Role of protein kinase C (PKC) in agonist-induced mu-opioid receptor down-regulation: I. PKC translocation to the membrane of SH-SY5Y neuroblastoma cells is induced by mu-opioid agonists

J Neurochem. 1999 Feb;72(2):585-93. doi: 10.1046/j.1471-4159.1999.0720585.x.


Agonist-induced down-regulation of opioid receptors appears to require the phosphorylation of the receptor protein. However, the identities of the specific protein kinases that perform this task remain uncertain. Protein kinase C (PKC) has been shown to catalyze the phosphorylation of several G protein-coupled receptors and potentiate their desensitization toward agonists. However, it is unknown whether opioid receptor agonists induce PKC activation under physiological conditions. Using cultured SH-SY5Y neuroblastoma cells, which naturally express mu- and delta-opioid receptors, we investigated whether mu-opioid receptor agonists can activate PKC by measuring enzyme translocation to the membrane fraction. PKC translocation and opioid receptor densities were simultaneously measured by 3H-phorbol ester and [3H]diprenorphine binding, respectively, to correlate alterations in PKC localization with changes in receptor binding sites. We observed that mu-opioid agonists have a dual effect on membrane PKC density depending on the period of drug exposure. Exposure for 2-6 h to [D-Ala2,N-Me-Phe4,Gly-ol]enkephalin or morphine promotes the translocation of PKC from the cytosol to the plasma membrane. Longer periods of opioid exposure (>12 h) produce a decrease in membrane-bound PKC density to a level well below basal. A significant decrease in [3H]diprenorphine binding sites is first observed at 2 h and continues to decline through the last time point measured (48 h). The opioid receptor antagonist naloxone attenuated both opioid-mediated PKC translocation and receptor down-regulation. These results demonstrate that opioids are capable of activating PKC, as evidenced by enhanced translocation of the enzyme to the cell membrane, and this finding suggests that PKC may have a physiological role in opioid receptor plasticity.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Analgesics / pharmacology
  • Analgesics, Opioid / pharmacology
  • Binding, Competitive / physiology
  • Biological Transport / drug effects
  • Carcinogens / pharmacology
  • Diprenorphine / pharmacology
  • Down-Regulation / drug effects
  • Down-Regulation / physiology*
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)-
  • Enkephalin, Leucine / analogs & derivatives
  • Enkephalin, Leucine / pharmacology
  • Enkephalins / pharmacology
  • Humans
  • Kinetics
  • Membrane Proteins / metabolism
  • Morphine / pharmacology
  • Naloxone / pharmacology
  • Narcotic Antagonists / pharmacology
  • Neuroblastoma
  • Phorbol 12,13-Dibutyrate / pharmacology
  • Protein Kinase C / metabolism*
  • Receptors, Opioid, mu / agonists*
  • Receptors, Opioid, mu / antagonists & inhibitors
  • Receptors, Opioid, mu / metabolism*
  • Second Messenger Systems / drug effects
  • Second Messenger Systems / physiology
  • Time Factors
  • Tritium
  • Tumor Cells, Cultured / drug effects
  • Tumor Cells, Cultured / enzymology


  • Analgesics
  • Analgesics, Opioid
  • Carcinogens
  • Enkephalins
  • Membrane Proteins
  • Narcotic Antagonists
  • Receptors, Opioid, mu
  • Tritium
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)-
  • Diprenorphine
  • Naloxone
  • Phorbol 12,13-Dibutyrate
  • Enkephalin, Leucine
  • enkephalin, Ser(2), Leu(5), Thr(6)-
  • Morphine
  • Protein Kinase C