title: Assembly of cyclin D-dependent kinase and titration of p27Kip1 regulated by mitogen-activated protein kinase kinase (MEK1).
abstract: A constitutively active form of mitogen-activated protein kinase kinase (MEK1) was synthesized under control of a zinc-inducible promoter in NIH 3T3 fibroblasts. Zinc treatment of serum-starved cells activated extracellular signal-regulated protein kinases (ERKs) and induced expression of cyclin D1. Newly synthesized cyclin D1 assembled with cyclin-dependent kinase-4 (CDK4) to form holoenzyme complexes that phosphorylated the retinoblastoma protein inefficiently. Activation of the MEK1/ERK pathway neither triggered degradation of the CDK inhibitor kinase inhibitory protein-1 (p27(Kip1)) nor led to activation of cyclin E- and A-dependent CDK2, and such cells did not enter the DNA synthetic (S) phase of the cell division cycle. In contrast, zinc induction of active MEK1 in cells also engineered to ectopically overexpress cyclin D1 and CDK4 subunits generated levels of cyclin D-dependent retinoblastoma protein kinase activity approximating those achieved in cells stimulated by serum. In this setting, p27(Kip1) was mobilized into complexes containing cyclin D1; cyclin E- and A-dependent CDK2 complexes were activated; and serum-starved cells entered S phase. Thus, although the activity of p27(Kip1) normally is canceled through a serum-dependent degradative process, overexpressed cyclin D1-CDK complexes sequestered p27(Kip1) and reduced the effective inhibitory threshold through a stoichiometric mechanism. A fraction of these cells completed S phase and divided, but they were unable to continuously proliferate, indicating that other serum-responsive factors ultimately became rate limiting for cell cycle progression. Therefore, the MEK/ERK pathway not only acts transcriptionally to induce the cyclin D1 gene but functions posttranslationally to regulate cyclin D1 assembly with CDK4 and to thereby help cancel p27(Kip1)-mediated inhibition.
authors.affiliation: Department of Tumor Cell Biology, St. Jude Children's Research Hospital, 332 North Lauderdale, Memphis, TN 38105, USA.
authors.forename: M
authors.initials: M
authors.lastname: Cheng
authors.forename: V
authors.initials: V
authors.lastname: Sexl
authors.forename: C J
authors.initials: CJ
authors.lastname: Sherr
authors.forename: M F
authors.initials: MF
authors.lastname: Roussel
mesh_terms: D016475:3T3 Cells; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D018797:Cell Cycle Proteins; D019938:Cyclin D1 / Q000096:biosynthesis; D051358:Cyclin-Dependent Kinase 4; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism*; D048369:MAP Kinase Kinase 1; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D011817:Rabbits; D016196:S Phase; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins
chemical_list: C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D008869:Microtubule-Associated Proteins; D011518:Proto-Oncogene Proteins; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C495902:Cdk4 protein, mouse; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases