Calcium/calmodulin-dependent protein kinase II supports morphine antinociceptive tolerance by phosphorylation of glycosylated phosducin-like protein

The long isoform of the phosducin-like protein (PhLP1) is widely expressed in the brain and it is thought to influence G-protein signalling by regulating the activity of Goy dimers. We show that in the mature nervous system, PhLP1 exists as both a 38 kDa non-glycosylated isoform and as glycosylated isoforms of about 45, 100 and 150 kDa. Additionally, neural PhLP1 is subject to serine phosphorylation, which augments upon the activation of Mu-opioid receptors (MORs), as does its association with G beta gamma subunits and 14-3-3 proteins. While the intracerebroventricular (icv) administration of morphine to mice rapidly reduced the association of MORs with G proteins, it increased the serine phosphorylation of these receptors. Moreover, activated Ca2+/calmodulin-dependent protein kinase II (CaMKII) accumulated in the MOR environment and phosphorylated PhLP1 was seen to co-precipitate with these opioid receptors. Opioid-induced phosphorylation of PhLP1 was impaired by inhibiting the activity of CaMKII and, in these circumstances, the association of PhLP1 with G beta gamma dimers and 14-3-3 proteins was diminished. Furthermore, these events were coupled with the recovery of G protein regulation by the MORs, while there was a decrease in serine phosphorylation of these receptors and morphine antinociceptive tolerance diminished. It seems that CaMKII phosphorylation of PhLP1 stabilizes the PhLP1.G beta gamma complex by promoting its binding to 14-3-3 proteins. When this complex fails to bind to 14-3-3 proteins, the association of PhLP1 with G beta gamma is probably disrupted by G alpha GDP subunits and the MORs recover control on G proteins. (C) 2007 Elsevier Ltd. All rights reserved.