Velizar Shivarov

Bulgarian Academy of Sciences, Sofia, Oblast Sofiya-Grad, Bulgaria

Are you Velizar Shivarov?

Claim your profile

Publications (19)64.99 Total impact

  • Leukemia & lymphoma. 10/2014;
  • Source
    Velizar Shivarov, Lars Bullinger
    [Show abstract] [Hide abstract]
    ABSTRACT: Gene expression profiling (GEP) is a well-established indispensable tool to study hematologic malignancies, including leukemias. Here, we summarize the insights in the molecular basis of leukemias, which have been obtained by means of GEP, focusing especially on acute myeloid leukemia (AML), one of the first diseases to be extensively studied by GEP. Profiling mRNA and microRNA expression are discussed in view of their applicability for class prediction, class discovery and comparison as well as outcome prediction, and special attention is paid to the recent advances in our understanding of the role of alternative RNA splicing in AML. In addition to microarray-based GEP approaches, over the last few years RNA sequencing (RNA-Seq) based on next generation sequencing (NGS) technology is gaining wider recognition as an advanced tool for transcriptome profiling. Therefore, the advantages of RNA-Seq based GEP and its current and potential implications in AML will be discussed. Finally, we will also highlight recent efforts to integrate already available and newly acquired omics data sets so that a more precise understanding of AML biology and clinical behavior can be achieved, which ultimately will contribute to further refine leukemia management.
    Experimental hematology 04/2014; · 3.11 Impact Factor
  • Source
    V Shivarov, M Ivanova, R V Tiu
    Blood Cancer Journal 02/2014; 4:e185. · 1.40 Impact Factor
  • Source
    Velizar Shivarov, Milena Ivanova, Elissaveta Naumova
    [Show abstract] [Hide abstract]
    ABSTRACT: Mutations in the human DNA methyl transferase 3A (DNMT3A) gene are recurrently identified in several hematologic malignancies such as Philadelphia chromosome-negative myeloproliferative neoplasms (MPN), myelodysplastic syndromes (MDS), MPN/MDS overlap syndromes and acute myeloid leukemia (AML). They have been shown to confer worse prognosis in some of these entities. Notably, about 2/3 of these mutations are missense mutations in codon R882 of the gene. We aimed at the development and validation of a novel easily applicable in routine practice method for quantitative detection of the DNMT3A p.R882C/H/R/S mutations bead-based suspension assay. Initial testing on plasmid constructs showed excellent performance of BNA(NC)-modified probes with an optimal hybridization temperature of 66°C. The method appeared to be quantitative and showed sensitivity of 2.5% for different mutant alleles, making it significantly superior to direct sequencing. The assay was further validated on plasmid standards at different ratios between wild type and mutant alleles and on clinical samples from 120 patients with known or suspected myeloid malignancies. This is the first report on the quantitative detection of DNMT3A R882 mutations using bead-based suspension assay with BNA(NC)-modified probes. Our data showed that it could be successfully implemented in the diagnostic work-up for patients with myeloid malignancies, as it is rapid, easy and reliable in terms of specificity and sensitivity.
    PLoS ONE 01/2014; 9(6):e99769. · 3.53 Impact Factor
  • Velizar Shivarov
    Leukemia Research. 01/2014;
  • Velizar Shivarov, Petya Dimitrova, Tchavdar Vassilev
    Haematologica 09/2013; 98(9):e111-3. · 5.94 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Somatic DNA methyl transferase 3A (DNMT3A) mutations have been recognized recently as recurrent molecular aberrations in acute myeloid leukemia (AML). The precise role of these mutations in leukemogenesis remains elusive but a number of studies have already been conducted to study their potential prognostic value in AML patients with variable results. We performed a meta-analysis on published data from over 4500 AML patients to provide robust evidence supporting DNMT3A mutation testing in clinical setting for AML patients. Our meta-analysis showed that DNMT3A mutations were associated with M4 and M5 AML subtypes. Those mutations conferred significantly worse prognosis with both shorter OS (p=0.0004) and shorter RFS (p=0.002). Notably, DNMT3A mutations appeared to be an independent adverse prognostic factor also in younger patients with normal cytogenetics AML (OS (p=0.01) and RFS (p=0.0005)) and also in the subgroup of patients with high risk genotypes defined according to the criteria of the European Leukemia Net (ELN) (OS (p=0.002)). Therefore, DNMT3A mutational status can improve the risk stratification of AML patients in the setting of integrated mutational profiling.
    Leukemia research 08/2013; · 2.36 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: MicroRNAs are a class of small noncoding RNAs playing a crucial role in physiological and pathological conditions, including acute myeloid leukemia. We aimed at examining whether in clinical settings the identification of patient-specific leukemia-associated profiles (LAMPs) of overexpressed microRNAs could be used for minimal residual disease (MRD) detection. Patients with identified LAMPs at diagnosis were further tested for the presence of LAMP after induction therapy. Those with identifiable MRD defined by LAMP expression after induction showed a trend toward a shorter overall survival. Larger studies are needed to confirm the utility of patient-specific LAMPs for MRD follow-up.
    Hematology (Amsterdam, Netherlands) 04/2013; · 1.33 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Isocitrate dehydrogenase 1 and 2 (IDH) mutations are frequently found in various cancer types such as gliomas, chondrosarcomas and myeloid malignancies. Their molecular detection has recently gained wide recognition in the diagnosis and prognosis of these neoplasms. For that purpose various molecular approaches have been used but a universally accepted method is still lacking. In this study we aimed to develop a novel bead-based liquid assay using Locked nucleic acids (LNA)-modified oligonucleotide probes for multiplexed detection of the most frequent IDH1 (p.R132C, p.R132G, p.R132H, p.R132L, p.R132S) and IDH2 (p.R140Q, p.R172K) mutations. The method includes four steps: 1) PCR amplification of the targeted fragments with biotinylated primers; 2) Direct hybridization to barcoded microbeads with specific LNA-modified oligonucleotide probes; 3) Incubation with phycoerythrin coupled streptavidin; 4) Acquisition of fluorescent intensities of each set of beads on a flow platform (LuminexCorp., USA). We tested the performance of the assay on both artificial plasmid constructs and on clinical samples from 114 patients with known or suspected myeloid malignancies. The method appeared to be superior to direct sequencing having a much higher sensitivity of 2.5% mutant alleles. Applying this method to patients' samples we identified a total of 9 mutations (one IDH1 p.R132C, seven IDH2 p.R140Q and one IDH2 p.R172K). In conclusion, this method could be successfully implemented in the diagnostic work-up for various tumors known to harbor IDH1/2 mutations (e.g. myeloid malignancies, gliomas, etc.). International initiatives are needed to validate the different existing methods for detection of IDH1/2 mutations in clinical settings.
    PLoS ONE 01/2013; 8(9):e76944. · 3.53 Impact Factor
  • Leukemia & lymphoma 11/2012; · 2.61 Impact Factor
  • Xiwen Gu, Velizar Shivarov, Matthew P Strout
    [Show abstract] [Hide abstract]
    ABSTRACT: Activation-induced cytidine deaminase (AID) is expressed in germinal center B cells and initiates the events that lead to somatic hypermutation and class switch recombination of immunoglobulin genes. In addition to this fundamental role in immune diversification, aberrant targeting of AID activity contributes to point mutations and translocations of oncogenes associated with B-cell lymphoma. This review discusses recent findings on the role of AID in lymphomagenesis. AID is expressed in many malignancies of mature B-cell origin and contributes to the development of lymphoma in several mouse models. The mechanism that guides AID to its genetic target is unknown and may be relatively nonspecific, as numerous nonimmunoglobulin genes appear to be targeted by AID in both normal and neoplastic B cells. Indeed, AID binds to genes on every chromosome throughout the genome and can induce double-stranded DNA breaks that lead to chromosome translocations at these sites. Emerging evidence supports a key role of AID in lymphomagenesis through genome-wide off-target induction of point mutations and chromosome translocations. Additional work is needed to further define the full scope and consequences of off-target AID activity in human lymphoma as well as to understand the protective mechanisms that break down during the development and progression of disease.
    Current opinion in hematology 04/2012; 19(4):292-8. · 5.19 Impact Factor
  • Leukemia & lymphoma 07/2011; 52(12):2396-8. · 2.61 Impact Factor
  • Leukemia & lymphoma 06/2011; 52(10):2023-6. · 2.61 Impact Factor
  • Leukemia & lymphoma 06/2011; 52(9):1809-10. · 2.61 Impact Factor
  • Source
    Petya Dimitrova, Tchavdar Vassilev, Velizar Shivarov
    Arthritis & Rheumatology 06/2011; 63(10):3174-5; author reply 3175-7. · 7.48 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: MPL exon 10 mutations were the second class of mutations shown to be associated with the pathogenesis of some Philadelphia chromosome - negative myeloproliferative neoplasms (MPNs). Recently, their identification gained wide recognition in the diagnostic work-up for suspected cases of JAK2 V617F negative MPNs. Various molecular approaches have been applied, yet universally accepted method is still lacking. We aimed at development and validation of a novel bead-based liquid assay using Locked nucleic acids (LNA)-modified oligonucleotide probes for multiplexed detection of the following MPL mutations: W515L/K/A/R. Testing on both artificial plasmid constructs and on clinical samples revealed that the method was comparable in terms of specificity to direct sequencing and had a much higher sensitivity of 1% mutant alleles. This method could be successfully implemented in the diagnostic work-up for MPNs. Furthermore, this system allows further multiplexing for single-tube identification of different mutations associated with MPNs.
    Leukemia research 05/2011; 35(8):1120-3. · 2.36 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Activation-induced cytidine deaminase (AID) is the essential enzyme inducing the DNA cleavage required for both somatic hypermutation and class switch recombination (CSR) of the immunoglobulin gene. We originally proposed the RNA-editing model for the mechanism of DNA cleavage by AID. We obtained evidence that fulfils three requirements for CSR by this model, namely (i) AID shuttling between nucleus and cytoplasm, (ii) de novo protein synthesis for CSR, and (iii) AID-RNA complex formation. The alternative hypothesis, designated as the DNA-deamination model, assumes that the in vitro DNA deamination activity of AID is representative of its physiological function in vivo. Furthermore, the resulting dU was removed by uracil DNA glycosylase (UNG) to generate a basic site, followed by phosphodiester bond cleavage by AP endonuclease. We critically examined each of these provisional steps. We identified a cluster of mutants (H48A, L49A, R50A and N51A) that had particularly higher CSR activities than expected from their DNA deamination activities. The most striking was the N51A mutant that had no ability to deaminate DNA in vitro but retained approximately 50 per cent of the wild-type level of CSR activity. We also provide further evidence that UNG plays a non-canonical role in CSR, namely in the repair step of the DNA breaks. Taking these results together, we favour the RNA-editing model for the function of AID in CSR.
    Philosophical Transactions of The Royal Society B Biological Sciences 12/2008; 364(1517):569-75. · 6.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In the present work we established a rapid, cost-effective and high-throughput method for genotyping using a multiplexed microsphere-based suspension array platform - Luminex xMAP which enabled us to analyze 3 SNPs in the MBL2 gene promoter and 5' UTR, and 3 coding SNPs exon 1 haplotypes, associated with different levels of MBL2 expression. Using this system MBL2 diversity in four different ethnic groups, namely, Asian (Japanese), Caucasian, Hispanic and African-American-assessed. Results showed significant variability in terms of allele, genotype, and haplotype distribution. Characteristic MBL haplotype patterns were defined for each ethnic group. A prevalence of haplotypes coding functional proteins capable of complement activation and pathogen opsonization was observed. Regardless of the significant diversity of individual haplotypes, a high, almost similar (25-28%) proportion of haplotypes associated with MBL deficiency was found in the four ethic groups. The proportion of individuals homozygous for the haplotypes resulting in complete MBL2 deficiency was also significant (2-10%). Considering the role of MBL2 in innate immunity and as a clinically relevant marker, the genotyping approach developed and the knowledge of the genetic variation in different ethnic groups will be relevant to future medical genetic studies.
    Human Immunology 11/2008; 69(12):877-84. · 2.30 Impact Factor
  • Source
    Velizar Shivarov, Reiko Shinkura, Tasuku Honjo
    [Show abstract] [Hide abstract]
    ABSTRACT: Activation-induced cytidine deaminase (AID) is essential for the DNA cleavage that initiates both somatic hypermutation (SHM) and class switch recombination (CSR) of the Ig gene. Two alternative mechanisms of DNA cleavage by AID have been proposed: RNA editing and DNA deamination. In support of the latter, AID has DNA deamination activity in cell-free systems that is assumed to represent its physiological function. To test this hypothesis, we generated various mouse AID mutants and compared their DNA deamination, CSR, and SHM activities. Here, we compared DNA deamination, CSR, and SHM activities of various AID mutants and found that most of their CSR or SHM activities were disproportionate with their DNA deamination activities. Specifically, we identified a cluster of mutants (H48A, L49A, R50A, and N51A) with low DNA deamination activity but relatively intact CSR activity. Of note is an AID mutant (N51A) that retained CSR function but lost DNA deamination activity. In addition, an APOBEC1 mutation at N57, homologous to N51 of AID, also abolished DNA deamination activity but retained RNA editing activity. These results indicate that DNA deamination activity does not represent the physiological function of AID.
    Proceedings of the National Academy of Sciences 11/2008; 105(41):15866-71. · 9.81 Impact Factor

Publication Stats

80 Citations
64.99 Total Impact Points

Top co-authors View all

Institutions

  • 2011
    • Bulgarian Academy of Sciences
      • Stefan Angelov Institute of Microbiology
      Sofia, Oblast Sofiya-Grad, Bulgaria
  • 2008
    • University Children's Hospital Sofia Bulgaria
      Ulpia Serdica, Sofia-Capital, Bulgaria
    • Kyoto University
      • Graduate School of Medicine / Faculty of Medicine
      Kyoto, Kyoto-fu, Japan