Role for the C-terminus in agonist-induced mu opioid receptor phosphorylation and desensitization
Deng, H.B.; Yu, Y.; Pak, Y.; O'Dowd, B.F.; George, S.R.; Surratt, C.K.; Uhl, G.R.; Wang, J.B.
Biochemistry 39(18): 5492-5499
Determining which domains and amino acid residues of the m opioid receptor are phosphorylated is critical for understanding the mechanism of m opioid receptor phosphorylation. The role of the C-terminus of the receptor was investigated by examining the C-terminally truncated or pointmutated m opioid receptors in receptor phosphorylation and desensitization. Both wild-type and mutated receptors were stably expressed in Chinese hamster ovary (CHO) cells. The receptor expression was confirmed by receptor radioligand binding and immunoblottting. After exposure to 5 mM of DAMGO, phosphorylation of the C-terminally truncated receptor and the mutant receptor T394A was reduced to 40 and 10% of that of the wild-type receptor, respectively. Mutation effects on agonist-induced desensitization were studied using adenylyl cyclase inhibition assays. The C-terminally truncated receptor and mutant receptor T394A both showed complete loss of DAMGO-induced desensitization, while the mutant T/S-7A receptor only lost part of its ability to desensitize. Taken together, these results suggest that the C-terminus of the m opioid receptor participates in receptor phosphorylation and desensitization with threonine 394, a crucial residue for both features. DAMGO-induced m opioid receptor phosphorylation and desensitization are associated and appear to involve both the m opioid receptor C-terminus and other domains of the receptor. Reprinted by permission of the publisher.