title: Cooperation of p27(Kip1) and p18(INK4c) in progestin-mediated cell cycle arrest in T-47D breast cancer cells.
abstract: The steroid hormone progesterone regulates proliferation and differentiation in the mammary gland and uterus by cell cycle phase-specific actions. The long-term effect of progestins on T-47D breast cancer cells is inhibition of cellular proliferation. This is accompanied by decreased G(1) cyclin-dependent kinase (CDK) activities, redistribution of the CDK inhibitor p27(Kip1) among these CDK complexes, and alterations in the elution profile of cyclin E-Cdk2 upon gel filtration chromatography, such that high-molecular-weight complexes predominate. This study aimed to determine the relative contribution of CDK inhibitors to these events. Following progestin treatment, the majority of cyclin E- and D-CDK complexes were bound to p27(Kip1) and few were bound to p21(Cip1). In vitro, recombinant His(6)-p27 could quantitatively reproduce the effects on cyclin E-Cdk2 kinase activity and the shift in molecular weight observed following progestin treatment. In contrast, cyclin D-Cdk4 was not inhibited by His(6)-p27 in vitro or p27(Kip1) in vivo. However, an increase in the expression of the Cdk4/6 inhibitor p18(INK4c) and its extensive association with Cdk4 and Cdk6 were apparent following progestin treatment. Recombinant p18(INK4c) led to the reassortment of cyclin-CDK-CDK inhibitor complexes in vitro, with consequent decrease in cyclin E-Cdk2 activity. These results suggest a concerted model of progestin action whereby p27(Kip1) and p18(INK4c) cooperate to inhibit cyclin E-Cdk2 and Cdk4. Since similar models have been developed for growth inhibition by transforming growth factor beta and during adipogenesis, interaction between the Cip/Kip and INK4 families of inhibitors may be a common theme in physiological growth arrest and differentiation.
authors.affiliation: Cancer Research Program, Garvan Institute of Medical Research, St. Vincent's Hospital, Sydney, New South Wales 2010, Australia.
authors.forename: A
authors.initials: A
authors.lastname: Swarbrick
authors.forename: C S
authors.initials: CS
authors.lastname: Lee
authors.forename: R L
authors.initials: RL
authors.lastname: Sutherland
authors.forename: E A
authors.initials: EA
authors.lastname: Musgrove
mesh_terms: D001943:Breast Neoplasms / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects*; D018797:Cell Cycle Proteins; D050763:Cyclin-Dependent Kinase Inhibitor p18; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D011282:Pregnenediones / Q000494:pharmacology; D011372:Progestins / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D050763:Cyclin-Dependent Kinase Inhibitor p18; D016213:Cyclins; D004791:Enzyme Inhibitors; D008869:Microtubule-Associated Proteins; D011282:Pregnenediones; D011372:Progestins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; C020175:16 alpha-ethyl-21-hydroxy-19-nor-4-pregnene-3,20-dione; D018844:Cyclin-Dependent Kinases