TY - JOUR
T1 - Agonist-dependent μ-opioid receptor signaling can lead to heterologous desensitization
AU - Chu, Ji
AU - Zheng, Hui
AU - Zhang, Yuhan
AU - Loh, Horace H
AU - Law, Ping-Yee
PY - 2010/4
Y1 - 2010/4
N2 - Desensitization of the μ-opioid receptor (MOR) has been implicated as an important regulatory process in the development of tolerance to opiates. Monitoring the release of intracellular Ca2+ ([Ca2+]i), we reported that [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO)-induced receptor desensitization requires receptor phosphorylation and recruitment of β-arrestins (βArrs), while morphine-induced receptor desensitization does not. In current studies, we established that morphine-induced MOR desensitization is protein kinase C (PKC)-dependent. By using RNA interference techniques and subtype specific inhibitors, PKCε was shown to be the PKC subtype activated by morphine and the subtype responsible for morphine-induced desensitization. In contrast, DAMGO did not increase PKCε activity and DAMGO-induced MOR desensitization was not affected by modulating PKCε activity. Among the various proteins within the receptor signaling complex, Gαi2 was phosphorylated by morphine-activated PKCε. Moreover, mutating three putative PKC phosphorylation sites, Ser44, Ser144 and Ser302 on Gαi2 to Ala attenuated morphine-induced, but not DAMGO-induced desensitization. In addition, pretreatment with morphine desensitized cannabinoid receptor CB1 agonist WIN 55212-2-induced [Ca2+]i release, and this desensitization could be reversed by pretreating the cells with PKCε inhibitor or overexpressing Gαi2 with the putative PKC phosphorylation sites mutated. Thus, depending on the agonist, activation of MOR could lead to heterologous desensitization and probable crosstalk between MOR and other Gαi-coupled receptors, such as the CB1.
AB - Desensitization of the μ-opioid receptor (MOR) has been implicated as an important regulatory process in the development of tolerance to opiates. Monitoring the release of intracellular Ca2+ ([Ca2+]i), we reported that [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO)-induced receptor desensitization requires receptor phosphorylation and recruitment of β-arrestins (βArrs), while morphine-induced receptor desensitization does not. In current studies, we established that morphine-induced MOR desensitization is protein kinase C (PKC)-dependent. By using RNA interference techniques and subtype specific inhibitors, PKCε was shown to be the PKC subtype activated by morphine and the subtype responsible for morphine-induced desensitization. In contrast, DAMGO did not increase PKCε activity and DAMGO-induced MOR desensitization was not affected by modulating PKCε activity. Among the various proteins within the receptor signaling complex, Gαi2 was phosphorylated by morphine-activated PKCε. Moreover, mutating three putative PKC phosphorylation sites, Ser44, Ser144 and Ser302 on Gαi2 to Ala attenuated morphine-induced, but not DAMGO-induced desensitization. In addition, pretreatment with morphine desensitized cannabinoid receptor CB1 agonist WIN 55212-2-induced [Ca2+]i release, and this desensitization could be reversed by pretreating the cells with PKCε inhibitor or overexpressing Gαi2 with the putative PKC phosphorylation sites mutated. Thus, depending on the agonist, activation of MOR could lead to heterologous desensitization and probable crosstalk between MOR and other Gαi-coupled receptors, such as the CB1.
KW - Desensitization
KW - G-protein-coupled receptor
KW - Gα subunit
KW - Protein kinase C
KW - μ-Opioid receptor
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U2 - 10.1016/j.cellsig.2009.12.003
DO - 10.1016/j.cellsig.2009.12.003
M3 - Article
C2 - 20043990
AN - SCOPUS:74449092214
SN - 0898-6568
VL - 22
SP - 684
EP - 696
JO - Cellular Signalling
JF - Cellular Signalling
IS - 4
ER -