title: Activation of the p53-p21(Cip1) pathway is required for CDK2 activation and S-phase entry in primary rat hepatocytes.
abstract: p53 plays a major role in the prevention of tumor development. It responds to a range of potentially oncogenic stresses by activating protective mechanisms, most notably cell-cycle arrest and apoptosis. The p53 gene is also induced during normal liver regeneration, and it has been hypothesized that p53 serve as a proliferative 'brake' to control excessive proliferation. However, it has lately been shown that p53 inhibition reduces hepatocyte growth factor-induced DNA synthesis of primary hepatocytes. Here we show that epidermal growth factor (EGF) activated p53 in a phosphatidylinositol-3 kinase-dependent way, and thus induced the cyclin-dependent kinase inhibitor p21(Cip1) in primary rat hepatocytes. p53 inactivation with a dominant-negative mutant (p53(V143A)) attenuated EGF-induced DNA synthesis and was associated with reduced CDK2 phosphorylation and retinoblastoma protein hyperphosphorylation. When p21(Cip1) was ectopically expressed in p53-inactivated cells, these effects were neutralized. In conclusion, our results demonstrate that in normal hepatocytes, EGF-induced expression of p53 is involved in regulating CDK2- and CDK4 activity, through p21(Cip1) expression.
authors.affiliation: Laboratory for Toxicopathology, Institute of Pathology, Rikshospitalet Radiumhospitalet Medical Centre, Rikshospitalet University Hospital, University of Oslo, Oslo, Norway. lene.wierod@medisin.uio.no
authors.forename: L
authors.initials: L
authors.lastname: Wierød
authors.forename: C M
authors.initials: CM
authors.lastname: Rosseland
authors.forename: B
authors.initials: B
authors.lastname: Lindeman
authors.forename: M P
authors.initials: MP
authors.lastname: Oksvold
authors.forename: H
authors.initials: H
authors.lastname: Grøsvik
authors.forename: E
authors.initials: E
authors.lastname: Skarpen
authors.forename: H S
authors.initials: HS
authors.lastname: Huitfeldt
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism*; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism* / Q000502:physiology; D004789:Enzyme Activation / Q000502:physiology; D004815:Epidermal Growth Factor / Q000037:antagonists & inhibitors / Q000502:physiology; D022781:Hepatocytes / Q000166:cytology* / Q000378:metabolism*; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D016196:S Phase / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; D016159:Tumor Suppressor Protein p53; D004815:Epidermal Growth Factor; D019869:Phosphatidylinositol 3-Kinases; C495892:Cdk2 protein, rat; C495903:Cdk4 protein, rat; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4