title: Macrophage-conditioned medium inhibits differentiation-induced Rb phosphorylation in 3T3-L1 preadipocytes.
abstract: This study examines the mechanisms underlying the anti-adipogenic effect of macrophage-secreted products. 3T3-L1 preadipocytes were induced to differentiate over 8 days in medium conditioned by murine J774 macrophages (MacCM). The inhibitory effect on lipid accumulation and expression of adipogenic markers was diminished when addition of MacCM was delayed to day 2 of differentiation. Clonal expansion, an early event required for 3T3-L1 adipogenesis, was reduced in the presence of MacCM (89%; n=3; p<0.001), and BrdU incorporation was impaired by 55% (n=3; p<0.01). Activation of ERK1/2 was not affected by MacCM, and neither was the expression of p27(kip1), a cyclin-dependent kinase inhibitor. However, phosphorylation of the retinoblastoma protein (Rb), required for cell cycle progression, was impaired by MacCM (94% inhibition; n=3; p<0.01). Differentiation-dependent expression, nuclear localization, and DNA binding ability of C/EBPbeta were not inhibited by MacCM. Alterations in cell cycle-associated proteins may be important with respect to the anti-adipogenic action of MacCM.
authors.affiliation: Department of Medicine, University of Ottawa, Chronic Disease Program, Ottawa Health Research Institute, Ottawa, Ontario, Canada.
authors.forename: Michelle N
authors.initials: MN
authors.lastname: Yarmo
authors.forename: Anne
authors.initials: A
authors.lastname: Landry
authors.forename: André S D
authors.initials: AS
authors.lastname: Molgat
authors.forename: AnneMarie
authors.initials: A
authors.lastname: Gagnon
authors.forename: Alexander
authors.initials: A
authors.lastname: Sorisky
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D050156:Adipogenesis; D000818:Animals; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism; D002453:Cell Cycle; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D017077:Culture Media, Conditioned; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D050356:Lipid Metabolism; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D010766:Phosphorylation; D016160:Retinoblastoma Protein / Q000378:metabolism*
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; C493961:Cdkn1b protein, mouse; D017077:Culture Media, Conditioned; D016160:Retinoblastoma Protein; D050760:Cyclin-Dependent Kinase Inhibitor p27; D048049:Extracellular Signal-Regulated MAP Kinases