title: Embryonic lethality after combined inactivation of Fancd2 and Mlh1 in mice.
abstract: DNA repair defects are frequently encountered in human cancers. These defects are utilized by traditional therapeutics but also offer novel cancer treatment strategies based on synthetic lethality. To determine the consequences of combined Fanconi anemia (FA) and mismatch repair pathway inactivation, defects in Fancd2 and Mlh1 were combined in one mouse model. Fancd2/Mlh1 double-mutant embryos displayed growth retardation resulting in embryonic lethality and significant underrepresentation among progeny. Additional inactivation of Trp53 failed to improve the survival of Fancd2/Mlh1-deficient embryos. Mouse fibroblasts were obtained and challenged with cross-linking agents. Fancd2-deficient cells displayed the FA-characteristic growth inhibition after mitomycin C (MMC) exposure. In primary fibroblasts, the absence of Mlh1 did not greatly affect the MMC sensitivity of Fancd2-deficient and Fancd2-proficient cells. However, in Trp53 mutant immortalized fibroblasts, Mlh1 deficiency reduced the growth-inhibiting effect of MMC in Fancd2 mutant and complemented cells. Similar data were obtained using psoralen/UVA, signifying that MLH1 influences the cellular sensitivity to DNA interstrand cross-links. Next, the effect of MLH1 deficiency on the formation of chromosomal aberrations in response to cross-linking agents was determined. Surprisingly, Mlh1 mutant fibroblasts displayed a modest but noticeable decrease in induced chromosomal breakage and interchange frequencies, suggesting that MLH1 promotes interstrand cross-link repair catastrophe. In conclusion, the combined inactivation of Fancd2 and Mlh1 did not result in synthetic lethality at the cellular level. Although the absence of Fancd2 sensitized Mlh1/Trp53 mutant fibroblasts to MMC, the differential survival of primary and immortalized fibroblasts advocates against systemic inactivation of FANCD2 to enhance treatment of MLH1-deficient tumors.
authors.affiliation: Oregon Stem Cell Center, Oregon Health and Science University, Portland, Oregon, USA. henrivandevrugt@gmail.com
authors.forename: Henri J
authors.initials: HJ
authors.lastname: van de Vrugt
authors.forename: Laura
authors.initials: L
authors.lastname: Eaton
authors.forename: Amy
authors.initials: A
authors.lastname: Hanlon Newell
authors.forename: Mushen
authors.initials: M
authors.lastname: Al-Dhalimy
authors.forename: R Michael
authors.initials: RM
authors.lastname: Liskay
authors.forename: Susan B
authors.initials: SB
authors.lastname: Olson
authors.forename: Markus
authors.initials: M
authors.lastname: Grompe
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D000818:Animals; D002869:Chromosome Aberrations; D053843:DNA Mismatch Repair; D004622:Embryo, Mammalian / Q000473:pathology; D005199:Fanconi Anemia / Q000235:genetics; D052236:Fanconi Anemia Complementation Group D2 Protein / Q000235:genetics*; D005260:Female; D005317:Fetal Growth Retardation / Q000235:genetics / Q000473:pathology; D020868:Gene Silencing; D007178:Inbreeding; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016685:Mitomycin / Q000494:pharmacology; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000235:genetics*; D011247:Pregnancy
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C499904:Fancd2 protein, mouse; D052236:Fanconi Anemia Complementation Group D2 Protein; C501485:Mlh1 protein, mouse; D009687:Nuclear Proteins; D016685:Mitomycin; D000070957:MutL Protein Homolog 1