Volume 27, Issue 3 pp. 190-199
Article

The carcinogen 2-acetylaminofluorene inhibits activation and nuclear accumulation of cyclin-dependent kinase 2 in growth-induced rat liver

Birgitte Lindeman

Corresponding Author

Birgitte Lindeman

Laboratory for Toxicopathology, Institute of Pathology, The National Hospital, University of Oslo, Norway

National Institute of Public Health, P.O. Box 4404 Torshov, 0403 Oslo, Norway.Search for more papers by this author
Ellen Skarpen

Ellen Skarpen

Laboratory for Toxicopathology, Institute of Pathology, The National Hospital, University of Oslo, Norway

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Morten P. Oksvold

Morten P. Oksvold

Laboratory for Toxicopathology, Institute of Pathology, The National Hospital, University of Oslo, Norway

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Henrik S. Huitfeldt

Henrik S. Huitfeldt

Laboratory for Toxicopathology, Institute of Pathology, The National Hospital, University of Oslo, Norway

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Abstract

Growth arrest in G1 is a common cellular response to DNA damage. In the present study, liver regeneration was combined with continuous exposure for 2-acetylaminofluorene (AAF) to study mechanisms of carcinogen-induced growth arrest in vivo. Growth arrest of uninitiated hepatocytes is central for AAF-induced promotion of premalignant lesions in rat liver. To characterize this growth arrest, we examined the activity of cyclin-dependent kinase (Cdk) 2 in unexposed liver and in AAF-exposed liver after growth induction by partial hepatectomy (PH). Rats were fed either a control diet or an AAF-supplemented diet. After 7 d, a two-third PH was performed and the animals were killed after 0, 12, 18, 24, and 36 h. Kinase assays showed that cyclin E– and Cdk2–associated activities were lower in AAF-exposed liver than in unexposed liver after PH. Although the total cellular levels of cyclin E and Cdk2 were similar, cyclin E–Cdk2 assembly was markedly reduced. In unexposed hepatocytes, Cdk2 translocated to the nuclei after PH. Much of the nuclear Cdk2 was in a rapidly migrating form, presumably representing the Thr160-phosphorylated form of Cdk2. In contrast, in AAF-exposed liver both nuclear Cdk2 accumulation and Thr160-phosphorylation of Cdk2 were reduced. Although p53 and p21waf1/cip1 were induced by AAF, the binding of p21 to cyclin E and Cdk2 was not increased in growth arrested liver. In conclusion, hepatocyte growth arrest caused by AAF exposure was characterized by a lowered Cdk2 activity that was accompanied by a reduced assembly of cyclin E–Cdk2 complexes but not by binding of p21. Mol. Carcinog. 27:190–199, 2000. © 2000 Wiley-Liss, Inc.

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