Opioid receptors in human neuroblastoma SH-SY5Y cells: evidence for distinct morphine (mu) and enkephalin (delta) binding sites

Opioid receptors reveal a discrete cellular mechanism of endosomal G protein activation

Many GPCRs initiate a second phase of G protein-mediated signaling from endosomes. This inherently requires the GPCR to increase cognate G protein activity on the endosome surface. Gs-coupled GPCRs are thought to achieve this by internalizing and mediating a second round of allosteric coupling to G proteins on the endosome membrane. Here, we provide evidence that the μ-opioid receptor (MOR), a Gi-coupled GPCR, is able to increase endosomal G protein activity in a different way. Leveraging conformational biosensors, we show that MOR activation triggers a transient increase of active-state Gi/o on the plasma membrane that is followed by a prolonged increase on endosomes. Contrary to the Gs-coupled GPCR paradigm, however, we show that the MOR-induced increase of active-state Gi/o on endosomes requires neither internalization of MOR nor the presence of activated MOR in the endosome membrane. We propose a distinct and additional cellular mechanism of endosomal signaling by Gi/o that is communicated through trafficking of the activated G protein rather than its activating GPCR.

Retromer Opposes Opioid-Induced Downregulation of the Mu Opioid Receptor

The mu opioid receptor (MOR) is protected from opioid-induced trafficking to lysosomes and proteolytic downregulation by its ability to access the endosomal recycling pathway through its C-terminal recycling motif, LENL. MOR sorting towards the lysosome results in downregulation of opioid signaling while recycling of MOR to the plasma membrane preserves signaling function. However, the mechanisms by which LENL promotes MOR recycling are unknown, and this sequence does not match any known consensus recycling motif. Here we took a functional genomics approach with a comparative genome-wide screen design to identify genes which control opioid receptor expression and downregulation. We identified 146 hits including all three subunits of the endosomal Retromer complex. We show that the LENL motif in MOR is a novel Retromer recycling motif and that LENL is a necessary, sufficient, and conserved mechanism to give MOR access to the Retromer recycling pathway and protect MOR from agonist-induced downregulation to multiple clinically relevant opioids including fentanyl and methadone.

Opioid receptors reveal a discrete cellular mechanism of endosomal G protein activation

Many GPCRs initiate a second phase of G protein-mediated signaling from endosomes, which inherently requires an increase in G protein activity on the endosome surface. Gs-coupled GPCRs are thought to achieve this by internalizing and allosterically activating cognate G proteins again on the endosome membrane. Here we demonstrate that the μ-opioid receptor (MOR), a Gi-coupled GPCR, increases endosomal G protein activity in a different way. Leveraging conformational biosensors, we resolve the subcellular activation dynamics of endogenously expressed MOR and Gi/o-subclass G proteins. We show that MOR activation triggers a transient increase of active-state Gi/o on the plasma membrane that is followed by a prolonged increase on endosomes. Contrary to the Gs-coupled GPCR paradigm, however, we show that the MOR-induced increase of active-state Gi/o on endosomes requires neither internalization of MOR nor activation of MOR in the endosome membrane. We propose a distinct and additional cellular mechanism for GPCR-triggered elevation of G protein activity on endosomes that is mediated by regulated trafficking of the activated G protein rather than its activating GPCR.

Morphine decreases cytotoxicity and mutagenicity of doxorubicin in vitro: Implications for cancer chemotherapy

Morphine is the most common opioid analgesic administered to treat pain in patients undergoing cancer chemotherapy. This study aimed to evaluate the cytotoxic and mutagenic effects of morphine alone and in combination with doxorubicin (Dox), an antineoplastic agent largely used in patients with solid cancers. Cytotoxicity was evaluated in neuroblastoma (SH-SY5Y) and fibroblast (V79) cells using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) colorimetric assay while mutagenicity was assessed using the Salmonella/microsome assay in the absence and in the presence of S9 mix. Morphine showed a cytotoxic effect mainly on SH-SY5Y cells and reduced the cytotoxic effects of Dox when evaluated in a co-treatment procedure. In the Salmonella/microsome assay, it was observed that morphine did not induce mutations and, in fact, decreased the mutagenic effects induced by Dox in TA98 and TA102 strains in the absence of metabolic activation. Furthermore, in the presence of metabolic activation, no induction of mutations was observed with morphine. In conclusion, morphine decreased Dox cytotoxicity in both neuronal and non-neuronal cells and showed antimutagenic effects in the TA102 strain which detects mutagens inducing DNA oxidative damages. However, morphine decreased frameshift mutations induced by Dox in non-cytotoxic concentrations, an effect suggesting interference of Dox intercalation activity that could decrease its chemotherapeutic efficacy. These compelling findings highlight the importance of conducting further studies to explore the potential implications of co-administering morphine and Dox during cancer chemotherapy.

The delta opioid receptor tool box

In recent years, the delta opioid receptor has attracted increasing interest as a target for the treatment of chronic pain and emotional disorders. Due to their therapeutic potential, numerous tools have been developed to study the delta opioid receptor from both a molecular and a functional perspective. This review summarizes the most commonly available tools, with an emphasis on their use and limitations. Here, we describe (1) the cell-based assays used to study the delta opioid receptor. (2) The features of several delta opioid receptor ligands, including peptide and non-peptide drugs. (3) The existing approaches to detect delta opioid receptors in fixed tissue, and debates that surround these techniques. (4) Behavioral assays used to study the in vivo effects of delta opioid receptor agonists; including locomotor stimulation and convulsions that are induced by some ligands, but not others. (5) The characterization of genetically modified mice used specifically to study the delta opioid receptor. Overall, this review aims to provide a guideline for the use of these tools with the final goal of increasing our understanding of delta opioid receptor physiology.

The cellular toxicology of mitragynine, the dominant alkaloid of the narcotic-like herb, Mitragyna speciosa Korth

The cytotoxicity of mitragynine, the dominant alkaloid of the narcotic-like herb, Mitragyna speciosa Korth (Kratom) involves cell cycle arrest, apoptosis and opiate receptors.

Solubilization and reconstitution of the mu-opioid receptor expressed in human neuronal SH-SY5Y and CHO cells

The zwitterionic detergent CHAPS was used to solubilize the human mu-opioid receptor (hMOR) from SH-SY5Y neuroblastoma cells and recombinant hMOR-CHO (CHO-T7-hMOR) and hMOR-SH-SY5Y (SH-SY5Y-T7-hMOR) cell membranes. Agonist stimulation and G-protein activation by the mu-selective opioid agonist DAMGO ([D-Ala2, N-MePhe4, Gly-ol]-enkephalin) were recovered after removing of CHAPS after polyethylene glycol (PEG) precipitation. Binding assays show that hMOR solubilized and reconstituted this way was functional and able to interact with both agonist peptides and with G-protein. The effective solubilization and reconstitution of hMOR from mammalian cells, without truncation and extensive modification, represent an essential step toward the purification of a receptor bearing important post-translational modifications.

Regulation of μ-opioid type 1 receptors by microRNA134 in dorsal root ganglion neurons following peripheral inflammation

BACKGROUND

MOR1 is the main transcript of μ-opioid receptor (MOR) gene, which represents a mandatory molecule for the analgesic effects of opioids and plays an important role in the pathology of inflammatory pain. MicroRNAs (miR) are non-coding molecules that primarily modulate gene expression at the post-transcriptional level in various pathophysiological conditions. Based on in silico analysis, an exact match to the seed sequence of miR-134 was found in 3'-untranslated region of MOR1. Given the important roles of MOR1 in pain modulation, the purpose of this study is to investigate whether miR-134 can regulate the MOR1 following allodynia.

METHODS

Using Freund's adjuvant (CFA)-induced chronic inflammatory pain model, we investigated the expression profiles of miR-134 and MOR1 in rat dorsal root ganglia (DRG) using quantitative real-time polymerase chain reaction, in situ hybridization and immunohistochemistry, respectively. The relationship of miR-134 and MOR1 expressions was analysed by linear regression. Luciferase assay was used to examine whether MOR1 was the target of miR-134.

RESULTS

Our results showed that miR-134 expression level was inversely related to MOR1 expression. Down-regulation of miR-134 and up-regulation of MOR1 in the same tissues after inflammatory pain were observed. Functional experiments showed that MOR1 expression in SH-SY5Y cells was up-regulated after inhibition of miR-134, indicating that MOR1 was a target of miR-134.

CONCLUSIONS

Our present data suggested a model that miR-134 participated in CFA-induced inflammatory pain by balancing the expression of MOR1 in DRGs, which implied that miR-134 may be a potential therapeutic target for the treatment of neuropathic pain including inflammation.

Opioid-induced down-regulation of RGS4: role of ubiquitination and implications for receptor cross-talk

Regulator of G protein signaling protein 4 (RGS4) acts as a GTPase accelerating protein to modulate μ- and δ- opioid receptor (MOR and DOR, respectively) signaling. In turn, exposure to MOR agonists leads to changes in RGS4 at the mRNA and/or protein level. Here we have used human neuroblastoma SH-SY5Y cells that endogenously express MOR, DOR, and RGS4 to study opioid-mediated down-regulation of RGS4. Overnight treatment of SH-SY5Y cells with the MOR agonist DAMGO or the DOR agonist DPDPE decreased RGS4 protein by ∼60% accompanied by a profound loss of opioid receptors but with no change in RGS4 mRNA. The decrease in RGS4 protein was prevented by the pretreatment with pertussis toxin or the opioid antagonist naloxone. The agonist-induced down-regulation of RGS4 proteins was completely blocked by treatment with the proteasome inhibitors MG132 or lactacystin or high concentrations of leupeptin, indicating involvement of ubiquitin-proteasome and lysosomal degradation. Polyubiquitinated RGS4 protein was observed in the presence of MG132 or the specific proteasome inhibitor lactacystin and promoted by opioid agonist. The loss of opioid receptors was not prevented by MG132, demonstrating a different degradation pathway. RGS4 is a GTPase accelerating protein for both Gα(i/o) and Gα(q) proteins. After overnight treatment with DAMGO to reduce RGS4 protein, signaling at the Gα(i/o)-coupled DOR and the Gα(q)-coupled M(3) muscarinic receptor (M(3)R) was increased but not signaling of the α(2) adrenergic receptor or bradykinin BK(2) receptor, suggesting the development of cross-talk between the DOR and M(3)R involving RGS4.

Reduction of cell proliferation and potentiation of Fas-induced apoptosis by the selective kappa-opioid receptor agonist U50 488 in the multiple myeloma LP-1 cells

As opioid receptors modulate proliferation and apoptosis of immune cells, we hypothesized that they could reduce malignant haematopoietic cells. After screening, we selected the human multiple myeloma LP-1 cells which express mu- (MOP-) and kappa-opioid receptors (KOP-R). U50 488 produces a modest but significant decrease in viability associated with an arrest in the G0/G1 phase, but not antagonized by NorBNI and not associated with modulation of p21(Cip1), p27(Kip1) or p53 expression. In contrast, no effect was observed with dynorphin, U69 593 and morphine. In conclusion, the anti-proliferative effects of U50 488 are not mediated by KOP-R in the LP-1 cells.

Somatostatin and opioid receptors do not regulate proliferation or apoptosis of the human multiple myeloma U266 cells

BACKGROUND

opioid and somatostatin receptors (SSTRs) that can assemble as heterodimer were individually reported to modulate malignant cell proliferation and to favour apoptosis.

MATERIALS AND METHODS

SSTRs and opioid receptors expression were examined by RT-PCR, western-blot and binding assays, cell proliferation was studied by XTT assay and propidium iodide (PI) staining and apoptosis by annexin V-PI labelling.

RESULTS

almost all human malignant haematological cell lines studied here expressed the five SSTRs. Further experiments were conducted on the human U266 multiple myeloma cells, which express also micro-opioid receptors (MOP-R). XTT assays and cell cycle studies provide no evidence for a significant effect upon opioid or somatostatin receptors stimulation. Furthermore, neither direct effect nor potentiation of the Fas-receptor pathway was detected on apoptosis after these treatments.

CONCLUSION

these data suggest that SSTRs or opioid receptors expression is not a guaranty for an anti-tumoral action in U266 cell line.

Synthesis and in vitro evaluation of a library of modified endomorphin 1 peptides

Endomorphin 1 (Endo-1=Tyr-Pro-Trp-Phe-NH(2)), an endogenous opioid with high affinity and selectivity for mu-opioid receptors, mediates acute and neuropathic pain in rodents. To overcome metabolic instability and poor membrane permeability, the N- and C-termini of Endo-1 were modified by lipoamino acids (Laa) and/or sugars, and 2',6'-dimethyltyrosine (Dmt) replacement of Tyr. Analogues were assessed for mu-opioid receptor affinity, inhibition of cAMP accumulation, enzymatic stability, and permeability across Caco-2 cell monolayers. C-terminus modification decreased receptor affinity, while N-terminus C8-Laa improved stability and permeability with slight change in receptor affinity. Dmt provided a promising lead compound: [C8Laa-Dmt[1]]-Endo-1 is nine times more stable (t(1/2)=43.5min), >8-fold more permeable in Caco-2 cell monolayers, and exhibits 140-fold greater mu-opioid receptor affinity (K(imu)=0.08nM).

Tracking the opioid receptors on the way of desensitization

Opioid receptors belong to the super family of G-protein coupled receptors (GPCRs) and are the targets of numerous opioid analgesic drugs. Prolonged use of these drugs results in a reduction of their effectiveness in pain relief also called tolerance, a phenomenon well known by physicians. Opioid receptor desensitization is thought to play a major role in tolerance and a lot of work has been dedicated to elucidate the molecular basis of desensitization. As described for most of GPCRs, opioid receptor desensitization involves their phosphorylation by kinases and their uncoupling from G-proteins realized by arrestins. More recently, opioid receptor trafficking was shown to contribute to desensitization. In this review, our knowledge on the molecular mechanisms of desensitization and recent progress on the role of opioid receptor internalization, recycling or degradation in desensitization will be reported. A better understanding of these regulatory mechanisms would be helpful to develop new analgesic drugs or new strategies for pain treatment by limiting opioid receptor desensitization and tolerance.

High-purity selection and maintenance of gene expression in human neuroblastoma cells stably over-expressing GFP fusion protein. Application for opioid receptors desensitization studies

Chronic use of opiates such as morphine is associated with drug tolerance, which is correlated with the desensitization of opioid receptors. This latter process involves phosphorylation of opioid receptors by G protein-coupled receptors kinases (GRKs) and subsequent uncoupling by beta-arrestins. To explore these molecular mechanisms, neuronal cell lines, endogenously expressing the opioid receptors, provide an ideal cellular model. Unfortunately, there are two major drawbacks: (1) these cells are refractory to cDNA introduction, resulting in low transfection efficiency; (2) continuous culturing of transfected cells invariably leads to phenotypic drift of the cultures even after an antibiotic selection. So, these cells were dropped in favor of heterologous expression systems, which are easier to transfect but whose relevance as adequate cellular model for studying opioid receptor regulation should be questioned, as recently demonstrated by [Haberstock-Debic, H., Kim, K.A.,Yu, Y.J., von Zastrow, M., 2005. Morphine promotes rapid, arrestin-dependent endocytosis of mu-opioid receptors in striatal neurons. J. Neurosci. 25, 7847-7857]. In this work, we describe a method, based on fluorescence-activated cell sorting (FACS), to select and maintain a high proportion of transfected SK-N-BE cells (a neuronal cell line endogenously expressing human Delta-Opioid Receptor (hDOR)), expressing the beta-arrestin1 fused to green fluorescent protein (GFP). While in functional experiments, we were not able to observe a major effect in non-sorted SK-N-BE cells expressing beta-arrestin1-GFP, the enrichment by 18-fold with FACS resulted in a robust increase of beta-arrestin1-GFP expression associated with strong hDOR desensitization. Moreover, this method also allows to counteract the phenotypic drift and to maintain a high-purity selection of SK-N-BE cells expressing beta-arrestin1-GFP. Thus, this approach provides a valuable tool for exploring opioid receptors desensitization in neuronal cells.

Methadone increases intracellular calcium in SH-SY5Y and SH-EP1-hα7 cells by activating neuronal nicotinic acetylcholine receptors

(-)-Methadone acts as an agonist at opioid receptors. Both (+)- and (-)-enantiomers of methadone have been suggested to be potent non-competitive antagonists of alpha3beta4 neuronal nicotinic acetylcholine receptors (nAChRs). In the present study, we have examined interactions of methadone with nAChRs by using receptor binding assays, patch-clamp recording and calcium fluorometry imaging with SH-SY5Y cells naturally expressing alpha7 and alpha3* nAChR subtypes and SH-EP1-halpha7 cells heterologously expressing human alpha7 nAChRs. Methadone potently inhibited binding of [3H]methyllycaconitine to alpha7 nAChRs and that of [3H]epibatidine to alpha3* nAChRs. Methadone pretreatment induced up-regulation of epibatidine binding sites in SH-SY5Y cells. Using whole-cell patch-clamp recording, both isomers of methadone activated cation currents via mecamylamine-sensitive nAChRs in SH-SY5Y cells. Nicotine and both (+)- and (-)-methadone evoked increases in [Ca2+]i in both fluo-3AM loaded cell lines, and these effects were blocked by mecamylamine and by the alpha7 selective antagonist methyllycaconitine, suggesting effects of methadone as alpha7-nAChR agonist. Sensitivity of sustained nicotine and methadone effects to blockade by CdCl2, ryanodine and xestospongin-c implicates voltage-operated Ca2+ channels and intracellular Ca2+ stores as downstream modulators of elevated [Ca2+]i. Collectively, our results suggest that methadone engages in complex and potentially pharmacologically significant interactions with nAChRs.

Delta opioid receptors are involved in morphine-induced inhibition of luteinizing hormone releasing hormone in SK-N-SH cells

Opioids play an important role in the regulation of lutenizing hormone releasing hormone (LHRH). In the present study, we attempted to find out the subtype of opioid receptors involved in the inhibitory effect of morphine on LHRH. Experiments were conducted on SK-N-SH neuroblastoma cells that express both micro and delta opioid receptors, LHRH mRNA, and release the LHRH peptide. Enzyme-linked immunosorbent assay (ELISA) was employed to measure the levels of LHRH. LHRH level was decreased by 1000 microM of morphine regardless of the duration of exposure or differentiation status of the SK-N-SH cells and was not reversed by naloxone. Selective antagonism of micro opioid receptors, but not delta opioid receptors, allowed lower concentrations (1-100 microM) of morphine to inhibit LHRH. The results of this study imply that (1) delta opioid receptors may mediate the inhibitory effect of lower concentrations of morphine on LHRH levels in SK-N-SH cells, and (2) inhibition of LHRH level by high concentrations of morphine may involve systems other than opioid receptors.

Different stimulatory opioid effects on intracellular Ca(2+) in SH-SY5Y cells

Present study revealed the stimulatory effects of delta opioid receptor on intracellular Ca(2+) concentration ([Ca(2+)](i)) in SH-SY5Y cells. Fura-2 based single cell fluorescence ratio (F345/F380) was used to monitor the fluctuation of [Ca(2+)](i). Application of the selective delta-opioid receptor agonist alone, [D-Pen(2,5)]-enkephalin (DPDPE), hardly had any effects on cells cultivated for 3-10 days. However, after the cells had been pre-stimulated with cholinoceptor agonist, carbachol, variable calcium elevation was found in 59% of the cultures. The response was naltridole-reversible and dose-dependent, and was abolished completely by thapsigargin (TG) treatment but not by administration of CdCl(2) or 0-Ca(2+) bath solutions. DPDPE-mediated [Ca(2+)](i) elevation was abolished by pertussis toxin (PTX) pretreatment but not cholera toxin (CTX), indicating coupling via G proteins of G(i)/G(o) subfamily. In 17.5% of the responding cells, biphase response was found which may be due to both the stimulatory and the inhibitory effects of opioid. On the other hand, in acutely dissociated cells, DPPDE alone induced [Ca(2+)](i) increase in 50% of the cultures. The probability and the amplitude of the elevation were decreased considerably by application of nifedipine or 0-Ca(2+) bath solution and was little affected by application of TG. DPDPE activated [Ca(2+)](i) increase via a PTX-insensitive and CTX-sensitive pathway suggesting coupling through G(s) subunit. All these indicated the opioid modulated the intracellular Ca(2+) regulation system through different pathways. SH-SY5Y cell line might be a suitable model for the investigation of the complex mechanism which underlies opioid function.

Opiate tolerance and dependence: receptors, G-proteins, and antiopiates

Despite the existence of a large body of information on the subject, the mechanisms of opiate tolerance and dependence are not yet fully understood. Although the traditional mechanisms of receptor down-regulation and desensitization seem to play a role, they cannot entirely explain the phenomena of tolerance and dependence. Therefore, other mechanisms, such as the presence of antiopiate systems and the coupling of opiate receptors to alternative G-proteins, should be considered. A further complication of studies of opiate tolerance and dependence is the multiplicity of endogenous opiate receptors and peptides. This review will focus on the endogenous opioid system--peptides, receptors, and coupling of receptors to intracellular signaling via G-proteins--in the context of their roles in tolerance and dependence. Opioid peptides include the recently discovered endomorphins and those encoded by three known genes--pro-opiomelanocortin, pro-enkephalin, and pro-dynorphin. They bind to three types of receptors--mu, delta, and kappa. Each of the receptor types is further divided into multiple subtypes. These receptors are widely known to be coupled to G-proteins of the Gi and Go subtypes, but an increasing body of results suggests coupling to other G-proteins, such as Gs. The coupling of opiate receptors to Gs, in particular, has implications for tolerance and dependence. Alterations at the receptor and transduction level have been the focus of many studies of opiate tolerance and dependence. In these studies, both receptor down-regulation and desensitization have been demonstrated in vivo and in vitro. Receptor down-regulation has been more easily observed in vitro, especially in response to morphine, a phenomenon which suggests that some factor which is missing in vitro prevents receptors from down-regulating in vivo and may play a critical role in tolerance and dependence. We suggest that antiopiate peptides may operate in vivo in this capacity, and we outline the evidence for the antiopiate properties of three peptides: neuropeptide FF, orphanin FQ/nociceptin, and Tyr-W-MIF-1. In addition, we provide new results suggesting that Tyr-W-MIF-1 may act as an antiopiate at the cellular level by inhibiting basal G-protein activation, in contrast to the activation of G-proteins by opiate agonists.

Changes in microtubular tau protein after morphine in a cultured human neuroblastoma cell line

1. Cultured human SH-SY5Y adrenergic neuroblastoma cells were used to examine the action of morphine sulfate on microtubular tau protein. 2. After 48 hr treatment morphine sulfate (200 microM) reduced tau protein in the cytoplasmic (supernatant) fraction of undifferentiated cells, and in the cytoplasmic as well as membrane (pellet) fractions of differentiated cells. 3. A 71% increase (P < 0.05) in total protein in the membrane (pellet) fraction of undifferentiated cells and a 188% increase (P < 0.01) in that of differentiated cells accompanied the decrease in tau protein. 4. A 51% reduction (P < 0.01) in the number of undifferentiated (but not differentiated) cells was seen after this drug (200 microM).

Luteinizing hormone-releasing hormone in undifferentiated and differentiated SK-N-SH human neuroblastoma cells

The presence of luteinizing hormone-releasing hormone (LHRH) in SK-N-SH human neuroblastoma cells was investigated by immunocytochemistry and enzyme-linked immunosorbent assays of whole cell extracts and culture medium. In addition, ribonuclease protection assays were utilized to quantitate LHRH messenger RNA. The expression of LHRH mRNA and LHRH protein level was correlated with neuronal differentiation induced by retinoic acid (RA). In differentiated SK-N-SH cells the LHRH mRNA level as well as the amount of LHRH in cell extracts and cell medium were significantly lower than in differentiated cells. These results suggest that RA affects the expression of LHRH mRNA and the level of LHRH protein in SK-N-SH cells. These data show that altering the growth state of the human neuroblastoma SK-N-SH cells toward more neuronal phenotype results in a significant decrease in expression of LHRH mRNA and the protein. The ability of RA to induce changes in LHRH at the mRNA and at the peptide levels will allow further study of RA regulation of LHRH at the neuronal level.

delta- and mu-opioid receptor mobilization of intracellular calcium in SH-SY5Y human neuroblastoma cells

1. In this study we have investigated delta and mu opioid receptor-mediated elevation of intracellular Ca2+ concentration ([Ca2+]i) in the human neuroblastoma cell line, SH-SY5Y. 2. The Ca(2+)-sensitive dye, fura-2, was used to measure [Ca2+]i in confluent monolayers of SH-SY5Y cells. Neither the delta-opioid agonist, DPDPE ([D-Pen2,5]-enkephalin) nor the mu-opioid agonist, DAMGO (Tyr-D-Ala-Gly-N-Me-Phe-Gly-ol enkephalin) elevated [Ca2+]i when applied alone. However, when either DPDPE or DAMGO was applied in the presence of the cholinoceptor agonist, carbachol (100 nM-1 mM) they evoked an elevation of [Ca2+]i above that caused by carbachol alone. 3. In the presence of 1 microM or 100 microM carbachol, DPDPE elevated [Ca2+]i with an EC50 of 10 nM. The elevation of [Ca2+]i was independent of the concentration of carbachol. The EC50 for DAMGO elevating [Ca2+]i in the presence of 1 microM and 100 microM carbachol was 270 nM and 145 nM respectively. 4. The delta-receptor antagonist, naltrindole (30 nM), blocked the elevations of [Ca2+]i by DPDPE (100 nM) without affecting those caused by DAMGO while the mu-receptor antagonist, CTAP (D-Phe-Cys-Tyr-D-Trp-Arg-Pen-Thr-NH2) (100 nM-1 microM) blocked the elevations of [Ca2+]i caused by DAMGO (1 microM) without affecting those caused by DPDPE. 5. Block of carbachol activation of muscarinic receptors with atropine (10 microM) abolished the elevation of [Ca2+]i by the opioids. The nicotinic receptor antagonist, mecamylamine (10 microM), did not affect the elevations of [Ca2+]i caused by opioids in the presence of carbachol. 6. Muscarinic receptor activation, not a rise in [Ca2+]i, was required to reveal the opioid response. The Ca2+ channel activator, maitotoxin (3 ng ml-1), also elevated [Ca2+]i but subsequent application of opioid in the presence of maitotoxin caused no further changes in [Ca2+]i. 7. The elevations of [Ca2+]i by DPDPE and DAMGO were abolished by pretreatment of the cells with pertussis toxin (200 ng ml-1, 16 h). This treatment did not significantly affect the response of the cells to carbachol. 8. The opioids appeared to elevate [Ca2+]i by mobilizing Ca2+ from intracellular stores. Both DPDPE and DAMGO continued to elevate [Ca2+]i when applied in nominally Ca(2+)-free external buffer or when applied in a buffer containing a cocktail of Ca2+ entry inhibitors. Thapsigargin (100 nM), an agent which discharges intracellular Ca2+ stores, also blocked the opioid elevations of [Ca2+]i. 9. delta and mu Opioids did not appear to mobilize intracellular Ca2+ by modulating the activity of protein kinases. The application of H-89 (10 microM), an inhibitor of protein kinase A, H-7 (100 microM), an inhibitor of protein kinase C, protein kinase A and cyclic GMP-dependent protein kinase, or Bis I, an inhibitor of protein kinase C, did not alter the opioid mobilization of [Ca2+]i. 10. Thus, in SH-SY5Y cells, opioids can mobilize Ca2+ from intracellular stores but they require ongoing muscarinic receptor activation. Opioids do not elevate [Ca2+]i when applied alone.

Differential expression of opioid receptor genes in human lymphoid cell lines and peripheral blood lymphocytes

The existence of receptors for opioid compounds on cells of the immune system has long been hypothesized, but has been very difficult to demonstrate unequivocally. We have used reverse-transcription polymerase chain reaction to obtain cDNA clones from the human MOLT-4 and CEM-3 T-leukemic cell lines which are nearly identical to portions of the delta and kappa opioid receptor cDNAs recently isolated from human brain and placenta, respectively. Northern analyses with riboprobes derived from the delta and kappa opioid receptor clones indicate these sequences are expressed at low levels in human peripheral blood lymphocytes and in several human lymphoid cell lines. Sequences corresponding to the mu opioid receptor cDNA were not detected in this study. The results suggest that delta and kappa opioid receptors may be responsible for mediating some direct effects of opioids in immune cells.

Phosphoinositide signalling in human neuroblastoma cells: biphasic effect of Li+ on the level of the inositolphosphate second messengers

Lithium has a biphasic effect of the agonist-dependent accumulation of Ins(1,4,5)P3 in human neuroblastoma SH-SY5Y cells. These effects consist of a transient reduction, followed by a long-lasting increase in Ins(1,4,5)P3 as compared to controls. The Li+ effects are dose dependent, and were observed at concentrations used in the treatment of bipolar disorders, and thus may have therapeutic implications. The mechanism of the Li+ effect on Ins(1,4,5)P3 accumulation requires further investigation. The transient reduction of Ins(1,4,5)P3 was observed under conditions where Li+ causes only a moderate increase in the inositol mono- and bi-phosphates. Supplementation with exogenous inositol had no effect on the level of Ins(1,4,5)P3, indicating that the mechanism of the Li(+)-dependent reduction of Ins(1,4,5)P3 is not due to inositol depletion. Li+ did not interfere with degradation of Ins(1,4,5)P3 after receptor-blockage with atropine, suggesting that Li+ has no direct effect on the Ins(1,4,5)P3 metabolizing enzymes. A direct effect of Li+ on the phospholipase C is also unlikely. Entry of Ca2+ into the cells is an important factor, which affects agonist-stimulated accumulation of Ins(1,4,5)P3, as well as absolute values of Li(+)-dependent increase in Ins(1,4,5)P3; however, it is not essential for the manifestation of Li+ effects. Our results also show that manifestation of Li+ effects in human neuroblastoma cells requires the stimulation of muscarinic receptors and activation of PLCs, PKCs, and/or that other staurosporine/H-7/GF 109203X-sensitive protein kinases are involved in the regulation of Ins(1,4,5)P3 during the plateau phase of ACh-stimulation. We also suggest an important role for these enzymes in the Li(+)-dependent elevation of Ins(1,4,5)P3.

Time-dependent effects of lithium on the agonist-stimulated accumulation of second messenger inositol 1,4,5-trisphosphate in SH-SY5Y human neuroblastoma cells

In order to approach the molecular mechanism of Li+'s mood-stabilizing action, the effect of Li+ (LiCl) on inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] mass was investigated in human neuroblastoma SH-SY5Y cells, which express muscarinic M3 receptors, coupled to PtdIns hydrolysis. Stimulation of these cells, with the cholinergic agonist acetylcholine, resulted in a rapid and transient increase in Ins(1,4,5)P3 with a maximum at 10 s. This was followed by a rapid decline in Ins(1,4,5)P3 within 30 s to a plateau level above baseline, which gradually declined to reach a new steady state, which was significantly higher than resting Ins(1,4,5)P3 at 30 min. Li+ had no effect on Ins(1,4,5)P3 in resting cells, as well as on the acetylcholine-dependent peak of Ins(1,4,5)P3. However, Li+ caused a transient reduction (at 45 s), followed by a long lasting increase in the Ins(1,4,5)P3 (30 min), as compared with controls. The Li+ effects were dose-dependent and were observed at concentrations used in the treatment of bipolar disorders. Supplementation with inositol had no effect on the level of Ins(1,4,5)P3, at least over the time periods studied. Stimulation of muscarinic receptors with consequent activation of phospholipase C were necessary for the manifestation of Li+ effects in SH-SY5Y cells, Li+ did not interfere with degradation of Ins(1,4,5)P3 after receptor-blockade with atropine, suggesting that Li+ has no direct effect on the Ins(1,4,5)P3-metabolizing enzymes. A direct effect of Li+ on the phospholipase C also is unlikely. Blockade of Ca2+ entry into the cells by Ni2+, or incubation with EGTA, which reduces agonist-stimulated accumulation of Ins(1,4,5)P3, had no effect on the Li(+)-dependent increase in Ins(1,4,5)P3.

Retinoic acid-induced differentiation of human neuroblastoma SH-SY5Y cells is associated with changes in the abundance of G proteins

Western blot analysis, using subtype-specific anti-G protein antibodies, revealed the presence of the following G protein subunits in human neuroblastoma SH-SY5Y cells: Gs alpha, Gi alpha 1, Gi alpha 2, Go alpha, Gz alpha, and G beta. Differentiation of the cells by all-trans-retinoic acid (RA) treatment (10 mumol/L; 6 days) caused substantial alterations in the abundance of distinct G protein subunits. Concomitant with an enhanced expression of mu-opioid binding sites, the levels of the inhibitory G proteins Gi alpha 1 and Gi alpha 2 were found to be significantly increased. This coordinate up-regulation is accompanied by functional changes in mu-opioid receptor-stimulated low-Km GTPase, mu-receptor-mediated adenylate cyclase inhibition, and receptor-independent guanosine 5'-(beta gamma-imido)triphosphate [Gpp(NH)p; 10 nmol/L]-mediated attenuation of adenylate cyclase activity. In contrast, increased levels of inhibitory G proteins had no effect on muscarinic cholinergic receptor-mediated adenylate cyclase inhibition. With respect to stimulatory receptor systems, a reciprocal regulation was observed for prostaglandin E1 (PGE1) receptors and Gs alpha, the G protein subunit activating adenylate cyclase. RA treatment of SH-SY5Y cells increases both the number of PGE1 binding sites and PGE1-stimulated adenylate cyclase activity, but significantly reduced amounts of Gs alpha were found. This down-regulation is paralleled by a decrease in the stimulatory activity of Gs alpha as assessed in S49 cyc- reconstitution assays.(ABSTRACT TRUNCATED AT 250 WORDS)

SK-N-BE: a human neuroblastoma cell line containing two subtypes of delta-opioid receptors

A human neuroblastoma cell line, SK-N-BE, was shown to express a substantial amount of opioid receptors (200-300 fmol/mg of protein). A ligand binding profile of these receptors revealed that they could belong to two distinct subtypes of delta-opioid receptors. Results from sucrose-gradient sedimentation experiments were compared with similar data obtained with the mu-opioid receptor of the rabbit cerebellum and the delta-opioid receptor of the hybrid NG108-15 cell line and have shown that the opioid receptor of the SK-N-BE cell line behaved hydrodynamically as an intermediate between mu- and delta-opioid receptors. Taken together, pharmacological and hydrodynamic studies suggest that the opioid receptors present in the SK-N-BE cell membranes could belong to two delta-opioid receptor subtypes interacting allosterically. Functional experiments suggest that at least one of these subtypes of delta-opioid receptor is negatively coupled to the adenylate cyclase via a Gi protein and that the opiate receptors of the SK-N-BE neuroblastoma cell line undergo a rapid down-regulation when preincubated in the presence of the high-affinity opioid, etorphine.

Alterations in the expression of G-proteins and regulation of adenylate cyclase in human neuroblastoma SH-SY5Y cells chronically exposed to low-efficacy mu-opioids

Western-blot analysis of human neuroblastoma SH-SY5Y cells (mu- and delta-receptors) revealed the presence of the following G-protein subunits: Gi alpha 1, Gi alpha 2, Gs alpha, G(o) alpha, Gz alpha, and G beta, a pattern resembling that observed in central nervous tissue. Chronic treatment of differentiated [all-trans-retinoic acid (10 microM; 6 days)] SH-SY5Y cells with D(-)-morphine (10 microM; 3 days) significantly increased the abundance of all G-protein subunits identified. Co-incubation of morphine-exposed cells together with naloxone (10 microM; 3 days) or the mu-selective opioid antagonist CTOP (10 microM; 3 days), but not with the delta-selective antagonist ICI-174,864 (10 microM; 3 days), completely abolished this effect, suggesting that the increase in G-protein abundance is specifically mediated by mu-receptors. Moreover, the biologically inactive enantiomer L(+)-morphine (10 microM; 3 days) failed to produce a similar effect. G-protein up-regulation developed in a time- and dose-dependent manner and is most likely due to enhanced protein synthesis de novo, since concomitant treatment of the cells with cycloheximide (100 micrograms/ml; 3 days) prevented this effect. Chronic treatment with the low-efficacy mu-selective opioid peptide morphiceptin (10 microM; 3 days), but not with the highly potent mu-agonist DAGO (0.1 microM; 3 days) produced a comparable increase in G-protein abundance. Coincident with quantitative effects on G-protein levels in morphine-tolerant/dependent SH-SY5Y cells, we found elevated levels of basal, forskolin (1 microM)- and prostaglandin-E1 (1 microM)-stimulated adenylate cyclase activities. Reconstitution experiments using S49 cyc- lymphoma-cell membranes suggest that this increase is most likely due to elevated levels of functionally intact Gs. Chronic treatment with both morphine and DAGO induces high degrees of tolerance in this cell line. However, the intrinsic activity of G1 was unchanged, as assessed in functional studies with low-nanomolar concentrations of guanosine 5'-[beta gamma- imido]triphosphate. Our data demonstrate that chronic treatment of SH-SY5Y cells with low-efficacy mu-opioids increases G-protein abundance, a phenomenon which might contribute to the biochemical mechanisms underlying opioid tolerance/dependence.

Interaction among mu-opioid receptors and alpha 2-adrenoceptors on SH-SY5Y human neuroblastoma cells

The clonal human neuroblastoma cell line SK-N-SH-SY5Y was previously shown to express mu-opioid and alpha 2-adrenoceptors which are both negatively coupled to adenylyl cyclase. Because of the potential use of alpha 2-agonists in the treatment of narcotic dependence, we tested the interactions among he alpha 2-agonists, clonidine and norepinephrine, and morphine on AC in SH-SY5Y cells. Pretreatment with retinoic acid resulting in partial neuronal differentiation greatly enhanced the cells' sensitivity towards adenylyl cyclase stimulation by prostaglandin E1, and its inhibition by morphine and alpha 2-agonists. Norepinephrine (EC50 = 69 nM) maximally inhibited prostaglandin E1-stimulated cAMP accumulation (by approximately 83%), and the alpha 2-agonist yohimbine reversed these effects. Clonidine (EC50 = 32 nM) was a partial agonist, with 50 to 60% maximal inhibition. The combined effects of morphine (maximum approximately 70% inhibition) and norepinephrine exceeded the effect of either agent alone, yielding more than 90% inhibition of prostaglandin E1-stimulated cAMP accumulation. As previously reported for morphine, only a partial tolerance was observed for adenylyl cyclase inhibition by norepinephrine. Further, no cross-tolerance was observed between clonidine and morphine. The combined results indicate that mu-opioid receptors and an alpha 2-adrenoceptor subtype are colocalized on the same cells in SH-SY5Y culture, which hence serves as a model to study opioid-alpha 2-adrenergic interactions.

Identification of alpha 2-adrenergic receptor sites in human retinoblastoma (Y-79) and neuroblastoma (SH-SY5Y) cells

The existence of specific alpha 2-adrenergic receptor sites has been shown in human retinoblastoma (Y-79) and neuroblastoma (SH-SH5Y) cells using direct radioligand binding. [3H]Rauwolscine, a selective alpha 2-adrenergic receptor antagonist, exhibited high affinity, saturable binding to both Y-79 and SH-SY5Y cell membranes. The binding of alpha 1 specific antagonist, [3H]Prazocine, was not detectable in either cell type. Competition studies with antagonists yielded pharmacological characteristics typical of alpha 2-adrenergic receptors: rauwolscine greater than yohimbine greater than phentolamine greater than prazocine. Based on the affinity constants of prazocine and oxymetazoline, it appears that Y-79 cells contain alpha 2A receptor, whereas SH-SY5Y cells probably represent a mixture of alpha 2A and alpha 2B receptors. alpha 2-agonists clonidine and (-)epinephrine inhibition curves yielded high and low affinity states of the receptor in SH-SY5Y cells. Gpp(NH)p and sodium ions reduced the proportion of high affinity sites of alpha 2 receptors. These two neuronal cell lines of human origin would prove useful in elucidating the action and regulation of human alpha 2-adrenergic receptors and their interaction with other receptor systems.

Down-regulation of 3H-lofentanil binding to opiate receptors in different cultured neuronal cells

There was stereospecific binding of 3H-lofentanil (KD value = 1.53 nM) to membranes of neuroblastoma-glioma NG 108-15 cells which are known to bear high affinity binding sites for enkephalin derivatives (delta-opiate receptor subtype). There was no high affinity specific binding of the mu-opiate specific ligand 3H-sufentanil. The specific binding of 3H-lofentanil to delta-opiate receptor subtype was down-regulated (decrease in Bmax value without change in the KD value) after prolonged incubation of the cells in the presence of leu- and met- enkephalin (0.1 microM). There was no down-regulation of the opiate receptors (3H-lofentanil and 3H-D-ala-D-leu-enkephalin specific binding) after incubation of NG 108-15 cells with drugs from the fentanyl series (alfentanil or sufentanil). In cultured neurones from rat forebrain (15 day old embryos), the 3H-lofentanil binding was specific with high affinity (KD: 0.048 nM) and a slow dissociation rate similar to that in adult rat cortex. Drugs of the fentanyl series (4-anilino-piperidines) were potent displacers whereas agonists of the delta- (enkephalin derivatives), sigma- (phencyclidine, haloperidol, 3-hydroxyphenyl-propylpiperidine) or K- (U 50488) opiate sites had a low affinity (Ki greater than 0.5 microM) for 3H-lofentanil specific binding sites. Since there was also specific binding of 3H-sufentanil, the opiate receptors in cultured neurones seem to be mainly of the mu-subtype and this is consistent with the ontogeny of opiate receptors subtypes. These receptors were down-regulated after incubation in the presence of etorphine, sufentanil and alfentanil but not enkephalin derivatives.(ABSTRACT TRUNCATED AT 250 WORDS)

Prolonged exposure of human neuroblastoma SH-SY5Y cell line to morphine and oxotremorine modulates signal transduction in adenylate cyclase system

Neurotransmitter receptors coupling to the adenylate cyclase (AC) system were studied in the human neuroblastoma SH-SY5Y cell line. Vasoactive intestinal polypeptide (VIP) caused an up to 40-fold enhancement of the AC activity, while prostaglandin E1 (PGE1) was able to increase the cAMP accumulation 2.5-fold. Stimulation either by VIP or PGE1 was attenuated with either morphine (MOR) or oxotremorine (OXO). Prolonged exposure to MOR and OXO caused a ligand-specific, i.e. homologous desensitization of the opioid and muscarinic acetylcholine receptors, respectively. Preceding desensitization, a supersensitive response of the AC system to VIP was observed. Pretreatment of cells with PT overnight reduced the inhibitory effects of both MOR and OXO. Nevertheless, in cells pretreated with PT and then also with OXO, MOR and OXO inhibited the VIP-induced AC response. Apparently, there are both PT-sensitive and -insensitive pathways to AC inhibition in SH-SY5Y cells.

The effect of opiates upon prostatic carcinoma cell growth

The effect of opiate receptor agonists upon cell growth of the prostatic carcinoma cell line DU145 were studied. Dynorphin-A increased growth significantly with a peak response at 10(-13) M, of 21 +/- 4% (mean +/- SEM). The dose response curve had a typical inverted-U shape. Dynorphin fragments 1-13 and 1-7 also increased growth at 10(-13) M, while the 2-13 fragment failed to increase growth. Naloxone increased growth at high concentration (10(-7) M) suggesting a stimulatory effect, while at the same time blocking the effect of dynorphin-A. This data demonstrates that agents which stimulate opiate receptors, especially the kappa receptor agonist dynorphin, increase the growth of prostatic carcinoma, and that this effect is controlled by changes at the N-terminal end of the peptide. This effect is blocked by Naloxone.