Contribution of hMTH1 to the maintenance of 8-oxoguanine levels in lung DNA of non-small-cell lung cancer patients.
BACKGROUND
The level of 8-oxoguanine (8-oxoG), a general marker of oxidative DNA damage, in DNA is the result of both an equilibrium between the rates of its formation and removal from DNA by DNA repair enzymes and the removal of 8-oxodGTP from the cellular nucleotide pool by hydrolysis to 8-oxodGMP, preventing its incorporation into DNA. To determine the contribution of each component to the level of 8-oxoG in DNA, we compared 8-oxoG-excising activity (encoded by hOGG1), 8-oxodGTPase activity (encoded by hMTH1), and 8-oxoG levels in DNA from tumors and surrounding normal lung tissues from non-small-cell lung cancer patients.


METHODS
We measured the level of 8-oxoG in DNA of 47 patients by high-performance liquid chromatography/electrochemical detection (HPLC/ECD), hOGG1 activity in tissue extracts of 56 patients by the nicking assay using an oligodeoxynucleotide containing a single 8-oxoG, and hMTH1 activity in tissue extracts of 33 patients by HPLC/UV detection. All statistical tests were two-sided.


RESULTS
The 8-oxoG level was lower in tumor DNA than in DNA from normal lung tissue (geometric mean: 5.81 versus 10.18 8-oxoG/10(6) G, geometric mean of difference = 1.75; P<.001). The hOGG1 activity was also lower in tumor than in normal lung tissue (geometric mean: 8.76 versus 20.91 pmol/h/mg protein, geometric mean of difference = 2.39; P<.001), whereas the hMTH1 activity was higher in tumor than in normal lung tissue (geometric mean: 28.79 versus 8.94 nmol/h/mg protein, geometric mean of difference = 0.31; P<.001). The activity of hMTH1 was three orders of magnitude higher than that of hOGG1 (nanomoles versus picomoles per hour per milligram of protein, respectively).


CONCLUSIONS
Several different components contribute to the maintenance of 8-oxoG levels in human DNA, with the greatest contributor being the removal of 8-oxodGTP from the cellular nucleotide pool by hMTH1.
Speina
Elzbieta
E
Department of Molecular Biology, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawińskiego 5a, 02-106 Warsaw, Poland.
Arczewska
Katarzyna D
KD
Gackowski
Daniel
D
Zielińska
Maja
M
Siomek
Agnieszka
A
Kowalewski
Janusz
J
Oliński
Ryszard
R
Tudek
Barbara
B
Kuśmierek
Jaroslaw T
JT
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016587:Antimutagenic Agents / Q000378:metabolism*; D002289:Carcinoma, Non-Small-Cell Lung / Q000201:enzymology / Q000235:genetics*; D002851:Chromatography, High Pressure Liquid; D004249:DNA Damage; D045647:DNA Glycosylases / Q000378:metabolism*; D045643:DNA Repair Enzymes / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000378:metabolism*; D004563:Electrochemistry; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000201:enzymology / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D018384:Oxidative Stress; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D012737:Sex Factors; D012907:Smoking / Q000378:metabolism
D016587:Antimutagenic Agents; D004273:DNA, Neoplasm; D010744:Phosphoric Monoester Hydrolases; D045647:DNA Glycosylases; C479058:oxoguanine glycosylase 1, human; C078207:8-oxodGTPase; D045643:DNA Repair Enzymes