ARF6 and GASP-1 are post-endocytic sorting proteins selectively involved in the intracellular trafficking of dopamine D₂ receptors mediated by GRK and PKC in transfected cells

BACKGROUND AND PURPOSE

GPCRs undergo both homologous and heterologous regulatory processes in which receptor phosphorylation plays a critical role. The protein kinases responsible for each pathway are well established; however, other molecular details that characterize each pathway remain unclear. In this study, the molecular mechanisms that determine the differences in the functional roles and intracellular trafficking between homologous and PKC-mediated heterologous internalization pathways for the dopamine D₂ receptor were investigated.

EXPERIMENTAL APPROACH

All of the S/T residues located within the intracellular loops of D₂ receptor were mutated, and the residues responsible for GRK- and PKC-mediated internalization were determined in HEK-293 cells and SH-SY5Y cells. The functional role of receptor internalization and the cellular components that determine the post-endocytic fate of internalized D₂ receptors were investigated in the transfected cells.

KEY RESULTS

T134, T225/S228/S229 and S325 were involved in PKC-mediated D₂ receptor desensitization. S229 and adjacent S/T residues mediated the PKC-dependent internalization of D₂ receptors, which induced down-regulation and desensitization. S/T residues within the second intracellular loop and T225 were the major residues involved in GRK-mediated internalization of D₂ receptors, which induced receptor resensitization. ARF6 mediated the recycling of D₂ receptors internalized in response to agonist stimulation. In contrast, GASP-1 mediated the down-regulation of D₂ receptors internalized in a PKC-dependent manner.

CONCLUSIONS AND IMPLICATIONS

GRK- and PKC-mediated internalizations of D₂ receptors occur through different intracellular trafficking pathways and mediate distinct functional roles. Distinct S/T residues within D₂ receptors and different sorting proteins are involved in the dissimilar regulation of D₂ receptors by GRK2 and PKC.

Evaluation of experimental pain tests to predict labour pain and epidural analgesic consumption

BACKGROUND

The aim of this study was to determine whether experimental pain tests (EPTs) using heat, pressure, and i.v. cannulation before induction of labour reliably predict epidural analgesic use and pain intensity during labour.

METHODS

Fifty healthy women with singleton, term pregnancies admitted for scheduled induction of labour comprised the study population for this prospective case-controlled study. Heat and pressure threshold, tolerance, and suprathreshold VAS pain ratings were determined using a Medoc thermal sensory analyser and Somedic pressure algometer, respectively, after admission before induction of labour. Verbal pain scores (VPS 0-10) were determined during peripheral 18 G i.v. placement. Response outcomes included time to epidural request, pain at epidural, labour pain [area under the curve (AUC) and worse score], and epidural local anaesthetic use. Bivariate analysis followed by forward-backward multiple regression modelling was performed to determine relationships between EPTs and labour pain response measures.

RESULTS

Heat tolerance was significantly correlated with worst labour pain (r=0.33, P=0.025) and pain with i.v. cannulation was correlated with time to epidural request (r=0.33, P=0.025). Multiple linear regression analysis found that labour pain AUC could be predicted with suprathreshold heat VAS, heat tolerance, and pressure tolerance (R(2)=0.26; P=0.007). There were strong correlations among the various pre-labour QSTs.

CONCLUSIONS

Pre-labour EPTs were not very reliable at predicting the labour pain experience. Consistent with postoperative studies, suprathreshold and tolerance tests appear more useful than the threshold for predicting labour pain responses. Pain rating during i.v. cannulation (an easy, rapid, point-of-care test) showed some utility as an EPT.

Opiate-induced changes in brain adenosine levels and narcotic drug responses

We have very little information about the metabolomic changes that mediate neurobehavioral responses, including addiction. It was possible that opioid-induced metabolomic changes in brain could mediate some of the pharmacodynamic effects of opioids. To investigate this, opiate-induced brain metabolomic responses were profiled using a semi-targeted method in C57BL/6 and 129Sv1 mice, which exhibit extreme differences in their tendency to become opiate dependent. Escalating morphine doses (10-40 mg/kg) administered over a 4-day period selectively induced a twofold decrease (p<0.00005) in adenosine abundance in the brainstem of C57BL/6 mice, which exhibited symptoms of narcotic drug dependence; but did not decrease adenosine abundance in 129Sv1 mice, which do not exhibit symptoms of dependence. Based on this finding, the effect of adenosine on dependence was investigated in genetically engineered mice with alterations in adenosine tone in the brain and in pharmacologic experiments. Morphine withdrawal behaviors were significantly diminished (p<0.0004) in genetically engineered mice with reduced adenosine tone in the brainstem, and by treatment with an adenosine receptor(1) (A(1)) agonist (2-chloro-N6-cyclopentyladenosine, 0.5mg/kg) or an A(2a) receptor (A(2a)) antagonist (SCH 58261, 1mg/kg). These results indicate that adenosine homeostasis plays a crucial role in narcotic drug responses. Opiate-induced changes in brain adenosine levels may explain many important neurobehavioral features associated with opiate addiction and withdrawal.

The N-terminal region of the dopamine D2 receptor, a rhodopsin-like GPCR, regulates correct integration into the plasma membrane and endocytic routes

BACKGROUND AND PURPOSE

Functional roles of the N-terminal region of rhodopsin-like GPCR family remain unclear. Using dopamine D(2) and D(3) receptors as a model system, we probed the roles of the N-terminal region in the signalling, intracellular trafficking of receptor proteins, and explored the critical factors that determine the functionality of the N-terminal region.

EXPERIMENTAL APPROACH

The N-terminal region of the D(2) receptor was gradually shortened or switched with that of the D(3) receptor or a non-specific sequence (FLAG), or potential N-terminal glycosylation sites were mutated. Effects of these manipulations on surface expression, internalization, post-endocytic behaviours and signalling were determined.

KEY RESULTS

Shortening the N-terminal region of the D(2) receptor enhanced receptor internalization and impaired surface expression and signalling; ligand binding, desensitization and down-regulation were not affected but their association with a particular microdomain, caveolae, was disrupted. Replacement of critical residues within the N-terminal region with the FLAG epitope failed to restore surface expression but partially restored the altered internalization and signalling. When the N-terminal regions were switched between D(2) and D(3) receptors, cell surface expression pattern of each receptor was switched. Mutations of potential N-terminal glycosylation sites inhibited surface expression but enhanced internalization of D(2) receptors.

CONCLUSIONS AND IMPLICATIONS

Shortening of N-terminus or mutation of glycosylation sites located within the N-terminus enhanced receptor internalization but impaired the surface expression of D(2) receptors. The N-terminal region of the D(2) receptor, in a sequence-specific manner, controls the receptor's conformation and integration into the plasma membrane, which determine its subcellular localization, intracellular trafficking and signalling properties.

Role of cAMP-PKA/CREB pathway in regulation of AQP 5 production in rat nasal epithelium

OBJECTIVES

Aquaporin 5 (AQP5) is a water-specific channel protein. In this study, we investigated the possible role of the cyclic adenosine monophosphate-protein kinase A/cyclic adenosine monophosphate response element binding protein (cAMP-PKA/CREB) pathway in the regulation of AQP5 in nasal epithelial cells.

METHODS

Rat nasal epithelial cells were cultured and treated with the PKA inhibitor H89 or cAMP inducing medicine forskolin for 12 or 24 hours in vitro. AQP5 and phosphorylated CREB (p-CREB) at serine133 (Ser133) were detected by immunocytochemistry, Western blotting or real-time PCR. Experiments were repeated 10 times.

RESULTS

After treatment with H89 for 12 or 24 hours, the number of cells positive for AQP5 and p-CREB (Ser133) were decreased, p-CREB (Ser133) and AQP5 protein decreased, and AQP5 mRNA decreased. After treatment with forskolin for 12 or 24 hours, the number of p-CREB (Ser133) and AQP5 positive cells increased, p-CREB (Ser133) and AQP5 protein increased, and AQP5 mRNA was increased.

CONCLUSION

Both H89 (PKA inhibitor) and forskolin (cAMP inducing medicine) regulate AQP5 production through the cAMP-PKA/CREB pathway, which could influence the secretory function of the submucosal glands in nasal epithelium.

Heading date gene, dth3 controlled late flowering in O. Glaberrima Steud. by down-regulating Ehd1

Heading date in rice is an important agronomic trait controlled by several genes. In this study, flowering time of variety Dianjingyou 1 (DJY1) was earlier than a near-isogenic line (named NIL) carried chromosome segment from African rice on chromosome 3S, when grown in both long-day (LD) and short-day (SD) conditions. By analyzing a large F2 population from NIL × DJY1, the locus DTH3 (QTL for days to heading on chromosome 3) controlling early heading date in DJY1 was fine mapped to a 64-kb segment which contained only one annotated gene, a MIKC-type MADS-box protein. We detected a 6-bp deletion and a single base substitution in the C-domain by sequencing DTH3 in DJY1 compared with dth3 in NIL, and overexpression of DTH3 caused early flowering in callus. Quantitative real-time PCR revealed that the transcript level of dth3 in NIL was lower than that DTH3 in DJY1 in both LD and SD conditions. The Early heading date 1 (Ehd1) which promotes the RFT1, was up-regulated by DTH3 in both LD and SD conditions. Based on Indel and dCAPs marker analysis, the dth3 allele was only present in African rice accessions. A phylogenetic analysis based on microsatellite genotyping suggested that African rice had a close genetic relationship to O. rufipogon and O. latifolia, and was similar to japonica cultivars. DTH3 affected flowering time and had no significant effect on the main agronomic traits.

Involvement of the NF-κB pathway in multidrug resistance induced by HBx in a hepatoma cell line

It is widely believed that hepatocellular cancer (HCC), especially HBV associated HCC, is highly resistant to chemotherapy. To investigate the molecular influence of HBx protein on multidrug resistance (MDR) in HCC and the potential role of the NF-κB pathway in this process. We established HBx-expressing cells by liposome-mediated transfection of the HBx into the HepG2 cell line. We found that HBx expression in HCC cells induces drug resistance against multiple drugs, a significantly lower apoptosis ratio in HepG2-HBx and HepG2.2.15 cells, compared with HepG2 and HepG2-3.1 cells (P < 0.05) after treating with 5-FU or adriamycin. And compared with the control group, the HBx-transfected cells showed a higher expression of MDR-associated and anti-apoptotic genes. Furthermore, we found that the NF-κB activity was remarkably high in the HBx-expressing cells as measured by p65 nuclear localization. In addition, the upregulated anti-apoptotic genes, Gadd45b and Survivin, in HBx-expressing HCC cells were downregulated by IMD-0354 treatment, which is the NF-κB pathway inhibitor. Taken together, these results suggest that HBx protein might be one of the causes for the occurrence of MDR in HCC, and the NF-κB pathway might be involved in this change.

Stereotactic radiosurgery for early-stage breast cancer: A new paradigm

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Background: Stereotactic radiosurgery (SRS) has not been widely used for breast cancer partly due to: 1) the lack of a suitable immobilization device; and 2) the lack of a delivery system that can concentrate a high radiation dose noninvasively. We have developed a SRS system that effectively addresses these obstacles and demonstrated the dosimetric feasibility of simultaneously ablating the intact tumor and sterilizing the tumor bed.

Methods: A breast immobilization device consists of a solid outer cup with embedded stereotactic frame and a porous inner cup; the two cups join at the chest wall side by a soft goggle-like lip for comfort. A negative pressure is applied to the space between the two cups to immobilize the breast tissues. 15 patients with surgical clips in their breast underwent a geometric reproducibility trial, in which the patients received two CT scans spaced 10-60 minutes while wearing the cup. A SRS delivery system uses 36 Co-60 sources that rotate around a focal point to produce 36 non-coplanar arcs. The breast cup is locked on the treatment couch with the patient in prone position. The couch moves dynamically during treatment, allowing the focal spots to “paint” the desired 3D dose distribution.

Results: The reproducibility of the 42 available clips was 1.83 mm ± 1.08 mm (2 std) and patients reported good comfort. 8 treatment plans simultaneously delivering an ablative dose of 18Gy to an intact tumor plus a 3mm margin (CTV1) and 10Gy to the tumor bed (CTV2 = CTV1+1cm) have been developed and verified with measurements. The dose-volume histograms showed very uniform dose coverage with 98% of CTV1 receiving 18Gy and 100% of tumor bed receiving 10Gy. On average, only 21% of the normal breast receives greater than 5Gy, safe to deliver 3 fractions of such doses.

Conclusions: A breast-specific SRS system has been developed. Dosimetric studies illustrated the feasibility of managing early-stage breast cancer with SRS. Clinical studies that will identify patients in whom current forms of surgery and postoperative radiation may be eliminated are planned, allowing completion of local therapies noninvasively within a few days rather than months.

Naloxone in the management of hepatic encephalopathy

BACKGROUND/AIM

This study aimed to assess the effectiveness and safety of naloxone in the management of hepatic encephalopathy (HE).

METHODS

Cochrane collaboration methodology was used in a meta-analysis of randomized controlled trials of naloxone therapy for HE.

RESULTS

Seventeen randomized trials were identified with 15 studies involving 1054 patients meeting criteria for inclusion. Naloxone use was associated with a significant improvement in HE [relative risk (RR) 1.46; 95% confidence interval (CI) 1.27-1.67; P = 0.0005]. This comparison showed statistical heterogeneity (P < 0.10, and χ2 = 44.93). Subgroup analysis indicated naloxone administered parenterally by intermittent or continuous infusions to be effective (RR 1.34; 95% CI 1.17-1.53; P < 0.0001). A significant in trials by infusion route (RR 1.42; 95% CI 1.19-1.69; P < 0.0001) interaction was observed.

CONCLUSIONS

Naloxone may improve HE. However, published data are limited.

Association of single-nucleotide polymorphisms in HLA class II/III region with knee osteoarthritis

OBJECTIVE

A genome-wide association study and a replication using Japanese, Spanish and Greek Caucasian populations have recently indicated two single-nucleotide polymorphisms (SNPs) (rs7775228 and rs10947262) associated with knee Osteoarthritis (OA) susceptibility. We have further evaluated the association in knee OA subjects from Han Chinese and Australian Caucasian origin.

METHODS

Two independent case-control association studies were performed using Han Chinese and Australian Caucasian populations. The two SNPs were genotyped in patients who had primary symptomatic knee OA with radiographic confirmation and/or received total knee replacement surgery as well as in matched controls. They were subjected to statistic analyses.

RESULTS

A total of 991 OA patients and 1536 controls were genotyped. No significant difference was detected in genotype or allele frequencies of the two SNPs between knee OA and control groups in the two populations (all P>0.05). The association was also negative even after stratification by sex, body mass index (BMI) and Kellgren/Lawrence scores. The significant heterogeneity was detected between Chinese and Japanese (both P<0.05). In the Caucasian samples, no significant heterogeneity was detected (both P>0.05). The result of meta-analysis showed significant association between knee OA and rs10947262 in total subjects [summary OR=1.26, 95%confidence intervals (CI)=1.07-1.27, P=3 × 10(-8)] and in Caucasian samples (summary OR=1.28, 95%CI=1.04-1.57, P=0.02).

CONCLUSION

We demonstrated no association between the two SNPs in human leukocyte antigen (HLA) class II/III region and knee OA in Han Chinese population. A significant association was detected between SNP rs10947262 and knee OA in Caucasian subjects. Further replication studies are required to identify the impact of controversial association.

Effect of oxygenation of transperitoneal ventilation on the death time after asphyxiation in rabbits

BACKGROUND

To observe the effects of transperitoneal ventilation on death time in asphyxiated rabbits.

METHODS

Twenty-four adult rabbits were randomly divided in three groups (N=8, each): control group (no transperitoneal ventilation), air group (transperitoneal ventilation with air) and oxygen group (transperitoneal ventilation with oxygen). All animals were anesthetized with pentobarbital (3%, 30 mg/kg) given via intramuscular injection. Autonomous breathing was maintained. Each rabbit's peritoneal cavity was punctured with two catheters, one of which was placed in the left lower abdomen and served as the inlet for gas; the other was placed in the right upper abdomen and served as the outlet for gas. Asphyxia was induced by clamping the rabbit's trachea; transperitoneal ventilation was then administered in the air group and the oxygen group. Rabbits' death times were recorded and their heart rate, blood pressure, PaO2, and PaCO2 were monitored and analyzed before asphyxia and every minute after asphyxia.

RESULTS

All animals died successively after asphyxia. The death time in the oxygen group was significantly longer than in the control group and the air group, with no significant difference between the control group and the air group. PaO2 of all three groups declined significantly and the levels of PaO2 within 1-4 minutes after asphyxia in the oxygen group were higher than in the other two groups. PaCO2 increased significantly in all groups with no significant difference among three groups within 1-3 minutes after asphyxia. The increase of PaCO2 at the fourth minute in the oxygen group was reduced in comparison to that observed in other groups.

CONCLUSION

These results suggest that transperitoneal ventilation can markedly prolong the death time of asphyxiated rabbits.

Using support vector regression coupled with the genetic algorithm for predicting acute toxicity to the fathead minnow

The potential toxicity of chemicals may present adverse effects to the environment and human health. The quantitative structure-activity relationship (QSAR) provides a useful method for hazard assessment. In this study, we constructed a QSAR model based on a highly heterogeneous data set of 571 compounds from the US Environmental Protection Agency, for predicting acute toxicity to the fathead minnow (Pimephales promelas). An approach coupling support vector regression (SVR) with the genetic algorithm (GA) was developed to build the model. The generated QSAR model showed excellent data fitting and prediction abilities: the squared correlation coefficients (r(2)) for the training set and the test set were 0.826 and 0.802, respectively. Only eight critical descriptors, most of which are closely related to the toxicity mechanism, were chosen by GA-SVR, making the derived model readily interpretable. In summary, the successful case reported here highlights that our GA-SVR approach can be used as a general machine learning method for toxicity prediction.