Dissezione dei meccanismi di riparazione implicati nella rimozione delle lesioni indotte dagli idrocarburi policiclici aromatici
Author(s)
Marotta, Edvige
Date Issued
October 14, 2008
Type
Doctoral Thesis
Abstract
Chemical agents that modify DNA causing irreversible damages or mutations, that can induce cancer, are said carcinogens. People are continually exposed to these substances that, being present in the environment, are also found in food and water . Amongst these agents we can find the polycyclic aromatic hydrocarbons (PAHs), a class of highly liposoluble compounds that can exist in both gaseous and solid form. They are characterized, structurally, by the presence of two or more aromatic rings condensates between themselves. To interact with DNA, these compounds must be metabolically activated originating bulky DNA adducts inducing formation of mismatch pairs that if not repaired, to the next replication, will cause mutations such as transversions and/or transitions. To ensure genomic stability, during evolution, cells elaborated several DNA repair mechanisms that detect and remove different types of lesions. These metabolic pathways can be summarize as follow: base excision repair (BER), nucleotide excision repair (NER), transcription coupled repair (TCR), homologous recombination repair (HHR) and non homologous end joining (NHEJ).
The aim of this work was to study which of these repair mechanisms is implicated in the removal of the lesions induced by polycyclic aromatic hydrocarbons (PAHs) and, specially, those arising by two metabolically activated intermediates (diol epoxides) of Benzo[a]Pyrene (BPDE) and Dibenzo[a,l]Pyrene (DBPDE).
Concerning this, the research was conducted employing different CHO cell lines (UV4, UV5, UV61,irs1SF, EM9 and V3-3) every deficient in one of the different DNA repair pathways above described and all arising from a common parental line, called AA8.
For this purpose we employed cytogenetic assays such as the study of induction of chromosomal aberrations (CA) and the sister chromatid exchanges (SCEs).
These two assays are well validated to detect genotoxic effects.
We found that the rank ordering of sensitivity for induction of chromosomal aberrations for BPDE, to be: UV4, irs1SF, UV5, UV61, EM9, V3-3 and AA8 (in descending order) and for induction of sister chromatid exchanges ,one cell cycle after the treatment was: UV5, UV4, V3-3, AA8, UV61, EM9 and irs1SF, whereas after second mitosis was: AA8, UV5, UV4, UV61, V3-3, EM9 and irs1SF (in descending order).
After DBPDE treatment, instead, the rank ordering of sensitivity for induction of chromosomal aberrations was: EM9, irs1SF, UV4, UV5, AA8, UV61 and V3-3 (in descending order)and for the induction of sister chromatid exchanges, one cycle after the treatment was found to be: EM9, V3-3, UV61, UV4, AA8, UV5 and irs1SF, whereas after two cell cycle was: V3-3, UV61, UV5, AA8, UV4, EM9 and irs1SF (in descending order).
These results suggest an important role of NER for cellular resistance to BPDE and of BER for cellular resistance to DBPDE, affecting both the inductions of chromosomal aberrations and sister chromatid exchanges. For both BPDE and DBPDE, HHR also seems to play a role in cellular resistance to these two compounds affecting mainly the induction of chromosomal aberrations, whereas NHEJ appears to play a role in cellular resistance to these two compounds, affecting only the induction of sister chromatid exchanges.
Additional information
Dottorato di ricerca in Evoluzione biologica e biochimica
Subjects
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