The carcinogen 2-acetylaminofluorene inhibits activation and nuclear accumulation of cyclin-dependent kinase 2 in growth-induced rat liver.
Growth arrest in G(1) 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 p21(waf1/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.
Lindeman
B
B
Laboratory for Toxicopathology, Institute of Pathology, The National Hospital, University of Oslo, Norway.
Skarpen
E
E
Oksvold
M P
MP
Huitfeldt
H S
HS
D015073:2-Acetylaminofluorene / Q000494:pharmacology*; D000818:Animals; D042846:CDC2-CDC28 Kinases; D002273:Carcinogens / Q000494:pharmacology*; D002455:Cell Division; D002467:Cell Nucleus / Q000378:metabolism*; D019927:Cyclin E / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism; D004789:Enzyme Activation; D008099:Liver / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D008115:Liver Regeneration; D008297:Male; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D016160:Retinoblastoma Protein / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D002273:Carcinogens; C493958:Cdkn1a protein, rat; D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D015073:2-Acetylaminofluorene; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495892:Cdk2 protein, rat; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases