Association of the GNB3 825T-allele with better survival in patients with glioblastoma multiforme

Subtype-dependent regulation of Gβγ signalling

G protein-coupled receptors (GPCRs) transmit information to the cell interior by transducing external signals to heterotrimeric G protein subunits, Gα and Gβγ subunits, localized on the inner leaflet of the plasma membrane. Though the initial focus was mainly on Gα-mediated events, Gβγ subunits were later identified as major contributors to GPCR-G protein signalling. A broad functional array of Gβγ signalling has recently been attributed to Gβ and Gγ subtype diversity, comprising 5 Gβ and 12 Gγ subtypes, respectively. In addition to displaying selectivity towards each other to form the Gβγ dimer, numerous studies have identified preferences of distinct Gβγ combinations for specific GPCRs, Gα subtypes and effector molecules. Importantly, Gβ and Gγ subtype-dependent regulation of downstream effectors, representing a diverse range of signalling pathways and physiological functions have been found. Here, we review the literature on the repercussions of Gβ and Gγ subtype diversity on direct and indirect regulation of GPCR/G protein signalling events and their physiological outcomes. Our discussion additionally provides perspective in understanding the intricacies underlying molecular regulation of subtype-specific roles of Gβγ signalling and associated diseases.

An Integrative Approach Uncovers Biomarkers that Associate with Clinically Relevant Disease Outcomes in Vulvar Carcinoma

Vulvar squamous cell carcinoma (VSCC) is a rare disease that has a high mortality rate (∼40%). However, little is known about its molecular signature. Therefore, an integrated genomics approach, based on comparative genome hybridization (aCGH) and genome-wide expression (GWE) array, was performed to identify driver genes in VSCC. To achieve that, DNA and RNA were extracted from frozen VSCC clinical specimens and examined by aCGH and GWE array, respectively. On the basis of the integration of data using the CONEXIC algorithm, PLXDC2 and GNB3 were validated by RT-qPCR. The expression of these genes was then analyzed by IHC in a large set of formalin-fixed paraffin-embedded specimens. These analyses identified 47 putative drivers, 46 of which were characterized by copy number gains that were concomitant with overexpression and one with a copy number loss and downregulation. Two of these genes, PLXDC2 and GNB3, were selected for further validation: PLXDC2 was downregulated and GNB3 was overexpressed compared with non-neoplastic tissue. By IHC, both proteins were ubiquitously expressed throughout vulvar tissue. High expression of GNB3 and low PLXDC2 immunostaining in the same sample was significantly associated with less lymph node metastasis and greater disease-free survival. On the basis of a robust methodology never used before for VSCC evaluation, two novel prognostic markers in vulvar cancer are identified: one with favorable prognosis (GNB3) and the other with unfavorable prognosis (PLXDC2).

IMPLICATIONS

This genomics study reveals markers that associate with prognosis and may provide guidance for better treatment in vulvar cancer. Mol Cancer Res; 14(8); 720-9. ©2016 AACR.

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.

The functional Aquaporin 1 -783G/C-polymorphism is associated with survival in patients with glioblastoma multiforme

BACKGROUND

Despite a dismal prognosis, variability exists regarding the survival-time in patients with glioblastoma-multiforme (GBM), which may be explained by genetic variation. A possible candidate-gene for such variation is Aquaporin-1 (AQP1), since Aquaporin-1-expression influences the pathogenesis and outcome of various malignancies. Functional genetic variants in the promoter of AQP1, modifying Aquaporin-1-expression, could be associated with altered survival in patients with GBM.

METHODS

We sequenced the human AQP1-promoter to detect novel sequence variants, which might impact on Aquaporin-1-expression and tested the hypothesis, that functional single nucleotide polymorphisms are associated with different survival-times of patients suffering from GBM.

RESULTS

Sequencing the AQP1-promoter revealed a novel -783G/C-polymorphism. Reporter-assays showed that substitution of G for C was associated both with increased transcriptional-activation of the AQP1-promoter by serum and with increased AQP1 mRNA expression. Finally, we assessed in a cohort of 155 Caucasian patients with GBM whether the functional single-nucleotide-783G/C-polymorphism is associated with survival-time. Cox-regression analyses revealed the AQP1 -783G/C genotype status as an independent prognostic-factor when jointly considering other predictors of survival. Homozygous CC subjects had a significantly worse outcome compared to GC/GG genotypes (hazard ratio: 3.09; 95% CI, 1.43-6.65; P = 0.004).

CONCLUSIONS

Our findings suggest the novel AQP1 polymorphism as a survival prognosticator in patients suffering from GBM that could help to identify a subgroup of patients at high risk for death. Further studies are necessary to reveal the exact molecular mechanisms.

MGMT promoter methylation in gliomas-assessment by pyrosequencing and quantitative methylation-specific PCR

BACKGROUND

Methylation of the O(6)-methylguanine-DNA methyltransferase (MGMT) gene promoter is a favorable prognostic factor in glioblastoma patients. However, reported methylation frequencies vary significantly partly due to lack of consensus in the choice of analytical method.

METHOD

We examined 35 low- and 99 high-grade gliomas using quantitative methylation specific PCR (qMSP) and pyrosequencing. Gene expression level of MGMT was analyzed by RT-PCR.

RESULTS

When examined by qMSP, 26% of low-grade and 37% of high-grade gliomas were found to be methylated, whereas 97% of low-grade and 55% of high-grade gliomas were found methylated by pyrosequencing. The average MGMT gene expression level was significantly lower in the group of patients with a methylated promoter independent of method used for methylation detection. Primary glioblastoma patients with a methylated MGMT promoter (as evaluated by both methylation detection methods) had approximately 5 months longer median survival compared to patients with an unmethylated promoter (log-rank test; pyrosequencing P = .02, qMSP P = .06). One third of the analyzed samples had conflicting methylation results when comparing the data from the qMSP and pyrosequencing. The overall survival analysis shows that these patients have an intermediate prognosis between the groups with concordant MGMT promoter methylation results when comparing the two methods.

CONCLUSION

In our opinion, MGMT promoter methylation analysis gives sufficient prognostic information to merit its inclusion in the standard management of patients with high-grade gliomas, and in this study pyrosequencing came across as the better analytical method.

Reduced prevalence of the C825T polymorphism of the G-protein beta subunit gene in women with breast cancer

OBJECTIVE

To evaluate the prevalence of the C825T polymorphism in the GNB3 gene in women with and without breast cancer and its possible association with clinical or pathological features of breast disease.

SUBJECTS AND METHODS

We included 134 women with breast cancer and a control group of 129 healthy women. The case group responded to a questionnaire on lifestyle, reproductive factors and family history. Clinical data were also evaluated. The risk for cancer was calculated and PCR was carried out for the detection of the polymorphism. Statistical analysis was performed using the package R Environment, with confidence intervals of 95% and a significance level of 5% (p and lt;0.05).

RESULTS

The frequency of the TT genotype was significantly greater in women of the control group (30.2%) than women with breast cancer (14.9%) (p=0.02). The polymorphism was not associated with clinical features, age at diagnosis (p=0.07), age at menarche (p=0.17), and age at menopause (p=0.60). The TT genotype did not have a higher frequency in patients with high BMI (p=0.98). The risk for cancer showed no correlation with the presence of the polymorphism.

CONCLUSIONS

Our data indicate that the C825T polymorphism in the GNB3 gene has no relationship to the risk for breast cancer or the characteristics of the disease.

Role of the GNAS1 T393C polymorphism in patients with glioblastoma multiforme

The T393C polymorphism of the GNAS1 locus, which encodes the Gαs protein, has recently been found to be associated with patient outcome in various malignancies. We investigated the association between GNAS1 genotype and survival among patients suffering from glioblastoma multiforme (GBM). One hundred and sixty-two patients with GBM were retrospectively investigated. Inclusion criteria were availability of DNA and, for surviving patients, a follow-up of at least 24 months. The results were analysed based on clinical data, type of surgical intervention, adjuvant therapy, and 2-year survival. At the 2-year follow up, 79.6% of patients had died. Two-year survival rates were as follows: CC-homozygous patients, 15.8%; CT-heterozygous patients, 23.1%; and TT-homozygous patients, 18.2% (p = 0.461). Subgroup analysis revealed different 2-year survival rates in the group that underwent stereotactic biopsy, with 0% for CC-homozygous, 2.8% for CT-heterozygous, and 15.4% survival for TT-homozygous patients, but the differences were not statistically significant (p = 0.229). Our results indicate that there is no association between the GNAS1 T393C polymorphism and 2-year survival among patients with GBM.

SNPs in genes encoding G proteins in pharmacogenetics

Heterotrimeric guanine-binding proteins (G proteins) transmit signals from the cell surface to intracellular signal cascades and are involved in various physiological and pathophysiological processes. Polymorphisms in the genes GNB3 (encoding the Gβ3 subunit), GNAS (encoding the Gαs subunit) and GNAQ (encoding the Gαq subunit) have been the primary focus of investigation. Polymorphisms in these genes could be associated with different complex phenotypes underlining that alterations in G-protein signaling can cause multiple disorders. G proteins present a point of convergence or ‘bottleneck’ between various receptors and effectors, thus making them a sensible tool for pharmacogenetic studies. The pharmacogenetic studies performed to date mostly demonstrate an association between G-protein polymorphisms and response to therapy or occurrence of adverse drug effects. Therefore, polymorphisms in genes encoding G-protein subunits may help to individualize drug treatment in various diseases with regard to both efficacy and safety.