Novel KCNQ1 and HERG missense mutations in Dutch long-QT families.

Congenital long QT syndrome (cLQTS) is electrocardiographically characterized by a prolonged QT interval and polymorphic ventricular arrhythmias (torsade de pointes). These cardiac arrhythmias may result in recurrent syncopes, seizure, or sudden death. LQTS can occur either as an autosomal dominant (Romano Ward) or as an autosomal recessive disorder (Jervell and Lange-Nielsen syndrome). Mutations in at least five genes have been associated with the LQTS. Four genes, encoding cardiac ion channels, have been identified. The most common forms of LQTS are due to mutations in the potassium-channel genes KCNQ1 and HERG. We have screened 24 Dutch LQTS families for mutations in KCNQ1 and HERG. Fourteen missense mutations were identified. Eight of these missense mutations were novel: three in KCNQ1 and five in HERG. Novel missense mutations in KCNQ1 were Y184S, S373P, and W392R and novel missense mutations in HERG were A558P, R582C, G604S, T613M, and F640L. The KCNQ1 mutation G189R and the HERG mutation R582C were detected in two families. The pathogenicity of the mutations was based on segregation in families, absence in control individuals, the nature of the amino acid substitution, and localization in the protein. Genotype-phenotype studies indicated that auditory stimuli as trigger of cardiac events differentiate LQTS2 and LQTS1. In LQTS1, exercise was the predominant trigger. In addition, a number of asymptomatic gene defect carriers were identified. Asymptomatic carriers are still at risk of the development of life-threatening arrhythmias, underlining the importance of DNA analyses for unequivocal diagnosis of patients with LQTS.

Auditory stimuli as a trigger for arrhythmic events differentiate HERG-related (LQTS2) patients from KVLQT1-related patients (LQTS1).

OBJECTIVE: This study was performed to identify a possible relationship between genotype and phenotype in the congenital familial long QT syndrome (cLQTS). BACKGROUND: The cLQTS, which occurs as an autosomal dominant or recessive trait, is characterized by QT-interval prolongation on the electrocardiogram and torsade de pointes arrhythmias, which may give rise to recurrent syncope or sudden cardiac death. Precipitators for cardiac events are exercise or emotion and occasionally acoustic stimuli. METHODS: The trigger for cardiac events (syncope, documented cardiac arrhythmias, sudden cardiac death) was analyzed in 11 families with a familial LQTS and a determined genotype. RESULTS: The families were subdivided in KVLQT1-related families (LQTS1, n = 5) and HERG (human ether-a-gogo-related gene)-related families (LQTS2, n = 6) based on single-strand conformation polymorphism analysis and sequencing. Whereas exercise-related cardiac events dominate the clinical picture of LQTS1 patients, auditory stimuli as a trigger for arrhythmic events were only seen in LQTS2 patients. CONCLUSIONS: Arrhythmic events triggered by auditory stimuli may differentiate LQTS2 from LQTS1 patients.

Reduced glucose consumption in the curly tail mouse does not initiate the pathogenesis leading to spinal neural tube defects.

At embryonic stages of neural tube closure, the mouse embryo exhibits a high rate of glycolysis with glucose as the main energy source. In the curly tail mouse, often used as model system for study of human neural tube defects, a delay in closure of the posterior neuropore (PNP) is proposed to be indirectly caused by a proliferation defect in the caudal region. Because glucose is important for proliferation, we tested glucose uptake in curly tail and control embryos, and in a BALB/c-curly tail recombinant strain. The structure and expression of Glut-1, a glucose transporter molecule that is abundantly present during those embryonic stages and that has been mapped in the region of the major curly tail gene, were also studied; however, no strain differences could be demonstrated. Glucose uptake was determined by measuring glucose depletion from the medium in long-term embryo cultures that encompassed the stages of PNP closure and by measuring accumulation of 3H-deoxyglucose in short-term cultures at the stages of early and final PNP closure. Both approaches indicated a reduced glucose uptake by curly tail and recombinant embryos. Surprisingly, the uptake per cell appeared normal, accompanied by a significantly lower DNA content of the mutant embryos. Therefore, it is unlikely that reduced cell proliferation is caused by a reduction in glucose supply during the pathogenesis of the defects in curly tail embryos. The reduced DNA content as well as the reduced glucose uptake per embryo are likely downstream effects of the aberrant proliferation pattern.

The long QT syndrome: a novel missense mutation in the S6 region of the KVLQT1 gene.

The Romano Ward long QT syndrome (LQTS) has an autosomal dominant mode of inheritance. Patients suffer from syncopal attacks often resulting in sudden cardiac death. The main diagnostic parameter is a prolonged QT(c) interval as judged by electro-cardiographic investigation. LQTS is a genetically heterogeneous disease with four loci having been identified to date: chromosome 11p15.5 (LQT1), 7q35-36 (LQT2), 3p21-24 (LQT3) and 4q25-26 (LQT4). The corresponding genes code for potassium channels KVLQT1 (LQT1) and HERG (LQT2) and the sodium channel SCN5A (LQT3). The KVLQT1 gene is characterized by six transmembrane domains (S1-S6), a pore region situated between the S5 and S6 domains and a C-terminal domain accounting for approximately 60% of the channel. This domain is thought to be co-associated with another protein, viz. minK (minimal potassium channel). We have studied a Romano Ward family with several affected individuals showing a severe LQTS phenotype (syncopes and occurrence of sudden death). Most affected individuals had considerable prolongations of QT(c). By using haplotyping with a set of markers covering the four LQT loci, strong linkage was established to the LQT1 locus, whereas the other loci (LQT2, LQT3 and LQT4) could be excluded. Single-strand conformation polymorphism analysis and direct sequencing were used to screen the KVLQT1 gene for mutations in the S1-S6 region, including the pore domain. We identified a Gly-216-Arg substitution in the S6 transmembrane domain of KVLQT1. The mutation was present in all affected family members but absent in normal control individuals, providing evidence that the mutated KVLQT1-gene product indeed caused LQTS in this family. The mutated KVLQT1-gene product thus probably results in a dominant negative suppression of channel activity.

Functional Analysis of the ACTGCTGA Sequence Motif in the Human Immunodeficiency Virus Type-1 Long Terminal Repeat Promoter.

The ACTGCTGA sequence (CTG motif) is located immediately upstream of the NF-kappaB enhancer in the human immunodeficiency virus type-1 (HIV-1) long terminal repeat (LTR). We previously reported on the frequent duplication of this motif in HIV-1-infected individuals. In this study we further characterized the role of the CTG element in transcription and its interaction with cellular proteins. We analyzed the biological activity of LTR promoters with dimeric, monomeric or deleted CTG motifs. Our results indicate that LTRs containing the monomeric CTG motif are the most active transcriptional promoters. Furthermore, mutant viruses with dimeric or deleted CTG motif were consistently out-competed by the wild-type virus in co-culture experiments. Gel mobility shift assays were used to identify a nuclear protein of approximately 68 kD that specifically interacts with this DNA sequence. Copyright 1994 S. Karger AG, Basel

Natural variants of the HIV-1 long terminal repeat: analysis of promoters with duplicated DNA regulatory motifs.

Sequence variation in the long terminal repeat (LTR) region of HIV-1 was analyzed in viral isolates of 17 infected individuals. Two classes of LTR size variants were found. One HIV-1 variant was detected containing an additional binding site for the transcription factor Sp1. Another LTR size variation was observed in four patients in a region just upstream of the NF-kappa B enhancer. This variation was the result of a duplication of a short DNA sequence (CTG-motif). Cell culture experiments demonstrated that the natural variant with four Sp1 sites had a slightly higher promoter activity and viral replication rate than the isogenic control LTR with three Sp1 sites. No positive effect of the duplicated CTG-motif could be detected. In order to measure small differences in virus production more accurately, equal amounts of a size variant and the wild-type plasmid were cotransfected into T-cells. The virus with four Sp1 sites did outgrow the three Sp1 virus in 35 days of culture and CTG-monomer virus outcompeted the CTG-dimer virus in 42 days. Based on these results we estimate a 5-10% difference in virus production of the LTR variants when compared to that of wild-type.

HLA-B27 as a receptor for cytomegalovirus.

Acute anterior uveitis (AAU) is strongly associated with the genetic marker and cell membrane protein HLA-B27. Although also other genetic factors must play a pathogenetic role, the HLA-class I molecule B27 is up to now the only hold. The normal task of HLA class I molecules is to present endogenous, mostly viral, peptides to receptors on cytotoxic T cells. It is possible that HLA molecules at the cell surface serve as viral receptors. Human cytomegalovirus (HCMV) particles have been found to bind beta 2m. This might promote infectivity by a binding to HLA alpha-chains on cell membranes. We studied this mechanism using mouse fibroblasts transfected for human HLA class I molecules. Susceptibility of these cells for HCMV was compared by measuring of HCMV immediate early antigen (IEA) expression. Earlier we observed that cells transfected with HLA-B27 alpha-chains and beta 2m were significantly more infected than cells expressing HLA-A2 + beta 2m or HLA-B7 or HLA-B27 without beta 2m. However, studying another four, separately transfected, cell lines, all expressing HLA-B27 and beta 2m, three of the five B27 cell lines showed low IEA levels. The degree of infectivity was independent of the degree of B27 expression. These results do not support the previous suggestion that HLA-B27 might act as an HCMV receptor.

Detection of latent human cytomegalovirus in organ tissue and the correlation with serological status.

The presence of human cytomegalovirus (HCMV) genome in spleen tissue was studied by using DNA hybridization techniques in seropositive and seronegative organ donors without clinical or laboratory confirmed HCMV infection. The serum samples of these patients were screened by latex agglutination test (LA) and enzyme linked immuno sorbent assay (ELISA) for the presence of HCMV antibodies, and confirmed by immunoblotting technique (IB). For the detection of HCMV sequences in spleen tissue dot blot DNA hybridization (DBH) using probes derived from immediate-early and late regions (ES and BH fragment respectively) of the HCMV genome were used. Samples positive in DBH were further tested by in situ DNA hybridization (ISH) using the ES probe. The number of spleen tissue specimens positive for HCMV nucleic acids indicated that HCMV may be present in human beings, even without serological evidence.

Expression of HLA class I heavy chains and beta 2-microglobulin does not affect human cytomegalovirus infectivity.

Human cytomegalovirus (HCMV) purified from urine or tissue culture supernatant has been reported to contain beta 2-microglobulin (beta 2m), which forms the light chain of HLA class I molecules. It has been postulated that HCMV covered with beta 2m binds to HLA class I alpha-chains at the cell surface. In the present study we used transfected human and mouse cell lines expressing distinct allelic forms of HLA class I and beta 2m to determine whether HLA class I molecules could act as cellular receptors for HCMV. The susceptibility of cells to HCMV infection was estimated by calculating the percentage of cells expressing HCMV immediate early antigens. Although the results showed some variation between different transfected cell clones, no correlation was found between expression of HLA class I on the cell membrane and HCMV infection. Preincubation of HLA class I-positive cells with antibodies against HLA class I antigens inhibited HCMV infection after binding and adsorption of HCMV. Trypsin prevented HCMV infection of both class I-positive and class I-negative cells. We conclude that these results do not support the assumption that HLA class I molecules are functional receptors for HCMV.

Phosphate-methylated DNA aimed at HIV-1 RNA loops and integrated DNA inhibits viral infectivity.

Phosphate-methylated DNA hybridizes strongly and specifically to natural DNA and RNA. Hybridization to single-stranded and double-stranded DNA leads to site-selective blocking of replication and transcription. Phosphate-methylated DNA was used to interrupt the life cycle of the human immunodeficiency virus type-1 (HIV-1), the causative agent of acquired immunodeficiency syndrome (AIDS). Both antisense and sense phosphate-methylated DNA 20-nucleotide oligomers, targeted at the transactivator responsive region and the primer binding site, caused complete inhibition of viral infectivity at a low concentration. Hybridization of phosphate-methylated DNA with folded and unfolded RNA was studied by ultraviolet and proton nuclear magnetic resonance spectroscopy. The combined results of hybridization studies and biological experiments suggest that the design of effective antisense phosphate-methylated DNA should focus on hairpin loop structures in the viral RNA. For sense systems, the 5' end of the integrated viral genome is considered to be the important target site.

Serum capacity to inhibit reverse transcriptase in vitro distinguishes HIV-1 infection from HIV-2 or SIV infection.

The inhibition of HIV-1 and SIV reverse transcriptase by human and rhesus macaque serum positive for HIV-1 or HIV-2/SIV antibodies was studied. The domain to which reverse transcriptase-inhibiting antibodies were elicited appeared to be highly antigenic. A total of 67% (48 of 72) of individuals had HIV-1 reverse transcriptase-inhibiting (RTI) antibodies 1 year after seroconversion for HIV-1, 90% (9 of 10) of HIV-2 antibody positive persons had SIV RTI antibodies, and all four experimentally SIV-infected rhesus macaques developed SIV RTI antibodies. Low cross-reactivity between HIV-1 and HIV-2/SIV RTI antibodies was observed. Of 10 HIV-1 RTI sera, 2 reduced SIV RT activity by more than 50% (mean reduction 85 versus 24%). Only 1 of 9 SIV RTI human sera reduced HIV-1 RT (mean reduction 74 versus 25%). This serum, however, showed a shared reactivity against both HIV-1 and HIV-2. These results indicate that the HIV-1 domain inducing RTI antibodies is antigenically different from the HIV-2/SIV domain.

Heat-shock induction of the human immunodeficiency virus long terminal repeat.

Rat cell lines were established in which the bacterial chloramphenicol acetyltransferase (CAT) gene under control of the human immunodeficiency virus (HIV) long terminal repeat (LTR) was stably integrated. The cell lines showed a repressed phenotype for CAT expression, but could be induced for it by inhibition of protein synthesis, as well as by heat-shock and chemical inducers of the cellular stress response, such as sodium arsenite, 8-hydroxyquinoline and the heavy metals cadmium and copper. A decameric sequence present in the NF-kB binding sites in the HIV LTR (GGGACTTTCC) resembles the cellular heat-shock core sequence and may therefore be involved in the heat-shock response.

Induction of gene expression under human cytomegalovirus immediate early enhancer-promoter control by inhibition of protein synthesis is cell cycle-dependent.

In this paper we describe stably transfected rat cell lines which harbour either the human cytomegalovirus (HCMV) immediate early (IE) gene encoding the 72K IE nuclear antigen (IEA) or the bacterial chloramphenicol acetyltransferase (CAT) gene both under transcriptional control of the HCMV IE enhancer-promoter (-484 to -19 relative to the IE cap site, +1). In these cell lines IE gene or CAT gene expression is repressed but can be induced by heat-shock, by sodium arsenite and by inhibitors of protein synthesis such as cycloheximide (CH). In addition, we present evidence suggesting that CH-mediated activation is cell cycle-dependent. Thus CH-mediated induction of the 72K IEA as well as CAT gene expression was impaired and accumulation of mRNAs did not occur when cellular DNA synthesis was inhibited. Activation of IE genes by CH occurred almost exclusively in those cells which were in S-phase. In contrast, activation of gene expression by sodium arsenite occurred independently of cellular DNA synthesis and was not restricted to cells in S-phase. The data are consistent with, but not proof of, the hypothesis that the activation of IE transcription, brought about by inhibition of protein synthesis, resulted from a disturbed chromatin conformation due to DNA synthesis continuing in the absence of a supply of chromatin-organizing proteins. The possible relevance of these observations with regard to HCMV latency and reactivation is discussed.

Analysis and isolation of cytomegalovirus DNA by field inversion gel electrophoresis.

High molecular weight human cytomegalovirus (CMV) DNA was isolated from agarose-embedded infected human diploid cells by employing field inversion gel electrophoresis. A high yield of CMV DNA molecules was obtained within 1 week of infecting the cell culture. Labelling of the viral DNA with biotin by nick translation enabled the detection of CMV-infected cells in sections of paraffin-embedded human adrenal gland by in situ hybridization.

Non-radioactive in situ hybridization for the detection of cytomegalovirus infections.

Acetylaminofluorene (AAF) modified cytomegalovirus (CMV) DNA probes have been applied for the rapid detection of CMV genomes by non-radioactive in situ hybridization in routinely obtained pathological material. To establish proper protocols, AAF modified mouse satellite DNA and mouse liver were used to investigate the procedural variables. Among these were type and time of fixation, glass slide coating for improved tissue adherence, protease permeabilization of sections, type and time of denaturation and hybridization, probe concentration, post-hybridization washing conditions and immunocytochemical detection. This research has led to a user-friendly procedure which, in addition to cells displaying a cytopathological effect typical for CMV infection, detects with high sensitivity CMV carrying cells that show no histo-pathological alterations. It can be readily applied in routine clinical-diagnostic laboratories.

Resistance to methylation de novo of the human cytomegalovirus immediate early enhancer in a model for virus latency and reactivation in vitro.

Rat-9G cells carry several stably integrated copies of the major immediate early (IE) transcription unit of the human cytomegalovirus (HCMV). In these cells IE expression is repressed but inducible. In this report we describe the DNA methylation status of HpaII, HhaI and AhaII sites within the IE gene, determined at different passage levels. Most, if not all, of the resident IE genes were progressively methylated in a similar fashion. This resulted in DNA methylation patterns in which sites surrounding the IE upstream region were preferentially methylated to a high degree. In contrast, sites within the 19 bp IE enhancer elements were markedly under-methylated. This particular DNA methylation pattern probably resulted from differences in DNA methylation rates, sites within the IE enhancer being methylated at only a very low rate. Methylation of the IE genes did not affect their inducibility, which might be related to the very low methylation level of the IE enhancer.

Transcriptional activation of the major immediate early transcription unit of human cytomegalovirus by heat-shock, arsenite and protein synthesis inhibitors.

In Rat-9G cells several copies of the major immediate early (IE) transcription unit (regions 1 and 2) of the human cytomegalovirus (HCMV) are stably integrated. The cells show a repressed phenotype for IE expression but can be induced by inhibition of protein synthesis. In this report we present evidence that the repressed phenotype is due to the absence of IE transcription and that heat-shock and sodium arsenite treatments each result in the transcriptional activation of the repressed IE transcription unit. Either treatment resulted in the induction of HCMV IE transcripts and IE nuclear antigen expression. An octameric DNA sequence present in three of the 18 bp IE enhancer elements (GGACTTTC) resembles the cellular heat-shock element core consensus sequence and may therefore be involved in the heat-shock response.