Induction of p53 renders ATM-deficient mice refractory to hepatocarcinogenesis.
OBJECTIVE
p53 Mutations are very common in human hepatocellular carcinoma, and induction of hepatic p53 expression causes lysis of implanted hepatoblastoma cells in a chimeric mouse. Ataxia Telangiectasia Mutated (ATM) kinase senses DNA strand breaks and induces p53. Our aims were to establish whether ATM deficiency alters the carcinogenic response of hepatocytes to diethylnitrosamine (DEN).


METHODS
Male ATM-deficient (ATM(-/-)), heterozygote (ATM(+/-)), and wild-type (WT) mice were injected with DEN at age 15 days, and animals were killed up to 12 months to assess p53, cell cycle, apoptosis, and liver tumor development.


RESULTS
Whereas >80% of WT and ATM(+/-) mice developed hepatocellular carcinoma (HCC), at 9-12 months, ATM(-/-) mice remained refractory to DEN-induced HCC up to 15 months. At 6 and 9 months, and compared with WT mice, p53 and p19(ARF) expression were greatly enhanced in ATM(-/-) liver associated with up-regulation of ATR and Chk1; cleaved caspase-3 immunohistochemistry and caspase-3 activity were also significantly increased. Whereas livers of DEN-treated ATM(-/-) mice showed markers of senescence (beta-galactosidase, Cxcl-1), up-regulation of telomerase occurred concurrently. The possibility that such balanced senescence could result in immortalization was demonstrated in hepatocytes prepared at 9 months from DEN-treated ATM(-/-) liver.


CONCLUSIONS
Hepatocarcinogenesis is abrogated in ATM-deficient mice in association with induction of ATR, Chk1, p53, and p19(ARF). Resultant cell cycle arrest and apoptosis of DNA-damaged cells are possible mechanisms that underlie this unique "refractoriness" to malignant transformation in DEN-initiated ATM(-/-) hepatocytes. The findings also show that prolonged up-regulation of p53 associated with some features of senescence does not inevitably cause organ failure.
Teoh
Narci
N
Australian National University Medical School at The Canberra Hospital, Canberra, Australia.
Pyakurel
Pawan
P
Dan
Yock Young
YY
Swisshelm
Karen
K
Hou
Jing
J
Mitchell
Claudia
C
Fausto
Nelson
N
Gu
Yansong
Y
Farrell
Geoffrey
G
D000818:Animals; D017209:Apoptosis; D064007:Ataxia Telangiectasia Mutated Proteins; D006528:Carcinoma, Hepatocellular / Q000139:chemically induced / Q000201:enzymology / Q000235:genetics / Q000473:pathology / Q000517:prevention & control*; D053148:Caspase 3 / Q000378:metabolism; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002471:Cell Transformation, Neoplastic / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D016922:Cellular Senescence; D000071877:Checkpoint Kinase 1; D002869:Chromosome Aberrations; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000172:deficiency* / Q000235:genetics; D004052:Diethylnitrosamine; D004195:Disease Models, Animal; D015972:Gene Expression Regulation, Neoplastic; D006579:Heterozygote; D007621:Karyotyping; D008113:Liver Neoplasms / Q000139:chemically induced / Q000201:enzymology / Q000235:genetics / Q000473:pathology / Q000517:prevention & control*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D019098:Telomerase / Q000378:metabolism; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000172:deficiency* / Q000235:genetics; D015854:Up-Regulation
C417743:Cdkn2a protein, mouse; D018797:Cell Cycle Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004268:DNA-Binding Proteins; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D004052:Diethylnitrosamine; D011494:Protein Kinases; C576897:Atr protein, mouse; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C000605869:Chek1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D019098:Telomerase; C505409:Casp3 protein, mouse; D053148:Caspase 3