Abstract

Metabolism of arachidonic and linoleic acid can be regulated by polypeptide growth factors in a variety of cell types. In Syrian hamster embryo (SHE) fibroblasts, epidermal growth factor (EGF) stimulates the conversion of exogenous linoleic acid to 13(S)-hydroxyoctadecadienoic acid (HODE). Inhibition of 13-HODE biosynthesis blocks the EGF-mitogenic response in SHE cells, and 13-HODE and its hydroperoxy precursor are potent and highly specific enhancers of EGF-dependent DNA synthesis. We demonstrated that EGF stimulates a biphasic production and release of endogenous 13-HODE. Through development of a stable isotope-dilution GC/MS assay for 13-HODE, we observed 13-HODE production as early as 5 min after EGF stimulation, and this initial phase peaked at 1 hr. A second rise in 13-HODE formation was seen at 2-4 hr, and this phase plateaued at 4-6 hr at a level of 30-40 ng/10(6) cells. EGF stimulation of 13-HODE biosynthesis is not mediated by transcriptional or translational regulation of the inducible form of prostaglandin H synthase. Based on enzyme inhibitor studies and structural characterization of products, the linoleate metabolite is apparently formed by an n-6 lipoxygenase that remains to be characterized. EGF stimulation of 13-HODE formation is linked with activation of the EGF receptor tyrosine kinase. Inhibition of EGF receptor tyrosine kinase activity with methyl-2,5-dihydroxycinnamate blocked EGF-dependent linoleic acid metabolism and EGF-regulated DNA synthesis. Potentiation of the EGF receptor tyrosine phosphorylation cascade through treatment of SHE cells with the tyrosine phosphatase inhibitor vanadate resulted in a 3-fold increase in EGF-stimulated 13-HODE production and a corresponding enhancement of the EGF mitogenic response. The coupling of EGF-regulated linoleic acid metabolism with the EGF receptor tyrosine kinase activity suggests the importance of specific linoleate compounds in mediating mitogenic signal transduction.