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

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