G1-arrested FaO cells re-enter the cell cycle upon stimulation with the rodent non-genotoxic hepatocarcinogen nafenopin.
The peroxisome proliferators are rodent non-genotoxic hepatocarcinogens that suppress apoptosis and induce DNA replication, cell proliferation and liver tumours. In order to investigate the effect of peroxisome proliferators on cell cycle progression, we arrested the well-differentiated rat hepatoma cell line FaO in the G1 phase of the cell cycle. Under these conditions, CDK2 and CDK4 protein expression remained unchanged compared with proliferating cells, but expression of cyclin D1 and p27(KIP1) was down-regulated and cyclin E accumulated in the inactive form. G1-arrested cells were able to enter the cell cycle on addition of exogenous growth factors such as epidermal growth factor (EGF) or hepatocyte growth factor (HGF) and replicate their DNA within 12 to 24 h of re-stimulation. Upon release from G1 arrest, CDK2 protein expression was down-regulated and, surprisingly, p27(KIP1) expression was restored. Cyclin D1 and phosphorylated cyclin E accumulated at 12 h but were degraded by 24 h after addition of EGF. Importantly, the peroxisome proliferator nafenopin and tumour necrosis factor alpha were able to induce DNA replication. Thus, the profile of expression of cell cycle regulatory proteins upon stimulation with nafenopin is comparable with that induced by growth factors such as EGF.
Chevalier
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Zeneca Central Toxicology Laboratory, Cancer Biology Group,Alderley Park, Macclesfield SK10 4TJ, UK.
Roberts
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D000818:Animals; D002087:Butyrates / Q000494:pharmacology; D042846:CDC2-CDC28 Kinases; D002273:Carcinogens / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism / Q000473:pathology; D018797:Cell Cycle Proteins; D019938:Cyclin D1 / Q000378:metabolism; D019927:Cyclin E / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000494:pharmacology; D016193:G1 Phase / Q000187:drug effects*; D008869:Microtubule-Associated Proteins / Q000096:biosynthesis; D009255:Nafenopin / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051381:Rats; D013997:Time Factors; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D025521:Tumor Suppressor Proteins
D002087:Butyrates; D002273:Carcinogens; C493962:Cdkn1b protein, rat; D018797:Cell Cycle Proteins; D019927:Cyclin E; D004791:Enzyme Inhibitors; D008869:Microtubule-Associated Proteins; D011518:Proto-Oncogene Proteins; D014409:Tumor Necrosis Factor-alpha; D025521:Tumor Suppressor Proteins; D009255:Nafenopin; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004815:Epidermal Growth Factor; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495892:Cdk2 protein, rat; C495903:Cdk4 protein, rat; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases