Non-synonymous gene polymorphisms in the secretory signal peptide of human TGF-β1 affect cellular synthesis but not secretion of TGF-β1

Genetics and Genomics of SOST: Functional Analysis of Variants and Genomic Regulation in Osteoblasts

SOST encodes the sclerostin protein, which acts as a key extracellular inhibitor of the canonical Wnt pathway in bone, playing a crucial role in skeletal development and bone homeostasis. The objective of this work was to assess the functionality of two variants previously identified (the rare variant rs570754792 and the missense variant p.Val10Ile) and to investigate the physical interactors of the SOST proximal promoter region in bone cells. Through a promoter luciferase reporter assay we show that the minor allele of rs570754792, a variant located in the extended TATA box motif, displays a significant decrease in promoter activity. Likewise, through western blot studies of extracellular and intracellular sclerostin, we observe a reduced expression of the p.Val10Ile mutant protein. Finally, using a circular chromosome conformation capture assay (4C-seq) in 3 bone cell types (MSC, hFOB, Saos-2), we have detected physical interactions between the SOST proximal promoter and the ECR5 enhancer, several additional enhancers located between EVT4 and MEOX1 and a distant region containing exon 18 of DHX8. In conclusion, SOST presents functional regulatory and missense variants that affect its expression and displays physical contacts with far reaching genomic sequences, which may play a role in its regulation within bone cells.

Missense mutations in the signal peptide of the porcine GH gene affect cellular synthesis and secretion

CONTEXT

In previous investigations, we have demonstrated the mutations in the signal peptide of porcine GH gene were associated with the body size.

METHODS

In this study, the fusion gene expression vectors which consisted of eight signal peptide mutants of GH gene and EGFP gene were constructed according to three missense mutations (p.Val9Ala, p.Gln22Arg and p.Asp25Gly), and they were transfected into the GH3 cell line.

RESULTS

The inhibition levels of EGFP gene transcriptions with different signal peptide mutants were significantly different. Typically, the allelic variants carrying Val in codon nine showed higher protein synthesis (P < 0.05), and the allelic variants carrying neutral Gln in codon 22 and Gly in codon 25 showed higher secretion proportion (P < 0.05) compared with the other groups as assessed by western blotting. In silico RNA folding prediction indicated that the mutations gave rise to different RNA secondary structures, suggesting that they might affect translation and protein synthesis.

CONCLUSION

We conclude that the missense mutations within the signal sequence influence the expression and the secretion of the protein. To the best of our knowledge, this is the first report addressing the functional consequences of the mutations in the signal peptide of porcine GH gene.

Polymorphism in TGFB1 is associated with worse non-relapse mortality and overall survival after stem cell transplantation with unrelated donors

Transforming growth factor β-1, encoded by the TGFB1 gene, is a cytokine that plays a central role in many physiological and pathogenic processes. We have sequenced TGFB1 regulatory region and assigned allelic genotypes in a large cohort of hematopoietic stem cell transplantation patients and donors. In this study, we analyzed 522 unrelated donor-patient pairs and examined the combined effect of all the common polymorphisms in this genomic region. In univariate analysis, we found that patients carrying a specific allele, 'p001', showed significantly reduced overall survival (5-year overall survival 30.7% for p001/p001 patients vs. 41.6% others; P=0.032) and increased non-relapse mortality (1-year non-relapse mortality: 39.0% vs. 25.4%; P=0.039) after transplantation. In multivariate analysis, the presence of a p001/p001 genotype in patients was confirmed as an independent factor for reduced overall survival [hazard ratio=1.53 (1.04-2.24); P=0.031], and increased non-relapse mortality [hazard ratio=1.73 (1.06-2.83); P=0.030]. In functional experiments we found a trend towards a higher percentage of surface transforming growth factor β-1-positive regulatory T cells after activation when the cells had a p001 allele (P=0.07). Higher or lower production of transforming growth factor β-1 in the inflammatory context of hematopoietic stem cell transplantation may influence the development of complications in these patients. Findings indicate that TGFB1 genotype could potentially be of use as a prognostic factor in hematopoietic stem cell transplantation risk assessment algorithms.

A signal peptide missense mutation associated with nicotine dependence alters α2*-nicotinic acetylcholine receptor function

A cytosine to thymidine (C → T) missense mutation in the signal peptide (SP) sequence (rs2472553) of the nicotinic acetylcholine receptor (nAChR) α2 subunit produces a threonine-to-isoleucine substitution (T22I) often associated with nicotine dependence (ND). We assessed effects on function of α2*-nAChR ('*'indicates presence of additional subunits) of this mutation, which could alter SP cleavage, RNA/protein secondary structure, and/or efficiency of transcription, translation, subunit assembly, receptor trafficking or cell surface expression. Two-electrode voltage clamp analyses indicate peak current responses to ACh or nicotine are decreased 2.8-5.8-fold for putative low sensitivity (LS; 10:1 ratio of α:β subunit cRNAs injected) α2β2- or α2β4-nAChR and increased for putative high sensitivity (HS; 1:10 α:β subunit ratio) α2β2- (5.7-15-fold) or α2β4- (1.9-2.2-fold) nAChR as a result of the mutation. Agonist potencies are decreased 1.6-4-fold for putative LS or HS α2(T22I)β2-nAChR or for either α2*-nAChR subtype formed in the presence of equal amounts of subunit cRNA, slightly decreased for LS α2(T22I)β4-nAChR, but increased 1.4-2.4-fold for HS α2(T22I)β4-nAChR relative to receptors containing wild-type α2 subunits. These effects suggest that the α2 subunit SP mutation generally favors formation of LS receptor isoforms. We hypothesize that lower sensitivity of human α2*-nAChR to nicotine could contribute to increased susceptibility to ND. To our knowledge this is the first report of a SP mutation having a functional effect in a member of cys-loop family of ligand-gated ion channels.

A novel missense mutation in the signal peptide of the human POMC gene: a possible additional link between early-onset type 2 diabetes and obesity

Rare mutations in several genes have a critical role in the control of homeostatic mechanisms such as food-intake, energy balance and glucose metabolism. In this study, we performed a mutational screening in a 58-year-old woman presenting early-onset type 2 diabetes and central obesity. The entire coding regions of MC4R, MC3R, HNF1A, GCK and POMC (pro-opiomelanocortin) genes were analyzed by direct sequencing. A new missense mutation was identified within the POMC gene signal peptide sequence, resulting in a heterozygous substitution of an arginine for a glycine at codon 15 (p.A15G) that was excluded in 300 healthy normal weight controls. The mutation segregated in the family and was associated with overweight, type 2 diabetes, hypertension and coronary heart disease in the carriers. Functional studies demonstrated that POMC protein was not detectable in β-TC3 cells transfected with A15G-POMC vector as well as in their culture media, despite POMC mRNA levels were comparable for amount and stability to those of wild-type-transfected cells. In silico RNA folding prediction indicated that the mutation gives rise to a different RNA secondary structure, suggesting that it might affect translation and protein synthesis. To the best of our knowledge, this is the first report addressing the functional consequences of a mutation in the signal peptide of POMC. These findings further support the hypothesis that POMC-derived peptides might have a role in the control of peripheral glucose metabolism and suggest that disruption of central POMC secretion might represent an additional link between type 2 diabetes and obesity.

Polymorphisms in the potential functional regions of the TGF-β 1 and TGF-β receptor genes and disease susceptibility in HBV-related hepatocellular carcinoma patients

Hepatocellular carcinoma (HCC) is a disease of multiple etiologies caused by the accumulation of genetic and epigenetic defects. Current evidence indicates that the transforming growth factor beta (TGF-β) signaling pathway has a significant impact on different cellular process. Members of the TGF-β superfamily (TGF-β1, the type I TGF-β receptor [TβRI], type II TGF-β receptor [TβRII], and type III TGF-β receptor]) play an important role in tumorigenesis. Numerous studies show that genetic polymorphisms in TGF-β superfamily genes are associated with HCC in East Asian populations. We studied 16 single nucleotide polymorphisms (SNPs) in four genes (TGF-β1, TβRI, TβRII, and TβRIII) to examine their associations with hepatocarcinogenesis. A total of 1228 Chinese Han participants were enrolled in the study (881 control participants who were negative for all hepatitis B virus [HBV] serum markers and 347 case participants with HBV-related HCC). Genotyping was conducted using the TaqMan method. The results showed that the frequency of the rs1805110 T allele was significantly higher in the case group than in the control group (P = 0.034). After stratification, the results for rs1805110 remained significant in male participants (P = 0.005), but there was no statistical difference in females. In males, the frequency of the C-C-G-C-A haplotype resulting from SNPs rs1805110, rs2810904, rs1805112, rs284878, and rs1804506 in TβRIII was significantly lower in the case group than in the control group (P = 0.001), whereas the reverse was true for the T-C-G-C-A haplotype (P = 0.036). We conclude that the rs1805110T allele is associated with susceptibility to HBV-related HCC in males.

Association of TLR7 variants with AIDS-like disease and AIDS vaccine efficacy in rhesus macaques

In HIV infection, TLR7-triggered IFN-α production exerts a direct antiviral effect through the inhibition of viral replication, but may also be involved in immune pathogenesis leading to AIDS. TLR7 could also be an important mediator of vaccine efficacy. In this study, we analyzed polymorphisms in the X-linked TLR7 gene in the rhesus macaque model of AIDS. Upon resequencing of the TLR7 gene in 36 rhesus macaques of Indian origin, 12 polymorphic sites were detected. Next, we identified three tightly linked single nucleotide polymorphisms (SNP) as being associated with survival time. Genotyping of 119 untreated, simian immunodeficiency virus (SIV)-infected male rhesus macaques, including an 'MHC adjusted' subset, revealed that the three TLR7 SNPs are also significantly associated with set-point viral load. Surprisingly, this effect was not observed in 72 immunized SIV-infected male monkeys. We hypothesize (i) that SNP c.13G>A in the leader peptide is causative for the observed genotype-phenotype association and that (ii) the underlying mechanism is related to RNA secondary structure formation. Therefore, we investigated a fourth SNP (c.-17C>T), located 17 bp upstream of the ATG translation initiation codon, that is also potentially capable of influencing RNA structure. In c.13A carriers, neither set-point viral load nor survival time were related to the c.-17C>T genotype. In c.13G carriers, by contrast, the c.-17C allele was significantly associated with prolonged survival. Again, no such association was detected among immunized SIV-infected macaques. Our results highlight the dual role of TLR7 in immunodeficiency virus infection and vaccination and imply that it may be important to control human AIDS vaccine trials, not only for MHC genotype, but also for TLR7 genotype.

Association of TGF-beta1 gene polymorphisms in exon1 and blood levels with essential hypertension

AIMS

Based on a case-control study, we investigated the relationship between +869T/C and +915G/C gene polymorphisms in transforming growth factor-beta1 (TGF-beta1), protein levels and essential hypertension (EH) in the Kazakh and Han Chinese populations selected from the Boertonggu countryside of Shawan region in the Xinjiang Uygur Autonomous Region of China (n=1600). The polymorphisms of TGF-beta1 and the blood levels were detected using polymerase chain reaction-restriction fragment length polymorphism assays and sandwich ELISA, respectively.

MAJOR FINDINGS

An association was found between +869C-allele with higher risk of EH in these two populations. We also found that the CG haplotype of the two polymorphisms was associated with EH in the Kazakh EH patients. The levels of TGF-beta(1) in the blood were positively correlated with diastolic blood pressure both in the Kazakh and Han EH patients. Levels of the TGF-beta1 protein in the Kazakh EH patients were significantly higher than those in the Han EH patients.

PRINCIPAL CONCLUSION

These results suggest that the TGF-beta1 +869 C allele is potentially a genetic factor of EH in these two ethnicities, the CG haplotype can be a genetic marker of EH in the Kazakh Chinese and the high concentration of TGF-beta1 is possibly associated with EH, especially in the Kazakh population.

Polymorphisms in TGFB1 and PDGFRB are associated with Moyamoya disease in European patients

BACKGROUND

The etiology of Moyamoya disease (MMD) is still widely unknown. Several publications on Moyamoya describe differences of cytokine and growth factor concentrations in different specimen. We analyzed the DNA of patients with MMD for single nucleotide polymorphisms (SNPs) in and upstream of the genes for previously described associated cytokines and growth factors.

METHOD

Thirteen SNPs were genotyped in or upstream to four genes-basic fibroblast growth factor (BFGF), cellular retinoic acid-binding protein 1 (CRABP1), platelet derived growth factor receptor beta (PDGFRB), and transforming growth factor beta 1 (TGFB1)-comparing 40 DNA samples of MMD patients to 68 healthy controls from central Europe. Genotyping was performed by sequencing the SNP-containing genetic regions with custom made primers.

FINDINGS

We found association of two SNPs: rs382861 [A/C] (p = 0.0373, OR = 1.81, 95% CI = 1.03-3.17) in the promoter region of PDGFRB and rs1800471[C/G] (p = 0.0345, OR = 7.65, 95% CI = 0.97-59.95), located in the first exon of TGFB1.

CONCLUSION

Our results indicate possible genetic risk factors for the genesis of MMD. TGFB1 and PDGFRB are involved in vascular growth and transformation processes which may play a role in the development of MMD. Further analyses in larger European cohorts and replication in patients of different ethnicity, as well as functional studies, may lead to possible early detection of patients at risk for developing MMD and subsequently to future preventive therapies.