title: Differential regulation of cyclins D1 and D3 in hepatocyte proliferation.
abstract: Substantial evidence suggests that cyclin D1 plays a pivotal role in the control of the hepatocyte cell cycle in response to mitogenic stimuli, whereas the closely related protein cyclin D3 has not been extensively evaluated. In the current study, we examined the regulation of cyclins D1 and D3 during hepatocyte proliferation in vivo after 70% partial hepatectomy (PH) and in culture. In contrast to cyclin D1, which was nearly undetectable in quiescent liver and substantially up-regulated after PH, cyclin D3 was constitutively expressed and induced only modestly. In the regenerating liver, the concentration of cyclin D3 was only about 10% of that of cyclin D1. Cyclin D1 formed complexes primarily with cyclin-dependent kinase 4 (cdk4), which were markedly activated in the regenerating liver and readily sequestered the cell cycle inhibitory proteins, p21 and p27. Cyclin D3 bound to both cdk4 and cdk6. Cyclin D3/cdk6 activity was readily detectable in quiescent liver and changed little after PH, and this complex appeared to play a minor role in sequestering p21 and p27. In cultured hepatocytes, epidermal growth factor or insulin had little effect, but the combination of these agents substantially induced cyclin D1 and cell cycle progression. Inhibition of Mek1 or phosphoinositide 3-kinase markedly inhibited cyclin D1 expression and replication. In contrast, cyclin D3 was expressed in the absence of mitogens and was only modestly affected by these manipulations. In addition, growth-inhibitory extracellular matrix conditions inhibited cyclin D1 but not cyclin D3 expression. In conclusion, these results support the concept that cyclin D1 is critically regulated by extracellular stimuli that control proliferation, whereas cyclin D3 is regulated through different pathways and plays a distinct role in the liver.
authors.affiliation: Department of Medicine, Hennepin County Medical Center, 701 Park Avenue, Minneapolis, MN 55415, USA.
authors.forename: David G
authors.initials: DG
authors.lastname: Rickheim
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Nelsen
authors.forename: John T
authors.initials: JT
authors.lastname: Fassett
authors.forename: Nikolai A
authors.initials: NA
authors.lastname: Timchenko
authors.forename: Linda K
authors.initials: LK
authors.lastname: Hansen
authors.forename: Jeffrey H
authors.initials: JH
authors.lastname: Albrecht
mesh_terms: D000818:Animals; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000378:metabolism; D002455:Cell Division; D002478:Cells, Cultured; D019938:Cyclin D1 / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D056743:Cyclin D3; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D004791:Enzyme Inhibitors / Q000378:metabolism; D005786:Gene Expression Regulation; D006498:Hepatectomy; D022781:Hepatocytes / Q000166:cytology* / Q000378:metabolism; D008099:Liver / Q000737:chemistry / Q000378:metabolism; D008115:Liver Regeneration; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051381:Rats; D025521:Tumor Suppressor Proteins / Q000378:metabolism
chemical_list: C534697:Ccnd3 protein, mouse; C534698:Ccnd3 protein, rat; C493957:Cdkn1a protein, mouse; C493958:Cdkn1a protein, rat; C493961:Cdkn1b protein, mouse; C493962:Cdkn1b protein, rat; D018797:Cell Cycle Proteins; D056743:Cyclin D3; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D011518:Proto-Oncogene Proteins; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017346:Protein Serine-Threonine Kinases; C495902:Cdk4 protein, mouse; C495903:Cdk4 protein, rat; C495912:Cdk6 protein, mouse; C495913:Cdk6 protein, rat; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases