Delta opioid activation of the mitogen-activated protein kinase cascade does not require transphosphorylation of receptor tyrosine kinases

• Type of Material: Article
• Authors: H Kenneth Kramer, Fordham University; Irma Onosprishvili, New York University; Matthew L Andria, New York University; Kayane Hanna, New York University; Karina Sheinkman, New York University; Lisa Haddad, Emory University; Eric J Simon, New York University
• Language: English
• Date: 2002-03-01
• Publisher: BioMed Central
• Publication Version: Final Published Version
• Copyright Statement: © 2002 Kramer et al; BioMed Central Ltd. Verbatim copying and redistribution of this article are permitted in any medium for any purpose, provided this notice is preserved along with the article's original URL.
• License: Creative Commons Attribution 2.0 Generic
• Final Published Version (URL): http://dx.doi.org/10.1186/1471-2210-2-5
• Title of Journal or Parent Work: BMC Pharmacology
• ISSN: 1471-2210
• Volume: 2
• Start Page: 5
• End Page: 5
• Grant/Funding Information: We also are very appreciative for the support of the National Institute on Drug Abuse (NIDA) in the form of a Career Development Award to Dr. Kramer (K01-DA00437), a research grant (R01-DA00017) and a Career Scientist Award (K05-DA00364) to Dr. Simon.
• Keywords: Mitogen-Activated Protein Kinases; Epidermal Growth Factor; Narcotics; Cell Line; MAP Kinase Signaling System; Receptors, Platelet-Derived Growth Factor; Humans; Enzyme Activation; Receptor Protein-Tyrosine Kinases; Receptors, Fibroblast Growth Factor; Receptor, Epidermal Growth Factor; Enkephalin, Leucine; Receptor, Insulin; Phosphorylation; Receptors, Opioid, delta
• Research Categories: Health Sciences, Pharmacology; Psychology, General

Abstract

Background: In this study, we investigated the mechanism(s) by which delta opioids induce their potent activation of extracellular signal-regulated protein kinases (ERKs) in different cell lines expressing the cloned δ-opioid receptor (δ-OR). While it has been known for some time that OR stimulation leads to the phosphorylation of both ERK isoforms, the exact progression of events has remained elusive. Results: Our results indicate that the transphosphorylation of an endogenous epidermal growth factor receptor (EGFR) in the human embryonic kidney (HEK-293) cell line does not occur when co-expressed δ-ORs are stimulated by the δ-opioid agonist, D-Ser-Leu-enkephalin-Thr (DSLET). Moreover, neither pre-incubation of cultures with the selective EGFR antagonist, AG1478, nor down-regulation of the EGFR to a point where EGF could no longer activate ERKs had an inhibitory effect on ERK activation by DSLET. These results appear to rule out any structural or catalytic role for the EGFR in the δ-opioid-mediated MAPK cascade. To confirm these results, we used C6 glioma cells, a cell line devoid of the EGFR. In δ-OR-expressing C6 glioma cells, opioids produce a robust phosphorylation of ERK 1 and 2, whereas EGF has no stimulatory effect. Furthermore, antagonists to the RTKs that are endogenously expressed in C6 glioma cells (insulin receptor (IR) and platelet-derived growth factor receptor (PDGFR)) were unable to reduce opioid-mediated ERK activation. Conclusion: Taken together, these data suggest that the transactivation of resident RTKs does not appear to be required for OR-mediated ERK phosphorylation and that the tyrosine-phosphorylated δ-OR, itself, is likely to act as its own signalling scaffold.