title: Mismatch repair-dependent metabolism of O6-methylguanine-containing DNA in Xenopus laevis egg extracts.
abstract: The cytotoxicity of SN1-type alkylating agents such as N-methyl-N'-nitrosourea (MNU), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), or the cancer chemotherapeutics temozolomide, dacarbazine and streptozotocin has been ascribed to the persistence of O(6)-methylguanine ((me)G) in genomic DNA. One hypothesis posits that (me)G toxicity is caused by futile attempts of the mismatch repair (MMR) system to process (me)G/C or (me)G/T mispairs arising during replication, while an alternative proposal suggests that the latter lesions activate DNA damage signaling, cell cycle arrest and apoptosis directly. Attempts to elucidate the molecular mechanism of (me)G-induced cell killing in vivo have been hampered by the fact that the above reagents induce several types of modifications in genomic DNA, which are processed by different repair pathways. In contrast, defined substrates studied in vitro did not undergo replication. We set out to re-examine this phenomenon in replication-competent Xenopus laevis egg extracts, using either phagemid substrates containing a single (me)G residue, or methylated sperm chromatin. Our findings provide further support for the futile cycling hypothesis.
authors.affiliation: Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland; Department of Biology, Swiss Federal Institute of Technology (ETH), Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
authors.forename: Maite
authors.initials: M
authors.lastname: Olivera Harris
authors.affiliation: Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
authors.forename: Lia
authors.initials: L
authors.lastname: Kallenberger
authors.affiliation: Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
authors.forename: Mariela
authors.initials: M
authors.lastname: Artola Borán
authors.affiliation: Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
authors.forename: Milica
authors.initials: M
authors.lastname: Enoiu
authors.affiliation: IFOM-European Institute of Oncology Campus, Via Adamello 16, 20139 Milano, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Costanzo
authors.affiliation: Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland; Department of Biology, Swiss Federal Institute of Technology (ETH), Winterthurerstrasse 190, CH-8057 Zurich, Switzerland. Electronic address: jiricny@imcr.uzh.ch.
authors.forename: Josef
authors.initials: J
authors.lastname: Jiricny
mesh_terms: D000818:Animals; D002457:Cell Extracts; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004249:DNA Damage; D053843:DNA Mismatch Repair / Q000502:physiology*; D004261:DNA Replication; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D010063:Ovum / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D002457:Cell Extracts; D006147:Guanine; D004247:DNA; C008449:O-(6)-methylguanine
keywords: DNA damage signaling; DNA replication; Mismatch repair; O(6)-methylguanine; S(N)1-type alkylating agents; Xenopus laevis egg extracts