Growth hormone secretion in night workers

Epidermal growth factor (EGF) stimulates the lipoxygenase metabolism of linoleic acid to 13(S)-hydroxyoctadecadienoic acid (HODE) in Syrian hamster embryo (SHE) fibroblasts. 13(S)-HODE is a potent and specific enhancer of EGF-dependent DNA synthesis in normal phenotypic SHE cells (supB+), but is inactive in variant SHE cells that have lost tumor suppressor gene function (supB-). EGF activation of quiescent SHE cells results in increased levels of 13-HODE esterified in cellular phospholipid and triglyceride. Steric analyses suggest that this metabolite is generated in part by direct oxygenation of membrane lipids by an n-6 lipoxygenase. In studies on the uptake and mobilization of 13-HODE in SHE cells, we observed EGF to stimulate a time- and dose-dependent incorporation and reacylation of the mono-hydroxy linoleate metabolite. The level of 13-HODE uptake in supB+ cells is twice that of supB-. Among classes of phospholipids, radiolabeled 13-HODE is esterified predominantly into phosphatidylcholine and this distribution pattern is similar for both SHE cell lines. Pretreatment of cells with the tyrosine kinase inhibitor methyl-2,5-dihydroxycinnamate blocks EGF-stimulated HODE incorporation. Inhibition of tyrosine phosphatase activity with vanadate potentiates HODE uptake in supB+ but not supB- cells. Moreover, activation of protein kinase C with phorbol ester stimulates HODE incorporation in the supB+ line only. The differential effects of EGF on 13-HODE uptake and mobilization in supB+ and supB- cells appear to be related to loss of the tumor suppressor phenotype. EGF-stimulated generation of esterified 13-HODE may be an important biological process in determining the mechanism and site of HODE interaction with the mitogenic signaling pathway.