[Show abstract][Hide abstract] ABSTRACT: Heterologously expressed proteins in Escherichia coli may undergo unwanted N-terminal processing by methionine and proline aminopeptidases. To overcome this problem, we present a system where the gene of interest is cloned as a fusion to a self-splicing mini-intein. This fusion construct is expressed in an engineered E. coli strain from which the pepP gene coding for aminopeptidase P has been deleted. We describe a protocol using human cationic trypsinogen as an example to demonstrate that recombinant proteins produced in this expression system contain homogeneous, unprocessed N-termini.
[Show abstract][Hide abstract] ABSTRACT: Two common haplotypes of the serine protease inhibitor Kazal type 1 (SPINK1) gene have been shown to increase the risk for chronic pancreatitis. A haplotype comprising the c.101A>G (p.N34S) missense variant and four intronic alterations has been found worldwide, whereas a second haplotype consisting of the c.-215G>A promoter variant and the c.194+2T>C intronic alteration has been observed frequently in Japan.
In the present study, the functional significance of the intronic variants in the pathogenic SPINK1 haplotypes was examined by utilising minigenes, which harbour individual introns placed in the appropriate context of the full-length SPINK1 cDNA. Cells transfected with the SPINK1 minigenes secrete active trypsin inhibitor, thereby allowing evaluation of mutational effects simultaneously on transcription, splicing, translation and secretion.
It was found that the c.194+2T>C intronic alteration abolished SPINK1 expression at the mRNA level, with consequent loss of inhibitor secretion, whereas the p.N34S-associated intronic variants had no detectable functional effect.
Taken together with previous studies, the results indicate that all known variants within the p.N34S-associated haplotype are functionally innocuous, suggesting that an as yet unidentified variant within this haplotype is responsible for the pathogenic effect. The marked negative impact of the c.194+2T>C variant on SPINK1 expression supports the notion that SPINK1 variants increase the risk of chronic pancreatitis by diminishing protective trypsin inhibitor levels.
[Show abstract][Hide abstract] ABSTRACT: Mutations of the SPINK1 gene encoding pancreatic secretory trypsin inhibitor have been identified in association with chronic pancreatitis. The vast majority of patients carry the N34S variant, whereas other genetic variants are relatively rare and their disease association is uncertain. The aim of this study was to characterise and compare the functional defects caused by the six published missense mutations that affect mature SPINK1-namely, N34S, D50E, Y54H, P55S, R65Q, and R67C.
Wild type and mutant SPINK1 were expressed in human embryonic kidney 293T cells via transient transfection. SPINK1 expression was characterised by RT-PCR, activity assays, and western blots.
Mutations N34S and P55S did not alter secretion of SPINK1 from HEK 293T cells, whereas mutation R65Q decreased secretion about twofold. Remarkably, mutations D50E, Y54H, and R67C abolished or markedly diminished secretion, but all three mutants were detected in cell extracts, indicating intracellular retention and degradation.
The results identify intracellular folding defects as a novel mechanism of SPINK1 deficiency associated with chronic pancreatitis. The dramatic effects of the D50E and Y54H mutations indicate that the interaction between Asp50 and Tyr54 is critical for proper folding of the inhibitor. The disease-causing biochemical defect in the N34S mutant is unrelated to secretion or trypsin inhibitory activity and remains enigmatic. Finally, the patent functional defects in mutants D50E, Y54H, and R67C suggest disease association of these rare SPINK variants.
[Show abstract][Hide abstract] ABSTRACT: Variants of the SPINK1 gene encoding pancreatic secretory trypsin inhibitor have been described in association with chronic pancreatitis (CP). These alterations are believed to cause a loss of function by either impairing the trypsin inhibitory activity or reducing expression. Here we report two novel SPINK1 variants in exon 1 that affect the secretory signal peptide. The disease-associated c.41T>G (p.L14R) alteration was found in two European families with autosomal dominant hereditary pancreatitis, whereas the c.36G>C (p.L12F) variant was identified as a frequent alteration in subjects of African descent. The functional effects of both alterations and the previously reported c.41T>C (p.L14P) variant were characterized by activity assays and Western blots of wild-type and mutant SPINK1 expressed in human embryonic kidney 293T and Chinese hamster ovary cells. Alterations p.L14R and p.L14P destined the inhibitor for rapid intracellular degradation and thereby abolished SPINK1 secretion, whereas the p.L12F variant showed no detrimental effect. The results provide the first clear experimental demonstration that alterations that markedly reduce SPINK1 expression are associated with classic hereditary pancreatitis. Therefore, these variants should be classified as severe and regarded as disease-causing rather than disease-modifiers.
Human Mutation 05/2007; 28(5):469-76. · 5.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Abnormalities of the dopamine neurotransmission have been hypothesized to play an important role in the pathophysiology of attention deficit hyperactivity disorder (ADHD). Promoter variants of the dopamine D4 receptor gene (DRD4) have attracted particular interest due to their possible role in regulation of gene transcription. Here we describe the haplotype analysis of the 120 base pair duplication (120-bp dup) and three SNPs (-616C/G, -615A/G, -521C/T) in the 5' region of the DRD4 gene among children with ADHD. We observed a trend (chi(2) = 14.905, df = 9, P = 0.093) in the four-locus haplotype distribution between ADHD probands (N = 173) and controls (N = 284). The homozygote genotype of the 1-repeat form of the 120-bp dup (1-1) had a significantly higher frequency among ADHD children than in controls (8.1% vs. 3.2%, chi(2) = 5.526, df = 1, P = 0.019, Odds Ratio = 2.71). In addition, a novel, 4-repeat allele was identified among ADHD patients. This particular allele has been cloned to the luciferase expression vector and its transcriptional activity has been compared to the 1- and 2-repeat allele. The number of repeats of the 120-bp dup was found to have an effect on transcriptional activity in both neuroblastoma and retinoblastoma cell lines in a dose-dependent manner (1-repeat > 2-repeat > 4-repeat). These results suggest that the 1-repeat form of the 120-bp dup might be a risk factor of ADHD, especially in the homozygous form and/or in the context of certain haplotypes.
American Journal of Medical Genetics Part B Neuropsychiatric Genetics 04/2007; 144B(2):231-6. · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The human dopamine D4 receptor (DRD4) gene has been extensively studied as a candidate gene for attention deficit hyperactivity disorder (ADHD). Both the 5' regulatory region and the coding sequence contain a number of polymorphisms. The most widely investigated polymorphism of the DRD4 gene is the 48 bp VNTR (Variable Number of Tandem Repeats) in the third exon. The promoter variants have received particular attention in the past few years due to their possible role in the regulation of gene expression. In this study we describe an association analysis of the 120 bp duplication and three sequence variations (SNPs, Single Nucleotide Polymorphism; -616 C/G, -615 A/G, -521 C/T) in the 5' region of the DRD4 gene is presented among children with ADHD. In case-control approach, the 1-repeat form of the 120 bp duplication had a significantly higher frequency among ADHD children than controls, both in allele-(p=0.047), and genotype (p=0.019) distributions. There was no significant difference between the ADHD and control groups in the allele or genotype frequencies of the investigated SNPs. The transcriptional effect of the 120 bp duplication was analysed in luciferase reporter system. The different 120 bp duplication alleles (1-repeat, 2-repeat and the newly identified 4-repeat allele) was found to have an effect on transcriptional activity of the DRD4 gene in both neuroblastoma and retinoblastoma cell lines in a dose-dependent manner. The higher was the repeat number of the 120 bp sequence in the promoter, the stronger was the decrease of the gene transcription (1-repeat > 2-repeat > 4-repeat; p<0.01). These results of association and functional analyses suggest that the 1-repeat form of the 120 bp duplication might be a risk factor of ADHD.
Neuropsychopharmacologia Hungarica: a Magyar Pszichofarmakológiai Egyesület lapja = official journal of the Hungarian Association of Psychopharmacology 03/2007; 9(1):11-8.
[Show abstract][Hide abstract] ABSTRACT: High-level expression of human trypsinogens as inclusion bodies in Escherichia coli requires deletion of the secretory signal sequence and placement of an initiator methionine at the N terminus. Trypsinogen preparations obtained this way contain a mixture of abnormal N termini, as a result of processing by cytoplasmic aminopeptidases. Here, we describe an expression system that produces recombinant human cationic trypsinogen with a native, intact N terminus, using intein-mediated protein splicing and an aminopeptidase P (pepP) deficient E. coli strain. As a first application of this system, the effect of the pancreatitis-associated mutation A16V on the autoactivation of human cationic trypsinogen was characterized. The use of the novel pepP knock-out E. coli strain should be generally applicable to the expression of recombinant proteins, which undergo unwanted N-terminal trimming by aminopeptidase P.
Protein Expression and Purification 08/2006; 48(1):104-11. · 1.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The human dopamine D4 receptor (DRD4) gene has been studied extensively as a candidate gene for certain psychological traits and several behavioural and psychiatric disorders. Both the 5' regulatory region and the coding sequence contain a number of polymorphisms. The promoter variants have received particular attention in the past few years due to their possible role in the regulation of gene transcription. Previously, the -521C/T SNP was shown to influence promoter activity. The aim of this study is to perform an in-depth analysis of this effect in the context of various neural cell lines.
Endogenous mRNA expression of the DRD4 gene was demonstrated in two neuroblastoma (SK-N-F1, IMR32) and one retinoblastoma cell line (Y79) by RT-PCR. In addition, very low DRD4 mRNA levels were also detected in HeLa cells. The transcriptional activity of a series of 5' promoter deletion mutants was determined by transient transfection of luciferase reporter constructs. The activity profile of these promoter fragments was similar in each of the cell lines tested. The highest luciferase reporter activity was obtained with a construct containing promoter sequences between nucleotides -668 to -389, while a putative silencer region was localised spanning from nucleotide -1571 to -800. Surprisingly, the -521 C/T polymorphism had no significant effect on transcriptional activity of the reporter construct with the highest activity (-668 to -389) in any of the three cell lines tested.
Our results do not confirm previous data assigning different transcriptional activities to the -521 C/T alleles of the human DRD4 promoter. Furthermore, these findings highlight the need for further characterization of the 5' regulatory region of the DRD4 gene and identification of additional functional promoter polymorphic sites, especially in the context of haplotype.
[Show abstract][Hide abstract] ABSTRACT: Polymorphic regions of the dopamine D4 receptor gene and its promoter region are in the focus of psychogenetic association studies. Besides the accurate phenotype characterization, highly reliable genotyping methods are also of outstanding importance in these works.
DNA samples of 598 healthy unrelated Caucasian individuals were used to validate the described molecular haplotyping methods and to determine the allele, genotype and haplotype frequencies and the linkage disequilibrium between the polymorphisms of the dopamine D4 receptor promoter region.
We described a double genotyping system for the -521CT and -616CG polymorphisms, using a polymerase chain reaction restriction fragment length polymorphism or an allele-specific amplification. Allele and genotype frequencies of the novel -615AG single-nucleotide polymorphism are also determined (-615G=13.21%). For molecular haplotyping of the three single-nucleotide polymorphisms and a 120-bp duplication polymorphism, the allele-specific amplification was combined with restriction digestion. The results of the elaborated haplotyping methods were validated by molecular haplotyping of cloned fragments.
The developed methods have been arranged into an 'economic' protocol that might be extended for higher reliability with a double haplotyping ('full mode'). Despite the close proximity of these sites, only a moderate linkage was found between the -615AG and -616CG (Delta(2)=0.162), between the -616AG and -521CT (Delta(2)=0.0221) and between the -615AG and -521CT single-nucleotide polymorphisms (Delta(2)=0.0346). The 120-bp duplication was shown to be in linkage equilibrium with any of the three single-nucleotide polymorphisms. Applications of these results should accelerate psychogenetic association studies of the dopamine D4 receptor gene.