Defective DNA strand break repair causes chromosomal instability and accelerates liver carcinogenesis in mice.
Chromosomal instability is a characteristic feature of hepatocellular carcinoma (HCC) but its origin and role in liver carcinogenesis are undefined. We tested whether a defect in the nonhomologous end-joining (NHEJ) DNA repair gene Ku70 was associated with chromosomal abnormalities and enhanced liver carcinogenesis. Male Ku70 NHEJ-deficient (Ku70-/-), heterozygote (Ku70 +/-), and wild-type (WT) mice were injected with diethylnitrosamine (DEN), a liver carcinogen, at age 15 days. Animals were killed at 3, 6, and 9 months for assessment of tumorigenesis and hepatocellular proliferation. For karyotype analysis, primary liver tumor cell cultures were prepared from HCCs arising in Ku70 mice of all genotypes. Compared to WT littermates, Ku70-/- mice injected with DEN displayed accelerated HCC development. Ku70-/- HCCs harbored clonal increases in numerical and structural aberrations of chromosomes 4, 5, 7, 8, 10, 14, and 19, many of which recapitulated the spectrum of equivalent chromosomal abnormalities observed in human HCC. Ku70-/- HCCs showed high proliferative activity with increased cyclin D1 and proliferating cell nuclear antigen expression, Aurora A kinase activity, enhanced ataxia telangiectasia mutated kinase and ubiquitination, and loss of p53 via proteasomal degradation, features which closely resemble those of human HCC.


CONCLUSIONS
These findings demonstrate that defects in the NHEJ DNA repair pathway may participate in the disruption of cell cycle checkpoints leading to chromosomal instability and accelerated development of HCC.
Australian National University Medical School, Canberra, Australia. narci.teoh@anu.edu.au
Narci C
NC
Teoh
Yock Young
YY
Dan
Karen
K
Swisshelm
Stacey
S
Lehman
Jocelyn H
JH
Wright
Jamil
J
Haque
Yansong
Y
Gu
Nelson
N
Fausto
D000199:Actins / Q000378:metabolism; D000818:Animals; D034961:Antigens, Nuclear / Q000235:genetics* / Q000378:metabolism; D064096:Aurora Kinase A; D064127:Aurora Kinases; D002273:Carcinogens; D006528:Carcinoma, Hepatocellular / Q000139:chemically induced / Q000235:genetics* / Q000473:pathology; D049109:Cell Proliferation; D002478:Cells, Cultured; D043171:Chromosomal Instability / Q000235:genetics*; D053903:DNA Breaks, Double-Stranded; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D004052:Diethylnitrosamine; D004195:Disease Models, Animal; D022781:Hepatocytes / Q000378:metabolism / Q000473:pathology; D006657:Histones / Q000378:metabolism; D000072200:Ku Autoantigen; D008113:Liver Neoplasms / Q000139:chemically induced / Q000235:genetics* / Q000473:pathology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
D000199:Actins; D034961:Antigens, Nuclear; D002273:Carcinogens; D004268:DNA-Binding Proteins; D006657:Histones; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; D004052:Diethylnitrosamine; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2; C576918:Aurka protein, mouse; D064096:Aurora Kinase A; D064127:Aurora Kinases; D017346:Protein Serine-Threonine Kinases; C000606509:Xrcc6 protein, human; C000606510:Xrcc6 protein, mouse; D000072200:Ku Autoantigen