title: Interaction of retinoblastoma protein and D cyclins during cell-growth inhibition by hexamethylenebisacetamide in TM2H mouse epithelial cells.
abstract: To explore the regulation and function of D-type cyclins in breast cancer cells, the mouse mammary hyperplastic epithelial cell line TM2H was treated with 5 mM hexamethylenebisacetamide (HMBA), a polar differentiation factor. The resulting growth-inhibitory effect of HMBA was completely reversible and was analyzed in terms of percent cells in G1; association of D-type cyclins with cyclin-dependent kinase (cdk) 4 and cdk6; G1 kinase activity; association of retinoblastoma protein (pRb) and phosphorylated pRb with D-type cyclins; and association of p16INK4a, p15INK4b, and p27Kip1 with cdk4 and cdk6. Synchronized TM2H cells were examined at 0, 3, 5, 9, 12, and 24 h after exposure to 5 mM HMBA. Inhibition of DNA synthesis, as measured by thymidine uptake, was first observed at 5 h (40%) and peaked at 24 h (80%). Flow cytometry at 9 h showed treated cells to be in G1 arrest. Western blot analysis showed weakly detectable cyclin D1 but readily detectable cyclin D2 and D3 proteins at 0 h; thereafter, cyclin D2 and D3 protein levels remained higher while cyclin D1 levels declined significantly in treated versus untreated cells. By 5 h (early G1), HMBA had markedly inhibited cdk4 and cdk6 kinase activity (67% and 75%, respectively) in treated versus untreated cells. By 9 and 12 h, pRb levels had increased 3.4-fold in treated versus untreated cells. At 5 h, cyclin D-associated pRb was totally hypophosphorylated in treated cells and hyperphosphorylated in untreated cells. The levels of pRb associated with cyclin D2 and D3 increased 2.89-fold and 4.6-fold, respectively, in treated versus untreated cells. At 5 h, treated cells showed a fivefold increase in cdk4-associated p27Kip1 and, at 9 h, a fourfold increase in cdk6-associated p27Kip1 over control levels. In confirmation of these data, HMBA was found to inhibit the growth of Rb-positive Du/145Rb cells but not their Rb-negative parental Du/145 cells. The data suggest that HMBA-induced growth inhibition is due to multifactorial mechanisms involving decreases in total cyclin D1 and inhibition of cdk4 and cdk6 kinase activities through elevation of levels of cdk4- and cdk6-associated p27Kip1 and concomitant increases in hypophosphorylated pRb and stable cyclin D2/pRb and cyclin D3/pRb complexes that help maintain pRb in a functional state.
authors.affiliation: Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: T K
authors.initials: TK
authors.lastname: Said
authors.forename: D
authors.initials: D
authors.lastname: Medina
mesh_terms: D000081:Acetamides / Q000494:pharmacology*; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D056741:Cyclin D; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism*; D004847:Epithelial Cells / Q000187:drug effects; D005434:Flow Cytometry; D016161:Genes, Retinoblastoma / Q000502:physiology; D006801:Humans; D006965:Hyperplasia; D008297:Male; D008321:Mammary Glands, Animal / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D011467:Prostate / Q000166:cytology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein / Q000096:biosynthesis / Q000378:metabolism*; D025521:Tumor Suppressor Proteins
chemical_list: D000081:Acetamides; D000970:Antineoplastic Agents; C493966:CDKN2B protein, human; D002352:Carrier Proteins; C493961:Cdkn1b protein, mouse; C493968:Cdkn2b protein, mouse; D018797:Cell Cycle Proteins; D056741:Cyclin D; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D016213:Cyclins; D008869:Microtubule-Associated Proteins; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017346:Protein Serine-Threonine Kinases; C495900:CDK4 protein, human; C495911:CDK6 protein, human; C495902:Cdk4 protein, mouse; C495912:Cdk6 protein, mouse; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases; C014026:hexamethylene bisacetamide