Up-regulation of delta opioid receptors in neuroblastoma hybrid cells: evidence for differences in the mechanisms of action of sodium butyrate and naltrexone.
Opioid binding in subcellular fractions from neurohybrid cells was assessed using two models of up-regulation. Homologous up-regulation was achieved by treating NG108-15 cells with the opioid antagonist naltrexone. Na butyrate was added to NCB-20 cell cultures to affect heterologous up-regulation. In both paradigms light and heavy membranes were resolved by concanavalin A (con A) pretreatment of cells followed by density centrifugation. [3H][D-Ala2,D-Leu5]enkephalin (DADLE) and [3H]diprenorphine Bmax values for these fractions increased without changes in affinity. In contrast to 48 h of antagonist treatment, 5 min of exposure to naltrexone down-regulated heavy membrane delta sites. Under both conditions of up-regulation, inhibition of LM [3H]DADLE specific binding by 5'-guanylylimidodiphosphate was enhanced suggesting greater receptor coupling to guanine nucleotide binding regulatory proteins. Although attenuated by addition of cycloheximide, [3H]DADLE binding to total homogenates increased upon naltrexone treatment of NG108-15 cells. Heavy membrane Bmax values were also augmented in the presence of cycloheximide and naltrexone for 48 h. Activities of beta-glucuronidase and beta-hexoseaminidase were diminished in total homogenates and subcellular fractions from naltrexone-treated cells, suggesting an opioid-induced alteration in lysosomal enzyme trafficking. Comparable receptor down- and up-regulation and attenuation of lysosomal enzyme activity were elicited by the delta-selective opioid peptide antagonist (allyl)2 Tyr-Aib-Aib-Phe-Leu-OH. These results suggest that homologous up-regulation entails initial down-regulation and blockade of receptor degradation.
Belcheva
M M
MM
E.A. Doisy Department of Biochemistry and Molecular Biology, St. Louis University School of Medicine, Missouri.
Barg
J
J
McHale
R J
RJ
Gao
X M
XM
Chuang
D M
DM
Coscia
C J
CJ
D001665:Binding Sites; D002087:Butyrates / Q000494:pharmacology*; D020148:Butyric Acid; D003513:Cycloheximide / Q000494:pharmacology; D004174:Diprenorphine / Q000378:metabolism; D016308:Enkephalin, Leucine-2-Alanine / Q000378:metabolism; D006822:Hybrid Cells / Q000187:drug effects / Q000378:metabolism; D009271:Naltrexone / Q000494:pharmacology*; D009447:Neuroblastoma / Q000378:metabolism*; D011957:Receptors, Opioid / Q000187:drug effects* / Q000378:metabolism; D017465:Receptors, Opioid, delta; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects*
D002087:Butyrates; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D020148:Butyric Acid; D004174:Diprenorphine; D009271:Naltrexone; D016308:Enkephalin, Leucine-2-Alanine; D003513:Cycloheximide