Time-resolved phosphoproteomic analysis elucidates hepatic 11,12-Epoxyeicosatrienoic acid signaling pathways

Epoxyeicosatrienoic acids (EETs) are potent lipid mediators with well-established effects in vascular tissues. Recent studies indicated an emerging role of these eicosanoids in metabolic diseases and the EET signaling pathway was shown to be involved in hepatic insulin sensitivity. However, compared to vascular tissues, there is only limited knowledge about the underlying signaling pathways in the liver. Therefore, we employed an LC-MS/MS-based time-resolved phosphoproteomics approach to characterize 11,12-EET-mediated signaling events in the liver cell line Hepa 1-6. 11,12-EET treatment resulted in the time-dependent regulation of phosphopeptides involved in processes as yet unknown to be affected by EETs, including RNA processing, splicing and translation regulation. Pathway analysis combined with western blot-based validation revealed enhanced AKT/mTOR/p70S6K signaling as demonstrated by increased acute phosphorylation of AKT (Ser473) and p70S6K (Thr389). In addition, 11,12-EET treatment led to differential regulation of phosphopeptides including important mediators of the DNA damage response and we observed a prolonged induction of the etoposide-induced DNA damage marker gamma H2AX in response to 11,12-EET. In summary, our findings extend current knowledge of 11,12-EET signaling events and emphasize the importance of the AKT/mTOR/p70S6K pathway in hepatic 11,12-EET signaling. Based on the results presented in this study, we furthermore propose a novel role of EET signaling in the regulation of the DNA damage response.