The mechanism of switching among multiple BER pathways.
To preserve genomic beta DNA from common endogenous and exogenous base and sugar damage, cells are provided with multiple base excision repair (BER) pathways: the DNA polymerase (Pol) beta-dependent single nucleotide BER and the long-patch (2-10 nt) BER that requires PCNA. It is a challenge to identify the factors that govern the mechanism of switching among these pathways. One of these factors is the type of DNA damage induced in DNA. By using different model lesions we have shown that base damages (like hypoxanthine and 1, N6-ethenoadenine) excised by monofunctional DNA glycosylases are repaired via both single-nucleotide and long-patch BER, while lesions repaired by a bifunctional DNA glycosylase (like 7,8-dihydro-8-oxoguanine) are repaired mainly by single-nucleotide BER. The presence of a genuine 5' nucleotide, as in the case of cleavage by a bifunctional DNA glycosylase-beta lyase, would then minimize the strand displacement events. Another key factor in the selection of the BER branch is the relative level of cellular polymerases. While wild-type embryonic mouse fibroblast cell lines repair abasic sites predominantly via single-nucleotide replacement reactions (80% of the repair events), cells homozygous for a deletion in the Pol beta gene repair these lesions exclusively via long-patch BER. Following treatment with methylmethane sulfonate, these mutant cells accumulate DNA single-strand breaks in their genome in keeping with the fact that repair induced by monofunctional alkylating agents goes predominantly via single-nucleotide BER. Since the long-patch BER is strongly stimulated by PCNA, the cellular content of this cell-cycle regulated factor is also extremely effective in driving the repair reaction to either BER branch. These findings raise the interesting possibility that different BER pathways might be acting as a function of the cell cycle stage.
Dogliotti
E
E
Laboratory of Comparative Toxicology and Ecotoxicology, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy.
Fortini
P
P
Pascucci
B
B
Parlanti
E
E
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D016466:CHO Cells / Q000201:enzymology; D019757:Carbon-Oxygen Lyases / Q000502:physiology; D002460:Cell Line; D002474:Cell-Free System; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000737:chemistry / Q000187:drug effects; D018736:DNA Adducts; D004249:DNA Damage; D045647:DNA Glycosylases; D011088:DNA Ligases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D019951:DNA Polymerase beta / Q000502:physiology; D004260:DNA Repair / Q000502:physiology*; D004261:DNA Replication; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D043382:DNA-Formamidopyrimidine Glycosylase; D043223:Deoxyribonuclease IV (Phage T4-Induced); D005347:Fibroblasts / Q000166:cytology; D005656:Fungal Proteins / Q000235:genetics / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D008957:Models, Genetic; D009153:Mutagens / Q000633:toxicity; D009699:N-Glycosyl Hydrolases / Q000502:physiology; D010084:Oxidation-Reduction; D018809:Proliferating Cell Nuclear Antigen / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000235:genetics
D001426:Bacterial Proteins; D018736:DNA Adducts; D004271:DNA, Fungal; D005656:Fungal Proteins; D009153:Mutagens; D018809:Proliferating Cell Nuclear Antigen; D004247:DNA; D019951:DNA Polymerase beta; D043223:Deoxyribonuclease IV (Phage T4-Induced); D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D043382:DNA-Formamidopyrimidine Glycosylase; D019757:Carbon-Oxygen Lyases; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D011088:DNA Ligases