title: Mechanisms of cyclin-dependent kinase inactivation by progestins.
abstract: The steroid hormone progesterone regulates proliferation and differentiation in the mammary gland and uterus by cell cycle phase-specific actions. In breast cancer cells the predominant effect of synthetic progestins is long-term growth inhibition and arrest in G1 phase. Progestin-mediated growth arrest of T-47D breast cancer cells was preceded by inhibition of cyclin D1-Cdk4, cyclin D3-Cdk4, and cyclin E-Cdk2 kinase activities in vitro and reduced phosphorylation of pRB and p107. This was accompanied by decreases in the expression of cyclins D1, D3, and E, decreased abundance of cyclin D1- and cyclin D3-Cdk4 complexes, increased association of the cyclin-dependent kinase (CDK) inhibitor p27 with the remaining Cdk4 complexes, and changes in the molecular masses and compositions of cyclin E complexes. In control cells cyclin E eluted from Superdex 200 as two peaks of approximately 120 and approximately 200 kDa, with the 120-kDa peak displaying greater cyclin E-associated kinase activity. Following progestin treatment, almost all of the cyclin E was in the 200-kDa, low-activity form, which was associated with the CDK inhibitors p21 and p27; this change preceded the inhibition of cell cycle progression. These data suggest preferential formation of this higher-molecular-weight, CDK inhibitor-bound form and a reduced number of cyclin E-Cdk2 complexes as mechanisms for the decreased cyclin E-associated kinase activity following progestin treatment. Ectopic expression of cyclin D1 in progestin-inhibited cells led to the reappearance of the 120-kDa active form of cyclin E-Cdk2 preceding the resumption of cell cycle progression. Thus, decreased cyclin expression and consequent increased CDK inhibitor association are likely to mediate the decreases in CDK activity accompanying progestin-mediated growth inhibition.
authors.affiliation: Cancer Research Program, Garvan Institute of Medical Research, St Vincent's Hospital, Sydney, New South Wales, Australia. l.musgrove@garvan.unsw.edu.au
authors.forename: E A
authors.initials: EA
authors.lastname: Musgrove
authors.forename: A
authors.initials: A
authors.lastname: Swarbrick
authors.forename: C S
authors.initials: CS
authors.lastname: Lee
authors.forename: A L
authors.initials: AL
authors.lastname: Cornish
authors.forename: R L
authors.initials: RL
authors.lastname: Sutherland
mesh_terms: D001943:Breast Neoplasms / Q000201:enzymology* / Q000378:metabolism; D042846:CDC2-CDC28 Kinases; D018797:Cell Cycle Proteins; D019938:Cyclin D1 / Q000378:metabolism*; D056743:Cyclin D3; D019927:Cyclin E / Q000378:metabolism; D056746:Cyclin G; D056766:Cyclin G1; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000378:metabolism; D005260:Female; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008970:Molecular Weight; D009687:Nuclear Proteins / Q000378:metabolism; D011372:Progestins / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein / Q000378:metabolism; D050720:Retinoblastoma-Like Protein p107; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
chemical_list: C534696:CCND3 protein, human; C534702:CCNG1 protein, human; D018797:Cell Cycle Proteins; D056743:Cyclin D3; D019927:Cyclin E; D056746:Cyclin G; D056766:Cyclin G1; D016213:Cyclins; D004791:Enzyme Inhibitors; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; D011372:Progestins; D011518:Proto-Oncogene Proteins; C493844:RBL1 protein, human; D016160:Retinoblastoma Protein; D050720:Retinoblastoma-Like Protein p107; 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