Eicosanoid activation of extracellular signal-regulated kinase 1/2 in human epidermoid carcinoma cells

12(S)-Hydroxyeicosatetraenoic acid (12(S)-HETE), a 12-lipoxygenase metaboli te of arachidonic acid, has multiple effects on tumor and endothelial cells , including stimulation of invasion and angiogenesis. However, the signalin g mechanisms controlling these physiological processes are poorly understoo d. In a human epidermoid carcinoma cell fine (i.e. A431), 12(S)-HETE activa tes extracellular signal-regulated kinases 1/2 (ERK1/2), which is mediated by upstream kinases MEK and Raf. 12(S)-HETE stimulates phosphorylation of p hospholipase C gamma1 and activity of protein kinase C alpha (PKC alpha). I n addition, independent of PKC 12(S)-HETE increases tyrosine phosphorylatio n of Shc, and Grb2, stimulates association between Shc and Src, and increas es the activity of Ras, via Src family kinases. Furthermore, at low (10-100 nM) concentrations 12(S)-HETE counteracts epidermal growth factor-stimulat ed activation of ERK1/2 via stimulating protein tyrosine phosphatases. We a lso present evidence that 12(S)-HETE stimulates ERK1/2 via G proteins and t hat A431 cells have multiple binding sites for 12(S)-HETE. Finally, inhibit ion of 12-lipoxygenase induced apoptosis of A431 cells, which was reversed by addition of exogenous 12(S)-HETE. Collectively we demonstrate that the a ctivation of ERK1/2 by 12(S)-HETE may be regulated by multiple receptors tr iggering PKC-dependent and PKC-independent pathways in A431 cells.