title: Mouse embryonic stem cells are hypersensitive to apoptosis triggered by the DNA damage O(6)-methylguanine due to high E2F1 regulated mismatch repair.
abstract: Exposure of stem cells to genotoxins may lead to embryonic lethality or teratogenic effects. This can be prevented by efficient DNA repair or by eliminating genetically damaged cells. Using undifferentiated mouse embryonic stem (ES) cells as a pluripotent model system, we compared ES cells with differentiated cells, with regard to apoptosis induction by alkylating agents forming the highly mutagenic and killing DNA adduct O(6)-methylguanine. Upon treatment with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), ES cells undergo apoptosis at much higher frequency than differentiated cells, although they express a high level of the repair protein O(6)-methylguanine-DNA methyltransferase (MGMT). Apoptosis induced by MNNG is due to O(6)-methylguanine DNA adducts, since inhibition of MGMT sensitized ES cells. The high sensitivity of ES cells to O(6)-methylating agents is due to high expression of the mismatch repair proteins MSH2 and MSH6 (MutSalpha), which declines during differentiation. High MutSalpha expression in ES cells was related to a high hyperphosphorylated retinoblastoma (ppRb) level and E2F1 activity that upregulates MSH2, causing, in turn, stabilization of MSH6. Non-repaired O(6)-methylguanine adducts were shown to cause DNA double-stranded breaks, stabilization of p53 and upregulation of Fas/CD95/Apo-1 at significantly higher level in ES cells than in fibroblasts. The high apoptotic response of ES cells to O(6)-methylguanine adducts may contribute to reduction of the mutational load in the progenitor population.
authors.affiliation: Department of Toxicology, University of Mainz, Obere Zahlbacher Strasse 67, D-55131 Mainz, Germany.
authors.forename: W P
authors.initials: WP
authors.lastname: Roos
authors.forename: M
authors.initials: M
authors.lastname: Christmann
authors.forename: S T
authors.initials: ST
authors.lastname: Fraser
authors.forename: B
authors.initials: B
authors.lastname: Kaina
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001483:Base Sequence; D002454:Cell Differentiation; D018736:DNA Adducts / Q000378:metabolism; D004249:DNA Damage; D019175:DNA Methylation; D053843:DNA Mismatch Repair; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D050687:E2F1 Transcription Factor / Q000378:metabolism*; D053595:Embryonic Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D008769:Methylnitronitrosoguanidine / Q000633:toxicity; D051379:Mice; D008954:Models, Biological; D051718:MutS Homolog 2 Protein / Q000235:genetics / Q000378:metabolism; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000378:metabolism; D039904:Pluripotent Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D041701:Swiss 3T3 Cells
chemical_list: D018736:DNA Adducts; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; C102997:Msh6 protein, mouse; D008769:Methylnitronitrosoguanidine; D006147:Guanine; C008449:O-(6)-methylguanine; D019853:O(6)-Methylguanine-DNA Methyltransferase; C497173:Msh2 protein, mouse; D051718:MutS Homolog 2 Protein