Effects of empagliflozin on progression of chronic kidney disease: a prespecified secondary analysis from the empa-kidney trial

BACKGROUND

Sodium-glucose co-transporter-2 (SGLT2) inhibitors reduce progression of chronic kidney disease and the risk of cardiovascular morbidity and mortality in a wide range of patients. However, their effects on kidney disease progression in some patients with chronic kidney disease are unclear because few clinical kidney outcomes occurred among such patients in the completed trials. In particular, some guidelines stratify their level of recommendation about who should be treated with SGLT2 inhibitors based on diabetes status and albuminuria. We aimed to assess the effects of empagliflozin on progression of chronic kidney disease both overall and among specific types of participants in the EMPA-KIDNEY trial.

METHODS

EMPA-KIDNEY, a randomised, controlled, phase 3 trial, was conducted at 241 centres in eight countries (Canada, China, Germany, Italy, Japan, Malaysia, the UK, and the USA), and included individuals aged 18 years or older with an estimated glomerular filtration rate (eGFR) of 20 to less than 45 mL/min per 1·73 m2, or with an eGFR of 45 to less than 90 mL/min per 1·73 m2 with a urinary albumin-to-creatinine ratio (uACR) of 200 mg/g or higher. We explored the effects of 10 mg oral empagliflozin once daily versus placebo on the annualised rate of change in estimated glomerular filtration rate (eGFR slope), a tertiary outcome. We studied the acute slope (from randomisation to 2 months) and chronic slope (from 2 months onwards) separately, using shared parameter models to estimate the latter. Analyses were done in all randomly assigned participants by intention to treat. EMPA-KIDNEY is registered at ClinicalTrials.gov, NCT03594110.

FINDINGS

Between May 15, 2019, and April 16, 2021, 6609 participants were randomly assigned and then followed up for a median of 2·0 years (IQR 1·5-2·4). Prespecified subgroups of eGFR included 2282 (34·5%) participants with an eGFR of less than 30 mL/min per 1·73 m2, 2928 (44·3%) with an eGFR of 30 to less than 45 mL/min per 1·73 m2, and 1399 (21·2%) with an eGFR 45 mL/min per 1·73 m2 or higher. Prespecified subgroups of uACR included 1328 (20·1%) with a uACR of less than 30 mg/g, 1864 (28·2%) with a uACR of 30 to 300 mg/g, and 3417 (51·7%) with a uACR of more than 300 mg/g. Overall, allocation to empagliflozin caused an acute 2·12 mL/min per 1·73 m2 (95% CI 1·83-2·41) reduction in eGFR, equivalent to a 6% (5-6) dip in the first 2 months. After this, it halved the chronic slope from -2·75 to -1·37 mL/min per 1·73 m2 per year (relative difference 50%, 95% CI 42-58). The absolute and relative benefits of empagliflozin on the magnitude of the chronic slope varied significantly depending on diabetes status and baseline levels of eGFR and uACR. In particular, the absolute difference in chronic slopes was lower in patients with lower baseline uACR, but because this group progressed more slowly than those with higher uACR, this translated to a larger relative difference in chronic slopes in this group (86% [36-136] reduction in the chronic slope among those with baseline uACR <30 mg/g compared with a 29% [19-38] reduction for those with baseline uACR ≥2000 mg/g; ptrend<0·0001).

INTERPRETATION

Empagliflozin slowed the rate of progression of chronic kidney disease among all types of participant in the EMPA-KIDNEY trial, including those with little albuminuria. Albuminuria alone should not be used to determine whether to treat with an SGLT2 inhibitor.

FUNDING

Boehringer Ingelheim and Eli Lilly.

Impact of primary kidney disease on the effects of empagliflozin in patients with chronic kidney disease: secondary analyses of the EMPA-KIDNEY trial

BACKGROUND

The EMPA-KIDNEY trial showed that empagliflozin reduced the risk of the primary composite outcome of kidney disease progression or cardiovascular death in patients with chronic kidney disease mainly through slowing progression. We aimed to assess how effects of empagliflozin might differ by primary kidney disease across its broad population.

METHODS

EMPA-KIDNEY, a randomised, controlled, phase 3 trial, was conducted at 241 centres in eight countries (Canada, China, Germany, Italy, Japan, Malaysia, the UK, and the USA). Patients were eligible if their estimated glomerular filtration rate (eGFR) was 20 to less than 45 mL/min per 1·73 m2, or 45 to less than 90 mL/min per 1·73 m2 with a urinary albumin-to-creatinine ratio (uACR) of 200 mg/g or higher at screening. They were randomly assigned (1:1) to 10 mg oral empagliflozin once daily or matching placebo. Effects on kidney disease progression (defined as a sustained ≥40% eGFR decline from randomisation, end-stage kidney disease, a sustained eGFR below 10 mL/min per 1·73 m2, or death from kidney failure) were assessed using prespecified Cox models, and eGFR slope analyses used shared parameter models. Subgroup comparisons were performed by including relevant interaction terms in models. EMPA-KIDNEY is registered with ClinicalTrials.gov, NCT03594110.

FINDINGS

Between May 15, 2019, and April 16, 2021, 6609 participants were randomly assigned and followed up for a median of 2·0 years (IQR 1·5-2·4). Prespecified subgroupings by primary kidney disease included 2057 (31·1%) participants with diabetic kidney disease, 1669 (25·3%) with glomerular disease, 1445 (21·9%) with hypertensive or renovascular disease, and 1438 (21·8%) with other or unknown causes. Kidney disease progression occurred in 384 (11·6%) of 3304 patients in the empagliflozin group and 504 (15·2%) of 3305 patients in the placebo group (hazard ratio 0·71 [95% CI 0·62-0·81]), with no evidence that the relative effect size varied significantly by primary kidney disease (pheterogeneity=0·62). The between-group difference in chronic eGFR slopes (ie, from 2 months to final follow-up) was 1·37 mL/min per 1·73 m2 per year (95% CI 1·16-1·59), representing a 50% (42-58) reduction in the rate of chronic eGFR decline. This relative effect of empagliflozin on chronic eGFR slope was similar in analyses by different primary kidney diseases, including in explorations by type of glomerular disease and diabetes (p values for heterogeneity all >0·1).

INTERPRETATION

In a broad range of patients with chronic kidney disease at risk of progression, including a wide range of non-diabetic causes of chronic kidney disease, empagliflozin reduced risk of kidney disease progression. Relative effect sizes were broadly similar irrespective of the cause of primary kidney disease, suggesting that SGLT2 inhibitors should be part of a standard of care to minimise risk of kidney failure in chronic kidney disease.

FUNDING

Boehringer Ingelheim, Eli Lilly, and UK Medical Research Council.

The efficient induction of human retinal ganglion-like cells provides a platform for studying optic neuropathies

Retinal ganglion cells (RGCs) are essential for vision perception. In glaucoma and other optic neuropathies, RGCs and their optic axons undergo degenerative change and cell death; this can result in irreversible vision loss. Here we developed a rapid protocol for directly inducing RGC differentiation from human induced pluripotent stem cells (hiPSCs) by the overexpression of ATOH7, BRN3B, and SOX4. The hiPSC-derived RGC-like cells (iRGCs) show robust expression of various RGC-specific markers by whole transcriptome profiling. A functional assessment was also carried out and this demonstrated that these iRGCs display stimulus-induced neuronal activity, as well as spontaneous neuronal activity. Ethambutol (EMB), an effective first-line anti-tuberculosis agent, is known to cause serious visual impairment and irreversible vision loss due to the RGC degeneration in a significant number of treated patients. Using our iRGCs, EMB was found to induce significant dose-dependent and time-dependent increases in cell death and neurite degeneration. Western blot analysis revealed that the expression levels of p62 and LC3-II were upregulated, and further investigations revealed that EMB caused a blockade of lysosome-autophagosome fusion; this indicates that impairment of autophagic flux is one of the adverse effects of that EMB has on iRGCs. In addition, EMB was found to elevate intracellular reactive oxygen species (ROS) levels increasing apoptotic cell death. This could be partially rescued by the co-treatment with the ROS scavenger NAC. Taken together, our findings suggest that this iRGC model, which achieves both high yield and high purity, is suitable for investigating optic neuropathies, as well as being useful when searching for potential drugs for therapeutic treatment and/or disease prevention.

Directed Differentiation of Human iPSCs into Microglia-Like Cells Using Defined Transcription Factors

The generation of a homogeneous population of microglia from human induced pluripotent stem cells (hiPSCs) is crucial to modeling neurological disorders, as well as the carrying out of drug screening and toxicity testing. Here, we provide a stepwise protocol for the simple, robust, and efficient differentiation of hiPSCs into microglia-like cells (iMGs) by overexpression of SPI1 and CEBPA. This protocol details hiPSC culture, lentivirus production, lentivirus delivery, and, finally, the differentiation and validation of the iMG cells.

Endoplasmic reticulum stress induces Alzheimer's disease-like phenotypes in the neuron derived from the induced pluripotent stem cell with D678H mutation on amyloid precursor protein

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is mainly caused by the interaction of genetic and environmental factors. The impact of environmental factors on the genetic mutation in the amyloid precursor protein (APP) is not well characterized. We hypothesized that Endoplasmic Reticulum (ER) stress would promote disease for the patient carrying the APP D678H mutation. Therefore, we analyzed the impact of a familial AD mutation on amyloid precursor protein (APP D678H) under ER stress. Induced pluripotent stem cell (iPSC) from APP D678H mutant carrier was differentiated into neurons, which were then analyzed for AD-like changes. Immunocytochemistry and whole-cell patch-clamp recording revealed that the derived neurons on day 28 after differentiation showed neuronal markers and electrophysiological properties similar to those of mature neurons. However, the APP D678H mutant neurons did not have significant alterations in the levels of amyloid-β (Aβ) and phosphorylated tau (pTau) compared to its isogenic wild-type neuron. Only under ER stress, the neurons with the APP D678H mutation had more Aβ and pTau via immune detection assays. The higher level of Aβ in the APP D678H mutant neurons was probably due to the increased level of β-site APP cleaving enzyme (BACE1) and decreased level of Aβ degrading enzymes under ER stress. Increased Aβ and pTau under ER stress reduced the N-methyl-D-aspartate receptor (NMDAR) in Western blot analysis and altered electrophysiological properties in the mutant neurons. Our study provides evidence that the interaction between genetic mutation and ER stress would induce AD-like changes.

Human iPSC-Derived Neurons as A Platform for Deciphering the Mechanisms behind Brain Aging

With an increased life expectancy among humans, aging has recently emerged as a major focus in biomedical research. The lack of in vitro aging models-especially for neurological disorders, where access to human brain tissues is limited-has hampered the progress in studies on human brain aging and various age-associated neurodegenerative diseases at the cellular and molecular level. In this review, we provide an overview of age-related changes in the transcriptome, in signaling pathways, and in relation to epigenetic factors that occur in senescent neurons. Moreover, we explore the current cell models used to study neuronal aging in vitro, including immortalized cell lines, primary neuronal culture, neurons directly converted from fibroblasts (Fib-iNs), and iPSC-derived neurons (iPSC-iNs); we also discuss the advantages and limitations of these models. In addition, the key phenotypes associated with cellular senescence that have been observed by these models are compared. Finally, we focus on the potential of combining human iPSC-iNs with genome editing technology in order to further our understanding of brain aging and neurodegenerative diseases, and discuss the future directions and challenges in the field.

Efficient conversion of human induced pluripotent stem cells into microglia by defined transcription factors

Microglia, the immune cells of the central nervous system, play critical roles in brain physiology and pathology. We report a novel approach that produces, within 10 days, the differentiation of human induced pluripotent stem cells (hiPSCs) into microglia (iMG) by forced expression of both SPI1 and CEBPA. High-level expression of the main microglial markers and the purity of the iMG cells were confirmed by RT-qPCR, immunostaining, and flow cytometry analyses. Whole-transcriptome analysis demonstrated that these iMGs resemble human fetal/adult microglia but not human monocytes. Moreover, these iMGs exhibited appropriate physiological functions, including various inflammatory responses, ADP/ATP-evoked migration, and phagocytic ability. When co-cultured with hiPSC-derived neurons, the iMGs respond and migrate toward injured neurons. This study has established a protocol for the rapid conversion of hiPSCs into functional iMGs, which should facilitate functional studies of human microglia using different disease models and also help with drug discovery.

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Efficient generation of human iMGs from iPSCs by forced expression of SPI1 and CEBPA

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The transcriptome profile of iMGs resembles that of human primary microglia

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The iMG cells possess appropriate physiological functioning

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An iN-iMG co-culture model is established for studying neuron-microglia interactions

Adapting re-usable elastomeric respirators to utilise anaesthesia circuit filters using a 3D-printed adaptor - a potential alternative to address N95 shortages during the COVID-19 pandemic

The COVID‐19 pandemic has increased the demand for disposable N95 respirators. Re‐usable elastomeric respirators may provide a suitable alternative. Proprietary elastomeric respirator filters may become depleted as demand increases. An alternative may be the virus/bacterial filters used in anaesthesia circuits, if they can be adequately fitted onto the elastomeric respirators. In addition, many re‐usable elastomeric respirators do not filter exhaled breaths. If used for sterile procedures, this would also require modification. We designed a 3D‐printed adaptor that permits elastomeric respirators to interface with anaesthesia circuit filters and created a simple modification to divert exhaled breaths through the filter. We conducted a feasibility study evaluating the performance of our modified elastomeric respirators. A convenience sample of eight volunteers was recruited. Quantitative fit testing, respiratory rate and end‐tidal carbon dioxide were recorded during fit testing exercises and after 1 h of wear. All eight volunteers obtained excellent quantitative fit testing throughout the trial. The mean (SD) end‐tidal carbon dioxide was 4.5 (0.5) kPa and 4.6 (0.4) kPa at baseline and after 1 h of wear (p = 0.148). The mean (SD) respiratory rate was 17 (4) breaths.min⁻¹ and 17 (3) breaths.min⁻¹ at baseline and after 1 h of wear (p = 0.435). Four out of eight subjects self‐reported discomfort; two reported facial pressure, one reported exhalation resistance and one reported transient dizziness on exertion. Re‐usable elastomeric respirators to utilise anaesthesia circuit filters through a 3D‐printed adaptor may be a potential alternative to disposable N95 respirators during the COVID‐19 pandemic.

Assessing the therapeutic potential of Graptopetalum paraguayense on Alzheimer's disease using patient iPSC-derived neurons

Alzheimer’s disease (AD) is the most common type of dementia and also one of the leading causes of death worldwide. However, the underlying mechanisms remain unclear, and currently there is no drug treatment that can prevent or cure AD. Here, we have applied the advantages of using induced pluripotent stem cell (iPSC)-derived neurons (iNs) from AD patients, which are able to offer human-specific drug responsiveness, in order to evaluate therapeutic candidates for AD. Using approach involving an inducible neurogenin-2 transgene, we have established a robust and reproducible protocol for differentiating human iPSCs into glutamatergic neurons. The AD-iN cultures that result have mature phenotypic and physiological properties, together with AD-like biochemical features that include extracellular β-amyloid (Aβ) accumulation and Tau protein phosphorylation. By screening using a gene set enrichment analysis (GSEA) approach, Graptopetalum paraguayense (GP) has been identified as a potential therapeutic agent for AD from among a range of Chinese herbal medicines. We found that administration of a GP extract caused a significantly reduction in the AD-associated phenotypes of the iNs, including decreased levels of extracellular Aβ40 and Aβ42, as well as reduced Tau protein phosphorylation at positions Ser214 and Ser396. Additionally, the effect of GP was more prominent in AD-iNs compared to non-diseased controls. These findings provide valuable information that suggests moving extracts of GP toward drug development, either for treating AD or as a health supplement to prevent AD. Furthermore, our human iN-based platform promises to be a useful strategy when it is used for AD drug discovery.

Cdk12 Regulates Neurogenesis and Late-Arising Neuronal Migration in the Developing Cerebral Cortex

DNA damage response (DDR) pathways are critical for ensuring that replication stress and various types of DNA lesion do not perturb production of neural cells during development. Cdk12 maintains genomic stability by regulating expression of DDR genes. Mutant mice in which Cdk12 is conditionally deleted in neural progenitor cells (NPCs) die after birth and exhibit microcephaly with a thinner cortical plate and an aberrant corpus callosum. We show that NPCs of mutant mice accumulate at G2 and M phase, and have lower expression of DDR genes, more DNA double-strand breaks and increased apoptosis. In addition to there being fewer neurons, there is misalignment of layers IV-II neurons and the presence of abnormal axonal tracts of these neurons, suggesting that Cdk12 is also required for the migration of late-arising cortical neurons. Using in utero electroporation, we demonstrate that the migrating mutant cells remain within the intermediate zone and fail to adopt a bipolar morphology. Overexpression of Cdk5 brings about a partially restoration of the neurons reaching layers IV-II in the mutant mice. Thus, Cdk12 is crucial to the repair of DNA damage during the proliferation of NPCs and is also central to the proper migration of late-arising neurons.

Anxiety and depression with neurogenesis defects in exchange protein directly activated by cAMP 2-deficient mice are ameliorated by a selective serotonin reuptake inhibitor, Prozac

Intracellular cAMP and serotonin are important modulators of anxiety and depression. Fluoxetine, a selective serotonin reuptake inhibitor (SSRI) also known as Prozac, is widely used against depression, potentially by activating cAMP response element-binding protein (CREB) and increasing brain-derived neurotrophic factor (BDNF) through protein kinase A (PKA). However, the role of Epac1 and Epac2 (Rap guanine nucleotide exchange factors, RAPGEF3 and RAPGEF4, respectively) as potential downstream targets of SSRI/cAMP in mood regulations is not yet clear. Here, we investigated the phenotypes of Epac1 (Epac1(-/-)) or Epac2 (Epac2(-/-)) knockout mice by comparing them with their wild-type counterparts. Surprisingly, Epac2(-/-) mice exhibited a wide range of mood disorders, including anxiety and depression with learning and memory deficits in contextual and cued fear-conditioning tests without affecting Epac1 expression or PKA activity. Interestingly, rs17746510, one of the three single-nucleotide polymorphisms (SNPs) in RAPGEF4 associated with cognitive decline in Chinese Alzheimer's disease (AD) patients, was significantly correlated with apathy and mood disturbance, whereas no significant association was observed between RAPGEF3 SNPs and the risk of AD or neuropsychiatric inventory scores. To further determine the detailed role of Epac2 in SSRI/serotonin/cAMP-involved mood disorders, we treated Epac2(-/-) mice with a SSRI, Prozac. The alteration in open field behavior and impaired hippocampal cell proliferation in Epac2(-/-) mice were alleviated by Prozac. Taken together, Epac2 gene polymorphism is a putative risk factor for mood disorders in AD patients in part by affecting the hippocampal neurogenesis.

Primary sensory neurons regulate Toll-like receptor-4-dependent activity of glial cells in dorsal root ganglia

Toll-like receptor-4 (TLR4) has been identified in primary sensory neurons, both in vivo and in vitro, but is reportedly absent from satellite glial cells (SGCs). Herein we reveal that, in rat dorsal root ganglia (DRG), SGCs do express TLR4 but this expression is inhibited by direct contact with neurons. Thus, TLR4 mRNA and protein is strongly up-regulated in isolated DRG glial cells in the absence of neurons. Lipopolysaccharide (LPS) increased cyclooxygenase-2 (COX-2) and tumor necrosis factor-α (TNFα) mRNA expression with greater efficacy in DRG glial cell cultures than in mixed DRG cell cultures containing TLR4-positive neurons. Using an insert co-culture system, we have shown that neuronal inhibition of glial cell TLR4 is likely to be dependent on cell-cell contact rather than diffusible factors from neurons. LPS stimulated prostaglandin E2 (PGE2) production from DRG glial cells in a TLR4- and COX-2-dependent manner. In addition, exogenous PGE2 potentiated LPS-stimulated COX-2 mRNA while inhibiting TNFα mRNA expression by DRG cells, suggestive of a complex regulatory system to control inflammation within the DRG. In addition to LPS, conditioned medium from heat-shocked DRG neurons also increased COX-2 mRNA expression in DRG glial cells in a partially TLR4-dependent manner. We therefore hypothesize that neuronal suppression of glial TLR4 activity is a protective mechanism to prevent uncontrolled inflammation within the DRG. Under conditions where DRG neuronal viability is compromised, DRG glial cells become responsive to PAMPs (pathogen-associated molecular patterns) and DAMPs (danger-associated molecular patterns) and generate a range of classical inflammatory responses.

Isolated dorsal root ganglion neurones inhibit receptor-dependent adenylyl cyclase activity in associated glial cells

BACKGROUND AND PURPOSE

Hyper-nociceptive PGE(2) EP(4) receptors and prostacyclin (IP) receptors are present in adult rat dorsal root ganglion (DRG) neurones and glial cells in culture. The present study has investigated the cell-specific expression of two other G(s) -protein coupled hyper-nociceptive receptor systems: β-adrenoceptors and calcitonin gene-related peptide (CGRP) receptors in isolated DRG cells and has examined the influence of neurone-glial cell interactions in regulating adenylyl cyclase (AC) activity.

EXPERIMENTAL APPROACH

Agonist-stimulated AC activity was determined in mixed DRG cell cultures from adult rats and compared with activity in DRG neurone-enriched cell cultures and pure DRG glial cell cultures.

KEY RESULTS

Pharmacological analysis showed the presence of G(s) -coupled β(2) -adrenoceptors and CGRP receptors, but not β(1) -adrenoceptors, in all three DRG cell preparations. Agonist-stimulated AC activity was weakest in DRG neurone-enriched cell cultures. DRG neurones inhibited IP receptor-stimulated glial cell AC activity by a process dependent on both cell-cell contact and neurone-derived soluble factors, but this is unlikely to involve purine or glutamine receptor activation.

CONCLUSIONS AND IMPLICATIONS

G(s) -coupled hyper-nociceptive receptors are readily expressed on DRG glial cells in isolated cell cultures and the activity of CGRP, EP(4) and IP receptors, but not β(2) -adrenoceptors, in glial cells is inhibited by DRG neurones. Studies using isolated DRG cells should be aware that hyper-nociceptive ligands may stimulate receptors on glial cells in addition to neurones, and that variable numbers of neurones and glial cells will influence absolute measures of AC activity and affect downstream functional responses.

Nerve growth factor-induced differentiation of PC12 cells is accompanied by elevated adenylyl cyclase activity

Rat pheochromocytoma (PC12) cells characteristically undergo differentiation when cultured with nerve growth factor (NGF). Here we show that NGF dramatically increased the adenylyl cyclase-activating property of forskolin in PC12 cells. This effect of NGF was well maintained even when NGF was removed after 4 days, even though the morphological features of neuronal differentiation were rapidly lost on removal of NGF. The enhanced cAMP production in response to forskolin could be due to a synergistic interaction between forskolin and endogenously released agonists acting on G(s)-coupled receptors. However, responses to forskolin were not attenuated by antagonists of adenosine A2 receptors or pituitary adenylate cyclase-activating polypeptide (PACAP) receptors, suggesting that adenosine and PACAP were not involved. Adenylyl cyclases 3, 6 and 9 were the predominant isoforms expressed in PC12 cells, but we found no evidence for NGF-induced changes in expression levels of any of the 9 adenylyl cyclase isoforms, nor in the expression of Gα(s). These findings highlight that NGF has a subtle influence on adenylyl cyclase activity in PC12 cells which may influence more than the neurite extension process classically associated with neuronal differentiation.

Expression of G protein β subunits in rat skeletal muscle after nerve injury: Implication in the regulation of neuregulin signaling

Tight regulation of gene transcription is critical in muscle development as well as during the formation and maintenance of the neuromuscular junction (NMJ). We previously demonstrated that the transcription of G protein beta1 (Gbeta1) is enhanced by treatment of cultured myotubes with neuregulin (NRG), a trophic factor that plays an important role in neural development. In the current study, we report that the transcript levels of Gbeta1 and Gbeta2 subunits in skeletal muscle are up-regulated following sciatic nerve injury or blockade of nerve activity. These observations prompted us to explore the possibility that G protein subunits regulate NRG-mediated signaling and gene transcription. We showed that overexpression of Gbeta1 or Gbeta2 in COS7 cells attenuates NRG-induced extracellular signal-regulated kinase (ERK) 1/2 activation, whereas suppression of Gbeta2 expression in C2C12 myotubes enhances NRG-mediated ERK1/2 activation and c-fos transcription. These results suggest that expression of Gbeta protein negatively regulates NRG-stimulated gene transcription in cultured myotubes. Taken together, our observations provide evidence that specific heterotrimeric G proteins regulate NRG-mediated signaling and gene transcription during rat muscle development.

CDK13/CDC2L5 interacts with L-type cyclins and regulates alternative splicing

Due to the strong sequence homology it has been suggested that CDC2L5 and CDK12 belong to a high molecular weight subfamily of CDC2 family with PITAI/VRE motifs [F. Marques, J.L. Moreau, G. Peaucellier, J.C. Lozano, P. Schatt, A. Picard, I. Callebaut, E. Perret, A.M. Geneviere, A new subfamily of high molecular mass CDC2-related kinases with PITAI/VRE motifs, Biochem. Biophys. Res. Commun. 279 (2000) 832-837]. Recently, we reported that CDK12 interacts with L-type cyclins and is involved in alternative splicing regulation [H.-H. Chen, Y.-C. Wang, M.-J. Fann, Identification and characterization of the CDK12/Cyclin L1 complex involved in alternative splicing regulation, Mol. Cel. Biol. 26 (2006) 2736-2745]. Here, we provide evidence that CDC2L5 also interacts with L-type cyclins and thus rename it as cyclin-dependent kinase 13 (CDK13). The kinase domain of CDK13 is sufficient to bind the cyclin domains of L-type cyclins. Moreover, CDK13 and L-type cyclins modulate each other's subcellular localization. When CDK13 and an E1a minigene reporter construct were over-expressed in HEK293T cells, CDK13 alters the splicing pattern of E1a transcripts in a dose-dependent manner. Similar to effects of CDK12, effects of CDK13 on splicing pattern are counteracted by SF2/ASF and SC35. These findings strengthen CDK12 and CDK13 as a subfamily of cyclin-dependent kinases that regulate alternative splicing.

Comparison between empirical prokinetics, Helicobacter test-and-treat and empirical endoscopy in primary-care patients presenting with dyspepsia: A one-year study

AIM: To investigate the optimal strategy to treat dyspeptic patients in primary care.

METHODS: Dyspeptic patients presenting to primary care outpatient clinics were randomly assigned to: (1) empirical endoscopy, (2) H pylori test-and-treat, and (3) empirical prokinetic treatment with cisapride. Early endoscopy was arranged if patients remained symptomatic after 2 wk. Symptom severity, quality-of-life (SF-36) as well as patient preference and satisfaction were assessed. All patients underwent endoscopy by wk 6. Patients were followed up for one year.

RESULTS: Two hundred and thirty four patients were recruited (163 female, mean age 49). 46% were H pylori positive. 26% of H pylori tested and 25% of empirical prokinetic patients showed no improvement at wk 2 follow-up and needed early endoscopy. 15% of patients receiving empirical cisapride responded well to treatment but peptic ulcer was the final diagnosis. Symptom resolution and quality-of-life were similar among the groups. Costs for the three strategies were HK$4343, $1771 and $1750 per patient. 66% of the patients preferred to have early endoscopy.

CONCLUSION: The three strategies are equally effective. Empirical prokinetic treatment was the least expensive but peptic ulcers may be missed with this treatment. The H pylori test-and-treat was the most cost-effective option.

Protocatechuic acid induces cell death in HepG2 hepatocellular carcinoma cells through a c-Jun N-terminal kinase-dependent mechanism

Protocatechuic acid (PCA), chlorogenic acid (CA) and luteolin (LT) are plant phenols found in Chinese medicinal herbs such as Lonicera japonica. Cytotoxicity assays showed that PCA, CA and LT (at 100 micromol/L) effectively killed the HepG2 hepatocellular carcinoma cells. Among these three naturally occurring compounds, only PCA was capable of stimulating the c-Jun N-terminal kinase (JNK) and p38 subgroups of the mitogen-activated protein kinase (MAPK) family. Coincidently, PCA-induced cell death was rescued by specific inhibitors for JNK and p38, while the cytotoxicities of CA and LT were partially eliminated by the antioxidant effect of N-acetyl-L-cysteine (NAC). Further investigation demonstrated that the aqueous extract of Lonicera japonica also triggered HepG2 cell death in a JNK-dependent manner, but the amount of PCA alone in this herbal extract was insufficient to contribute the subsequent cytotoxic effect. Collectively, our results suggest that PCA is a naturally occurring compound capable of inducing JNK-dependent hepatocellular carcinoma cell death.

GABAB heterodimeric receptors promote Ca2+ influx via store-operated channels in rat cortical neurons and transfected Chinese hamster ovary cells

The GABAB receptors are generally considered to be classical Gi-coupled receptors that lack the ability to mobilize intracellular Ca2+ without the aid of promiscuous G proteins. Here, we report the ability of GABAB receptors to promote calcium influx into primary cultures of rat cortical neurons and transfected Chinese hamster ovary cells. Chinese hamster ovary cells were transfected with GABAB1(a) or GABAB1(b) subunits along with GABAB2 subunits. In experiments using the fluorometric imaging plate reader platform, GABA and selective agonists promoted increases in intracellular Ca2+ levels in transfected Chinese hamster ovary cells and cortical neurons with the expected order of potency. These effects were fully antagonized by selective GABAB receptor antagonists. To investigate the intracellular pathways responsible for mediating these effects we employed several pharmacological inhibitors. Pertussis toxin abolished GABAB mediated Ca2+ increases, as did the phospholipase Cbeta inhibitor U73122. Inhibitor 2-aminethoxydiphenyl borane acts as an antagonist at inositol 1,4,5-trisphosphate receptors and at store-operated channels. In all cell types, 2-aminethoxydiphenyl borane prevented Ca2+ mobilization. The selective store-operated channel inhibitor 1-[2-(4-methoxyphenyl)-2-[3-(4-methoxyphenyl)propoxy]ethyl-1H-imidazole hydrochloride prevented increases in intracellular Ca2+ levels as did performing the assays in Ca2+ free buffers. In conclusion, GABAB receptors expressed in Chinese hamster ovary cells and endogenously expressed in rat cortical neurons promote Ca2+ entry into the cell via the activation of store-operated channels, using a mechanism that is dependent on Gi/o heterotrimeric proteins and phospholipase Cbeta. These findings suggest that the neuronal effects mediated by GABAB receptors may, in part, rely on the receptor's ability to promote Ca2+ influx.

An aqueous extract of the popular Chinese nutraceutical Kwei Ling Ko (Tortoise shell-Rhizome jelly) activates the PPARgamma pathway and down-regulates the NFkappaB activity

It is generally believed that the popular nutraceutical 'Kwei Ling Ko' (KLK; Tortoise shell-Rhizome jelly) has antiinflammatory effects, but the mechanism by which its effects are manifested remains unknown. Peroxisome proliferation-activated receptors (PPARs) are members of the nuclear hormone receptor/transcription factor superfamily with multiple roles in adipocyte differentiation, glucose homeostasis, immunomodulation and antiinflammatory regulation. As PPAR is required for adipocyte induction, we used adipogenesis as a possible screen for the activation of the PPAR pathway. Interestingly, an aqueous extract of KLK (sKLK) was able to induce the adipocyte differentiation of fibroblast cell lines. Adipogenesis was confirmed by flow cytometric analysis using a fluorescent lipid stain. Up-regulation of PPARgamma transcripts during adipogenesis was also demonstrated by reverse transcription-polymerase chain reaction (RT-PCR). The sKLK-induced adipogenesis was similar to that elicited by insulin. The activity of nuclear factor-kappaB (NFkappaB), a transcription factor responsible for the regulation of proinflammatory genes, was also down-regulated in response to sKLK. Luciferase reporter gene assays further demonstrated that sKLK inhibited both basal and tumor necrosis factor-alpha-stimulated NFkappaB activation. The activities reported in this study support an immunomodulatory effect for sKLK. As activation of PPAR pathway has a dual role in adipogenesis and anti-inflammation, our observations are consistent with the notion that KLK possesses antiinflammatory properties.

Reporter gene assays and their applications to bioassays of natural products

Medicinal plants represent precious resources from which bioactive compounds can be isolated and developed into invaluable therapeutic agents. With the advent of modern drug discovery technologies such as combinatorial chemistry and high-throughput drug screening platforms, there is an increasing interest in utilizing medicinal plants as a source of drug leads. A wide spectrum of bioassays can be employed for the detection of bioactivity in extracts, fractions, as well as purified compounds of herbal origin. Amongst the different types of bioassays, reporter gene assays are highly versatile and reliable. The present review provides an overview of the most popular reporter genes in terms of their basic methodology, capacities and limitations. The different types of intracellular and extracellular reporter gene products and their potential applications in bioassays of natural products are also discussed.

Development and inter-rater reliability of a standardized verbal instruction manual for the Chinese Geriatric Depression Scale-short form

The Geriatric Depression Scale (GDS) is a common screening tool for elderly depression in Hong Kong. This study aimed at (1) developing a standardized manual for the verbal administration and scoring of the GDS-SF, and (2) comparing the inter-rater reliability between the standardized and non-standardized verbal administration of GDS-SF. Two studies were reported. In Study 1, the process of developing the manual was described. In Study 2, we compared the inter-rater reliabilities of GDS-SF scores using the standardized verbal instructions and the traditional non-standardized administration. Results of Study 2 indicated that the standardized procedure in verbal administration and scoring improved the inter-rater reliabilities of GDS-SF.

Upper gastrointestinal evaluation of Chinese patients with non-cardiac chest pain

AIMS

To test the usefulness of upper gastrointestinal investigations and quality of life assessment in Chinese patients with non-cardiac chest pain.

METHODS

Seventy-eight consecutive patients with non-cardiac chest pain underwent upper endoscopy. Eight patients had upper gastrointestinal pathology (10%). The remaining 70 patients received acid perfusion test, oesophageal manometry and 24-h ambulatory oesophageal pH (n=65)/manometry (n=61), and the results were compared with those of healthy controls (n=20). Symptoms and quality of life (SF-36) were assessed by standard validated questionnaire.

RESULTS

Significant acid reflux symptoms were present in five (5/70, 7%) patients. Abnormal 24-h oesophageal pH, indicating gastro-oesophageal reflux, was found in 19 (19/65, 29%) patients. The percentage of simultaneous contractions was higher and the percentage peristalsis was lower in patients with non-cardiac chest pain when compared with normal subjects by 24-h ambulatory manometry. Patients with non-cardiac chest pain had a lower SF-36 score when compared to controls.

CONCLUSIONS

Typical acid reflux symptoms are uncommon in Chinese patients with non-cardiac chest pain, but abnormal 24-h pH results, indicating gastro-oesophageal reflux, were found in 29% of patients. Ineffective contractions were more frequently found in patients with non-cardiac chest pain by 24-h ambulatory manometry, which may have a bearing on the impaired quality of life in such patients. Upper gastrointestinal investigations are useful for the evaluation of Chinese patients with non-cardiac chest pain.

Prostanoid signal integration and cross talk

The enzymatic machinery for the production of prostanoids and the receptors responsible for detecting their presence are widely distributed in the body. One pair of prostanoids, prostacyclin and thromboxane A(2), are particularly important in the control of haemodynamics and haemostasis. Prostacyclin achieves its antiplatelet effect by acting as a physiological antagonist, but displays some selectivity towards thromboxane A(2)-mediated platelet activation, possibly by virtue of the inability of thromboxane A(2) receptors to couple directly to G(i) proteins, and because platelet-derived endoperoxides can act as substrates for prostacyclin synthesis in endothelial cells. At low concentrations, prostaglandin E(2) can synergize with thromboxane A(2) by acting on the EP(3) subtype of prostaglandin E(2) receptor, resulting in opposition to the protective function of prostacyclin. In contrast, high concentrations of prostaglandin E(2) act on the prostacyclin receptor, and possibly the prostaglandin D(2) receptor, to turn off platelet activation. Integration of prostanoid signalling in the vascular system is similarly complex, and interpretation of data is further complicated by the regional distribution of prostanoid receptors in different vascular beds, and the poor selectivity of agonists and antagonists.

Role of extracellular signal-regulated kinases in opioid-induced adenylyl cyclase superactivation in human embryonic kidney 293 cells

The mu-opioid receptor stimulates the activity of extracellular signal-regulated protein kinase 1/2 (ERK1/2) in recombinant human embryonic kidney (HEK) 293 cells but this stimulatory response is abolished by prolonged opioid treatment. Chronic opioid treatment of the same cells has also been shown to induce adenylyl cyclase (AC) superactivation. This study examined the role of ERK1/2 activity in opioid-induced AC superactivation. Acute opioid treatment of HEK 293 cells expressing mu-opioid receptors resulted in the activation of ERK1/2, and this response was abolished in the presence of U0126, a MEK1/2 inhibitor. Despite a complete blockade of ERK1/2 phosphorylation, U0126 did not affect opioid-induced AC superactivation, indicating that ERK1/2 activity was not required for opioid-induced AC superactivation in HEK 293 cells.

Prostacyclin receptor-independent inhibition of phospholipase C activity by non-prostanoid prostacyclin mimetics

1. Chinese hamster ovary (CHO) cells were transiently transfected with the mouse prostacyclin (mIP) receptor to examine IP agonist-mediated stimulation of [(3)H]-cyclic AMP and [(3)H]-inositol phosphate production. 2. The prostacyclin analogues, cicaprost, iloprost, carbacyclin and prostaglandin E(1), stimulated adenylyl cyclase activity with EC(50) values of 5, 6, 25 and 95 nM, respectively. These IP agonists also stimulated the phospholipase C pathway with 10 - 40 fold lower potency than stimulation of adenylyl cyclase. 3. The non-prostanoid prostacyclin mimetics, octimibate, BMY 42393 and BMY 45778, also stimulated adenylyl cyclase activity, with EC(50) values of 219, 166 and 398 nM, respectively, but failed to stimulate [(3)H]-inositol phosphate production. 4. Octimibate, BMY 42393 and BMY 45778 inhibited iloprost-stimulated [(3)H]-inositol phosphate production in a non-competitive manner. 5. Activation of the endogenously-expressed P(2) purinergic receptor by ATP led to an increase in [(3)H]-inositol phosphate production which was inhibited by the non-prostanoid prostacyclin mimetics in non-transfected CHO cells. Prostacyclin analogues and other prostanoid receptor ligands failed to inhibit ATP-stimulated [(3)H]-inositol phosphate production. 6. A comparison between the IP receptor-specific non-prostanoid ONO-1310 and the structurally-related EP(3) receptor-specific agonist ONO-AP-324, indicated that the inhibitory effect of non-prostanoids was specific for those compounds known to activate IP receptors. 7. The non-prostanoid prostacyclin mimetics also inhibited phospholipase C activity when stimulated by constitutively-active mutant Galpha(q)RC, Galpha(14)RC and Galpha(16)QL transiently expressed in CHO cells. These drugs did not inhibit adenylyl cyclase activity when stimulated by the constitutively-active mutant Galpha(s)QL. 8. These results suggest that non-prostanoid prostacyclin mimetics can specifically inhibit [(3)H]-inositol phosphate production by targeting G(q/11) and/or phospholipase C in CHO cells, and that this effect is independent of IP receptors.

A reporter gene assay for the detection of phytoestrogens in traditional Chinese medicine

Bupleurum & Peony Formula (Jia Wei Xiao Yao San) is a herbal formula which possesses a clinical history for the treatment of menopausal syndrome and menstrual irregularity. The present investigation reports the ability to monitor the formula's phytoestrogen content that will allow for the implementation of a standardization protocol that is based on a quantifiable biological response. Utilizing an oestrogen-sensitive chimeric receptor/reporter gene element which has been stably transfected into HeLa cells, the botanical formula was shown to induce the expression of the reporter gene, luciferase, in a dose dependent manner. Pretreatment of the HeLa cells with the botanical formula produced a 5-fold increase in bioluminescence compared with the control. Additionally, our studies showed that the response of the cells, when challenged by the botanical formula, was oestrogen specific. Pretreatment of the cells with tamoxifen effectively blocked the activation of the chimeric oestrogen receptor by the botanical formula. The cell line provides a sensitive assay that can easily detect the presence of phytoestrogens in complex botanical formulas.

Bacterial formyl peptide mediated chemotaxis and extracellular acidification in shrimp haemocytes

The bacterial formyl peptide N-formylmethionine-leucine-phenylalanine (fMLP) is a potent chemoattractant for mammalian neutrophils. In this study, we demonstrated the binding of fluorescent dye-conjugated-fMLP to haemocytes of the penaeid shrimp Penaeus penicillatus (Alcock), through the use of flow cytometry. Fluorescence microscopy with rhodamine-fMLP suggested that fMLP receptors are present only in sub-populations of the haemocytes: granulocytes and the semi-granular cells. In addition, fMLP dose-dependently mediated chemotaxis in sub-populations of haemocytes. Microphysiometry experiments demonstrated rapid extracellular acidification upon addition of fMLP, which is in agreement with the observation in neutrophils. t-BOC, the specific fMLP receptor antagonist, was able to block the binding, chemotaxis and extracellular acidification induced by the peptide. The ability of shrimp haemocytes to migrate toward fMLP in vitro suggests that this mechanism may be important for the accumulation of these cells in infected tissues of the shrimps.

The cyclic AMP-mediated expression of acetylcholinesterase in myotubes shows contrasting activation and repression between avian and mammalian enzymes

Cyclic adenosine 3',5'-monophosphate (cAMP)-dependent signalling pathway has been proposed to regulate acetylcholinesterase (AChE) expression in chick muscle; however, its role in mammalian enzyme is not known. We provide several lines of evidence to suggest that the cAMP-mediated AChE expression in myotube is oppositely regulated between avian and mammalian enzymes. Human AChE promoter was tagged with luciferase, namely Hp-Luc, which was transfected into cultured chick myotubes. Application of cAMP and forskolin induced the expression of chick AChE but reduced human AChE promoter-driven luciferase activity. Transfection of cDNAs encoding active mutants of G proteins altered the intracellular cAMP level in myotubes as well as the expression of chick and human AChE. When the constitutively active forms of Activating Transcription Factor-1 (EWS/ATF-1 oncogene) were over expressed in Hp-Luc transfected myotubes, the expression of chick AChE transcript and protein increased from approximately 1.8- to approximately 2.5-fold, but the luciferase activity was decreased by over 60%. Overexpression of cAMP-responsive element binding protein (CREB) in Hp-Luc transfected myotubes markedly enhanced the cAMP-mediated AChE expression in up- and downregulated chick and human enzymes, respectively. In addition, CREB bound the CRE sequence of human AChE promoter. Mutation on the CRE site markedly enhanced the expression of the promoter-driven luciferase; however, its response to cAMP inhibition in cultured myotubes was still retained. These findings suggest that a cAMP-dependent pathway is contrasting activation and repression of AChE expression in chick and human muscles.

Chimeric Galphaq subunits can distinguish the long form of the Xenopus Mel1c melatonin receptor from the mammalian mt1 and MT2 melatonin receptors

The family of melatonin receptors is composed of the mt1, MT2, and Mel1c subtypes. The Mel1c is further divided into one long and two short isoforms. A recent study has shown that, unlike mt1 and MT2, the long form of Mel1c is incapable of activating the pertussis toxin-insensitive G16. Here we used three well-characterized Galphaq chimeras to explore the coupling specificity of the melatonin receptors. The qi5, qo5, and qz5 chimeras can link numerous Gi-coupled receptors to the stimulation of phosphoinositide-specific phospholipase C. Both mt1 and MT2 receptors interacted productively with the Galphaq chimeras, while the long form of Mel1c was totally ineffective. Among the Galphaq chimeras, qo5 was less efficiently coupled to the melatonin receptors. Such differential coupling is best explained by structural differences between the melatonin receptors as well as among the Galphaq chimeras. Since the long form of Mel1c receptor possesses an exceptionally large C-terminal tail, we tested the ability of four melatonin receptor C-terminal tail chimeras (Chi 1-4) to interact with the Galphaq chimeras. The presence of the large C-terminal tail of Mel1c in Chi 1 and Chi 3 markedly hindered their coupling to the Galphaq chimeras. On the other hand, the attachment of either the mtl or MT2 C-terminal tail to a Mel1c backbone produced chimeras (Chi 2 and Chi 4) that were capable of activating the Galphaq chimeras. These findings suggest the involvement of C-terminal regions of melatonin receptors in the recognition of G proteins.

G(z) signaling: emerging divergence from G(i) signaling

A large variety of neurotransmitters, hormones, and chemokines regulate cellular functions via cell surface receptors that are coupled to guanine nucleotide-binding regulatory proteins (G proteins) belonging to the G(i) subfamily. All members of the G(i) subfamily, with the sole exception of G(z), are substrates for the pertussis toxin ADP-ribosyl transferase. G(z) also exhibits unique biochemical and regulatory properties. Initial portrayals of the cellular functions of G(z) bear high resemblance to those of other G(i) proteins both in terms of the receptors and effectors linked to G(z). However, recent discoveries have begun to insinuate a distinct role for G(z) in cellular communication. Functional interactions of the alpha subunit of G(z) (Galpha(z)) with the NKR-P1 receptor, Galpha(z)-specific regulator of G protein signaling, p21-activated kinase, G protein-regulated inducers of neurite outgrowth, and the Eya2 transcription cofactor have been demonstrated. These findings provide possible links for G(z) to participate in cellular development, survival, proliferation, differentiation and even apoptosis. In this review, we have drawn a sketch of a signaling network with G(z) as the centerpiece. The emerging picture is one that distinguishes G(z) from other members of the G(i) subfamily.

Opioid-induced adenylyl cyclase supersensitization in human embryonic kidney 293 cells requires pertussis toxin-sensitive G proteins other than G(i1) and G(i3)

Chronic activation of opioid receptors in cultured mammalian cells is known to induce adenylyl cyclase (AC) supersensitization via the pertussis toxin-sensitive G(i/o) proteins. To examine the role of G(i1) and G(i3) in opioid-induced AC supersensitization, pertussis toxin-resistant mutants of Galpha(i1) and Galpha(i3) (Galpha(i1)CG and Galpha(i3)CG) were stably co-expressed with different opioid receptors (mu, delta or kappa) in human embryonic kidney (HEK 293) cells. Although the opioid receptors were capable of inhibiting AC via Galpha(i1)CG and Galpha(i3)CG in pertussis toxin-treated cells, AC supersensitization induced by chronic opioid treatment remained sensitive to pertussis toxin. Our results demonstrated that despite their ability to interact with opioid receptors, the pertussis toxin-sensitive G(i1) and G(i3) proteins on their own are incapable of supporting opioid-induced AC supersensitization.

Regulation of c-Jun N-terminal kinase by the ORL(1) receptor through multiple G proteins

Nociceptin is an endogenous peptide that produces its biological effects by binding to the opioid receptor-like (ORL(1)) receptor. It has been shown that activation of ORL(1) receptor leads to inhibition of the adenylyl cyclase activity, but stimulation of the extracellular signal-regulated kinase and p38 subgroups of mitogen-activated protein kinases. In this report, we demonstrate that activation of the G protein-coupled ORL(1) receptor in transfected COS-7 cells leads to stimulation of the JNK subgroup of mitogen-activated protein kinases in a Ras/Rac-dependent manner, and it was insensitive to wortmannin. This increased JNK activity was mainly mediated by PTX-sensitive G(i) proteins, and partially contributed by a PTX-insensitive component. Among all known PTX-insensitive G proteins, G(z), G(12), G(14), and G(16) seemed to have functional coupling with the ORL(1) receptor in terms of JNK activation. Stimulation of the endogenous ORL(1) receptor in NG108-15 cells also led to activation of a PTX-sensitive JNK activity in a wortmannin-insensitive manner. The induced JNK activation is accompanied by the active phosphorylation of c-Jun and activating transcription factor-2. This is the first report that demonstrates the stimulatory effect of ORL(1) receptor on JNK, and the subsequent activation of c-Jun and activating transcription factor-2.

The amino terminus of Galpha(z) is required for receptor recognition, whereas its alpha4/beta6 loop is essential for inhibition of adenylyl cyclase

G(z) couples to most of the known G(i)-linked receptors and its alpha subunit (Galpha(z)) inhibits adenylyl cyclases as efficiently as Galpha(i) subtypes. A series of chimeric Galpha subunits with different portions of Galpha(z) and Galpha(t1) (a regulator of cGMP phosphodiesterase) were constructed to study the essential structural elements of Galpha(z) that determine receptor coupling and effector interaction. The receptor-mediated functions of the chimeras were assessed in two aspects: 1) stimulation of type 2 adenylyl cyclase through the release of betagamma subunits from the chimeras, and 2) inhibition of isoproterenol-stimulated adenylyl cyclase by the chimeric Galpha subunits. The results suggested that the presence of both termini of Galpha(z) were critical for coupling to delta-opioid receptor, with the N-terminal region being more important. Moreover, a stretch of amino acids (295-319) corresponding to the alpha4/beta6 loop was identified as one of the adenylyl cyclase inhibitory domains of Galpha(z).

G(z) can mediate the acute actions of mu- and kappa-opioids but is not involved in opioid-induced adenylyl cyclase supersensitization

The three subtypes of opioid receptors (delta, micro, and kappa) are known to regulate multiple effectors through either pertussis toxin-sensitive or -insensitive G proteins. In opioid-induced inhibition of adenylyl cyclase, both G(i) and G(z) proteins can serve as the signal transducer. Our previous study showed that opioid-induced adenylyl cyclase supersensitization in human embryonic kidney (HEK) 293 cells expressing the delta-opioid receptor requires G(i) but not G(z) proteins. Herein, we studied the ability of mu- and kappa-opioid receptors to regulate the activities of adenylyl cyclase through G(z). In HEK 293 cells coexpressing G(z) with the mu- or kappa-opioid receptors, opioid agonists induced inhibition of adenylyl cyclase in a pertussis toxin-insensitive manner. However, adenylyl cyclase supersensitization induced by chronic opioid treatments remained sensitive to pertussis toxin. We also showed that the responsiveness of cAMP-dependent response element-binding proteins to forskolin was not altered after prolonged opioid treatment but was higher in cells coexpressing G(z). Although the mu- and kappa-opioid receptors mediated acute activation of extracellular signal-regulated protein kinase 1/2 via both G(i) and G(z), these responses were abolished by chronic opioid treatment. These studies showed that G(z) could mediate acute actions of mu- and kappa-opioids but G(z) alone was insufficient to mediate adenylyl cyclase supersensitization induced by the chronic activation of opioid receptors.

Deciphering the role of Gi2 in opioid-induced adenylyl cyclase supersensitization

Prolonged opioid treatment of HEK 293 cells expressing opioid receptors are known to induce adenylyl cyclase supersensitization, a process that requires pertussis toxin (PTX)-sensitive G(i/o) proteins. Here, the role of Gi2 in adenylyl cyclase supersensitization was investigated. A PTX-insensitive G alpha(i2)/z chimera was stably co-expressed with mu-, kappa- or delta-opioid receptors in HEK 293 cells. Functional coupling of G alpha(i2)/z to the opioid receptors was demonstrated by opioid-induced inhibition of adenylyl cyclase and stimulation of ERK1/2 phosphorylation in PTX-treated cells. Chronic opioid treatment of each cell line led to adenylyl cyclase supersensitization but this response was blocked by PTX. Our results demonstrated that although PTX-sensitive G proteins are obligatory for opioid-induced adenylyl cyclase supersensitization, Gi2 alone was insufficient to mediate this response.

Immunoglobulin G1 Fc fragment-tagged human opioid receptor-like receptor retains the ability to inhibit cAMP accumulation

The human opioid receptor-like (ORL(1)) receptor was tagged with the immunoglobulin G1 Fc fragment at the carboxy-terminus and expressed in human embryonic kidney 293 cells. Expression of the ORL(1)-Fc receptor was confirmed by immunohistochemical staining. The fusion protein was enriched by affinity chromatography and then verified by immunodetection. The function of the ORL(1)-Fc receptor was determined by examining nociceptin/OFQ-induced inhibition of cAMP accumulation. The ORL(1)-Fc receptor inhibited the forskolin-stimulated cAMP accumulation. The inhibitory response was selectively induced by nociceptin/OFQ in a dose-dependent and pertussis toxin-sensitive manner. Our results indicate that the carboxy-terminal Fc-tagged ORL(1) receptor retained the ability to interact with G(i) proteins to inhibit adenylyl cyclase.

Molecular mechanisms and regulation of opioid receptor signaling

Cloning of multiple opioid receptors has presented opportunities to investigate the mechanisms of multiple opioid receptor signaling and the regulation of these signals. The subsequent identification of receptor gene structures has also provided opportunities to study the regulation of receptor gene expression and to manipulate the concentration of the gene products in vivo. Thus, in the current review, we examine recent advances in the delineation basis for the multiple opioid receptor signaling, and their regulation at multiple levels. We discuss the use of receptor knockout animals to investigate the function and the pharmacology of these multiple opioid receptors. The reasons and basis for the multiple opioid receptor are addressed.

Evidence for transduction of mu but not kappa opioid modulation of extracellular signal-regulated kinase activity by G(z) and G(12) proteins

Chronic treatment with micro or kappa opioid agonists (>/=2 h) inhibits EGF-induced ERK activation in opioid receptor overexpressing COS-7 cells. Although acute mu and kappa opioids activate ERK via a pertussis toxin-sensitive G protein, pertussis toxin insensitivity of the chronic mu (but not kappa) action was observed. Here, we tested several pertussis toxin-insensitive G proteins as candidates to transduce acute and/or chronic opioid modulation of ERK. Overexpressed Galpha(z) (but not Galpha(12)) transduced acute mu (but not kappa) ERK activation in pertussis toxin-treated COS-7 cells. Chronic mu (but not kappa) inhibited EGF stimulation of ERK in pertussis toxin-treated cells overexpressing Galpha(z) or Galpha(12). Transfection of Galpha(13) or Galpha(q) blocked inhibition under the same conditions. Overexpressed interfering and non-interfering Galpha(z) mutants differentially affected mu inhibition of ERK consistent with G(z) transduction. In this and prior studies, Galpha(z) and Galpha(12) immunoreactivity were detected in untransfected COS-7 cells, suggesting that these G proteins may be endogenous mediators of chronic mu inhibitory actions on ERK.

Mutational analysis of the structure and function of opioid receptors

The cloning of the opioid receptors allows the investigation of receptor domains involved in the peptidic and nonpeptidic ligand interaction and activation of the opioid receptors. Receptor chimera studies and mutational analysis of the primary sequences of the opioid receptors have provided insights into the structural domains required for the ligand recognition and receptor activation. In the current review, we examine the current reports on the possible involvement of extracellular domains and transmembrane domains in the high-affinity binding of peptidic and nonpeptidic ligands to the opioid receptor. The structural requirement for the receptors' selectivity toward different ligands is discussed. The receptor domains involved in the activation and subsequent cellular regulation of the receptors' activities as determined by mutational analysis will also be discussed. Finally, the validity of the conclusions based on single amino acid mutations is examined.

Cloning of a novel G-protein-coupled receptor from the sea anemone nervous system

We describe the cloning and analysis of genomic and cDNA copies of a gene from sea anemones that encodes a new member of the G-protein-coupled receptor family. The receptor shows similarity to previously described receptors for biogenic amines such as adrenaline, serotonin, and octopamine, as well as a variety of small molecule agonists and peptides, although we have been unable to determine which ligand is the natural agonist. Antibodies generated against the recombinant receptor protein identify a single protein with a molecular weight of 66 kDa in membrane preparations. Immunofluorescence studies using the same antibody have enabled localization of the receptor in the nervous system. Western blotting and RT-PCR analysis reveal that a homologue of this receptor is expressed in jellyfish and soft coral. We suggest that the receptor plays a role in neurotransmission in the sea anemone and other members of the phylum Cnidaria.

Preactivation permits subsequent stimulation of phospholipase C by G(i)-coupled receptors

In the complex signal transduction networks involving G protein-coupled receptors there are numerous examples where G(i)-linked receptors augment G(q)-dependent signals. The mechanistic basis of such occurrences is thought to entail signal convergence at phospholipase Cbeta (PLCbeta) via the G protein betagamma-dimers. Herein, we explored the possibility that augmentation by betagamma-dimers requires preactivation of PLCbeta. COS-7 cells were transiently cotransfected with cDNAs encoding various combinations of receptors and G protein subunits. The G(i)-coupled delta- and kappa-opioid receptors could not stimulate PLCbeta unless they were coexpressed with Galpha(16). The opioid-induced response was dose-dependent and partially inhibited by pertussis toxin or coexpression with transducin, indicating the involvement of betagamma-subunits released from the G(i) proteins. When PLCbeta was preactivated by constitutively active mutants of Galpha(16), Galpha(q), or Galpha(14), opioids enhanced the activity by 80 to 300% and such responses were mostly pertussis toxin-sensitive. The opioid-induced enhancement was dose-dependent and could not be blocked by staurosporin, a protein kinase C inhibitor. Other G(i)-coupled receptors that were ineffective on their own also acquired the ability to stimulate PLCbeta in the presence of a constitutively active mutant of Galpha(q). Coactivation of endogenous or exogenous G(q)-coupled receptors with the delta-opioid receptor produced strong stimulations of PLCbeta and such responses could be partially blocked by pertussis toxin. These results show that enhancement of G(q)-dependent signals by G(i)-coupled receptors requires activated PLCbeta and is mediated via the betagamma-dimer.

Activation of B-Raf and regulation of the mitogen-activated protein kinase pathway by the G(o) alpha chain

Many receptors coupled to the pertussis toxin-sensitive G(i/o) proteins stimulate the mitogen-activated protein kinase (MAPK) pathway. The role of the alpha chains of these G proteins in MAPK activation is poorly understood. We investigated the ability of Galpha(o) to regulate MAPK activity by transient expression of the activated mutant Galpha(o)-Q205L in Chinese hamster ovary cells. Galpha(o)-Q205L was not sufficient to activate MAPK but greatly enhanced the response to the epidermal growth factor (EGF) receptor. This effect was not associated with changes in the state of tyrosine phosphorylation of the EGF receptor. Galpha(o)-Q205L also potentiated MAPK stimulation by activated Ras. In Chinese hamster ovary cells, EGF receptors activate B-Raf but not Raf-1 or A-Raf. We found that expression of activated Galpha(o) stimulated B-Raf activity independently of the activation of the EGF receptor or Ras. Inactivation of protein kinase C and inhibition of phosphatidylinositol-3 kinase abolished both B-Raf activation and EGF receptor-dependent MAPK stimulation by Galpha(o). Moreover, Galpha(o)-Q205L failed to affect MAPK activation by fibroblast growth factor receptors, which stimulate Raf-1 and A-Raf but not B-Raf activity. These results suggest that Galpha(o) can regulate the MAPK pathway by activating B-Raf through a mechanism that requires a concomitant signal from tyrosine kinase receptors or Ras to efficiently stimulate MAPK activity. Further experiments showed that receptor-mediated activation of Galpha(o) caused a B-Raf response similar to that observed after expression of the mutant subunit. The finding that Galpha(o) induces Ras-independent and protein kinase C- and phosphatidylinositol-3 kinase-dependent activation of B-Raf and conditionally stimulates MAPK activity provides direct evidence for intracellular signals connecting this G protein subunit to the MAPK pathway.

Regulation of adenylyl cyclase, ERK1/2, and CREB by Gz following acute and chronic activation of the delta-opioid receptor

Opioid tolerance and physical dependence in mammals can be rapidly induced by chronic exposure to opioid agonists. Recently, opioid receptors have been shown to interact with the pertussis toxin (PTX)-insensitive Gz (a member of the Gi subfamily), which inhibits adenylyl cyclase and stimulates mitogen-activated protein kinases (MAPKs). Here, we established stable human embryonic kidney 293 cell lines expressing delta-opioid receptors with or without Gz to examine the role of Gz in opioid receptor-regulated signaling systems. Each cell line was acutely or chronically treated with [D-Pen2,D-Pen5]enkephalin (DPDPE), a delta-selective agonist, in the absence or presence of PTX. Subsequently, the activities of adenylyl cyclase, cyclic AMP (cAMP)-dependent response element-binding proteins (CREBs), and MAPKs were measured by determining cAMP accumulation and phosphorylation of CREBs and the extracellular signal-regulated protein kinases (ERKs) 1 and 2. In cells coexpressing Gz, DPDPE inhibited forskolin-stimulated cAMP accumulation in a PTX-insensitive manner, but Gz could not replace Gi to mediate adenylyl cyclase supersensitization upon chronic opioid treatment. DPDPE-induced adenylyl cyclase supersensitization was not associated with an increase in the phosphorylation of CREBs. Both Gi and Gz mediated DPDPE-induced activation of ERK1/2, but these responses were abolished by chronic opioid treatment. Collectively, our results show that although Gz mediated opioid-induced inhibition of adenylyl cyclase and activation of ERK1/2, Gz alone was insufficient to mediate opioid-induced adenylyl cyclase supersensitization.