The Gβ3 splice variant associated with the C825T gene polymorphism is an unstable and functionally inactive protein

TNF-α impairs EP4 signaling through the association of TRAF2-GRK2 in primary fibroblast-like synoviocytes

Our previous study showed that chronic treatment with tumor necrosis factor-α (TNF-α) decreased cAMP concentration in fibroblast-like synoviocytes (FLSs) of collagen-induced arthritis (CIA) rats. In this study we investigated how TNF-α impairs cAMP homeostasis, particularly clarifying the potential downstream molecules of TNF-α and prostaglandin receptor 4 (EP4) signaling that would interact with each other. Using a cAMP FRET biosensor PM-ICUE3, we demonstrated that TNF-α (20 ng/mL) blocked ONO-4819-triggered EP4 signaling, but not Butaprost-triggered EP2 signaling in normal rat FLSs. We showed that TNF-α (0.02-20 ng/mL) dose-dependently reduced EP4 membrane distribution in normal rat FLS. TNF-α significantly increased TNF receptor 2 (TNFR2) expression and stimulated proliferation in human FLS (hFLS) via ecruiting TNF receptor-associated factor 2 (TRAF2) to cell membrane. More interestingly, we revealed that TRAF2 interacted with G protein-coupled receptor kinase (GRK2) in the cytoplasm of primary hFLS and helped to bring GRK2 to cell membrane in response of TNF-α stimulation, the complex of TRAF2 and GRK2 then separated on the membrane, and translocated GRK2 induced the desensitization and internalization of EP4, leading to reduced production of intracellular cAMP. Silencing of TRAF2 by siRNA substantially diminished TRAF2-GRK2 interaction, blocked the translocation of GRK2, and resulted in upregulated expression of membrane EP4 and intracellular cAMP. In CIA rats, administration of paroxetine to inhibit GRK2 effectively improved the symptoms and clinic parameters with significantly reduced joint synovium inflammation and bone destruction. These results elucidate a novel form of cross-talk between TNFR (a cytokine receptor) and EP4 (a typical G protein-coupled receptor) signaling pathways. The interaction between TRAF2 and GRK2 may become a potential new drug target for the treatment of inflammatory diseases.

Gene polymorphism association studies in cluster headache: A field synopsis and systematic meta-analyses

BACKGROUND

A plethora of studies have attempted to identify genetic determinants of disease susceptibility and treatment response of patients with cluster headache (CH), but results are often conflicting, and no comprehensive overview with a quantitative summary of the evidence in this field is available.

METHODS

A systematic search of relevant publications was performed without any language restrictions on PubMed, Web of Knowledge, Cochrane Library, and OpenGrey, up to December 2020. A standardized data extraction form was used to collect relevant data from each included study. Meta-analyses were conducted for gene polymorphisms investigated in at least two studies and the Bayesian false discovery probability (BFDP) test was applied to the pooled odds ratios (ORs) to assess the credibility of the observed associations.

RESULTS

Among the 27 articles identified by the systematic review, 17 studies evaluating 12 single nucleotide polymorphisms (SNPs) were included in the quantitative data analysis. The pooled results showed no significant association with CH risk of 10 SNPs, including five SNPs of HCRTR2 (rs2653349, rs2653342, rs3122156, rs10498801, and rs3800539), two SNPs of ADH4 (rs1800759 and rs1126671), CLOCK rs1801260, and two SNPs (rs1006417 and ADCYAP1R1 rs12668955) previously identified by a genome-wide association study (GWAS). Conversely, the pooled results revealed the association of the HCRTR2 rs9357855 A allele with a higher risk of CH (A vs. G, OR: 1.33, 95% CI: 1.04-1.72, p = 0.026), and of GNB3 rs5443 with a higher response rate of patients with CH to triptan drugs (CT+TT vs. CC, OR: 1.96, 95% CI: 1.04-3.72, p = 0.038). However, assuming a prior probability of 0.001, the respective BFDP values being higher than 0.8 (BFDP_rs9357855  = 0.998; BFDP_rs5443  = 0.998) revealed lack of noteworthy results.

CONCLUSIONS

Well-designed GWASs and large replication studies are still needed to identify reliable genetic variants of disease susceptibility and treatment response of patients with CH.

Analysis of HCRTR2, GNB3, and ADH4 Gene Polymorphisms in a Southeastern European Caucasian Cluster Headache Population

Studies point to an increased hereditary risk of cluster headache. HCRTR2 gene rs2653349 and ADH4 gene rs1800759 polymorphisms have been associated with cluster headache susceptibility. Also, GNB3 rs5443 polymorphism, associated with increased signal transduction via GPCRs, seems to influence triptan treatment response. DNA from 114 cluster headache patients and 570 non-related controls, representing a general Southeastern European Caucasian (SEC) population, was extracted from buccal swabs and genotyped using real-time PCR. Gene distribution for the rs2653349 was GG = 79.8%, GA = 18.4%, and AA = 1.8% for patients and GG = 79.1%, GA = 19.1%, and AA = 1.8% for controls. The frequency of the mutated A allele was 11.0% for patients and 11.3% for controls. The frequencies for rs5443 were CC = 44.7%, CT = 44.7%, and TT = 10.5% for patients and CC = 43.9%, CT = 42.6%, and TT = 13.5% for controls. The frequency of the mutated T allele was 32.9% for patients and 34.8% for controls. A 2.7-fold more frequent appearance of the mutated T allele was observed in patients with better triptan treatment response, although not statistically significant. For rs1800759, the frequencies were CC = 36.0%, CA = 43.0%, and AA = 21.0% for patients and CC = 34.0%, CA = 50.2%, and AA = 15.8% for controls. The frequency of the mutated A allele was 42.5% and 40.9% for patients and controls, respectively. The mutated T allele of GNB3 rs5443 polymorphism was more prevalent in patients with better triptan treatment response, indicating a possible trend of association between this polymorphism and triptan treatment response in SEC population. According to our observation, no association of HCRTR2 rs2653349 and ADH4 rs1800759 polymorphisms and cluster headache in SEC population could be documented.

Influence of G-protein β-Polypeptide 3 C825T Polymorphism on Antihypertensive Response to Telmisartan and Amlodipine in Chinese Patients

Background:

G-protein β-polypeptide 3 (GNB3) is a β subunit isoform of G-protein that plays important role in signal transduction of membrane G-protein coupled receptors (GPCRs). The GNB3 splice variant C825T (rs5443) is associated with risk for essential hypertension (EH) and efficacy of therapeutic drugs targeting GPCRs. It is unknown whether the polymorphism is associated with blood pressure (BP) response to telmisartan or amlodipine, two widely prescribed antihypertensive drugs.

Methods:

A total of 93 subjects initially diagnosed as EH were recruited and underwent a 4-week treatment with telmisartan (42 patients) or amlodipine (51 patients) monotherapy. Both baseline and after-treatment BP were measured. GNB3 C825T polymorphism was genotyped by polymerase chain reaction-restriction fragment length polymorphism.

Results:

Baseline systolic BP (SBP) and diastolic BP (DBP) were comparable among C825T genotypes in both telmisartan and amlodipine treatment groups. Patients with the CT or TT genotypes showed significantly lower body mass index (BMI) as compared with CC homozygotes in both groups (P < 0.05, respectively). GNB3 825TT homozygotes showed significantly higher after-treatment DBP and mean arterial pressure (MAP) than those carrying at least one 825C allele (P < 0.01) in the telmisartan treatment group. No difference in after-treatment SBP, DBP, and MAP levels among C825T genotypes was observed in the amlodipine treatment group. No significant difference in absolute changes in BP levels was observed among the genotypes in either treatment group.

Conclusion:

The GNB3 C825T splice variant is associated with the DBP-lowering effect of telmisartan but not amlodipine in Chinese EH patients.

Correction of the Pathogenic Alternative Splicing, Caused by the Common GNB3 c.825C>T Allele, Using a Novel, Antisense Morpholino

The very common GNB3 c.825C>T polymorphism (rs5443) is present in approximately half of all human chromosomes. Significantly, the presence of the GNB3 825T allele has been strongly associated with predisposition to essential hypertension. Paradoxically the presence of the GNB3 825T allele, in exon 10, introduces a pathogenic alternative RNA splice site into the middle of exon 9. To attempt to correct this pathogenic aberrant splicing, we, therefore, bioinformatically designed, using a Gene Tools(®) algorithm, a GNB3-specific, antisense morpholino. It was hoped that this morpholino would behave in vitro as either a potential splice blocker and/or exon skipper, to both bind and inhibit/reduce the aberrant splicing of the GNB3 825T allele. On transfecting a human lymphoblast cell line homozygous for the 825T allele, with this antisense morpholino, we encouragingly observed both a significant reduction (from ∼58% to ∼5%) in the production of the aberrant smaller GNB3 transcript, and a subsequent increase in the normal GNB3 transcript (from ∼42% to ∼95%). Our results demonstrate the potential use of a GNB3-specific antisense morpholino, as a pharmacogenetic therapy for essential hypertension.

Ablation of the GNB3 gene in mice does not affect body weight, metabolism or blood pressure, but causes bradycardia

G protein β3 (Gβ3) is an isoform of heterotrimeric G protein β subunits involved in transducing G protein coupled receptor (GPCR) signaling. Polymorphisms in Gβ3 (GNB3) are associated with many human disorders (e.g. hypertension, diabetes and obesity) but the role of GNB3 in these pathogeneses remains unclear. Here, Gβ3-null mice (GNB3(-/-)) were characterized to determine how Gβ3 functions to regulate blood pressure, body weight and metabolism. We found Gβ3 expression restricted to limited types of tissues, including the retina, several regions of the brain and heart ventricles. Gβ3-deficient mice were normal as judged by body weight gain by age or by feeding with high-fat diet (HFD); glucose tolerance and insulin sensitivity; baseline blood pressure and angiotensin II infusion-induced hypertension. During tail-cuff blood pressure measurements, however, Gβ3-null mice had slower heart rates (~450 vs ~500 beats/min). This bradycardia was not observed in isolated and perfused Gβ3-null mouse hearts. Moreover, mouse hearts isolated from GNB3(-/-) and controls responded equivalently to muscarinic receptor- and β-adrenergic receptor-stimulated bradycardia and tachycardia, respectively. Since no difference was seen in isolated hearts, Gβ3 is unlikely to be involved directly in the GPCR signaling activity that controls heart pacemaker activity. These results demonstrate that although Gβ3 appears dispensable in mice for the regulation of blood pressure, body weight and metabolic features associated with obesity and diabetes, Gβ3 may regulate heart rate.

PLEKHG2 promotes heterotrimeric G protein βγ-stimulated lymphocyte migration via Rac and Cdc42 activation and actin polymerization

PLEKHG2 is a Dbl family Rho guanine nucleotide exchange factor (RhoGEF) whose gene was originally identified as being upregulated in a leukemia mouse model and was later shown to be activated by heterotrimeric G protein βγ (Gβγ) subunits. However, its function and activation mechanisms remain elusive. Here we show that, compared to its expression in primary human T cells, its expression is upregulated in several leukemia cell lines, including Jurkat T cells. Downregulation of PLEKHG2 in Jurkat T cells by small interfering RNAs (siRNAs) specifically inhibited Gβγ-stimulated Rac and Cdc42, but not RhoA, activation. Consequently, suppressing PLEKHG2 expression blocked actin polymerization and SDF1α-stimulated lymphocyte migration. Additional studies indicate that Gβγ likely activates PLEKHG2, in part by binding the N terminus of PLEKHG2 to release an autoinhibition imposed by its C terminus, which interacts with a region encompassing the catalytic Dbl homology (DH) domain. As a result, overexpressing either the N terminus or the C terminus of PLEKHG2 blocked Gβγ-stimulated Rac and Cdc42 activation and prevented Jurkat T cells from forming membrane protrusions and migrating. Together, our studies have provided the first evidence for the endogenous function of PLEKHG2, which may serve as a key Gβγ-stimulated RhoGEF that regulates lymphocyte chemotaxis via Rac and Cdc42 activation and actin polymerization.