Accumulation of 8-hydroxy-2'-deoxyguanosine adducts in HBx recombinant HepG2 cells and HBx transgenic mice.
OBJECTIVE
Transgenic mice overexpressing hepatitis B x protein (HBx) show an increased susceptibility to mutations if exposed to mutagens. Also involved in HBx signalling, reactive oxygen intermediates (ROI) can induce DNA adducts such as 8-hydroxy-2'-deoxyguanosine that can in turn lead to G/T transversion mutations. Therefore, we investigated whether HBx expression increases the level of the mutational precursor 8-hydroxy-2'-deoxyguanosine in hepatocellular DNA.


METHODS
8-hydroxy-2'-deoxyguanosine concentrations of DNA hydrolysates of HBx protein expressing HepG2 cells and livers of HBx transgenic mouse lines were determined electrochemically after HPLC fractionation.


RESULTS
8-hydroxy-2'-deoxyguanosine concentrations in genomic DNA of HBx protein expressing cell lines correlated with the factor of transactivation. The 8-hydroxy-2'-deoxyguanosine levels were reduced after incubation of HBx recombinant cell lines with 0.1 or 1 mM of the antioxidant N-acetylcysteine. Hepatic 8-hydroxy-2'-deoxyguanosine concentrations in DNA of old transgenic mice were significantly, i.e. twofold, (p < 0.01) increased as compared to those of old nontransgenic or young transgenic controls and of control mice expressing a second HBV transactivator (MHBs(t76)).


CONCLUSIONS
HBx expression results in elevated DNA adduct levels. This could reflect a direct inhibitory interaction of HBx with cellular repair mechanisms. Alternatively, this may be an effect of an increased generation of reactive oxygen intermediates through HBx.
Gehrke
Ralph
R
Department of Virus Research, Max-Planck-Institut für Biochemie, Martinsried, Germany.
Brauchle
Maria A
MA
Reifenberg
Kurt
K
Hildt
Eberhard
E
Gruetzner
Uwe
U
Schmitz
Volker
V
Schlicht
Hans-Jürgen
HJ
Hofschneider
Peter Hans
PH
Caselmann
Wolfgang H
WH
Rabe
Christian
C
D000080242:8-Hydroxy-2'-Deoxyguanosine; D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D018736:DNA Adducts / Q000032:analysis / Q000187:drug effects / Q000378:metabolism; D004274:DNA, Recombinant / Q000235:genetics / Q000378:metabolism; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000032:analysis* / Q000378:metabolism; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D054334:Viral Regulatory and Accessory Proteins
D018736:DNA Adducts; D004274:DNA, Recombinant; D015534:Trans-Activators; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; D000080242:8-Hydroxy-2'-Deoxyguanosine; D003849:Deoxyguanosine; D000111:Acetylcysteine