Biomedical subjects

Gideon Rechavi

Publications and source records attributed to Gideon Rechavi.

At least 37 records · Page 2Linked to original sources

PubMed2005

Proliferation response of leukemic cells to CD70 ligation oscillates with recurrent remission and relapse in a low-grade lymphoma.

Interactions of the TNF-related cell surface ligand CD70 with its receptor CD27 provide a costimulatory signal in B and T cell activation. Functional CD70-CD27 interactions could contribute to lymphoma and leukemia progression. This possibility was studied using DNA microarrays on a unique case of low-grade lymphoma/leukemia characterized by recurrent cycles of acute leukemic phase alternating with spontaneous remission. Upon induction of the acute phase expression of CD70 and CD27 in the leukemic cells increased 38- and 25-fold, respectively. Coexpression of membrane CD70 and CD27 on the leukemic (CD5+CD19+) cells was maximal 2-3 days following initiation of the attack. Soluble CD27 in the patient's serum was elevated during remission and further increased in the attack. Functional tests showed that neither anti-CD70 nor anti-CD27 Abs affect the rate of apoptosis. However, the anti-CD70 Ab specifically enhanced proliferation of the remission phase leukemic cells, whereas proliferation of the acute-phase counterparts that express higher level of membrane CD70 was unaffected. Hence, in this lymphoma/leukemia, membrane CD70 is presented on the leukemic cells in a responsive state during the remission and a nonresponsive state during the attack. Presumably, CD70 in its responsive state provides a costimulatory receptor for initiating the next acute phase while its nonresponsive state enables the remission.

Antigens, CD↗

PubMed2005

BCL6 is regulated by p53 through a response element frequently disrupted in B-cell non-Hodgkin lymphoma.

The BCL6 transcriptional repressor mediates survival, proliferation, and differentiation blockade of B cells during the germinal-center reaction and is frequently misregulated in B-cell non-Hodgkin lymphoma (BNHL). The p53 tumor-suppressor gene is central to tumorigenesis. Microarray analysis identified BCL6 as a primary target of p53. The BCL6 intron 1 contains a region in which 3 types of genetic alterations are frequent in BNHL: chromosomal translocations, point mutations, and internal deletions. We therefore defined it as TMDR (translocations, mutations, and deletions region). The BCL6 gene contains a p53 response element (p53RE) residing within the TMDR. This p53RE contains a motif known to be preferentially targeted by somatic hypermutation. This p53RE is evolutionarily conserved only in primates. The p53 protein binds to this RE in vitro and in vivo. Reporter assays revealed that the BCL6 p53RE can confer p53-dependent transcriptional activation. BCL6 mRNA and protein levels increased after chemotherapy/radiotherapy in human but not in murine tissues. The increase in BCL6 mRNA levels was attenuated by the p53 inhibitor PFT-alpha. Thus, we define the BCL6 gene as a new p53 target, regulated through a RE frequently disrupted in BNHL.

Animals↗

PubMed2005

Gene expression analysis reveals a strong signature of an interferon-induced pathway in childhood lymphoblastic leukemia as well as in breast and ovarian cancer.

On the basis of epidemiological studies, infection was suggested to play a role in the etiology of human cancer. While for some cancers such a role was indeed demonstrated, there is no direct biological support for the role of viral pathogens in the pathogenesis of childhood leukemia. Using a novel bioinformatic tool that alternates between clustering and standard statistical methods of analysis, we performed a 'double-blind' search of published gene expression data of subjects with different childhood acute lymphoblastic leukemia (ALL) subtypes, looking for unanticipated partitions of patients, induced by unexpected groups of genes with correlated expression. We discovered a group of about 30 genes, related to the interferon response pathway, whose expression levels divide the ALL samples into two subgroups; high in 50, low in 285 patients. Leukemic subclasses prevalent in early childhood (the age most susceptible to infection) are over-represented in the high-expression subgroup. Similar partitions, induced by the same genes, were found also in breast and ovarian cancer but not in lung cancer, prostate cancer and lymphoma. About 40% of breast cancer samples expressed the 'interferon-related' signature. It is of interest that several studies demonstrated mouse mammary tumor virus-like sequences in about 40% of breast cancer samples. Our discovery of an unanticipated strong signature of an interferon-induced pathway provides molecular support for a role for either inflammation or viral infection in the pathogenesis of childhood leukemia as well as breast and ovarian cancer.

Base Sequence↗

PubMed2005

Impaired genomic stability and increased oxidative stress exacerbate different features of Ataxia-telangiectasia.

Ataxia-telangiectasia (A-T) is a multisystem, cancer-predisposing genetic disorder caused by deficiency of the ATM protein. To dissect the A-T phenotype, we augmented specific features of the human disease by generating mouse strains that combine Atm deficiency with dysfunction of other proteins. Increasing oxidative stress by combining deficiencies in Atm and superoxide dismutase 1 (Sod1) exacerbated growth retardation and markedly reduced the mean survival time following ionizing radiation. In contrast, increasing genomic instability by combining deficiencies of Atm and the mismatch repair protein Mlh1 caused a moderate increase in radiation sensitivity and dramatic increase in aggressive lymphomas, compared with thes Atm-/- single knockout. Remarkably, Atm, Mlh1 or Mlh1/Atm single or double heterozygosity did not significantly affect the life span of the various genotypes. Mlh1/Atm double null tumors were polyclonal, whereas the tumors in other genotypes were mono- or oligoclonal, demonstrating the high predisposition of thymocytes with this genotype to become malignant. Chromosomal aberrations in the tumors were localized mainly in chromosomes 12 and 15. The genomic region on chromosome 15, which contains the gene for the c-Myc oncoprotein, was commonly amplified, and elevated levels of the c-Myc protein were subsequently observed in the tumors. Our data suggest that impaired genomic instability is an important contributing factor to cancer predisposition in A-T, whereas oxidative stress is more important in the radiation sensitivity and growth retardation facets of this disease.

Animals↗

PubMed2005

The nuclear-envelope protein and transcriptional repressor LAP2beta interacts with HDAC3 at the nuclear periphery, and induces histone H4 deacetylation.

Nuclear-envelope proteins have been implicated in diverse and fundamental cell functions, among them transcriptional regulation. Gene expression at the territory of the nuclear periphery is known to be repressed by epigenetic modifications such as histone deacetylation and methylation. However, the mechanism by which nuclear-envelope proteins are involved in such modifications is still obscure. We have previously shown that LAP2beta, an integral nuclear-envelope protein that contains the chromatin-binding LEM domain, was able to repress the transcriptional activity of the E2F5-DP3 heterodimer. Here, we show that LAP2beta's repressive activity is more general, encompassing various E2F members as well as other transcription factors such as p53 and NF-kappaB. We further show that LAP2beta interacts at the nuclear envelope with HDAC3, a class-I histone deacetylase, and that TSA (an HDAC inhibitor) abrogates LAP2beta's repressive activity. Finally, we show that LAP2beta is capable of inducing histone-H4 deacetylation. Our data provide evidence for the existence of a previously unknown repressive complex, composed of an integral nuclear membrane protein and a histone modifier, at the nuclear periphery.

Cell Line, Tumor↗

PubMed2005

Identification of RNA editing sites in the SNP database.

The relationship between human inherited genomic variations and phenotypic differences has been the focus of much research effort in recent years. These studies benefit from millions of single-nucleotide polymorphism (SNP) records available in public databases, such as dbSNP. The importance of identifying false dbSNP records increases with the growing role played by SNPs in linkage analysis for disease traits. In particular, the emerging understanding of the abundance of DNA and RNA editing calls for a careful distinction between inherited SNPs and somatic DNA and RNA modifications. In order to demonstrate that some of the SNP database records are actually somatic modification, we focus on one type of these modifications, namely A-to-I RNA editing, and present evidence for hundreds of dbSNP records that are actually editing sites. We provide a list of 102 RNA editing sites previously annotated in dbSNP database as SNPs, and experimentally validate seven of these. Interestingly, we show how dbSNP can serve as a starting point to look for new editing sites. Our results, for this particular type of RNA editing, demonstrate the need for a careful analysis of SNP databases in light of the increasing recognition of the significance of somatic sequence modifications.

Base Sequence↗

PubMed2005

Apolipoprotein E4 enhances brain inflammation by modulation of the NF-kappaB signaling cascade.

Apolipoprotein E4 (apoE4), the major genetic risk factor of Alzheimer's disease (AD), is associated with enhanced brain inflammation. Genome-wide gene expression profiling was employed to study the effects of apoE genotype on hippocampal gene expression in LPS-treated mice, transgenic for either apoE4 or the AD benign allele, apoE3. This revealed that the expression of inflammation-related genes following intracerebroventricular injection of LPS was significantly higher and more prolonged in apoE4 than in apoE3 transgenic mice. Clustering analysis revealed gene clusters which responded differently in apoE4 and apoE3 mice and were significantly enriched in NF-kappaB response elements. Direct measurement of NF-kappaB-regulated genes revealed that their extent of activation was greater in the apoE4 mice. Immunohistochemistry experiments revealed that microglial and NF-kappaB activation were more pronounced in apoE4 than in apoE3 mice. These findings suggest that the increased brain inflammation in apoE4 mice is related to disregulation of NF-kappaB signaling pathway.

Alzheimer Disease↗

PubMed2005

Disruption of cooperation between Ras and MycN in human neuroblastoma cells promotes growth arrest.

PURPOSE: Our aim was to examine whether active Ras and MycN cooperation contributes to the malignant phenotype of human neuroblastoma with amplified MycN gene, an aggressive incurable tumor. EXPERIMENTAL DESIGN: Human neuroblastoma LAN-1 cells, in which the MycN gene is amplified, were used to examine the impact of the Ras inhibitor farnesylthiosalicylic acid on cell growth, on the levels Ras and MycN proteins, and on profiles of gene expression. RESULTS: We show that LAN-1 cells express relatively large amounts of MycN and active Ras-GTP. Inhibition of active Ras by farnesylthiosalicylic acid led to attenuation of the Raf-MEK-ERK and phosphoinositide 3-kinase-Akt-glycogen synthase-3 (GSK-3) pathways, to reduction in cyclin D1, phospho-retinoblastoma, and E2F, and to increase in the cyclin-dependent kinase inhibitor p27 and in retinoblastoma-binding protein-1, an inhibitor of E2F transcriptional activity. Ras inhibition by farnesylthiosalicylic acid or by a dominant-negative Ras also led to complete disappearance of MycN protein from the nuclei of LAN-1 cells. This was a result of blocking of Akt inactivation of GSK-3, leading to GSK-3-dependent phosphorylation with consequent proteosomal degradation of MycN. Loss of active Ras and of MycN in LAN-1 cells was manifested in profiles of gene expression that could be expected from the loss of MycN transcriptional activity and of Ras signaling. These changes explain the farnesylthiosalicylic acid-induced inhibition of LAN-1 cell growth. CONCLUSIONS: Active Ras is needed to block MycN degradation, promoting cooperative Ras- and MycN-dependent cell cycle progression in LAN-1 cells. Ras inhibitors are therefore likely candidates for the treatment of advanced neuroblastoma characterized by high expression of MycN.

Carrier Proteins↗

PubMed2005

Dissection of a DNA-damage-induced transcriptional network using a combination of microarrays, RNA interference and computational promoter analysis.

BACKGROUND: Gene-expression microarrays and RNA interferences (RNAi) are among the most prominent techniques in functional genomics. The combination of the two holds promise for systematic, large-scale dissection of transcriptional networks. Recent studies, however, raise the concern that nonspecific responses to small interfering RNAs (siRNAs) might obscure the consequences of silencing the gene of interest, throwing into question the ability of this experimental strategy to achieve precise network dissections. RESULTS: We used microarrays and RNAi to dissect a transcriptional network induced by DNA damage in a human cellular system. We recorded expression profiles with and without exposure of the cells to a radiomimetic drug that induces DNA double-strand breaks (DSBs). Profiles were measured in control cells and in cells knocked-down for the Rel-A subunit of NFkappaB and for p53, two pivotal stress-induced transcription factors, and for the protein kinase ATM, the major transducer of the cellular responses to DSBs. We observed that NFkappaB and p53 mediated most of the damage-induced gene activation; that they controlled the activation of largely disjoint sets of genes; and that ATM was required for the activation of both pathways. Applying computational promoter analysis, we demonstrated that the dissection of the network into ATM/NFkappaB and ATM/p53-mediated arms was highly accurate. CONCLUSIONS: Our results demonstrate that the combined experimental strategy of expression arrays and RNAi is indeed a powerful method for the dissection of complex transcriptional networks, and that computational promoter analysis can provide a strong complementary means for assessing the accuracy of this dissection.

Ataxia Telangiectasia Mutated Proteins↗

PubMed2005

Nuclear envelopathies--raising the nuclear veil.

The nuclear envelope separates the chromosomes from cytoplasm in eukaryotic cells and consists of three main domains: inner and outer nuclear membranes and nuclear pore complexes. The inner nuclear membrane maintains close associations with the underlying chromatin and nuclear lamina. For many years, the nuclear envelope was thought to function mainly as an architectural stabilizer of the nucleus, participating in assembly and disassembly processes during mitosis. However, recent findings demonstrate that nuclear envelope proteins are involved in fundamental nuclear functions, such as gene transcription and DNA replication, and that inherited or de novo mutated proteins cause human diseases, termed "nuclear envelopathies." These findings emphasize the importance of understanding the functions of this cellular domain, in both physiologic and pathologic states. To date, mutations in the genes encoding the nuclear envelope proteins emerin, MAN1, lamin A/C, and lamin B receptor were found to cause nuclear envelopathies. The diseases that are caused by mutations in LMNA gene are collectively called "laminopathies." Nuclear envelopathies have diverse clinical phenotypes, ranging from cardiac and skeletal myopathies to partial lipodystrophy, peripheral neuropathy, and premature aging. This raises the question of how do such ubiquitously expressed proteins give rise to tissue-specific disease phenotypes. One possible explanation is the involvement of nuclear envelope proteins in the regulation of gene transcription, a novel mechanism that has been the focus of research in our lab in recent years. In this review, we describe recent discoveries in the field of nuclear envelopathies and discuss current proposed pathophysiological mechanisms underlying these diseases.

Animals↗

PubMed2005

p53--a key player in tumoral and evolutionary adaptation: a lesson from the Israeli blind subterranean mole rat.

p53 is a transcription factor involved in maintaining genomic integrity by regulating genes involved in cell cycle arrest, DNA repair, and programmed cell death. Various post transcriptional modifications result in activated p53 with varying binding affinity to its targets. The other members of the p53 family (p63, p73) and associated proteins also contribute to the specificity of gene activation resulting in the final cell responses. p53 is commonly mutated in human cancer and is activated by diverse cellular events, including hypoxia. Many sources of genetic diversity, including random or stress-related mutagenesis, affect normal species evolution. The blind subterranean mole rat lives in sealed underground tunnels, subjected to routine hypoxia due to abrupt and sharp changes in O2 supply. We cloned the mole rat's p53 gene and identified two amino acid substitutions in its binding domain, in the same positions that are mutated in cancer. These substitutions lead to increased p53 activation of DNA-repair elements and reduced activation of apoptotic genes. We propose that sequence-specific changes in the mole rat's p53 gene provide an example of how transcription factors that regulate many genes can also account for rapid and broad phenotypic diversity by altering the binding affinity to individual target genes.

Animals↗

PubMed2005

Evolutionarily conserved human targets of adenosine to inosine RNA editing.

A-to-I RNA editing by ADARs is a post-transcriptional mechanism for expanding the proteomic repertoire. Genetic recoding by editing was so far observed for only a few mammalian RNAs that are predominantly expressed in nervous tissues. However, as these editing targets fail to explain the broad and severe phenotypes of ADAR1 knockout mice, additional targets for editing by ADARs were always expected. Using comparative genomics and expressed sequence analysis, we identified and experimentally verified four additional candidate human substrates for ADAR-mediated editing: FLNA, BLCAP, CYFIP2 and IGFBP7. Additionally, editing of three of these substrates was verified in the mouse while two of them were validated in chicken. Interestingly, none of these substrates encodes a receptor protein but two of them are strongly expressed in the CNS and seem important for proper nervous system function. The editing pattern observed suggests that some of the affected proteins might have altered physiological properties leaving the possibility that they can be related to the phenotypes of ADAR1 knockout mice.

Adenosine↗

PubMed2005

Ras inhibition in glioblastoma down-regulates hypoxia-inducible factor-1alpha, causing glycolysis shutdown and cell death.

Active Ras and phosphatidylinositol-3-kinase-dependent pathways contribute to the malignant phenotype of glioblastoma multiformes (GBM). Here we show that the Ras inhibitor trans-farnesylthiosalicylic acid (FTS) exhibits profound antioncogenic effects in U87 GBM cells. FTS inhibited active Ras and attenuated Ras signaling to extracellular signal-regulated kinase, phosphatidylinositol-3-kinase, and Akt. Concomitantly, hypoxia-inducible factor 1alpha (HIF-1alpha) disappeared, expression of key glycolysis pathway enzymes and of other HIF-1alpha-regulated genes (including vascular endothelial growth factor and the Glut-1 glucose transporter) was down-regulated, and glycolysis was halted. This led to a dramatic reduction in ATP, resulting in a severe energy crisis. In addition, the expression of E2F-regulated genes was down-regulated in the FTS-treated cells. Consequently, U87 cell growth was arrested and the cells died. These results show that FTS is a potent down-regulator of HIF-1alpha and might therefore block invasiveness, survival, and angiogenesis in GBM.

Cell Death↗

PubMed2005

Vascular gene expression and phenotypic correlation during differentiation of human embryonic stem cells.

The study of the cascade of events of induction and sequential gene activation that takes place during human embryonic development is hindered by the unavailability of postimplantation embryos at different stages of development. Spontaneous differentiation of human embryonic stem cells (hESCs) can occur by means of the formation of embryoid bodies (EBs), which resemble certain aspects of early embryos to some extent. Embryonic vascular formation, vasculogenesis, is a sequential process that involves complex regulatory cascades. In this study, changes of gene expression along the development of human EBs for 4 weeks were studied by large-scale gene screening. Two main clusters were identified-one of down-regulated genes such as POU5, NANOG, TDGF1/Cripto (TDGF, teratocarcinoma-derived growth factor-1), LIN28, CD24, TERF1 (telomeric repeat binding factor-1), LEFTB (left-right determination, factor B), and a second of up-regulated genes such as TWIST, WNT5A, WT1, AFP, ALB, NCAM1. Focusing on the vascular system development, genes known to be involved in vasculogenesis and angiogenesis were explored. Up-regulated genes include vasculogenic growth factors such as VEGFA, VEGFC, FIGF (VEGFD), ANG1, ANG2, TGFbeta3, and PDGFB, as well as the related receptors FLT1, FLT4, PDGFRB, TGFbetaR2, and TGFbetaR3, other markers such as CD34, VCAM1, PECAM1, VE-CAD, and transcription factors TAL1, GATA2, and GATA3. The reproducibility of the array data was verified independently and illustrated that many genes known to be involved in vascular development are activated during the differentiation of hESCs in culture. Hence, the analysis of the vascular system can be extended to other differentiation pathways, allocating human EBs as an in vitro model to study early human development.

Antigens, CD34↗

PubMed2005

Microarray studies of prognostic stratification and transformation of follicular lymphomas.

Follicular lymphoma (FL) is a common, indolent malignancy with a natural history of transformation to the more aggressive form of diffuse large B-cell lymphoma (DLBCL) in 25-60% of cases. In order to understand the pathogenesis of lymphoma genesis and evolution, the molecular changes characteristic of FL and transformed DLBCL are being studied. The most common abnormality associated with FL is the t(14;18)(q32;q21) chromosomal translocation, but many more molecular aberrations have been found in patient subgroups. The study of gene expression profiling using DNA microarrays enables large scale, comparative analyses of gene expression. Its implementation in the research on FL has led to advances in disease diagnosis and classification and has the potential to lead to pathogenesis-based individualised therapies.

Cell Transformation, Neoplastic↗

PubMed2005

Acquisition of a Ph chromosome with minor BCR/ABL fusion in treatment-related myelodysplastic syndrome with chromosome 7 abnormalities in a patient treated for Hodgkin disease.

The patient reported in this study originally had Hodgkin disease that was treated heavily with multiple courses of combined chemotherapy and radiotherapy. Secondary myelodysplastic syndrome (MDS) with a complex karyotype with monosomy 7, deletion 7q31, and double deletion 7q31 developed 8 years later. During the course of the disease, conventional cytogenetics and interphase FISH (I-FISH) analysis detected a Ph chromosome and BCR/ABL fusion with mBCR rearrangement. Using a multiparametric cell scanning system that enables combined analysis with probes specific for 7/7q- and BCR/ABL in a single cell, we were able to demonstrate the presence of the BCR/ABL fusion only in cells with monosomy of chromosome 7 and 7q31 deletion, but not in cells with a normal chromosome 7 or with a double deletion of 7q31. We propose two possible models that may explain the appearance of the BCR/ABL fusion in the pre-existing treatment-related MDS clones characterized by chromosome 7 rearrangements.

Adult↗

PubMed2005

Is abundant A-to-I RNA editing primate-specific?

A-to-I RNA editing is common in all eukaryotes, and is associated with various neurological functions. Recently, A-to-I editing was found to occur frequently in the human transcriptome. In this article, we show that the frequency of A-to-I editing in humans is at least an order of magnitude higher than in the mouse, rat, chicken or fly genomes. The extraordinary frequency of RNA editing in human is explained by the dominance of the primate-specific Alu element in the human transcriptome, which increases the number of double-stranded RNA substrates.

3' Untranslated Regions↗

PubMed2005

Letter from the editor: Adenosine-to-inosine RNA editing in Alu repeats in the human genome.

Adenosine-to-inosine (A-to-I) RNA editing increases the complexity of the human transcriptome and is essential for maintenance of normal life in mammals. Most A-to-I substitutions occur within repetitive elements in the genome, mainly in Alu repeats. The phenomenon of A-to-I editing is far less abundant in mice, rats, chickens and flies than in humans, which correlates with the relative under-representation of Alu repeats in these non-primate genomes. Here, we review the recent results of bioinformatic and laboratory approaches that have estimated the extent of the editing phenomenon. We discuss the possible biological relevance of the editing pathway, its possible interaction with other cellular pathways that respond to double-stranded RNA and its possible contribution to the accelerated evolution of primates.

Adenosine↗