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PubMed2002

An unbalanced translocation involving chromosome 14 is the probable cause for loss of potentially functional rearranged immunoglobulin heavy chain genes in the Epstein-Barr virus-positive Hodgkin's lymphoma-derived cell line L591.

In the vast majority of cases, Hodgkin-Reed Sternberg (H-RS) cells, the malignant cells in Hodgkin's lymphoma (HL), are derived from germinal centre B cells. In some cases, somatic mutations within the rearranged immunoglobulin heavy (IgH) chain genes were detected, rendering potentially functional gene rearrangements non-functional. In these H-RS cells the expression of high-affinity B-cell receptors (BCR) was prevented. As in other cases only one non-productive IgH chain gene rearrangement was amplified from H-RS cells, it was speculated whether, in these cases, the functionally rearranged IgH chain genes were lost. An alternative explanation might be that the rearranged genes could not be amplified owing to a high load of somatic mutations within the primer binding sites. Here, we showed that, in the HL-derived Epstein-Barr virus (EBV)-positive cell line L591, only one non-functional somatically mutated IgH gene rearrangement could be detected. The other potentially functional IgH gene rearrangement was lost as a result of an unbalanced translocation affecting the long arm of chromosome 14. Moreover, L591 cells express the EBV latent membrane proteins LMP1 and LMP2A, which might have contributed to the 'escape' of these cells from apoptosis within the germinal centre. We conclude that, apart from the introduction of 'crippling mutations' into the rearranged VDJ genes rearrangement, deletions of the IGH locus may be regarded as another mechanism to prevent the expression of a BCR in H-RS cells.

Amino Acid Sequence↗

PubMed1996

Homocysteine response to methionine challenge in four obligate heterozygotes for homocystinuria and relationship with cystathionine beta-synthase mutations.

Fasting and post-methionine load plasma total homocysteine concentrations were investigated in the parents of two homocystinuric patients. Three genetic mutations in the cystathionine beta-synthase gene were found. In the patient of family 1, a frequent Caucasian mutation. T833C, was found on one allele, while the mutation on the other allele has not yet been defined. In the patient of family 2, a mutation C569T, recently described by Sperandeo and colleagues, was found on one allele, while a novel mutation, G346A, was characterized on the other allele. The frequent gene mutation T833C was detected in a heterozygous mother who, surprisingly, exhibited strictly normal fasting and post-methionine load homocysteinaemia. In contrast, in the other family, we found a novel mutation (G346A) in the mother located near Lys 119, the putative binding site of phosphopyridoxal phosphate. This mother exhibited increased fasting and post-methionine load homocysteinaemia. These observations could explain the conflicting results reported for vascular pathologies in parents of homocystinuric patients and direct the search for genetic mutations in these vascular pathologies.

Adolescent↗

PubMed2001

Effect of multiple mutations in the core promoter and pre-core/core region of hepatitis B virus genome on the response to interferon in e antigen-positive chronic hepatitis B.

BACKGROUND AND AIMS: Hepatitis B virus (HBV) genomic mutations may be one of the factors that influence the efficacy of interferon (IFN) therapy. The aim of this study was to investigate the effects of mutations in different parts of the HBV genome on IFN therapy. METHODS: We studied the baseline clinical, biochemical, serologic and virologic parameters in 17 patients with e antigen-positive chronic hepatitis B. The DNA sequence of the X gene and pre-core/core gene in serum samples of these patients was analyzed before the initiation of IFN therapy. RESULTS: All five patients with the T1762-A1764 mutation were IFN responsive, while among the 12 remaining patients, only two responded to therapy. Among five patients with both a pre-core A1896 mutation and a mutation in the epitope aa 107-118 of the core region, four were non-responders whereas the fifth responded to therapy. In three other patients with A1896 mutations, one with simultaneous mutations in five lymphocytic epitopes did not respond to therapy; the two remaining patients with concomitant mutations in one or two epitopes were responsive. Serum HBV-DNA levels were lower and titers of antibody to hepatitis B virus core antigen-immunoglobin M (anti-HBc-IgM) were higher in the responders than in the non-responders. Hepatitis B virus genotypes B and C were found to be in all these Chinese patients. CONCLUSIONS: These results suggest that HBV genomic mutations, serum viral loads and titers of anti-HBc-IgM might be predictive of the efficacy of IFN therapy. These clinical findings should be further investigated by in vivo and in vitro experiments.

Adult↗

PubMed2000

The Effects of a Bottleneck on Inbreeding Depression and the Genetic Load.

We study the effects of a population bottleneck on the inbreeding depression and genetic load caused by deleterious mutations in an outcrossing population. The calculations assume that loci have multiplicative fitness effects and that linkage disequilibrium is negligible. Inbreeding depression decreases immediately after a sudden reduction of population size, but the drop is at most only several percentage points, even for severe bottlenecks. Highly recessive mutations experience a purging process that causes inbreeding depression to decline for a number of additional generations. On the basis of available parameter estimates, the absolute fall in inbreeding depression may often be only a few percentage points for bottlenecks of 10 or more individuals. With a very high lethal mutation rate and a very slow population growth, however, the decline may be on the order of 25%. We examine when purging might favor a switch from outbreeding to selfing and find it occurs only under very limited conditions unless population growth is very slow. In contrast to inbreeding depression, a bottleneck causes an immediate increase in the genetic load. Purging causes the load to decline and then overshoot its equilibrium value. The changes are typically modest: the absolute increase in the total genetic load will be at most a few percentage points for bottlenecks of size 10 or more unless the lethal mutation rate is very high and the population growth rate very slow.

bottlenecks↗

PubMed2006

Low HBV-DNA levels in end-stage renal disease patients with HBeAg-negative chronic hepatitis B.

In end-stage renal disease patients treated by hemodialysis with HBeAg-negative chronic hepatitis B virus (HBV) infection, the evaluation of the presence of viral replication is essential in the assessment for renal transplantation. Data on HBV viral load, prevalence of precore mutations, as well as the influence of HCV coinfection on HBV-DNA levels in this group of patients is scarce. The aim of this study was to determine the HBV viral load in HBsAg-positive/HBeAg-negative hemodialysis patients; to compare HBV-DNA levels between isolated HBV infection carriers and HBV-HCV coinfected patients, and to evaluate the prevalence of precore mutations in these patients. Fifty hemodialysis patients with chronic HBeAg-negative HBV infection were studied. Viral load was determined by PCR (Amplicor HBV Monitor-Roche). The detection of precore mutations was made by sequencing. Of a total of 50 patients, 76% were male, with a mean age of 44 +/- 11 years. Anti-HCV was positive in 56% of patients. HBV-DNA was undetectable in 58% of patients; 24% had HBV-DNA <10,000 copies/ml, 12% between 10,000-100,000 copies/ml, and only 6% had HBV-DNA >100,000 copies/ml. There was no difference in the viral load of patients infected only by HBV and HBV-HCV co-infected patients (P = 0.96). Precore mutations were detected in only 8% of cases. In conclusion, hemodialysis patients with HBeAg-negative HBV infection had a low viral load. Precore mutations were infrequent and the presence of anti-HCV has not influenced the levels of HBV-DNA.

Adult↗

PubMed1997

Value of a ligase chain reaction assay for detection of ganciclovir resistance-related mutation 594 in UL97 gene of human cytomegalovirus.

Human cytomegalovirus (HCMV) isolates resistant to ganciclovir were found in patients undergoing therapy. Therefore, we have developed a new specific and sensitive method--a ligase chain reaction (LCR) assay--for detection of frequently encountered 594 mutated codon in ganciclovir (GCV) resistant virus. Previous studies characterized an alanine to valine change on codon 594 in resistant strains. A novel substitution in 594, alanine to glycine, is described which is also capable of conferring ganciclovir resistance. LCR products were analyzed on polyacrylamide gel- and the mutant was detected using a non radioactive method. The LCR product detection was then adapted to a microtitre plate format with a colorimetric detection. This method allowed the distinction of mutated GCV-resistant strains from sensitive strains with a high sensitivity, and the detection of a low percentage of mutated DNA in virus load. This assay could be useful in following the evolution of mutated DNA compared to viral infection.

Alanine↗

PubMed2006

Pollinator limitation and inbreeding depression in orchid species with and without nectar rewards.

Many orchids produce no nectar rewards. Foraging pollinators should visit more flowers per inflorescence in species with nectar, which could increase geitonogamous self-fertilization. If a history of selfing decreases genetic load, then nectar-producing orchids should harbour lower inbreeding depression than nectarless species. Here, I tested this hypothesis by quantifying inbreeding depression and pollinator limitation in populations of three closely related orchid species, one of which provides nectar. I also compared inbreeding depression for nectarless and nectar-producing species of orchids using published studies. All field populations expressed pollinator limitation, but the nectar-providing species was intermediate to the two nectarless species. All populations expressed inbreeding depression, and levels increased in later life-history stages. There was no tendency for nectarless species to express higher inbreeding depression either in experiments or published studies. Nectarless orchids may not express higher levels of inbreeding depression because pollinators fail to visit more flowers in nectar-bearing species, because such visitations do not result in greater selfing, and/or because higher selfing may be ineffective in purging the mutations that cause load.

Ecosystem↗

PubMed1995

vpr deletion mutant of simian immunodeficiency virus induces AIDS in rhesus monkeys.

In previous experiments, animals infected with SIVmac239 containing a point mutation in the vpr and nef genes developed AIDS-like symptoms after early reversion of the vpr and nef genes. Here we show that two animals in which the nef gene but not the vpr gene had reverted in the first few months did not develop disease during a 3-year observation period even after reversion to a functional vpr gene 70 weeks postinfection. To study the influence of a stable vpr mutation on virus load and pathogenesis, a 43-bp deletion was introduced into the vpr gene of SIVmac239on, a nef-open mutant of SIVmac239. Four rhesus monkeys were inoculated with the vpr deletion mutant (SIV delta vpr), and two control animals were infected with SIVmac239on. Both control animals had persistent antigenemia, high cell-associated virus loads, and elevated neopterin levels. They had to be euthanized 20 and 30 weeks postinfection because of AIDS-related symptoms. However, all four rhesus monkeys inoculated with SIV delta vpr showed only transiently detectable antigenemia. The cell-associated virus loads were high in three of the four animals. Two animals with AIDS-like symptoms had to be euthanized 71 and 73 weeks postinfection. The two remaining monkeys infected with SIV delta vpr were still alive 105 weeks postinfection. In contrast to the SIVmac239on-infected animals, SIV delta vpr-infected animals had strong humoral immune responses and intermittent cellular immune responses to SIV antigens. Our data show that a functional vpr gene is not necessary for pathogenesis. However, vpr-deficient SIVmac239 variants might be slightly attenuated, allowing some animals to resist progression to disease for an extended period of time.

Animals↗

PubMed2004

Mutation screening of the mitochondrial genome using denaturing high-performance liquid chromatography.

Over 170 known mutations of the mitochondrial genome are responsible for disease. Due to the unique features of mitochondrial genetics, such patients are clinically diverse and difficult to diagnose. As pathogenic mitochondrial DNA (mtDNA) mutations are mostly heteroplasmic, denaturing high-performance liquid chromatography (DHPLC) could be used to detect these heteroplasmic species and therefore act as a rapid screening test for mtDNA mutations. The entire mitochondrial genome was amplified by PCR in 40 overlapping regions. In addition, known mtDNA mutants were constructed for each of these regions using a PCR-based site-directed mutagenesis approach. These mutants were used as positive controls and showed a detection limit of 3-10% heteroplasmy by DHPLC (depending on the specific mutation) compared to 40% for conventional sequencing. To further validate the screening test, mtDNA from 17 patients with seven different pathogenic mutations was used to compare mutation detection by DHPLC and conventional sequencing. DHPLC had a sensitivity of 88% compared to 82% for sequencing. This increased to 100% sensitivity for DHPLC when excluding the m.8993T>G mutation. DHPLC analysis is therefore a sensitive, rapid and cost-effective method to screen for mutations in the mitochondrial genome. The role of pyrosequencing in the quantitation of mutant load for known mtDNA mutations was highlighted using the m.3243A>G mutation as an illustrative example. Pyrosequencing analysis was able to discriminate samples containing as little as 5% heteroplasmy and proved to be an accurate and reproducible method for estimation of mutant load.

Base Sequence↗

PubMed2025

Identification of a Highly Cooperative PROTAC Degrader Targeting GTP-Loaded KRAS(On) Alleles.

Kirsten rat sarcoma viral oncogene homologue (KRAS) is a frequently mutated oncogene in multiple types of cancer and is a high priority target for oncology drug development. There are many different KRAS mutations, including mutations that favor the GTP-loaded hydrolysis-incompetent "active" state of KRAS, KRAS(on), that can lead to tumorigenesis. However, small molecule interventions thus far have predominantly targeted single mutations of "inactive" GDP-loaded KRAS, KRAS(off), such as KRASG12C. Here, we address this gap through the development of heterobifunctional VHL-based PROTACs capable of engaging and degrading KRAS(on), thus addressing a wider range of KRAS mutations. By studying ternary complex affinity, stability, and binding modes using SPR and X-ray cocrystal structures, we identified PROTACs that exhibit high positive cooperativity in forming ternary complexes with VHL and GCP-loaded KRAS as representative of KRAS(on) variants. Degrader activity profiling in relevant cancer cells supported the discovery of ACBI4, a PROTAC which forms a highly stable and cooperative ternary complex between VHL and GTP-bound KRAS and which potently degrades KRASG12R, leading to antiproliferative effect in KRAS mutant-driven cancer cells. ACBI4 provides a new chemical tool for studying the impact of degrading KRAS(on) mutants, which is not possible with current pan-KRAS inhibitors or degraders.

Proto-Oncogene Proteins p21(ras)↗

PubMed2000

Inbreeding depression due to mildly deleterious mutations in finite populations: size does matter.

We studied the effects of population size on the inbreeding depression and genetic load caused by deleterious mutations at a single locus. Analysis shows how the inbreeding depression decreases as population size becomes smaller and/or the rate of inbreeding increases. This pattern contrasts with that for the load, which increases as population size becomes smaller but decreases as inbreeding rate goes up. The depression and load both approach asymptotic limits when the population size becomes very large or very small. Numerical results show that the transition between the small and the large population regimes is quite rapid, and occurs largely over a range of population sizes that vary by a factor of 10. The effects of drift on inbreeding depression may bias some estimates of the genomic rate of deleterious mutation. These effects could also be important in the evolution of breeding systems in hermaphroditic organisms and in the conservation of endangered populations.

Genetics, Population↗

PubMed2001

The Reed-Sternberg cell in classical Hodgkin's disease.

There has been substantial advances in our understanding of the nature of the Hodgkin/Reed-Sternberg (H/RS) cell in recent years. There is now compelling evidence that the H/RS cells in the vast majority of cases of classical Hodgkin's disease (CHD) are derived from the B-cell lineage and a major clonal population is present. The immunoglobulin heavy chain variable region gene generally has a high load of somatic mutations suggesting that the H/RS cells are derived from germinal center (GC) (GC) or post-GC cells. The cellular milieu in the tumour is largely determined by the cytokines and chemokines secreted by the H/RS cells and the surrounding reactive elements. The pattern of secretion is partially determined by signals transduced through direct surface interactions between H/RS cells and infiltrating T-cells. Immunosuppressive cytokines and cytokines that preferentially induce a TH2 type of immune response may be partially responsible for the escape of the H/RS cells from immune surveillance. Multiple genes that have been shown to be involved in neoplastic transformation have been studied in HD. The significance of the data generated has been difficult to interpret. Efforts have been made to study the global gene expression pattern of the H/RS cells. There are many difficulties inherent in this approach, but new insight into the pathogenesis and evolution of HD would be expected from the studies.

Clone Cells↗

PubMed1996

Annexin II modulates volume-activated chloride currents in vascular endothelial cells.

The membrane-associated, microfilament-binding protein annexin II is abundantly expressed in endothelial cells from calf pulmonary artery (CPAE cells). We have analyzed its role in the regulation of volume-activated chloride currents (ICl, vol) by loading the cells via the patch pipette with a peptide comprising the N-terminal 14 residues of annexin II. This sequence harbors the binding site for the intracellular annexin II ligand, p11, and the peptide interferes with the annexin II-p11 complex formation. Loading of a CPAE cell with this peptide caused a gradual decrease in the amplitude of ICl, vol during repetitive stimulations with a 28% hypotonic extracellular solution. This run down of the current was virtually absent in untreated cells and in cells that were loaded with a mutated 14-amino acid peptide, which has a single amino acid replacement known to result in a more than 1000 times reduced affinity for binding to p11. We conclude that annexin II-p11 complex formation is either directly or indirectly involved in the activation of ICl, vol in endothelial cells.

Animals↗

PubMedDate not supplied

Genetic load among four Andhra caste populations.

The effect of inbreeding on mortality is assessed through genetic load estimates among four caste populations, the Chakali, Kummari, Mangali, and Madiga of Andhra Pradesh, India. The regression coefficient "B" is positive and statistically not significant except in the Mangali where reduced fetal wastage with increased inbreeding coefficient is noted. The B/A values of the majority of populations suggest that the genetic load is mainly segregational. It is suggested that among the Kummari, the load is predominantly mutational for prereproductive mortality. Relatively higher values of intercept "A" are observed in the present study for low socioeconomic caste groups.

Consanguinity↗

PubMed1996

Hodgkin and Reed-Sternberg cells in Hodgkin's disease represent the outgrowth of a dominant tumor clone derived from (crippled) germinal center B cells.

In Hodgkin's disease (HD), the Hodgkin and Reed-Sternberg (HRS) cells represent only a minute population in the diseased tissue. The investigation of lineage derivation and clonal origin of these cells has yielded conflicting results. We have analyzed HRS cells micromanipulated from infiltrated tissue sections of 10 primary HD patients for rearranged V genes, extending a previous study. Clonally related rearrangements were found in nine cases, indicating that HRS cells represent a dominant clone of B lineage-derived cells in at least a large fraction of cases of HD. Rearranged VH genes from HRS cells carried a high load of somatic mutation, indicating that HRS cells are derived from germinal center (GC) cells or their progeny. Stop codons in some in-frame V gene rearrangements suggest that the HRS cell precursors reside inside GCs, have acquired crippling mutations that prevent antigenic selection, but escape apoptosis through some transforming event.

Adolescent↗

PubMed2004

The rise and fall of triple nucleoside reverse transcriptase inhibitor (NRTI) regimens.

Triple nucleoside reverse transcriptase inhibitor (NRTI) regimens have attracted much interest due to their potential to (1) simplify dosing, with potential gains in adherence to treatment, and (2) reduce or even reverse dyslipidaemia associated with protease inhibitor (PI) therapy. A variety of triple NRTI combinations have been investigated, in both antiretroviral-naive and antiretroviral-experienced HIV-infected patients. Many of these trials have generated disappointing results, and some have been prematurely discontinued due to poor efficacy. This article reviews the background to the development of triple NRTI regimens, and the mounting evidence that this approach is suboptimal for antiretroviral-naive patients. Indeed, some triple NRTI regimens should never be used in this population. A role for triple NRTI combinations as a simplification strategy in treatment-experienced patients whose HIV is well controlled has been suggested, but emerging evidence indicates that such an approach can, under adequate selection pressure, lead to the emergence of mutations and viral load rebound. This commentary discusses the factors that appear to influence patients' responses to triple NRTI therapy, and their implications for patient selection.

Clinical Trials as Topic↗

PubMed1997

Germinal center development.

Using a set of surface markers including IgD and CD38, human tonsillar B cells were classified into discrete subpopulations. Molecular and functional analysis allowed us to identify: i) two sets of naive B cells (Bm1 and Bm2); ii) germinal center founder cells (Bm2'); iii) an obscure population of germinal center B cells, displaying a high load of somatic mutations in IgV genes, C mu to C delta switch and preferential Ig lambda light chain usage: these cells may represent the precursors of normal and malignant IgD-secreting plasma cells; iv) the centroblasts (Bm3) in which somatic mutation machinery is activated; v) the centrocytes (Bm4) in which isotype switch occurs; vi) the memory B cells. The characterization of these subpopulations showed that: i) programmed cell death is set before somatic mutations, possibly providing an efficient way for affinity maturation; ii) only high affinity centrocytes are allowed to switch isotype; iii) CD40-ligation inhibits plasmacytic differentiation of mature B lymphocytes; iv) memory B cells preferentially differentiate into plasma cells; v) IgD isotype switch occurs in normal B cells; vi) receptor editing may be induced by somatic mutations in germinal centers. We also characterized two types of antigen-presenting cells in germinal centers: follicular dendritic cells that select high affinity B cells, and a new subset of germinal center dendritic cells that activate germinal center T cells.

Animals↗

PubMed1999

Cellular origin and clonality of classic Hodgkin's lymphoma: immunophenotypic and molecular studies.

The cellular origin of Hodgkin and Reed-Sternberg (HRS) cells, the neoplastic cells of classic Hodgkin's lymphoma (HL), resisted clarification until the second half of this decade. One major obstacle to successful experimental investigations was the rarity of the HRS cells in the tissue affected by HL. Immunophenotypical studies using monoclonal antibodies already pointed in the early 1980s towards a lymphocytic origin for HRS cells, but were not definitive because of the usually variable expression of B-cell and/or T-cell antigens, and the additional expression of markers typical for other cell lineages, especially dendritic cells. Attempts to elucidate the cellular derivation of HRS cells by demonstrating the clonal rearrangements of the immunoglobulin (Ig) or T-cell receptor (TCR) genes in the DNA of whole-tissue extracts also remained inconclusive due to inconsistent results. In frustration with whole-tissue DNA studies, genetic approaches were turned to the single cell level. Among the techniques developed for the isolation of HRS cells, the extraction of single CD30+ HRS cells from immunostained frozen sections by means of hydraulic micromanipulation proved to be the most suitable. Using this method, monoclonal Ig gene rearrangements were detected in the HRS cells in 36 of 38 (95%) HL cases. Sequence analysis demonstrated high loads of somatic mutation in the rearranged variable regions. Molecular investigation of three cases of HL occurring in association with non-Hodgkin's lymphomas (NHLs) showed that all of the lymphoma lesions had an identical precursor with the molecular features of a germinal center B cell. In summary, these findings indicate that (1) approximately 95% of classic HLs originate from B cells; (2) the direct cellular precursors of the HRS cells are germinal center B cells; (3) the transforming event that causes HL leads to the complete morphologic and immunophenotypical change of the HRS cell precursors; and (4) the HRS cell population of a given case exclusively arises from a single transformed cell and expands by clonal growth. It remains to be shown whether the 5% of HLs for which a B-cell derivation could not be demonstrated are T-cell related.

Cell Lineage↗