MAP kinase activation by mu opioid receptor in cord blood CD34(+)CD38(-) cells

Morphine stimulates cervical cancer cells and alleviates cytotoxicity of chemotherapeutic drugs via opioid receptor-dependent and -independent mechanisms

Morphine is frequently applied in cancer patients for pain management. However, its effects on cancer are not well understood but observed to be specific to certain cancer types. We previously revealed the stimulatory properties of morphine in esophageal carcinoma. This work addressed the effects of morphine and its underlying mechanisms in cervical cancer. Proliferation, apoptosis, and migration assays were performed to examine the effects of morphine alone and its combinatory effects with chemotherapeutic drugs. Immunoblotting and biochemical analysis were performed to determine the underlying mechanisms of morphine's action. Morphine promoted proliferation in opioid receptor-dependent manner and stimulated migration in opioid receptor-independent manner. However, morphine did not affect cervical cancer cell survival. Morphine also interfered with all tested chemotherapeutic drugs (e.g., cisplatin, 5-FU, and paclitaxel) and alleviates their efficacy. Mechanistically, morphine-stimulated growth via activating EGFR-mediated signaling pathways and is opioid-receptor-dependent; morphine-stimulated migration via activating RhoA-mediated signaling pathways and this is opioid receptor-independent. Our work suggests a strong correlation of this opioid receptor on growth factor signaling to stimulate growth and opioid receptor-independent activation of RhoA and consequent migration. Our findings have the potential to guide the clinical use of morphine for patients with cervical cancer.

Fentanyl activates ovarian cancer and alleviates chemotherapy-induced toxicity via opioid receptor-dependent activation of EGFR

BACKGROUND

Fentanyl is an opioid analgesic and is widely used in ovarian cancer patients for pain management. Although increasing evidence has suggested the direct role of fentanyl on cancer, little is known on the effect of fentanyl on ovarian cancer cells.

METHODS

Proliferation, migration and apoptosis assays were performed in ovarian cancer cells after fentanyl treatment. Xenograft mouse model was generated to investigate the in vivo efficacy of fentanyl. Combination index was analyzed for the combination of fentanyl and chemotherapeutic drugs. Immunoblotting approach was used to analyze signaling involved in fentanyl's action focusing on EGFR.

RESULTS

Fentanyl at nanomolar concentration does-dependently increased migration and proliferation of a panel of ovarian cancer cell lines. Fentanyl at the same concentrations either did not or stimulated proliferation to a less extent in normal cells than in ovarian cancer cells. Consistently, fentanyl significantly promoted ovarian cancer growth in vivo. The combination of fentanyl with cisplatin or paclitaxel was antagonist in inhibiting cell proliferation. Although fentanyl did not affect cell apoptosis, it significantly alleviated ovarian cancer cell death induced by chemotherapeutic drugs. Mechanistically, fentanyl specifically activated EGFR and its-mediated downstream pathways. Knockdown of EGFR abolished the stimulatory effects of fentanyl on ovarian cancer cells. We finally demonstrated that the activation of EGFR by fentanyl is associated with opioid µ receptor system.

CONCLUSIONS

Fentanyl activates ovarian cancer via simulating EGFR signaling pathways in an opioid µ receptor-dependent manner. The activation of EGFR signaling by fentanyl may provide a new guide in clinical use of fentanyl in ovarian cancer patients.

Endogenous Opioids and Their Role in Stem Cell Biology and Tissue Rescue

Opioids are considered the oldest drugs known by humans and have been used for sedation and pain relief for several centuries. Nowadays, endogenous opioid peptides are divided into four families: enkephalins, dynorphins, endorphins, and nociceptin/orphanin FQ. They exert their action through the opioid receptors (ORs), transmembrane proteins belonging to the super-family of G-protein-coupled receptors, and are expressed throughout the body; the receptors are the δ opioid receptor (DOR), μ opioid receptor (MOR), κ opioid receptor (KOR), and nociceptin/orphanin FQ receptor (NOP). Endogenous opioids are mainly studied in the central nervous system (CNS), but their role has been investigated in other organs, both in physiological and in pathological conditions. Here, we revise their role in stem cell (SC) biology, since these cells are a subject of great scientific interest due to their peculiar features and their involvement in cell-based therapies in regenerative medicine. In particular, we focus on endogenous opioids’ ability to modulate SC proliferation, stress response (to oxidative stress, starvation, or damage following ischemia–reperfusion), and differentiation towards different lineages, such as neurogenesis, vasculogenesis, and cardiogenesis.

Opioid receptors signaling network

Opioid receptors belong to the class A G-protein-coupled receptors and are activated by alkaloid opiates such as morphine, and endogenous ligands such as endorphins and enkephalins. Opioid receptors are widely distributed in the human body and are involved in numerous physiological processes through three major classical opioid receptor subtypes; the mu, delta and kappa along with a lesser characterized subtype, opioid receptor-like (ORL1). Opioids are the most potent analgesics and have been extensively used as a therapeutic drug for the treatment of pain and related disorders. Chronic administration of clinically used opioids is associated with adverse effects such as drug tolerance, addiction and constipation. Several investigations attempted to identify the molecular signaling networks associated with endogenous as well as synthetic opiates, however, there is a paucity of a cumulative depiction of these signaling events. Here, we report a systemic collection of downstream molecules pertaining to four subtypes of opioid receptors (MOR, KOR, DOR and ORL1) in the form of a signaling pathway map. We manually curated reactions induced by the activation of opioid receptors from the literature into five categories- molecular association, activation/inhibition, catalysis, transport, and gene regulation. This led to a dataset of 180 molecules, which is collectively represented in the opioid receptor signaling network following NetPath criteria. We believe that the public availability of an opioid receptor signaling pathway map can accelerate biomedical research in this area because of its high therapeutic significance. The opioid receptors signaling pathway map is uploaded to a freely available web resource, WikiPathways enabling ease of access ( https://www.wikipathways.org/index.php/Pathway:WP5093 ).

Comparative analysis of the effects of opioids in angiogenesis

BACKGROUND

Angiogenesis, the formation of blood vessel from pre-existing ones, plays an important role in many pathophysiological diseases, such as cancer. Opioids are often used in clinic for the management of chronic pain in cancer patients at terminal phases. Here, we investigated and compared the effects and mechanisms of four opioids on angiogenesis.

METHODS

We performed angiogenesis assays on human umbilical vein endothelial cells (HUVEC) that represent an in vitro model to assess the toxicity of drugs to endothelium.

RESULTS

Morphine and oxycodone at 0.1 μM to 100 μM dose-dependently increased endothelial cell tube formation and proliferation. We observed the same in endothelial cells exposed to fentanyl at 0.1 μM to 10 μM but there was a gradual loss of stimulation by fentanyl at 100 μM and 1000 μM. Morphine and fentanyl reduced endothelial cell apoptosis-induced by serum withdrawal whereas oxycodone did not display anti-apoptotic effect, via decreasing Bax level. Oxycodone at the same concentrations was less potent than morphine and fentanyl. Different from other three opioids, codeine at all tested concentrations did not affect endothelial cell tube formation, proliferation and survival. Mechanism studies demonstrated that opioids acted on endothelial cells via μ-opioid receptor-independent pathway. Although we observed the increased phosphorylation of mitogen-activated protein kinase (MAPK) in cells exposed to morphine, fentanyl and oxycodone, the rescue studies demonstrated that the stimulatory effects of morphine but not fentanyl nor oxycodone were reversed by a specific MAPK inhibitor.

CONCLUSION

Our work demonstrates the differential effects and mechanisms of opioids on angiogenesis.

The pro- and anti-cancer effects of oxycodone are associated with epithelial growth factor receptor level in cancer cells

Background: Oxycodone is an opioid medication used for the treatment of pain in cancer patients. However, little is known on the direct effects of oxycodone on cancer cells. Aim: To determine the effects and mechanisms of oxycodone in cancer cells. Materials and Methods: Proliferation, survival and migration assays were performed on multiple types of cancer cells. Epithelial growth factor receptor (EGFR)/ERK/Akt pathway and oxidative stress were investigated after oxycodone treatment. Results: Oxycodone can either stimulate growth and migration without affecting survival in MDA-468 cells or inhibit growth and survival without affecting migration in SKBR3 and Caco2 cells. In addition, oxycodone can either attenuate or stimulate efficacy of chemotherapeutic drugs in cancer, depending on the type of cancer cells and nature of action of oxycodone as single drug alone. Our mechanism studies suggest that the stimulatory and inhibitory effects of oxycodone are associated with EGFR expression levels in cancer cells. In cancer cells with high EGFR level, oxycodone activates EGFR signaling in cancer cells, leading to stimulatory effects in multiple biological activities, and this is dependent on opioid receptor. In cancer cells with low EGFR level, oxycodone induces mitochondria-mediated caspase activity and oxidative stress and damage, leading to cell death. Conclusions: Our work is the first to demonstrate systematic analysis of oxycodone’s effects and mechanism of action in cancer. The activation of EGFR signaling by oxycodone may provide a new guide in the clinical use of oxycodone, in particular for cancer patients with high EGFR levels.

Morphine Stimulates Migration and Growth and Alleviates the Effects of Chemo Drugs via AMPK-Dependent Induction of Epithelial-Mesenchymal Transition in Esophageal Carcinoma Cells

The role of morphine, an opioid analgesic drug, in cancer biology has increasingly garnered attention due to its frequent usage in postoperative period for pain management in cancer patients. In this work, we demonstrated that morphine, at clinically relevant concentrations, stimulated migration and growth, and alleviated chemo drugs' efficacy in esophageal carcinoma cells. Although morphine did not affect survival, it protected esophageal carcinoma cells from chemo drugs-induced apoptosis. Mechanistical studies showed that morphine increased RhoA but not Rac1 activity. In addition, morphine activated AMP-activated protein kinase (AMPK) pathway, induced epithelial-mesenchymal transition (EMT) via upregulating Snail and Slug levels, and increased oxidative stress in esophageal carcinoma cells. Rescue studies further demonstrated that the stimulatory effects of morphine in esophageal carcinoma cells are through activation of AMPK pathway but not RhoA or opioid receptor. In addition, morphine induced EMT in an AMPK-dependent manner whereas increased RhoA activity in an AMPK-independent manner. Our work demonstrates the protective role of morphine on esophageal carcinoma cells via AMPK activation, which may provide a new guide in clinical use of morphine for patients with esophageal carcinoma.

Oxycodone stimulates normal and malignant hematopoietic progenitors via opioid-receptor-independent-β-catenin activation

Oxycodone is a common type of opioid used for the treatment of moderate to severe pain. Besides its analgesic effects on neuron cells, the effects of oxycodone on other cell types are yet to be elucidated. We previously demonstrated that oxycodone displayed both pro- and anti-cancer effects on bulk cancer cells. This work further investigated the effects of oxycodone on normal and malignant hematopoietic stem cells. Using hematopoietic CD34⁺ cells isolated from normal bone marrow (NBM) or patients with acute myeloid leukemia (AML), we showed that oxycodone activates hematopoietic cells regardless of cell development stage and malignant status. Oxycodone dose-dependently increases colony formation and self-renewal capacity of NBM and AML stem/progenitor cells, and promotes proliferation of AML bulk cells. NBM stem/progenitor cells are more sensitive to oxycodone than AML counterparts. In addition, oxycodone alleviates chemotherapy drug-induced toxicity in AML stem/progenitor cells. Mechanism studies demonstrate that oxycodone acts on hematopoietic cells in an opioid-receptor-independent manner. Oxycodone did not affect epithelial growth factor receptor (EGFR) signaling neither but stimulated Wnt/β-catenin signaling. Rescue studies via depleting β-catenin using genetic and pharmacological approaches confirmed that β-catenin was required for the activation of hematopoietic cells induced by oxycodone. Our work demonstrates 1) the protective role of oxycodone in malignant hematopoietic cells from chemotherapy; 2) stimulatory effects of oxycodone in normal hematopoietic stem cells; and 3) ability of oxycodone in Wnt signaling activation.

Is p38 MAPK Associated to Drugs of Abuse-Induced Abnormal Behaviors?

The family members of the mitogen-activated protein kinases (MAPK) mediate a wide variety of cellular behaviors in response to extracellular stimuli. p38 MAPKs are key signaling molecules in cellular responses to external stresses and regulation of pro-inflammatory cytokines. Some studies have suggested that p38 MAPK in the region of the nucleus accumbens is involved in abnormal behavioral responses induced by drugs of abuse. In this review, we discuss the role of the p38 MAPK in the rewarding effects of drugs of abuse. We also summarize the implication of p38 MAPK in stress, anxiety, and depression. We opine that p38 MAPK activation is more closely associated to stress-induced aversive responses rather than drug effects per se, in particular cocaine. p38 MAPK is only involved in cocaine reward, predominantly when promoted by stress. Downstream substrates of p38 that may contribute to the p38 MAPK associated-behavioral responses are proposed. Finally, we suggest p38 MAPK inhibitors as possible therapeutic interventions against stress-related disorders by potentially increasing resilience against stress and addiction relapse induced by adverse experiences.

Fentanyl inhibits acute myeloid leukemia differentiated cells and committed progenitors via opioid receptor-independent suppression of Ras and STAT5 pathways

Fentanyl is a common sedative/analgesic used for intrathecal chemotherapy injection in children with acute leukemia. Given the contradictory findings that fentanyl has both inhibitory and stimulatory activities in cancer cells, we investigated the biological effects of fentanyl alone and its combination with standard of care in acute myeloid leukemia (AML) cells at all stages of development. We showed that fentanyl at clinically relevant concentration inhibited growth and colony formation of AML differentiated cells and committed progenitors without affecting their survival. Compared to AML cells without FLT3 mutation, cells harboring FLT3-ITD mutation are likely to be more sensitive to fentanyl. However, fentanyl did not affect the most primitive AML stem cells. Fentanyl significantly augmented the efficacy of cytarabine but not midostaurin in AML differentiated cells and committed progenitors. We further demonstrated that fentanyl inhibited AML cells via suppressing Ras/Raf/MEK/ERK and STAT5 pathway, and this was not dependent on opioid receptor system. Our findings demonstrate the anti-leukemia activity of fentanyl and synergistic effects between fentanyl and cytarabine in AML, via opioid receptor-independent suppression of Ras and STAT5 pathways. Our work is the first to suggest the beneficial effects of fentanyl in children with leukemia.

Neurological Regulation of the Bone Marrow Niche

The bone marrow (BM) hematopoietic niche is the microenvironment where in the adult hematopoietic stem and progenitor cells (HSPCs) are maintained and regulated. This regulation is tightly controlled through direct cell-cell interactions with mesenchymal stromal stem (MSCs) and reticular cells, adipocytes, osteoblasts and endothelial cells, through binding to extracellular matrix molecules and through signaling by cytokines and hematopoietic growth factors. These interactions provide a healthy environment and secure the maintenance of the HSPC pool, their proliferation, differentiation and migration. Recent studies have shown that innervation of the BM and interactions with the peripheral sympathetic neural system are important for maintenance of the hematopoietic niche, through direct interactions with HSCPs or via interactions with other cells of the HSPC microenvironment. Signaling through adrenergic receptors (ARs), opioid receptors (ORs), endocannabinoid receptors (CRs) on HSPCs and MSCs has been shown to play an important role in HSPC homeostasis and mobilization. In addition, a wide range of neuropeptides and neurotransmitters, such as Neuropeptide Y (NPY), Substance P (SP) and Tachykinins, as well as neurotrophins and neuropoietic growth factors have been shown to be involved in regulation of the hematopoietic niche. Here, a comprehensive overview is given of their role and interactions with important cells in the hematopoietic niche, including HSPCs and MSCs, and their effect on HSPC maintenance, regulation and mobilization.

Substance abuse, HIV-1 and hepatitis

During the course of human immunodeficiency virus type 1 (HIV-1) disease, the virus has been shown to effectively escape the immune response with the subsequent establishment of latent viral reservoirs in specific cell populations within the peripheral blood (PB) and associated lymphoid tissues, bone marrow (BM), brain, and potentially other end organs. HIV-1, along with hepatitis B and C viruses (HBV and HCV), are known to share similar routes of transmission, including intravenous drug use, blood transfusions, sexual intercourse, and perinatal exposure. Substance abuse, including the use of opioids and cocaine, is a significant risk factor for exposure to HIV-1 and the development of acquired immune deficiency syndrome, as well as HBV and HCV exposure, infection, and disease. Thus, coinfection with HIV-1 and HBV or HCV is common and may be impacted by chronic substance abuse during the course of disease. HIV- 1 impacts the natural course of HBV and HCV infection by accelerating the progression of HBV/HCV-associated liver disease toward end-stage cirrhosis and quantitative depletion of the CD4+ T-cell compartment. HBV or HCV coinfection with HIV-1 is also associated with increased mortality when compared to either infection alone. This review focuses on the impact of substance abuse and coinfection with HBV and HCV in the PB, BM, and brain on the HIV-1 pathogenic process as it relates to viral pathogenesis, disease progression, and the associated immune response during the course of this complex interplay. The impact of HIV-1 and substance abuse on hepatitis virus-induced disease is also a focal point.

Blood-forming stem cells are nervous: direct and indirect regulation of immature human CD34+ cells by the nervous system

The nervous system regulates immunity through hormonal and neuronal routes as part of host defense and repair mechanism. Here, we review the emerging evidence for regulation of human hematopoietic stem and progenitor cells (HSPC) by the nervous system both directly and indirectly via their bone marrow (BM) niche-supporting stromal cells. Functional expression of several neurotransmitter receptors was demonstrated on HSPC, mainly on the more primitive CD34(+)/CD38(-/low) fraction. The myeloid cytokines, G-CSF and GM-CSF, dynamically upregulate neuronal receptor expression on human HSPC. This is followed by an increased response to neurotransmitters, leading to enhanced proliferation and motility of human CD34(+) progenitors, repopulation of the murine BM and their egress to the circulation. Importantly, recent observations showed rapid mobilization of human HSPC to high SDF-1 expressing ischemic tissues of stroke individuals followed by neoangiogenesis, neurological and functional recovery. Along with decreased levels of circulating immature CD34(+) cells and SDF-1 blood levels found in patients with early-stage Alzheimer's disease, these findings suggest a possible involvement of human HSPC in brain homeostasis and thus their potential clinical applications in neuropathology.

Inducible expression of functional mu opioid receptors in murine dendritic cells

Opioids are known to exert direct effects on the immune system, and the expression of functional opioid receptors has been reported on several immune cell types. Dendritic cells (DCs) are important inducers and regulators of immune responses. In this study, we investigated whether murine dendritic cells express functional mu opioid receptors (MOR). RT-PCR analysis and double immunofluorescence staining revealed the expression of MOR in activated murine dendritic cells. We also studied the dynamic expression of MOR messenger RNA in murine dendritic cells in response to different Toll-like receptor ligands. Functionally, treatment of DCs with endomorphin 1 (EM1), a specific agonist of MOR, can inhibit the forskolin-induced formation of cyclic adenosine monophosphate level in activated DCs. Moreover, EM1 treatment resulted in less activation of p38 MAPK and more activation of ERK signaling in lipopolysaccharide-stimulated DCs. Consistently, treatment of DCs with EM1 altered cytokine production by increasing IL-10 and decreasing IL-12 and IL-23. Our results suggest that MOR is inducibly expressed on activated DCs and functionally mediates EM1-induced effects on DCs. Thus, dendritic cells might be involved in crosstalk between the neuroendocrine and the immune system.

Nuclear factor kappaB signaling in opioid functions and receptor gene expression

Opiates are the most powerful of all known analgesics. The prototype opiate morphine has been used as a painkiller for several thousand years. Chronic usage of opiates not only causes drug tolerance, dependence, and addiction, but also suppresses immune functions and affects cell proliferation and cell survival. The diverse functions of opiates underscore the complexity of opioid receptor signaling. Several downstream signaling effector systems, including adenylyl cyclase, mitogen-activated protein kinase, Ca2+ channels, K+ channels, and phosphatidylinositol 3-kinase/Akt, have been identified to be critical in opioid functions. Nuclear factor-kappaB (NF-kappaB), one of the most diverse and critical transcription factors, is one of the downstream molecules that may either directly or indirectly transmit the receptor-mediated upstream signals to the nucleus, resulting in the regulation of the NF-kappaB-dependent genes, which are critical for the opioid-induced biological responses of neuronal and immune cells. In this minireview, we focus on current understanding of the involvement of NF-kappaB signaling in opioid functions and receptor gene expression in cells.

Signal transduction induced by opioids in immune cells: a review

New data regarding signal transduction triggered by opioid ligands in immune cells are reviewed, and the signal transduction in neuronal cells is documented. Similar signaling pathways are induced by opioids in immune as well as neuronal cells. Opioids altered second messenger cAMP, intracellular calcium, and second messenger-induced kinases in immune cells. Met-enkephalin, preferentially delta-opioid, was bimodally regulated, while kappa-opioids inhibited these second messengers. delta-, kappa- and micro-opioids altered nitric oxide secretion, inducing cGMP as the second messenger in immune cells. Coupling of opioid agonists to opioid receptors activated mitogen-activated protein/extracellular signal-regulated protein kinases and various transcription factors in immune cells. Activator protein 1 (AP-1), c-fos, and nuclear factor-kappaB (NF-kappaB) are transcription factors shared by neuronal and immune cells. Delta-opioids activated AP-1, c-fos, activating transcription factor 2, Ikaros-1 and Ikaros-2 transcription factors in immune cells. Induction of kappa-opioid receptor gene by retinoic acid resulted in increased binding of Sp1 transcription factor to the promoter of the kappa-opioid receptor. Micro-opioids inhibited synthesis of common transcription factors AP-1, c-fos, NF-kappaB, and nuclear factor of activated T cells in activated or stimulated immune cells, whereas micro-opioids activated NF-kappaB, GATA-3, and Kruppel-like factor 7 transcription factors in non-stimulated immune cells.

κ-opioids induce a reversible inhibition of CFU-GM from CD133+ cord blood cells

BACKGROUND

Opioid agonists have been shown to exert an inhibitory action on a number of malignant and non-malignant cell types. However, there are no reports dealing with their effect on hemopoietic progenitors. Based upon our previous experience of opioid agonists we examined whether opioids could interfere with the growth of CFU-GM from CD133(+) cord blood cells.

METHODS

Cord blood samples were subjected to CD133(+) column selection, with subsequent exposure to opioid agonists and antagonists or both, in semi-solid cultures for CFU-GM growth. Colonies of day 7 of culture were replated in fresh medium in the absence of opioids. The colonies were evaluated at 7 and 14 days of culture. RT-PCR was performed for the detection of opioid and somatostatin receptors. Apoptosis tests and immunophenotypic evaluations were employed in liquid cultures in conditions identical to those of the semi-solid ones.

RESULTS AND DISCUSSION

Our results suggest that opioids can induce a significant inhibition of CFU-GM growth, which is reversible and not mediated through opioid or somatostatin receptors, while apoptosis is not implicated. Whether this finding could be used for clinical intervention remains to be examined.

Opioids as modulators of cell death and survival--unraveling mechanisms and revealing new indications

Opioids are powerful analgesics but also drugs of abuse. Because opioid addicts are susceptible to certain infections, opioids have been suspected to suppress the immune response. This was supported by the finding that various immune-competent cells express opioid receptors and undergo apoptosis when treated with opioid alkaloids. Recent evidence suggests that opioids may also effect neuronal survival and proliferation or migrating properties of tumor cells. A multitude of signaling pathways has been suggested to be involved in these extra-analgesic effects of opioids. Growth-promoting effects were found to be mediated through Akt and Erk signaling cascades. Death-promoting effects have been ascribed to inhibition of nuclear factor-kappaB, increase of Fas expression, p53 stabilization, cytokine and chemokine release, and activation of nitric oxide synthase, p38, and c-Jun-N-terminal kinase. Some of the observed effects were inhibited with opioid receptor antagonists or pertussis toxin; others were unaffected. It is still unclear whether these properties are mediated through typical opioid receptor activation and inhibitory G-protein-signaling. The present review tries to unravel controversial findings and provides a hypothesis that may help to integrate diverse results.

The stimulatory effect of mu- and delta-opioid receptors on bovine pinealocyte melatonin synthesis

Mammalian pinealocytes synthesize and secrete melatonin. The synthesis of melatonin is regulated by several biogenic amine, amino acid and peptide transmitters. In our previous study, the delta- and mu-opioid receptors have been identified and characterized in bovine pinealocytes. In order to elaborate the function of different types of opioid receptors in regulating melatonin synthesis, we used a selective mu-opioid receptor agonist, Tyr-[D-Ala(2), N-methyl-phe(4), glycol(5)] (DAMGO), a selective delta-opioid receptor agonist, Enkephalin [D-Pen(2), D-Pen(5)], (DPDPE) and a selective kappa-opioid receptor agonist, ((+)-(5alpha, 7alpha, 8beta)-N-methyl-N-[7- (1-pyrrolidinyl)-1-oxaspiro [4,5] dec-8-yl]-benzene acetamide) (U69593) to investigate the activity of N-acetyltransferase (NAT) activity and melatonin secretion. The results of the present study show that both DAMGO and DPDPE stimulated NAT activity and increased the level of melatonin in cultured bovine pinealocytes. These stimulatory effects were blocked by naloxone, an opioid receptor antagonist. However, the kappa-opioid receptor agonist U69593 was unable to alter either the activity of NAT or the level of melatonin. In order to clarify the mechanism of how the activation of mu- and delta-opioid receptors in bovine pinealocytes leads to an increase in NAT activity, cyclic AMP levels were measured after bovine pinealocytes were treated with morphine, DAMGO and DPDPE. The results indicated that these stimulatory effects acted via induction of cAMP production. This study reveals that the stimulatory effect of opioid receptor on melatonin synthesis is mediated via the activation of adenylate cyclase system.

Regulation of STAT3 by mu-opioid receptors in human neuroblastoma SH-SY5Y cells

Heptahelical opioid receptors are implicated in the transcriptional regulation of neuronal development. Here we demonstrated that activation of mu-opioid receptors in human neuroblastoma SH-SY5Y cells led to the activation of signal transducer and activator of transcription 3 (STAT3), a transcription factor central to the regulation of numerous biological processes. The mu-opioid-induced activation of STAT3 is sensitive to receptor was further shown to pertussis toxin treatment and required JAK and Src tyrosine kinases, but not phosphatidylinositol 3-kinase. This mu-opioid-induced response was mediated via the extracellular signal-regulated protein kinase in a Raf-1-independent manner. The present study provides a foundation to explore the importance of STAT3 signaling in the regulation of neuronal growth and differentiation by the mu-opioid receptor.

Morphine negatively regulates interferon-gamma promoter activity in activated murine T cells through two distinct cyclic AMP-dependent pathways

To explore the mechanism by which morphine promotes the incidence of HIV infection, we evaluated the regulatory role of morphine on the interferon-gamma (IFN-gamma) promoter in activated T cells from wild type and mu-opioid receptor knockout mice. Our results show that morphine inhibited anti-CD3/CD28-stimulated IFN-gamma promoter activity in a dose-dependent manner. Chronic morphine treatment of T cells increased intracellular cAMP. To evaluate the role of cAMP in morphine's modulatory function, the effects of dibutyryl cyclic AMP and forskolin were investigated. Both dibutyryl cyclic AMP and forskolin treatment inhibited IFN-gamma promoter activity. Treatment with pertussis toxin, but not with a protein kinase A inhibitor, antagonized morphine's inhibitory effects. Morphine inhibited phosphorylation of ERK1/2 and p38 MAPK; in addition, morphine treatment in the presence of either ERK1/2 or p38 MAPK inhibitor (PD98059 or SB203580) resulted in an additive inhibition of IFN-gamma promoter activity. The transcription factor activator protein-1, NF-kappaB, and nuclear factor of activated T cells (NFAT) were negatively regulated by morphine. Overexpression of NF-kappaB p65 rescued the inhibitory effect of morphine on IFN-gamma promoter activity. However, only when NFATc1 was co-overexpressed with c-fos was the inhibitory effect of morphine on IFN-gamma promoter counteracted. The inhibitory effects of morphine were not observed in T cells obtained from mu-opioid receptor knockout mice, suggesting that morphine modulation of IFN-gamma promoter activity is mediated through the mu-opioid receptor. In summary, our data indicate that morphine modulation of IFN-gamma promoter activity is mediated through two distinct cAMP-dependent pathways, the NF-kappaB signaling pathway and the ERK1/2, p38 MAPK, AP-1/NFAT pathway.

The peripheral cannabinoid receptor Cb2, a novel oncoprotein, induces a reversible block in neutrophilic differentiation

We previously identified a novel common virus integration site, Evi11, by means of retroviral insertional mutagenesis. We demonstrated that the gene encoding the peripheral cannabinoid receptor (Cb2) is the potential target, suggesting that Cb2 is a proto-oncogene. To elucidate a role for this G protein-coupled receptor (GPCR) in leukemic transformation we generated a Cb2-EGFP cDNA construct that was introduced into 32D/G-CSF-R cells. These cells require interleukin 3 (IL-3) to proliferate in vitro, whereas in the presence of granulocyte-colony-stimulating factor (G-CSF) they differentiate toward mature neutrophils. We demonstrate that 32D/G-CSF-R/Cb2-EGFP cells migrate in a transwell assay in reponse to the Cb2 ligand 2-arachidonoylglycerol (2-AG), indicating that the fusion protein was functional. When cultured in the presence of G-CSF neutrophilic differentiation of Cb2-EGFP-expressing 32D/G-CSF-R cells was completely blocked. Moreover, a Cb2-specific antagonist fully recovered the G-CSF-induced neutrophilic differentiation of 32D/G-CSF-R/Cb2-EGFP cells. To investigate which signal transduction pathway(s) may be involved in the block of neutrophilic maturation, differentiation experiments were carried out using specific inhibitors of signaling routes. Interestingly, full rescue of G-CSF-induced neutrophilic differentiation was observed when cells were cultured with the mitogen-induced extracellular kinase (MEK) inhibitors, PD98059 or U0126, and partial recovery was detected with the phosphoinositide 3-kinase (PI3-K) inhibitor LY-294002. These studies demonstrate that the Cb2 receptor is an oncoprotein that blocks neutrophilic differentiation when overexpressed in myeloid precursor cells. Cb2 appears to mediate its activity through MEK/extracellular signal-related kinase (ERK) and PI3-K pathways.