE cells does result in the bind of the EGFR of both variants. This and other data point to a mutation or defect in the PTP-1-D present in the supB' cells. Furthermore, the activity of the PTP-1-D is greater in the supB+ variant compared to the supB' cell. We are in the process of cloning the PTP-1-D and the EGFR receptor from the SHE cells. We are also deterring if the 13(S)-HpODE alters either the activity or the association of the PTP-1-D with the EGFR.
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