Leon H F Mullenders

Leiden University Medical Centre, Leyden, South Holland, Netherlands

Are you Leon H F Mullenders?

Claim your profile

Publications (203)1079.96 Total impact

  • Experimental Cell Research 08/2014; · 3.37 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Rev3, the catalytic subunit of DNA polymerase ζ, is essential for translesion synthesis of cytotoxic DNA photolesions, whereas the Rev1 protein plays a noncatalytic role in translesion synthesis. Here, we reveal that mammalian Rev3(-/-) and Rev1(-/-) cell lines additionally display a nucleotide excision repair (NER) defect, specifically during S phase. This defect is correlated with the normal recruitment but protracted persistence at DNA damage sites of factors involved in an early stage of NER, while repair synthesis is affected. Remarkably, the NER defect becomes apparent only at 2 h post-irradiation indicating that Rev3 affects repair synthesis only indirectly, rather than performing an enzymatic role in NER. We provide evidence that the NER defect is caused by scarceness of Replication protein A (Rpa) available to NER, resulting from its sequestration at stalled replication forks. Also the induction of replicative stress using hydroxyurea precludes the accumulation of Rpa at photolesion sites, both in Rev3(-/-) and in wild-type cells. These data support a model in which the limited Rpa pool coordinates replicative stress and NER, resulting in increased cytotoxicity of ultraviolet light when replicative stress exceeds a threshold.
    Nucleic Acids Research 01/2014; · 8.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ultraviolet radiation is a highly mutagenic agent that damages the DNA by the formation of mutagenic photoproducts at dipyrimidine sites and by oxidative DNA lesions via reactive oxygen species (ROS). ROS can also give rise to mutations via oxidation of dNTPs in the nucleotide pool, e.g. 8-oxo-dGTP and 2-OH-dATP and subsequent incorporation during DNA replication. Here we show that expression of human MutT homolog 1 (hMTH1) which sanitizes the nucleotide pool by dephosphorylating oxidized dNTPs, protects against mutagenesis induced by long wave UVA light and by UVB light but not by short wave UVC light. Mutational spectra analyses of UVA-induced mutations at the endogenous Thymidine kinase gene in human lymphoblastoid cells revealed that hMTH1 mainly protects cells from transitions at GC and AT base pairs.
    Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 10/2013; · 4.44 Impact Factor
  • Source
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Distinct types of DNA damage elicit signaling and repair pathways that counteract the adverse effect of DNA lesions to maintain genome stability. The negatively charged polymer poly(ADP-ribose), which is catalyzed by poly(ADP-ribose) polymerase (PARP) enzymes, is a post-translational modification that serves as a chromatin-based platform for the recruitment of a variety of repair factors and chromatin-remodeling enzymes. Recent work implicates PARP3 in the efficient joining of DNA double-strand breaks during non-homologous end-joining (NHEJ), whereas PARP1 modulates the repair of UV-induced DNA lesions. Here we discuss emerging roles of PARP enzymes in mechanistically distinct DNA repair pathways and highlight unresolved issues and questions for future research.
    Trends in Biochemical Sciences 04/2013; · 13.52 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: BACKGROUND: The risk of developing cutaneous squamous cell carcinoma (SCC) is markedly increased in organ transplant recipients (OTRs) compared to the normal population. Next to sun exposure, the immunosuppressive regimen is an important risk factor for the development of SCC in OTRs. Various gene mutations (e.g. TP53) and genetic alterations (e.g. loss of CDKN2A, amplification of RAS) have been found in SCCs. The aim of this genome-wide study was to identify pathways and genomic alterations that are consistently involved in the formation of SCCs and their precursor lesions, actinic keratoses (AKs). METHODS: To perform the analysis in an isogenic background, RNA and DNA were isolated from SCC, AK and normal (unexposed) epidermis (NS) from each of 13 OTRs. Samples were subjected to genome-wide expression analysis and genome SNP analysis using Illumina's HumanWG-6 BeadChips and Infinium II HumanHap550 Genotyping BeadChips, respectively. mRNA expression results were verified by quantitative PCR. RESULTS: Hierarchical cluster analysis of mRNA expression profiles showed SCC, AK and NS samples to separate into three distinct groups. Several thousand genes were differentially expressed between epidermis, AK and SCC; most upregulated in SCCs were hyperproliferation related genes and stress markers, such as keratin 6 (KRT6), KRT16 and KRT17. Matching to oncogenic pathways revealed activation of downstream targets of RAS and cMYC in SCCs and of NFkappaB and TNF already in AKs. In contrast to what has been reported previously, genome-wide SNP analysis showed very few copy number variations in AKs and SCCs, and these variations had no apparent relationship with observed changes in mRNA expression profiles. CONCLUSION: Vast differences in gene expression profiles exist between SCC, AK and NS from immunosuppressed OTRs. Moreover, several pathways activated in SCCs were already activated in AKs, confirming the assumption that AKs are the precursor lesions of SCCs. Since the drastic changes in gene expression appeared unlinked to specific genomic gains or losses, the causal events driving SCC development require further investigation. Other molecular mechanisms, such as DNA methylation or miRNA alterations, may affect gene expression in SCCs of OTRs. Further study is required to identify the mechanisms of early activation of NFkappaB and TNF, and to establish whether these pathways offer a feasible target for preventive intervention among OTRs.
    BMC Cancer 02/2013; 13(1):58. · 3.32 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In pluripotent stem cells, DNA damage triggers loss of pluripotency and apoptosis as a safeguard to exclude damaged DNA from the lineage. An intricate DNA damage response (DDR) signaling network ensures that the response is proportional to the severity of the damage. We combined an RNA interference screen targeting all kinases, phosphatases, and transcription factors with global transcriptomics and phosphoproteomics to map the DDR in mouse embryonic stem cells treated with the DNA cross-linker cisplatin. Networks derived from canonical pathways shared in all three data sets were implicated in DNA damage repair, cell cycle and survival, and differentiation. Experimental probing of these networks identified a mode of DNA damage-induced Wnt signaling that limited apoptosis. Silencing or deleting the p53 gene demonstrated that genotoxic stress elicited Wnt signaling in a p53-independent manner. Instead, this response occurred through reduced abundance of Csnk1a1 (CK1α), a kinase that inhibits β-catenin. Together, our findings reveal a balance between p53-mediated elimination of stem cells (through loss of pluripotency and apoptosis) and Wnt signaling that attenuates this response to tune the outcome of the DDR.
    Science Signaling 01/2013; 6(259):ra5. · 7.65 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The WD40-repeat protein DDB2 is essential for efficient recognition and subsequent removal of ultraviolet (UV)-induced DNA lesions by nucleotide excision repair (NER). However, how DDB2 promotes NER in chromatin is poorly understood. Here, we identify poly(ADP-ribose) polymerase 1 (PARP1) as a novel DDB2-associated factor. We demonstrate that DDB2 facilitated poly(ADP-ribosyl)ation of UV-damaged chromatin through the activity of PARP1, resulting in the recruitment of the chromatin-remodeling enzyme ALC1. Depletion of ALC1 rendered cells sensitive to UV and impaired repair of UV-induced DNA lesions. Additionally, DDB2 itself was targeted by poly(ADP-ribosyl)ation, resulting in increased protein stability and a prolonged chromatin retention time. Our in vitro and in vivo data support a model in which poly(ADP-ribosyl)ation of DDB2 suppresses DDB2 ubiquitylation and outline a molecular mechanism for PARP1-mediated regulation of NER through DDB2 stabilization and recruitment of the chromatin remodeler ALC1.
    The Journal of Cell Biology 10/2012; 199(2):235-49. · 9.69 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In pluripotent stem cells, DNA damage triggers repair mechanisms, loss of pluripotency, and apoptosis, which acts as a safeguard to exclude cells containing damaged DNA from the lineage. The DNA damage response (DDR) signaling network that ensures that the response is proportional to the severity of the damage remains unresolved. Here, an RNAi screen targeting all kinases, phosphatases, and transcription factors was combined with global transcriptomics and phosphoproteomics to map the DDR in embryonic stem cells (ESC) treated with the DNA cross linker, cisplatin (CP). Integrated signaling networks were derived from shared overrepresented canonical pathways implicated in DNA damage repair, cell cycle & survival, and differentiation. Experimental probing of these networks identified a novel mode of DNA-damage induced Wnt/β-catenin signaling that constrains apoptosis. In contrast to loss-of-pluripotency and apoptosis, which are mediated by p53; silencing or deletion of the p53 gene demonstrates that genotoxic stress elicits Wnt signaling in a p53-independent manner. Instead, the latter occurs through downregulation of suppressors of Wnt/β-catenin signaling, including Csnk1a1 (CK1α). Our findings reveal a balance between p53-signaling that triggers elimination of stem cells and Wnt/β-catenin signaling that attenuates this response to tune the outcome of the DDR.
    19th MDO and 12th European Regional International society for the study of xenobiotics Meeting, The Netherlands; 06/2012
  • Ruben E A Musson, Leon H F Mullenders, Nico P M Smit
    [Show abstract] [Hide abstract]
    ABSTRACT: Calcineurin is a Ca(2+)-dependent serine/threonine phosphatase and the target of the immunosuppressive drugs cyclosporin and tacrolimus, which are used in transplant recipients to prevent rejection. Unfortunately, the therapeutic use of this drugs is complicated by a high incidence of skin malignancy, which has set off a number of studies into the role of calcineurin signaling in skin, particularly with respect to cell cycle control and DNA repair. Both UVA1 radiation and arsenic species are known to promote skin cancer development via production of reactive oxygen species. In light of the well-documented sensitivity of calcineurin to oxidative stress, we examined and compared the effects of UVA1 and arsenite on calcineurin signaling. In this paper, we show that physiologically relevant doses of UVA1 radiation and low micromolar concentrations of arsenite strongly inhibit calcineurin phosphatase activity in Jurkat and skin cells and decrease NFAT nuclear translocation in Jurkat cells. The effects on calcineurin signaling could be partly prevented by inhibition of NADPH oxidase in Jurkat cells or increased dismutation of superoxide in Jurkat and skin cells. In addition, both UVA1 and arsenite decreased NF-κB activity, although at lower concentrations, arsenite enhanced NF-κB activity. These data indicate that UVA1 and arsenite affect a signal transduction route of growingly acknowledged importance in skin and that calcineurin may serve as a potential link between ROS exposure and impaired tumor suppression.
    Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 05/2012; 735(1-2):32-8. · 4.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Nucleotide excision repair (NER) is the principal pathway that removes helix-distorting deoxyribonucleic acid (DNA) damage from the mammalian genome. Recognition of DNA lesions by xeroderma pigmentosum group C (XPC) protein in chromatin is stimulated by the damaged DNA-binding protein 2 (DDB2), which is part of a CUL4A-RING ubiquitin ligase (CRL4) complex. In this paper, we report a new function of DDB2 in modulating chromatin structure at DNA lesions. We show that DDB2 elicits unfolding of large-scale chromatin structure independently of the CRL4 ubiquitin ligase complex. Our data reveal a marked adenosine triphosphate (ATP)-dependent reduction in the density of core histones in chromatin containing UV-induced DNA lesions, which strictly required functional DDB2 and involved the activity of poly(adenosine diphosphate [ADP]-ribose) polymerase 1. Finally, we show that lesion recognition by XPC, but not DDB2, was strongly reduced in ATP-depleted cells and was regulated by the steady-state levels of poly(ADP-ribose) chains.
    The Journal of Cell Biology 04/2012; 197(2):267-81. · 9.69 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The recent steep increase in population dose from radiation-based medical diagnostics, such as computed tomography (CT) scans, requires insight into human health risks, especially in terms of cancer development. Since the induction of genetic damage is considered a prominent cause underlying the carcinogenic potential of ionizing radiation, we quantified the induction of micronuclei and loss of heterozygosity events in human cells after exposure to clinically relevant low doses of X rays. A linear dose-response relationship for induction of micronuclei was observed in human fibroblasts with significantly increased frequencies at doses as low as 20 mGy. Strikingly, cells exposed during S-phase displayed the highest induction, whereas non S-phase cells showed no significant induction below 100 mGy. Similarly, the induction of loss of heterozygosity in human lymphoblastoid cells quantified at HLA loci, was linear with dose and reached significance at 50 mGy. Together the findings favor a linear-no-threshold model for genetic damage induced by acute exposure to ionizing radiation. We speculate that the higher radiosensitivity of S-phase cells might relate to the excessive cancer risk observed in highly proliferative tissues in radiation exposed organisms.
    Radiation Research 04/2012; 177(5):602-13. · 2.70 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cellular responses to DNA-damaging agents involve the activation of various DNA damage signaling and transduction pathways. Using quantitative and high-resolution tandem mass spectrometry, we determined global changes in protein level and phosphorylation site profiles following treatment of SILAC (stable isotope labeling by amino acids in cell culture)-labeled murine embryonic stem cells with the anticancer drug cisplatin. Network and pathway analyses indicated that processes related to the DNA damage response and cytoskeleton organization were significantly affected. Although the ATM (ataxia telangiectasia mutated) and ATR (ATM and Rad3-related) consensus sequence (S/T-Q motif) was significantly overrepresented among hyperphosphorylated peptides, about half of the >2-fold-upregulated phosphorylation sites based on the consensus sequence were not direct substrates of ATM and ATR. Eleven protein kinases mainly belonging to the mitogen-activated protein kinase (MAPK) family were identified as being regulated in their kinase domain activation loop. The biological importance of three of these kinases (cyclin-dependent kinase 7 [CDK7], Plk1, and KPCD1) in the protection against cisplatin-induced cytotoxicity was demonstrated by small interfering RNA (siRNA)-mediated knockdown. Our results indicate that the cellular response to cisplatin involves a variety of kinases and phosphatases not only acting in the nucleus but also regulating cytoplasmic targets, resulting in extensive cytoskeletal rearrangements. Integration of transcriptomic and proteomic data revealed a poor correlation between changes in the relative levels of transcripts and their corresponding proteins, but a large overlap in affected pathways at the levels of mRNA, protein, and phosphoprotein. This study provides an integrated view of pathways activated by genotoxic stress and deciphers kinases that play a pivotal role in regulating cellular processes other than the DNA damage response.
    Molecular and Cellular Biology 12/2011; 31(24):4964-77. · 5.04 Impact Factor
  • Source
    DNA Repair and Human Health, 10/2011; , ISBN: 978-953-307-612-6
  • Source
    DNA Repair and Human Health, 10/2011; , ISBN: 978-953-307-612-6
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The accumulation of DNA damage is a slow but hazardous phenomenon that may lead to cell death, accelerated aging features and cancer. One of the most versatile and important defense mechanisms against the accumulation of DNA damage is nucleotide excision repair (NER), in which the Xeroderma pigmentosum group C (XPC) protein plays a prominent role. NER can be divided into global genome repair (GG-NER) and transcription coupled repair (TC-NER). XPC is a key factor in GG-NER where it functions in DNA damage recognition and after which the repair machinery is recruited to eliminate the DNA damage. Defective XPC functioning has been shown to result in a cancer prone phenotype, in human as well as in mice. Mutation accumulation in XPC deficient mice is accelerated and increased, resulting in an increased tumor incidence. More recently XPC has also been linked to functions outside of NER since XPC deficient mice show a divergent tumor spectrum compared to other NER deficient mouse models. Multiple in vivo and in vitro experiments indicate that XPC appears to be involved in the initiation of several DNA damage-induced cellular responses. XPC seems to function in the removal of oxidative DNA damage, redox homeostasis and cell cycle control. We hypothesize that this combination of increased oxidative DNA damage sensitivity, disturbed redox homeostasis together with inefficient cell cycle control mechanisms are causes of the observed increased cancer susceptibility in oxygen exposed tissues. Such a phenotype is absent in other NER-deficient mice, including Xpa.
    Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 07/2011; 728(3):107-17. · 4.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A network of DNA damage surveillance systems is triggered by sensing of DNA lesions and the initiation of a signal transduction cascade that activates genome-protection pathways including nucleotide excision repair (NER). NER operates through coordinated assembly of repair factors into pre- and post-incision complexes. Recent work identifies RPA as a key regulator of the transition from dual incision to repair-synthesis in UV-irradiated non-cycling cells, thereby averting the generation of unprocessed repair intermediates. These intermediates could lead to recombinogenic events and trigger a persistent ATR-dependent checkpoint signaling. It is now evident that DNA damage signaling is not limited to NER proficient cells. ATR-dependent checkpoint activation also occurs in UV-exposed non-cycling repair deficient cells coinciding with the formation of endonuclease APE1-mediated DNA strand breaks. In addition, the encounter of elongating RNA polymerase II (RNAPIIo) with DNA damage lesions and its persistent stalling provides a strong DNA damage signaling leading to cell cycle arrest, apoptosis and increased mutagenesis. The mechanism underlying the strong and strand specific induction of UV-induced mutations in NER deficient cells has been recently resolved by the finding that gene transcription itself increases UV-induced mutagenesis in a strand specific manner via increased deamination of cytosines. The cell removes the RNAPIIo-blocking DNA lesions by transcription-coupled repair (TC-NER) without displacement of the DNA damage stalled RNAPIIo. Deficiency in TC-NER associates with mutations in the CSA and CSB genes giving rise to the rare human disorder Cockayne syndrome (CS). CSB functions as a repair coupling factor to attract NER proteins, chromatin remodelers and the CSA-E3-ubiquitin ligase complex to the stalled RNAPIIo; CSA is dispensable for attraction of NER proteins, yet in cooperation with CSB is required to recruit XAB2, the nucleosomal binding protein HMGN1 and TFIIS. The molecular mechanisms by which these proteins bring about efficient TC-NER and trigger signaling after transcription arrest remain elusive; particularly the role of chromatin remodeling in TC-NER needs to be clarified in the context of anticipated structural changes that allow repair and transcription restart.
    DNA repair 05/2011; 10(7):743-50. · 3.36 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Heterozygous Patched1 (Ptc1(+/-)) mice are prone to medulloblastoma (MB), and exposure of newborn mice to ionizing radiation dramatically increases the frequency and shortens the latency of MB. In Ptc1(+/-) mice, MB is characterized by loss of the normal remaining Ptc1 allele, suggesting that genome rearrangements may be key events in MB development. Recent evidence indicates that brain tumors may be linked to defects in DNA-damage repair processes, as various combinations of targeted deletions in genes controlling cell-cycle checkpoints, apoptosis and DNA repair result in MB in mice. Non-homologous end joining (NHEJ) and homologous recombination (HR) contribute to genome stability, and deficiencies in either pathway predispose to genome rearrangements. To test the role of defective HR or NHEJ in tumorigenesis, control and irradiated Ptc1(+/-) mice with two, one or no functional Rad54 or DNA-protein kinase catalytic subunit (DNA-PKcs) alleles were monitored for MB development. We also examined the effect of Rad54 or DNA-PKcs deletion on the processing of endogenous and radiation-induced double-strand breaks (DSBs) in neural precursors of the developing cerebellum, the cells of origin of MB. We found that, although HR and NHEJ collaborate in protecting cells from DNA damage and apoptosis, they have opposite roles in MB tumorigenesis. In fact, although Rad54 deficiency increased both spontaneous and radiation-induced MB development, DNA-PKcs disruption suppressed MB tumorigenesis. Together, our data provide the first evidence that Rad54-mediated HR in vivo is important for suppressing tumorigenesis by maintaining genomic stability.
    Oncogene 05/2011; 30(47):4740-9. · 8.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Various in vitro test systems have been developed for genotoxic risk assessment in early drug development. However, these genotoxicity tests often show limited specificity, and provide limited insights into the mode of toxicity of the tested compounds. To identify genes that could serve as specific biomarkers for genotoxicity or oxidative stress, we exposed mouse embryonic stem (ES) cells to various genotoxic and oxidative stress-inducing compounds and performed genome-wide expression profiling. Differentially expressed genes were classified based on the fold-change of expression and their specificity for either genotoxic or oxidative stress. Promoter regions of four selected genes (Ephx1, Btg2, Cbr3 and Perp) were fused to a DsRed fluorescent reporter gene and stably integrated in mouse ES cells. Established stable reporter cell lines displayed significant induction of DsRed expression upon exposure to different classes of genotoxic and oxidative stress-inducing compounds. In contrast, exposure to non-genotoxic carcinogenic compounds did not induce DsRed expression even at cytotoxic doses. Expression of the Cbr3-DsRed reporter was more responsive to compounds that induce oxidative stress while the other three DsRed reporters reacted more specific to direct-acting genotoxic agents. Therefore, the differential response of the Btg2- and Cbr3-DsRed reporters can serve as indicator for the main action mechanism of genotoxic and oxidative stress-inducing compounds. In addition, we provide evidence that inhibition of DNA replication results in preferential activation of the Btg2-DsRed genotoxicity reporter. In conclusion, we have generated sensitive mouse ES cell reporter systems that allow detection of genotoxic and oxidative stress-inducing properties of chemical compounds and can be used in high-throughput assays.
    Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 03/2011; 709-710:49-59. · 4.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cockayne syndrome (CS) cells are defective in transcription-coupled repair (TCR) and sensitive to oxidizing agents, including ionizing radiation. We examined the hypothesis that TCR plays a role in ionizing radiation-induced oxidative DNA damage repair or alternatively that CS plays a role in transcription elongation after irradiation. Irradiation with doses up to 100 Gy did not inhibit RNA polymerase II-dependent transcription in normal and CS-B fibroblasts. In contrast, RNA polymerase I-dependent transcription was severely inhibited at 5 Gy in normal cells, indicating different mechanisms of transcription response to X rays. The frequency of radiation-induced base damage was 2 × 10(-7) lesions/base/Gy, implying that 150 Gy is required to induce one lesion/30-kb transcription unit; no TCR of X-ray-induced base damage in the p53 gene was observed. Therefore, it is highly unlikely that defective TCR underlies the sensitivity of CS to ionizing radiation. Overall genome repair levels of radiation-induced DNA damage measured by repair replication were significantly reduced in CS-A and CS-B cells. Taken together, the results do not provide evidence for a key role of TCR in repair of radiation-induced oxidative damages in human cells; rather, impaired repair of oxidative lesions throughout the genome may contribute to the CS phenotype.
    Radiation Research 02/2011; 175(4):432-43. · 2.70 Impact Factor

Publication Stats

7k Citations
1,079.96 Total Impact Points


  • 1970–2014
    • Leiden University Medical Centre
      • • Department of Toxicogenetics
      • • Department of Dermatology
      Leyden, South Holland, Netherlands
  • 2011
    • University of Copenhagen
      • The Novo Nordisk Foundation Center for Protein Research
      København, Capital Region, Denmark
  • 2010
    • Albany State University
      Georgia, United States
    • University of Münster
      Muenster, North Rhine-Westphalia, Germany
    • Technische Universität Berlin
      • Institut für Lebensmitteltechnologie und Lebensmittelchemie
      Berlin, Land Berlin, Germany
  • 2009
    • Hungarian Academy of Sciences
      • Institute of Genetics
      Budapeŝto, Budapest, Hungary
  • 2001–2009
    • University of Amsterdam
      • • Faculty of Medicine AMC
      • • Swammerdam Institute for Life Sciences
      Amsterdam, North Holland, Netherlands
    • University of North Carolina at Chapel Hill
      • Department of Biochemistry and Biophysics
      North Carolina, United States
  • 2007
    • Bulgarian Academy of Sciences
      Ulpia Serdica, Sofia-Capital, Bulgaria
  • 1998–2006
    • University Medical Center Utrecht
      Utrecht, Utrecht, Netherlands
    • University of Barcelona
      • Departament d'Anatomia Patològica, Farmacologia i Microbiologia
      Barcelona, Catalonia, Spain
  • 1983–2005
    • Leiden University
      • Leiden Amsterdam Center for Drug Research
      Leyden, South Holland, Netherlands
  • 2004
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2002
    • Autonomous University of Barcelona
      • Departamento de Genética y Microbiología
      Cerdanyola del Vallès, Catalonia, Spain
  • 1997
    • Universität Bremen
      Bremen, Bremen, Germany
  • 1996
    • University of Cologne
      • Institute for Genetics
      Köln, North Rhine-Westphalia, Germany