Leumorphin has an anti-apoptotic effect by activating epidermal growth factor receptor kinase in rat pheochromocytoma PC12 cells

Endogenous opioid peptides, found in the central and peripheral nervous systems, perform neuromodulatory roles, and display a wide range of functional and pharmacological properties in vitro and in vivo. In this study, we investigated the effects of prodynorphin gene products on intracellular signaling events and cell survival in rat pheochromocytoma PC12 cells. Leumorphin, but not other prodynorphin gene products including dynorphin A, beta-neoendorphin and rimorphin (dynorphin B), increased cell viability in PC12 cells. The cytoprotective effect of leumorphin was dependent on the phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways, but was insensitive to both naloxone, a general antagonist of the opioid receptor, and nor-binaltorphimine, a specific antagonist of the kappa opioid receptor. Moreover, a competition-binding assay clearly revealed that leumorphin had another binding site(s) in addition to that for the kappa opioid receptor. Interestingly, leumorphin induced activation of the epidermal growth factor receptor via a Src-dependent mechanism, which was proved to be responsible for the increased survival response. Flow cytometric and microscopic analysis showed that leumorphin rescued cells from serum deprivation-induced apoptosis. Collectively, we suggest that leumorphin prevents apoptosis via epidermal growth factor receptor-mediated activation of the phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways, which occur independent of the kappa opioid receptor.