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PL 7 Chromosome aberrations induced by genotoxins
S2
List of Invited "Plenary Lectures'
IPL 41
Tumor suppressor genes: At the crossroads of molecular carcinogenesis and molecular epidemiology
Curtis C. Harris. LHC. Natiollal Cancer Institute; Bethesda. MD, USA Carcinogenesis is a multistage process involving activation of protooncogenes, e.g., K-ras, cyclin 0 1 and erb-Bz, and inactivation oftwnor suppressor genes, e.g., pS3. Rb and p 161NK4. Carcinogens can affect any of these stages through genetic and epigenetic mechan isms. Mutational spectra of cancer-related genes . e.g., pS3, K-ras and pl6'NK4, can provide a molecular link between etiological agents and human cancer. Most transvers ions in lung, breast , and esophageal carcinomas are dispersed among numerous evolutionarily conserved codons within the pS3 domain responsible for sequence specific DNA binding and transcription al activity. Transitions predominate in colon , brain, and lymphoid malignancies. Mutational hotspots at CpG dinucleotides in codons 17S, 248, 273 and 282 may reflect an endogenous mutagen ic mechanism, i.e., deam ination of S-methylcytosine to thymid ine. Oxyradicals may enhance the rate of deamination. G:C to T:A transversions are the most frequent substitutions observed in cancers of the lung, breast, stomach and liver, and are more likely to be due to bulky carcinogen-DNA adducts. O:C to T:A transversions are more common in lung cancers from smokers when compared to never smokers. These transversions also are more frequent in lung cancers from smoking women when compared to men. The pS3 mutational hotspots in human lung cancer correspond, in part, to benzola)pyrene diol epoxide binding to Gs in codons IS7, 248 and 273. The high frequency of G to T pS3 mutations in the nontranscribed DNA strand is a reflection of strand specific repair. pS3 may also contribute to DNA repair and apoptosis by protein-protein interactions with transcript ion-repa ir factors. XPB and XPD, in TFIlH . pS3 mutation. allelic delet ions andlor posllranslationally-modified protein can be early events in bronchial , mammary or esophageal carcinogenes is and generally indicate a poor prognosis. Since many of the effect ive anticancer therapies utilize pS3-dependent apoptosis, our recent finding of pS3 transmitt ing an apoptotic signal via XPB and XPD DNA helicases in the TF llH complex suggest new molecular targets of cancer therapy.
IpL 51
No abstrad reeelved
IPL 61
DNA damage repair syndromes In man and mouse
J.H.J. Hoeijrnakers. MGC Dept. O/Cell Biology & Genetics. Erasmus Uniu, PO Box /738. 3000 DR Rotterdam. The Netherlands Nature has equ ipped all organisms with an intricate network of DNA repair pathways , to cope with damage induced by genotoxic agents. These pathways ensure genome stability and prevent carcinogenesis. Examples of multi-step damage repair (NER and BER, for removal of a wide variety of lesionsO, recombination repair (for repair of double strand breaks) and post-replication repair (for error-prone translesion DNA synthesis) . Defects in DNA repair results in hypersensitivity to genotoxic agents and carcinogenesis . The NER pathway for elimination of UY-induced lesions is understood in great detail and is associated with three clin ically and genetically heterogeneous human syndromes characterized by marked sun sens itivity: xeroderma pigmentosum (XP), Cockayne syndrome (CS) and Trichoth iodystrophy (TID). XP patients show an over IOOOx increased risk of skin cancer, in contrast to CS and ITO. The latter disorders display severe developmenlol abnormalities and neurodysfunetion. In addit ion TID is characterized by sulphur-defic ient brittle hair and nails, due to a reduced synthesis of cysteinerich matrix prote ins. At least 10 genes are involved, virtually all of which have been cloned. Some of the encoded prote ins appeared also implicated in other cellular processes, explaining puzzling clinical features associated with defects in these genes . The proteins defective in in ITD and in 2 of the complementation groups with combined XP/CS reside in the TFllH complex, involved in basal transcription and in NER . Many of the CS and TID features may be due to a erippled TFllH transcription funct ion, affecting the expression of a specific set of genes . To understand the complex genotypephenotype relat ionsh ip we have generated mouse models by gene targeting
of relevant repair genes in embronyal stem cells, that perm it evaluat ion of the biological impact ot these systems . Keyword(s): hwnan DNA repair syndromes; nucleotide excision repair; mouse models
IPL 71
Chromosome aberral/ons Induced by genotoxlns
Adayapalam T. Natarajan, Dept. Radiation Genetics & Chemical Mutagenesis, Leiden University, Wassenaarseweg 72. 2333 AL Leiden; The Netherlands; J. A. Cohen Inter-Un iversity Institute 0/ Radiopathology and Radiation Protection. Leiden; The Netherlands All genotoxic agents induce chromosomal aberrations efficiently. The types and the frequenc ies of aberrations induced depend upon the nature of agents, cell cycle stage treated and the cell type employed. With the advent of Fluorescen ce in situ hybridization (FISH) and the availability of different types DNA probes for both human and rodents, the resolution of detecting various types of aberration has increased. It is possible to identifY many types of translocations and complex chromosome exchanges. Karyotypic features of the species studied appear to influence the relative yields of dicentrics and translocations induced by radiation. It is generally believed that genotoxic agents, especially ionizing radiation, induce DNA lesions randomly over the genome. However. studies using DNA libraries for specific chromosomes, show differential sensitivity in their response to radiation and chemical mutagens. Chromosome /I 4 in human and chromosome /I 8 in Chinese hamster involve in radiation induced exchange aberrat ions much higher than expected on the basis of their DNA content. Human Chromosome II 4 is low in CpO islands, whereas Chinese hamster II 8 is very rich in interstitial telomeric sequences. We have observed in Chinese hamster, that euchromatic regions have more chromosomal lesions and repair fast, whereas heterochromatic regions susta in less damage and repair slowly following X-irradiation. When human lymphocytes are treated with EMS and challenged with araC, the aberration frequencies are higher in chromosomes containing high gene density (/II, 19, 20) in comparison to chromosomes with low gene density i.e.,/I 4, I g (Surralles et ai, 1997). When arm specific DNA libraries are employed to paint the two arms of a chromosome in different colours, one can detect inter-arm intrac hanges easily. The frequencies of X-ray induced intrachanges (pencentric inversions, centric rings) are about 7 times higher than interchanges between the arms of human chromosomes /I lor 3. This increase is due to the prox imity effect. Thus, factors such as chromatin condensation status, content of interstitial telomeric repeats, the content of active genes present in a chromosome as well as the proximity of chromosome regions in interphase nucleus, will greatly influence the yield of chromosomal aberrat ions and contribute to the heterogeneity in response of different chromosomes following genotoxic insult.
No abstract receIved
Monitoring the genetic effects of radiation In the children atomic bomb survlvon
or
Chiyoko Satoh, Norio Takahashi. Jun-ichi Asakawa, Mieko Kodaira. Department 0/ Genetics, Radiation Effects Research Foundat ion, Hirosh ima. Japall In our DNA-oriented studies to detect possible genet ic effects of atomic bomb radiation, the offspring of survivors are being screened for deletion! insertion!rearrangement (O/IIR) types of mutat ions. The DNA is obtained from lymphoblastoid cell lines. From the 1000 families for which cell lines have been established, SO families , containing 64 children, including the most heavily exposed survivors (l.8 Sv mean gonadal dose). were selected along with SO control families with 60 children. Twenty eight, 24 , and 6 mutations. respectively, were detected in six minisatellites, DNA fingerprints and six microsatellites from the 124 children. These gena cell mutations, however. showed no evidence of being induced by radiation .
List of Invited "Plenary Lectures'
IPL 41
Tumor suppressor genes: At the crossroads of molecular carcinogenesis and molecular epidemiology
Curtis C. Harris. LHC. Natiollal Cancer Institute; Bethesda. MD, USA Carcinogenesis is a multistage process involving activation of protooncogenes, e.g., K-ras, cyclin 0 1 and erb-Bz, and inactivation oftwnor suppressor genes, e.g., pS3. Rb and p 161NK4. Carcinogens can affect any of these stages through genetic and epigenetic mechan isms. Mutational spectra of cancer-related genes . e.g., pS3, K-ras and pl6'NK4, can provide a molecular link between etiological agents and human cancer. Most transvers ions in lung, breast , and esophageal carcinomas are dispersed among numerous evolutionarily conserved codons within the pS3 domain responsible for sequence specific DNA binding and transcription al activity. Transitions predominate in colon , brain, and lymphoid malignancies. Mutational hotspots at CpG dinucleotides in codons 17S, 248, 273 and 282 may reflect an endogenous mutagen ic mechanism, i.e., deam ination of S-methylcytosine to thymid ine. Oxyradicals may enhance the rate of deamination. G:C to T:A transversions are the most frequent substitutions observed in cancers of the lung, breast, stomach and liver, and are more likely to be due to bulky carcinogen-DNA adducts. O:C to T:A transversions are more common in lung cancers from smokers when compared to never smokers. These transversions also are more frequent in lung cancers from smoking women when compared to men. The pS3 mutational hotspots in human lung cancer correspond, in part, to benzola)pyrene diol epoxide binding to Gs in codons IS7, 248 and 273. The high frequency of G to T pS3 mutations in the nontranscribed DNA strand is a reflection of strand specific repair. pS3 may also contribute to DNA repair and apoptosis by protein-protein interactions with transcript ion-repa ir factors. XPB and XPD, in TFIlH . pS3 mutation. allelic delet ions andlor posllranslationally-modified protein can be early events in bronchial , mammary or esophageal carcinogenes is and generally indicate a poor prognosis. Since many of the effect ive anticancer therapies utilize pS3-dependent apoptosis, our recent finding of pS3 transmitt ing an apoptotic signal via XPB and XPD DNA helicases in the TF llH complex suggest new molecular targets of cancer therapy.
IpL 51
No abstrad reeelved
IPL 61
DNA damage repair syndromes In man and mouse
J.H.J. Hoeijrnakers. MGC Dept. O/Cell Biology & Genetics. Erasmus Uniu, PO Box /738. 3000 DR Rotterdam. The Netherlands Nature has equ ipped all organisms with an intricate network of DNA repair pathways , to cope with damage induced by genotoxic agents. These pathways ensure genome stability and prevent carcinogenesis. Examples of multi-step damage repair (NER and BER, for removal of a wide variety of lesionsO, recombination repair (for repair of double strand breaks) and post-replication repair (for error-prone translesion DNA synthesis) . Defects in DNA repair results in hypersensitivity to genotoxic agents and carcinogenesis . The NER pathway for elimination of UY-induced lesions is understood in great detail and is associated with three clin ically and genetically heterogeneous human syndromes characterized by marked sun sens itivity: xeroderma pigmentosum (XP), Cockayne syndrome (CS) and Trichoth iodystrophy (TID). XP patients show an over IOOOx increased risk of skin cancer, in contrast to CS and ITO. The latter disorders display severe developmenlol abnormalities and neurodysfunetion. In addit ion TID is characterized by sulphur-defic ient brittle hair and nails, due to a reduced synthesis of cysteinerich matrix prote ins. At least 10 genes are involved, virtually all of which have been cloned. Some of the encoded prote ins appeared also implicated in other cellular processes, explaining puzzling clinical features associated with defects in these genes . The proteins defective in in ITD and in 2 of the complementation groups with combined XP/CS reside in the TFllH complex, involved in basal transcription and in NER . Many of the CS and TID features may be due to a erippled TFllH transcription funct ion, affecting the expression of a specific set of genes . To understand the complex genotypephenotype relat ionsh ip we have generated mouse models by gene targeting
of relevant repair genes in embronyal stem cells, that perm it evaluat ion of the biological impact ot these systems . Keyword(s): hwnan DNA repair syndromes; nucleotide excision repair; mouse models
IPL 71
Chromosome aberral/ons Induced by genotoxlns
Adayapalam T. Natarajan, Dept. Radiation Genetics & Chemical Mutagenesis, Leiden University, Wassenaarseweg 72. 2333 AL Leiden; The Netherlands; J. A. Cohen Inter-Un iversity Institute 0/ Radiopathology and Radiation Protection. Leiden; The Netherlands All genotoxic agents induce chromosomal aberrations efficiently. The types and the frequenc ies of aberrations induced depend upon the nature of agents, cell cycle stage treated and the cell type employed. With the advent of Fluorescen ce in situ hybridization (FISH) and the availability of different types DNA probes for both human and rodents, the resolution of detecting various types of aberration has increased. It is possible to identifY many types of translocations and complex chromosome exchanges. Karyotypic features of the species studied appear to influence the relative yields of dicentrics and translocations induced by radiation. It is generally believed that genotoxic agents, especially ionizing radiation, induce DNA lesions randomly over the genome. However. studies using DNA libraries for specific chromosomes, show differential sensitivity in their response to radiation and chemical mutagens. Chromosome /I 4 in human and chromosome /I 8 in Chinese hamster involve in radiation induced exchange aberrat ions much higher than expected on the basis of their DNA content. Human Chromosome II 4 is low in CpO islands, whereas Chinese hamster II 8 is very rich in interstitial telomeric sequences. We have observed in Chinese hamster, that euchromatic regions have more chromosomal lesions and repair fast, whereas heterochromatic regions susta in less damage and repair slowly following X-irradiation. When human lymphocytes are treated with EMS and challenged with araC, the aberration frequencies are higher in chromosomes containing high gene density (/II, 19, 20) in comparison to chromosomes with low gene density i.e.,/I 4, I g (Surralles et ai, 1997). When arm specific DNA libraries are employed to paint the two arms of a chromosome in different colours, one can detect inter-arm intrac hanges easily. The frequencies of X-ray induced intrachanges (pencentric inversions, centric rings) are about 7 times higher than interchanges between the arms of human chromosomes /I lor 3. This increase is due to the prox imity effect. Thus, factors such as chromatin condensation status, content of interstitial telomeric repeats, the content of active genes present in a chromosome as well as the proximity of chromosome regions in interphase nucleus, will greatly influence the yield of chromosomal aberrat ions and contribute to the heterogeneity in response of different chromosomes following genotoxic insult.
No abstract receIved
Monitoring the genetic effects of radiation In the children atomic bomb survlvon
or
Chiyoko Satoh, Norio Takahashi. Jun-ichi Asakawa, Mieko Kodaira. Department 0/ Genetics, Radiation Effects Research Foundat ion, Hirosh ima. Japall In our DNA-oriented studies to detect possible genet ic effects of atomic bomb radiation, the offspring of survivors are being screened for deletion! insertion!rearrangement (O/IIR) types of mutat ions. The DNA is obtained from lymphoblastoid cell lines. From the 1000 families for which cell lines have been established, SO families , containing 64 children, including the most heavily exposed survivors (l.8 Sv mean gonadal dose). were selected along with SO control families with 60 children. Twenty eight, 24 , and 6 mutations. respectively, were detected in six minisatellites, DNA fingerprints and six microsatellites from the 124 children. These gena cell mutations, however. showed no evidence of being induced by radiation .