Our laboratory has characterized linoleic acid metabolism as playing a central role in transducing the epidermal growth factor (EGF) mitogenic signal in several fibroblast cell lines. Inhibition of EGF receptor tyrosine kinase activity blocks the formation of linoleic acid metabolites, while inhibition of tyrosine phosphatase activity potentiates EGF-dependent biosynthesis of linoleate derivatives. These results link activation of lipoxygenase metabolism of linoleic acid to the tyrosine kinase activity of the EGF receptor. The erbB oncogene family encodes a truncated EGF receptor that retains homologous tyrosine kinase catalytic activity. Overexpression and amplification of the erbB oncogene has been observed in several types of human carcinoma. We have transfected normal fibroblasts with plasmid DNA vectors containing c- erbB-2 and established stable transfected cell lines. Inhibitors of linoleic acid metabolism attenuate the EGF-stimulated proliferative response of transfected cells. erbB-Transfected cells demonstrate increased lipoxygenase metabolism of both linoleic and arachidonic acid. Analytical chemical characterization identified the major metabolites as 13-hydroxyoctadecadienoic acid(HODE) and 15-hydroxy-eicosatetraenoic acid(HETE). We found 13-HODE to be a highly specific and potent enhancer of DNA synthesis in erbB-transfected cells. We have also examined the metabolism of linoleic and arachidonic acid in a variety of human breast carcinoma cell lines which vary in their expression of EGF receptor, c-erbB-2/HER2, and estrogen receptor. We have observed a close association between high levels of c-erbB-2 and EGF receptor expression and the extent of linoleic acid metabolism in these cells. Inhibition of lipoxygenase metabolism attenuates DNA synthesis in the erbB-2/EGFR over-expressing cells. Our current focus is to define the involvement of linoleate metabolites in transducing proliferative and apoptotic signals in human breast cancer cell lines and to investigate the relationship between erbB-2 transformation and linoleic acid metabolism.
