CELL SIGNALLING: THEROLE OF PHOSPHORYLATION IN PRODUCING RECEPTOR DESENSITIZATION AND DRUG TOLERANCE. (#663QL)

摘要

Among the myriad of mechanisms proposed to modulate the sensitivity and function of G protein-coupled receptors (GPCRs), only one - receptor phosphorylation - remains a consistent theme across numerous receptor types. While a role for G protein receptor kinases (GRKs) in opioid receptor (OR) regulation has been exhaustively investigated, other protein kinases, including extracellular signal-regulated protein kinases (ERKs) and protein and receptor tyrosine kinases (PTKs and RTKs) appear to be importantly involved in regulating agonist-stimulated opioid receptors. Our laboratory has determined that opioid-activated, Src-like protein tyrosine kinases are responsible for mediating the tyrosine phosphorylation of the delta opioid receptor in a time- and concentration-dependent manner. In addition, tyrosine phosphorylation of the DOR is necessary for agonist-dependent desensitization, internalization and down-regulation to occur in HEK-δOR cell lines. Furthermore, it appears that two tyrosines in the C-terminus are the predominant recipients of Src-dependent phosphorylation, since the mutation of either site to Phe greatly increases the resistance of the δ-OR to desensitization and internalization. Surprisingly, the loss of C-terminal tyrosines also has a profound effect on acute delta opioid receptor signalling, as these tyrosine-deficient mutants can no longer signal via the MAPK pathway. Our data will demonstrate that opioid receptors are capable of acting as scaffolds for the formation of a multi-protein complex that is required for both Ras translocation and ERK activation.