The truncated ghrelin receptor polypeptide (GHS-R1b) is localized in the endoplasmic reticulum where it forms heterodimers with ghrelin receptors (GHS-R1a) to attenuate their cell surface expression.

The ghrelin receptor (GHS-R1a) is remarkable amongst G-protein-coupled receptors for its high degree of constitutive activity, and this agonist-independent activity may be important for its physiological function in the control of food intake and body weight. Ghrelin receptors form heterodimers with the truncated ghrelin receptor polypeptide (GHS-R1b), which has a dominant-negative effect on ghrelin receptor function. Here we show that GHS-R1b has an intracellular localization distinct from ghrelin receptors, being primarily localized in the endoplasmic reticulum. Immunocytochemical studies suggest that GHS-R1b decreases the plasma membrane expression of ghrelin receptors, but the overall distribution profile of ghrelin receptors in isolated subcellular fractions is unaffected by GHS-R1b. Using bioluminescence resonance energy transfer methods, we have shown that while ghrelin receptor homodimers are evenly distributed in all subcellular fractions, GHS-R1a/GHS-R1b heterodimers are concentrated within the endoplasmic reticulum and these results suggest that GHS-R1b traps ghrelin receptors within the endoplasmic reticulum by the process of oligomerization. Furthermore, ghrelin receptors constitutively activated extracellular signal-regulated kinases 1/2 in the endoplasmic reticulum, but this small response was not affected by GHS-R1b and its physiological relevance is uncertain. Taken together, these results suggest that ghrelin receptors can be retained in the endoplasmic reticulum by heterodimerization with GHS-R1b, and constitutive activation of phospholipase C is attenuated due to decreased cell surface expression of ghrelin receptors. However, sufficient ghrelin receptor homodimers can still be expressed on the cell surface for maximal responses to agonist stimulation.

Penicilliosis in children without HIV infection--are they immunodeficient?

BACKGROUND: Penicillium marneffei infection is indigenous to Southeast Asia. Majority of penicilliosis occurs in patients with AIDS, and less commonly with secondary immunodeficiencies. Penicilliosis is rare in otherwise healthy persons, but information on their immunological status is often lacking. METHODS: From 1996 to 2009, we diagnosed penicilliosis in 5 children. Their clinical features, immunological findings, and genetic studies were analyzed. A systematic review of the English and Chinese literature was performed. Case reports/series on patients <18 years with penicilliosis were included, and patients stated to be human immunodeficiency virus (HIV)-positive excluded. RESULTS: All of our 5 patients were HIV negative. Presentations included fungemia (n = 2), multifocal lymphadenopathy (n = 2), and necrotizing pneumonia (n = 1). Four patients had recurrent mucocutaneous candidiasis. Hyperimmunoglobin E syndrome was diagnosed in 1 patient, while another had functional defect in interleukin-12/interferon-γ axis. Three patients were lymphopenic with low natural killer cell counts, but a specific immune defect was not identified. Systematic review of 509 reports on human penicilliosis identified 32 patients aged 3 months to 16 years with no known HIV infection. Twenty-four patients (75%) had disseminated disease, and 55% died of penicilliosis. Eight patients had primary immunodeficiencies or blood disorders, while 4 others had abnormal immune functions. Immune evaluations of the remaining patients were unstated. CONCLUSION: Penicilliosis is a severe disease causing high mortality in children. As an AIDS-defining illness, penicilliosis should be regarded as an indicator for underlying immunodeficiency in HIV-negative individuals. Immunological investigations should be performed, especially in those with recurrent infections. Multicentered collaborative studies are needed to collect information on long-term prognosis and define immune defects underlying penicilliosis.

Molecular diagnosis of severe combined immunodeficiency--identification of IL2RG, JAK3, IL7R, DCLRE1C, RAG1, and RAG2 mutations in a cohort of Chinese and Southeast Asian children.

Severe combined immunodeficiencies (SCID) are a group of rare inherited disorders with profound defects in T cell and B cell immunity. From 2005 to 2010, our unit performed testing for IL2RG, JAK3, IL7R, RAG1, RAG2, DCLRE1C, LIG4, AK2, and ZAP70 mutations in 42 Chinese and Southeast Asian infants with SCID adopting a candidate gene approach, based on patient's gender, immune phenotype, and inheritance pattern. Mutations were identified in 26 patients, including IL2RG (n = 19), IL7R (n = 2), JAK3 (n = 2), RAG1 (n = 1), RAG2 (n = 1), and DCLRE1C (n = 1). Among 12 patients who underwent hematopoietic stem cell transplantation, eight patients survived. Complications and morbidities during transplant period were significant, especially disseminated bacillus Calmette-Guérin disease which was often difficult to control. This is the first cohort study on SCID in the Chinese and Southeast Asian population, based on a multi-centered collaborative research network. The foremost issue is service provision for early detection, diagnosis, management, and definitive treatment for patients with SCID. National management guidelines for SCID should be established, and research into an efficient platform for genetic diagnosis is needed.

Olvanil, a non-pungent vanilloid enhances the gastrointestinal toxicity of cisplatin in the ferret.

Pungent transient receptor potential vanilloid (TRPV1) channel activators have been shown to have broad inhibitory anti-emetic activity against centrally- and peripherally acting challenges but only at doses that have adverse effects on the cardiovascular system and on temperature homeostasis. In the present studies, we investigated the anti-emetic potential of the non-pungent TRPV1 activator, olvanil (0.05-5 mg/kg, s.c., 3 times per day, for 3 days) to antagonise the acute and delayed emesis induced by cisplatin (5 mg/kg, i.p.) in ferrets that had been implanted with radiotelemetry devices to enable an analysis of heart rate and temperature. Cisplatin induced an acute (day 1: 48.0+/-18.3 retches+vomits) and delayed (day 2: 111.7+/-35.5; day 3: 147.5+/-20.2 retches+vomits) emetic response that was associated with reduced food (-98.7% at day 3, P<0.001) and water consumption (-70.2% at day 3, P<0.001) and progressive weight loss (-12.0% at day 3, P<0.001). Olvanil did not prevent either emesis or the weight loss and negative effects on food and water consumption (P>0.05); the effect on food consumption appeared potentiated by a further 21.2% at 0.05 mg/kg (P<0.05) and 19.9% at 0.5 mg/kg (P<0.05). Cisplatin did not alter body temperature (basal: 37.7+/-0.1 degrees C) or heart rate (basal: 233.7+/-5.5 beats per min (BPM); P>0.05), but hypothermia (-1.6 degrees C) and increases in locomotor activity (50-90%) were recorded in animals concomitantly treated with olvanil (P<0.05). These data indicate that non-pungent activators as exemplified by olvanil are unlikely to be useful clinically for the control of the gastrointestinal side effects induced by cisplatin.

Olvanil: a non-pungent TRPV1 activator has anti-emetic properties in the ferret.

Anti-emetic drugs such as the tachykinin NK(1) receptor antagonists are useful to control emesis induced by diverse challenges. Evidence suggests pungent capsaicin-like TRPV1 activators also have broad inhibitory anti-emetic activity. However, pungent compounds are associated with undesirable effects including adverse actions on the cardiovascular system and on temperature homeostasis. In the present investigations using the ferret, we examine if the non-pungent vanilloid, olvanil, has useful anti-emetic properties without adversely affecting behaviour, blood pressure or temperature control. Olvanil (0.05-5 mg/kg, s.c.) was compared to the pungent vanilloid, resiniferatoxin (RTX; 0.1 mg/kg, s.c.), and to the anandamide reuptake inhibitor, AM404 (10 mg/kg, s.c.), for a potential to inhibit emesis induced by apomorphine (0.25 mg/kg, s.c.), copper sulphate (50 mg/kg, intragastric), and cisplatin (10 mg/kg, i.p.). Changes in blood pressure and temperature were also recorded using radiotelemetry implants. In peripheral administration studies, RTX caused transient hypertension, hypothermia and reduced food and water intake, but also significantly inhibited emesis induced by apomorphine, copper sulphate, or cisplatin. Olvanil did not have a similar adverse profile, and antagonised apomorphine- and cisplatin-induced emesis but not that induced by copper sulphate. AM404 reduced only emesis induced by cisplatin without affecting other parameters measured. Following intracerebral administration only olvanil antagonised cisplatin-induced emesis, but this was associated with transient hypothermia. In conclusion, olvanil demonstrated clear anti-emetic activity in the absence of overt cardiovascular, homeostatic, or behavioural effects associated with the pungent vanilloid, RTX. Our studies indicate that non-pungent vanilloids may have a useful spectrum of anti-emetic properties via central and/or peripheral mechanisms after peripheral administration.

The truncated ghrelin receptor polypeptide (GHS-R1b) acts as a dominant-negative mutant of the ghrelin receptor.

The dimerization properties of the ghrelin receptor (GRLN-R) and its non-signalling, naturally occurring, truncated splice variant (GHS-R1b) have been investigated in human embryonic kidney 293 cells heterologously expressing these proteins. Using the techniques of bioluminescence resonance energy transfer and co-immunoprecipitation, we detected the formation of GRLN-R homodimers and GRLN-R/GHS-R1b heterodimers, but ghrelin-induced conformational changes were only detected in the GRLN-R homodimers. When the expression of GHS-R1b exceeded that of GRLN-R, there was a decrease in the cell surface expression of GRLN-R with a consequent decrease in constitutive activation of phosphatidylinositol-specific phospholipase C (PI-PLC). Furthermore, there was no change in ghrelin affinity, and the efficacy of cell signalling as measured by stimulation of PI-PLC and extracellular signal-regulated kinase 1/2 was unchanged. Cellular localization studies suggest that GRLN-R is normally distributed between the plasma membrane and cytosolic fractions, but in the presence of GHS-R1b, GRLN-R is localized to the nucleus. Therefore, we propose that the decrease in GRLN-R constitutive signalling was due to translocation of GRLN-R to the nucleus due to the formation of GRLN-R/GHS-R1b heterodimers. Therefore, GHS-R1b appears to act as a dominant-negative mutant of the full-length GRLN-R.

Over-expression of the truncated ghrelin receptor polypeptide attenuates the constitutive activation of phosphatidylinositol-specific phospholipase C by ghrelin receptors but has no effect on ghrelin-stimulated extracellular signal-regulated kinase 1/2 activity.

In addition to regulating growth hormone release from the pituitary, ghrelin receptors also influence cell proliferation and apoptosis. By studying mitogen-activated protein kinase activity in human embryonic kidney 293 cells over-expressing ghrelin receptors, we aimed to identify the specific cell signalling pathways used by ghrelin receptors, and to determine if the truncated ghrelin receptor polypeptide had any influence on the functional activity of ghrelin receptors. We found that ghrelin activated extracellular signal-regulated kinases 1/2 with an EC50 value of 10 nM, and that this response was inhibited by the ghrelin receptor antagonists D-Lys3-GHRP-6 and [D-Arg1,D-Phe5,D-Trp(7,9),Leu11]-substance P. Ghrelin had little or no effect on the activity of c-Jun N-terminal kinase, p38 kinase or Akt. Ghrelin appeared to activate extracellular signal-regulated kinases 1/2 through a calcium-independent novel protein kinase C isoform which may utilize diacylglycerol derived from hydrolysis of phosphatidylcholine rather than from phosphatidylinositol. Ghrelin-stimulated extracellular signal-regulated kinases 1/2 activity was independent of transactivation of epidermal growth factor receptors, and even when ghrelin receptor internalization was blocked by concanavalin A or a beta-arrestin mutant, there was no decrease in phosphorylated extracellular signal-regulated kinases 1/2, suggesting this is a G protein-dependent process. The truncated ghrelin receptor polypeptide had no effect on ghrelin receptor signalling to extracellular signal-regulated kinases 1/2, but decreased the constitutive activation of phosphatidylinositol-specific phospholipase C by ghrelin receptors. In conclusion, our results suggest that any up-regulation of the truncated ghrelin receptor polypeptide might preferentially attenuate functional activity dependent on the constitutive activation of ghrelin receptors, while leaving ghrelin-dependent signalling unaffected.

Prostacyclin receptor-mediated activation of extracellular signal-regulated kinases 1 and 2.

The prostacyclin mimetic cicaprost increased phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) in Chinese hamster ovary cells transiently expressing human (hIP-CHO) or mouse prostacyclin (mIP-CHO) receptors, but not in human neuroblastoma SK-N-SH cells or rat/mouse neuroblastoma-glioma NG108-15 cells which endogenously express IP receptors. Cicaprost stimulated ERK1/2 activity in hIP-CHO and mIP-CHO cells with EC50 values of 60 and 83 nM, respectively, and this response was significantly inhibited by protein kinase C inhibitors and agents which elevate cyclic AMP. A poor correlation was discovered between the level of ERK1/2 activity and the ability of agents to increase or decrease cyclic AMP production. The potent inhibitory effect of 3-isobutyl-1-methyl xanthine on cicaprost-stimulated phospho-ERK1/2 may be due to inhibition of phosphoinositide 3-kinase. Therefore, IP receptor-mediated activation of ERK1/2 in CHO cells occurs through a Gq/11/protein kinase C-dependent and a phosphoinoside 3-kinase-dependent process which is insensitive to IP receptor-generated cyclic AMP.