The oxidized deoxynucleoside triphosphate pool is a significant contributor to genetic instability in mismatch repair-deficient cells.
Oxidation is a common form of DNA damage to which purines are particularly susceptible. We previously reported that oxidized dGTP is potentially an important source of DNA 8-oxodGMP in mammalian cells and that the incorporated lesions are removed by DNA mismatch repair (MMR). MMR deficiency is associated with a mutator phenotype and widespread microsatellite instability (MSI). Here, we identify oxidized deoxynucleoside triphosphates (dNTPs) as an important cofactor in this genetic instability. The high spontaneous hprt mutation rate of MMR-defective msh2(-/-) mouse embryonic fibroblasts was attenuated by expression of the hMTH1 protein, which degrades oxidized purine dNTPs. A high level of hMTH1 abolished their mutator phenotype and restored the hprt mutation rate to normal. Molecular analysis of hprt mutants showed that the presence of hMTH1 reduced the incidence of mutations in all classes, including frameshifts, and also implicated incorporated 2-oxodAMP in the mutator phenotype. In hMSH6-deficient DLD-1 human colorectal carcinoma cells, overexpression of hMTH1 markedly attenuated the spontaneous mutation rate and reduced MSI. It also reduced the incidence of -G and -A frameshifts in the hMLH1-defective DU145 human prostatic cancer cell line. Our findings indicate that incorporation of oxidized purines from the dNTP pool may contribute significantly to the extreme genetic instability of MMR-defective human tumors.
Russo
Maria Teresa
MT
Chemical Carcinogenesis Unit, Istituto Superiore di Sanità, Rome, Italy.
Blasi
Monica Francesca
MF
Chiera
Federica
F
Fortini
Paola
P
Degan
Paolo
P
Macpherson
Peter
P
Furuichi
Masato
M
Nakabeppu
Yusaku
Y
Karran
Peter
P
Aquilina
Gabriele
G
Bignami
Margherita
M
D000818:Animals; D001483:Base Sequence; D004249:DNA Damage; D004260:DNA Repair / Q000235:genetics*; D045643:DNA Repair Enzymes; D003854:Deoxyribonucleotides / Q000378:metabolism*; D042822:Genomic Instability; D051379:Mice; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism
D003854:Deoxyribonucleotides; D010744:Phosphoric Monoester Hydrolases; C078207:8-oxodGTPase; D045643:DNA Repair Enzymes