title: Differences in the mechanisms of growth control in contact-inhibited and serum-deprived human fibroblasts.
abstract: In the present work we studied mechanisms of growth control in contact-inhibited and serum-deprived human diploid fibroblasts. The observation that the effects on [3H]thymidine incorporation and reduction of retinoblastoma gene product-phosphorylation were additive when contact-inhibition and serum-deprivation were combined led us to the conclusion that the underlying mechanisms might be different. Both contact-inhibition and serum-deprivation led to a strong decrease of cdk4-kinase-activity and cdk2-phosphorylation at Thr 160, while the total amounts of cdk4 and cdk2 remained constant. In contact-inhibited cells, we revealed a strong protein accumulation of the cdk2-inhibitor p27 and a slight, but significant increase of the cdk4-inhibitor p16. In serum-deprived cells, the protein levels in p27 and p16 remained low. In contrast, we detected a rapid decrease of cyclin D1 and cyclin D3 which did not occur in contact-inhibited cells. These results indicate that serum-deprivation and contact-inhibition have different mechanisms although they affect the same pathway cyclin D-cdk4, pRB, cyclin E-cdk2.
authors.affiliation: Institute of Toxicology, Johannes-Gutenberg University, Mainz, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Dietrich
authors.forename: K
authors.initials: K
authors.lastname: Wallenfang
authors.forename: F
authors.initials: F
authors.lastname: Oesch
authors.forename: R
authors.initials: R
authors.lastname: Wieser
mesh_terms: D042846:CDC2-CDC28 Kinases; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000235:genetics; D003470:Culture Media; D016895:Culture Media, Serum-Free; D019938:Cyclin D1 / Q000378:metabolism; D056743:Cyclin D3; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D004171:Diploidy; D005347:Fibroblasts; D016193:G1 Phase; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism*; D016196:S Phase; D025521:Tumor Suppressor Proteins
chemical_list: C534696:CCND3 protein, human; D018797:Cell Cycle Proteins; D003470:Culture Media; D016895:Culture Media, Serum-Free; D056743:Cyclin D3; D019941:Cyclin-Dependent Kinase Inhibitor p16; D016213:Cyclins; D008869:Microtubule-Associated Proteins; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495900:CDK4 protein, human; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases