title: Regulation of the hepatocyte cell cycle by type I collagen matrix: role of cyclin D1.
abstract: Rat hepatocytes adherent to a rigid film of type I collagen will spread and enter S phase, while those attached to collagen gel or a dried collagen substrate remain round and quiescent. The current studies were initiated to determine the mechanism by which these different substrates differentially influence cell cycle progression. Cyclin D1 mRNA and protein expression and associated kinase activity was low on dried collagen relative to collagen film. In contrast, cyclin E and cdk2 protein levels were similar on the two substrates. Although cyclin E and cdk2 were present, cells on dried collagen lacked cdk2 kinase activity. p27 protein levels did not differ between dried collagen and film, but more p27 was associated with cdk2 in cells on dried collagen than those on collagen film. Cyclin D1 expression on collagen film was inhibited by cytochalasin D and exoenzyme C3, suggesting a role for the GTP-binding protein, Rho, in regulating cyclin D1 expression. Cyclin D1 over-expression induced hepatocytes into S phase in the absence of cell shape change on dried collagen or collagen gel. These results demonstrate a novel, substrate-dependent mechanism for cyclin D1 expression in hepatocytes, and also demonstrate that cyclin D1 over-expression allows shape-independent S phase entry.
authors.affiliation: Department of Laboratory Medicine and Pathology, and Cancer Center, University of Minnesota, Minneapolis, MN 55455, USA. hanse066@tc.umn.edu
authors.forename: L K
authors.initials: LK
authors.lastname: Hansen
authors.forename: J H
authors.initials: JH
authors.lastname: Albrecht
mesh_terms: D036002:ADP Ribose Transferases / Q000494:pharmacology; D000199:Actins / Q000502:physiology; D000818:Animals; D001905:Botulinum Toxins; D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins; D048429:Cell Size; D003094:Collagen / Q000737:chemistry / Q000502:physiology*; D019938:Cyclin D1 / Q000235:genetics / Q000502:physiology*; D019927:Cyclin E / Q000032:analysis; D051357:Cyclin-Dependent Kinase 2; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000032:analysis; D015638:Cytochalasin D / Q000494:pharmacology; D004261:DNA Replication; D003890:Desiccation; D005109:Extracellular Matrix / Q000502:physiology*; D005782:Gels; D008099:Liver / Q000166:cytology*; D008869:Microtubule-Associated Proteins / Q000032:analysis; D011489:Protein Denaturation; D017346:Protein Serine-Threonine Kinases / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D011917:Rats, Inbred Lew; D025521:Tumor Suppressor Proteins
chemical_list: D000199:Actins; C493962:Cdkn1b protein, rat; D018797:Cell Cycle Proteins; D019927:Cyclin E; D005782:Gels; D008869:Microtubule-Associated Proteins; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D015638:Cytochalasin D; D003094:Collagen; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495892:Cdk2 protein, rat; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D001905:Botulinum Toxins